The Emacs Editor

Emacs is the extensible, customizable, self-documenting real-time display editor. This manual describes how to edit with Emacs and some of the ways to customize it; it corresponds to GNU Emacs version 24.3.

The homepage for GNU Emacs is at http://www.gnu.org/software/emacs/.
To view this manual in other formats, click here.
You can also purchase a printed copy from the FSF store.

For information on extending Emacs, see Emacs Lisp.

This is the GNU Emacs Manual, updated for Emacs version 24.3.

Copyright © 1985–1987, 1993–2013 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being “The GNU Manifesto,” “Distribution” and “GNU GENERAL PUBLIC LICENSE,” with the Front-Cover texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License.”

(a) The FSF's Back-Cover Text is: “You have the freedom to copy and modify this GNU manual. Buying copies from the FSF supports it in developing GNU and promoting software freedom.”

Distrib How to get the latest Emacs distribution.
Intro An introduction to Emacs concepts.
Important General Concepts
Screen How to interpret what you see on the screen.
User Input Kinds of input events (characters, buttons, function keys).
Keys Key sequences: what you type to request one editing action.
Commands Named functions run by key sequences to do editing.
Entering Emacs Starting Emacs from the shell.
Exiting Stopping or killing Emacs.
Fundamental Editing Commands
Basic The most basic editing commands.
Minibuffer Entering arguments that are prompted for.
M-x Invoking commands by their names.
Help Commands for asking Emacs about its commands.
Important Text-Changing Commands
Mark The mark: how to delimit a "region" of text.
Killing Killing (cutting) and yanking (copying) text.
Registers Saving a text string or a location in the buffer.
Display Controlling what text is displayed.
Search Finding or replacing occurrences of a string.
Fixit Commands especially useful for fixing typos.
Keyboard Macros Recording a sequence of keystrokes to be replayed.
Major Structures of Emacs
Files All about handling files.
Buffers Multiple buffers; editing several files at once.
Windows Viewing multiple pieces of text in one frame.
Frames Using multiple "windows" on your display.
International Using non-ASCII character sets.
Advanced Features
Modes Major and minor modes alter Emacs's basic behavior.
Indentation Editing the white space at the beginnings of lines.
Text Commands and modes for editing human languages.
Programs Commands and modes for editing programs.
Building Compiling, running and debugging programs.
Maintaining Features for maintaining large programs.
Abbrevs Defining text abbreviations to reduce typing.
Dired Directory and file manager.
Calendar/Diary Calendar and diary facilities.
Sending Mail Sending mail in Emacs.
Rmail Reading mail in Emacs.
Gnus A flexible mail and news reader.
Document View Viewing PDF, PS and DVI files.
Shell Executing shell commands from Emacs.
Emacs Server Using Emacs as an editing server.
Printing Printing hardcopies of buffers or regions.
Sorting Sorting lines, paragraphs or pages within Emacs.
Picture Mode Editing pictures made up of text characters.
Editing Binary Files Editing binary files with Hexl mode.
Saving Emacs Sessions Saving Emacs state from one session to the next.
Recursive Edit Performing edits while "within another command".
Emulation Emulating some other editors with Emacs.
Hyperlinking Following links in buffers.
Amusements Various games and hacks.
Packages Installing additional features.
Customization Modifying the behavior of Emacs.
Recovery from Problems
Quitting Quitting and aborting.
Lossage What to do if Emacs is hung or malfunctioning.
Bugs How and when to report a bug.
Contributing How to contribute improvements to Emacs.
Service How to get help for your own Emacs needs.
Appendices
Copying The GNU General Public License gives you permission to redistribute GNU Emacs on certain terms; it also explains that there is no warranty.
GNU Free Documentation License The license for this documentation.
Emacs Invocation Hairy startup options.
X Resources X resources for customizing Emacs.
Antinews Information about Emacs version 23.
Mac OS / GNUstep Using Emacs under Mac OS and GNUstep.
Microsoft Windows Using Emacs on Microsoft Windows and MS-DOS.
Manifesto What's GNU? Gnu's Not Unix!
Glossary Terms used in this manual.
Acknowledgments Major contributors to GNU Emacs.
Indexes (each index contains a large menu)
Key Index An item for each standard Emacs key sequence.
Option Index An item for every command-line option.
Command Index An item for each command name.
Variable Index An item for each documented variable.
Concept Index An item for each concept.

Detailed Node Listing

Here are some other nodes which are really subnodes of the ones already listed, mentioned here so you can get to them in one step:

The Organization of the Screen
Point The place in the text where editing commands operate.
Echo Area Short messages appear at the bottom of the screen.
Mode Line Interpreting the mode line.
Menu Bar How to use the menu bar.
Basic Editing Commands
Inserting Text Inserting text by simply typing it.
Moving Point Moving the cursor to the place where you want to change something.
Erasing Deleting and killing text.
Basic Undo Undoing recent changes in the text.
Basic Files Visiting, creating, and saving files.
Basic Help Asking what a character does.
Blank Lines Making and deleting blank lines.
Continuation Lines How Emacs displays lines too wide for the screen.
Position Info What line, row, or column is point on?
Arguments Numeric arguments for repeating a command N times.
Repeating Repeating the previous command quickly.
The Minibuffer
Basic Minibuffer Basic usage of the minibuffer.
Minibuffer File Entering file names with the minibuffer.
Minibuffer Edit How to edit in the minibuffer.
Completion An abbreviation facility for minibuffer input.
Minibuffer History Reusing recent minibuffer arguments.
Repetition Re-executing commands that used the minibuffer.
Passwords Entering passwords in the echo area.
Yes or No Prompts Replying yes or no in the echo area.
Completion
Completion Example Examples of using completion.
Completion Commands A list of completion commands.
Completion Exit Completion and minibuffer text submission.
Completion Styles How completion matches are chosen.
Completion Options Options for completion.
Help
Help Summary Brief list of all Help commands.
Key Help Asking what a key does in Emacs.
Name Help Asking about a command, variable or function name.
Apropos Asking what pertains to a given topic.
Help Mode Special features of Help mode and Help buffers.
Package Keywords Finding Lisp libraries by keywords (topics).
Language Help Help relating to international language support.
Misc Help Other help commands.
Help Files Commands to display auxiliary help files.
Help Echo Help on active text and tooltips ("balloon help").
The Mark and the Region
Setting Mark Commands to set the mark.
Marking Objects Commands to put region around textual units.
Using Region Summary of ways to operate on contents of the region.
Mark Ring Previous mark positions saved so you can go back there.
Global Mark Ring Previous mark positions in various buffers.
Shift Selection Using shifted cursor motion keys.
Disabled Transient Mark Leaving regions unhighlighted by default.
Killing and Moving Text
Deletion and Killing Commands that remove text.
Yanking Commands that insert text.
Cut and Paste Clipboard and selections on graphical displays.
Accumulating Text Other methods to add text to the buffer.
Rectangles Operating on text in rectangular areas.
CUA Bindings Using C-x/C-c/C-v to kill and yank.
Deletion and Killing
Deletion Commands for deleting small amounts of text and blank areas.
Killing by Lines How to kill entire lines of text at one time.
Other Kill Commands Commands to kill large regions of text and syntactic units such as words and sentences.
Kill Options Options that affect killing.
Yanking
Kill Ring Where killed text is stored.
Earlier Kills Yanking something killed some time ago.
Appending Kills Several kills in a row all yank together.
"Cut and Paste" Operations on Graphical Displays
Clipboard How Emacs uses the system clipboard.
Primary Selection The temporarily selected text selection.
Secondary Selection Cutting without altering point and mark.
Registers
Position Registers Saving positions in registers.
Text Registers Saving text in registers.
Rectangle Registers Saving rectangles in registers.
Configuration Registers Saving window configurations in registers.
Number Registers Numbers in registers.
File Registers File names in registers.
Bookmarks Bookmarks are like registers, but persistent.
Controlling the Display
Scrolling Commands to move text up and down in a window.
Recentering A scroll command that centers the current line.
Auto Scrolling Redisplay scrolls text automatically when needed.
Horizontal Scrolling Moving text left and right in a window.
Narrowing Restricting display and editing to a portion of the buffer.
View Mode Viewing read-only buffers.
Follow Mode Follow mode lets two windows scroll as one.
Faces How to change the display style using faces.
Colors Specifying colors for faces.
Standard Faces The main predefined faces.
Text Scale Increasing or decreasing text size in a buffer.
Font Lock Minor mode for syntactic highlighting using faces.
Highlight Interactively Tell Emacs what text to highlight.
Fringes Enabling or disabling window fringes.
Displaying Boundaries Displaying top and bottom of the buffer.
Useless Whitespace Showing possibly spurious trailing whitespace.
Selective Display Hiding lines with lots of indentation.
Optional Mode Line Optional mode line display features.
Text Display How text characters are normally displayed.
Cursor Display Features for displaying the cursor.
Line Truncation Truncating lines to fit the screen width instead of continuing them to multiple screen lines.
Visual Line Mode Word wrap and screen line-based editing.
Display Custom Information on variables for customizing display.
Searching and Replacement
Incremental Search Search happens as you type the string.
Nonincremental Search Specify entire string and then search.
Word Search Search for sequence of words.
Symbol Search Search for a source code symbol.
Regexp Search Search for match for a regexp.
Regexps Syntax of regular expressions.
Regexp Backslash Regular expression constructs starting with `\'.
Regexp Example A complex regular expression explained.
Search Case To ignore case while searching, or not.
Replace Search, and replace some or all matches.
Other Repeating Search Operating on all matches for some regexp.
Incremental Search
Basic Isearch Basic incremental search commands.
Repeat Isearch Searching for the same string again.
Error in Isearch When your string is not found.
Special Isearch Special input in incremental search.
Isearch Yank Commands that grab text into the search string or else edit the search string.
Isearch Scroll Scrolling during an incremental search.
Isearch Minibuffer Incremental search of the minibuffer history.
Replacement Commands
Unconditional Replace Replacing all matches for a string.
Regexp Replace Replacing all matches for a regexp.
Replacement and Case How replacements preserve case of letters.
Query Replace How to use querying.
Commands for Fixing Typos
Undo The Undo commands.
Transpose Exchanging two characters, words, lines, lists...
Fixing Case Correcting case of last word entered.
Spelling Apply spelling checker to a word, or a whole file.
Keyboard Macros
Basic Keyboard Macro Defining and running keyboard macros.
Keyboard Macro Ring Where previous keyboard macros are saved.
Keyboard Macro Counter Inserting incrementing numbers in macros.
Keyboard Macro Query Making keyboard macros do different things each time.
Save Keyboard Macro Giving keyboard macros names; saving them in files.
Edit Keyboard Macro Editing keyboard macros.
Keyboard Macro Step-Edit Interactively executing and editing a keyboard macro.
File Handling
File Names How to type and edit file-name arguments.
Visiting Visiting a file prepares Emacs to edit the file.
Saving Saving makes your changes permanent.
Reverting Reverting cancels all the changes not saved.
Autorevert Auto Reverting non-file buffers.
Auto Save Auto Save periodically protects against loss of data.
File Aliases Handling multiple names for one file.
Directories Creating, deleting, and listing file directories.
Comparing Files Finding where two files differ.
Diff Mode Mode for editing file differences.
Misc File Ops Other things you can do on files.
Compressed Files Accessing compressed files.
File Archives Operating on tar, zip, jar etc. archive files.
Remote Files Accessing files on other machines.
Quoted File Names Quoting special characters in file names.
File Name Cache Completion against a list of files you often use.
File Conveniences Convenience Features for Finding Files.
Filesets Handling sets of files.
Saving Files
Save Commands Commands for saving files.
Backup How Emacs saves the old version of your file.
Customize Save Customizing the saving of files.
Interlocking How Emacs protects against simultaneous editing of one file by two users.
File Shadowing Copying files to "shadows" automatically.
Time Stamps Emacs can update time stamps on saved files.
Backup Files
Backup Names How backup files are named.
Backup Deletion Emacs deletes excess numbered backups.
Backup Copying Backups can be made by copying or renaming.
Auto Reverting Non-File Buffers
Auto Reverting the Buffer Menu Auto Revert of the Buffer Menu.
Auto Reverting Dired Auto Revert of Dired buffers.
Supporting additional buffers How to add more Auto Revert support.
Auto-Saving: Protection Against Disasters
Auto Save Files The file where auto-saved changes are actually made until you save the file.
Auto Save Control Controlling when and how often to auto-save.
Recover Recovering text from auto-save files.
Using Multiple Buffers
Select Buffer Creating a new buffer or reselecting an old one.
List Buffers Getting a list of buffers that exist.
Misc Buffer Renaming; changing read-onlyness; copying text.
Kill Buffer Killing buffers you no longer need.
Several Buffers How to go through the list of all buffers and operate variously on several of them.
Indirect Buffers An indirect buffer shares the text of another buffer.
Buffer Convenience Convenience and customization features for buffer handling.
Convenience Features and Customization of Buffer Handling
Uniquify Making buffer names unique with directory parts.
Iswitchb Switching between buffers with substrings.
Buffer Menus Configurable buffer menu.
Multiple Windows
Basic Window Introduction to Emacs windows.
Split Window New windows are made by splitting existing windows.
Other Window Moving to another window or doing something to it.
Pop Up Window Finding a file or buffer in another window.
Change Window Deleting windows and changing their sizes.
Displaying Buffers How Emacs picks a window for displaying a buffer.
Window Convenience Convenience functions for window handling.
Displaying a Buffer in a Window
Window Choice How display-buffer works.
Frames and Graphical Displays
Mouse Commands Moving, cutting, and pasting, with the mouse.
Word and Line Mouse Mouse commands for selecting whole words or lines.
Mouse References Using the mouse to select an item from a list.
Menu Mouse Clicks Mouse clicks that bring up menus.
Mode Line Mouse Mouse clicks on the mode line.
Creating Frames Creating additional Emacs frames with various contents.
Frame Commands Iconifying, deleting, and switching frames.
Fonts Changing the frame font.
Speedbar How to make and use a speedbar frame.
Multiple Displays How one Emacs instance can talk to several displays.
Frame Parameters Changing the colors and other modes of frames.
Scroll Bars How to enable and disable scroll bars; how to use them.
Drag and Drop Using drag and drop to open files and insert text.
Menu Bars Enabling and disabling the menu bar.
Tool Bars Enabling and disabling the tool bar.
Dialog Boxes Controlling use of dialog boxes.
Tooltips Displaying information at the current mouse position.
Mouse Avoidance Preventing the mouse pointer from obscuring text.
Non-Window Terminals Multiple frames on terminals that show only one.
Text-Only Mouse Using the mouse in text terminals.
International Character Set Support
International Chars Basic concepts of multibyte characters.
Disabling Multibyte Controlling whether to use multibyte characters.
Language Environments Setting things up for the language you use.
Input Methods Entering text characters not on your keyboard.
Select Input Method Specifying your choice of input methods.
Coding Systems Character set conversion when you read and write files, and so on.
Recognize Coding How Emacs figures out which conversion to use.
Specify Coding Specifying a file's coding system explicitly.
Output Coding Choosing coding systems for output.
Text Coding Choosing conversion to use for file text.
Communication Coding Coding systems for interprocess communication.
File Name Coding Coding systems for file names.
Terminal Coding Specifying coding systems for converting terminal input and output.
Fontsets Fontsets are collections of fonts that cover the whole spectrum of characters.
Defining Fontsets Defining a new fontset.
Modifying Fontsets Modifying an existing fontset.
Undisplayable Characters When characters don't display.
Unibyte Mode You can pick one European character set to use without multibyte characters.
Charsets How Emacs groups its internal character codes.
Bidirectional Editing Support for right-to-left scripts.
Major and Minor Modes
Major Modes Text mode vs. Lisp mode vs. C mode...
Minor Modes Each minor mode is a feature you can turn on independently of any others.
Choosing Modes How modes are chosen when visiting files.
Indentation
Indentation Commands More commands for performing indentation.
Tab Stops Stop points for indentation in Text modes.
Just Spaces Using only space characters for indentation.
Indent Convenience Optional indentation features.
Commands for Human Languages
Words Moving over and killing words.
Sentences Moving over and killing sentences.
Paragraphs Moving over paragraphs.
Pages Moving over pages.
Filling Filling or justifying text.
Case Changing the case of text.
Text Mode The major modes for editing text files.
Outline Mode Editing outlines.
Org Mode The Emacs organizer.
TeX Mode Editing TeX and LaTeX files.
HTML Mode Editing HTML and SGML files.
Nroff Mode Editing input to the nroff formatter.
Enriched Text Editing text "enriched" with fonts, colors, etc.
Text Based Tables Commands for editing text-based tables.
Two-Column Splitting text columns into separate windows.
Filling Text
Auto Fill Auto Fill mode breaks long lines automatically.
Fill Commands Commands to refill paragraphs and center lines.
Fill Prefix Filling paragraphs that are indented or in a comment, etc.
Adaptive Fill How Emacs can determine the fill prefix automatically.
Outline Mode
Outline Format What the text of an outline looks like.
Outline Motion Special commands for moving through outlines.
Outline Visibility Commands to control what is visible.
Outline Views Outlines and multiple views.
Foldout Folding means zooming in on outlines.
Org Mode
Org Organizer Managing TODO lists and agendas.
Org Authoring Exporting Org buffers to various formats.
TeX Mode
TeX Editing Special commands for editing in TeX mode.
LaTeX Editing Additional commands for LaTeX input files.
TeX Print Commands for printing part of a file with TeX.
TeX Misc Customization of TeX mode, and related features.
Enriched Text
Enriched Mode Entering and exiting Enriched mode.
Hard and Soft Newlines There are two different kinds of newlines.
Editing Format Info How to edit text properties.
Enriched Faces Bold, italic, underline, etc.
Enriched Indentation Changing the left and right margins.
Enriched Justification Centering, setting text flush with the left or right margin, etc.
Enriched Properties The "special" text properties submenu.
Editing Text-based Tables
Table Definition What is a text based table.
Table Creation How to create a table.
Table Recognition How to activate and deactivate tables.
Cell Commands Cell-oriented commands in a table.
Cell Justification Justifying cell contents.
Table Rows and Columns Inserting and deleting rows and columns.
Table Conversion Converting between plain text and tables.
Table Misc Table miscellany.
Editing Programs
Program Modes Major modes for editing programs.
Defuns Commands to operate on major top-level parts of a program.
Program Indent Adjusting indentation to show the nesting.
Parentheses Commands that operate on parentheses.
Comments Inserting, killing, and aligning comments.
Documentation Getting documentation of functions you plan to call.
Hideshow Displaying blocks selectively.
Symbol Completion Completion on symbol names of your program or language.
Glasses Making identifiersLikeThis more readable.
Semantic Suite of editing tools based on source code parsing.
Misc for Programs Other Emacs features useful for editing programs.
C Modes Special commands of C, C++, Objective-C, Java, IDL, Pike and AWK modes.
Asm Mode Asm mode and its special features.
Fortran Fortran mode and its special features.
Top-Level Definitions, or Defuns
Left Margin Paren An open-paren or similar opening delimiter starts a defun if it is at the left margin.
Moving by Defuns Commands to move over or mark a major definition.
Imenu Making buffer indexes as menus.
Which Function Which Function mode shows which function you are in.
Indentation for Programs
Basic Indent Indenting a single line.
Multi-line Indent Commands to reindent many lines at once.
Lisp Indent Specifying how each Lisp function should be indented.
C Indent Extra features for indenting C and related modes.
Custom C Indent Controlling indentation style for C and related modes.
Commands for Editing with Parentheses
Expressions Expressions with balanced parentheses.
Moving by Parens Commands for moving up, down and across in the structure of parentheses.
Matching Insertion of a close-delimiter flashes matching open.
Manipulating Comments
Comment Commands Inserting, killing, and aligning comments.
Multi-Line Comments Commands for adding and editing multi-line comments.
Options for Comments Customizing the comment features.
Documentation Lookup
Info Lookup Looking up library functions and commands in Info files.
Man Page Looking up man pages of library functions and commands.
Lisp Doc Looking up Emacs Lisp functions, etc.
C and Related Modes
Motion in C Commands to move by C statements, etc.
Electric C Colon and other chars can automatically reindent.
Hungry Delete A more powerful DEL command.
Other C Commands Filling comments, viewing expansion of macros, and other neat features.
Fortran Mode
Fortran Motion Moving point by statements or subprograms.
Fortran Indent Indentation commands for Fortran.
Fortran Comments Inserting and aligning comments.
Fortran Autofill Auto fill support for Fortran.
Fortran Columns Measuring columns for valid Fortran.
Fortran Abbrev Built-in abbrevs for Fortran keywords.
Fortran Indentation
ForIndent Commands Commands for indenting and filling Fortran.
ForIndent Cont How continuation lines indent.
ForIndent Num How line numbers auto-indent.
ForIndent Conv Conventions you must obey to avoid trouble.
ForIndent Vars Variables controlling Fortran indent style.
Compiling and Testing Programs
Compilation Compiling programs in languages other than Lisp (C, Pascal, etc.).
Compilation Mode The mode for visiting compiler errors.
Compilation Shell Customizing your shell properly for use in the compilation buffer.
Grep Searching Searching with grep.
Flymake Finding syntax errors on the fly.
Debuggers Running symbolic debuggers for non-Lisp programs.
Executing Lisp Various modes for editing Lisp programs, with different facilities for running the Lisp programs.
Lisp Libraries How Lisp programs are loaded into Emacs.
Lisp Eval Executing a single Lisp expression in Emacs.
Lisp Interaction Executing Lisp in an Emacs buffer.
External Lisp Communicating through Emacs with a separate Lisp.
Running Debuggers Under Emacs
Starting GUD How to start a debugger subprocess.
Debugger Operation Connection between the debugger and source buffers.
Commands of GUD Key bindings for common commands.
GUD Customization Defining your own commands for GUD.
GDB Graphical Interface An enhanced mode that uses GDB features to implement a graphical debugging environment.
GDB Graphical Interface
GDB User Interface Layout Control the number of displayed buffers.
Source Buffers Use the mouse in the fringe/margin to control your program.
Breakpoints Buffer A breakpoint control panel.
Threads Buffer Displays your threads.
Stack Buffer Select a frame from the call stack.
Other GDB Buffers Other buffers for controlling the GDB state.
Watch Expressions Monitor variable values in the speedbar.
Multithreaded Debugging Debugging programs with several threads.
Maintaining Large Programs
Version Control Using version control systems.
Change Log Maintaining a change history for your program.
Tags Go directly to any function in your program in one command. Tags remembers which file it is in.
EDE An integrated development environment for Emacs.
Emerge A convenient way of merging two versions of a program.
Version Control
Introduction to VC How version control works in general.
VC Mode Line How the mode line shows version control status.
Basic VC Editing How to edit a file under version control.
Log Buffer Features available in log entry buffers.
Registering Putting a file under version control.
Old Revisions Examining and comparing old versions.
VC Change Log Viewing the VC Change Log.
VC Undo Canceling changes before or after committing.
VC Directory Mode Listing files managed by version control.
Branches Multiple lines of development.
Miscellaneous VC Various other commands and features of VC.
Customizing VC Variables that change VC's behavior.
Introduction to Version Control
Why Version Control? Understanding the problems it addresses.
Version Control Systems Supported version control back-end systems.
VCS Concepts Words and concepts related to version control.
VCS Merging How file conflicts are handled.
VCS Changesets How changes are grouped.
VCS Repositories Where version control repositories are stored.
Types of Log File The VCS log in contrast to the ChangeLog.
Basic Editing under Version Control
VC With A Merging VCS Without locking: default mode for CVS.
VC With A Locking VCS RCS in its default mode, SCCS, and optionally CVS.
Advanced C-x v v Advanced features available with a prefix argument.
VC Directory Mode
VC Directory Buffer What the buffer looks like and means.
VC Directory Commands Commands to use in a VC directory buffer.
Version Control Branches
Switching Branches How to get to another existing branch.
VC Pull Updating the contents of a branch.
Merging Transferring changes between branches.
Creating Branches How to start a new branch.
Miscellaneous Commands and Features of VC
Change Logs and VC Generating a change log file from log entries.
VC Delete/Rename Deleting and renaming version-controlled files.
Revision Tags Symbolic names for revisions.
Version Headers Inserting version control headers into working files.
Customizing VC
General VC Options Options that apply to multiple back ends.
RCS and SCCS Options for RCS and SCCS.
CVS Options Options for CVS.
Change Logs
Change Log Commands Commands for editing change log files.
Format of ChangeLog What the change log file looks like.
Tags Tables
Tag Syntax Tag syntax for various types of code and text files.
Create Tags Table Creating a tags table with etags.
Etags Regexps Create arbitrary tags using regular expressions.
Select Tags Table How to visit a tags table.
Find Tag Commands to find the definition of a specific tag.
Tags Search Using a tags table for searching and replacing.
List Tags Using tags for completion, and listing them.
Merging Files with Emerge
Overview of Emerge How to start Emerge. Basic concepts.
Submodes of Emerge Fast mode vs. Edit mode. Skip Prefers mode and Auto Advance mode.
State of Difference You do the merge by specifying state A or B for each difference.
Merge Commands Commands for selecting a difference, changing states of differences, etc.
Exiting Emerge What to do when you've finished the merge.
Combining in Emerge How to keep both alternatives for a difference.
Fine Points of Emerge Miscellaneous issues.
Abbrevs
Abbrev Concepts Fundamentals of defined abbrevs.
Defining Abbrevs Defining an abbrev, so it will expand when typed.
Expanding Abbrevs Controlling expansion: prefixes, canceling expansion.
Editing Abbrevs Viewing or editing the entire list of defined abbrevs.
Saving Abbrevs Saving the entire list of abbrevs for another session.
Dynamic Abbrevs Abbreviations for words already in the buffer.
Dabbrev Customization What is a word, for dynamic abbrevs. Case handling.
Editing Pictures
Basic Picture Basic concepts and simple commands of Picture Mode.
Insert in Picture Controlling direction of cursor motion after "self-inserting" characters.
Tabs in Picture Various features for tab stops and indentation.
Rectangles in Picture Clearing and superimposing rectangles.
Dired, the Directory Editor
Dired Enter How to invoke Dired.
Dired Navigation Special motion commands in the Dired buffer.
Dired Deletion Deleting files with Dired.
Flagging Many Files Flagging files based on their names.
Dired Visiting Other file operations through Dired.
Marks vs Flags Flagging for deletion vs marking.
Operating on Files How to copy, rename, print, compress, etc. either one file or several files.
Shell Commands in Dired Running a shell command on the marked files.
Transforming File Names Using patterns to rename multiple files.
Comparison in Dired Running diff by way of Dired.
Subdirectories in Dired Adding subdirectories to the Dired buffer.
Subdir Switches Subdirectory switches in Dired.
Subdirectory Motion Moving across subdirectories, and up and down.
Hiding Subdirectories Making subdirectories visible or invisible.
Dired Updating Discarding lines for files of no interest.
Dired and Find Using find to choose the files for Dired.
Wdired Operating on files by editing the Dired buffer.
Image-Dired Viewing image thumbnails in Dired.
Misc Dired Features Various other features.
The Calendar and the Diary
Calendar Motion Moving through the calendar; selecting a date.
Scroll Calendar Bringing earlier or later months onto the screen.
Counting Days How many days are there between two dates?
General Calendar Exiting or recomputing the calendar.
Writing Calendar Files Writing calendars to files of various formats.
Holidays Displaying dates of holidays.
Sunrise/Sunset Displaying local times of sunrise and sunset.
Lunar Phases Displaying phases of the moon.
Other Calendars Converting dates to other calendar systems.
Diary Displaying events from your diary.
Appointments Reminders when it's time to do something.
Importing Diary Converting diary events to/from other formats.
Daylight Saving How to specify when daylight saving time is active.
Time Intervals Keeping track of time intervals.
Advanced Calendar/Diary Usage Advanced Calendar/Diary customization.
Movement in the Calendar
Calendar Unit Motion Moving by days, weeks, months, and years.
Move to Beginning or End Moving to start/end of weeks, months, and years.
Specified Dates Moving to the current date or another specific date.
Conversion To and From Other Calendars
Calendar Systems The calendars Emacs understands (aside from Gregorian).
To Other Calendar Converting the selected date to various calendars.
From Other Calendar Moving to a date specified in another calendar.
Mayan Calendar Moving to a date specified in a Mayan calendar.
The Diary
Displaying the Diary Viewing diary entries and associated calendar dates.
Format of Diary File Entering events in your diary.
Date Formats Various ways you can specify dates.
Adding to Diary Commands to create diary entries.
Special Diary Entries Anniversaries, blocks of dates, cyclic entries, etc.
More advanced features of the Calendar and Diary
Calendar Customizing Calendar layout and hooks.
Holiday Customizing Defining your own holidays.
Date Display Format Changing the format.
Time Display Format Changing the format.
Diary Customizing Defaults you can set.
Non-Gregorian Diary Diary entries based on other calendars.
Diary Display A choice of ways to display the diary.
Fancy Diary Display Sorting diary entries, using included diary files.
Sexp Diary Entries More flexible diary entries.
Sending Mail
Mail Format Format of a mail message.
Mail Headers Details of some standard mail header fields.
Mail Aliases Abbreviating and grouping mail addresses.
Mail Commands Special commands for editing mail being composed.
Mail Signature Adding a signature to every message.
Mail Amusements Distracting the NSA; adding fortune messages.
Mail Methods Using alternative mail-composition methods.
Mail Commands
Mail Sending Commands to send the message.
Header Editing Commands to move to header fields and edit them.
Citing Mail Quoting a message you are replying to.
Mail Misc Attachments, spell checking, etc.
Reading Mail with Rmail
Rmail Basics Basic concepts of Rmail, and simple use.
Rmail Scrolling Scrolling through a message.
Rmail Motion Moving to another message.
Rmail Deletion Deleting and expunging messages.
Rmail Inbox How mail gets into the Rmail file.
Rmail Files Using multiple Rmail files.
Rmail Output Copying message out to files.
Rmail Labels Classifying messages by labeling them.
Rmail Attributes Certain standard labels, called attributes.
Rmail Reply Sending replies to messages you are viewing.
Rmail Summary Summaries show brief info on many messages.
Rmail Sorting Sorting messages in Rmail.
Rmail Display How Rmail displays a message; customization.
Rmail Coding How Rmail handles decoding character sets.
Rmail Editing Editing message text and headers in Rmail.
Rmail Digest Extracting the messages from a digest message.
Rmail Rot13 Reading messages encoded in the rot13 code.
Movemail More details of fetching new mail.
Remote Mailboxes Retrieving mail from remote mailboxes.
Other Mailbox Formats Retrieving mail from local mailboxes in various formats.
Rmail Summaries
Rmail Make Summary Making various sorts of summaries.
Rmail Summary Edit Manipulating messages from the summary.
Gnus
Buffers of Gnus The group, summary, and article buffers.
Gnus Startup What you should know about starting Gnus.
Gnus Group Buffer A short description of Gnus group commands.
Gnus Summary Buffer A short description of Gnus summary commands.
Document Viewing
DocView Navigation Navigating DocView buffers.
DocView Searching Searching inside documents.
DocView Slicing Specifying which part of a page is displayed.
DocView Conversion Influencing and triggering conversion.
Running Shell Commands from Emacs
Single Shell How to run one shell command and return.
Interactive Shell Permanent shell taking input via Emacs.
Shell Mode Special Emacs commands used with permanent shell.
Shell Prompts Two ways to recognize shell prompts.
Shell History Repeating previous commands in a shell buffer.
Directory Tracking Keeping track when the subshell changes directory.
Shell Options Options for customizing Shell mode.
Terminal emulator An Emacs window as a terminal emulator.
Term Mode Special Emacs commands used in Term mode.
Remote Host Connecting to another computer.
Serial Terminal Connecting to a serial port.
Shell Command History
Shell Ring Fetching commands from the history list.
Shell History Copying Moving to a command and then copying it.
History References Expanding ‘!’-style history references.
Using Emacs as a Server
Invoking emacsclient Connecting to the Emacs server.
emacsclient Options Emacs client startup options.
Printing Hard Copies
PostScript Printing buffers or regions as PostScript.
PostScript Variables Customizing the PostScript printing commands.
Printing Package An optional advanced printing interface.
Hyperlinking and Navigation Features
Browse-URL Following URLs.
Goto Address mode Activating URLs.
FFAP Finding files etc. at point.
Emacs Lisp Packages
Package Menu Buffer for viewing and managing packages.
Package Installation Options for package installation.
Package Files Where packages are installed.
Customization
Easy Customization Convenient way to browse and change settings.
Variables Many Emacs commands examine Emacs variables to decide what to do; by setting variables, you can control their functioning.
Key Bindings The keymaps say what command each key runs. By changing them, you can "redefine" keys.
Init File How to write common customizations in the initialization file.
Easy Customization Interface
Customization Groups How settings are classified.
Browsing Custom Browsing and searching for settings.
Changing a Variable How to edit an option's value and set the option.
Saving Customizations Saving customizations for future Emacs sessions.
Face Customization How to edit the attributes of a face.
Specific Customization Customizing specific settings or groups.
Custom Themes Collections of customization settings.
Creating Custom Themes How to create a new custom theme.
Variables
Examining Examining or setting one variable's value.
Hooks Hook variables let you specify programs for parts of Emacs to run on particular occasions.
Locals Per-buffer values of variables.
File Variables How files can specify variable values.
Directory Variables How variable values can be specified by directory.
Local Variables in Files
Specifying File Variables Specifying file local variables.
Safe File Variables Making sure file local variables are safe.
Customizing Key Bindings
Keymaps Generalities. The global keymap.
Prefix Keymaps Keymaps for prefix keys.
Local Keymaps Major and minor modes have their own keymaps.
Minibuffer Maps The minibuffer uses its own local keymaps.
Rebinding How to redefine one key's meaning conveniently.
Init Rebinding Rebinding keys with your initialization file.
Modifier Keys Using modifier keys in key bindings.
Function Keys Rebinding terminal function keys.
Named ASCII Chars Distinguishing <TAB> from C-i, and so on.
Mouse Buttons Rebinding mouse buttons in Emacs.
Disabling Disabling a command means confirmation is required before it can be executed. This is done to protect beginners from surprises.
The Emacs Initialization File
Init Syntax Syntax of constants in Emacs Lisp.
Init Examples How to do some things with an init file.
Terminal Init Each terminal type can have an init file.
Find Init How Emacs finds the init file.
Init Non-ASCII Using non-ASCII characters in an init file.
Dealing with Emacs Trouble
DEL Does Not Delete What to do if <DEL> doesn't delete.
Stuck Recursive `[...]' in mode line around the parentheses.
Screen Garbled Garbage on the screen.
Text Garbled Garbage in the text.
Memory Full How to cope when you run out of memory.
Crashing What Emacs does when it crashes.
After a Crash Recovering editing in an Emacs session that crashed.
Emergency Escape What to do if Emacs stops responding.
Reporting Bugs
Known Problems How to read about known problems and bugs.
Bug Criteria Have you really found a bug?
Understanding Bug Reporting How to report a bug effectively.
Checklist Steps to follow for a good bug report.
Sending Patches How to send a patch for GNU Emacs.
Command Line Arguments for Emacs Invocation
Action Arguments Arguments to visit files, load libraries, and call functions.
Initial Options Arguments that take effect while starting Emacs.
Command Example Examples of using command line arguments.
Environment Environment variables that Emacs uses.
Display X Changing the default display and using remote login.
Font X Choosing a font for text, under X.
Colors X Choosing display colors.
Window Size X Start-up window size, under X.
Borders X Internal and external borders, under X.
Title X Specifying the initial frame's title.
Icons X Choosing what sort of icon to use, under X.
Misc X Other display options.
Environment Variables
General Variables Environment variables that all versions of Emacs use.
Misc Variables Certain system-specific variables.
MS-Windows Registry An alternative to the environment on MS-Windows.
X Options and Resources
Resources Using X resources with Emacs (in general).
Table of Resources Table of specific X resources that affect Emacs.
Lucid Resources X resources for Lucid menus.
LessTif Resources X resources for LessTif and Motif menus.
GTK resources Resources for GTK widgets.
GTK resources
GTK Resource Basics Basic usage of GTK+ resources.
GTK Widget Names How GTK+ widgets are named.
GTK Names in Emacs GTK widgets used by Emacs.
GTK styles What can be customized in a GTK widget.
Emacs and Mac OS / GNUstep
Mac / GNUstep Basics Basic Emacs usage under GNUstep or Mac OS.
Mac / GNUstep Customization Customizations under GNUstep or Mac OS.
Mac / GNUstep Events How window system events are handled.
GNUstep Support Details on status of GNUstep support.
Emacs and Microsoft Windows/MS-DOS
Windows Startup How to start Emacs on Windows.
Text and Binary Text files use CRLF to terminate lines.
Windows Files File-name conventions on Windows.
ls in Lisp Emulation of ls for Dired.
Windows HOME Where Emacs looks for your .emacs and where it starts up.
Windows Keyboard Windows-specific keyboard features.
Windows Mouse Windows-specific mouse features.
Windows Processes Running subprocesses on Windows.
Windows Printing How to specify the printer on MS-Windows.
Windows Fonts Specifying fonts on MS-Windows.
Windows Misc Miscellaneous Windows features.
MS-DOS Using Emacs on MS-DOS.
Emacs and MS-DOS
MS-DOS Keyboard Keyboard conventions on MS-DOS.
MS-DOS Mouse Mouse conventions on MS-DOS.
MS-DOS Display Fonts, frames and display size on MS-DOS.
MS-DOS File Names File name conventions on MS-DOS.
MS-DOS Printing Printing specifics on MS-DOS.
MS-DOS and MULE Support for internationalization on MS-DOS.
MS-DOS Processes Running subprocesses on MS-DOS.

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Distribution

GNU Emacs is free software; this means that everyone is free to use it and free to redistribute it under certain conditions. GNU Emacs is not in the public domain; it is copyrighted and there are restrictions on its distribution, but these restrictions are designed to permit everything that a good cooperating citizen would want to do. What is not allowed is to try to prevent others from further sharing any version of GNU Emacs that they might get from you. The precise conditions are found in the GNU General Public License that comes with Emacs and also appears in this manual1. See Copying.

One way to get a copy of GNU Emacs is from someone else who has it. You need not ask for our permission to do so, or tell any one else; just copy it. If you have access to the Internet, you can get the latest distribution version of GNU Emacs by anonymous FTP; see http://www.gnu.org/software/emacs on our website for more information.

You may also receive GNU Emacs when you buy a computer. Computer manufacturers are free to distribute copies on the same terms that apply to everyone else. These terms require them to give you the full sources, including whatever changes they may have made, and to permit you to redistribute the GNU Emacs received from them under the usual terms of the General Public License. In other words, the program must be free for you when you get it, not just free for the manufacturer.

If you find GNU Emacs useful, please send a donation to the Free Software Foundation to support our work. Donations to the Free Software Foundation are tax deductible in the US. If you use GNU Emacs at your workplace, please suggest that the company make a donation. For more information on how you can help, see http://www.gnu.org/help/help.html.

We also sell hardcopy versions of this manual and An Introduction to Programming in Emacs Lisp, by Robert J. Chassell. You can visit our online store at http://shop.fsf.org/. The income from sales goes to support the foundation's purpose: the development of new free software, and improvements to our existing programs including GNU Emacs.

If you need to contact the Free Software Foundation, see http://www.fsf.org/about/contact/, or write to 

     Free Software Foundation
     51 Franklin Street, Fifth Floor
     Boston, MA 02110-1301
     USA

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Introduction

You are reading about GNU Emacs, the GNU incarnation of the advanced, self-documenting, customizable, extensible editor Emacs. (The `G' in `GNU' is not silent.)

We call Emacs advanced because it can do much more than simple insertion and deletion of text. It can control subprocesses, indent programs automatically, show multiple files at once, and more. Emacs editing commands operate in terms of characters, words, lines, sentences, paragraphs, and pages, as well as expressions and comments in various programming languages.

Self-documenting means that at any time you can use special commands, known as help commands, to find out what your options are, or to find out what any command does, or to find all the commands that pertain to a given topic. See Help.

Customizable means that you can easily alter the behavior of Emacs commands in simple ways. For instance, if you use a programming language in which comments start with ‘<**’ and end with ‘**>’, you can tell the Emacs comment manipulation commands to use those strings (see Comments). To take another example, you can rebind the basic cursor motion commands (up, down, left and right) to any keys on the keyboard that you find comfortable. See Customization.

Extensible means that you can go beyond simple customization and create entirely new commands. New commands are simply programs written in the Lisp language, which are run by Emacs's own Lisp interpreter. Existing commands can even be redefined in the middle of an editing session, without having to restart Emacs. Most of the editing commands in Emacs are written in Lisp; the few exceptions could have been written in Lisp but use C instead for efficiency. Writing an extension is programming, but non-programmers can use it afterwards. See Emacs Lisp Intro, if you want to learn Emacs Lisp programming.

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1 The Organization of the Screen

On a graphical display, such as on GNU/Linux using the X Window System, Emacs occupies a “graphical window”. On a text terminal, Emacs occupies the entire terminal screen. We will use the term frame to mean a graphical window or terminal screen occupied by Emacs. Emacs behaves very similarly on both kinds of frames. It normally starts out with just one frame, but you can create additional frames if you wish (see Frames).

Each frame consists of several distinct regions. At the top of the frame is a menu bar, which allows you to access commands via a series of menus. On a graphical display, directly below the menu bar is a tool bar, a row of icons that perform editing commands if you click on them. At the very bottom of the frame is an echo area, where informative messages are displayed and where you enter information when Emacs asks for it.

The main area of the frame, below the tool bar (if one exists) and above the echo area, is called the window. Henceforth in this manual, we will use the word “window” in this sense. Graphical display systems commonly use the word “window” with a different meaning; but, as stated above, we refer to those “graphical windows” as “frames”.

An Emacs window is where the buffer—the text you are editing—is displayed. On a graphical display, the window possesses a scroll bar on one side, which can be used to scroll through the buffer. The last line of the window is a mode line. This displays various information about what is going on in the buffer, such as whether there are unsaved changes, the editing modes that are in use, the current line number, and so forth.

When you start Emacs, there is normally only one window in the frame. However, you can subdivide this window horizontally or vertically to create multiple windows, each of which can independently display a buffer (see Windows).

At any time, one window is the selected window. On a graphical display, the selected window shows a more prominent cursor (usually solid and blinking); other windows show a less prominent cursor (usually a hollow box). On a text terminal, there is only one cursor, which is shown in the selected window. The buffer displayed in the selected window is called the current buffer, and it is where editing happens. Most Emacs commands implicitly apply to the current buffer; the text displayed in unselected windows is mostly visible for reference. If you use multiple frames on a graphical display, selecting a particular frame selects a window in that frame.

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1.1 Point

The cursor in the selected window shows the location where most editing commands take effect, which is called point2. Many Emacs commands move point to different places in the buffer; for example, you can place point by clicking mouse button 1 (normally the left button) at the desired location.

By default, the cursor in the selected window is drawn as a solid block and appears to be on a character, but you should think of point as between two characters; it is situated before the character under the cursor. For example, if your text looks like ‘frob’ with the cursor over the ‘b’, then point is between the ‘o’ and the ‘b’. If you insert the character ‘!’ at that position, the result is ‘fro!b’, with point between the ‘!’ and the ‘b’. Thus, the cursor remains over the ‘b’, as before.

If you are editing several files in Emacs, each in its own buffer, each buffer has its own value of point. A buffer that is not currently displayed remembers its value of point if you later display it again. Furthermore, if a buffer is displayed in multiple windows, each of those windows has its own value of point.

See Cursor Display, for options that control how Emacs displays the cursor.

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1.2 The Echo Area

The line at the very bottom of the frame is the echo area. It is used to display small amounts of text for various purposes.

The echo area is so-named because one of the things it is used for is echoing, which means displaying the characters of a multi-character command as you type. Single-character commands are not echoed. Multi-character commands (see Keys) are echoed if you pause for more than a second in the middle of a command. Emacs then echoes all the characters of the command so far, to prompt you for the rest. Once echoing has started, the rest of the command echoes immediately as you type it. This behavior is designed to give confident users fast response, while giving hesitant users maximum feedback.

The echo area is also used to display an error message when a command cannot do its job. Error messages may be accompanied by beeping or by flashing the screen.

Some commands display informative messages in the echo area to tell you what the command has done, or to provide you with some specific information. These informative messages, unlike error messages, are not accompanied with a beep or flash. For example, C-x = (hold down <CTRL> and type x, then let go of <CTRL> and type =) displays a message describing the character at point, its position in the buffer, and its current column in the window. Commands that take a long time often display messages ending in ‘...’ while they are working (sometimes also indicating how much progress has been made, as a percentage), and add ‘done’ when they are finished.

Informative echo area messages are saved in a special buffer named *Messages*. (We have not explained buffers yet; see Buffers, for more information about them.) If you miss a message that appeared briefly on the screen, you can switch to the *Messages* buffer to see it again. The *Messages* buffer is limited to a certain number of lines, specified by the variable message-log-max. (We have not explained variables either; see Variables, for more information about them.) Beyond this limit, one line is deleted from the beginning whenever a new message line is added at the end.

See Display Custom, for options that control how Emacs uses the echo area.

The echo area is also used to display the minibuffer, a special window where you can input arguments to commands, such as the name of a file to be edited. When the minibuffer is in use, the text displayed in the echo area begins with a prompt string, and the active cursor appears within the minibuffer, which is temporarily considered the selected window. You can always get out of the minibuffer by typing C-g. See Minibuffer.

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1.3 The Mode Line

At the bottom of each window is a mode line, which describes what is going on in the current buffer. When there is only one window, the mode line appears right above the echo area; it is the next-to-last line in the frame. On a graphical display, the mode line is drawn with a 3D box appearance. Emacs also usually draws the mode line of the selected window with a different color than that of unselected windows, in order to make it stand out.

The text displayed in the mode line has the following format: 

      cs:ch-fr  buf      pos line   (major minor)

On a text terminal, this text is followed by a series of dashes extending to the right edge of the window. These dashes are omitted on a graphical display.

The cs string and the colon character after it describe the character set and newline convention used for the current buffer. Normally, Emacs automatically handles these settings for you, but it is sometimes useful to have this information.

cs describes the character set of the text in the buffer (see Coding Systems). If it is a dash (‘-’), that indicates no special character set handling (with the possible exception of end-of-line conventions, described in the next paragraph). ‘=’ means no conversion whatsoever, and is usually used for files containing non-textual data. Other characters represent various coding systems—for example, ‘1’ represents ISO Latin-1.

On a text terminal, cs is preceded by two additional characters that describe the coding systems for keyboard input and terminal output. Furthermore, if you are using an input method, cs is preceded by a string that identifies the input method (see Input Methods).

The character after cs is usually a colon. If a different string is displayed, that indicates a nontrivial end-of-line convention for encoding a file. Usually, lines of text are separated by newline characters in a file, but two other conventions are sometimes used. The MS-DOS convention uses a “carriage-return” character followed by a “linefeed” character; when editing such files, the colon changes to either a backslash (‘\’) or ‘(DOS)’, depending on the operating system. Another convention, employed by older Macintosh systems, uses a “carriage-return” character instead of a newline; when editing such files, the colon changes to either a forward slash (‘/’) or ‘(Mac)’. On some systems, Emacs displays ‘(Unix)’ instead of the colon for files that use newline as the line separator.

The next element on the mode line is the string indicated by ch. This shows two dashes (‘--’) if the buffer displayed in the window has the same contents as the corresponding file on the disk; i.e., if the buffer is “unmodified”. If the buffer is modified, it shows two stars (‘**’). For a read-only buffer, it shows ‘%*’ if the buffer is modified, and ‘%%’ otherwise.

The character after ch is normally a dash (‘-’). However, if the default-directory for the current buffer is on a remote machine, ‘@’ is displayed instead (see File Names).

fr gives the selected frame name (see Frames). It appears only on text terminals. The initial frame's name is ‘F1’.

buf is the name of the buffer displayed in the window. Usually, this is the same as the name of a file you are editing. See Buffers.

pos tells you whether there is additional text above the top of the window, or below the bottom. If your buffer is small and all of it is visible in the window, pos is ‘All’. Otherwise, it is ‘Top’ if you are looking at the beginning of the buffer, ‘Bot’ if you are looking at the end of the buffer, or ‘nn%’, where nn is the percentage of the buffer above the top of the window. With Size Indication mode, you can display the size of the buffer as well. See Optional Mode Line.

line is the character ‘L’ followed by the line number at point. (You can display the current column number too, by turning on Column Number mode. See Optional Mode Line.)

major is the name of the major mode used in the buffer. A major mode is a principal editing mode for the buffer, such as Text mode, Lisp mode, C mode, and so forth. See Major Modes. Some major modes display additional information after the major mode name. For example, Compilation buffers and Shell buffers display the status of the subprocess.

minor is a list of some of the enabled minor modes, which are optional editing modes that provide additional features on top of the major mode. See Minor Modes.

Some features are listed together with the minor modes whenever they are turned on, even though they are not really minor modes. ‘Narrow’ means that the buffer being displayed has editing restricted to only a portion of its text (see Narrowing). ‘Def’ means that a keyboard macro is currently being defined (see Keyboard Macros).

In addition, if Emacs is inside a recursive editing level, square brackets (‘[...]’) appear around the parentheses that surround the modes. If Emacs is in one recursive editing level within another, double square brackets appear, and so on. Since recursive editing levels affect Emacs globally, such square brackets appear in the mode line of every window. See Recursive Edit.

You can change the appearance of the mode line as well as the format of its contents. See Optional Mode Line. In addition, the mode line is mouse-sensitive; clicking on different parts of the mode line performs various commands. See Mode Line Mouse.

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1.4 The Menu Bar

Each Emacs frame normally has a menu bar at the top which you can use to perform common operations. There's no need to list them here, as you can more easily see them yourself.

On a graphical display, you can use the mouse to choose a command from the menu bar. An arrow on the right edge of a menu item means it leads to a subsidiary menu, or submenu. A ‘...’ at the end of a menu item means that the command will prompt you for further input before it actually does anything.

Some of the commands in the menu bar have ordinary key bindings as well; if so, a key binding is shown in parentheses after the item itself. To view the full command name and documentation for a menu item, type C-h k, and then select the menu bar with the mouse in the usual way (see Key Help).

Instead of using the mouse, you can also invoke the first menu bar item by pressing <F10> (to run the command menu-bar-open). You can then navigate the menus with the arrow keys. To activate a selected menu item, press <RET>; to cancel menu navigation, press <ESC>.

On a text terminal, you can use the menu bar by typing M-` or <F10> (these run the command tmm-menubar). This lets you select a menu item with the keyboard. A provisional choice appears in the echo area. You can use the up and down arrow keys to move through the menu to different items, and then you can type <RET> to select the item. Each menu item is also designated by a letter or digit (usually the initial of some word in the item's name). This letter or digit is separated from the item name by ‘==>’. You can type the item's letter or digit to select the item.

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2 Kinds of User Input

GNU Emacs is primarily designed for use with the keyboard. While it is possible to use the mouse to issue editing commands through the menu bar and tool bar, that is not as efficient as using the keyboard. Therefore, this manual mainly documents how to edit with the keyboard.

Keyboard input into Emacs is based on a heavily-extended version of ASCII. Simple characters, like ‘a’, ‘B’, ‘3’, ‘=’, and the space character (denoted as <SPC>), are entered by typing the corresponding key. Control characters, such as <RET>, <TAB>, <DEL>, <ESC>, <F1>, <Home>, and <left>, are also entered this way, as are certain characters found on non-English keyboards (see International).

Emacs also recognizes control characters that are entered using modifier keys. Two commonly-used modifier keys are <Control> (usually labeled <Ctrl>), and <Meta> (usually labeled <Alt>)3. For example, Control-a is entered by holding down the <Ctrl> key while pressing a; we will refer to this as C-a for short. Similarly Meta-a, or M-a for short, is entered by holding down the <Alt> key and pressing a. Modifier keys can also be applied to non-alphanumerical characters, e.g., C-<F1> or M-<left>.

You can also type Meta characters using two-character sequences starting with <ESC>. Thus, you can enter M-a by typing <ESC> a. You can enter C-M-a by typing <ESC> C-a. Unlike <Meta>, <ESC> is entered as a separate character. You don't hold down <ESC> while typing the next character; instead, press <ESC> and release it, then enter the next character. This feature is useful on certain text terminals where the <Meta> key does not function reliably.

On graphical displays, the window manager might block some keyboard inputs, including M-<TAB>, M-<SPC>, C-M-d and C-M-l. If you have this problem, you can either customize your window manager to not block those keys, or “rebind” the affected Emacs commands (see Customization).

Simple characters and control characters, as well as certain non-keyboard inputs such as mouse clicks, are collectively referred to as input events. For details about how Emacs internally handles input events, see Input Events.

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3 Keys

Some Emacs commands are invoked by just one input event; for example, C-f moves forward one character in the buffer. Other commands take two or more input events to invoke, such as C-x C-f and C-x 4 C-f.

A key sequence, or key for short, is a sequence of one or more input events that is meaningful as a unit. If a key sequence invokes a command, we call it a complete key; for example, C-f, C-x C-f and C-x 4 C-f are all complete keys. If a key sequence isn't long enough to invoke a command, we call it a prefix key; from the preceding example, we see that C-x and C-x 4 are prefix keys. Every key sequence is either a complete key or a prefix key.

A prefix key combines with the following input event to make a longer key sequence. For example, C-x is a prefix key, so typing C-x alone does not invoke a command; instead, Emacs waits for further input (if you pause for longer than a second, it echoes the C-x key to prompt for that input; see Echo Area). C-x combines with the next input event to make a two-event key sequence, which could itself be a prefix key (such as C-x 4), or a complete key (such as C-x C-f). There is no limit to the length of key sequences, but in practice they are seldom longer than three or four input events.

You can't add input events onto a complete key. For example, because C-f is a complete key, the two-event sequence C-f C-k is two key sequences, not one.

By default, the prefix keys in Emacs are C-c, C-h, C-x, C-x <RET>, C-x @, C-x a, C-x n, C-x r, C-x v, C-x 4, C-x 5, C-x 6, <ESC>, M-g, and M-o. (<F1> and <F2> are aliases for C-h and C-x 6.) This list is not cast in stone; if you customize Emacs, you can make new prefix keys. You could even eliminate some of the standard ones, though this is not recommended for most users; for example, if you remove the prefix definition of C-x 4, then C-x 4 C-f becomes an invalid key sequence. See Key Bindings.

Typing the help character (C-h or <F1>) after a prefix key displays a list of the commands starting with that prefix. The sole exception to this rule is <ESC>: <ESC> C-h is equivalent to C-M-h, which does something else entirely. You can, however, use <F1> to display a list of commands starting with <ESC>.

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4 Keys and Commands

This manual is full of passages that tell you what particular keys do. But Emacs does not assign meanings to keys directly. Instead, Emacs assigns meanings to named commands, and then gives keys their meanings by binding them to commands.

Every command has a name chosen by a programmer. The name is usually made of a few English words separated by dashes; for example, next-line or forward-word. Internally, each command is a special type of Lisp function, and the actions associated with the command are performed by running the function. See What Is a Function.

The bindings between keys and commands are recorded in tables called keymaps. See Keymaps.

When we say that “C-n moves down vertically one line” we are glossing over a subtle distinction that is irrelevant in ordinary use, but vital for Emacs customization. The command next-line does a vertical move downward. C-n has this effect because it is bound to next-line. If you rebind C-n to the command forward-word, C-n will move forward one word instead.

In this manual, we will often speak of keys like C-n as commands, even though strictly speaking the key is bound to a command. Usually we state the name of the command which really does the work in parentheses after mentioning the key that runs it. For example, we will say that “The command C-n (next-line) moves point vertically down”, meaning that the command next-line moves vertically down, and the key C-n is normally bound to it.

Since we are discussing customization, we should tell you about variables. Often the description of a command will say, “To change this, set the variable mumble-foo.” A variable is a name used to store a value. Most of the variables documented in this manual are meant for customization: some command or other part of Emacs examines the variable and behaves differently according to the value that you set. You can ignore the information about variables until you are interested in customizing them. Then read the basic information on variables (see Variables) and the information about specific variables will make sense.

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5 Entering Emacs

The usual way to invoke Emacs is with the shell command emacs. From a terminal window running in the X Window System, you can run Emacs in the background with emacs &; this way, Emacs won't tie up the terminal window, so you can use it to run other shell commands.

When Emacs starts up, the initial frame displays a special buffer named ‘*GNU Emacs*’. This startup screen contains information about Emacs and links to common tasks that are useful for beginning users. For instance, activating the ‘Emacs Tutorial’ link opens the Emacs tutorial; this does the same thing as the command C-h t (help-with-tutorial). To activate a link, either move point onto it and type <RET>, or click on it with mouse-1 (the left mouse button).

Using a command line argument, you can tell Emacs to visit one or more files as soon as it starts up. For example, emacs foo.txt starts Emacs with a buffer displaying the contents of the file ‘foo.txt’. This feature exists mainly for compatibility with other editors, which are designed to be launched from the shell for short editing sessions. If you call Emacs this way, the initial frame is split into two windows—one showing the specified file, and the other showing the startup screen. See Windows.

Generally, it is unnecessary and wasteful to start Emacs afresh each time you want to edit a file. The recommended way to use Emacs is to start it just once, just after you log in, and do all your editing in the same Emacs session. See Files, for information on visiting more than one file. If you use Emacs this way, the Emacs session accumulates valuable context, such as the kill ring, registers, undo history, and mark ring data, which together make editing more convenient. These features are described later in the manual.

To edit a file from another program while Emacs is running, you can use the emacsclient helper program to open a file in the existing Emacs session. See Emacs Server.

Emacs accepts other command line arguments that tell it to load certain Lisp files, where to put the initial frame, and so forth. See Emacs Invocation.

If the variable inhibit-startup-screen is non-nil, Emacs does not display the startup screen. In that case, if one or more files were specified on the command line, Emacs simply displays those files; otherwise, it displays a buffer named *scratch*, which can be used to evaluate Emacs Lisp expressions interactively. See Lisp Interaction. You can set the variable inhibit-startup-screen using the Customize facility (see Easy Customization), or by editing your initialization file (see Init File).4

You can also force Emacs to display a file or directory at startup by setting the variable initial-buffer-choice to a non-nil value. (In that case, even if you specify one or more files on the command line, Emacs opens but does not display them.) The value of initial-buffer-choice should be the name of the desired file or directory.

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6 Exiting Emacs

C-x C-c
Kill Emacs (save-buffers-kill-terminal).
C-z
On a text terminal, suspend Emacs; on a graphical display, “minimize” the selected frame (suspend-emacs).

Killing Emacs means terminating the Emacs program. To do this, type C-x C-c (save-buffers-kill-terminal). A two-character key sequence is used to make it harder to type by accident. If there are any modified file-visiting buffers when you type C-x C-c, Emacs first offers to save these buffers. If you do not save them all, it asks for confirmation again, since the unsaved changes will be lost. Emacs also asks for confirmation if any subprocesses are still running, since killing Emacs will also kill the subprocesses (see Shell).

C-x C-c behaves specially if you are using Emacs as a server. If you type it from a “client frame”, it closes the client connection. See Emacs Server.

Emacs can, optionally, record certain session information when you kill it, such as the files you were visiting at the time. This information is then available the next time you start Emacs. See Saving Emacs Sessions.

If the value of the variable confirm-kill-emacs is non-nil, C-x C-c assumes that its value is a predicate function, and calls that function. If the result of the function call is non-nil, the session is killed, otherwise Emacs continues to run. One convenient function to use as the value of confirm-kill-emacs is the function yes-or-no-p. The default value of confirm-kill-emacs is nil.

To kill Emacs without being prompted about saving, type M-x kill-emacs.

C-z runs the command suspend-frame. On a graphical display, this command minimizes (or iconifies) the selected Emacs frame, hiding it in a way that lets you bring it back later (exactly how this hiding occurs depends on the window system). On a text terminal, the C-z command suspends Emacs, stopping the program temporarily and returning control to the parent process (usually a shell); in most shells, you can resume Emacs after suspending it with the shell command %emacs.

Text terminals usually listen for certain special characters whose meaning is to kill or suspend the program you are running. This terminal feature is turned off while you are in Emacs. The meanings of C-z and C-x C-c as keys in Emacs were inspired by the use of C-z and C-c on several operating systems as the characters for stopping or killing a program, but that is their only relationship with the operating system. You can customize these keys to run any commands of your choice (see Keymaps).

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7 Basic Editing Commands

Here we explain the basics of how to enter text, make corrections, and save the text in a file. If this material is new to you, we suggest you first run the Emacs learn-by-doing tutorial, by typing C-h t (help-with-tutorial).

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7.1 Inserting Text

You can insert an ordinary graphic character (e.g., ‘a’, ‘B’, ‘3’, and ‘=’) by typing the associated key. This adds the character to the buffer at point. Insertion moves point forward, so that point remains just after the inserted text. See Point.

To end a line and start a new one, type <RET> (newline). (The <RET> key may be labeled <Return> or <Enter> on your keyboard, but we refer to it as <RET> in this manual.) This command inserts a newline character into the buffer. If point is at the end of the line, the effect is to create a new blank line after it; if point is in the middle of a line, the line is split at that position.

As we explain later in this manual, you can change the way Emacs handles text insertion by turning on minor modes. For instance, the minor mode called Auto Fill mode splits lines automatically when they get too long (see Filling). The minor mode called Overwrite mode causes inserted characters to replace (overwrite) existing text, instead of shoving it to the right. See Minor Modes.

Only graphic characters can be inserted by typing the associated key; other keys act as editing commands and do not insert themselves. For instance, DEL runs the command delete-backward-char by default (some modes bind it to a different command); it does not insert a literal ‘DEL’ character (ASCII character code 127).

To insert a non-graphic character, or a character that your keyboard does not support, first quote it by typing C-q (quoted-insert). There are two ways to use C-q:

To use decimal or hexadecimal instead of octal, set the variable read-quoted-char-radix to 10 or 16. If the radix is 16, the letters a to f serve as part of a character code, just like digits. Case is ignored.

Alternatively, you can use the command C-x 8 <RET> (insert-char). This prompts for the Unicode name or code-point of a character, using the minibuffer. If you enter a name, the command provides completion (see Completion). If you enter a code-point, it should be as a hexadecimal number (the convention for Unicode), or a number with a specified radix, e.g., #o23072 (octal); See Integer Basics. The command then inserts the corresponding character into the buffer. For example, both of the following insert the infinity sign (Unicode code-point U+221E): 

     C-x 8 <RET> infinity <RET>
     C-x 8 <RET> 221e <RET>

A numeric argument to C-q or C-x 8 <RET> specifies how many copies of the character to insert (see Arguments).

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7.2 Changing the Location of Point

To do more than insert characters, you have to know how to move point (see Point). The keyboard commands C-f, C-b, C-n, and C-p move point to the right, left, down, and up, respectively. You can also move point using the arrow keys present on most keyboards: <right>, <left>, <down>, and <up>; however, many Emacs users find that it is slower to use the arrow keys than the control keys, because you need to move your hand to the area of the keyboard where those keys are located.

You can also click the left mouse button to move point to the position clicked. Emacs also provides a variety of additional keyboard commands that move point in more sophisticated ways.

C-f
Move forward one character (forward-char).
<right>
This command (right-char) behaves like C-f, with one exception: when editing right-to-left scripts such as Arabic, it instead moves backward if the current paragraph is a right-to-left paragraph. See Bidirectional Editing.
C-b
Move backward one character (backward-char).
<left>
This command (left-char) behaves like C-b, except it moves forward if the current paragraph is right-to-left. See Bidirectional Editing.
C-n
<down>
Move down one screen line (next-line). This command attempts to keep the horizontal position unchanged, so if you start in the middle of one line, you move to the middle of the next.
C-p
<up>
Move up one screen line (previous-line). This command preserves position within the line, like C-n.
C-a
<Home>
Move to the beginning of the line (move-beginning-of-line).
C-e
<End>
Move to the end of the line (move-end-of-line).
M-f
Move forward one word (forward-word).
C-<right>
M-<right>
This command (right-word) behaves like M-f, except it moves backward by one word if the current paragraph is right-to-left. See Bidirectional Editing.
M-b
Move backward one word (backward-word).
C-<left>
M-<left>
This command (left-word) behaves like M-f, except it moves forward by one word if the current paragraph is right-to-left. See Bidirectional Editing.
M-r
Without moving the text on the screen, reposition point on the left margin of the center-most text line of the window; on subsequent consecutive invocations, move point to the left margin of the top-most line, the bottom-most line, and so forth, in cyclic order (move-to-window-line-top-bottom).

A numeric argument says which screen line to place point on, counting downward from the top of the window (zero means the top line). A negative argument counts lines up from the bottom (−1 means the bottom line). See Arguments, for more information on numeric arguments.

M-<
Move to the top of the buffer (beginning-of-buffer). With numeric argument n, move to n/10 of the way from the top.
M->
Move to the end of the buffer (end-of-buffer).
C-v
<PageDown>
<next>
Scroll the display one screen forward, and move point onscreen if necessary (scroll-up-command). See Scrolling.
M-v
<PageUp>
<prior>
Scroll one screen backward, and move point onscreen if necessary (scroll-down-command). See Scrolling.
M-g c
Read a number n and move point to buffer position n. Position 1 is the beginning of the buffer.
M-g M-g
M-g g
Read a number n and move point to the beginning of line number n (goto-line). Line 1 is the beginning of the buffer. If point is on or just after a number in the buffer, that is the default for n. Just type <RET> in the minibuffer to use it. You can also specify n by giving M-g M-g a numeric prefix argument. See Select Buffer, for the behavior of M-g M-g when you give it a plain prefix argument.
M-g <TAB>
Read a number n and move to column n in the current line. Column 0 is the leftmost column. If called with a prefix argument, move to the column number specified by the argument's numeric value.
C-x C-n
Use the current column of point as the semipermanent goal column for C-n and C-p (set-goal-column). When a semipermanent goal column is in effect, those commands always try to move to this column, or as close as possible to it, after moving vertically. The goal column remains in effect until canceled.
C-u C-x C-n
Cancel the goal column. Henceforth, C-n and C-p try to preserve the horizontal position, as usual.

When a line of text in the buffer is longer than the width of the window, Emacs usually displays it on two or more screen lines. For convenience, C-n and C-p move point by screen lines, as do the equivalent keys <down> and <up>. You can force these commands to move according to logical lines (i.e., according to the text lines in the buffer) by setting the variable line-move-visual to nil; if a logical line occupies multiple screen lines, the cursor then skips over the additional screen lines. For details, see Continuation Lines. See Variables, for how to set variables such as line-move-visual.

Unlike C-n and C-p, most of the Emacs commands that work on lines work on logical lines. For instance, C-a (move-beginning-of-line) and C-e (move-end-of-line) respectively move to the beginning and end of the logical line. Whenever we encounter commands that work on screen lines, such as C-n and C-p, we will point these out.

When line-move-visual is nil, you can also set the variable track-eol to a non-nil value. Then C-n and C-p, when starting at the end of the logical line, move to the end of the next logical line. Normally, track-eol is nil.

C-n normally stops at the end of the buffer when you use it on the last line in the buffer. However, if you set the variable next-line-add-newlines to a non-nil value, C-n on the last line of a buffer creates an additional line at the end and moves down into it.

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7.3 Erasing Text

<DEL>
<Backspace>
Delete the character before point, or the region if it is active (delete-backward-char).
<Delete>
Delete the character after point, or the region if it is active (delete-forward-char).
C-d
Delete the character after point (delete-char).
C-k
Kill to the end of the line (kill-line).
M-d
Kill forward to the end of the next word (kill-word).
M-<DEL>
Kill back to the beginning of the previous word (backward-kill-word).

The <DEL> (delete-backward-char) command removes the character before point, moving the cursor and the characters after it backwards. If point was at the beginning of a line, this deletes the preceding newline, joining this line to the previous one.

If, however, the region is active, <DEL> instead deletes the text in the region. See Mark, for a description of the region.

On most keyboards, <DEL> is labeled <Backspace>, but we refer to it as <DEL> in this manual. (Do not confuse <DEL> with the <Delete> key; we will discuss <Delete> momentarily.) On some text terminals, Emacs may not recognize the <DEL> key properly. See DEL Does Not Delete, if you encounter this problem.

The <delete> (delete-forward-char) command deletes in the “opposite direction”: it deletes the character after point, i.e., the character under the cursor. If point was at the end of a line, this joins the following line onto this one. Like <DEL>, it deletes the text in the region if the region is active (see Mark).

C-d (delete-char) deletes the character after point, similar to <delete>, but regardless of whether the region is active.

See Deletion, for more detailed information about the above deletion commands.

C-k (kill-line) erases (kills) a line at a time. If you type C-k at the beginning or middle of a line, it kills all the text up to the end of the line. If you type C-k at the end of a line, it joins that line with the following line.

See Killing, for more information about C-k and related commands.

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7.4 Undoing Changes

C-/
Undo one entry of the undo records—usually, one command worth (undo).
C-x u
C-_
The same.

Emacs records a list of changes made in the buffer text, so you can undo recent changes. This is done using the undo command, which is bound to C-/ (as well as C-x u and C-_). Normally, this command undoes the last change, moving point back to where it was before the change. The undo command applies only to changes in the buffer; you can't use it to undo cursor motion.

Although each editing command usually makes a separate entry in the undo records, very simple commands may be grouped together. Sometimes, an entry may cover just part of a complex command.

If you repeat C-/ (or its aliases), each repetition undoes another, earlier change, back to the limit of the undo information available. If all recorded changes have already been undone, the undo command displays an error message and does nothing.

To learn more about the undo command, see Undo.

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7.5 Files

Text that you insert in an Emacs buffer lasts only as long as the Emacs session. To keep any text permanently, you must put it in a file.

Suppose there is a file named test.emacs in your home directory. To begin editing this file in Emacs, type 

     C-x C-f test.emacs <RET>

Here the file name is given as an argument to the command C-x C-f (find-file). That command uses the minibuffer to read the argument, and you type <RET> to terminate the argument (see Minibuffer).

Emacs obeys this command by visiting the file: it creates a buffer, copies the contents of the file into the buffer, and then displays the buffer for editing. If you alter the text, you can save the new text in the file by typing C-x C-s (save-buffer). This copies the altered buffer contents back into the file test.emacs, making them permanent. Until you save, the changed text exists only inside Emacs, and the file test.emacs is unaltered.

To create a file, just visit it with C-x C-f as if it already existed. This creates an empty buffer, in which you can insert the text you want to put in the file. Emacs actually creates the file the first time you save this buffer with C-x C-s.

To learn more about using files in Emacs, see Files.

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7.6 Help

If you forget what a key does, you can find out by typing C-h k (describe-key), followed by the key of interest; for example, C-h k C-n tells you what C-n does.

The prefix key C-h stands for “help”. The key <F1> serves as an alias for C-h. Apart from C-h k, there are many other help commands providing different kinds of help.

See Help, for details.

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7.7 Blank Lines

Here are special commands and techniques for inserting and deleting blank lines.

C-o
Insert a blank line after the cursor (open-line).
C-x C-o
Delete all but one of many consecutive blank lines (delete-blank-lines).

We have seen how <RET> (newline) starts a new line of text. However, it may be easier to see what you are doing if you first make a blank line and then insert the desired text into it. This is easy to do using the key C-o (open-line), which inserts a newline after point but leaves point in front of the newline. After C-o, type the text for the new line.

You can make several blank lines by typing C-o several times, or by giving it a numeric argument specifying how many blank lines to make. See Arguments, for how. If you have a fill prefix, the C-o command inserts the fill prefix on the new line, if typed at the beginning of a line. See Fill Prefix.

The easy way to get rid of extra blank lines is with the command C-x C-o (delete-blank-lines). If point lies within a run of several blank lines, C-x C-o deletes all but one of them. If point is on a single blank line, C-x C-o deletes it. If point is on a nonblank line, C-x C-o deletes all following blank lines, if any exists.

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7.8 Continuation Lines

Sometimes, a line of text in the buffer—a logical line—is too long to fit in the window, and Emacs displays it as two or more screen lines. This is called line wrapping or continuation, and the long logical line is called a continued line. On a graphical display, Emacs indicates line wrapping with small bent arrows in the left and right window fringes. On a text terminal, Emacs indicates line wrapping by displaying a ‘\’ character at the right margin.

Most commands that act on lines act on logical lines, not screen lines. For instance, C-k kills a logical line. As described earlier, C-n (next-line) and C-p (previous-line) are special exceptions: they move point down and up, respectively, by one screen line (see Moving Point).

Emacs can optionally truncate long logical lines instead of continuing them. This means that every logical line occupies a single screen line; if it is longer than the width of the window, the rest of the line is not displayed. On a graphical display, a truncated line is indicated by a small straight arrow in the right fringe; on a text terminal, it is indicated by a ‘$’ character in the right margin. See Line Truncation.

By default, continued lines are wrapped at the right window edge. Since the wrapping may occur in the middle of a word, continued lines can be difficult to read. The usual solution is to break your lines before they get too long, by inserting newlines. If you prefer, you can make Emacs insert a newline automatically when a line gets too long, by using Auto Fill mode. See Filling.

Sometimes, you may need to edit files containing many long logical lines, and it may not be practical to break them all up by adding newlines. In that case, you can use Visual Line mode, which enables word wrapping: instead of wrapping long lines exactly at the right window edge, Emacs wraps them at the word boundaries (i.e., space or tab characters) nearest to the right window edge. Visual Line mode also redefines editing commands such as C-a, C-n, and C-k to operate on screen lines rather than logical lines. See Visual Line Mode.

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7.9 Cursor Position Information

Here are commands to get information about the size and position of parts of the buffer, and to count words and lines.

M-x what-line
Display the line number of point.
M-x line-number-mode
M-x column-number-mode
Toggle automatic display of the current line number or column number. See Optional Mode Line.
M-=
Display the number of lines, words, and characters that are present in the region (count-words-region). See Mark, for information about the region.
M-x count-words
Display the number of lines, words, and characters that are present in the buffer. If the region is active (see Mark), display the numbers for the region instead.
C-x =
Display the character code of character after point, character position of point, and column of point (what-cursor-position).
M-x hl-line-mode
Enable or disable highlighting of the current line. See Cursor Display.
M-x size-indication-mode
Toggle automatic display of the size of the buffer. See Optional Mode Line.

M-x what-line displays the current line number in the echo area. This command is usually redundant, because the current line number is shown in the mode line (see Mode Line). However, if you narrow the buffer, the mode line shows the line number relative to the accessible portion (see Narrowing). By contrast, what-line displays both the line number relative to the narrowed region and the line number relative to the whole buffer.

M-= (count-words-region) displays a message reporting the number of lines, words, and characters in the region (see Mark, for an explanation of the region). With a prefix argument, C-u M-=, the command displays a count for the entire buffer.

The command M-x count-words does the same job, but with a different calling convention. It displays a count for the region if the region is active, and for the buffer otherwise.

The command C-x = (what-cursor-position) shows information about the current cursor position and the buffer contents at that position. It displays a line in the echo area that looks like this: 

     Char: c (99, #o143, #x63) point=28062 of 36168 (78%) column=53

After ‘Char:’, this shows the character in the buffer at point. The text inside the parenthesis shows the corresponding decimal, octal and hex character codes; for more information about how C-x = displays character information, see International Chars. After ‘point=’ is the position of point as a character count (the first character in the buffer is position 1, the second character is position 2, and so on). The number after that is the total number of characters in the buffer, and the number in parenthesis expresses the position as a percentage of the total. After ‘column=’ is the horizontal position of point, in columns counting from the left edge of the window.

If the buffer has been narrowed, making some of the text at the beginning and the end temporarily inaccessible, C-x = displays additional text describing the currently accessible range. For example, it might display this: 

     Char: C (67, #o103, #x43) point=252 of 889 (28%) <231-599> column=0

where the two extra numbers give the smallest and largest character position that point is allowed to assume. The characters between those two positions are the accessible ones. See Narrowing.

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7.10 Numeric Arguments

In the terminology of mathematics and computing, argument means “data provided to a function or operation”. You can give any Emacs command a numeric argument (also called a prefix argument). Some commands interpret the argument as a repetition count. For example, giving C-f an argument of ten causes it to move point forward by ten characters instead of one. With these commands, no argument is equivalent to an argument of one, and negative arguments cause them to move or act in the opposite direction.

The easiest way to specify a numeric argument is to type a digit and/or a minus sign while holding down the <META> key. For example, 

     M-5 C-n

moves down five lines. The keys M-1, M-2, and so on, as well as M--, are bound to commands (digit-argument and negative-argument) that set up an argument for the next command. Meta-- without digits normally means −1.

If you enter more than one digit, you need not hold down the <META> key for the second and subsequent digits. Thus, to move down fifty lines, type 

     M-5 0 C-n

Note that this does not insert five copies of ‘0’ and move down one line, as you might expect—the ‘0’ is treated as part of the prefix argument.

(What if you do want to insert five copies of ‘0’? Type M-5 C-u 0. Here, C-u “terminates” the prefix argument, so that the next keystroke begins the command that you want to execute. Note that this meaning of C-u applies only to this case. For the usual role of C-u, see below.)

Instead of typing M-1, M-2, and so on, another way to specify a numeric argument is to type C-u (universal-argument) followed by some digits, or (for a negative argument) a minus sign followed by digits. A minus sign without digits normally means −1.

C-u alone has the special meaning of “four times”: it multiplies the argument for the next command by four. C-u C-u multiplies it by sixteen. Thus, C-u C-u C-f moves forward sixteen characters. Other useful combinations are C-u C-n, C-u C-u C-n (move down a good fraction of a screen), C-u C-u C-o (make “a lot” of blank lines), and C-u C-k (kill four lines).

You can use a numeric argument before a self-inserting character to insert multiple copies of it. This is straightforward when the character is not a digit; for example, C-u 6 4 a inserts 64 copies of the character ‘a’. But this does not work for inserting digits; C-u 6 4 1 specifies an argument of 641. You can separate the argument from the digit to insert with another C-u; for example, C-u 6 4 C-u 1 does insert 64 copies of the character ‘1’.

Some commands care whether there is an argument, but ignore its value. For example, the command M-q (fill-paragraph) fills text; with an argument, it justifies the text as well. (See Filling, for more information on M-q.) For these commands, it is enough to specify the argument with a single C-u.

Some commands use the value of the argument as a repeat count, but do something special when there is no argument. For example, the command C-k (kill-line) with argument n kills n lines, including their terminating newlines. But C-k with no argument is special: it kills the text up to the next newline, or, if point is right at the end of the line, it kills the newline itself. Thus, two C-k commands with no arguments can kill a nonblank line, just like C-k with an argument of one. (See Killing, for more information on C-k.)

A few commands treat a plain C-u differently from an ordinary argument. A few others may treat an argument of just a minus sign differently from an argument of −1. These unusual cases are described when they come up; they exist to make an individual command more convenient, and they are documented in that command's documentation string.

We use the term prefix argument to emphasize that you type such arguments before the command, and to distinguish them from minibuffer arguments (see Minibuffer), which are entered after invoking the command.

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7.11 Repeating a Command

Many simple commands, such as those invoked with a single key or with M-x command-name <RET>, can be repeated by invoking them with a numeric argument that serves as a repeat count (see Arguments). However, if the command you want to repeat prompts for input, or uses a numeric argument in another way, that method won't work.

The command C-x z (repeat) provides another way to repeat an Emacs command many times. This command repeats the previous Emacs command, whatever that was. Repeating a command uses the same arguments that were used before; it does not read new arguments each time.

To repeat the command more than once, type additional z's: each z repeats the command one more time. Repetition ends when you type a character other than z, or press a mouse button.

For example, suppose you type C-u 2 0 C-d to delete 20 characters. You can repeat that command (including its argument) three additional times, to delete a total of 80 characters, by typing C-x z z z. The first C-x z repeats the command once, and each subsequent z repeats it once again.

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8 The Minibuffer

The minibuffer is where Emacs commands read complicated arguments, such as file names, buffer names, Emacs command names, or Lisp expressions. We call it the “minibuffer” because it's a special-purpose buffer with a small amount of screen space. You can use the usual Emacs editing commands in the minibuffer to edit the argument text.

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8.1 Using the Minibuffer

When the minibuffer is in use, it appears in the echo area, with a cursor. The minibuffer starts with a prompt, usually ending with a colon. The prompt states what kind of input is expected, and how it will be used. The prompt is highlighted using the minibuffer-prompt face (see Faces).

The simplest way to enter a minibuffer argument is to type the text, then <RET> to submit the argument and exit the minibuffer. Alternatively, you can type C-g to exit the minibuffer by cancelling the command asking for the argument (see Quitting).

Sometimes, the prompt shows a default argument, inside parentheses before the colon. This default will be used as the argument if you just type <RET>. For example, commands that read buffer names usually show a buffer name as the default; you can type <RET> to operate on that default buffer.

If you enable Minibuffer Electric Default mode, a global minor mode, Emacs hides the default argument as soon as you modify the contents of the minibuffer (since typing <RET> would no longer submit that default). If you ever bring back the original minibuffer text, the prompt again shows the default. Furthermore, if you change the variable minibuffer-eldef-shorten-default to a non-nil value, the default argument is displayed as ‘[default]’ instead of ‘(default default)’, saving some screen space. To enable this minor mode, type M-x minibuffer-electric-default-mode.

Since the minibuffer appears in the echo area, it can conflict with other uses of the echo area. If an error message or an informative message is emitted while the minibuffer is active, the message hides the minibuffer for a few seconds, or until you type something; then the minibuffer comes back. While the minibuffer is in use, keystrokes do not echo.

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8.2 Minibuffers for File Names

Commands such as C-x C-f (find-file) use the minibuffer to read a file name argument (see Basic Files). When the minibuffer is used to read a file name, it typically starts out with some initial text ending in a slash. This is the default directory. For example, it may start out like this: 

     Find file: /u2/emacs/src/

Here, ‘Find file: ’ is the prompt and ‘/u2/emacs/src/’ is the default directory. If you now type buffer.c as input, that specifies the file /u2/emacs/src/buffer.c. See File Names, for information about the default directory.

You can specify the parent directory with ..: /a/b/../foo.el is equivalent to /a/foo.el. Alternatively, you can use M-<DEL> to kill directory names backwards (see Words).

To specify a file in a completely different directory, you can kill the entire default with C-a C-k (see Minibuffer Edit). Alternatively, you can ignore the default, and enter an absolute file name starting with a slash or a tilde after the default directory. For example, you can specify /etc/termcap as follows: 

     Find file: /u2/emacs/src//etc/termcap

Emacs interprets a double slash as “ignore everything before the second slash in the pair”. In the example above, /u2/emacs/src/ is ignored, so the argument you supplied is /etc/termcap. The ignored part of the file name is dimmed if the terminal allows it. (To disable this dimming, turn off File Name Shadow mode with the command M-x file-name-shadow-mode.)

Emacs interprets ~/ as your home directory. Thus, ~/foo/bar.txt specifies a file named bar.txt, inside a directory named foo, which is in turn located in your home directory. In addition, ~user-id/ means the home directory of a user whose login name is user-id. Any leading directory name in front of the ~ is ignored: thus, /u2/emacs/~/foo/bar.txt is equivalent to ~/foo/bar.txt.

On MS-Windows and MS-DOS systems, where a user doesn't always have a home directory, Emacs uses several alternatives. For MS-Windows, see Windows HOME; for MS-DOS, see MS-DOS File Names. On these systems, the ~user-id/ construct is supported only for the current user, i.e., only if user-id is the current user's login name.

To prevent Emacs from inserting the default directory when reading file names, change the variable insert-default-directory to nil. In that case, the minibuffer starts out empty. Nonetheless, relative file name arguments are still interpreted based on the same default directory.

You can also enter remote file names in the minibuffer. See Remote Files.

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8.3 Editing in the Minibuffer

The minibuffer is an Emacs buffer, albeit a peculiar one, and the usual Emacs commands are available for editing the argument text. (The prompt, however, is read-only, and cannot be changed.)

Since <RET> in the minibuffer submits the argument, you can't use it to insert a newline. You can do that with C-q C-j, which inserts a C-j control character, which is formally equivalent to a newline character (see Inserting Text). Alternatively, you can use the C-o (open-line) command (see Blank Lines).

Inside a minibuffer, the keys <TAB>, <SPC>, and ? are often bound to completion commands, which allow you to easily fill in the desired text without typing all of it. See Completion. As with <RET>, you can use C-q to insert a <TAB>, <SPC>, or ‘?’ character.

For convenience, C-a (move-beginning-of-line) in a minibuffer moves point to the beginning of the argument text, not the beginning of the prompt. For example, this allows you to erase the entire argument with C-a C-k.

When the minibuffer is active, the echo area is treated much like an ordinary Emacs window. For instance, you can switch to another window (with C-x o), edit text there, then return to the minibuffer window to finish the argument. You can even kill text in another window, return to the minibuffer window, and yank the text into the argument. There are some restrictions on the minibuffer window, however: for instance, you cannot split it. See Windows.

Normally, the minibuffer window occupies a single screen line. However, if you add two or more lines' worth of text into the minibuffer, it expands automatically to accommodate the text. The variable resize-mini-windows controls the resizing of the minibuffer. The default value is grow-only, which means the behavior we have just described. If the value is t, the minibuffer window will also shrink automatically if you remove some lines of text from the minibuffer, down to a minimum of one screen line. If the value is nil, the minibuffer window never changes size automatically, but you can use the usual window-resizing commands on it (see Windows).

The variable max-mini-window-height controls the maximum height for resizing the minibuffer window. A floating-point number specifies a fraction of the frame's height; an integer specifies the maximum number of lines; nil means do not resize the minibuffer window automatically. The default value is 0.25.

The C-M-v command in the minibuffer scrolls the help text from commands that display help text of any sort in another window. You can also scroll the help text with M-<prior> and M-<next> (or, equivalently, M-<PageUp> and M-<PageDown>). This is especially useful with long lists of possible completions. See Other Window.

Emacs normally disallows most commands that use the minibuffer while the minibuffer is active. To allow such commands in the minibuffer, set the variable enable-recursive-minibuffers to t.

When not active, the minibuffer is in minibuffer-inactive-mode, and clicking Mouse-1 there shows the *Messages* buffer. If you use a dedicated frame for minibuffers, Emacs also recognizes certain keys there, for example n to make a new frame.

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8.4 Completion

You can often use a feature called completion to help enter arguments. This means that after you type part of the argument, Emacs can fill in the rest, or some of it, based on what was typed so far.

When completion is available, certain keys (usually <TAB>, <RET>, and <SPC>) are rebound in the minibuffer to special completion commands (see Completion Commands). These commands attempt to complete the text in the minibuffer, based on a set of completion alternatives provided by the command that requested the argument. You can usually type ? to see a list of completion alternatives.

Although completion is usually done in the minibuffer, the feature is sometimes available in ordinary buffers too. See Symbol Completion.

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8.4.1 Completion Example

A simple example may help here. M-x uses the minibuffer to read the name of a command, so completion works by matching the minibuffer text against the names of existing Emacs commands. Suppose you wish to run the command auto-fill-mode. You can do that by typing M-x auto-fill-mode <RET>, but it is easier to use completion.

If you type M-x a u <TAB>, the <TAB> looks for completion alternatives (in this case, command names) that start with ‘au’. There are several, including auto-fill-mode and autoconf-mode, but they all begin with auto, so the ‘au’ in the minibuffer completes to ‘auto’. (More commands may be defined in your Emacs session. For example, if a command called authorize-me was defined, Emacs could only complete as far as ‘aut’.)

If you type <TAB> again immediately, it cannot determine the next character; it could be ‘-’, ‘a’, or ‘c’. So it does not add any characters; instead, <TAB> displays a list of all possible completions in another window.

Next, type -f. The minibuffer now contains ‘auto-f’, and the only command name that starts with this is auto-fill-mode. If you now type <TAB>, completion fills in the rest of the argument ‘auto-fill-mode’ into the minibuffer.

Hence, typing just a u <TAB> - f <TAB> allows you to enter ‘auto-fill-mode’.

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8.4.2 Completion Commands

Here is a list of the completion commands defined in the minibuffer when completion is allowed.

<TAB>
Complete the text in the minibuffer as much as possible; if unable to complete, display a list of possible completions (minibuffer-complete).
<SPC>
Complete up to one word from the minibuffer text before point (minibuffer-complete-word). This command is not available for arguments that often include spaces, such as file names.
<RET>
Submit the text in the minibuffer as the argument, possibly completing first (minibuffer-complete-and-exit). See Completion Exit.
?
Display a list of completions (minibuffer-completion-help).

<TAB> (minibuffer-complete) is the most fundamental completion command. It searches for all possible completions that match the existing minibuffer text, and attempts to complete as much as it can. See Completion Styles, for how completion alternatives are chosen.

<SPC> (minibuffer-complete-word) completes like <TAB>, but only up to the next hyphen or space. If you have ‘auto-f’ in the minibuffer and type <SPC>, it finds that the completion is ‘auto-fill-mode’, but it only inserts ‘ill-’, giving ‘auto-fill-’. Another <SPC> at this point completes all the way to ‘auto-fill-mode’.

If <TAB> or <SPC> is unable to complete, it displays a list of matching completion alternatives (if there are any) in another window. You can display the same list with ? (minibuffer-completion-help). The following commands can be used with the completion list:

Mouse-1
Mouse-2
Clicking mouse button 1 or 2 on a completion alternative chooses it (mouse-choose-completion).


M-v
<PageUp>
<prior>
Typing M-v, while in the minibuffer, selects the window showing the completion list (switch-to-completions). This paves the way for using the commands below. <PageUp> or <prior> does the same. You can also select the window in other ways (see Windows).


<RET>
While in the completion list buffer, this chooses the completion at point (choose-completion).


<Right>
While in the completion list buffer, this moves point to the following completion alternative (next-completion).


<Left>
While in the completion list buffer, this moves point to the previous completion alternative (previous-completion).

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8.4.3 Completion Exit

When a command reads an argument using the minibuffer with completion, it also controls what happens when you type <RET> (minibuffer-complete-and-exit) to submit the argument. There are four types of behavior:

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8.4.4 How Completion Alternatives Are Chosen

Completion commands work by narrowing a large list of possible completion alternatives to a smaller subset that “matches” what you have typed in the minibuffer. In Completion Example, we gave a simple example of such matching. The procedure of determining what constitutes a “match” is quite intricate. Emacs attempts to offer plausible completions under most circumstances.

Emacs performs completion using one or more completion styles—sets of criteria for matching minibuffer text to completion alternatives. During completion, Emacs tries each completion style in turn. If a style yields one or more matches, that is used as the list of completion alternatives. If a style produces no matches, Emacs falls back on the next style.

The list variable completion-styles specifies the completion styles to use. Each list element is the name of a completion style (a Lisp symbol). The default completion styles are (in order):

basic
A matching completion alternative must have the same beginning as the text in the minibuffer before point. Furthermore, if there is any text in the minibuffer after point, the rest of the completion alternative must contain that text as a substring.


partial-completion
This aggressive completion style divides the minibuffer text into words separated by hyphens or spaces, and completes each word separately. (For example, when completing command names, ‘em-l-m’ completes to ‘emacs-lisp-mode’.)

Furthermore, a ‘*’ in the minibuffer text is treated as a wildcard—it matches any character at the corresponding position in the completion alternative.

emacs22
This completion style is similar to basic, except that it ignores the text in the minibuffer after point. It is so-named because it corresponds to the completion behavior in Emacs 22.

The following additional completion styles are also defined, and you can add them to completion-styles if you wish (see Customization):

substring
A matching completion alternative must contain the text in the minibuffer before point, and the text in the minibuffer after point, as substrings (in that same order).

Thus, if the text in the minibuffer is ‘foobar’, with point between ‘foo’ and ‘bar’, that matches ‘afoobbarc’, where a, b, and c can be any string including the empty string.

initials
This very aggressive completion style attempts to complete acronyms and initialisms. For example, when completing command names, it matches ‘lch’ to ‘list-command-history’.

There is also a very simple completion style called emacs21. In this style, if the text in the minibuffer is ‘foobar’, only matches starting with ‘foobar’ are considered.

You can use different completion styles in different situations, by setting the variable completion-category-overrides. For example, the default setting says to use only basic and substring completion for buffer names.

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8.4.5 Completion Options

Case is significant when completing case-sensitive arguments, such as command names. For example, when completing command names, ‘AU’ does not complete to ‘auto-fill-mode’. Case differences are ignored when completing arguments in which case does not matter.

When completing file names, case differences are ignored if the variable read-file-name-completion-ignore-case is non-nil. The default value is nil on systems that have case-sensitive file-names, such as GNU/Linux; it is non-nil on systems that have case-insensitive file-names, such as Microsoft Windows. When completing buffer names, case differences are ignored if the variable read-buffer-completion-ignore-case is non-nil; the default is nil.

When completing file names, Emacs usually omits certain alternatives that are considered unlikely to be chosen, as determined by the list variable completion-ignored-extensions. Each element in the list should be a string; any file name ending in such a string is ignored as a completion alternative. Any element ending in a slash (/) represents a subdirectory name. The standard value of completion-ignored-extensions has several elements including ".o", ".elc", and "~". For example, if a directory contains ‘foo.c’ and ‘foo.elc’, ‘foo’ completes to ‘foo.c’. However, if all possible completions end in “ignored” strings, they are not ignored: in the previous example, ‘foo.e’ completes to ‘foo.elc’. Emacs disregards completion-ignored-extensions when showing completion alternatives in the completion list.

If completion-auto-help is set to nil, the completion commands never display the completion list buffer; you must type ? to display the list. If the value is lazy, Emacs only shows the completion list buffer on the second attempt to complete. In other words, if there is nothing to complete, the first <TAB> echoes ‘Next char not unique’; the second <TAB> shows the completion list buffer.

If completion-cycle-threshold is non-nil, completion commands can “cycle” through completion alternatives. Normally, if there is more than one completion alternative for the text in the minibuffer, a completion command completes up to the longest common substring. If you change completion-cycle-threshold to t, the completion command instead completes to the first of those completion alternatives; each subsequent invocation of the completion command replaces that with the next completion alternative, in a cyclic manner. If you give completion-cycle-threshold a numeric value n, completion commands switch to this cycling behavior only when there are n or fewer alternatives.

Icomplete mode presents a constantly-updated display that tells you what completions are available for the text you've entered so far. The command to enable or disable this minor mode is M-x icomplete-mode.

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8.5 Minibuffer History

Every argument that you enter with the minibuffer is saved in a minibuffer history list so you can easily use it again later. You can use the following arguments to quickly fetch an earlier argument into the minibuffer:

M-p
<Up>
Move to the previous item in the minibuffer history, an earlier argument (previous-history-element).
M-n
<Down>
Move to the next item in the minibuffer history (next-history-element).
M-r regexp <RET>
Move to an earlier item in the minibuffer history that matches regexp (previous-matching-history-element).
M-s regexp <RET>
Move to a later item in the minibuffer history that matches regexp (next-matching-history-element).

While in the minibuffer, M-p or <Up> (previous-history-element) moves through the minibuffer history list, one item at a time. Each M-p fetches an earlier item from the history list into the minibuffer, replacing its existing contents. Typing M-n or <Down> (next-history-element) moves through the minibuffer history list in the opposite direction, fetching later entries into the minibuffer.

If you type M-n in the minibuffer when there are no later entries in the minibuffer history (e.g., if you haven't previously typed M-p), Emacs tries fetching from a list of default arguments: values that you are likely to enter. You can think of this as moving through the “future history” list.

If you edit the text inserted by the M-p or <M-n> minibuffer history commands, this does not change its entry in the history list. However, the edited argument does go at the end of the history list when you submit it.

You can use M-r (previous-matching-history-element) to search through older elements in the history list, and M-s (next-matching-history-element) to search through newer entries. Each of these commands asks for a regular expression as an argument, and fetches the first matching entry into the minibuffer. See Regexps, for an explanation of regular expressions. A numeric prefix argument n means to fetch the nth matching entry. These commands are unusual, in that they use the minibuffer to read the regular expression argument, even though they are invoked from the minibuffer. An upper-case letter in the regular expression makes the search case-sensitive (see Search Case).

You can also search through the history using an incremental search. See Isearch Minibuffer.

Emacs keeps separate history lists for several different kinds of arguments. For example, there is a list for file names, used by all the commands that read file names. Other history lists include buffer names, command names (used by M-x), and command arguments (used by commands like query-replace).

The variable history-length specifies the maximum length of a minibuffer history list; adding a new element deletes the oldest element if the list gets too long. If the value is t, there is no maximum length.

The variable history-delete-duplicates specifies whether to delete duplicates in history. If it is non-nil, adding a new element deletes from the list all other elements that are equal to it. The default is nil.

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8.6 Repeating Minibuffer Commands

Every command that uses the minibuffer once is recorded on a special history list, the command history, together with the values of its arguments, so that you can repeat the entire command. In particular, every use of M-x is recorded there, since M-x uses the minibuffer to read the command name.

C-x <ESC> <ESC>
Re-execute a recent minibuffer command from the command history (repeat-complex-command).
M-x list-command-history
Display the entire command history, showing all the commands C-x <ESC> <ESC> can repeat, most recent first.

C-x <ESC> <ESC> re-executes a recent command that used the minibuffer. With no argument, it repeats the last such command. A numeric argument specifies which command to repeat; 1 means the last one, 2 the previous, and so on.

C-x <ESC> <ESC> works by turning the previous command into a Lisp expression and then entering a minibuffer initialized with the text for that expression. Even if you don't know Lisp, it will probably be obvious which command is displayed for repetition. If you type just <RET>, that repeats the command unchanged. You can also change the command by editing the Lisp expression before you execute it. The executed command is added to the front of the command history unless it is identical to the most recent item.

Once inside the minibuffer for C-x <ESC> <ESC>, you can use the usual minibuffer history commands (see Minibuffer History) to move through the history list. After finding the desired previous command, you can edit its expression as usual and then execute it by typing <RET>.

Incremental search does not, strictly speaking, use the minibuffer. Therefore, although it behaves like a complex command, it normally does not appear in the history list for C-x <ESC> <ESC>. You can make incremental search commands appear in the history by setting isearch-resume-in-command-history to a non-nil value. See Incremental Search.

The list of previous minibuffer-using commands is stored as a Lisp list in the variable command-history. Each element is a Lisp expression that describes one command and its arguments. Lisp programs can re-execute a command by calling eval with the command-history element.

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8.7 Entering passwords

Sometimes, you may need to enter a password into Emacs. For instance, when you tell Emacs to visit a file on another machine via a network protocol such as FTP, you often need to supply a password to gain access to the machine (see Remote Files).

Entering a password is similar to using a minibuffer. Emacs displays a prompt in the echo area (such as ‘Password: ’); after you type the required password, press <RET> to submit it. To prevent others from seeing your password, every character you type is displayed as a dot (‘.’) instead of its usual form.

Most of the features and commands associated with the minibuffer can not be used when entering a password. There is no history or completion, and you cannot change windows or perform any other action with Emacs until you have submitted the password.

While you are typing the password, you may press <DEL> to delete backwards, removing the last character entered. C-u deletes everything you have typed so far. C-g quits the password prompt (see Quitting). C-y inserts the current kill into the password (see Killing). You may type either <RET> or <ESC> to submit the password. Any other self-inserting character key inserts the associated character into the password, and all other input is ignored.

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8.8 Yes or No Prompts

An Emacs command may require you to answer a “yes or no” question during the course of its execution. Such queries come in two main varieties.

For the first type of “yes or no” query, the prompt ends with ‘(y or n)’. Such a query does not actually use the minibuffer; the prompt appears in the echo area, and you answer by typing either ‘y’ or ‘n’, which immediately delivers the response. For example, if you type C-x C-w (write-file) to save a buffer, and enter the name of an existing file, Emacs issues a prompt like this: 

     File `foo.el' exists; overwrite? (y or n)

Because this query does not actually use the minibuffer, the usual minibuffer editing commands cannot be used. However, you can perform some window scrolling operations while the query is active: C-l recenters the selected window; M-v (or <PageDown> or <next>) scrolls forward; C-v (or <PageUp>, or <prior>) scrolls backward; C-M-v scrolls forward in the next window; and C-M-S-v scrolls backward in the next window. Typing C-g dismisses the query, and quits the command that issued it (see Quitting).

The second type of “yes or no” query is typically employed if giving the wrong answer would have serious consequences; it uses the minibuffer, and features a prompt ending with ‘(yes or no)’. For example, if you invoke C-x k (kill-buffer) on a file-visiting buffer with unsaved changes, Emacs activates the minibuffer with a prompt like this: 

     Buffer foo.el modified; kill anyway? (yes or no)

To answer, you must type ‘yes’ or ‘no’ into the minibuffer, followed by <RET>. The minibuffer behaves as described in the previous sections; you can switch to another window with C-x o, use the history commands M-p and M-f, etc. Type C-g to quit the minibuffer and the querying command.

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9 Running Commands by Name

Every Emacs command has a name that you can use to run it. For convenience, many commands also have key bindings. You can run those commands by typing the keys, or run them by name. Most Emacs commands have no key bindings, so the only way to run them is by name. (See Key Bindings, for how to set up key bindings.)

By convention, a command name consists of one or more words, separated by hyphens; for example, auto-fill-mode or manual-entry. Command names mostly use complete English words to make them easier to remember.

To run a command by name, start with M-x, type the command name, then terminate it with <RET>. M-x uses the minibuffer to read the command name. The string ‘M-x’ appears at the beginning of the minibuffer as a prompt to remind you to enter a command name to be run. <RET> exits the minibuffer and runs the command. See Minibuffer, for more information on the minibuffer.

You can use completion to enter the command name. For example, to invoke the command forward-char, you can type 

     M-x forward-char <RET>

or 

     M-x forw <TAB> c <RET>

Note that forward-char is the same command that you invoke with the key C-f. The existence of a key binding does not stop you from running the command by name.

To cancel the M-x and not run a command, type C-g instead of entering the command name. This takes you back to command level.

To pass a numeric argument to the command you are invoking with M-x, specify the numeric argument before M-x. The argument value appears in the prompt while the command name is being read, and finally M-x passes the argument to that command.

When the command you run with M-x has a key binding, Emacs mentions this in the echo area after running the command. For example, if you type M-x forward-word, the message says that you can run the same command by typing M-f. You can turn off these messages by setting the variable suggest-key-bindings to nil.

In this manual, when we speak of running a command by name, we often omit the <RET> that terminates the name. Thus we might say M-x auto-fill-mode rather than M-x auto-fill-mode <RET>. We mention the <RET> only for emphasis, such as when the command is followed by arguments.

M-x works by running the command execute-extended-command, which is responsible for reading the name of another command and invoking it.

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10 Help

Emacs provides a wide variety of help commands, all accessible through the prefix key C-h (or, equivalently, the function key <F1>). These help commands are described in the following sections. You can also type C-h C-h to view a list of help commands (help-for-help). You can scroll the list with <SPC> and <DEL>, then type the help command you want. To cancel, type C-g.

Many help commands display their information in a special help buffer. In this buffer, you can type <SPC> and <DEL> to scroll and type <RET> to follow hyperlinks. See Help Mode.

If you are looking for a certain feature, but don't know what it is called or where to look, we recommend three methods. First, try an apropos command, then try searching the manual index, then look in the FAQ and the package keywords.

C-h a topics <RET>
This searches for commands whose names match the argument topics. The argument can be a keyword, a list of keywords, or a regular expression (see Regexps). See Apropos.
C-h i d m emacs <RET> i topic <RET>
This searches for topic in the indices of the Emacs Info manual, displaying the first match found. Press , to see subsequent matches. You can use a regular expression as topic.
C-h i d m emacs <RET> s topic <RET>
Similar, but searches the text of the manual rather than the indices.
C-h C-f
This displays the Emacs FAQ, using Info.
C-h p
This displays the available Emacs packages based on keywords. See Package Keywords.

C-h or <F1> means “help” in various other contexts as well. For instance, you can type them after a prefix key to view a list of the keys that can follow the prefix key. (A few prefix keys don't support C-h in this way, because they define other meanings for it, but they all support <F1> for help.)

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10.1 Help Summary

Here is a summary of help commands for accessing the built-in documentation. Most of these are described in more detail in the following sections.

C-h a topics <RET>
Display a list of commands whose names match topics (apropos-command).
C-h b
Display all active key bindings; minor mode bindings first, then those of the major mode, then global bindings (describe-bindings).
C-h c key
Show the name of the command that the key sequence key is bound to (describe-key-briefly). Here c stands for “character”. For more extensive information on key, use C-h k.
C-h d topics <RET>
Display the commands and variables whose documentation matches topics (apropos-documentation).
C-h e
Display the *Messages* buffer (view-echo-area-messages).
C-h f function <RET>
Display documentation on the Lisp function named function (describe-function). Since commands are Lisp functions, this works for commands too.
C-h h
Display the HELLO file, which shows examples of various character sets.
C-h i
Run Info, the GNU documentation browser (info). The Emacs manual is available in Info.
C-h k key
Display the name and documentation of the command that key runs (describe-key).
C-h l
Display a description of your last 300 keystrokes (view-lossage).
C-h m
Display documentation of the current major mode (describe-mode).
C-h n
Display news of recent Emacs changes (view-emacs-news).
C-h p
Find packages by topic keyword (finder-by-keyword). This lists packages using a package menu buffer. See Packages.
C-h P package <RET>
Display documentation about the package named package (describe-package).
C-h r
Display the Emacs manual in Info (info-emacs-manual).
C-h s
Display the contents of the current syntax table (describe-syntax). The syntax table says which characters are opening delimiters, which are parts of words, and so on. See Syntax Tables, for details.
C-h t
Enter the Emacs interactive tutorial (help-with-tutorial).
C-h v var <RET>
Display the documentation of the Lisp variable var (describe-variable).
C-h w command <RET>
Show which keys run the command named command (where-is).
C-h C coding <RET>
Describe the coding system coding (describe-coding-system).
C-h C <RET>
Describe the coding systems currently in use.
C-h F command <RET>
Enter Info and go to the node that documents the Emacs command command (Info-goto-emacs-command-node).
C-h I method <RET>
Describe the input method method (describe-input-method).
C-h K key
Enter Info and go to the node that documents the key sequence key (Info-goto-emacs-key-command-node).
C-h L language-env <RET>
Display information on the character sets, coding systems, and input methods used in language environment language-env (describe-language-environment).
C-h S symbol <RET>
Display the Info documentation on symbol symbol according to the programming language you are editing (info-lookup-symbol).
C-h .
Display the help message for a special text area, if point is in one (display-local-help). (These include, for example, links in *Help* buffers.)

Next: , Previous: Help Summary, Up: Help

10.2 Documentation for a Key

The help commands to get information about a key sequence are C-h c (describe-key-briefly) and C-h k (describe-key).

C-h c key displays in the echo area the name of the command that key is bound to. For example, C-h c C-f displays ‘forward-char’.

C-h k key is similar but gives more information: it displays a help buffer containing the command's documentation string, which describes exactly what the command does.

C-h K key displays the section of the Emacs manual that describes the command corresponding to key.

C-h c, C-h k and C-h K work for any sort of key sequences, including function keys, menus, and mouse events. For instance, after C-h k you can select a menu item from the menu bar, to view the documentation string of the command it runs.

C-h w command <RET> lists the keys that are bound to command. It displays the list in the echo area. If it says the command is not on any key, that means you must use M-x to run it. C-h w runs the command where-is.

Next: , Previous: Key Help, Up: Help

10.3 Help by Command or Variable Name

C-h f function <RET> (describe-function) displays the documentation of Lisp function function, in a window. Since commands are Lisp functions, you can use this method to view the documentation of any command whose name you know. For example, 

     C-h f auto-fill-mode <RET>

displays the documentation of auto-fill-mode. This is the only way to get the documentation of a command that is not bound to any key (one which you would normally run using M-x).

C-h f is also useful for Lisp functions that you use in a Lisp program. For example, if you have just written the expression (make-vector len) and want to check that you are using make-vector properly, type C-h f make-vector <RET>. Because C-h f allows all function names, not just command names, you may find that some of your favorite completion abbreviations that work in M-x don't work in C-h f. An abbreviation that is unique among command names may not be unique among all function names.

If you type C-h f <RET>, it describes the function called by the innermost Lisp expression in the buffer around point, provided that function name is a valid, defined Lisp function. (That name appears as the default while you enter the argument.) For example, if point is located following the text ‘(make-vector (car x)’, the innermost list containing point is the one that starts with ‘(make-vector’, so C-h f <RET> describes the function make-vector.

C-h f is also useful just to verify that you spelled a function name correctly. If the minibuffer prompt for C-h f shows the function name from the buffer as the default, it means that name is defined as a Lisp function. Type C-g to cancel the C-h f command if you don't really want to view the documentation.

C-h v (describe-variable) is like C-h f but describes Lisp variables instead of Lisp functions. Its default is the Lisp symbol around or before point, if that is the name of a defined Lisp variable. See Variables.

Help buffers that describe Emacs variables and functions normally have hyperlinks to the corresponding source code, if you have the source files installed (see Hyperlinking).

To find a command's documentation in a manual, use C-h F (Info-goto-emacs-command-node). This knows about various manuals, not just the Emacs manual, and finds the right one.

Next: , Previous: Name Help, Up: Help

10.4 Apropos

The apropos commands answer questions like, “What are the commands for working with files?” More precisely, you specify an apropos pattern, which means either a word, a list of words, or a regular expression.

Each of the following apropos commands reads an apropos pattern in the minibuffer, searches for items that match the pattern, and displays the results in a different window.

C-h a
Search for commands (apropos-command). With a prefix argument, search for noninteractive functions too.
M-x apropos
Search for functions and variables. Both interactive functions (commands) and noninteractive functions can be found by this.
M-x apropos-variable
Search for user-customizable variables. With a prefix argument, search for non-customizable variables too.
M-x apropos-value
Search for variables whose values match the specified pattern. With a prefix argument, search also for functions with definitions matching the pattern, and Lisp symbols with properties matching the pattern.
C-h d
Search for functions and variables whose documentation strings match the specified pattern (apropos-documentation).

The simplest kind of apropos pattern is one word. Anything containing that word matches the pattern. Thus, to find commands that work on files, type C-h a file <RET>. This displays a list of all command names that contain ‘file’, including copy-file, find-file, and so on. Each command name comes with a brief description and a list of keys you can currently invoke it with. In our example, it would say that you can invoke find-file by typing C-x C-f.

For more information about a function definition, variable or symbol property listed in an apropos buffer, you can click on it with Mouse-1 or Mouse-2, or move there and type <RET>.

When you specify more than one word in the apropos pattern, a name must contain at least two of the words in order to match. Thus, if you are looking for commands to kill a chunk of text before point, you could try C-h a kill back backward behind before <RET>. The real command name kill-backward will match that; if there were a command kill-text-before, it would also match, since it contains two of the specified words.

For even greater flexibility, you can specify a regular expression (see Regexps). An apropos pattern is interpreted as a regular expression if it contains any of the regular expression special characters, ‘^$*+?.\[’.

Following the conventions for naming Emacs commands, here are some words that you'll find useful in apropos patterns. By using them in C-h a, you will also get a feel for the naming conventions.

char, line, word, sentence, paragraph, region, page, sexp, list, defun, rect, buffer, frame, window, face, file, dir, register, mode, beginning, end, forward, backward, next, previous, up, down, search, goto, kill, delete, mark, insert, yank, fill, indent, case, change, set, what, list, find, view, describe, default.

If the variable apropos-do-all is non-nil, the apropos commands always behave as if they had been given a prefix argument.

By default, all apropos commands except apropos-documentation list their results in alphabetical order. If the variable apropos-sort-by-scores is non-nil, these commands instead try to guess the relevance of each result, and display the most relevant ones first. The apropos-documentation command lists its results in order of relevance by default; to list them in alphabetical order, change the variable apropos-documentation-sort-by-scores to nil.

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10.5 Help Mode Commands

Help buffers provide the same commands as View mode (see View Mode); for instance, <SPC> scrolls forward, and <DEL> scrolls backward. A few special commands are also provided:

<RET>
Follow a cross reference at point (help-follow).
<TAB>
Move point forward to the next hyperlink (forward-button).
S-<TAB>
Move point back to the previous hyperlink (backward-button).
Mouse-1
Mouse-2
Follow a hyperlink that you click on.
C-c C-c
Show all documentation about the symbol at point (help-follow-symbol).
C-c C-b
Go back to the previous help topic (help-go-back).

When a function name, variable name, or face name (see Faces) appears in the documentation in the help buffer, it is normally an underlined hyperlink. To view the associated documentation, move point there and type <RET> (help-follow), or click on the hyperlink with Mouse-1 or Mouse-2. Doing so replaces the contents of the help buffer; to retrace your steps, type C-c C-b (help-go-back).

A help buffer can also contain hyperlinks to Info manuals, source code definitions, and URLs (web pages). The first two are opened in Emacs, and the third using a web browser via the browse-url command (see Browse-URL).

In a help buffer, <TAB> (forward-button) moves point forward to the next hyperlink, while S-<TAB> (backward-button) point back to the previous hyperlink. These commands act cyclically; for instance, typing <TAB> at the last hyperlink moves back to the first hyperlink.

To view all documentation about any symbol in the text, move point to there and type C-c C-c (help-follow-symbol). This shows all available documentation about the symbol—as a variable, function and/or face.

Next: , Previous: Help Mode, Up: Help

10.6 Keyword Search for Packages

Most optional features in Emacs are grouped into packages. Emacs contains several hundred built-in packages, and more can be installed over the network (see Packages).

To make it easier to find packages related to a topic, most packages are associated with one or more keywords based on what they do. Type C-h p (finder-by-keyword) to bring up a list of package keywords, together with a description of what the keywords mean. To view a list of packages for a given keyword, type <RET> on that line; this displays the list of packages in a Package Menu buffer (see Package Menu).

C-h P (describe-package) prompts for the name of a package, and displays a help buffer describing the attributes of the package and the features that it implements.

Next: , Previous: Package Keywords, Up: Help

10.7 Help for International Language Support

For information on a specific language environment (see Language Environments), type C-h L (describe-language-environment). This displays a help buffer describing the languages supported by the language environment, and listing the associated character sets, coding systems, and input methods, as well as some sample text for that language environment.

The command C-h h (view-hello-file) displays the file etc/HELLO, which demonstrates various character sets by showing how to say “hello” in many languages.

The command C-h I (describe-input-method) describes an input method—either a specified input method, or by default the input method currently in use. See Input Methods.

The command C-h C (describe-coding-system) describes coding systems—either a specified coding system, or the ones currently in use. See Coding Systems.

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10.8 Other Help Commands

C-h i (info) runs the Info program, which browses structured documentation files. The entire Emacs manual is available within Info, along with many other manuals for the GNU system. Type h after entering Info to run a tutorial on using Info.

With a numeric argument n, C-h i selects the Info buffer ‘*info*<n>’. This is useful if you want to browse multiple Info manuals simultaneously. If you specify just C-u as the prefix argument, C-h i prompts for the name of a documentation file, so you can browse a file which doesn't have an entry in the top-level Info menu.

The help commands C-h F function <RET> and C-h K key, described above, enter Info and go straight to the documentation of function or key.

When editing a program, if you have an Info version of the manual for the programming language, you can use C-h S (info-lookup-symbol) to find an entry for a symbol (keyword, function or variable) in the proper manual. The details of how this command works depend on the major mode.

If something surprising happens, and you are not sure what you typed, use C-h l (view-lossage). C-h l displays your last 300 input keystrokes. If you see commands that you don't know, you can use C-h c to find out what they do.

To review recent echo area messages, use C-h e (view-echo-area-messages). This displays the buffer *Messages*, where those messages are kept.

Each Emacs major mode typically redefines a few keys and makes other changes in how editing works. C-h m (describe-mode) displays documentation on the current major mode, which normally describes the commands and features that are changed in this mode.

C-h b (describe-bindings) and C-h s (describe-syntax) show other information about the current environment within Emacs. C-h b displays a list of all the key bindings now in effect: first the local bindings of the current minor modes, then the local bindings defined by the current major mode, and finally the global bindings (see Key Bindings). C-h s displays the contents of the syntax table, with explanations of each character's syntax (see Syntax Tables).

You can get a list of subcommands for a particular prefix key by typing C-h (describe-prefix-bindings) after the prefix key. (There are a few prefix keys for which this does not work—those that provide their own bindings for C-h. One of these is <ESC>, because <ESC> C-h is actually C-M-h, which marks a defun.)

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10.9 Help Files

Apart from the built-in documentation and manuals, Emacs contains several other files describing topics like copying conditions, release notes, instructions for debugging and reporting bugs, and so forth. You can use the following commands to view these files. Apart from C-h g, they all have the form C-h C-char.

C-h C-c
Display the rules under which you can copy and redistribute Emacs (describe-copying).
C-h C-d
Display help for debugging Emacs (view-emacs-debugging).
C-h C-e
Display information about where to get external packages (view-external-packages).
C-h C-f
Display the Emacs frequently-answered-questions list (view-emacs-FAQ).
C-h g
Display information about the GNU Project (describe-gnu-project).
C-h C-m
Display information about ordering printed copies of Emacs manuals (view-order-manuals).
C-h C-n
Display the “news” file, which lists the new features in this version of Emacs (view-emacs-news).
C-h C-o
Display how to order or download the latest version of Emacs and other GNU software (describe-distribution).
C-h C-p
Display the list of known Emacs problems, sometimes with suggested workarounds (view-emacs-problems).
C-h C-t
Display the Emacs to-do list (view-emacs-todo).
C-h C-w
Display the full details on the complete absence of warranty for GNU Emacs (describe-no-warranty).

Previous: Help Files, Up: Help

10.10 Help on Active Text and Tooltips

In Emacs, stretches of “active text” (text that does something special in response to mouse clicks or <RET>) often have associated help text. This includes hyperlinks in Emacs buffers, as well as parts of the mode line. On graphical displays, as well as some text terminals which support mouse tracking, moving the mouse over the active text displays the help text as a tooltip. See Tooltips.

On terminals that don't support mouse-tracking, you can display the help text for active buffer text at point by typing C-h . (display-local-help). This shows the help text in the echo area. To display help text automatically whenever it is available at point, set the variable help-at-pt-display-when-idle to t.

Next: , Previous: Help, Up: Top

11 The Mark and the Region

Many Emacs commands operate on an arbitrary contiguous part of the current buffer. To specify the text for such a command to operate on, you set the mark at one end of it, and move point to the other end. The text between point and the mark is called the region. The region always extends between point and the mark, no matter which one comes earlier in the text; each time you move point, the region changes.

Setting the mark at a position in the text also activates it. When the mark is active, we say also that the region is active; Emacs indicates its extent by highlighting the text within it, using the region face (see Face Customization).

After certain non-motion commands, including any command that changes the text in the buffer, Emacs automatically deactivates the mark; this turns off the highlighting. You can also explicitly deactivate the mark at any time, by typing C-g (see Quitting).

The above default behavior is known as Transient Mark mode. Disabling Transient Mark mode switches Emacs to an alternative behavior, in which the region is usually not highlighted. See Disabled Transient Mark.

Setting the mark in one buffer has no effect on the marks in other buffers. When you return to a buffer with an active mark, the mark is at the same place as before. When multiple windows show the same buffer, they can have different values of point, and thus different regions, but they all share one common mark position. See Windows. Ordinarily, only the selected window highlights its region; however, if the variable highlight-nonselected-windows is non-nil, each window highlights its own region.

Next: , Up: Mark

11.1 Setting the Mark

Here are some commands for setting the mark:

C-<SPC>
Set the mark at point, and activate it (set-mark-command).
C-@
The same.
C-x C-x
Set the mark at point, and activate it; then move point where the mark used to be (exchange-point-and-mark).
Drag-Mouse-1
Set point and the mark around the text you drag across.
Mouse-3
Set the mark at point, then move point to where you click (mouse-save-then-kill).
‘Shifted cursor motion keys’
Set the mark at point if the mark is inactive, then move point. See Shift Selection.

The most common way to set the mark is with C-<SPC> (set-mark-command)5. This sets the mark where point is, and activates it. You can then move point away, leaving the mark behind.

For example, suppose you wish to convert part of the buffer to upper case. To accomplish this, go to one end of the desired text, type C-<SPC>, and move point until the desired portion of text is highlighted. Now type C-x C-u (upcase-region). This converts the text in the region to upper case, and then deactivates the mark.

Whenever the mark is active, you can deactivate it by typing C-g (see Quitting). Most commands that operate on the region also automatically deactivate the mark, like C-x C-u in the above example.

Instead of setting the mark in order to operate on a region, you can also use it to “remember” a position in the buffer (by typing C-<SPC> C-<SPC>), and later jump back there (by typing C-u C-<SPC>). See Mark Ring, for details.

The command C-x C-x (exchange-point-and-mark) exchanges the positions of point and the mark. C-x C-x is useful when you are satisfied with the position of point but want to move the other end of the region (where the mark is). Using C-x C-x a second time, if necessary, puts the mark at the new position with point back at its original position. Normally, if the mark is inactive, this command first reactivates the mark wherever it was last set, to ensure that the region is left highlighted. However, if you call it with a prefix argument, it leaves the mark inactive and the region unhighlighted; you can use this to jump to the mark in a manner similar to C-u C-<SPC>.

You can also set the mark with the mouse. If you press the left mouse button (down-mouse-1) and drag the mouse across a range of text, this sets the mark where you first pressed the mouse button and puts point where you release it. Alternatively, clicking the right mouse button (mouse-3) sets the mark at point and then moves point to where you clicked. See Mouse Commands, for a more detailed description of these mouse commands.

Finally, you can set the mark by holding down the shift key while typing certain cursor motion commands (such as S-<right>, S-C-f, S-C-n, etc.). This is called shift-selection. It sets the mark at point before moving point, but only if there is no active mark set via shift-selection. The mark set by mouse commands and by shift-selection behaves slightly differently from the usual mark: any subsequent unshifted cursor motion command deactivates it automatically. For details, See Shift Selection.

Many commands that insert text, such as C-y (yank), set the mark at the other end of the inserted text, without activating it. This lets you easily return to that position (see Mark Ring). You can tell that a command does this when it shows ‘Mark set’ in the echo area.

Under X, every time the active region changes, Emacs saves the text in the region to the primary selection. This lets you insert that text into other X applications with mouse-2 clicks. See Primary Selection.

Next: , Previous: Setting Mark, Up: Mark

11.2 Commands to Mark Textual Objects

Here are commands for placing point and the mark around a textual object such as a word, list, paragraph or page:

M-@
Set mark after end of next word (mark-word). This does not move point.
C-M-@
Set mark after end of following balanced expression (mark-sexp). This does not move point.
M-h
Move point to the beginning of the current paragraph, and set mark at the end (mark-paragraph).
C-M-h
Move point to the beginning of the current defun, and set mark at the end (mark-defun).
C-x C-p
Move point to the beginning of the current page, and set mark at the end (mark-page).
C-x h
Move point to the beginning of the buffer, and set mark at the end (mark-whole-buffer).

M-@ (mark-word) sets the mark at the end of the next word (see Words, for information about words). Repeated invocations of this command extend the region by advancing the mark one word at a time. As an exception, if the mark is active and located before point, M-@ moves the mark backwards from its current position one word at a time.

This command also accepts a numeric argument n, which tells it to advance the mark by n words. A negative argument moves the mark back by n words.

Similarly, C-M-@ (mark-sexp) puts the mark at the end of the next balanced expression (see Expressions). Repeated invocations extend the region to subsequent expressions, while positive or negative numeric arguments move the mark forward or backward by the specified number of expressions.

The other commands in the above list set both point and mark, so as to delimit an object in the buffer. M-h (mark-paragraph) marks paragraphs (see Paragraphs), C-M-h (mark-defun) marks top-level definitions (see Moving by Defuns), and C-x C-p (mark-page) marks pages (see Pages). Repeated invocations again play the same role, extending the region to consecutive objects; similarly, numeric arguments specify how many objects to move the mark by.

C-x h (mark-whole-buffer) sets up the entire buffer as the region, by putting point at the beginning and the mark at the end.

Next: , Previous: Marking Objects, Up: Mark

11.3 Operating on the Region

Once you have a region, here are some of the ways you can operate on it:

Some commands have a default behavior when the mark is inactive, but operate on the region if the mark is active. For example, M-$ (ispell-word) normally checks the spelling of the word at point, but it checks the text in the region if the mark is active (see Spelling). Normally, such commands use their default behavior if the region is empty (i.e., if mark and point are at the same position). If you want them to operate on the empty region, change the variable use-empty-active-region to t.

As described in Erasing, the <DEL> (backward-delete-char) and <delete> (delete-forward-char) commands also act this way. If the mark is active, they delete the text in the region. (As an exception, if you supply a numeric argument n, where n is not one, these commands delete n characters regardless of whether the mark is active). If you change the variable delete-active-region to nil, then these commands don't act differently when the mark is active. If you change the value to kill, these commands kill the region instead of deleting it (see Killing).

Other commands always operate on the region, and have no default behavior. Such commands usually have the word region in their names, like C-w (kill-region) and C-x C-u (upcase-region). If the mark is inactive, they operate on the “inactive region”—that is, on the text between point and the position at which the mark was last set (see Mark Ring). To disable this behavior, change the variable mark-even-if-inactive to nil. Then these commands will instead signal an error if the mark is inactive.

By default, text insertion occurs normally even if the mark is active—for example, typing a inserts the character ‘a’, then deactivates the mark. If you enable Delete Selection mode, a minor mode, then inserting text while the mark is active causes the text in the region to be deleted first. To toggle Delete Selection mode on or off, type M-x delete-selection-mode.

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11.4 The Mark Ring

Each buffer remembers previous locations of the mark, in the mark ring. Commands that set the mark also push the old mark onto this ring. One of the uses of the mark ring is to remember spots that you may want to go back to.

C-<SPC> C-<SPC>
Set the mark, pushing it onto the mark ring, without activating it.
C-u C-<SPC>
Move point to where the mark was, and restore the mark from the ring of former marks.

The command C-<SPC> C-<SPC> is handy when you want to use the mark to remember a position to which you may wish to return. It pushes the current point onto the mark ring, without activating the mark (which would cause Emacs to highlight the region). This is actually two consecutive invocations of C-<SPC> (set-mark-command); the first C-<SPC> sets the mark, and the second C-<SPC> deactivates it. (When Transient Mark mode is off, C-<SPC> C-<SPC> instead activates Transient Mark mode temporarily; see Disabled Transient Mark.)

To return to a marked position, use set-mark-command with a prefix argument: C-u C-<SPC>. This moves point to where the mark was, and deactivates the mark if it was active. Each subsequent C-u C-<SPC> jumps to a prior position stored in the mark ring. The positions you move through in this way are not lost; they go to the end of the ring.

If you set set-mark-command-repeat-pop to non-nil, then immediately after you type C-u C-<SPC>, you can type C-<SPC> instead of C-u C-<SPC> to cycle through the mark ring. By default, set-mark-command-repeat-pop is nil.

Each buffer has its own mark ring. All editing commands use the current buffer's mark ring. In particular, C-u C-<SPC> always stays in the same buffer.

The variable mark-ring-max specifies the maximum number of entries to keep in the mark ring. This defaults to 16 entries. If that many entries exist and another one is pushed, the earliest one in the list is discarded. Repeating C-u C-<SPC> cycles through the positions currently in the ring.

If you want to move back to the same place over and over, the mark ring may not be convenient enough. If so, you can record the position in a register for later retrieval (see Saving Positions in Registers).

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11.5 The Global Mark Ring

In addition to the ordinary mark ring that belongs to each buffer, Emacs has a single global mark ring. Each time you set a mark, this is recorded in the global mark ring in addition to the current buffer's own mark ring, if you have switched buffers since the previous mark setting. Hence, the global mark ring records a sequence of buffers that you have been in, and, for each buffer, a place where you set the mark. The length of the global mark ring is controlled by global-mark-ring-max, and is 16 by default.

The command C-x C-<SPC> (pop-global-mark) jumps to the buffer and position of the latest entry in the global ring. It also rotates the ring, so that successive uses of C-x C-<SPC> take you to earlier buffers and mark positions.

Next: , Previous: Global Mark Ring, Up: Mark

11.6 Shift Selection

If you hold down the shift key while typing a cursor motion command, this sets the mark before moving point, so that the region extends from the original position of point to its new position. This feature is referred to as shift-selection. It is similar to the way text is selected in other editors.

The mark set via shift-selection behaves a little differently from what we have described above. Firstly, in addition to the usual ways of deactivating the mark (such as changing the buffer text or typing C-g), the mark is deactivated by any unshifted cursor motion command. Secondly, any subsequent shifted cursor motion command avoids setting the mark anew. Therefore, a series of shifted cursor motion commands will continuously adjust the region.

Shift-selection only works if the shifted cursor motion key is not already bound to a separate command (see Customization). For example, if you bind S-C-f to another command, typing S-C-f runs that command instead of performing a shift-selected version of C-f (forward-char).

A mark set via mouse commands behaves the same as a mark set via shift-selection (see Setting Mark). For example, if you specify a region by dragging the mouse, you can continue to extend the region using shifted cursor motion commands. In either case, any unshifted cursor motion command deactivates the mark.

To turn off shift-selection, set shift-select-mode to nil. Doing so does not disable setting the mark via mouse commands.

Previous: Shift Selection, Up: Mark

11.7 Disabling Transient Mark Mode

The default behavior of the mark and region, in which setting the mark activates it and highlights the region, is called Transient Mark mode. This is a minor mode that is enabled by default. It can be toggled with M-x transient-mark-mode, or with the ‘Active Region Highlighting’ menu item in the ‘Options’ menu. Turning it off switches Emacs to an alternative mode of operation:

While Transient Mark mode is off, you can activate it temporarily using C-<SPC> C-<SPC> or C-u C-x C-x.

C-<SPC> C-<SPC>
Set the mark at point (like plain C-<SPC>) and enable Transient Mark mode just once, until the mark is deactivated. (This is not really a separate command; you are using the C-<SPC> command twice.)
C-u C-x C-x
Exchange point and mark, activate the mark and enable Transient Mark mode temporarily, until the mark is next deactivated. (This is the C-x C-x command, exchange-point-and-mark, with a prefix argument.)

These commands set or activate the mark, and enable Transient Mark mode only until the mark is deactivated. One reason you may want to use them is that some commands operate on the entire buffer instead of the region when Transient Mark mode is off. Enabling Transient Mark mode momentarily gives you a way to use these commands on the region.

When you specify a region with the mouse (see Setting Mark), or with shift-selection (see Shift Selection), this likewise activates Transient Mark mode temporarily and highlights the region.

Next: , Previous: Mark, Up: Top

12 Killing and Moving Text

In Emacs, killing means erasing text and copying it into the kill ring. Yanking means bringing text from the kill ring back into the buffer. (Some applications use the terms “cutting” and “pasting” for similar operations.) The kill ring is so-named because it can be visualized as a set of blocks of text arranged in a ring, which you can access in cyclic order. See Kill Ring.

Killing and yanking are the most common way to move or copy text within Emacs. It is very versatile, because there are commands for killing many different types of syntactic units.

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12.1 Deletion and Killing

Most commands which erase text from the buffer save it in the kill ring. These are known as kill commands, and their names normally contain the word ‘kill’ (e.g., kill-line). The kill ring stores several recent kills, not just the last one, so killing is a very safe operation: you don't have to worry much about losing text that you previously killed. The kill ring is shared by all buffers, so text that is killed in one buffer can be yanked into another buffer.

When you use C-/ (undo) to undo a kill command (see Undo), that brings the killed text back into the buffer, but does not remove it from the kill ring.

On graphical displays, killing text also copies it to the system clipboard. See Cut and Paste.

Commands that erase text but do not save it in the kill ring are known as delete commands; their names usually contain the word ‘delete’. These include C-d (delete-char) and <DEL> (delete-backward-char), which delete only one character at a time, and those commands that delete only spaces or newlines. Commands that can erase significant amounts of nontrivial data generally do a kill operation instead.

You can also use the mouse to kill and yank. See Cut and Paste.

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12.1.1 Deletion

Deletion means erasing text and not saving it in the kill ring. For the most part, the Emacs commands that delete text are those that erase just one character or only whitespace.

<DEL>
<Backspace>
Delete the previous character, or the text in the region if it is active (delete-backward-char).
<Delete>
Delete the next character, or the text in the region if it is active (delete-forward-char).
C-d
Delete the next character (delete-char).
M-\
Delete spaces and tabs around point (delete-horizontal-space).
M-<SPC>
Delete spaces and tabs around point, leaving one space (just-one-space).
C-x C-o
Delete blank lines around the current line (delete-blank-lines).
M-^
Join two lines by deleting the intervening newline, along with any indentation following it (delete-indentation).

We have already described the basic deletion commands <DEL> (delete-backward-char), <delete> (delete-forward-char), and C-d (delete-char). See Erasing. With a numeric argument, they delete the specified number of characters. If the numeric argument is omitted or one, they delete all the text in the region if it is active (see Using Region).

The other delete commands are those that delete only whitespace characters: spaces, tabs and newlines. M-\ (delete-horizontal-space) deletes all the spaces and tab characters before and after point. With a prefix argument, this only deletes spaces and tab characters before point. M-<SPC> (just-one-space) does likewise but leaves a single space before point, regardless of the number of spaces that existed previously (even if there were none before). With a numeric argument n, it leaves n spaces before point if n is positive; if n is negative, it deletes newlines in addition to spaces and tabs, leaving -n spaces before point.

C-x C-o (delete-blank-lines) deletes all blank lines after the current line. If the current line is blank, it deletes all blank lines preceding the current line as well (leaving one blank line, the current line). On a solitary blank line, it deletes that line.

M-^ (delete-indentation) joins the current line and the previous line, by deleting a newline and all surrounding spaces, usually leaving a single space. See M-^.

Next: , Previous: Deletion, Up: Deletion and Killing

12.1.2 Killing by Lines

C-k
Kill rest of line or one or more lines (kill-line).
C-S-backspace
Kill an entire line at once (kill-whole-line)

The simplest kill command is C-k (kill-line). If used at the end of a line, it kills the line-ending newline character, merging the next line into the current one (thus, a blank line is entirely removed). Otherwise, C-k kills all the text from point up to the end of the line; if point was originally at the beginning of the line, this leaves the line blank.

Spaces and tabs at the end of the line are ignored when deciding which case applies. As long as point is after the last visible character in the line, you can be sure that C-k will kill the newline. To kill an entire non-blank line, go to the beginning and type C-k twice.

In this context, “line” means a logical text line, not a screen line (see Continuation Lines).

When C-k is given a positive argument n, it kills n lines and the newlines that follow them (text on the current line before point is not killed). With a negative argument −n, it kills n lines preceding the current line, together with the text on the current line before point. C-k with an argument of zero kills the text before point on the current line.

If the variable kill-whole-line is non-nil, C-k at the very beginning of a line kills the entire line including the following newline. This variable is normally nil.

C-S-backspace (kill-whole-line) kills a whole line including its newline, regardless of the position of point within the line. Note that many text terminals will prevent you from typing the key sequence C-S-backspace.

Next: , Previous: Killing by Lines, Up: Deletion and Killing

12.1.3 Other Kill Commands

C-w
Kill the region (kill-region).
M-w
Copy the region into the kill ring (kill-ring-save).
M-d
Kill the next word (kill-word). See Words.
M-<DEL>
Kill one word backwards (backward-kill-word).
C-x <DEL>
Kill back to beginning of sentence (backward-kill-sentence). See Sentences.
M-k
Kill to the end of the sentence (kill-sentence).
C-M-k
Kill the following balanced expression (kill-sexp). See Expressions.
M-z char
Kill through the next occurrence of char (zap-to-char).

One of the commonly-used kill commands is C-w (kill-region), which kills the text in the region (see Mark). Similarly, M-w (kill-ring-save) copies the text in the region into the kill ring without removing it from the buffer. If the mark is inactive when you type C-w or M-w, the command acts on the text between point and where you last set the mark (see Using Region).

Emacs also provides commands to kill specific syntactic units: words, with M-<DEL> and M-d (see Words); balanced expressions, with C-M-k (see Expressions); and sentences, with C-x <DEL> and M-k (see Sentences).

The command M-z (zap-to-char) combines killing with searching: it reads a character and kills from point up to (and including) the next occurrence of that character in the buffer. A numeric argument acts as a repeat count; a negative argument means to search backward and kill text before point.

Previous: Other Kill Commands, Up: Deletion and Killing

12.1.4 Options for Killing

Some specialized buffers contain read-only text, which cannot be modified and therefore cannot be killed. The kill commands work specially in a read-only buffer: they move over text and copy it to the kill ring, without actually deleting it from the buffer. Normally, they also beep and display an error message when this happens. But if you set the variable kill-read-only-ok to a non-nil value, they just print a message in the echo area to explain why the text has not been erased.

If you change the variable kill-do-not-save-duplicates to a non-nil value, identical subsequent kills yield a single kill-ring entry, without duplication.

Next: , Previous: Deletion and Killing, Up: Killing

12.2 Yanking

Yanking means reinserting text previously killed. The usual way to move or copy text is to kill it and then yank it elsewhere.

C-y
Yank the last kill into the buffer, at point (yank).
M-y
Replace the text just yanked with an earlier batch of killed text (yank-pop). See Earlier Kills.
C-M-w
Cause the following command, if it is a kill command, to append to the previous kill (append-next-kill). See Appending Kills.

The basic yanking command is C-y (yank). It inserts the most recent kill, leaving the cursor at the end of the inserted text. It also sets the mark at the beginning of the inserted text, without activating the mark; this lets you jump easily to that position, if you wish, with C-u C-<SPC> (see Mark Ring).

With a plain prefix argument (C-u C-y), the command instead leaves the cursor in front of the inserted text, and sets the mark at the end. Using any other prefix argument specifies an earlier kill; e.g., C-u 4 C-y reinserts the fourth most recent kill. See Earlier Kills.

On graphical displays, C-y first checks if another application has placed any text in the system clipboard more recently than the last Emacs kill. If so, it inserts the clipboard's text instead. Thus, Emacs effectively treats “cut” or “copy” clipboard operations performed in other applications like Emacs kills, except that they are not recorded in the kill ring. See Cut and Paste, for details.

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12.2.1 The Kill Ring

The kill ring is a list of blocks of text that were previously killed. There is only one kill ring, shared by all buffers, so you can kill text in one buffer and yank it in another buffer. This is the usual way to move text from one buffer to another. (There are several other methods: for instance, you could store the text in a register; see Registers. See Accumulating Text, for some other ways to move text around.)

The maximum number of entries in the kill ring is controlled by the variable kill-ring-max. The default is 60. If you make a new kill when this limit has been reached, Emacs makes room by deleting the oldest entry in the kill ring.

The actual contents of the kill ring are stored in a variable named kill-ring; you can view the entire contents of the kill ring with C-h v kill-ring.

Next: , Previous: Kill Ring, Up: Yanking

12.2.2 Yanking Earlier Kills

As explained in Yanking, you can use a numeric argument to C-y to yank text that is no longer the most recent kill. This is useful if you remember which kill ring entry you want. If you don't, you can use the M-y (yank-pop) command to cycle through the possibilities.

If the previous command was a yank command, M-y takes the text that was yanked and replaces it with the text from an earlier kill. So, to recover the text of the next-to-the-last kill, first use C-y to yank the last kill, and then use M-y to replace it with the previous kill. M-y is allowed only after a C-y or another M-y.

You can understand M-y in terms of a “last yank” pointer which points at an entry in the kill ring. Each time you kill, the “last yank” pointer moves to the newly made entry at the front of the ring. C-y yanks the entry which the “last yank” pointer points to. M-y moves the “last yank” pointer to a different entry, and the text in the buffer changes to match. Enough M-y commands can move the pointer to any entry in the ring, so you can get any entry into the buffer. Eventually the pointer reaches the end of the ring; the next M-y loops back around to the first entry again.

M-y moves the “last yank” pointer around the ring, but it does not change the order of the entries in the ring, which always runs from the most recent kill at the front to the oldest one still remembered.

M-y can take a numeric argument, which tells it how many entries to advance the “last yank” pointer by. A negative argument moves the pointer toward the front of the ring; from the front of the ring, it moves “around” to the last entry and continues forward from there.

Once the text you are looking for is brought into the buffer, you can stop doing M-y commands and it will stay there. It's just a copy of the kill ring entry, so editing it in the buffer does not change what's in the ring. As long as no new killing is done, the “last yank” pointer remains at the same place in the kill ring, so repeating C-y will yank another copy of the same previous kill.

When you call C-y with a numeric argument, that also sets the “last yank” pointer to the entry that it yanks.

Previous: Earlier Kills, Up: Yanking

12.2.3 Appending Kills

Normally, each kill command pushes a new entry onto the kill ring. However, two or more kill commands in a row combine their text into a single entry, so that a single C-y yanks all the text as a unit, just as it was before it was killed.

Thus, if you want to yank text as a unit, you need not kill all of it with one command; you can keep killing line after line, or word after word, until you have killed it all, and you can still get it all back at once.

Commands that kill forward from point add onto the end of the previous killed text. Commands that kill backward from point add text onto the beginning. This way, any sequence of mixed forward and backward kill commands puts all the killed text into one entry without rearrangement. Numeric arguments do not break the sequence of appending kills. For example, suppose the buffer contains this text: 

     This is a line -!-of sample text.

with point shown by -!-. If you type M-d M-<DEL> M-d M-<DEL>, killing alternately forward and backward, you end up with ‘a line of sample’ as one entry in the kill ring, and ‘This is text.’ in the buffer. (Note the double space between ‘is’ and ‘text’, which you can clean up with M-<SPC> or M-q.)

Another way to kill the same text is to move back two words with M-b M-b, then kill all four words forward with C-u M-d. This produces exactly the same results in the buffer and in the kill ring. M-f M-f C-u M-<DEL> kills the same text, all going backward; once again, the result is the same. The text in the kill ring entry always has the same order that it had in the buffer before you killed it.

If a kill command is separated from the last kill command by other commands (not just numeric arguments), it starts a new entry on the kill ring. But you can force it to append by first typing the command C-M-w (append-next-kill) right before it. The C-M-w tells the following command, if it is a kill command, to append the text it kills to the last killed text, instead of starting a new entry. With C-M-w, you can kill several separated pieces of text and accumulate them to be yanked back in one place.

A kill command following M-w (kill-ring-save) does not append to the text that M-w copied into the kill ring.

Next: , Previous: Yanking, Up: Killing

12.3 “Cut and Paste” Operations on Graphical Displays

In most graphical desktop environments, you can transfer data (usually text) between different applications using a system facility called the clipboard. On X, two other similar facilities are available: the primary selection and the secondary selection. When Emacs is run on a graphical display, its kill and yank commands integrate with these facilities, so that you can easily transfer text between Emacs and other graphical applications.

By default, Emacs uses UTF-8 as the coding system for inter-program text transfers. If you find that the pasted text is not what you expected, you can specify another coding system by typing C-x <RET> x or C-x <RET> X. You can also request a different data type by customizing x-select-request-type. See Communication Coding.

Next: , Up: Cut and Paste

12.3.1 Using the Clipboard

The clipboard is the facility that most graphical applications use for “cutting and pasting”. When the clipboard exists, the kill and yank commands in Emacs make use of it.

When you kill some text with a command such as C-w (kill-region), or copy it to the kill ring with a command such as M-w (kill-ring-save), that text is also put in the clipboard.

When an Emacs kill command puts text in the clipboard, the existing clipboard contents are normally lost. Optionally, you can change save-interprogram-paste-before-kill to t. Then Emacs will first save the clipboard to its kill ring, preventing you from losing the old clipboard data—at the risk of high memory consumption if that data turns out to be large.

Yank commands, such as C-y (yank), also use the clipboard. If another application “owns” the clipboard—i.e., if you cut or copied text there more recently than your last kill command in Emacs—then Emacs yanks from the clipboard instead of the kill ring.

Normally, rotating the kill ring with M-y (yank-pop) does not alter the clipboard. However, if you change yank-pop-change-selection to t, then M-y saves the new yank to the clipboard.

To prevent kill and yank commands from accessing the clipboard, change the variable x-select-enable-clipboard to nil.

Many X desktop environments support a feature called the clipboard manager. If you exit Emacs while it is the current “owner” of the clipboard data, and there is a clipboard manager running, Emacs transfers the clipboard data to the clipboard manager so that it is not lost. In some circumstances, this may cause a delay when exiting Emacs; if you wish to prevent Emacs from transferring data to the clipboard manager, change the variable x-select-enable-clipboard-manager to nil.

Prior to Emacs 24, the kill and yank commands used the primary selection (see Primary Selection), not the clipboard. If you prefer this behavior, change x-select-enable-clipboard to nil, x-select-enable-primary to t, and mouse-drag-copy-region to t. In this case, you can use the following commands to act explicitly on the clipboard: clipboard-kill-region kills the region and saves it to the clipboard; clipboard-kill-ring-save copies the region to the kill ring and saves it to the clipboard; and clipboard-yank yanks the contents of the clipboard at point.

Next: , Previous: Clipboard, Up: Cut and Paste

12.3.2 Cut and Paste with Other Window Applications

Under the X Window System, there exists a primary selection containing the last stretch of text selected in an X application (usually by dragging the mouse). Typically, this text can be inserted into other X applications by mouse-2 clicks. The primary selection is separate from the clipboard. Its contents are more “fragile”; they are overwritten each time you select text with the mouse, whereas the clipboard is only overwritten by explicit “cut” or “copy” commands.

Under X, whenever the region is active (see Mark), the text in the region is saved in the primary selection. This applies regardless of whether the region was made by dragging or clicking the mouse (see Mouse Commands), or by keyboard commands (e.g., by typing C-<SPC> and moving point; see Setting Mark).

If you change the variable select-active-regions to only, Emacs saves only temporarily active regions to the primary selection, i.e., those made with the mouse or with shift selection (see Shift Selection). If you change select-active-regions to nil, Emacs avoids saving active regions to the primary selection entirely.

To insert the primary selection into an Emacs buffer, click mouse-2 (mouse-yank-primary) where you want to insert it. See Mouse Commands.

MS-Windows provides no primary selection, but Emacs emulates it within a single Emacs session by storing the selected text internally. Therefore, all the features and commands related to the primary selection work on Windows as they do on X, for cutting and pasting within the same session, but not across Emacs sessions or with other applications.

Previous: Primary Selection, Up: Cut and Paste

12.3.3 Secondary Selection

In addition to the primary selection, the X Window System provides a second similar facility known as the secondary selection. Nowadays, few X applications make use of the secondary selection, but you can access it using the following Emacs commands:

M-Drag-Mouse-1
Set the secondary selection, with one end at the place where you press down the button, and the other end at the place where you release it (mouse-set-secondary). The selected text is highlighted, using the secondary-selection face, as you drag. The window scrolls automatically if you drag the mouse off the top or bottom of the window, just like mouse-set-region (see Mouse Commands).

This command does not alter the kill ring.


M-Mouse-1
Set one endpoint for the secondary selection (mouse-start-secondary).


M-Mouse-3
Set the secondary selection, with one end at the position clicked and the other at the position specified with M-Mouse-1 (mouse-secondary-save-then-kill). This also puts the selected text in the kill ring. A second M-Mouse-3 at the same place kills the secondary selection just made.


M-Mouse-2
Insert the secondary selection where you click, placing point at the end of the yanked text (mouse-yank-secondary).

Double or triple clicking of M-Mouse-1 operates on words and lines, much like Mouse-1.

If mouse-yank-at-point is non-nil, M-Mouse-2 yanks at point. Then it does not matter precisely where you click, or even which of the frame's windows you click on. See Mouse Commands.

Next: , Previous: Cut and Paste, Up: Killing

12.4 Accumulating Text

Usually we copy or move text by killing it and yanking it, but there are other convenient methods for copying one block of text in many places, or for copying many scattered blocks of text into one place. Here we describe the commands to accumulate scattered pieces of text into a buffer or into a file.

M-x append-to-buffer
Append region to the contents of a specified buffer.
M-x prepend-to-buffer
Prepend region to the contents of a specified buffer.
M-x copy-to-buffer
Copy region into a specified buffer, deleting that buffer's old contents.
M-x insert-buffer
Insert the contents of a specified buffer into current buffer at point.
M-x append-to-file
Append region to the contents of a specified file, at the end.

To accumulate text into a buffer, use M-x append-to-buffer. This reads a buffer name, then inserts a copy of the region into the buffer specified. If you specify a nonexistent buffer, append-to-buffer creates the buffer. The text is inserted wherever point is in that buffer. If you have been using the buffer for editing, the copied text goes into the middle of the text of the buffer, starting from wherever point happens to be at that moment.

Point in that buffer is left at the end of the copied text, so successive uses of append-to-buffer accumulate the text in the specified buffer in the same order as they were copied. Strictly speaking, append-to-buffer does not always append to the text already in the buffer—it appends only if point in that buffer is at the end. However, if append-to-buffer is the only command you use to alter a buffer, then point is always at the end.

M-x prepend-to-buffer is just like append-to-buffer except that point in the other buffer is left before the copied text, so successive prependings add text in reverse order. M-x copy-to-buffer is similar, except that any existing text in the other buffer is deleted, so the buffer is left containing just the text newly copied into it.

The command M-x insert-buffer can be used to retrieve the accumulated text from another buffer. This prompts for the name of a buffer, and inserts a copy of all the text in that buffer into the current buffer at point, leaving point at the beginning of the inserted text. It also adds the position of the end of the inserted text to the mark ring, without activating the mark. See Buffers, for background information on buffers.

Instead of accumulating text in a buffer, you can append text directly into a file with M-x append-to-file. This prompts for a filename, and adds the text of the region to the end of the specified file. The file is changed immediately on disk.

You should use append-to-file only with files that are not being visited in Emacs. Using it on a file that you are editing in Emacs would change the file behind Emacs's back, which can lead to losing some of your editing.

Another way to move text around is to store it in a register. See Registers.

Next: , Previous: Accumulating Text, Up: Killing

12.5 Rectangles

Rectangle commands operate on rectangular areas of the text: all the characters between a certain pair of columns, in a certain range of lines. Emacs has commands to kill rectangles, yank killed rectangles, clear them out, fill them with blanks or text, or delete them. Rectangle commands are useful with text in multicolumn formats, and for changing text into or out of such formats.

To specify a rectangle for a command to work on, set the mark at one corner and point at the opposite corner. The rectangle thus specified is called the region-rectangle. If point and the mark are in the same column, the region-rectangle is empty. If they are in the same line, the region-rectangle is one line high.

The region-rectangle is controlled in much the same way as the region is controlled. But remember that a given combination of point and mark values can be interpreted either as a region or as a rectangle, depending on the command that uses them.

C-x r k
Kill the text of the region-rectangle, saving its contents as the “last killed rectangle” (kill-rectangle).
C-x r M-w
Save the text of the region-rectangle as the “last killed rectangle” (copy-rectangle-as-kill).
C-x r d
Delete the text of the region-rectangle (delete-rectangle).
C-x r y
Yank the last killed rectangle with its upper left corner at point (yank-rectangle).
C-x r o
Insert blank space to fill the space of the region-rectangle (open-rectangle). This pushes the previous contents of the region-rectangle to the right.
C-x r N
Insert line numbers along the left edge of the region-rectangle (rectangle-number-lines). This pushes the previous contents of the region-rectangle to the right.
C-x r c
Clear the region-rectangle by replacing all of its contents with spaces (clear-rectangle).
M-x delete-whitespace-rectangle
Delete whitespace in each of the lines on the specified rectangle, starting from the left edge column of the rectangle.
C-x r t string <RET>
Replace rectangle contents with string on each line (string-rectangle).
M-x string-insert-rectangle <RET> string <RET>
Insert string on each line of the rectangle.

The rectangle operations fall into two classes: commands to erase or insert rectangles, and commands to make blank rectangles.

There are two ways to erase the text in a rectangle: C-x r d (delete-rectangle) to delete the text outright, or C-x r k (kill-rectangle) to remove the text and save it as the last killed rectangle. In both cases, erasing the region-rectangle is like erasing the specified text on each line of the rectangle; if there is any following text on the line, it moves backwards to fill the gap.

“Killing” a rectangle is not killing in the usual sense; the rectangle is not stored in the kill ring, but in a special place that only records the most recent rectangle killed. This is because yanking a rectangle is so different from yanking linear text that different yank commands have to be used. Yank-popping is not defined for rectangles.

C-x r M-w (copy-rectangle-as-kill) is the equivalent of M-w for rectangles: it records the rectangle as the “last killed rectangle”, without deleting the text from the buffer.

To yank the last killed rectangle, type C-x r y (yank-rectangle). The rectangle's first line is inserted at point, the rectangle's second line is inserted at the same horizontal position one line vertically below, and so on. The number of lines affected is determined by the height of the saved rectangle.

For example, you can convert two single-column lists into a double-column list by killing one of the single-column lists as a rectangle, and then yanking it beside the other list.

You can also copy rectangles into and out of registers with C-x r r r and C-x r i r. See Rectangle Registers.

There are two commands you can use for making blank rectangles: C-x r c (clear-rectangle) blanks out existing text in the region-rectangle, and C-x r o (open-rectangle) inserts a blank rectangle.

M-x delete-whitespace-rectangle deletes horizontal whitespace starting from a particular column. This applies to each of the lines in the rectangle, and the column is specified by the left edge of the rectangle. The right edge of the rectangle does not make any difference to this command.

The command C-x r N (rectangle-number-lines) inserts line numbers along the left edge of the region-rectangle. Normally, the numbering begins from 1 (for the first line of the rectangle). With a prefix argument, the command prompts for a number to begin from, and for a format string with which to print the numbers (see Formatting Strings).

The command C-x r t (string-rectangle) replaces the contents of a region-rectangle with a string on each line. The string's width need not be the same as the width of the rectangle. If the string's width is less, the text after the rectangle shifts left; if the string is wider than the rectangle, the text after the rectangle shifts right.

The command M-x string-insert-rectangle is similar to string-rectangle, but inserts the string on each line, shifting the original text to the right.

Previous: Rectangles, Up: Killing

12.6 CUA Bindings

The command M-x cua-mode sets up key bindings that are compatible with the Common User Access (CUA) system used in many other applications.

When CUA mode is enabled, the keys C-x, C-c, C-v, and C-z invoke commands that cut (kill), copy, paste (yank), and undo respectively. The C-x and C-c keys perform cut and copy only if the region is active. Otherwise, they still act as prefix keys, so that standard Emacs commands like C-x C-c still work. Note that this means the variable mark-even-if-inactive has no effect for C-x and C-c (see Using Region).

To enter an Emacs command like C-x C-f while the mark is active, use one of the following methods: either hold Shift together with the prefix key, e.g., S-C-x C-f, or quickly type the prefix key twice, e.g., C-x C-x C-f.

To disable the overriding of standard Emacs binding by CUA mode, while retaining the other features of CUA mode described below, set the variable cua-enable-cua-keys to nil.

In CUA mode, typed text replaces the active region as in Delete-Selection mode (see Mouse Commands).

CUA mode provides enhanced rectangle support with visible rectangle highlighting. Use C-RET to start a rectangle, extend it using the movement commands, and cut or copy it using C-x or C-c. RET moves the cursor to the next (clockwise) corner of the rectangle, so you can easily expand it in any direction. Normal text you type is inserted to the left or right of each line in the rectangle (on the same side as the cursor).

With CUA you can easily copy text and rectangles into and out of registers by providing a one-digit numeric prefix to the kill, copy, and yank commands, e.g., C-1 C-c copies the region into register 1, and C-2 C-v yanks the contents of register 2.

CUA mode also has a global mark feature which allows easy moving and copying of text between buffers. Use C-S-SPC to toggle the global mark on and off. When the global mark is on, all text that you kill or copy is automatically inserted at the global mark, and text you type is inserted at the global mark rather than at the current position.

For example, to copy words from various buffers into a word list in a given buffer, set the global mark in the target buffer, then navigate to each of the words you want in the list, mark it (e.g., with S-M-f), copy it to the list with C-c or M-w, and insert a newline after the word in the target list by pressing <RET>.

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13 Registers

Emacs registers are compartments where you can save text, rectangles, positions, and other things for later use. Once you save text or a rectangle in a register, you can copy it into the buffer once, or many times; once you save a position in a register, you can jump back to that position once, or many times.

Each register has a name that consists of a single character, which we will denote by r; r can be a letter (such as ‘a’) or a number (such as ‘1’); case matters, so register ‘a’ is not the same as register ‘A’.

A register can store a position, a piece of text, a rectangle, a number, a window configuration, or a file name, but only one thing at any given time. Whatever you store in a register remains there until you store something else in that register. To see what register r contains, use M-x view-register:

M-x view-register <RET> r
Display a description of what register r contains.

Bookmarks record files and positions in them, so you can return to those positions when you look at the file again. Bookmarks are similar in spirit to registers, so they are also documented in this chapter.

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13.1 Saving Positions in Registers

C-x r <SPC> r
Record the position of point and the current buffer in register r (point-to-register).
C-x r j r
Jump to the position and buffer saved in register r (jump-to-register).

Typing C-x r <SPC> (point-to-register), followed by a character r, saves both the position of point and the current buffer in register r. The register retains this information until you store something else in it.

The command C-x r j r switches to the buffer recorded in register r, and moves point to the recorded position. The contents of the register are not changed, so you can jump to the saved position any number of times.

If you use C-x r j to go to a saved position, but the buffer it was saved from has been killed, C-x r j tries to create the buffer again by visiting the same file. Of course, this works only for buffers that were visiting files.

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13.2 Saving Text in Registers

When you want to insert a copy of the same piece of text several times, it may be inconvenient to yank it from the kill ring, since each subsequent kill moves that entry further down the ring. An alternative is to store the text in a register and later retrieve it.

C-x r s r
Copy region into register r (copy-to-register).
C-x r i r
Insert text from register r (insert-register).
M-x append-to-register <RET> r
Append region to text in register r.

When register r contains text, you can use C-x r + (increment-register) to append to that register. Note that command C-x r + behaves differently if r contains a number. See Number Registers.

M-x prepend-to-register <RET> r
Prepend region to text in register r.

C-x r s r stores a copy of the text of the region into the register named r. If the mark is inactive, Emacs first reactivates the mark where it was last set. The mark is deactivated at the end of this command. See Mark. C-u C-x r s r, the same command with a prefix argument, copies the text into register r and deletes the text from the buffer as well; you can think of this as “moving” the region text into the register.

M-x append-to-register <RET> r appends the copy of the text in the region to the text already stored in the register named r. If invoked with a prefix argument, it deletes the region after appending it to the register. The command prepend-to-register is similar, except that it prepends the region text to the text in the register instead of appending it.

When you are collecting text using append-to-register and prepend-to-register, you may want to separate individual collected pieces using a separator. In that case, configure a register-separator and store the separator text in to that register. For example, to get double newlines as text separator during the collection process, you can use the following setting. 

     (setq register-separator ?+)
     (set-register register-separator "\n\n")

C-x r i r inserts in the buffer the text from register r. Normally it leaves point before the text and sets the mark after, without activating it. With a numeric argument, it instead puts point after the text and the mark before.

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13.3 Saving Rectangles in Registers

A register can contain a rectangle instead of linear text. See Rectangles, for basic information on how to specify a rectangle in the buffer.

C-x r r r
Copy the region-rectangle into register r (copy-rectangle-to-register). With numeric argument, delete it as well.
C-x r i r
Insert the rectangle stored in register r (if it contains a rectangle) (insert-register).

The C-x r i r (insert-register) command, previously documented in Text Registers, inserts a rectangle rather than a text string, if the register contains a rectangle.

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13.4 Saving Window Configurations in Registers

You can save the window configuration of the selected frame in a register, or even the configuration of all windows in all frames, and restore the configuration later. See Windows, for information about window configurations.

C-x r w r
Save the state of the selected frame's windows in register r (window-configuration-to-register).
C-x r f r
Save the state of all frames, including all their windows, in register r (frame-configuration-to-register).

Use C-x r j r to restore a window or frame configuration. This is the same command used to restore a cursor position. When you restore a frame configuration, any existing frames not included in the configuration become invisible. If you wish to delete these frames instead, use C-u C-x r j r.

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13.5 Keeping Numbers in Registers

There are commands to store a number in a register, to insert the number in the buffer in decimal, and to increment it. These commands can be useful in keyboard macros (see Keyboard Macros).

C-u number C-x r n r
Store number into register r (number-to-register).
C-u number C-x r + r
If r contains a number, increment the number in that register by number. Note that command C-x r + (increment-register) behaves differently if r contains text. See Text Registers.
C-x r i r
Insert the number from register r into the buffer.

C-x r i is the same command used to insert any other sort of register contents into the buffer. C-x r + with no numeric argument increments the register value by 1; C-x r n with no numeric argument stores zero in the register.

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13.6 Keeping File Names in Registers

If you visit certain file names frequently, you can visit them more conveniently if you put their names in registers. Here's the Lisp code used to put a file name in a register: 

     (set-register ?r '(file . name))

For example, 

     (set-register ?z '(file . "/gd/gnu/emacs/19.0/src/ChangeLog"))

puts the file name shown in register ‘z’.

To visit the file whose name is in register r, type C-x r j r. (This is the same command used to jump to a position or restore a frame configuration.)

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13.7 Bookmarks

Bookmarks are somewhat like registers in that they record positions you can jump to. Unlike registers, they have long names, and they persist automatically from one Emacs session to the next. The prototypical use of bookmarks is to record “where you were reading” in various files.

C-x r m <RET>
Set the bookmark for the visited file, at point.
C-x r m bookmark <RET>
Set the bookmark named bookmark at point (bookmark-set).
C-x r b bookmark <RET>
Jump to the bookmark named bookmark (bookmark-jump).
C-x r l
List all bookmarks (list-bookmarks).
M-x bookmark-save
Save all the current bookmark values in the default bookmark file.

The prototypical use for bookmarks is to record one current position in each of several files. So the command C-x r m, which sets a bookmark, uses the visited file name as the default for the bookmark name. If you name each bookmark after the file it points to, then you can conveniently revisit any of those files with C-x r b, and move to the position of the bookmark at the same time.

To display a list of all your bookmarks in a separate buffer, type C-x r l (list-bookmarks). If you switch to that buffer, you can use it to edit your bookmark definitions or annotate the bookmarks. Type C-h m in the bookmark buffer for more information about its special editing commands.

When you kill Emacs, Emacs saves your bookmarks, if you have changed any bookmark values. You can also save the bookmarks at any time with the M-x bookmark-save command. Bookmarks are saved to the file ~/.emacs.d/bookmarks (for compatibility with older versions of Emacs, if you have a file named ~/.emacs.bmk, that is used instead). The bookmark commands load your default bookmark file automatically. This saving and loading is how bookmarks persist from one Emacs session to the next.

If you set the variable bookmark-save-flag to 1, each command that sets a bookmark will also save your bookmarks; this way, you don't lose any bookmark values even if Emacs crashes. The value, if a number, says how many bookmark modifications should go by between saving. If you set this variable to nil, Emacs only saves bookmarks if you explicitly use M-x bookmark-save.

Bookmark position values are saved with surrounding context, so that bookmark-jump can find the proper position even if the file is modified slightly. The variable bookmark-search-size says how many characters of context to record on each side of the bookmark's position.

Here are some additional commands for working with bookmarks:

M-x bookmark-load <RET> filename <RET>
Load a file named filename that contains a list of bookmark values. You can use this command, as well as bookmark-write, to work with other files of bookmark values in addition to your default bookmark file.
M-x bookmark-write <RET> filename <RET>
Save all the current bookmark values in the file filename.
M-x bookmark-delete <RET> bookmark <RET>
Delete the bookmark named bookmark.
M-x bookmark-insert-location <RET> bookmark <RET>
Insert in the buffer the name of the file that bookmark bookmark points to.
M-x bookmark-insert <RET> bookmark <RET>
Insert in the buffer the contents of the file that bookmark bookmark points to.

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14 Controlling the Display

Since only part of a large buffer fits in the window, Emacs has to show only a part of it. This chapter describes commands and variables that let you specify which part of the text you want to see, and how the text is displayed.

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14.1 Scrolling

If a window is too small to display all the text in its buffer, it displays only a portion of it. Scrolling commands change which portion of the buffer is displayed.

Scrolling “forward” or “up” advances the portion of the buffer displayed in the window; equivalently, it moves the buffer text upwards relative to the window. Scrolling “backward” or “down” displays an earlier portion of the buffer, and moves the text downwards relative to the window.

In Emacs, scrolling “up” or “down” refers to the direction that the text moves in the window, not the direction that the window moves relative to the text. This terminology was adopted by Emacs before the modern meaning of “scrolling up” and “scrolling down” became widespread. Hence, the strange result that <PageDown> scrolls “up” in the Emacs sense.

The portion of a buffer displayed in a window always contains point. If you move point past the bottom or top of the window, scrolling occurs automatically to bring it back onscreen (see Auto Scrolling). You can also scroll explicitly with these commands:

C-v
<next>
<PageDown>
Scroll forward by nearly a full window (scroll-up-command).
M-v
<prior>
<PageUp>
Scroll backward (scroll-down-command).

C-v (scroll-up-command) scrolls forward by nearly the whole window height. The effect is to take the two lines at the bottom of the window and put them at the top, followed by lines that were not previously visible. If point was in the text that scrolled off the top, it ends up on the window's new topmost line. The <next> (or <PageDown>) key is equivalent to C-v.

M-v (scroll-down-command) scrolls backward in a similar way. The <prior> (or <PageUp>) key is equivalent to M-v.

The number of lines of overlap left by these scroll commands is controlled by the variable next-screen-context-lines, whose default value is 2. You can supply the commands with a numeric prefix argument, n, to scroll by n lines; Emacs attempts to leave point unchanged, so that the text and point move up or down together. C-v with a negative argument is like M-v and vice versa.

By default, these commands signal an error (by beeping or flashing the screen) if no more scrolling is possible, because the window has reached the beginning or end of the buffer. If you change the variable scroll-error-top-bottom to t, the command moves point to the farthest possible position. If point is already there, the command signals an error.

Some users like scroll commands to keep point at the same screen position, so that scrolling back to the same screen conveniently returns point to its original position. You can enable this behavior via the variable scroll-preserve-screen-position. If the value is t, Emacs adjusts point to keep the cursor at the same screen position whenever a scroll command moves it off-window, rather than moving it to the topmost or bottommost line. With any other non-nil value, Emacs adjusts point this way even if the scroll command leaves point in the window. This variable affects all the scroll commands documented in this section, as well as scrolling with the mouse wheel (see Mouse Commands); in general, it affects any command that has a non-nil scroll-command property. See Property Lists.

The commands M-x scroll-up and M-x scroll-down behave similarly to scroll-up-command and scroll-down-command, except they do not obey scroll-error-top-bottom. Prior to Emacs 24, these were the default commands for scrolling up and down. The commands M-x scroll-up-line and M-x scroll-down-line scroll the current window by one line at a time. If you intend to use any of these commands, you might want to give them key bindings (see Init Rebinding).

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14.2 Recentering

C-l
Scroll the selected window so the current line is the center-most text line; on subsequent consecutive invocations, make the current line the top line, the bottom line, and so on in cyclic order. Possibly redisplay the screen too (recenter-top-bottom).
M-x recenter
Scroll the selected window so the current line is the center-most text line. Possibly redisplay the screen too.
C-M-l
Scroll heuristically to bring useful information onto the screen (reposition-window).

The C-l (recenter-top-bottom) command recenters the selected window, scrolling it so that the current screen line is exactly in the center of the window, or as close to the center as possible.

Typing C-l twice in a row (C-l C-l) scrolls the window so that point is on the topmost screen line. Typing a third C-l scrolls the window so that point is on the bottom-most screen line. Each successive C-l cycles through these three positions.

You can change the cycling order by customizing the list variable recenter-positions. Each list element should be the symbol top, middle, or bottom, or a number; an integer means to move the line to the specified screen line, while a floating-point number between 0.0 and 1.0 specifies a percentage of the screen space from the top of the window. The default, (middle top bottom), is the cycling order described above. Furthermore, if you change the variable scroll-margin to a non-zero value n, C-l always leaves at least n screen lines between point and the top or bottom of the window (see Auto Scrolling).

You can also give C-l a prefix argument. A plain prefix argument, C-u C-l, simply recenters point. A positive argument n puts point n lines down from the top of the window. An argument of zero puts point on the topmost line. A negative argument -n puts point n lines from the bottom of the window. When given an argument, C-l does not clear the screen or cycle through different screen positions.

If the variable recenter-redisplay has a non-nil value, each invocation of C-l also clears and redisplays the screen; the special value tty (the default) says to do this on text-terminal frames only. Redisplaying is useful in case the screen becomes garbled for any reason (see Screen Garbled).

The more primitive command M-x recenter behaves like recenter-top-bottom, but does not cycle among screen positions.

C-M-l (reposition-window) scrolls the current window heuristically in a way designed to get useful information onto the screen. For example, in a Lisp file, this command tries to get the entire current defun onto the screen if possible.

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14.3 Automatic Scrolling

Emacs performs automatic scrolling when point moves out of the visible portion of the text. Normally, automatic scrolling centers point vertically in the window, but there are several ways to alter this behavior.

If you set scroll-conservatively to a small number n, then moving point just a little off the screen (no more than n lines) causes Emacs to scroll just enough to bring point back on screen; if doing so fails to make point visible, Emacs scrolls just far enough to center point in the window. If you set scroll-conservatively to a large number (larger than 100), automatic scrolling never centers point, no matter how far point moves; Emacs always scrolls text just enough to bring point into view, either at the top or bottom of the window depending on the scroll direction. By default, scroll-conservatively is 0, which means to always center point in the window.

Another way to control automatic scrolling is to customize the variable scroll-step. Its value determines the number of lines by which to automatically scroll, when point moves off the screen. If scrolling by that number of lines fails to bring point back into view, point is centered instead. The default value is zero, which (by default) causes point to always be centered after scrolling.

A third way to control automatic scrolling is to customize the variables scroll-up-aggressively and scroll-down-aggressively, which directly specify the vertical position of point after scrolling. The value of scroll-up-aggressively should be either nil (the default), or a floating point number f between 0 and 1. The latter means that when point goes below the bottom window edge (i.e., scrolling forward), Emacs scrolls the window so that point is f parts of the window height from the bottom window edge. Thus, larger f means more aggressive scrolling: more new text is brought into view. The default value, nil, is equivalent to 0.5.

Likewise, scroll-down-aggressively is used when point goes above the bottom window edge (i.e., scrolling backward). The value specifies how far point should be from the top margin of the window after scrolling. Thus, as with scroll-up-aggressively, a larger value is more aggressive.

Note that the variables scroll-conservatively, scroll-step, and scroll-up-aggressively / scroll-down-aggressively control automatic scrolling in contradictory ways. Therefore, you should pick no more than one of these methods to customize automatic scrolling. In case you customize multiple variables, the order of priority is: scroll-conservatively, then scroll-step, and finally scroll-up-aggressively / scroll-down-aggressively.

The variable scroll-margin restricts how close point can come to the top or bottom of a window (even if aggressive scrolling specifies a fraction f that is larger than the window portion between the top and the bottom margins). Its value is a number of screen lines; if point comes within that many lines of the top or bottom of the window, Emacs performs automatic scrolling. By default, scroll-margin is 0.

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14.4 Horizontal Scrolling

Horizontal scrolling means shifting all the lines sideways within a window, so that some of the text near the left margin is not displayed. When the text in a window is scrolled horizontally, text lines are truncated rather than continued (see Line Truncation). If a window shows truncated lines, Emacs performs automatic horizontal scrolling whenever point moves off the left or right edge of the screen. To disable automatic horizontal scrolling, set the variable auto-hscroll-mode to nil. Note that when the automatic horizontal scrolling is turned off, if point moves off the edge of the screen, the cursor disappears to indicate that. (On text terminals, the cursor is left at the edge instead.)

The variable hscroll-margin controls how close point can get to the window's left and right edges before automatic scrolling occurs. It is measured in columns. For example, if the value is 5, then moving point within 5 columns of an edge causes horizontal scrolling away from that edge.

The variable hscroll-step determines how many columns to scroll the window when point gets too close to the edge. Zero, the default value, means to center point horizontally within the window. A positive integer value specifies the number of columns to scroll by. A floating-point number specifies the fraction of the window's width to scroll by.

You can also perform explicit horizontal scrolling with the following commands:

C-x <
Scroll text in current window to the left (scroll-left).
C-x >
Scroll to the right (scroll-right).

C-x < (scroll-left) scrolls text in the selected window to the left by the full width of the window, less two columns. (In other words, the text in the window moves left relative to the window.) With a numeric argument n, it scrolls by n columns.

If the text is scrolled to the left, and point moves off the left edge of the window, the cursor will freeze at the left edge of the window, until point moves back to the displayed portion of the text. This is independent of the current setting of auto-hscroll-mode, which, for text scrolled to the left, only affects the behavior at the right edge of the window.

C-x > (scroll-right) scrolls similarly to the right. The window cannot be scrolled any farther to the right once it is displayed normally, with each line starting at the window's left margin; attempting to do so has no effect. This means that you don't have to calculate the argument precisely for C-x >; any sufficiently large argument will restore the normal display.

If you use those commands to scroll a window horizontally, that sets a lower bound for automatic horizontal scrolling. Automatic scrolling will continue to scroll the window, but never farther to the right than the amount you previously set by scroll-left.

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14.5 Narrowing

Narrowing means focusing in on some portion of the buffer, making the rest temporarily inaccessible. The portion which you can still get to is called the accessible portion. Canceling the narrowing, which makes the entire buffer once again accessible, is called widening. The bounds of narrowing in effect in a buffer are called the buffer's restriction.

Narrowing can make it easier to concentrate on a single subroutine or paragraph by eliminating clutter. It can also be used to limit the range of operation of a replace command or repeating keyboard macro.

C-x n n
Narrow down to between point and mark (narrow-to-region).
C-x n w
Widen to make the entire buffer accessible again (widen).
C-x n p
Narrow down to the current page (narrow-to-page).
C-x n d
Narrow down to the current defun (narrow-to-defun).

When you have narrowed down to a part of the buffer, that part appears to be all there is. You can't see the rest, you can't move into it (motion commands won't go outside the accessible part), you can't change it in any way. However, it is not gone, and if you save the file all the inaccessible text will be saved. The word ‘Narrow’ appears in the mode line whenever narrowing is in effect.

The primary narrowing command is C-x n n (narrow-to-region). It sets the current buffer's restrictions so that the text in the current region remains accessible, but all text before the region or after the region is inaccessible. Point and mark do not change.

Alternatively, use C-x n p (narrow-to-page) to narrow down to the current page. See Pages, for the definition of a page. C-x n d (narrow-to-defun) narrows down to the defun containing point (see Defuns).

The way to cancel narrowing is to widen with C-x n w (widen). This makes all text in the buffer accessible again.

You can get information on what part of the buffer you are narrowed down to using the C-x = command. See Position Info.

Because narrowing can easily confuse users who do not understand it, narrow-to-region is normally a disabled command. Attempting to use this command asks for confirmation and gives you the option of enabling it; if you enable the command, confirmation will no longer be required for it. See Disabling.

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14.6 View Mode

View mode is a minor mode that lets you scan a buffer by sequential screenfuls. It provides commands for scrolling through the buffer conveniently but not for changing it. Apart from the usual Emacs cursor motion commands, you can type <SPC> to scroll forward one windowful, <DEL> to scroll backward, and s to start an incremental search.

Typing q (View-quit) disables View mode, and switches back to the buffer and position before View mode was enabled. Typing e (View-exit) disables View mode, keeping the current buffer and position.

M-x view-buffer prompts for an existing Emacs buffer, switches to it, and enables View mode. M-x view-file prompts for a file and visits it with View mode enabled.

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14.7 Follow Mode

Follow mode is a minor mode that makes two windows, both showing the same buffer, scroll as a single tall “virtual window”. To use Follow mode, go to a frame with just one window, split it into two side-by-side windows using C-x 3, and then type M-x follow-mode. From then on, you can edit the buffer in either of the two windows, or scroll either one; the other window follows it.

In Follow mode, if you move point outside the portion visible in one window and into the portion visible in the other window, that selects the other window—again, treating the two as if they were parts of one large window.

To turn off Follow mode, type M-x follow-mode a second time.

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14.8 Text Faces

Emacs can display text in several different styles, called faces. Each face can specify various face attributes, such as the font, height, weight, slant, foreground and background color, and underlining or overlining. Most major modes assign faces to the text automatically, via Font Lock mode. See Font Lock, for more information about how these faces are assigned.

To see what faces are currently defined, and what they look like, type M-x list-faces-display. With a prefix argument, this prompts for a regular expression, and displays only faces with names matching that regular expression (see Regexps).

It's possible for a given face to look different in different frames. For instance, some text terminals do not support all face attributes, particularly font, height, and width, and some support a limited range of colors. In addition, most Emacs faces are defined so that their attributes are different on light and dark frame backgrounds, for reasons of legibility. By default, Emacs automatically chooses which set of face attributes to display on each frame, based on the frame's current background color. However, you can override this by giving the variable frame-background-mode a non-nil value. A value of dark makes Emacs treat all frames as if they have a dark background, whereas a value of light makes it treat all frames as if they have a light background.

You can customize a face to alter its attributes, and save those customizations for future Emacs sessions. See Face Customization, for details.

The default face is the default for displaying text, and all of its attributes are specified. Its background color is also used as the frame's background color. See Colors.

Another special face is the cursor face. On graphical displays, the background color of this face is used to draw the text cursor. None of the other attributes of this face have any effect; the foreground color for text under the cursor is taken from the background color of the underlying text. On text terminals, the appearance of the text cursor is determined by the terminal, not by the cursor face.

You can also use X resources to specify attributes of any particular face. See Resources.

Emacs can display variable-width fonts, but some Emacs commands, particularly indentation commands, do not account for variable character display widths. Therefore, we recommend not using variable-width fonts for most faces, particularly those assigned by Font Lock mode.

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14.9 Colors for Faces

Faces can have various foreground and background colors. When you specify a color for a face—for instance, when customizing the face (see Face Customization)—you can use either a color name or an RGB triplet.

A color name is a pre-defined name, such as ‘dark orange’ or ‘medium sea green’. To view a list of color names, type M-x list-colors-display. To control the order in which colors are shown, customize list-colors-sort. If you run this command on a graphical display, it shows the full range of color names known to Emacs (these are the standard X11 color names, defined in X's rgb.txt file). If you run the command on a text terminal, it shows only a small subset of colors that can be safely displayed on such terminals. However, Emacs understands X11 color names even on text terminals; if a face is given a color specified by an X11 color name, it is displayed using the closest-matching terminal color.

An RGB triplet is a string of the form ‘#RRGGBB’. Each of the R, G, and B components is a hexadecimal number specifying the component's relative intensity, one to four digits long (usually two digits are used). The components must have the same number of digits. For hexadecimal values A to F, either upper or lower case are acceptable.

The M-x list-colors-display command also shows the equivalent RGB triplet for each named color. For instance, ‘medium sea green’ is equivalent to ‘#3CB371’.

You can change the foreground and background colors of a face with M-x set-face-foreground and M-x set-face-background. These commands prompt in the minibuffer for a face name and a color, with completion, and then set that face to use the specified color. They affect the face colors on all frames, but their effects do not persist for future Emacs sessions, unlike using the customization buffer or X resources. You can also use frame parameters to set foreground and background colors for a specific frame; See Frame Parameters.

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14.10 Standard Faces

Here are the standard faces for specifying text appearance. You can apply them to specific text when you want the effects they produce.

default
This face is used for ordinary text that doesn't specify any face. Its background color is used as the frame's background color.
bold
This face uses a bold variant of the default font.
italic
This face uses an italic variant of the default font.
bold-italic
This face uses a bold italic variant of the default font.
underline
This face underlines text.
fixed-pitch
This face forces use of a fixed-width font. It's reasonable to customize this face to use a different fixed-width font, if you like, but you should not make it a variable-width font.
variable-pitch
This face forces use of a variable-width font.
shadow
This face is used for making the text less noticeable than the surrounding ordinary text. Usually this can be achieved by using shades of gray in contrast with either black or white default foreground color.

Here's an incomplete list of faces used to highlight parts of the text temporarily for specific purposes. (Many other modes define their own faces for this purpose.)

highlight
This face is used for text highlighting in various contexts, such as when the mouse cursor is moved over a hyperlink.
isearch
This face is used to highlight the current Isearch match (see Incremental Search).
query-replace
This face is used to highlight the current Query Replace match (see Replace).
lazy-highlight
This face is used to highlight “lazy matches” for Isearch and Query Replace (matches other than the current one).
region
This face is used for displaying an active region (see Mark). When Emacs is built with GTK support, its colors are taken from the current GTK theme.
secondary-selection
This face is used for displaying a secondary X selection (see Secondary Selection).
trailing-whitespace
The face for highlighting excess spaces and tabs at the end of a line when show-trailing-whitespace is non-nil (see Useless Whitespace).
escape-glyph
The face for displaying control characters and escape sequences (see Text Display).
nobreak-space
The face for displaying “no-break” space characters (see Text Display).

The following faces control the appearance of parts of the Emacs frame:

mode-line
This face is used for the mode line of the currently selected window, and for menu bars when toolkit menus are not used. By default, it's drawn with shadows for a “raised” effect on graphical displays, and drawn as the inverse of the default face on non-windowed terminals.
mode-line-inactive
Like mode-line, but used for mode lines of the windows other than the selected one (if mode-line-in-non-selected-windows is non-nil). This face inherits from mode-line, so changes in that face affect mode lines in all windows.
mode-line-highlight
Like highlight, but used for portions of text on mode lines.
mode-line-buffer-id
This face is used for buffer identification parts in the mode line.
header-line
Similar to mode-line for a window's header line, which appears at the top of a window just as the mode line appears at the bottom. Most windows do not have a header line—only some special modes, such Info mode, create one.
vertical-border
This face is used for the vertical divider between windows on text terminals.
minibuffer-prompt
This face is used for the prompt strings displayed in the minibuffer. By default, Emacs automatically adds this face to the value of minibuffer-prompt-properties, which is a list of text properties used to display the prompt text. (This variable takes effect when you enter the minibuffer.)
fringe
The face for the fringes to the left and right of windows on graphic displays. (The fringes are the narrow portions of the Emacs frame between the text area and the window's right and left borders.) See Fringes.
cursor
The :background attribute of this face specifies the color of the text cursor. See Cursor Display.
tooltip
This face is used for tooltip text. By default, if Emacs is built with GTK support, tooltips are drawn via GTK and this face has no effect. See Tooltips.
mouse
This face determines the color of the mouse pointer.

The following faces likewise control the appearance of parts of the Emacs frame, but only on text terminals, or when Emacs is built on X with no toolkit support. (For all other cases, the appearance of the respective frame elements is determined by system-wide settings.)

scroll-bar
This face determines the visual appearance of the scroll bar. See Scroll Bars.
tool-bar
This face determines the color of tool bar icons. See Tool Bars.
menu
This face determines the colors and font of Emacs's menus. See Menu Bars.

Next: , Previous: Standard Faces, Up: Display

14.11 Text Scale

To increase the height of the default face in the current buffer, type C-x C-+ or C-x C-=. To decrease it, type C-x C--. To restore the default (global) face height, type C-x C-0. These keys are all bound to the same command, text-scale-adjust, which looks at the last key typed to determine which action to take.

The final key of these commands may be repeated without the leading C-x. For instance, C-x C-= C-= C-= increases the face height by three steps. Each step scales the text height by a factor of 1.2; to change this factor, customize the variable text-scale-mode-step. As an exception, a numeric argument of 0 to the text-scale-adjust command restores the default height, similar to typing C-x C-0.

The commands text-scale-increase and text-scale-decrease increase or decrease the height of the default face, just like C-x C-+ and C-x C-- respectively. You may find it convenient to bind to these commands, rather than text-scale-adjust.

The command text-scale-set scales the height of the default face in the current buffer to an absolute level specified by its prefix argument.

The above commands automatically enable the minor mode text-scale-mode if the current font scaling is other than 1, and disable it otherwise.

Next: , Previous: Text Scale, Up: Display

14.12 Font Lock mode

Font Lock mode is a minor mode, always local to a particular buffer, which assigns faces to (or fontifies) the text in the buffer. Each buffer's major mode tells Font Lock mode which text to fontify; for instance, programming language modes fontify syntactically relevant constructs like comments, strings, and function names.

Font Lock mode is enabled by default. To toggle it in the current buffer, type M-x font-lock-mode. A positive numeric argument unconditionally enables Font Lock mode, and a negative or zero argument disables it.

Type M-x global-font-lock-mode to toggle Font Lock mode in all buffers. To impose this setting for future Emacs sessions, customize the variable global-font-lock-mode (see Easy Customization), or add the following line to your init file: 

     (global-font-lock-mode 0)

If you have disabled Global Font Lock mode, you can still enable Font Lock for specific major modes by adding the function font-lock-mode to the mode hooks (see Hooks). For example, to enable Font Lock mode for editing C files, you can do this: 

     (add-hook 'c-mode-hook 'font-lock-mode)

Font Lock mode uses several specifically named faces to do its job, including font-lock-string-face, font-lock-comment-face, and others. The easiest way to find them all is to use M-x customize-group <RET> font-lock-faces <RET>. You can then use that customization buffer to customize the appearance of these faces. See Face Customization.

You can customize the variable font-lock-maximum-decoration to alter the amount of fontification applied by Font Lock mode, for major modes that support this feature. The value should be a number (with 1 representing a minimal amount of fontification; some modes support levels as high as 3); or t, meaning “as high as possible” (the default). You can also specify different numbers for particular major modes; for example, to use level 1 for C/C++ modes, and the default level otherwise, use the value 

     '((c-mode . 1) (c++-mode . 1)))

Comment and string fontification (or “syntactic” fontification) relies on analysis of the syntactic structure of the buffer text. For the sake of speed, some modes, including Lisp mode, rely on a special convention: an open-parenthesis or open-brace in the leftmost column always defines the beginning of a defun, and is thus always outside any string or comment. Therefore, you should avoid placing an open-parenthesis or open-brace in the leftmost column, if it is inside a string or comment. See Left Margin Paren, for details.

The variable font-lock-beginning-of-syntax-function, which is always buffer-local, specifies how Font Lock mode can find a position guaranteed to be outside any comment or string. In modes which use the leftmost column parenthesis convention, the default value of the variable is beginning-of-defun—that tells Font Lock mode to use the convention. If you set this variable to nil, Font Lock no longer relies on the convention. This avoids incorrect results, but the price is that, in some cases, fontification for a changed text must rescan buffer text from the beginning of the buffer. This can considerably slow down redisplay while scrolling, particularly if you are close to the end of a large buffer.

Font Lock highlighting patterns already exist for most modes, but you may want to fontify additional patterns. You can use the function font-lock-add-keywords, to add your own highlighting patterns for a particular mode. For example, to highlight ‘FIXME:’ words in C comments, use this: 

     (add-hook 'c-mode-hook
               (lambda ()
                (font-lock-add-keywords nil
                 '(("\\<\\(FIXME\\):" 1
                    font-lock-warning-face t)))))

To remove keywords from the font-lock highlighting patterns, use the function font-lock-remove-keywords. See Search-based Fontification.

Fontifying large buffers can take a long time. To avoid large delays when a file is visited, Emacs initially fontifies only the visible portion of a buffer. As you scroll through the buffer, each portion that becomes visible is fontified as soon as it is displayed; this type of Font Lock is called Just-In-Time (or JIT) Lock. You can control how JIT Lock behaves, including telling it to perform fontification while idle, by customizing variables in the customization group ‘jit-lock’. See Specific Customization.

Next: , Previous: Font Lock, Up: Display

14.13 Interactive Highlighting

Highlight Changes mode is a minor mode that highlights the parts of the buffer that were changed most recently, by giving that text a different face. To enable or disable Highlight Changes mode, use M-x highlight-changes-mode.

Hi Lock mode is a minor mode that highlights text that matches regular expressions you specify. For example, you can use it to highlight all the references to a certain variable in a program source file, highlight certain parts in a voluminous output of some program, or highlight certain names in an article. To enable or disable Hi Lock mode, use the command M-x hi-lock-mode. To enable Hi Lock mode for all buffers, use M-x global-hi-lock-mode or place (global-hi-lock-mode 1) in your .emacs file.

Hi Lock mode works like Font Lock mode (see Font Lock), except that you specify explicitly the regular expressions to highlight. You control them with these commands:

C-x w h regexp <RET> face <RET>
Highlight text that matches regexp using face face (highlight-regexp). The highlighting will remain as long as the buffer is loaded. For example, to highlight all occurrences of the word “whim” using the default face (a yellow background) C-x w h whim <RET> <RET>. Any face can be used for highlighting, Hi Lock provides several of its own and these are pre-loaded into a list of default values. While being prompted for a face use M-n and M-p to cycle through them.

You can use this command multiple times, specifying various regular expressions to highlight in different ways.

C-x w r regexp <RET>
Unhighlight regexp (unhighlight-regexp).

If you invoke this from the menu, you select the expression to unhighlight from a list. If you invoke this from the keyboard, you use the minibuffer. It will show the most recently added regular expression; use M-p to show the next older expression and M-n to select the next newer expression. (You can also type the expression by hand, with completion.) When the expression you want to unhighlight appears in the minibuffer, press <RET> to exit the minibuffer and unhighlight it.

C-x w l regexp <RET> face <RET>
Highlight entire lines containing a match for regexp, using face face (highlight-lines-matching-regexp).
C-x w b
Insert all the current highlighting regexp/face pairs into the buffer at point, with comment delimiters to prevent them from changing your program. (This key binding runs the hi-lock-write-interactive-patterns command.)

These patterns are extracted from the comments, if appropriate, if you invoke M-x hi-lock-find-patterns, or if you visit the file while Hi Lock mode is enabled (since that runs hi-lock-find-patterns).

C-x w i
Extract regexp/face pairs from comments in the current buffer (hi-lock-find-patterns). Thus, you can enter patterns interactively with highlight-regexp, store them into the file with hi-lock-write-interactive-patterns, edit them (perhaps including different faces for different parenthesized parts of the match), and finally use this command (hi-lock-find-patterns) to have Hi Lock highlight the edited patterns.

The variable hi-lock-file-patterns-policy controls whether Hi Lock mode should automatically extract and highlight patterns found in a file when it is visited. Its value can be nil (never highlight), ask (query the user), or a function. If it is a function, hi-lock-find-patterns calls it with the patterns as argument; if the function returns non-nil, the patterns are used. The default is ask. Note that patterns are always highlighted if you call hi-lock-find-patterns directly, regardless of the value of this variable.

Also, hi-lock-find-patterns does nothing if the current major mode's symbol is a member of the list hi-lock-exclude-modes.

Next: , Previous: Highlight Interactively, Up: Display

14.14 Window Fringes

On graphical displays, each Emacs window normally has narrow fringes on the left and right edges. The fringes are used to display symbols that provide information about the text in the window. You can type M-x fringe-mode to disable the fringes, or modify their width. This command affects fringes in all frames; to modify fringes on the selected frame only, use M-x set-fringe-style.

The most common use of the fringes is to indicate a continuation line (see Continuation Lines). When one line of text is split into multiple screen lines, the left fringe shows a curving arrow for each screen line except the first, indicating that “this is not the real beginning”. The right fringe shows a curving arrow for each screen line except the last, indicating that “this is not the real end”. If the line's direction is right-to-left (see Bidirectional Editing), the meanings of the curving arrows in the fringes are swapped.

The fringes indicate line truncation with short horizontal arrows meaning “there's more text on this line which is scrolled horizontally out of view”. Clicking the mouse on one of the arrows scrolls the display horizontally in the direction of the arrow.

The fringes can also indicate other things, such as buffer boundaries (see Displaying Boundaries), and where a program you are debugging is executing (see Debuggers).

The fringe is also used for drawing the cursor, if the current line is exactly as wide as the window and point is at the end of the line. To disable this, change the variable overflow-newline-into-fringe to nil; this causes Emacs to continue or truncate lines that are exactly as wide as the window.

Next: , Previous: Fringes, Up: Display

14.15 Displaying Boundaries

On graphical displays, Emacs can indicate the buffer boundaries in the fringes. If you enable this feature, the first line and the last line are marked with angle images in the fringes. This can be combined with up and down arrow images which say whether it is possible to scroll the window.

The buffer-local variable indicate-buffer-boundaries controls how the buffer boundaries and window scrolling is indicated in the fringes. If the value is left or right, both angle and arrow bitmaps are displayed in the left or right fringe, respectively.

If value is an alist, each element (indicator . position) specifies the position of one of the indicators. The indicator must be one of top, bottom, up, down, or t which specifies the default position for the indicators not present in the alist. The position is one of left, right, or nil which specifies not to show this indicator.

For example, ((top . left) (t . right)) places the top angle bitmap in left fringe, the bottom angle bitmap in right fringe, and both arrow bitmaps in right fringe. To show just the angle bitmaps in the left fringe, but no arrow bitmaps, use ((top . left) (bottom . left)).

Next: , Previous: Displaying Boundaries, Up: Display

14.16 Useless Whitespace

It is easy to leave unnecessary spaces at the end of a line, or empty lines at the end of a buffer, without realizing it. In most cases, this trailing whitespace has no effect, but sometimes it can be a nuisance.

You can make trailing whitespace at the end of a line visible by setting the buffer-local variable show-trailing-whitespace to t. Then Emacs displays trailing whitespace, using the face trailing-whitespace.

This feature does not apply when point is at the end of the line containing the whitespace. Strictly speaking, that is “trailing whitespace” nonetheless, but displaying it specially in that case looks ugly while you are typing in new text. In this special case, the location of point is enough to show you that the spaces are present.

Type M-x delete-trailing-whitespace to delete all trailing whitespace. This command deletes all extra spaces at the end of each line in the buffer, and all empty lines at the end of the buffer; to ignore the latter, change the variable delete-trailing-lines to nil. If the region is active, the command instead deletes extra spaces at the end of each line in the region.

On graphical displays, Emacs can indicate unused lines at the end of the window with a small image in the left fringe (see Fringes). The image appears for screen lines that do not correspond to any buffer text, so blank lines at the end of the buffer stand out because they lack this image. To enable this feature, set the buffer-local variable indicate-empty-lines to a non-nil value. You can enable or disable this feature for all new buffers by setting the default value of this variable, e.g., (setq-default indicate-empty-lines t).

Whitespace mode is a buffer-local minor mode that lets you “visualize” many kinds of whitespace in the buffer, by either drawing the whitespace characters with a special face or displaying them as special glyphs. To toggle this mode, type M-x whitespace-mode. The kinds of whitespace visualized are determined by the list variable whitespace-style. Here is a partial list of possible elements (see the variable's documentation for the full list):

face
Enable all visualizations which use special faces. This element has a special meaning: if it is absent from the list, none of the other visualizations take effect except space-mark, tab-mark, and newline-mark.
trailing
Highlight trailing whitespace.
tabs
Highlight tab characters.
spaces
Highlight space and non-breaking space characters.
lines
Highlight lines longer than 80 lines. To change the column limit, customize the variable whitespace-line-column.
newline
Highlight newlines.
empty
Highlight empty lines.
space-mark
Draw space and non-breaking characters with a special glyph.
tab-mark
Draw tab characters with a special glyph.
newline-mark
Draw newline characters with a special glyph.

Next: , Previous: Useless Whitespace, Up: Display

14.17 Selective Display

Emacs has the ability to hide lines indented more than a given number of columns. You can use this to get an overview of a part of a program.

To hide lines in the current buffer, type C-x $ (set-selective-display) with a numeric argument n. Then lines with at least n columns of indentation disappear from the screen. The only indication of their presence is that three dots (‘...’) appear at the end of each visible line that is followed by one or more hidden ones.

The commands C-n and C-p move across the hidden lines as if they were not there.

The hidden lines are still present in the buffer, and most editing commands see them as usual, so you may find point in the middle of the hidden text. When this happens, the cursor appears at the end of the previous line, after the three dots. If point is at the end of the visible line, before the newline that ends it, the cursor appears before the three dots.

To make all lines visible again, type C-x $ with no argument.

If you set the variable selective-display-ellipses to nil, the three dots do not appear at the end of a line that precedes hidden lines. Then there is no visible indication of the hidden lines. This variable becomes local automatically when set.

See also Outline Mode for another way to hide part of the text in a buffer.

Next: , Previous: Selective Display, Up: Display

14.18 Optional Mode Line Features

The buffer percentage pos indicates the percentage of the buffer above the top of the window. You can additionally display the size of the buffer by typing M-x size-indication-mode to turn on Size Indication mode. The size will be displayed immediately following the buffer percentage like this: 

     POS of SIZE

Here SIZE is the human readable representation of the number of characters in the buffer, which means that ‘k’ for 10^3, ‘M’ for 10^6, ‘G’ for 10^9, etc., are used to abbreviate.

The current line number of point appears in the mode line when Line Number mode is enabled. Use the command M-x line-number-mode to turn this mode on and off; normally it is on. The line number appears after the buffer percentage pos, with the letter ‘L’ to indicate what it is.

Similarly, you can display the current column number by turning on Column number mode with M-x column-number-mode. The column number is indicated by the letter ‘C’. However, when both of these modes are enabled, the line and column numbers are displayed in parentheses, the line number first, rather than with ‘L’ and ‘C’. For example: ‘(561,2)’. See Minor Modes, for more information about minor modes and about how to use these commands.

If you have narrowed the buffer (see Narrowing), the displayed line number is relative to the accessible portion of the buffer. Thus, it isn't suitable as an argument to goto-line. (Use what-line command to see the line number relative to the whole file.)

If the buffer is very large (larger than the value of line-number-display-limit), Emacs won't compute the line number, because that would be too slow; therefore, the line number won't appear on the mode-line. To remove this limit, set line-number-display-limit to nil.

Line-number computation can also be slow if the lines in the buffer are too long. For this reason, Emacs doesn't display line numbers if the average width, in characters, of lines near point is larger than the value of line-number-display-limit-width. The default value is 200 characters.

Emacs can optionally display the time and system load in all mode lines. To enable this feature, type M-x display-time or customize the option display-time-mode. The information added to the mode line looks like this: 

     hh:mmpm l.ll

Here hh and mm are the hour and minute, followed always by ‘am’ or ‘pm’. l.ll is the average number, collected for the last few minutes, of processes in the whole system that were either running or ready to run (i.e., were waiting for an available processor). (Some fields may be missing if your operating system cannot support them.) If you prefer time display in 24-hour format, set the variable display-time-24hr-format to t.

The word ‘Mail’ appears after the load level if there is mail for you that you have not read yet. On graphical displays, you can use an icon instead of ‘Mail’ by customizing display-time-use-mail-icon; this may save some space on the mode line. You can customize display-time-mail-face to make the mail indicator prominent. Use display-time-mail-file to specify the mail file to check, or set display-time-mail-directory to specify the directory to check for incoming mail (any nonempty regular file in the directory is considered as “newly arrived mail”).

When running Emacs on a laptop computer, you can display the battery charge on the mode-line, by using the command display-battery-mode or customizing the variable display-battery-mode. The variable battery-mode-line-format determines the way the battery charge is displayed; the exact mode-line message depends on the operating system, and it usually shows the current battery charge as a percentage of the total charge.

On graphical displays, the mode line is drawn as a 3D box. If you don't like this effect, you can disable it by customizing the mode-line face and setting its box attribute to nil. See Face Customization.

By default, the mode line of nonselected windows is displayed in a different face, called mode-line-inactive. Only the selected window is displayed in the mode-line face. This helps show which window is selected. When the minibuffer is selected, since it has no mode line, the window from which you activated the minibuffer has its mode line displayed using mode-line; as a result, ordinary entry to the minibuffer does not change any mode lines.

You can disable use of mode-line-inactive by setting variable mode-line-in-non-selected-windows to nil; then all mode lines are displayed in the mode-line face.

You can customize the mode line display for each of the end-of-line formats by setting each of the variables eol-mnemonic-unix, eol-mnemonic-dos, eol-mnemonic-mac, and eol-mnemonic-undecided to the strings you prefer.

Next: , Previous: Optional Mode Line, Up: Display

14.19 How Text Is Displayed

Most characters are printing characters: when they appear in a buffer, they are displayed literally on the screen. Printing characters include ASCII numbers, letters, and punctuation characters, as well as many non-ASCII characters.

The ASCII character set contains non-printing control characters. Two of these are displayed specially: the newline character (Unicode code point U+000A) is displayed by starting a new line, while the tab character (U+0009) is displayed as a space that extends to the next tab stop column (normally every 8 columns). The number of spaces per tab is controlled by the buffer-local variable tab-width, which must have an integer value between 1 and 1000, inclusive. Note that how the tab character in the buffer is displayed has nothing to do with the definition of <TAB> as a command.

Other ASCII control characters, whose codes are below U+0020 (octal 40, decimal 32), are displayed as a caret (‘^’) followed by the non-control version of the character, with the escape-glyph face. For instance, the ‘control-A’ character, U+0001, is displayed as ‘^A’.

The raw bytes with codes U+0080 (octal 200) through U+009F (octal 237) are displayed as octal escape sequences, with the escape-glyph face. For instance, character code U+0098 (octal 230) is displayed as ‘\230’. If you change the buffer-local variable ctl-arrow to nil, the ASCII control characters are also displayed as octal escape sequences instead of caret escape sequences.

Some non-ASCII characters have the same appearance as an ASCII space or hyphen (minus) character. Such characters can cause problems if they are entered into a buffer without your realization, e.g., by yanking; for instance, source code compilers typically do not treat non-ASCII spaces as whitespace characters. To deal with this problem, Emacs displays such characters specially: it displays U+00A0 (no-break space) with the nobreak-space face, and it displays U+00AD (soft hyphen), U+2010 (hyphen), and U+2011 (non-breaking hyphen) with the escape-glyph face. To disable this, change the variable nobreak-char-display to nil. If you give this variable a non-nil and non-t value, Emacs instead displays such characters as a highlighted backslash followed by a space or hyphen.

You can customize the way any particular character code is displayed by means of a display table. See Display Tables.

On graphical displays, some characters may have no glyphs in any of the fonts available to Emacs. These glyphless characters are normally displayed as boxes containing the hexadecimal character code. Similarly, on text terminals, characters that cannot be displayed using the terminal encoding (see Terminal Coding) are normally displayed as question signs. You can control the display method by customizing the variable glyphless-char-display-control. See Glyphless Character Display, for details.

Next: , Previous: Text Display, Up: Display

14.20 Displaying the Cursor

On a text terminal, the cursor's appearance is controlled by the terminal, largely out of the control of Emacs. Some terminals offer two different cursors: a “visible” static cursor, and a “very visible” blinking cursor. By default, Emacs uses the very visible cursor, and switches to it when you start or resume Emacs. If the variable visible-cursor is nil when Emacs starts or resumes, it uses the normal cursor.

On a graphical display, many more properties of the text cursor can be altered. To customize its color, change the :background attribute of the face named cursor (see Face Customization). (The other attributes of this face have no effect; the text shown under the cursor is drawn using the frame's background color.) To change its shape, customize the buffer-local variable cursor-type; possible values are box (the default), hollow (a hollow box), bar (a vertical bar), (bar . n) (a vertical bar n pixels wide), hbar (a horizontal bar), (hbar . n) (a horizontal bar n pixels tall), or nil (no cursor at all).

To disable cursor blinking, change the variable blink-cursor-mode to nil (see Easy Customization), or add the line (blink-cursor-mode 0) to your init file. Alternatively, you can change how the cursor looks when it “blinks off” by customizing the list variable blink-cursor-alist. Each element in the list should have the form (on-type . off-type); this means that if the cursor is displayed as on-type when it blinks on (where on-type is one of the cursor types described above), then it is displayed as off-type when it blinks off.

Some characters, such as tab characters, are “extra wide”. When the cursor is positioned over such a character, it is normally drawn with the default character width. You can make the cursor stretch to cover wide characters, by changing the variable x-stretch-cursor to a non-nil value.

The cursor normally appears in non-selected windows as a non-blinking hollow box. (For a bar cursor, it instead appears as a thinner bar.) To turn off cursors in non-selected windows, change the variable cursor-in-non-selected-windows to nil.

To make the cursor even more visible, you can use HL Line mode, a minor mode that highlights the line containing point. Use M-x hl-line-mode to enable or disable it in the current buffer. M-x global-hl-line-mode enables or disables the same mode globally.

Next: , Previous: Cursor Display, Up: Display

14.21 Line Truncation

As an alternative to continuation (see Continuation Lines), Emacs can display long lines by truncation. This means that all the characters that do not fit in the width of the screen or window do not appear at all. On graphical displays, a small straight arrow in the fringe indicates truncation at either end of the line. On text terminals, this is indicated with ‘$’ signs in the leftmost and/or rightmost columns.

Horizontal scrolling automatically causes line truncation (see Horizontal Scrolling). You can explicitly enable line truncation for a particular buffer with the command M-x toggle-truncate-lines. This works by locally changing the variable truncate-lines. If that variable is non-nil, long lines are truncated; if it is nil, they are continued onto multiple screen lines. Setting the variable truncate-lines in any way makes it local to the current buffer; until that time, the default value, which is normally nil, is in effect.

If a split window becomes too narrow, Emacs may automatically enable line truncation. See Split Window, for the variable truncate-partial-width-windows which controls this.

Next: , Previous: Line Truncation, Up: Display

14.22 Visual Line Mode

Another alternative to ordinary line continuation is to use word wrap. Here, each long logical line is divided into two or more screen lines, like in ordinary line continuation. However, Emacs attempts to wrap the line at word boundaries near the right window edge. This makes the text easier to read, as wrapping does not occur in the middle of words.

Word wrap is enabled by Visual Line mode, an optional minor mode. To turn on Visual Line mode in the current buffer, type M-x visual-line-mode; repeating this command turns it off. You can also turn on Visual Line mode using the menu bar: in the Options menu, select the ‘Line Wrapping in this Buffer’ submenu, followed by the ‘Word Wrap (Visual Line Mode)’ menu item. While Visual Line mode is enabled, the mode-line shows the string ‘wrap’ in the mode display. The command M-x global-visual-line-mode toggles Visual Line mode in all buffers.

In Visual Line mode, some editing commands work on screen lines instead of logical lines: C-a (beginning-of-visual-line) moves to the beginning of the screen line, C-e (end-of-visual-line) moves to the end of the screen line, and C-k (kill-visual-line) kills text to the end of the screen line.

To move by logical lines, use the commands M-x next-logical-line and M-x previous-logical-line. These move point to the next logical line and the previous logical line respectively, regardless of whether Visual Line mode is enabled. If you use these commands frequently, it may be convenient to assign key bindings to them. See Init Rebinding.

By default, word-wrapped lines do not display fringe indicators. Visual Line mode is often used to edit files that contain many long logical lines, so having a fringe indicator for each wrapped line would be visually distracting. You can change this by customizing the variable visual-line-fringe-indicators.

Previous: Visual Line Mode, Up: Display

14.23 Customization of Display

This section describes variables that control miscellaneous aspects of the appearance of the Emacs screen. Beginning users can skip it.

If the variable visible-bell is non-nil, Emacs attempts to make the whole screen blink when it would normally make an audible bell sound. This variable has no effect if your terminal does not have a way to make the screen blink.

The variable echo-keystrokes controls the echoing of multi-character keys; its value is the number of seconds of pause required to cause echoing to start, or zero, meaning don't echo at all. The value takes effect when there is something to echo. See Echo Area.

On graphical displays, Emacs displays the mouse pointer as an hourglass if Emacs is busy. To disable this feature, set the variable display-hourglass to nil. The variable hourglass-delay determines the number of seconds of “busy time” before the hourglass is shown; the default is 1.

If the mouse pointer lies inside an Emacs frame, Emacs makes it invisible each time you type a character to insert text, to prevent it from obscuring the text. (To be precise, the hiding occurs when you type a “self-inserting” character. See Inserting Text.) Moving the mouse pointer makes it visible again. To disable this feature, set the variable make-pointer-invisible to nil.

On graphical displays, the variable underline-minimum-offset determines the minimum distance between the baseline and underline, in pixels, for underlined text. By default, the value is 1; increasing it may improve the legibility of underlined text for certain fonts. (However, Emacs will never draw the underline below the current line area.) The variable x-underline-at-descent-line determines how to draw underlined text. The default is nil, which means to draw it at the baseline level of the font; if you change it to nil, Emacs draws the underline at the same height as the font's descent line.

The variable overline-margin specifies the vertical position of an overline above the text, including the height of the overline itself, in pixels; the default is 2.

On some text terminals, bold face and inverse video together result in text that is hard to read. Call the function tty-suppress-bold-inverse-default-colors with a non-nil argument to suppress the effect of bold-face in this case.

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15 Searching and Replacement

Like other editors, Emacs has commands to search for occurrences of a string. Emacs also has commands to replace occurrences of a string with a different string. There are also commands that do the same thing, but search for patterns instead of fixed strings.

You can also search multiple files under the control of a tags table (see Tags Search) or through the Dired A command (see Operating on Files), or ask the grep program to do it (see Grep Searching).

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15.1 Incremental Search

The principal search command in Emacs is incremental: it begins searching as soon as you type the first character of the search string. As you type in the search string, Emacs shows you where the string (as you have typed it so far) would be found. When you have typed enough characters to identify the place you want, you can stop. Depending on what you plan to do next, you may or may not need to terminate the search explicitly with <RET>.

C-s
Incremental search forward (isearch-forward).
C-r
Incremental search backward (isearch-backward).

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15.1.1 Basics of Incremental Search

C-s
Begin incremental search (isearch-forward).
C-r
Begin reverse incremental search (isearch-backward).

C-s (isearch-forward) starts a forward incremental search. It reads characters from the keyboard, and moves point just past the end of the next occurrence of those characters in the buffer.

For instance, if you type C-s and then F, that puts the cursor after the first ‘F’ that occurs in the buffer after the starting point. Then if you then type O, the cursor moves to just after the first ‘FO’; the ‘F’ in that ‘FO’ might not be the first ‘F’ previously found. After another O, the cursor moves to just after the first ‘FOO’.

At each step, Emacs highlights the current match—the buffer text that matches the search string—using the isearch face (see Faces). The current search string is also displayed in the echo area.

If you make a mistake typing the search string, type <DEL>. Each <DEL> cancels the last character of the search string.

When you are satisfied with the place you have reached, type <RET>. This stops searching, leaving the cursor where the search brought it. Also, any command not specially meaningful in searches stops the searching and is then executed. Thus, typing C-a exits the search and then moves to the beginning of the line. <RET> is necessary only if the next command you want to type is a printing character, <DEL>, <RET>, or another character that is special within searches (C-q, C-w, C-r, C-s, C-y, M-y, M-r, M-c, M-e, and some others described below).

As a special exception, entering <RET> when the search string is empty launches nonincremental search (see Nonincremental Search).

When you exit the incremental search, it adds the original value of point to the mark ring, without activating the mark; you can thus use C-u C-<SPC> to return to where you were before beginning the search. See Mark Ring. It only does this if the mark was not already active.

To search backwards, use C-r (isearch-backward) instead of C-s to start the search. A backward search finds matches that end before the starting point, just as a forward search finds matches that begin after it.

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15.1.2 Repeating Incremental Search

Suppose you search forward for ‘FOO’ and find a match, but not the one you expected to find: the ‘FOO’ you were aiming for occurs later in the buffer. In this event, type another C-s to move to the next occurrence of the search string. You can repeat this any number of times. If you overshoot, you can cancel some C-s characters with <DEL>. Similarly, each C-r in a backward incremental search repeats the backward search.

If you pause for a little while during incremental search, Emacs highlights all the other possible matches for the search string that are present on the screen. This helps you anticipate where you can get to by typing C-s or C-r to repeat the search. The other matches are highlighted differently from the current match, using the customizable face lazy-highlight (see Faces). If you don't like this feature, you can disable it by setting isearch-lazy-highlight to nil.

After exiting a search, you can search for the same string again by typing just C-s C-s. The first C-s is the key that invokes incremental search, and the second C-s means “search again”. Similarly, C-r C-r searches backward for the last search string. In determining the last search string, it doesn't matter whether the string was searched for with C-s or C-r.

If you are searching forward but you realize you were looking for something before the starting point, type C-r to switch to a backward search, leaving the search string unchanged. Similarly, C-s in a backward search switches to a forward search.

If a search is failing and you ask to repeat it by typing another C-s, it starts again from the beginning of the buffer. Repeating a failing reverse search with C-r starts again from the end. This is called wrapping around, and ‘Wrapped’ appears in the search prompt once this has happened. If you keep on going past the original starting point of the search, it changes to ‘Overwrapped’, which means that you are revisiting matches that you have already seen.

To reuse earlier search strings, use the search ring. The commands M-p and M-n move through the ring to pick a search string to reuse. These commands leave the selected search ring element in the minibuffer, where you can edit it.

To edit the current search string in the minibuffer without replacing it with items from the search ring, type M-e. Type C-s or C-r to finish editing the string and search for it.

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15.1.3 Errors in Incremental Search

If your string is not found at all, the echo area says ‘Failing I-Search’, and the cursor moves past the place where Emacs found as much of your string as it could. Thus, if you search for ‘FOOT’, and there is no ‘FOOT’, you might see the cursor after the ‘FOO’ in ‘FOOL’. In the echo area, the part of the search string that failed to match is highlighted using the face isearch-fail.

At this point, there are several things you can do. If your string was mistyped, you can use <DEL> to erase some of it and correct it. If you like the place you have found, you can type <RET> to remain there. Or you can type C-g, which removes from the search string the characters that could not be found (the ‘T’ in ‘FOOT’), leaving those that were found (the ‘FOO’ in ‘FOOT’). A second C-g at that point cancels the search entirely, returning point to where it was when the search started.

The quit command, C-g, does special things during searches; just what it does depends on the status of the search. If the search has found what you specified and is waiting for input, C-g cancels the entire search, moving the cursor back to where you started the search. If C-g is typed when there are characters in the search string that have not been found—because Emacs is still searching for them, or because it has failed to find them—then the search string characters which have not been found are discarded from the search string. With them gone, the search is now successful and waiting for more input, so a second C-g will cancel the entire search.

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15.1.4 Special Input for Incremental Search

Some of the characters you type during incremental search have special effects.

By default, incremental search performs lax space matching: each space, or sequence of spaces, matches any sequence of one or more spaces in the text. Hence, ‘foo bar’ matches ‘foo bar’, ‘foo bar’, ‘foo bar’, and so on (but not ‘foobar’). More precisely, Emacs matches each sequence of space characters in the search string to a regular expression specified by the variable search-whitespace-regexp. For example, set it to ‘"[[:space:]\n]+"’ to make spaces match sequences of newlines as well as spaces. To toggle lax space matching, type M-s SPC (isearch-toggle-lax-whitespace). To disable this feature entirely, change search-whitespace-regexp to nil; then each space in the search string matches exactly one space

If the search string you entered contains only lower-case letters, the search is case-insensitive; as long as an upper-case letter exists in the search string, the search becomes case-sensitive. If you delete the upper-case character from the search string, it ceases to have this effect. See Search Case.

To search for a newline character, type C-j.

To search for other control characters, such as <control-S>, quote it by typing C-q first (see Inserting Text). To search for non-ASCII characters, you can either use C-q and enter its octal code, or use an input method (see Input Methods). If an input method is enabled in the current buffer when you start the search, you can use it in the search string also. While typing the search string, you can toggle the input method with the command C-\ (isearch-toggle-input-method). You can also turn on a non-default input method with C-^ (isearch-toggle-specified-input-method), which prompts for the name of the input method. When an input method is active during incremental search, the search prompt includes the input method mnemonic, like this: 

     I-search [im]:

where im is the mnemonic of the active input method. Any input method you enable during incremental search remains enabled in the current buffer afterwards.

Typing M-% in incremental search invokes query-replace or query-replace-regexp (depending on search mode) with the current search string used as the string to replace. See Query Replace.

Typing M-<TAB> in incremental search invokes isearch-complete, which attempts to complete the search string using the search ring as a list of completion alternatives. See Completion. In many operating systems, the M-<TAB> key sequence is captured by the window manager; you then need to rebind isearch-complete to another key sequence if you want to use it (see Rebinding).

When incremental search is active, you can type C-h C-h to access interactive help options, including a list of special key bindings. These key bindings are part of the keymap isearch-mode-map (see Keymaps).

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15.1.5 Isearch Yanking

Within incremental search, C-y (isearch-yank-kill) appends the current kill to the search string. M-y (isearch-yank-pop), if called after C-y, replaces that appended text with an earlier kill, similar to the usual M-y (yank-pop) command (see Yanking). Mouse-2 appends the current X selection (see Primary Selection).

C-w (isearch-yank-word-or-char) appends the next character or word at point to the search string. This is an easy way to search for another occurrence of the text at point. (The decision of whether to copy a character or a word is heuristic.)

Similarly, M-s C-e (isearch-yank-line) appends the rest of the current line to the search string. If point is already at the end of a line, it appends the next line.

If the search is currently case-insensitive, both C-w and M-s C-e convert the text they copy to lower case, so that the search remains case-insensitive.

C-M-w (isearch-del-char) deletes the last character from the search string, and C-M-y (isearch-yank-char) appends the character after point to the search string. An alternative method to add the character after point is to enter the minibuffer with M-e (see Repeat Isearch) and type C-f at the end of the search string in the minibuffer.

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15.1.6 Scrolling During Incremental Search

Normally, scrolling commands exit incremental search. If you change the variable isearch-allow-scroll to a non-nil value, that enables the use of the scroll-bar, as well as keyboard scrolling commands like C-v, M-v, and C-l (see Scrolling). This applies only to calling these commands via their bound key sequences—typing M-x will still exit the search. You can give prefix arguments to these commands in the usual way. This feature won't let you scroll the current match out of visibility, however.

The isearch-allow-scroll feature also affects some other commands, such as C-x 2 (split-window-below) and C-x ^ (enlarge-window), which don't exactly scroll but do affect where the text appears on the screen. It applies to any command whose name has a non-nil isearch-scroll property. So you can control which commands are affected by changing these properties.

For example, to make C-h l usable within an incremental search in all future Emacs sessions, use C-h c to find what command it runs (see Key Help), which is view-lossage. Then you can put the following line in your init file (see Init File): 

     (put 'view-lossage 'isearch-scroll t)

This feature can be applied to any command that doesn't permanently change point, the buffer contents, the match data, the current buffer, or the selected window and frame. The command must not itself attempt an incremental search.

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15.1.7 Searching the Minibuffer

If you start an incremental search while the minibuffer is active, Emacs searches the contents of the minibuffer. Unlike searching an ordinary buffer, the search string is not shown in the echo area, because that is used to display the minibuffer.

If an incremental search fails in the minibuffer, it tries searching the minibuffer history. See Minibuffer History. You can visualize the minibuffer and its history as a series of “pages”, with the earliest history element on the first page and the current minibuffer on the last page. A forward search, C-s, searches forward to later pages; a reverse search, C-r, searches backwards to earlier pages. Like in ordinary buffer search, a failing search can wrap around, going from the last page to the first page or vice versa.

When the current match is on a history element, that history element is pulled into the minibuffer. If you exit the incremental search normally (e.g., by typing <RET>), it remains in the minibuffer afterwards. Canceling the search, with C-g, restores the contents of the minibuffer when you began the search.

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15.2 Nonincremental Search

Emacs also has conventional nonincremental search commands, which require you to type the entire search string before searching begins.

C-s <RET> string <RET>
Search for string.
C-r <RET> string <RET>
Search backward for string.

To start a nonincremental search, first type C-s <RET>. This enters the minibuffer to read the search string; terminate the string with <RET>, and then the search takes place. If the string is not found, the search command signals an error.

When you type C-s <RET>, the C-s invokes incremental search as usual. That command is specially programmed to invoke the command for nonincremental search, search-forward, if the string you specify is empty. (Such an empty argument would otherwise be useless.) C-r <RET> does likewise, invoking the command search-backward.

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15.3 Word Search

A word search finds a sequence of words without regard to the type of punctuation between them. For instance, if you enter a search string that consists of two words separated by a single space, the search matches any sequence of those two words separated by one or more spaces, newlines, or other punctuation characters. This is particularly useful for searching text documents, because you don't have to worry whether the words you are looking for are separated by newlines or spaces.

M-s w
If incremental search is active, toggle word search mode (isearch-toggle-word); otherwise, begin an incremental forward word search (isearch-forward-word).
M-s w <RET> words <RET>
Search for words, using a forward nonincremental word search.
M-s w C-r <RET> words <RET>
Search backward for words, using a nonincremental word search.

To begin a forward incremental word search, type M-s w. If incremental search is not already active, this runs the command isearch-forward-word. If incremental search is already active (whether a forward or backward search), M-s w switches to a word search while keeping the direction of the search and the current search string unchanged. You can toggle word search back off by typing M-s w again.

To begin a nonincremental word search, type M-s w <RET> for a forward search, or M-s w C-r <RET> for a backward search. These run the commands word-search-forward and word-search-backward respectively.

Incremental and nonincremental word searches differ slightly in the way they find a match. In a nonincremental word search, the last word in the search string must exactly match a whole word. In an incremental word search, the matching is more lax: the last word in the search string can match part of a word, so that the matching proceeds incrementally as you type. This additional laxity does not apply to the lazy highlight, which always matches whole words.

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15.4 Symbol Search

A symbol search is much like an ordinary search, except that the boundaries of the search must match the boundaries of a symbol. The meaning of symbol in this context depends on the major mode, and usually refers to a source code token, such as a Lisp symbol in Emacs Lisp mode. For instance, if you perform an incremental symbol search for the Lisp symbol forward-word, it would not match isearch-forward-word. This feature is thus mainly useful for searching source code.

M-s _
If incremental search is active, toggle symbol search mode (isearch-toggle-symbol); otherwise, begin an incremental forward symbol search (isearch-forward-symbol).
M-s _ <RET> symbol <RET>
Search forward for symbol, nonincrementally.
M-s _ C-r <RET> symbol <RET>
Search backward for symbol, nonincrementally.

To begin a forward incremental symbol search, type M-s _. If incremental search is not already active, this runs the command isearch-forward-symbol. If incremental search is already active, M-s _ switches to a symbol search, preserving the direction of the search and the current search string; you can disable symbol search by typing M-s _ again. In incremental symbol search, only the beginning of the search string is required to match the beginning of a symbol.

To begin a nonincremental symbol search, type M-s _ <RET> for a forward search, or M-s _ C-r <RET> or a backward search. In nonincremental symbol searches, the beginning and end of the search string are required to match the beginning and end of a symbol, respectively.

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15.5 Regular Expression Search

A regular expression (or regexp for short) is a pattern that denotes a class of alternative strings to match. Emacs provides both incremental and nonincremental ways to search for a match for a regexp. The syntax of regular expressions is explained in the next section.

C-M-s
Begin incremental regexp search (isearch-forward-regexp).
C-M-r
Begin reverse incremental regexp search (isearch-backward-regexp).

Incremental search for a regexp is done by typing C-M-s (isearch-forward-regexp), by invoking C-s with a prefix argument (whose value does not matter), or by typing M-r within a forward incremental search. This command reads a search string incrementally just like C-s, but it treats the search string as a regexp rather than looking for an exact match against the text in the buffer. Each time you add text to the search string, you make the regexp longer, and the new regexp is searched for. To search backward for a regexp, use C-M-r (isearch-backward-regexp), C-r with a prefix argument, or M-r within a backward incremental search.

All of the special key sequences in an ordinary incremental search do similar things in an incremental regexp search. For instance, typing C-s immediately after starting the search retrieves the last incremental search regexp used and searches forward for it. Incremental regexp and non-regexp searches have independent defaults. They also have separate search rings, which you can access with M-p and M-n.

Just as in ordinary incremental search, any <SPC> typed in incremental regexp search matches any sequence of one or more whitespace characters. The variable search-whitespace-regexp specifies the regexp for the lax space matching, and M-s SPC (isearch-toggle-lax-whitespace) toggles the feature. See Special Isearch.

In some cases, adding characters to the regexp in an incremental regexp search can make the cursor move back and start again. For example, if you have searched for ‘foo’ and you add ‘\|bar’, the cursor backs up in case the first ‘bar’ precedes the first ‘foo’. See Regexps.

Forward and backward regexp search are not symmetrical, because regexp matching in Emacs always operates forward, starting with the beginning of the regexp. Thus, forward regexp search scans forward, trying a forward match at each possible starting position. Backward regexp search scans backward, trying a forward match at each possible starting position. These search methods are not mirror images.

Nonincremental search for a regexp is done with the commands re-search-forward and re-search-backward. You can invoke these with M-x, or by way of incremental regexp search with C-M-s <RET> and C-M-r <RET>.

If you use the incremental regexp search commands with a prefix argument, they perform ordinary string search, like isearch-forward and isearch-backward. See Incremental Search.

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15.6 Syntax of Regular Expressions

This manual describes regular expression features that users typically use. See Regular Expressions, for additional features used mainly in Lisp programs.

Regular expressions have a syntax in which a few characters are special constructs and the rest are ordinary. An ordinary character matches that same character and nothing else. The special characters are ‘$^.*+?[\’. The character ‘]’ is special if it ends a character alternative (see later). The character ‘-’ is special inside a character alternative. Any other character appearing in a regular expression is ordinary, unless a ‘\’ precedes it. (When you use regular expressions in a Lisp program, each ‘\’ must be doubled, see the example near the end of this section.)

For example, ‘f’ is not a special character, so it is ordinary, and therefore ‘f’ is a regular expression that matches the string ‘f’ and no other string. (It does not match the string ‘ff’.) Likewise, ‘o’ is a regular expression that matches only ‘o’. (When case distinctions are being ignored, these regexps also match ‘F’ and ‘O’, but we consider this a generalization of “the same string”, rather than an exception.)

Any two regular expressions a and b can be concatenated. The result is a regular expression which matches a string if a matches some amount of the beginning of that string and b matches the rest of the string. For example, concatenating the regular expressions ‘f’ and ‘o’ gives the regular expression ‘fo’, which matches only the string ‘fo’. Still trivial. To do something nontrivial, you need to use one of the special characters. Here is a list of them.

. (Period)
is a special character that matches any single character except a newline. For example, the regular expressions ‘a.b’ matches any three-character string that begins with ‘a’ and ends with ‘b’.
*
is not a construct by itself; it is a postfix operator that means to match the preceding regular expression repetitively any number of times, as many times as possible. Thus, ‘o*’ matches any number of ‘o’s, including no ‘o’s.

‘*’ always applies to the smallest possible preceding expression. Thus, ‘fo*’ has a repeating ‘o’, not a repeating ‘fo’. It matches ‘f’, ‘fo’, ‘foo’, and so on.

The matcher processes a ‘*’ construct by matching, immediately, as many repetitions as can be found. Then it continues with the rest of the pattern. If that fails, backtracking occurs, discarding some of the matches of the ‘*’-modified construct in case that makes it possible to match the rest of the pattern. For example, in matching ‘ca*ar’ against the string ‘caaar’, the ‘a*’ first tries to match all three ‘a’s; but the rest of the pattern is ‘ar’ and there is only ‘r’ left to match, so this try fails. The next alternative is for ‘a*’ to match only two ‘a’s. With this choice, the rest of the regexp matches successfully.

+
is a postfix operator, similar to ‘*’ except that it must match the preceding expression at least once. Thus, ‘ca+r’ matches the strings ‘car’ and ‘caaaar’ but not the string ‘cr’, whereas ‘ca*r’ matches all three strings.
?
is a postfix operator, similar to ‘*’ except that it can match the preceding expression either once or not at all. Thus, ‘ca?r’ matches ‘car’ or ‘cr’, and nothing else.
*?, +?, ??
are non-greedy variants of the operators above. The normal operators ‘*’, ‘+’, ‘?’ match as much as they can, as long as the overall regexp can still match. With a following ‘?’, they will match as little as possible.

Thus, both ‘ab*’ and ‘ab*?’ can match the string ‘a’ and the string ‘abbbb’; but if you try to match them both against the text ‘abbb’, ‘ab*’ will match it all (the longest valid match), while ‘ab*?’ will match just ‘a’ (the shortest valid match).

Non-greedy operators match the shortest possible string starting at a given starting point; in a forward search, though, the earliest possible starting point for match is always the one chosen. Thus, if you search for ‘a.*?$’ against the text ‘abbab’ followed by a newline, it matches the whole string. Since it can match starting at the first ‘a’, it does.

\{n\}
is a postfix operator specifying n repetitions—that is, the preceding regular expression must match exactly n times in a row. For example, ‘x\{4\}’ matches the string ‘xxxx’ and nothing else.
\{n,m\}
is a postfix operator specifying between n and m repetitions—that is, the preceding regular expression must match at least n times, but no more than m times. If m is omitted, then there is no upper limit, but the preceding regular expression must match at least n times.
‘\{0,1\}’ is equivalent to ‘?’.
‘\{0,\}’ is equivalent to ‘*’.
‘\{1,\}’ is equivalent to ‘+’.
[ ... ]
is a character set, beginning with ‘[’ and terminated by ‘]’.

In the simplest case, the characters between the two brackets are what this set can match. Thus, ‘[ad]’ matches either one ‘a’ or one ‘d’, and ‘[ad]*’ matches any string composed of just ‘a’s and ‘d’s (including the empty string). It follows that ‘c[ad]*r’ matches ‘cr’, ‘car’, ‘cdr’, ‘caddaar’, etc.

You can also include character ranges in a character set, by writing the starting and ending characters with a ‘-’ between them. Thus, ‘[a-z]’ matches any lower-case ASCII letter. Ranges may be intermixed freely with individual characters, as in ‘[a-z$%.]’, which matches any lower-case ASCII letter or ‘$’, ‘%’ or period.

You can also include certain special character classes in a character set. A ‘[:’ and balancing ‘:]’ enclose a character class inside a character alternative. For instance, ‘[[:alnum:]]’ matches any letter or digit. See Char Classes, for a list of character classes.

To include a ‘]’ in a character set, you must make it the first character. For example, ‘[]a]’ matches ‘]’ or ‘a’. To include a ‘-’, write ‘-’ as the first or last character of the set, or put it after a range. Thus, ‘[]-]’ matches both ‘]’ and ‘-’.

To include ‘^’ in a set, put it anywhere but at the beginning of the set. (At the beginning, it complements the set—see below.)

When you use a range in case-insensitive search, you should write both ends of the range in upper case, or both in lower case, or both should be non-letters. The behavior of a mixed-case range such as ‘A-z’ is somewhat ill-defined, and it may change in future Emacs versions.

[^ ... ]
‘[^’ begins a complemented character set, which matches any character except the ones specified. Thus, ‘[^a-z0-9A-Z]’ matches all characters except ASCII letters and digits.

‘^’ is not special in a character set unless it is the first character. The character following the ‘^’ is treated as if it were first (in other words, ‘-’ and ‘]’ are not special there).

A complemented character set can match a newline, unless newline is mentioned as one of the characters not to match. This is in contrast to the handling of regexps in programs such as grep.

^
is a special character that matches the empty string, but only at the beginning of a line in the text being matched. Otherwise it fails to match anything. Thus, ‘^foo’ matches a ‘foo’ that occurs at the beginning of a line.

For historical compatibility reasons, ‘^’ can be used with this meaning only at the beginning of the regular expression, or after ‘\(’ or ‘\|’.

$
is similar to ‘^’ but matches only at the end of a line. Thus, ‘x+$’ matches a string of one ‘x’ or more at the end of a line.

For historical compatibility reasons, ‘$’ can be used with this meaning only at the end of the regular expression, or before ‘\)’ or ‘\|’.

\
has two functions: it quotes the special characters (including ‘\’), and it introduces additional special constructs.

Because ‘\’ quotes special characters, ‘\$’ is a regular expression that matches only ‘$’, and ‘\[’ is a regular expression that matches only ‘[’, and so on.

See the following section for the special constructs that begin with ‘\’.

Note: for historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, ‘*foo’ treats ‘*’ as ordinary since there is no preceding expression on which the ‘*’ can act. It is poor practice to depend on this behavior; it is better to quote the special character anyway, regardless of where it appears.

As a ‘\’ is not special inside a character alternative, it can never remove the special meaning of ‘-’ or ‘]’. So you should not quote these characters when they have no special meaning either. This would not clarify anything, since backslashes can legitimately precede these characters where they have special meaning, as in ‘[^\]’ ("[^\\]" for Lisp string syntax), which matches any single character except a backslash.

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15.7 Backslash in Regular Expressions

For the most part, ‘\’ followed by any character matches only that character. However, there are several exceptions: two-character sequences starting with ‘\’ that have special meanings. The second character in the sequence is always an ordinary character when used on its own. Here is a table of ‘\’ constructs.

\|
specifies an alternative. Two regular expressions a and b with ‘\|’ in between form an expression that matches some text if either a matches it or b matches it. It works by trying to match a, and if that fails, by trying to match b.

Thus, ‘foo\|bar’ matches either ‘foo’ or ‘bar’ but no other string.

‘\|’ applies to the largest possible surrounding expressions. Only a surrounding ‘\( ... \)’ grouping can limit the grouping power of ‘\|’.

Full backtracking capability exists to handle multiple uses of ‘\|’.

\( ... \)
is a grouping construct that serves three purposes:
  1. To enclose a set of ‘\|’ alternatives for other operations. Thus, ‘\(foo\|bar\)x’ matches either ‘foox’ or ‘barx’.
  2. To enclose a complicated expression for the postfix operators ‘*’, ‘+’ and ‘?’ to operate on. Thus, ‘ba\(na\)*’ matches ‘bananana’, etc., with any (zero or more) number of ‘na’ strings.
  3. To record a matched substring for future reference.

This last application is not a consequence of the idea of a parenthetical grouping; it is a separate feature that is assigned as a second meaning to the same ‘\( ... \)’ construct. In practice there is usually no conflict between the two meanings; when there is a conflict, you can use a “shy” group.

\(?: ... \)
specifies a “shy” group that does not record the matched substring; you can't refer back to it with ‘\d’. This is useful in mechanically combining regular expressions, so that you can add groups for syntactic purposes without interfering with the numbering of the groups that are meant to be referred to.
\d
matches the same text that matched the dth occurrence of a ‘\( ... \)’ construct. This is called a back reference.

After the end of a ‘\( ... \)’ construct, the matcher remembers the beginning and end of the text matched by that construct. Then, later on in the regular expression, you can use ‘\’ followed by the digit d to mean “match the same text matched the dth time by the ‘\( ... \)’ construct”.

The strings matching the first nine ‘\( ... \)’ constructs appearing in a regular expression are assigned numbers 1 through 9 in the order that the open-parentheses appear in the regular expression. So you can use ‘\1’ through ‘\9’ to refer to the text matched by the corresponding ‘\( ... \)’ constructs.

For example, ‘\(.*\)\1’ matches any newline-free string that is composed of two identical halves. The ‘\(.*\)’ matches the first half, which may be anything, but the ‘\1’ that follows must match the same exact text.

If a particular ‘\( ... \)’ construct matches more than once (which can easily happen if it is followed by ‘*’), only the last match is recorded.

\`
matches the empty string, but only at the beginning of the string or buffer (or its accessible portion) being matched against.
\'
matches the empty string, but only at the end of the string or buffer (or its accessible portion) being matched against.
\=
matches the empty string, but only at point.
\b
matches the empty string, but only at the beginning or end of a word. Thus, ‘\bfoo\b’ matches any occurrence of ‘foo’ as a separate word. ‘\bballs?\b’ matches ‘ball’ or ‘balls’ as a separate word.

‘\b’ matches at the beginning or end of the buffer regardless of what text appears next to it.

\B
matches the empty string, but not at the beginning or end of a word.
\<
matches the empty string, but only at the beginning of a word. ‘\<’ matches at the beginning of the buffer only if a word-constituent character follows.
\>
matches the empty string, but only at the end of a word. ‘\>’ matches at the end of the buffer only if the contents end with a word-constituent character.
\w
matches any word-constituent character. The syntax table determines which characters these are. See Syntax Tables.
\W
matches any character that is not a word-constituent.
\_<
matches the empty string, but only at the beginning of a symbol. A symbol is a sequence of one or more symbol-constituent characters. A symbol-constituent character is a character whose syntax is either ‘w’ or ‘_’. ‘\_<’ matches at the beginning of the buffer only if a symbol-constituent character follows.
\_>
matches the empty string, but only at the end of a symbol. ‘\_>’ matches at the end of the buffer only if the contents end with a symbol-constituent character.
\sc
matches any character whose syntax is c. Here c is a character that designates a particular syntax class: thus, ‘w’ for word constituent, ‘-’ or ‘ ’ for whitespace, ‘.’ for ordinary punctuation, etc. See Syntax Tables.
\Sc
matches any character whose syntax is not c.


\cc
matches any character that belongs to the category c. For example, ‘\cc’ matches Chinese characters, ‘\cg’ matches Greek characters, etc. For the description of the known categories, type M-x describe-categories <RET>.
\Cc
matches any character that does not belong to category c.

The constructs that pertain to words and syntax are controlled by the setting of the syntax table. See Syntax Tables.

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15.8 Regular Expression Example

Here is an example of a regexp—similar to the regexp that Emacs uses, by default, to recognize the end of a sentence, not including the following space (i.e., the variable sentence-end-base): 

     [.?!][]\"')}]*

This contains two parts in succession: a character set matching period, ‘?’, or ‘!’, and a character set matching close-brackets, quotes, or parentheses, repeated zero or more times.

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15.9 Searching and Case

Searches in Emacs normally ignore the case of the text they are searching through, if you specify the text in lower case. Thus, if you specify searching for ‘foo’, then ‘Foo’ and ‘foo’ also match. Regexps, and in particular character sets, behave likewise: ‘[ab]’ matches ‘a’ or ‘A’ or ‘b’ or ‘B’.

An upper-case letter anywhere in the incremental search string makes the search case-sensitive. Thus, searching for ‘Foo’ does not find ‘foo’ or ‘FOO’. This applies to regular expression search as well as to string search. The effect ceases if you delete the upper-case letter from the search string.

Typing M-c within an incremental search toggles the case sensitivity of that search. The effect does not extend beyond the current incremental search to the next one, but it does override the effect of adding or removing an upper-case letter in the current search.

If you set the variable case-fold-search to nil, then all letters must match exactly, including case. This is a per-buffer variable; altering the variable normally affects only the current buffer, unless you change its default value. See Locals. This variable applies to nonincremental searches also, including those performed by the replace commands (see Replace) and the minibuffer history matching commands (see Minibuffer History).

Several related variables control case-sensitivity of searching and matching for specific commands or activities. For instance, tags-case-fold-search controls case sensitivity for find-tag. To find these variables, do M-x apropos-variable <RET> case-fold-search <RET>.

Next: , Previous: Search Case, Up: Search

15.10 Replacement Commands

Emacs provides several commands for performing search-and-replace operations. In addition to the simple M-x replace-string command, there is M-% (query-replace), which presents each occurrence of the pattern and asks you whether to replace it.

The replace commands normally operate on the text from point to the end of the buffer. When the region is active, they operate on it instead (see Mark). The basic replace commands replace one search string (or regexp) with one replacement string. It is possible to perform several replacements in parallel, using the command expand-region-abbrevs (see Expanding Abbrevs).

Unlike incremental search, the replacement commands do not use lax space matching (see Special Isearch) by default. To enable lax space matching for replacement, change the variable replace-lax-whitespace to t. (This only affects how Emacs finds the text to replace, not the replacement text.)

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15.10.1 Unconditional Replacement

M-x replace-string <RET> string <RET> newstring <RET>
Replace every occurrence of string with newstring.

To replace every instance of ‘foo’ after point with ‘bar’, use the command M-x replace-string with the two arguments ‘foo’ and ‘bar’. Replacement happens only in the text after point, so if you want to cover the whole buffer you must go to the beginning first. All occurrences up to the end of the buffer are replaced; to limit replacement to part of the buffer, activate the region around that part. When the region is active, replacement is limited to the region (see Mark).

When replace-string exits, it leaves point at the last occurrence replaced. It adds the prior position of point (where the replace-string command was issued) to the mark ring, without activating the mark; use C-u C-<SPC> to move back there. See Mark Ring.

A prefix argument restricts replacement to matches that are surrounded by word boundaries.

See Replacement and Case, for details about case-sensitivity in replace commands.

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15.10.2 Regexp Replacement

The M-x replace-string command replaces exact matches for a single string. The similar command M-x replace-regexp replaces any match for a specified pattern.

M-x replace-regexp <RET> regexp <RET> newstring <RET>
Replace every match for regexp with newstring.

In replace-regexp, the newstring need not be constant: it can refer to all or part of what is matched by the regexp. ‘\&’ in newstring stands for the entire match being replaced. ‘\d’ in newstring, where d is a digit, stands for whatever matched the dth parenthesized grouping in regexp. (This is called a “back reference”.) ‘\#’ refers to the count of replacements already made in this command, as a decimal number. In the first replacement, ‘\#’ stands for ‘0’; in the second, for ‘1’; and so on. For example, 

     M-x replace-regexp <RET> c[ad]+r <RET> \&-safe <RET>

replaces (for example) ‘cadr’ with ‘cadr-safe’ and ‘cddr’ with ‘cddr-safe’. 

     M-x replace-regexp <RET> \(c[ad]+r\)-safe <RET> \1 <RET>

performs the inverse transformation. To include a ‘\’ in the text to replace with, you must enter ‘\\’.

If you want to enter part of the replacement string by hand each time, use ‘\?’ in the replacement string. Each replacement will ask you to edit the replacement string in the minibuffer, putting point where the ‘\?’ was.

The remainder of this subsection is intended for specialized tasks and requires knowledge of Lisp. Most readers can skip it.

You can use Lisp expressions to calculate parts of the replacement string. To do this, write ‘\,’ followed by the expression in the replacement string. Each replacement calculates the value of the expression and converts it to text without quoting (if it's a string, this means using the string's contents), and uses it in the replacement string in place of the expression itself. If the expression is a symbol, one space in the replacement string after the symbol name goes with the symbol name, so the value replaces them both.

Inside such an expression, you can use some special sequences. ‘\&’ and ‘\n’ refer here, as usual, to the entire match as a string, and to a submatch as a string. n may be multiple digits, and the value of ‘\n’ is nil if subexpression n did not match. You can also use ‘\#&’ and ‘\#n’ to refer to those matches as numbers (this is valid when the match or submatch has the form of a numeral). ‘\#’ here too stands for the number of already-completed replacements.

Repeating our example to exchange ‘x’ and ‘y’, we can thus do it also this way: 

     M-x replace-regexp <RET> \(x\)\|y <RET>
     \,(if \1 "y" "x") <RET>

For computing replacement strings for ‘\,’, the format function is often useful (see Formatting Strings). For example, to add consecutively numbered strings like ‘ABC00042’ to columns 73 to 80 (unless they are already occupied), you can use 

     M-x replace-regexp <RET> ^.\{0,72\}$ <RET>
     \,(format "%-72sABC%05d" \& \#) <RET>

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15.10.3 Replace Commands and Case

If the first argument of a replace command is all lower case, the command ignores case while searching for occurrences to replace—provided case-fold-search is non-nil. If case-fold-search is set to nil, case is always significant in all searches.

In addition, when the newstring argument is all or partly lower case, replacement commands try to preserve the case pattern of each occurrence. Thus, the command 

     M-x replace-string <RET> foo <RET> bar <RET>

replaces a lower case ‘foo’ with a lower case ‘bar’, an all-caps ‘FOO’ with ‘BAR’, and a capitalized ‘Foo’ with ‘Bar’. (These three alternatives—lower case, all caps, and capitalized, are the only ones that replace-string can distinguish.)

If upper-case letters are used in the replacement string, they remain upper case every time that text is inserted. If upper-case letters are used in the first argument, the second argument is always substituted exactly as given, with no case conversion. Likewise, if either case-replace or case-fold-search is set to nil, replacement is done without case conversion.

Previous: Replacement and Case, Up: Replace

15.10.4 Query Replace

M-% string <RET> newstring <RET>
Replace some occurrences of string with newstring.
C-M-% regexp <RET> newstring <RET>
Replace some matches for regexp with newstring.

If you want to change only some of the occurrences of ‘foo’ to ‘bar’, not all of them, use M-% (query-replace). This command finds occurrences of ‘foo’ one by one, displays each occurrence and asks you whether to replace it. Aside from querying, query-replace works just like replace-string (see Unconditional Replace). In particular, it preserves case provided case-replace is non-nil, as it normally is (see Replacement and Case). A numeric argument means to consider only occurrences that are bounded by word-delimiter characters.

C-M-% performs regexp search and replace (query-replace-regexp). It works like replace-regexp except that it queries like query-replace.

These commands highlight the current match using the face query-replace. They highlight other matches using lazy-highlight just like incremental search (see Incremental Search). By default, query-replace-regexp will show the substituted replacement string for the current match in the minibuffer. If you want to keep special sequences ‘\&’ and ‘\n’ unexpanded, customize query-replace-show-replacement variable.

The characters you can type when you are shown a match for the string or regexp are:

<SPC>
to replace the occurrence with newstring.
<DEL>
to skip to the next occurrence without replacing this one.
, (Comma)
to replace this occurrence and display the result. You are then asked for another input character to say what to do next. Since the replacement has already been made, <DEL> and <SPC> are equivalent in this situation; both move to the next occurrence.

You can type C-r at this point (see below) to alter the replaced text. You can also type C-x u to undo the replacement; this exits the query-replace, so if you want to do further replacement you must use C-x <ESC> <ESC> <RET> to restart (see Repetition).

<RET>
to exit without doing any more replacements.
. (Period)
to replace this occurrence and then exit without searching for more occurrences.
!
to replace all remaining occurrences without asking again.
Y (Upper-case)
to replace all remaining occurrences in all remaining buffers in multi-buffer replacements (like the Dired `Q' command which performs query replace on selected files). It answers this question and all subsequent questions in the series with "yes", without further user interaction.
N (Upper-case)
to skip to the next buffer in multi-buffer replacements without replacing remaining occurrences in the current buffer. It answers this question "no", gives up on the questions for the current buffer, and continues to the next buffer in the sequence.
^
to go back to the position of the previous occurrence (or what used to be an occurrence), in case you changed it by mistake or want to reexamine it.
C-r
to enter a recursive editing level, in case the occurrence needs to be edited rather than just replaced with newstring. When you are done, exit the recursive editing level with C-M-c to proceed to the next occurrence. See Recursive Edit.
C-w
to delete the occurrence, and then enter a recursive editing level as in C-r. Use the recursive edit to insert text to replace the deleted occurrence of string. When done, exit the recursive editing level with C-M-c to proceed to the next occurrence.
e
to edit the replacement string in the minibuffer. When you exit the minibuffer by typing <RET>, the minibuffer contents replace the current occurrence of the pattern. They also become the new replacement string for any further occurrences.
C-l
to redisplay the screen. Then you must type another character to specify what to do with this occurrence.
C-h
to display a message summarizing these options. Then you must type another character to specify what to do with this occurrence.

Some other characters are aliases for the ones listed above: y, n and q are equivalent to <SPC>, <DEL> and <RET>.

Aside from this, any other character exits the query-replace, and is then reread as part of a key sequence. Thus, if you type C-k, it exits the query-replace and then kills to end of line.

To restart a query-replace once it is exited, use C-x <ESC> <ESC>, which repeats the query-replace because it used the minibuffer to read its arguments. See C-x ESC ESC.

See Operating on Files, for the Dired Q command which performs query replace on selected files. See also Transforming File Names, for Dired commands to rename, copy, or link files by replacing regexp matches in file names.

Previous: Replace, Up: Search

15.11 Other Search-and-Loop Commands

Here are some other commands that find matches for a regular expression. They all ignore case in matching, if the pattern contains no upper-case letters and case-fold-search is non-nil. Aside from occur and its variants, all operate on the text from point to the end of the buffer, or on the region if it is active.

M-x multi-isearch-buffers
Prompt for one or more buffer names, ending with <RET>; then, begin a multi-buffer incremental search in those buffers. (If the search fails in one buffer, the next C-s tries searching the next specified buffer, and so forth.) With a prefix argument, prompt for a regexp and begin a multi-buffer incremental search in buffers matching that regexp.
M-x multi-isearch-buffers-regexp
This command is just like multi-isearch-buffers, except it performs an incremental regexp search.


M-x occur
Prompt for a regexp, and display a list showing each line in the buffer that contains a match for it. To limit the search to part of the buffer, narrow to that part (see Narrowing). A numeric argument n specifies that n lines of context are to be displayed before and after each matching line.

In the *Occur* buffer, you can click on each entry, or move point there and type <RET>, to visit the corresponding position in the buffer that was searched. o and C-o display the match in another window; C-o does not select it. Alternatively, you can use the C-x ` (next-error) command to visit the occurrences one by one (see Compilation Mode).

Typing e in the *Occur* buffer switches to Occur Edit mode, in which edits made to the entries are also applied to the text in the originating buffer. Type C-c C-c to return to Occur mode.

The command M-x list-matching-lines is a synonym for M-x occur.


M-s o
Run occur using the search string of the last incremental string search. You can also run M-s o when an incremental search is active; this uses the current search string.
M-x multi-occur
This command is just like occur, except it is able to search through multiple buffers. It asks you to specify the buffer names one by one.
M-x multi-occur-in-matching-buffers
This command is similar to multi-occur, except the buffers to search are specified by a regular expression that matches visited file names. With a prefix argument, it uses the regular expression to match buffer names instead.
M-x how-many
Prompt for a regexp, and print the number of matches for it in the buffer after point. If the region is active, this operates on the region instead.
M-x flush-lines
Prompt for a regexp, and delete each line that contains a match for it, operating on the text after point. This command deletes the current line if it contains a match starting after point. If the region is active, it operates on the region instead; if a line partially contained in the region contains a match entirely contained in the region, it is deleted.

If a match is split across lines, flush-lines deletes all those lines. It deletes the lines before starting to look for the next match; hence, it ignores a match starting on the same line at which another match ended.

M-x keep-lines
Prompt for a regexp, and delete each line that does not contain a match for it, operating on the text after point. If point is not at the beginning of a line, this command always keeps the current line. If the region is active, the command operates on the region instead; it never deletes lines that are only partially contained in the region (a newline that ends a line counts as part of that line).

If a match is split across lines, this command keeps all those lines.

Next: , Previous: Search, Up: Top

16 Commands for Fixing Typos

In this chapter we describe commands that are useful when you catch a mistake while editing. The most fundamental of these commands is the undo command C-/ (also bound to C-x u and C-_). This undoes a single command, or a part of a command (as in the case of query-replace), or several consecutive character insertions. Consecutive repetitions of C-/ undo earlier and earlier changes, back to the limit of the undo information available.

Aside from the commands described here, you can erase text using deletion commands such as <DEL> (delete-backward-char). These were described earlier in this manual. See Erasing.

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16.1 Undo

The undo command reverses recent changes in the buffer's text. Each buffer records changes individually, and the undo command always applies to the current buffer. You can undo all the changes in a buffer for as far back as the buffer's records go. Usually, each editing command makes a separate entry in the undo records, but some commands such as query-replace divide their changes into multiple entries for flexibility in undoing. Consecutive character insertion commands are usually grouped together into a single undo record, to make undoing less tedious.

C-/
C-x u
C-_
Undo one entry in the current buffer's undo records (undo).

To begin to undo, type C-/ (or its aliases, C-_ or C-x u)6. This undoes the most recent change in the buffer, and moves point back to where it was before that change. Consecutive repetitions of C-/ (or its aliases) undo earlier and earlier changes in the current buffer. If all the recorded changes have already been undone, the undo command signals an error.

Any command other than an undo command breaks the sequence of undo commands. Starting from that moment, the entire sequence of undo commands that you have just performed are themselves placed into the undo record, as a single set of changes. Therefore, to re-apply changes you have undone, type C-f or any other command that harmlessly breaks the sequence of undoing; then type C-/ to undo the undo command.

Alternatively, if you want to resume undoing, without redoing previous undo commands, use M-x undo-only. This is like undo, but will not redo changes you have just undone.

If you notice that a buffer has been modified accidentally, the easiest way to recover is to type C-/ repeatedly until the stars disappear from the front of the mode line (see Mode Line). Whenever an undo command makes the stars disappear from the mode line, it means that the buffer contents are the same as they were when the file was last read in or saved. If you do not remember whether you changed the buffer deliberately, type C-/ once. When you see the last change you made undone, you will see whether it was an intentional change. If it was an accident, leave it undone. If it was deliberate, redo the change as described above.

When there is an active region, any use of undo performs selective undo: it undoes the most recent change within the region, instead of the entire buffer. However, when Transient Mark mode is off (see Disabled Transient Mark), C-/ always operates on the entire buffer, ignoring the region. In this case, you can perform selective undo by supplying a prefix argument to the undo command: C-u C-/. To undo further changes in the same region, repeat the undo command (no prefix argument is needed).

Some specialized buffers do not make undo records. Buffers whose names start with spaces never do; these buffers are used internally by Emacs to hold text that users don't normally look at or edit.

When the undo information for a buffer becomes too large, Emacs discards the oldest records from time to time (during garbage collection). You can specify how much undo information to keep by setting the variables undo-limit, undo-strong-limit, and undo-outer-limit. Their values are expressed in bytes.

The variable undo-limit sets a soft limit: Emacs keeps undo data for enough commands to reach this size, and perhaps exceed it, but does not keep data for any earlier commands beyond that. Its default value is 80000. The variable undo-strong-limit sets a stricter limit: any previous command (though not the most recent one) that pushes the size past this amount is forgotten. The default value of undo-strong-limit is 120000.

Regardless of the values of those variables, the most recent change is never discarded unless it gets bigger than undo-outer-limit (normally 12,000,000). At that point, Emacs discards the undo data and warns you about it. This is the only situation in which you cannot undo the last command. If this happens, you can increase the value of undo-outer-limit to make it even less likely to happen in the future. But if you didn't expect the command to create such large undo data, then it is probably a bug and you should report it. See Reporting Bugs.

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16.2 Transposing Text

C-t
Transpose two characters (transpose-chars).
M-t
Transpose two words (transpose-words).
C-M-t
Transpose two balanced expressions (transpose-sexps).
C-x C-t
Transpose two lines (transpose-lines).

The common error of transposing two characters can be fixed, when they are adjacent, with the C-t command (transpose-chars). Normally, C-t transposes the two characters on either side of point. When given at the end of a line, rather than transposing the last character of the line with the newline, which would be useless, C-t transposes the last two characters on the line. So, if you catch your transposition error right away, you can fix it with just a C-t. If you don't catch it so fast, you must move the cursor back between the two transposed characters before you type C-t. If you transposed a space with the last character of the word before it, the word motion commands are a good way of getting there. Otherwise, a reverse search (C-r) is often the best way. See Search.

M-t transposes the word before point with the word after point (transpose-words). It moves point forward over a word, dragging the word preceding or containing point forward as well. The punctuation characters between the words do not move. For example, ‘FOO, BAR’ transposes into ‘BAR, FOO’ rather than ‘BAR FOO,’.

C-M-t (transpose-sexps) is a similar command for transposing two expressions (see Expressions), and C-x C-t (transpose-lines) exchanges lines. They work like M-t except as regards what units of text they transpose.

A numeric argument to a transpose command serves as a repeat count: it tells the transpose command to move the character (word, expression, line) before or containing point across several other characters (words, expressions, lines). For example, C-u 3 C-t moves the character before point forward across three other characters. It would change ‘f-!-oobar’ into ‘oobf-!-ar’. This is equivalent to repeating C-t three times. C-u - 4 M-t moves the word before point backward across four words. C-u - C-M-t would cancel the effect of plain C-M-t.

A numeric argument of zero is assigned a special meaning (because otherwise a command with a repeat count of zero would do nothing): to transpose the character (word, expression, line) ending after point with the one ending after the mark.

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16.3 Case Conversion

M-- M-l
Convert last word to lower case. Note Meta-- is Meta-minus.
M-- M-u
Convert last word to all upper case.
M-- M-c
Convert last word to lower case with capital initial.

A very common error is to type words in the wrong case. Because of this, the word case-conversion commands M-l, M-u and M-c have a special feature when used with a negative argument: they do not move the cursor. As soon as you see you have mistyped the last word, you can simply case-convert it and go on typing. See Case.

Previous: Fixing Case, Up: Fixit

16.4 Checking and Correcting Spelling

This section describes the commands to check the spelling of a single word or of a portion of a buffer. These commands only work if the spelling checker program Aspell, Ispell or Hunspell is installed. These programs are not part of Emacs, but one of them is usually installed in GNU/Linux and other free operating systems. See Aspell.

M-$
Check and correct spelling of the word at point (ispell-word). If the region is active, do it for all words in the region instead.
M-x ispell
Check and correct spelling of all words in the buffer. If the region is active, do it for all words in the region instead.
M-x ispell-buffer
Check and correct spelling in the buffer.
M-x ispell-region
Check and correct spelling in the region.
M-x ispell-message
Check and correct spelling in a draft mail message, excluding cited material.
M-x ispell-change-dictionary <RET> dict <RET>
Restart the Aspell/Ispell/Hunspell process, using dict as the dictionary.
M-x ispell-kill-ispell
Kill the Aspell/Ispell/Hunspell subprocess.
M-<TAB>
<ESC> <TAB>
Complete the word before point based on the spelling dictionary (ispell-complete-word).
M-x flyspell-mode
Enable Flyspell mode, which highlights all misspelled words.
M-x flyspell-prog-mode
Enable Flyspell mode for comments and strings only.

To check the spelling of the word around or before point, and optionally correct it as well, type M-$ (ispell-word). If a region is active, M-$ checks the spelling of all words within the region. See Mark. (When Transient Mark mode is off, M-$ always acts on the word around or before point, ignoring the region; see Disabled Transient Mark.)

Similarly, the command M-x ispell performs spell-checking in the region if one is active, or in the entire buffer otherwise. The commands M-x ispell-buffer and M-x ispell-region explicitly perform spell-checking on the entire buffer or the region respectively. To check spelling in an email message you are writing, use M-x ispell-message; that command checks the whole buffer, except for material that is indented or appears to be cited from other messages. See Sending Mail.

When one of these commands encounters what appears to be an incorrect word, it asks you what to do. It usually displays a list of numbered “near-misses”—words that are close to the incorrect word. Then you must type a single-character response. Here are the valid responses:

digit
Replace the word, just this time, with one of the displayed near-misses. Each near-miss is listed with a digit; type that digit to select it.
<SPC>
Skip this word—continue to consider it incorrect, but don't change it here.
r new <RET>
Replace the word, just this time, with new. (The replacement string will be rescanned for more spelling errors.)
R new <RET>
Replace the word with new, and do a query-replace so you can replace it elsewhere in the buffer if you wish. (The replacements will be rescanned for more spelling errors.)
a
Accept the incorrect word—treat it as correct, but only in this editing session.
A
Accept the incorrect word—treat it as correct, but only in this editing session and for this buffer.
i
Insert this word in your private dictionary file so that Aspell or Ispell or Hunspell will consider it correct from now on, even in future sessions.
m
Like i, but you can also specify dictionary completion information.
u
Insert the lower-case version of this word in your private dictionary file.
l word <RET>
Look in the dictionary for words that match word. These words become the new list of “near-misses”; you can select one of them as the replacement by typing a digit. You can use ‘*’ in word as a wildcard.
C-g
X
Quit interactive spell checking, leaving point at the word that was being checked. You can restart checking again afterward with C-u M-$.
x
Quit interactive spell checking and move point back to where it was when you started spell checking.
q
Quit interactive spell checking and kill the spell-checker subprocess.
?
Show the list of options.

In Text mode and related modes, M-<TAB> (ispell-complete-word) performs in-buffer completion based on spelling correction. Insert the beginning of a word, and then type M-<TAB>; this shows a list of completions. (If your window manager intercepts M-<TAB>, type <ESC> <TAB> or C-M-i.) Each completion is listed with a digit or character; type that digit or character to choose it.

Once started, the Aspell or Ispell or Hunspell subprocess continues to run, waiting for something to do, so that subsequent spell checking commands complete more quickly. If you want to get rid of the process, use M-x ispell-kill-ispell. This is not usually necessary, since the process uses no processor time except when you do spelling correction.

Ispell, Aspell and Hunspell look up spelling in two dictionaries: the standard dictionary and your personal dictionary. The standard dictionary is specified by the variable ispell-local-dictionary or, if that is nil, by the variable ispell-dictionary. If both are nil, the spelling program's default dictionary is used. The command M-x ispell-change-dictionary sets the standard dictionary for the buffer and then restarts the subprocess, so that it will use a different standard dictionary. Your personal dictionary is specified by the variable ispell-personal-dictionary. If that is nil, the spelling program looks for a personal dictionary in a default location.

A separate dictionary is used for word completion. The variable ispell-complete-word-dict specifies the file name of this dictionary. The completion dictionary must be different because it cannot use root and affix information. For some languages, there is a spell checking dictionary but no word completion dictionary.

Flyspell mode is a minor mode that performs automatic spell checking as you type. When it finds a word that it does not recognize, it highlights that word. Type M-x flyspell-mode to toggle Flyspell mode in the current buffer. To enable Flyspell mode in all text mode buffers, add flyspell-mode to text-mode-hook. See Hooks.

When Flyspell mode highlights a word as misspelled, you can click on it with Mouse-2 to display a menu of possible corrections and actions. You can also correct the word by editing it manually in any way you like.

Flyspell Prog mode works just like ordinary Flyspell mode, except that it only checks words in comments and string constants. This feature is useful for editing programs. Type M-x flyspell-prog-mode to enable or disable this mode in the current buffer. To enable this mode in all programming mode buffers, add flyspell-prog-mode to prog-mode-hook (see Hooks).

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17 Keyboard Macros

In this chapter we describe how to record a sequence of editing commands so you can repeat it conveniently later.

A keyboard macro is a command defined by an Emacs user to stand for another sequence of keys. For example, if you discover that you are about to type C-n M-d C-d forty times, you can speed your work by defining a keyboard macro to do C-n M-d C-d, and then executing it 39 more times.

You define a keyboard macro by executing and recording the commands which are its definition. Put differently, as you define a keyboard macro, the definition is being executed for the first time. This way, you can see the effects of your commands, so that you don't have to figure them out in your head. When you close the definition, the keyboard macro is defined and also has been, in effect, executed once. You can then do the whole thing over again by invoking the macro.

Keyboard macros differ from ordinary Emacs commands in that they are written in the Emacs command language rather than in Lisp. This makes it easier for the novice to write them, and makes them more convenient as temporary hacks. However, the Emacs command language is not powerful enough as a programming language to be useful for writing anything intelligent or general. For such things, Lisp must be used.

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17.1 Basic Use

<F3>
Start defining a keyboard macro (kmacro-start-macro-or-insert-counter).
<F4>
If a keyboard macro is being defined, end the definition; otherwise, execute the most recent keyboard macro (kmacro-end-or-call-macro).
C-u <F3>
Re-execute last keyboard macro, then append keys to its definition.
C-u C-u <F3>
Append keys to the last keyboard macro without re-executing it.
C-x C-k r
Run the last keyboard macro on each line that begins in the region (apply-macro-to-region-lines).

To start defining a keyboard macro, type <F3>. From then on, your keys continue to be executed, but also become part of the definition of the macro. ‘Def’ appears in the mode line to remind you of what is going on. When you are finished, type <F4> (kmacro-end-or-call-macro) to terminate the definition. For example, 

     <F3> M-f foo <F4>

defines a macro to move forward a word and then insert ‘foo’. Note that <F3> and <F4> do not become part of the macro.

After defining the macro, you can call it with <F4>. For the above example, this has the same effect as typing M-f foo again. (Note the two roles of the <F4> command: it ends the macro if you are in the process of defining one, or calls the last macro otherwise.) You can also supply <F4> with a numeric prefix argument ‘n’, which means to invoke the macro ‘n’ times. An argument of zero repeats the macro indefinitely, until it gets an error or you type C-g (or, on MS-DOS, C-<BREAK>).

The above example demonstrates a handy trick that you can employ with keyboard macros: if you wish to repeat an operation at regularly spaced places in the text, include a motion command as part of the macro. In this case, repeating the macro inserts the string ‘foo’ after each successive word.

After terminating the definition of a keyboard macro, you can append more keystrokes to its definition by typing C-u <F3>. This is equivalent to plain <F3> followed by retyping the whole definition so far. As a consequence, it re-executes the macro as previously defined. If you change the variable kmacro-execute-before-append to nil, the existing macro will not be re-executed before appending to it (the default is t). You can also add to the end of the definition of the last keyboard macro without re-executing it by typing C-u C-u <F3>.

When a command reads an argument with the minibuffer, your minibuffer input becomes part of the macro along with the command. So when you replay the macro, the command gets the same argument as when you entered the macro. For example, 

     <F3> C-a C-k C-x b foo <RET> C-y C-x b <RET> <F4>

defines a macro that kills the current line, yanks it into the buffer ‘foo’, then returns to the original buffer.

Most keyboard commands work as usual in a keyboard macro definition, with some exceptions. Typing C-g (keyboard-quit) quits the keyboard macro definition. Typing C-M-c (exit-recursive-edit) can be unreliable: it works as you'd expect if exiting a recursive edit that started within the macro, but if it exits a recursive edit that started before you invoked the keyboard macro, it also necessarily exits the keyboard macro too. Mouse events are also unreliable, even though you can use them in a keyboard macro: when the macro replays the mouse event, it uses the original mouse position of that event, the position that the mouse had while you were defining the macro. The effect of this may be hard to predict.

The command C-x C-k r (apply-macro-to-region-lines) repeats the last defined keyboard macro on each line that begins in the region. It does this line by line, by moving point to the beginning of the line and then executing the macro.

In addition to the <F3> and <F4> commands described above, Emacs also supports an older set of key bindings for defining and executing keyboard macros. To begin a macro definition, type C-x ( (kmacro-start-macro); as with <F3>, a prefix argument appends this definition to the last keyboard macro. To end a macro definition, type C-x ) (kmacro-end-macro). To execute the most recent macro, type C-x e (kmacro-end-and-call-macro). If you enter C-x e while defining a macro, the macro is terminated and executed immediately. Immediately after typing C-x e, you can type <e> repeatedly to immediately repeat the macro one or more times. You can also give C-x e a repeat argument, just like <F4>.

C-x ) can be given a repeat count as an argument. This means to repeat the macro right after defining it. The macro definition itself counts as the first repetition, since it is executed as you define it, so C-u 4 C-x ) executes the macro immediately 3 additional times.

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17.2 The Keyboard Macro Ring

All defined keyboard macros are recorded in the keyboard macro ring. There is only one keyboard macro ring, shared by all buffers.

C-x C-k C-k
Execute the keyboard macro at the head of the ring (kmacro-end-or-call-macro-repeat).
C-x C-k C-n
Rotate the keyboard macro ring to the next macro (defined earlier) (kmacro-cycle-ring-next).
C-x C-k C-p
Rotate the keyboard macro ring to the previous macro (defined later) (kmacro-cycle-ring-previous).

All commands which operate on the keyboard macro ring use the same C-x C-k prefix. Most of these commands can be executed and repeated immediately after each other without repeating the C-x C-k prefix. For example, 

     C-x C-k C-p C-p C-k C-k C-k C-n C-n C-k C-p C-k C-d

will rotate the keyboard macro ring to the “second previous” macro, execute the resulting head macro three times, rotate back to the original head macro, execute that once, rotate to the “previous” macro, execute that, and finally delete it from the macro ring.

The command C-x C-k C-k (kmacro-end-or-call-macro-repeat) executes the keyboard macro at the head of the macro ring. You can repeat the macro immediately by typing another C-k, or you can rotate the macro ring immediately by typing C-n or C-p.

When a keyboard macro is being defined, C-x C-k C-k behaves like <F4> except that, immediately afterward, you can use most key bindings of this section without the C-x C-k prefix. For instance, another C-k will re-execute the macro.

The commands C-x C-k C-n (kmacro-cycle-ring-next) and C-x C-k C-p (kmacro-cycle-ring-previous) rotate the macro ring, bringing the next or previous keyboard macro to the head of the macro ring. The definition of the new head macro is displayed in the echo area. You can continue to rotate the macro ring immediately by repeating just C-n and C-p until the desired macro is at the head of the ring. To execute the new macro ring head immediately, just type C-k.

Note that Emacs treats the head of the macro ring as the “last defined keyboard macro”. For instance, <F4> will execute that macro, and C-x C-k n will give it a name.

The maximum number of macros stored in the keyboard macro ring is determined by the customizable variable kmacro-ring-max.

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17.3 The Keyboard Macro Counter

Each keyboard macro has an associated counter, which is initialized to 0 when you start defining the macro. This counter allows you to insert a number into the buffer that depends on the number of times the macro has been called. The counter is incremented each time its value is inserted into the buffer.

<F3>
In a keyboard macro definition, insert the keyboard macro counter value in the buffer (kmacro-start-macro-or-insert-counter).
C-x C-k C-i
Insert the keyboard macro counter value in the buffer (kmacro-insert-counter).
C-x C-k C-c
Set the keyboard macro counter (kmacro-set-counter).
C-x C-k C-a
Add the prefix arg to the keyboard macro counter (kmacro-add-counter).
C-x C-k C-f
Specify the format for inserting the keyboard macro counter (kmacro-set-format).

When you are defining a keyboard macro, the command <F3> (kmacro-start-macro-or-insert-counter) inserts the current value of the keyboard macro's counter into the buffer, and increments the counter by 1. (If you are not defining a macro, <F3> begins a macro definition instead. See Basic Keyboard Macro.) You can use a numeric prefix argument to specify a different increment. If you just specify a C-u prefix, that is the same as an increment of zero: it inserts the current counter value without changing it.

As an example, let us show how the keyboard macro counter can be used to build a numbered list. Consider the following key sequence: 

     <F3> C-a <F3> . <SPC> <F4>

As part of this keyboard macro definition, the string ‘0. ’ was inserted into the beginning of the current line. If you now move somewhere else in the buffer and type <F4> to invoke the macro, the string ‘1. ’ is inserted at the beginning of that line. Subsequent invocations insert ‘2. ’, ‘3. ’, and so forth.

The command C-x C-k C-i (kmacro-insert-counter) does the same thing as <F3>, but it can be used outside a keyboard macro definition. When no keyboard macro is being defined or executed, it inserts and increments the counter of the macro at the head of the keyboard macro ring.

The command C-x C-k C-c (kmacro-set-counter) sets the current macro counter to the value of the numeric argument. If you use it inside the macro, it operates on each repetition of the macro. If you specify just C-u as the prefix, while executing the macro, that resets the counter to the value it had at the beginning of the current repetition of the macro (undoing any increments so far in this repetition).

The command C-x C-k C-a (kmacro-add-counter) adds the prefix argument to the current macro counter. With just C-u as argument, it resets the counter to the last value inserted by any keyboard macro. (Normally, when you use this, the last insertion will be in the same macro and it will be the same counter.)

The command C-x C-k C-f (kmacro-set-format) prompts for the format to use when inserting the macro counter. The default format is ‘%d’, which means to insert the number in decimal without any padding. You can exit with empty minibuffer to reset the format to this default. You can specify any format string that the format function accepts and that makes sense with a single integer extra argument (see Formatting Strings). Do not put the format string inside double quotes when you insert it in the minibuffer.

If you use this command while no keyboard macro is being defined or executed, the new format affects all subsequent macro definitions. Existing macros continue to use the format in effect when they were defined. If you set the format while defining a keyboard macro, this affects the macro being defined from that point on, but it does not affect subsequent macros. Execution of the macro will, at each step, use the format in effect at that step during its definition. Changes to the macro format during execution of a macro, like the corresponding changes during its definition, have no effect on subsequent macros.

The format set by C-x C-k C-f does not affect insertion of numbers stored in registers.

If you use a register as a counter, incrementing it on each repetition of the macro, that accomplishes the same thing as a keyboard macro counter. See Number Registers. For most purposes, it is simpler to use a keyboard macro counter.

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17.4 Executing Macros with Variations

In a keyboard macro, you can create an effect similar to that of query-replace, in that the macro asks you each time around whether to make a change.

C-x q
When this point is reached during macro execution, ask for confirmation (kbd-macro-query).

While defining the macro, type C-x q at the point where you want the query to occur. During macro definition, the C-x q does nothing, but when you run the macro later, C-x q asks you interactively whether to continue.

The valid responses when C-x q asks are:

<SPC> (or y)
Continue executing the keyboard macro.
<DEL> (or n)
Skip the remainder of this repetition of the macro, and start right away with the next repetition.
<RET> (or q)
Skip the remainder of this repetition and cancel further repetitions.
C-r
Enter a recursive editing level, in which you can perform editing which is not part of the macro. When you exit the recursive edit using C-M-c, you are asked again how to continue with the keyboard macro. If you type a <SPC> at this time, the rest of the macro definition is executed. It is up to you to leave point and the text in a state such that the rest of the macro will do what you want.

C-u C-x q, which is C-x q with a numeric argument, performs a completely different function. It enters a recursive edit reading input from the keyboard, both when you type it during the definition of the macro, and when it is executed from the macro. During definition, the editing you do inside the recursive edit does not become part of the macro. During macro execution, the recursive edit gives you a chance to do some particularized editing on each repetition. See Recursive Edit.

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17.5 Naming and Saving Keyboard Macros

C-x C-k n
Give a command name (for the duration of the Emacs session) to the most recently defined keyboard macro (kmacro-name-last-macro).
C-x C-k b
Bind the most recently defined keyboard macro to a key sequence (for the duration of the session) (kmacro-bind-to-key).
M-x insert-kbd-macro
Insert in the buffer a keyboard macro's definition, as Lisp code.

If you wish to save a keyboard macro for later use, you can give it a name using C-x C-k n (kmacro-name-last-macro). This reads a name as an argument using the minibuffer and defines that name to execute the last keyboard macro, in its current form. (If you later add to the definition of this macro, that does not alter the name's definition as a macro.) The macro name is a Lisp symbol, and defining it in this way makes it a valid command name for calling with M-x or for binding a key to with global-set-key (see Keymaps). If you specify a name that has a prior definition other than a keyboard macro, an error message is shown and nothing is changed.

You can also bind the last keyboard macro (in its current form) to a key, using C-x C-k b (kmacro-bind-to-key) followed by the key sequence you want to bind. You can bind to any key sequence in the global keymap, but since most key sequences already have other bindings, you should select the key sequence carefully. If you try to bind to a key sequence with an existing binding (in any keymap), this command asks you for confirmation before replacing the existing binding.

To avoid problems caused by overriding existing bindings, the key sequences C-x C-k 0 through C-x C-k 9 and C-x C-k A through C-x C-k Z are reserved for your own keyboard macro bindings. In fact, to bind to one of these key sequences, you only need to type the digit or letter rather than the whole key sequences. For example, 

     C-x C-k b 4

will bind the last keyboard macro to the key sequence C-x C-k 4.

Once a macro has a command name, you can save its definition in a file. Then it can be used in another editing session. First, visit the file you want to save the definition in. Then use this command: 

     M-x insert-kbd-macro <RET> macroname <RET>

This inserts some Lisp code that, when executed later, will define the same macro with the same definition it has now. (You need not understand Lisp code to do this, because insert-kbd-macro writes the Lisp code for you.) Then save the file. You can load the file later with load-file (see Lisp Libraries). If the file you save in is your init file ~/.emacs (see Init File) then the macro will be defined each time you run Emacs.

If you give insert-kbd-macro a numeric argument, it makes additional Lisp code to record the keys (if any) that you have bound to macroname, so that the macro will be reassigned the same keys when you load the file.

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17.6 Editing a Keyboard Macro

C-x C-k C-e
Edit the last defined keyboard macro (kmacro-edit-macro).
C-x C-k e name <RET>
Edit a previously defined keyboard macro name (edit-kbd-macro).
C-x C-k l
Edit the last 300 keystrokes as a keyboard macro (kmacro-edit-lossage).

You can edit the last keyboard macro by typing C-x C-k C-e or C-x C-k <RET> (kmacro-edit-macro). This formats the macro definition in a buffer and enters a specialized major mode for editing it. Type C-h m once in that buffer to display details of how to edit the macro. When you are finished editing, type C-c C-c.

You can edit a named keyboard macro or a macro bound to a key by typing C-x C-k e (edit-kbd-macro). Follow that with the keyboard input that you would use to invoke the macro—C-x e or M-x name or some other key sequence.

You can edit the last 300 keystrokes as a macro by typing C-x C-k l (kmacro-edit-lossage).

Previous: Edit Keyboard Macro, Up: Keyboard Macros

17.7 Stepwise Editing a Keyboard Macro

You can interactively replay and edit the last keyboard macro, one command at a time, by typing C-x C-k SPC (kmacro-step-edit-macro). Unless you quit the macro using q or C-g, the edited macro replaces the last macro on the macro ring.

This macro editing feature shows the last macro in the minibuffer together with the first (or next) command to be executed, and prompts you for an action. You can enter ? to get a summary of your options. These actions are available:

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18 File Handling

The operating system stores data permanently in named files, so most of the text you edit with Emacs comes from a file and is ultimately stored in a file.

To edit a file, you must tell Emacs to read the file and prepare a buffer containing a copy of the file's text. This is called visiting the file. Editing commands apply directly to text in the buffer; that is, to the copy inside Emacs. Your changes appear in the file itself only when you save the buffer back into the file.

In addition to visiting and saving files, Emacs can delete, copy, rename, and append to files, keep multiple versions of them, and operate on file directories.

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18.1 File Names

Many Emacs commands that operate on a file require you to specify the file name, using the minibuffer (see Minibuffer File).

While in the minibuffer, you can use the usual completion and history commands (see Minibuffer). Note that file name completion ignores file names whose extensions appear in the variable completion-ignored-extensions (see Completion Options). Note also that most commands use “permissive completion with confirmation” for reading file names: you are allowed to submit a nonexistent file name, but if you type <RET> immediately after completing up to a nonexistent file name, Emacs prints ‘[Confirm]’ and you must type a second <RET> to confirm. See Completion Exit, for details.

Each buffer has a default directory, stored in the buffer-local variable default-directory. Whenever Emacs reads a file name using the minibuffer, it usually inserts the default directory into the minibuffer as the initial contents. You can inhibit this insertion by changing the variable insert-default-directory to nil (see Minibuffer File). Regardless, Emacs always assumes that any relative file name is relative to the default directory, e.g., entering a file name without a directory specifies a file in the default directory.

When you visit a file, Emacs sets default-directory in the visiting buffer to the directory of its file. When you create a new buffer that is not visiting a file, via a command like C-x b, its default directory is usually copied from the buffer that was current at the time (see Select Buffer). You can use the command M-x pwd to see the value of default-directory in the current buffer. The command M-x cd prompts for a directory name, and sets the buffer's default-directory to that directory (doing this does not change the buffer's file name, if any).

As an example, when you visit the file /u/rms/gnu/gnu.tasks, the default directory is set to /u/rms/gnu/. If you invoke a command that reads a file name, entering just ‘foo’ in the minibuffer, with a directory omitted, specifies the file /u/rms/gnu/foo; entering ‘../.login’ specifies /u/rms/.login; and entering ‘new/foo’ specifies /u/rms/gnu/new/foo.

When typing a file name into the minibuffer, you can make use of a couple of shortcuts: a double slash is interpreted as “ignore everything before the second slash in the pair”, and ‘~/’ is interpreted as your home directory. See Minibuffer File.

The character ‘$’ is used to substitute an environment variable into a file name. The name of the environment variable consists of all the alphanumeric characters after the ‘$’; alternatively, it can be enclosed in braces after the ‘$’. For example, if you have used the shell command export FOO=rms/hacks to set up an environment variable named FOO, then both /u/$FOO/test.c and /u/${FOO}/test.c are abbreviations for /u/rms/hacks/test.c. If the environment variable is not defined, no substitution occurs, so that the character ‘$’ stands for itself. Note that environment variables affect Emacs only if they are applied before Emacs is started.

To access a file with ‘$’ in its name, if the ‘$’ causes expansion, type ‘$$’. This pair is converted to a single ‘$’ at the same time that variable substitution is performed for a single ‘$’. Alternatively, quote the whole file name with ‘/:’ (see Quoted File Names). File names which begin with a literal ‘~’ should also be quoted with ‘/:’.

You can include non-ASCII characters in file names. See File Name Coding.

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18.2 Visiting Files

C-x C-f
Visit a file (find-file).
C-x C-r
Visit a file for viewing, without allowing changes to it (find-file-read-only).
C-x C-v
Visit a different file instead of the one visited last (find-alternate-file).
C-x 4 f
Visit a file, in another window (find-file-other-window). Don't alter what is displayed in the selected window.
C-x 5 f
Visit a file, in a new frame (find-file-other-frame). Don't alter what is displayed in the selected frame.
M-x find-file-literally
Visit a file with no conversion of the contents.

Visiting a file means reading its contents into an Emacs buffer so you can edit them. Emacs makes a new buffer for each file that you visit.

To visit a file, type C-x C-f (find-file) and use the minibuffer to enter the name of the desired file. While in the minibuffer, you can abort the command by typing C-g. See File Names, for details about entering file names into minibuffers.

If the specified file exists but the system does not allow you to read it, an error message is displayed in the echo area. Otherwise, you can tell that C-x C-f has completed successfully by the appearance of new text on the screen, and by the buffer name shown in the mode line (see Mode Line). Emacs normally constructs the buffer name from the file name, omitting the directory name. For example, a file named /usr/rms/emacs.tex is visited in a buffer named ‘emacs.tex’. If there is already a buffer with that name, Emacs constructs a unique name; the normal method is to append ‘<2>’, ‘<3>’, and so on, but you can select other methods. See Uniquify.

To create a new file, just visit it using the same command, C-x C-f. Emacs displays ‘(New file)’ in the echo area, but in other respects behaves as if you had visited an existing empty file.

After visiting a file, the changes you make with editing commands are made in the Emacs buffer. They do not take effect in the visited file, until you save the buffer (see Saving). If a buffer contains changes that have not been saved, we say the buffer is modified. This implies that some changes will be lost if the buffer is not saved. The mode line displays two stars near the left margin to indicate that the buffer is modified.

If you visit a file that is already in Emacs, C-x C-f switches to the existing buffer instead of making another copy. Before doing so, it checks whether the file has changed since you last visited or saved it. If the file has changed, Emacs offers to reread it.

If you try to visit a file larger than large-file-warning-threshold (the default is 10000000, which is about 10 megabytes), Emacs asks you for confirmation first. You can answer y to proceed with visiting the file. Note, however, that Emacs cannot visit files that are larger than the maximum Emacs buffer size, which is limited by the amount of memory Emacs can allocate and by the integers that Emacs can represent (see Buffers). If you try, Emacs displays an error message saying that the maximum buffer size has been exceeded.

If the file name you specify contains shell-style wildcard characters, Emacs visits all the files that match it. (On case-insensitive filesystems, Emacs matches the wildcards disregarding the letter case.) Wildcards include ‘?’, ‘*’, and ‘[...]’ sequences. To enter the wild card ‘?’ in a file name in the minibuffer, you need to type C-q ?. See Quoted File Names, for information on how to visit a file whose name actually contains wildcard characters. You can disable the wildcard feature by customizing find-file-wildcards.

If you visit the wrong file unintentionally by typing its name incorrectly, type C-x C-v (find-alternate-file) to visit the file you really wanted. C-x C-v is similar to C-x C-f, but it kills the current buffer (after first offering to save it if it is modified). When C-x C-v reads the file name to visit, it inserts the entire default file name in the buffer, with point just after the directory part; this is convenient if you made a slight error in typing the name.

If you “visit” a file that is actually a directory, Emacs invokes Dired, the Emacs directory browser. See Dired. You can disable this behavior by setting the variable find-file-run-dired to nil; in that case, it is an error to try to visit a directory.

Files which are actually collections of other files, or file archives, are visited in special modes which invoke a Dired-like environment to allow operations on archive members. See File Archives, for more about these features.

If you visit a file that the operating system won't let you modify, or that is marked read-only, Emacs makes the buffer read-only too, so that you won't go ahead and make changes that you'll have trouble saving afterward. You can make the buffer writable with C-x C-q (read-only-mode). See Misc Buffer.

If you want to visit a file as read-only in order to protect yourself from entering changes accidentally, visit it with the command C-x C-r (find-file-read-only) instead of C-x C-f.

C-x 4 f (find-file-other-window) is like C-x C-f except that the buffer containing the specified file is selected in another window. The window that was selected before C-x 4 f continues to show the same buffer it was already showing. If this command is used when only one window is being displayed, that window is split in two, with one window showing the same buffer as before, and the other one showing the newly requested file. See Windows.

C-x 5 f (find-file-other-frame) is similar, but opens a new frame, or selects any existing frame showing the specified file. See Frames.

On graphical displays, there are two additional methods for visiting files. Firstly, when Emacs is built with a suitable GUI toolkit, commands invoked with the mouse (by clicking on the menu bar or tool bar) use the toolkit's standard “File Selection” dialog instead of prompting for the file name in the minibuffer. On GNU/Linux and Unix platforms, Emacs does this when built with GTK, LessTif, and Motif toolkits; on MS-Windows and Mac, the GUI version does that by default. For information on how to customize this, see Dialog Boxes.

Secondly, Emacs supports “drag and drop”: dropping a file into an ordinary Emacs window visits the file using that window. As an exception, dropping a file into a window displaying a Dired buffer moves or copies the file into the displayed directory. For details, see Drag and Drop, and Misc Dired Features.

Each time you visit a file, Emacs automatically scans its contents to detect what character encoding and end-of-line convention it uses, and converts these to Emacs's internal encoding and end-of-line convention within the buffer. When you save the buffer, Emacs performs the inverse conversion, writing the file to disk with its original encoding and end-of-line convention. See Coding Systems.

If you wish to edit a file as a sequence of ASCII characters with no special encoding or conversion, use the M-x find-file-literally command. This visits a file, like C-x C-f, but does not do format conversion (see Format Conversion), character code conversion (see Coding Systems), or automatic uncompression (see Compressed Files), and does not add a final newline because of require-final-newline (see Customize Save). If you have already visited the same file in the usual (non-literal) manner, this command asks you whether to visit it literally instead.

Two special hook variables allow extensions to modify the operation of visiting files. Visiting a file that does not exist runs the functions in find-file-not-found-functions; this variable holds a list of functions, which are called one by one (with no arguments) until one of them returns non-nil. This is not a normal hook, and the name ends in ‘-functions’ rather than ‘-hook’ to indicate that fact.

Successful visiting of any file, whether existing or not, calls the functions in find-file-hook, with no arguments. This variable is a normal hook. In the case of a nonexistent file, the find-file-not-found-functions are run first. See Hooks.

There are several ways to specify automatically the major mode for editing the file (see Choosing Modes), and to specify local variables defined for that file (see File Variables).

Next: , Previous: Visiting, Up: Files

18.3 Saving Files

Saving a buffer in Emacs means writing its contents back into the file that was visited in the buffer.

Next: , Up: Saving

18.3.1 Commands for Saving Files

These are the commands that relate to saving and writing files.

C-x C-s
Save the current buffer to its file (save-buffer).
C-x s
Save any or all buffers to their files (save-some-buffers).
M-~
Forget that the current buffer has been changed (not-modified). With prefix argument (C-u), mark the current buffer as changed.
C-x C-w
Save the current buffer with a specified file name (write-file).
M-x set-visited-file-name
Change the file name under which the current buffer will be saved.

When you wish to save the file and make your changes permanent, type C-x C-s (save-buffer). After saving is finished, C-x C-s displays a message like this: 

     Wrote /u/rms/gnu/gnu.tasks

If the current buffer is not modified (no changes have been made in it since the buffer was created or last saved), saving is not really done, because it would have no effect. Instead, C-x C-s displays a message like this in the echo area: 

     (No changes need to be saved)

With a prefix argument, C-u C-x C-s, Emacs also marks the buffer to be backed up when the next save is done. See Backup.

The command C-x s (save-some-buffers) offers to save any or all modified buffers. It asks you what to do with each buffer. The possible responses are analogous to those of query-replace:

y
Save this buffer and ask about the rest of the buffers.
n
Don't save this buffer, but ask about the rest of the buffers.
!
Save this buffer and all the rest with no more questions.
<RET>
Terminate save-some-buffers without any more saving.
.
Save this buffer, then exit save-some-buffers without even asking about other buffers.
C-r
View the buffer that you are currently being asked about. When you exit View mode, you get back to save-some-buffers, which asks the question again.
d
Diff the buffer against its corresponding file, so you can see what changes you would be saving. This calls the command diff-buffer-with-file (see Comparing Files).
C-h
Display a help message about these options.

C-x C-c, the key sequence to exit Emacs, invokes save-some-buffers and therefore asks the same questions.

If you have changed a buffer but do not wish to save the changes, you should take some action to prevent it. Otherwise, each time you use C-x s or C-x C-c, you are liable to save this buffer by mistake. One thing you can do is type M-~ (not-modified), which clears out the indication that the buffer is modified. If you do this, none of the save commands will believe that the buffer needs to be saved. (‘~’ is often used as a mathematical symbol for `not'; thus M-~ is `not', metafied.) Alternatively, you can cancel all the changes made since the file was visited or saved, by reading the text from the file again. This is called reverting. See Reverting. (You could also undo all the changes by repeating the undo command C-x u until you have undone all the changes; but reverting is easier.)

M-x set-visited-file-name alters the name of the file that the current buffer is visiting. It reads the new file name using the minibuffer. Then it marks the buffer as visiting that file name, and changes the buffer name correspondingly. set-visited-file-name does not save the buffer in the newly visited file; it just alters the records inside Emacs in case you do save later. It also marks the buffer as “modified” so that C-x C-s in that buffer will save.

If you wish to mark the buffer as visiting a different file and save it right away, use C-x C-w (write-file). This is equivalent to set-visited-file-name followed by C-x C-s, except that C-x C-w asks for confirmation if the file exists. C-x C-s used on a buffer that is not visiting a file has the same effect as C-x C-w; that is, it reads a file name, marks the buffer as visiting that file, and saves it there. The default file name in a buffer that is not visiting a file is made by combining the buffer name with the buffer's default directory (see File Names).

If the new file name implies a major mode, then C-x C-w switches to that major mode, in most cases. The command set-visited-file-name also does this. See Choosing Modes.

If Emacs is about to save a file and sees that the date of the latest version on disk does not match what Emacs last read or wrote, Emacs notifies you of this fact, because it probably indicates a problem caused by simultaneous editing and requires your immediate attention. See Simultaneous Editing.

Next: , Previous: Save Commands, Up: Saving

18.3.2 Backup Files

On most operating systems, rewriting a file automatically destroys all record of what the file used to contain. Thus, saving a file from Emacs throws away the old contents of the file—or it would, except that Emacs carefully copies the old contents to another file, called the backup file, before actually saving.

Emacs makes a backup for a file only the first time the file is saved from a buffer. No matter how many times you subsequently save the file, its backup remains unchanged. However, if you kill the buffer and then visit the file again, a new backup file will be made.

For most files, the variable make-backup-files determines whether to make backup files. On most operating systems, its default value is t, so that Emacs does write backup files.

For files managed by a version control system (see Version Control), the variable vc-make-backup-files determines whether to make backup files. By default it is nil, since backup files are redundant when you store all the previous versions in a version control system. See General VC Options.

At your option, Emacs can keep either a single backup for each file, or make a series of numbered backup files for each file that you edit. See Backup Names.

The default value of the backup-enable-predicate variable prevents backup files being written for files in the directories used for temporary files, specified by temporary-file-directory or small-temporary-file-directory.

You can explicitly tell Emacs to make another backup file from a buffer, even though that buffer has been saved before. If you save the buffer with C-u C-x C-s, the version thus saved will be made into a backup file if you save the buffer again. C-u C-u C-x C-s saves the buffer, but first makes the previous file contents into a new backup file. C-u C-u C-u C-x C-s does both things: it makes a backup from the previous contents, and arranges to make another from the newly saved contents if you save again.

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18.3.2.1 Single or Numbered Backups

When Emacs makes a backup file, its name is normally constructed by appending ‘~’ to the file name being edited; thus, the backup file for eval.c would be eval.c~.

If access control stops Emacs from writing backup files under the usual names, it writes the backup file as ~/.emacs.d/%backup%~. Only one such file can exist, so only the most recently made such backup is available.

Emacs can also make numbered backup files. Numbered backup file names contain ‘.~’, the number, and another ‘~’ after the original file name. Thus, the backup files of eval.c would be called eval.c.~1~, eval.c.~2~, and so on, all the way through names like eval.c.~259~ and beyond.

The variable version-control determines whether to make single backup files or multiple numbered backup files. Its possible values are:

nil
Make numbered backups for files that have numbered backups already. Otherwise, make single backups. This is the default.
t
Make numbered backups.
never
Never make numbered backups; always make single backups.

The usual way to set this variable is globally, through your init file or the customization buffer. However, you can set version-control locally in an individual buffer to control the making of backups for that buffer's file (see Locals). You can have Emacs set version-control locally whenever you visit a given file (see File Variables). Some modes, such as Rmail mode, set this variable.

If you set the environment variable VERSION_CONTROL, to tell various GNU utilities what to do with backup files, Emacs also obeys the environment variable by setting the Lisp variable version-control accordingly at startup. If the environment variable's value is ‘t’ or ‘numbered’, then version-control becomes t; if the value is ‘nil’ or ‘existing’, then version-control becomes nil; if it is ‘never’ or ‘simple’, then version-control becomes never.

You can customize the variable backup-directory-alist to specify that files matching certain patterns should be backed up in specific directories. This variable applies to both single and numbered backups. A typical use is to add an element ("." . dir) to make all backups in the directory with absolute name dir; Emacs modifies the backup file names to avoid clashes between files with the same names originating in different directories. Alternatively, adding, ("." . ".~") would make backups in the invisible subdirectory .~ of the original file's directory. Emacs creates the directory, if necessary, to make the backup.

If you define the variable make-backup-file-name-function to a suitable Lisp function, that overrides the usual way Emacs constructs backup file names.

Next: , Previous: Backup Names, Up: Backup

18.3.2.2 Automatic Deletion of Backups

To prevent excessive consumption of disk space, Emacs can delete numbered backup versions automatically. Generally Emacs keeps the first few backups and the latest few backups, deleting any in between. This happens every time a new backup is made.

The two variables kept-old-versions and kept-new-versions control this deletion. Their values are, respectively, the number of oldest (lowest-numbered) backups to keep and the number of newest (highest-numbered) ones to keep, each time a new backup is made. The backups in the middle (excluding those oldest and newest) are the excess middle versions—those backups are deleted. These variables' values are used when it is time to delete excess versions, just after a new backup version is made; the newly made backup is included in the count in kept-new-versions. By default, both variables are 2.

If delete-old-versions is t, Emacs deletes the excess backup files silently. If it is nil, the default, Emacs asks you whether it should delete the excess backup versions. If it has any other value, then Emacs never automatically deletes backups.

Dired's . (Period) command can also be used to delete old versions. See Dired Deletion.

Previous: Backup Deletion, Up: Backup

18.3.2.3 Copying vs. Renaming

Backup files can be made by copying the old file or by renaming it. This makes a difference when the old file has multiple names (hard links). If the old file is renamed into the backup file, then the alternate names become names for the backup file. If the old file is copied instead, then the alternate names remain names for the file that you are editing, and the contents accessed by those names will be the new contents.

The method of making a backup file may also affect the file's owner and group. If copying is used, these do not change. If renaming is used, you become the file's owner, and the file's group becomes the default (different operating systems have different defaults for the group).

The choice of renaming or copying is made as follows:

When a file is managed with a version control system (see Version Control), Emacs does not normally make backups in the usual way for that file. But check-in and check-out are similar in some ways to making backups. One unfortunate similarity is that these operations typically break hard links, disconnecting the file name you visited from any alternate names for the same file. This has nothing to do with Emacs—the version control system does it.

Next: , Previous: Backup, Up: Saving

18.3.3 Customizing Saving of Files

If the value of the variable require-final-newline is t, saving or writing a file silently puts a newline at the end if there isn't already one there. If the value is visit, Emacs adds a newline at the end of any file that doesn't have one, just after it visits the file. (This marks the buffer as modified, and you can undo it.) If the value is visit-save, Emacs adds such newlines both on visiting and on saving. If the value is nil, Emacs leaves the end of the file unchanged; any other non-nil value means to asks you whether to add a newline. The default is nil.

Some major modes are designed for specific kinds of files that are always supposed to end in newlines. Such major modes set the variable require-final-newline to the value of mode-require-final-newline, which defaults to t. By setting the latter variable, you can control how these modes handle final newlines.

When Emacs saves a file, it invokes the fsync system call to force the data immediately out to disk. This is important for safety if the system crashes or in case of power outage. However, it can be disruptive on laptops using power saving, as it may force a disk spin-up each time you save a file. If you accept an increased risk of data loss, you can set write-region-inhibit-fsync to a non-nil value to disable the synchronization.

Next: , Previous: Customize Save, Up: Saving

18.3.4 Protection against Simultaneous Editing

Simultaneous editing occurs when two users visit the same file, both make changes, and then both save them. If nobody is informed that this is happening, whichever user saves first would later find that his changes were lost.

On some systems, Emacs notices immediately when the second user starts to change the file, and issues an immediate warning. On all systems, Emacs checks when you save the file, and warns if you are about to overwrite another user's changes. You can prevent loss of the other user's work by taking the proper corrective action instead of saving the file.

When you make the first modification in an Emacs buffer that is visiting a file, Emacs records that the file is locked by you. (It does this by creating a specially-named symbolic link in the same directory.) Emacs removes the lock when you save the changes. The idea is that the file is locked whenever an Emacs buffer visiting it has unsaved changes.

You can prevent the creation of lock files by setting the variable create-lockfiles to nil. Caution: by doing so you will lose the benefits that this feature provides.

If you begin to modify the buffer while the visited file is locked by someone else, this constitutes a collision. When Emacs detects a collision, it asks you what to do, by calling the Lisp function ask-user-about-lock. You can redefine this function for the sake of customization. The standard definition of this function asks you a question and accepts three possible answers:

s
Steal the lock. Whoever was already changing the file loses the lock, and you gain the lock.
p
Proceed. Go ahead and edit the file despite its being locked by someone else.
q
Quit. This causes an error (file-locked), and the buffer contents remain unchanged—the modification you were trying to make does not actually take place.

If Emacs or the operating system crashes, this may leave behind lock files which are stale, so you may occasionally get warnings about spurious collisions. When you determine that the collision is spurious, just use p to tell Emacs to go ahead anyway.

Note that locking works on the basis of a file name; if a file has multiple names, Emacs does not prevent two users from editing it simultaneously under different names.

A lock file cannot be written in some circumstances, e.g., if Emacs lacks the system permissions or the system does not support symbolic links. In these cases, Emacs can still detect the collision when you try to save a file, by checking the file's last-modification date. If the file has changed since the last time Emacs visited or saved it, that implies that changes have been made in some other way, and will be lost if Emacs proceeds with saving. Emacs then displays a warning message and asks for confirmation before saving; answer yes to save, and no or C-g cancel the save.

If you are notified that simultaneous editing has already taken place, one way to compare the buffer to its file is the M-x diff-buffer-with-file command. See Comparing Files.

Next: , Previous: Interlocking, Up: Saving

18.3.5 Shadowing Files

M-x shadow-initialize
Set up file shadowing.
M-x shadow-define-literal-group
Declare a single file to be shared between sites.
M-x shadow-define-regexp-group
Make all files that match each of a group of files be shared between hosts.
M-x shadow-define-cluster <RET> name <RET>
Define a shadow file cluster name.
M-x shadow-copy-files
Copy all pending shadow files.
M-x shadow-cancel
Cancel the instruction to shadow some files.

You can arrange to keep identical shadow copies of certain files in more than one place—possibly on different machines. To do this, first you must set up a shadow file group, which is a set of identically-named files shared between a list of sites. The file group is permanent and applies to further Emacs sessions as well as the current one. Once the group is set up, every time you exit Emacs, it will copy the file you edited to the other files in its group. You can also do the copying without exiting Emacs, by typing M-x shadow-copy-files.

To set up a shadow file group, use M-x shadow-define-literal-group or M-x shadow-define-regexp-group. See their documentation strings for further information.

Before copying a file to its shadows, Emacs asks for confirmation. You can answer “no” to bypass copying of this file, this time. If you want to cancel the shadowing permanently for a certain file, use M-x shadow-cancel to eliminate or change the shadow file group.

A shadow cluster is a group of hosts that share directories, so that copying to or from one of them is sufficient to update the file on all of them. Each shadow cluster has a name, and specifies the network address of a primary host (the one we copy files to), and a regular expression that matches the host names of all the other hosts in the cluster. You can define a shadow cluster with M-x shadow-define-cluster.

Previous: File Shadowing, Up: Saving

18.3.6 Updating Time Stamps Automatically

You can arrange to put a time stamp in a file, so that it is updated automatically each time you edit and save the file. The time stamp must be in the first eight lines of the file, and you should insert it like this: 

     Time-stamp: <>

or like this: 

     Time-stamp: " "

Then add the function time-stamp to the hook before-save-hook (see Hooks). When you save the file, this function then automatically updates the time stamp with the current date and time. You can also use the command M-x time-stamp to update the time stamp manually. For other customizations, see the Custom group time-stamp. Note that the time stamp is formatted according to your locale setting (see Environment).

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18.4 Reverting a Buffer

If you have made extensive changes to a file-visiting buffer and then change your mind, you can revert the changes and go back to the saved version of the file. To do this, type M-x revert-buffer. Since reverting unintentionally could lose a lot of work, Emacs asks for confirmation first.

The revert-buffer command tries to position point in such a way that, if the file was edited only slightly, you will be at approximately the same part of the text as before. But if you have made major changes, point may end up in a totally different location.

Reverting marks the buffer as “not modified”. It also clears the buffer's undo history (see Undo). Thus, the reversion cannot be undone—if you change your mind yet again, you can't use the undo commands to bring the reverted changes back.

Some kinds of buffers that are not associated with files, such as Dired buffers, can also be reverted. For them, reverting means recalculating their contents. Buffers created explicitly with C-x b cannot be reverted; revert-buffer reports an error if you try.

When you edit a file that changes automatically and frequently—for example, a log of output from a process that continues to run—it may be useful for Emacs to revert the file without querying you. To request this behavior, set the variable revert-without-query to a list of regular expressions. When a file name matches one of these regular expressions, find-file and revert-buffer will revert it automatically if it has changed—provided the buffer itself is not modified. (If you have edited the text, it would be wrong to discard your changes.)

You can also tell Emacs to revert buffers periodically. To do this for a specific buffer, enable the minor mode Auto-Revert mode by typing M-x auto-revert-mode. This automatically reverts the current buffer every five seconds; you can change the interval through the variable auto-revert-interval. To do the same for all file buffers, type M-x global-auto-revert-mode to enable Global Auto-Revert mode. These minor modes do not check or revert remote files, because that is usually too slow.

One use of Auto-Revert mode is to “tail” a file such as a system log, so that changes made to that file by other programs are continuously displayed. To do this, just move the point to the end of the buffer, and it will stay there as the file contents change. However, if you are sure that the file will only change by growing at the end, use Auto-Revert Tail mode instead (auto-revert-tail-mode). It is more efficient for this. Auto-Revert Tail mode works also for remote files.

See VC Undo, for commands to revert to earlier versions of files under version control. See VC Mode Line, for Auto Revert peculiarities when visiting files under version control.

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18.5 Auto Reverting Non-File Buffers

Global Auto Revert Mode normally only reverts file buffers. There are two ways to auto-revert certain non-file buffers: by enabling Auto Revert Mode in those buffers (using M-x auto-revert-mode); and by setting global-auto-revert-non-file-buffers to a non-nil value. The latter enables Auto Reverting for all types of buffers for which it is implemented (listed in the menu below).

Like file buffers, non-file buffers should normally not revert while you are working on them, or while they contain information that might get lost after reverting. Therefore, they do not revert if they are “modified”. This can get tricky, because deciding when a non-file buffer should be marked modified is usually more difficult than for file buffers.

Another tricky detail is that, for efficiency reasons, Auto Revert often does not try to detect all possible changes in the buffer, only changes that are “major” or easy to detect. Hence, enabling auto-reverting for a non-file buffer does not always guarantee that all information in the buffer is up-to-date, and does not necessarily make manual reverts useless.

At the other extreme, certain buffers automatically revert every auto-revert-interval seconds. (This currently only applies to the Buffer Menu.) In this case, Auto Revert does not print any messages while reverting, even when auto-revert-verbose is non-nil.

The details depend on the particular types of buffers and are explained in the corresponding sections.

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18.5.1 Auto Reverting the Buffer Menu

If auto-reverting of non-file buffers is enabled, the Buffer Menu automatically reverts every auto-revert-interval seconds, whether there is a need for it or not. (It would probably take longer to check whether there is a need than to actually revert.)

If the Buffer Menu inappropriately gets marked modified, just revert it manually using g and auto-reverting will resume. However, if you marked certain buffers to get deleted or to be displayed, you have to be careful, because reverting erases all marks. The fact that adding marks sets the buffer's modified flag prevents Auto Revert from automatically erasing the marks.

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18.5.2 Auto Reverting Dired buffers

Auto-reverting Dired buffers currently works on GNU or Unix style operating systems. It may not work satisfactorily on some other systems.

Dired buffers only auto-revert when the file list of the buffer's main directory changes (e.g., when a new file is added). They do not auto-revert when information about a particular file changes (e.g., when the size changes) or when inserted subdirectories change. To be sure that all listed information is up to date, you have to manually revert using g, even if auto-reverting is enabled in the Dired buffer. Sometimes, you might get the impression that modifying or saving files listed in the main directory actually does cause auto-reverting. This is because making changes to a file, or saving it, very often causes changes in the directory itself; for instance, through backup files or auto-save files. However, this is not guaranteed.

If the Dired buffer is marked modified and there are no changes you want to protect, then most of the time you can make auto-reverting resume by manually reverting the buffer using g. There is one exception. If you flag or mark files, you can safely revert the buffer. This will not erase the flags or marks (unless the marked file has been deleted, of course). However, the buffer will stay modified, even after reverting, and auto-reverting will not resume. This is because, if you flag or mark files, you may be working on the buffer and you might not want the buffer to change without warning. If you want auto-reverting to resume in the presence of marks and flags, mark the buffer non-modified using M-~. However, adding, deleting or changing marks or flags will mark it modified again.

Remote Dired buffers are not auto-reverted (because it may be slow). Neither are Dired buffers for which you used shell wildcards or file arguments to list only some of the files. *Find* and *Locate* buffers do not auto-revert either.

Previous: Auto Reverting Dired, Up: Autorevert

18.5.3 Adding Support for Auto-Reverting additional Buffers.

This section is intended for Elisp programmers who would like to add support for auto-reverting new types of buffers.

To support auto-reverting the buffer must first of all have a revert-buffer-function. See Reverting.

In addition, it must have a buffer-stale-function.

— Variable: buffer-stale-function

The value of this variable is a function to check whether a non-file buffer needs reverting. This should be a function with one optional argument noconfirm. The function should return non-nil if the buffer should be reverted. The buffer is current when this function is called.

While this function is mainly intended for use in auto-reverting, it could be used for other purposes as well. For instance, if auto-reverting is not enabled, it could be used to warn the user that the buffer needs reverting. The idea behind the noconfirm argument is that it should be t if the buffer is going to be reverted without asking the user and nil if the function is just going to be used to warn the user that the buffer is out of date. In particular, for use in auto-reverting, noconfirm is t. If the function is only going to be used for auto-reverting, you can ignore the noconfirm argument.

If you just want to automatically auto-revert every auto-revert-interval seconds (like the Buffer Menu), use: 

          (set (make-local-variable 'buffer-stale-function)
               #'(lambda (&optional noconfirm) 'fast))

in the buffer's mode function.

The special return value ‘fast’ tells the caller that the need for reverting was not checked, but that reverting the buffer is fast. It also tells Auto Revert not to print any revert messages, even if auto-revert-verbose is non-nil. This is important, as getting revert messages every auto-revert-interval seconds can be very annoying. The information provided by this return value could also be useful if the function is consulted for purposes other than auto-reverting.

Once the buffer has a revert-buffer-function and a buffer-stale-function, several problems usually remain.

The buffer will only auto-revert if it is marked unmodified. Hence, you will have to make sure that various functions mark the buffer modified if and only if either the buffer contains information that might be lost by reverting, or there is reason to believe that the user might be inconvenienced by auto-reverting, because he is actively working on the buffer. The user can always override this by manually adjusting the modified status of the buffer. To support this, calling the revert-buffer-function on a buffer that is marked unmodified should always keep the buffer marked unmodified.

It is important to assure that point does not continuously jump around as a consequence of auto-reverting. Of course, moving point might be inevitable if the buffer radically changes.

You should make sure that the revert-buffer-function does not print messages that unnecessarily duplicate Auto Revert's own messages, displayed if auto-revert-verbose is t, and effectively override a nil value for auto-revert-verbose. Hence, adapting a mode for auto-reverting often involves getting rid of such messages. This is especially important for buffers that automatically revert every auto-revert-interval seconds.

If the new auto-reverting is part of Emacs, you should mention it in the documentation string of global-auto-revert-non-file-buffers.

Similarly, you should add a section to this chapter. This section should at the very least make clear whether enabling auto-reverting for the buffer reliably assures that all information in the buffer is completely up to date (or will be after auto-revert-interval seconds).

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18.6 Auto-Saving: Protection Against Disasters

From time to time, Emacs automatically saves each visited file in a separate file, without altering the file you actually use. This is called auto-saving. It prevents you from losing more than a limited amount of work if the system crashes.

When Emacs determines that it is time for auto-saving, it considers each buffer, and each is auto-saved if auto-saving is enabled for it and it has been changed since the last time it was auto-saved. The message ‘Auto-saving...’ is displayed in the echo area during auto-saving, if any files are actually auto-saved. Errors occurring during auto-saving are caught so that they do not interfere with the execution of commands you have been typing.

Next: , Up: Auto Save

18.6.1 Auto-Save Files

Auto-saving does not normally save in the files that you visited, because it can be very undesirable to save a change that you did not want to make permanent. Instead, auto-saving is done in a different file called the auto-save file, and the visited file is changed only when you request saving explicitly (such as with C-x C-s).

Normally, the auto-save file name is made by appending ‘#’ to the front and rear of the visited file name. Thus, a buffer visiting file foo.c is auto-saved in a file #foo.c#. Most buffers that are not visiting files are auto-saved only if you request it explicitly; when they are auto-saved, the auto-save file name is made by appending ‘#’ to the front and rear of buffer name, then adding digits and letters at the end for uniqueness. For example, the *mail* buffer in which you compose messages to be sent might be auto-saved in a file named #*mail*#704juu. Auto-save file names are made this way unless you reprogram parts of Emacs to do something different (the functions make-auto-save-file-name and auto-save-file-name-p). The file name to be used for auto-saving in a buffer is calculated when auto-saving is turned on in that buffer.

The variable auto-save-file-name-transforms allows a degree of control over the auto-save file name. It lets you specify a series of regular expressions and replacements to transform the auto save file name. The default value puts the auto-save files for remote files (see Remote Files) into the temporary file directory on the local machine.

When you delete a substantial part of the text in a large buffer, auto save turns off temporarily in that buffer. This is because if you deleted the text unintentionally, you might find the auto-save file more useful if it contains the deleted text. To reenable auto-saving after this happens, save the buffer with C-x C-s, or use C-u 1 M-x auto-save-mode.

If you want auto-saving to be done in the visited file rather than in a separate auto-save file, set the variable auto-save-visited-file-name to a non-nil value. In this mode, there is no real difference between auto-saving and explicit saving.

A buffer's auto-save file is deleted when you save the buffer in its visited file. (You can inhibit this by setting the variable delete-auto-save-files to nil.) Changing the visited file name with C-x C-w or set-visited-file-name renames any auto-save file to go with the new visited name.

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18.6.2 Controlling Auto-Saving

Each time you visit a file, auto-saving is turned on for that file's buffer if the variable auto-save-default is non-nil (but not in batch mode; see Initial Options). The default for this variable is t, so auto-saving is the usual practice for file-visiting buffers. To toggle auto-saving in the current buffer, type M-x auto-save-mode. Auto Save mode acts as a buffer-local minor mode (see Minor Modes).

Emacs auto-saves periodically based on how many characters you have typed since the last auto-save. The variable auto-save-interval specifies how many characters there are between auto-saves. By default, it is 300. Emacs doesn't accept values that are too small: if you customize auto-save-interval to a value less than 20, Emacs will behave as if the value is 20.

Auto-saving also takes place when you stop typing for a while. By default, it does this after 30 seconds of idleness (at this time, Emacs may also perform garbage collection; see Garbage Collection). To change this interval, customize the variable auto-save-timeout. The actual time period is longer if the current buffer is long; this is a heuristic which aims to keep out of your way when you are editing long buffers, in which auto-save takes an appreciable amount of time. Auto-saving during idle periods accomplishes two things: first, it makes sure all your work is saved if you go away from the terminal for a while; second, it may avoid some auto-saving while you are actually typing.

Emacs also does auto-saving whenever it gets a fatal error. This includes killing the Emacs job with a shell command such as ‘kill %emacs’, or disconnecting a phone line or network connection.

You can perform an auto-save explicitly with the command M-x do-auto-save.

Previous: Auto Save Control, Up: Auto Save

18.6.3 Recovering Data from Auto-Saves

You can use the contents of an auto-save file to recover from a loss of data with the command M-x recover-file <RET> file <RET>. This visits file and then (after your confirmation) restores the contents from its auto-save file #file#. You can then save with C-x C-s to put the recovered text into file itself. For example, to recover file foo.c from its auto-save file #foo.c#, do: 

     M-x recover-file <RET> foo.c <RET>
     yes <RET>
     C-x C-s

Before asking for confirmation, M-x recover-file displays a directory listing describing the specified file and the auto-save file, so you can compare their sizes and dates. If the auto-save file is older, M-x recover-file does not offer to read it.

If Emacs or the computer crashes, you can recover all the files you were editing from their auto save files with the command M-x recover-session. This first shows you a list of recorded interrupted sessions. Move point to the one you choose, and type C-c C-c.

Then recover-session asks about each of the files that were being edited during that session, asking whether to recover that file. If you answer y, it calls recover-file, which works in its normal fashion. It shows the dates of the original file and its auto-save file, and asks once again whether to recover that file.

When recover-session is done, the files you've chosen to recover are present in Emacs buffers. You should then save them. Only this—saving them—updates the files themselves.

Emacs records information about interrupted sessions in files named .saves-pid-hostname in the directory ~/.emacs.d/auto-save-list/. This directory is determined by the variable auto-save-list-file-prefix. If you set auto-save-list-file-prefix to nil, sessions are not recorded for recovery.

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18.7 File Name Aliases

Symbolic links and hard links both make it possible for several file names to refer to the same file. Hard links are alternate names that refer directly to the file; all the names are equally valid, and no one of them is preferred. By contrast, a symbolic link is a kind of defined alias: when foo is a symbolic link to bar, you can use either name to refer to the file, but bar is the real name, while foo is just an alias. More complex cases occur when symbolic links point to directories.

Normally, if you visit a file which Emacs is already visiting under a different name, Emacs displays a message in the echo area and uses the existing buffer visiting that file. This can happen on systems that support hard or symbolic links, or if you use a long file name on a system that truncates long file names, or on a case-insensitive file system. You can suppress the message by setting the variable find-file-suppress-same-file-warnings to a non-nil value. You can disable this feature entirely by setting the variable find-file-existing-other-name to nil: then if you visit the same file under two different names, you get a separate buffer for each file name.

If the variable find-file-visit-truename is non-nil, then the file name recorded for a buffer is the file's truename (made by replacing all symbolic links with their target names), rather than the name you specify. Setting find-file-visit-truename also implies the effect of find-file-existing-other-name.

Sometimes, a directory is ordinarily accessed through a symbolic link, and you may want Emacs to preferentially show its “linked” name. To do this, customize directory-abbrev-alist. Each element in this list should have the form (from . to), which means to replace from with to whenever from appears in a directory name. The from string is a regular expression (see Regexps). It is matched against directory names anchored at the first character, and should start with ‘\`’ (to support directory names with embedded newlines, which would defeat ‘^’). The to string should be an ordinary absolute directory name pointing to the same directory. Do not use ‘~’ to stand for a home directory in the to string; Emacs performs these substitutions separately. Here's an example, from a system on which /home/fsf is normally accessed through a symbolic link named /fsf: 

     (("\\`/home/fsf" . "/fsf"))

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18.8 File Directories

The file system groups files into directories. A directory listing is a list of all the files in a directory. Emacs provides commands to create and delete directories, and to make directory listings in brief format (file names only) and verbose format (sizes, dates, and authors included). Emacs also includes a directory browser feature called Dired; see Dired.

C-x C-d dir-or-pattern <RET>
Display a brief directory listing (list-directory).
C-u C-x C-d dir-or-pattern <RET>
Display a verbose directory listing.
M-x make-directory <RET> dirname <RET>
Create a new directory named dirname.
M-x delete-directory <RET> dirname <RET>
Delete the directory named dirname. If it isn't empty, you will be asked whether you want to delete it recursively.

The command to display a directory listing is C-x C-d (list-directory). It reads using the minibuffer a file name which is either a directory to be listed or a wildcard-containing pattern for the files to be listed. For example, 

     C-x C-d /u2/emacs/etc <RET>

lists all the files in directory /u2/emacs/etc. Here is an example of specifying a file name pattern: 

     C-x C-d /u2/emacs/src/*.c <RET>

Normally, C-x C-d displays a brief directory listing containing just file names. A numeric argument (regardless of value) tells it to make a verbose listing including sizes, dates, and owners (like ‘ls -l’).

The text of a directory listing is mostly obtained by running ls in an inferior process. Two Emacs variables control the switches passed to ls: list-directory-brief-switches is a string giving the switches to use in brief listings ("-CF" by default), and list-directory-verbose-switches is a string giving the switches to use in a verbose listing ("-l" by default).

In verbose directory listings, Emacs adds information about the amount of free space on the disk that contains the directory. To do this, it runs the program specified by directory-free-space-program with arguments directory-free-space-args.

The command M-x delete-directory prompts for a directory name using the minibuffer, and deletes the directory if it is empty. If the directory is not empty, you will be asked whether you want to delete it recursively. On systems that have a “Trash” (or “Recycle Bin”) feature, you can make this command move the specified directory to the Trash instead of deleting it outright, by changing the variable delete-by-moving-to-trash to t. See Misc File Ops, for more information about using the Trash.

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18.9 Comparing Files

The command M-x diff prompts for two file names, using the minibuffer, and displays the differences between the two files in a buffer named *diff*. This works by running the diff program, using options taken from the variable diff-switches. The value of diff-switches should be a string; the default is "-c" to specify a context diff. See Diff, for more information about the diff program.

The output of the diff command is shown using a major mode called Diff mode. See Diff Mode.

The command M-x diff-backup compares a specified file with its most recent backup. If you specify the name of a backup file, diff-backup compares it with the source file that it is a backup of. In all other respects, this behaves like M-x diff.

The command M-x diff-buffer-with-file compares a specified buffer with its corresponding file. This shows you what changes you would make to the file if you save the buffer.

The command M-x compare-windows compares the text in the current window with that in the next window. (For more information about windows in Emacs, Windows.) Comparison starts at point in each window, after pushing each initial point value on the mark ring in its respective buffer. Then it moves point forward in each window, one character at a time, until it reaches characters that don't match. Then the command exits.

If point in the two windows is followed by non-matching text when the command starts, M-x compare-windows tries heuristically to advance up to matching text in the two windows, and then exits. So if you use M-x compare-windows repeatedly, each time it either skips one matching range or finds the start of another.

With a numeric argument, compare-windows ignores changes in whitespace. If the variable compare-ignore-case is non-nil, the comparison ignores differences in case as well. If the variable compare-ignore-whitespace is non-nil, compare-windows normally ignores changes in whitespace, and a prefix argument turns that off.

You can use M-x smerge-mode to turn on Smerge mode, a minor mode for editing output from the diff3 program. This is typically the result of a failed merge from a version control system “update” outside VC, due to conflicting changes to a file. Smerge mode provides commands to resolve conflicts by selecting specific changes.

See Emerge, for the Emerge facility, which provides a powerful interface for merging files.

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18.10 Diff Mode

Diff mode is a major mode used for the output of M-x diff and other similar commands. This kind of output is called a patch, because it can be passed to the patch command to automatically apply the specified changes. To select Diff mode manually, type M-x diff-mode.

The changes specified in a patch are grouped into hunks, which are contiguous chunks of text that contain one or more changed lines. Hunks can also include unchanged lines to provide context for the changes. Each hunk is preceded by a hunk header, which specifies the old and new line numbers at which the hunk occurs. Diff mode highlights each hunk header, to distinguish it from the actual contents of the hunk.

You can edit a Diff mode buffer like any other buffer. (If it is read-only, you need to make it writable first. See Misc Buffer.) Whenever you change a hunk, Diff mode attempts to automatically correct the line numbers in the hunk headers, to ensure that the patch remains “correct”. To disable automatic line number correction, change the variable diff-update-on-the-fly to nil.

Diff mode treats each hunk as an “error message”, similar to Compilation mode. Thus, you can use commands such as C-x ' to visit the corresponding source locations. See Compilation Mode.

In addition, Diff mode provides the following commands to navigate, manipulate and apply parts of patches:

M-n
Move to the next hunk-start (diff-hunk-next).

This command has a side effect: it refines the hunk you move to, highlighting its changes with better granularity. To disable this feature, type M-x diff-auto-refine-mode to toggle off the minor mode Diff Auto-Refine mode. To disable Diff Auto Refine mode by default, add this to your init file (see Hooks): 

          (add-hook 'diff-mode-hook
                    (lambda () (diff-auto-refine-mode -1)))

M-p
Move to the previous hunk-start (diff-hunk-prev). Like M-n, this has the side-effect of refining the hunk you move to, unless you disable Diff Auto-Refine mode.
M-}
Move to the next file-start, in a multi-file patch (diff-file-next).
M-{
Move to the previous file-start, in a multi-file patch (diff-file-prev).
M-k
Kill the hunk at point (diff-hunk-kill).
M-K
In a multi-file patch, kill the current file part. (diff-file-kill).
C-c C-a
Apply this hunk to its target file (diff-apply-hunk). With a prefix argument of C-u, revert this hunk.
C-c C-b
Highlight the changes of the hunk at point with a finer granularity (diff-refine-hunk). This allows you to see exactly which parts of each changed line were actually changed.
C-c C-c
Go to the source file and line corresponding to this hunk (diff-goto-source).
C-c C-e
Start an Ediff session with the patch (diff-ediff-patch). See Ediff.
C-c C-n
Restrict the view to the current hunk (diff-restrict-view). See Narrowing. With a prefix argument of C-u, restrict the view to the current file of a multiple-file patch. To widen again, use C-x n w (widen).
C-c C-r
Reverse the direction of comparison for the entire buffer (diff-reverse-direction).
C-c C-s
Split the hunk at point (diff-split-hunk). This is for manually editing patches, and only works with the unified diff format produced by the -u or --unified options to the diff program. If you need to split a hunk in the context diff format produced by the -c or --context options to diff, first convert the buffer to the unified diff format with C-c C-u.
C-c C-d
Convert the entire buffer to the context diff format (diff-unified->context). With a prefix argument, convert only the text within the region.
C-c C-u
Convert the entire buffer to unified diff format (diff-context->unified). With a prefix argument, convert unified format to context format. When the mark is active, convert only the text within the region.
C-c C-w
Refine the current hunk so that it disregards changes in whitespace (diff-refine-hunk).
C-x 4 A
Generate a ChangeLog entry, like C-x 4 a does (see Change Log), for each one of the hunks (diff-add-change-log-entries-other-window). This creates a skeleton of the log of changes that you can later fill with the actual descriptions of the changes. C-x 4 a itself in Diff mode operates on behalf of the current hunk's file, but gets the function name from the patch itself. This is useful for making log entries for functions that are deleted by the patch.

Patches sometimes include trailing whitespace on modified lines, as an unintentional and undesired change. There are two ways to deal with this problem. Firstly, if you enable Whitespace mode in a Diff buffer (see Useless Whitespace), it automatically highlights trailing whitespace in modified lines. Secondly, you can use the command M-x diff-delete-trailing-whitespace, which searches for trailing whitespace in the lines modified by the patch, and removes that whitespace in both the patch and the patched source file(s). This command does not save the modifications that it makes, so you can decide whether to save the changes (the list of modified files is displayed in the echo area). With a prefix argument, it tries to modify the original source files rather than the patched source files.

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18.11 Miscellaneous File Operations

Emacs has commands for performing many other operations on files. All operate on one file; they do not accept wildcard file names.

M-x delete-file prompts for a file and deletes it. If you are deleting many files in one directory, it may be more convenient to use Dired rather than delete-file. See Dired Deletion.

M-x move-file-to-trash moves a file into the system Trash (or Recycle Bin). This is a facility available on most operating systems; files that are moved into the Trash can be brought back later if you change your mind.

By default, Emacs deletion commands do not use the Trash. To use the Trash (when it is available) for common deletion commands, change the variable delete-by-moving-to-trash to t. This affects the commands M-x delete-file and M-x delete-directory (see Directories), as well as the deletion commands in Dired (see Dired Deletion). Supplying a prefix argument to M-x delete-file or M-x delete-directory makes them delete outright, instead of using the Trash, regardless of delete-by-moving-to-trash.

If a file is under version control (see Version Control), you should delete it using M-x vc-delete-file instead of M-x delete-file. See VC Delete/Rename.

M-x copy-file reads the file old and writes a new file named new with the same contents.

M-x copy-directory copies directories, similar to the cp -r shell command. It prompts for a directory old and a destination new. If new is an existing directory, it creates a copy of the old directory and puts it in new. If new is not an existing directory, it copies all the contents of old into a new directory named new.

M-x rename-file reads two file names old and new using the minibuffer, then renames file old as new. If the file name new already exists, you must confirm with yes or renaming is not done; this is because renaming causes the old meaning of the name new to be lost. If old and new are on different file systems, the file old is copied and deleted. If the argument new is just a directory name, the real new name is in that directory, with the same non-directory component as old. For example, M-x rename-file RET ~/foo RET /tmp RET renames ~/foo to /tmp/foo. The same rule applies to all the remaining commands in this section. All of them ask for confirmation when the new file name already exists, too.

If a file is under version control (see Version Control), you should rename it using M-x vc-rename-file instead of M-x rename-file. See VC Delete/Rename.

M-x add-name-to-file adds an additional name to an existing file without removing its old name. The new name is created as a “hard link” to the existing file. The new name must belong on the same file system that the file is on. On MS-Windows, this command works only if the file resides in an NTFS file system. On MS-DOS, it works by copying the file.

M-x make-symbolic-link reads two file names target and linkname, then creates a symbolic link named linkname, which points at target. The effect is that future attempts to open file linkname will refer to whatever file is named target at the time the opening is done, or will get an error if the name target is nonexistent at that time. This command does not expand the argument target, so that it allows you to specify a relative name as the target of the link. On MS-Windows, this command works only on MS Windows Vista and later.

M-x insert-file (also C-x i) inserts a copy of the contents of the specified file into the current buffer at point, leaving point unchanged before the contents. The position after the inserted contents is added to the mark ring, without activating the mark (see Mark Ring).

M-x insert-file-literally is like M-x insert-file, except the file is inserted “literally”: it is treated as a sequence of ASCII characters with no special encoding or conversion, similar to the M-x find-file-literally command (see Visiting).

M-x write-region is the inverse of M-x insert-file; it copies the contents of the region into the specified file. M-x append-to-file adds the text of the region to the end of the specified file. See Accumulating Text. The variable write-region-inhibit-fsync applies to these commands, as well as saving files; see Customize Save.

M-x set-file-modes reads a file name followed by a file mode, and applies that file mode to the specified file. File modes, also called file permissions, determine whether a file can be read, written to, or executed, and by whom. This command reads file modes using the same symbolic or octal format accepted by the chmod command; for instance, ‘u+x’ means to add execution permission for the user who owns the file. It has no effect on operating systems that do not support file modes. chmod is a convenience alias for this function.

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18.12 Accessing Compressed Files

Emacs automatically uncompresses compressed files when you visit them, and automatically recompresses them if you alter them and save them. Emacs recognizes compressed files by their file names. File names ending in ‘.gz’ indicate a file compressed with gzip. Other endings indicate other compression programs.

Automatic uncompression and compression apply to all the operations in which Emacs uses the contents of a file. This includes visiting it, saving it, inserting its contents into a buffer, loading it, and byte compiling it.

To disable this feature, type the command M-x auto-compression-mode. You can disable it permanently by customizing the variable auto-compression-mode.

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18.13 File Archives

A file whose name ends in ‘.tar’ is normally an archive made by the tar program. Emacs views these files in a special mode called Tar mode which provides a Dired-like list of the contents (see Dired). You can move around through the list just as you would in Dired, and visit the subfiles contained in the archive. However, not all Dired commands are available in Tar mode.

If Auto Compression mode is enabled (see Compressed Files), then Tar mode is used also for compressed archives—files with extensions ‘.tgz’, .tar.Z and .tar.gz.

The keys e, f and <RET> all extract a component file into its own buffer. You can edit it there, and if you save the buffer, the edited version will replace the version in the Tar buffer. Clicking with the mouse on the file name in the Tar buffer does likewise. v extracts a file into a buffer in View mode (see View Mode). o extracts the file and displays it in another window, so you could edit the file and operate on the archive simultaneously.

d marks a file for deletion when you later use x, and u unmarks a file, as in Dired. C copies a file from the archive to disk and R renames a file within the archive. g reverts the buffer from the archive on disk. The keys M, G, and O change the file's permission bits, group, and owner, respectively.

Saving the Tar buffer writes a new version of the archive to disk with the changes you made to the components.

You don't need the tar program to use Tar mode—Emacs reads the archives directly. However, accessing compressed archives requires the appropriate uncompression program.

A separate but similar Archive mode is used for arc, jar, lzh, zip, rar, 7z, and zoo archives, as well as exe files that are self-extracting executables.

The key bindings of Archive mode are similar to those in Tar mode, with the addition of the m key which marks a file for subsequent operations, and M-<DEL> which unmarks all the marked files. Also, the a key toggles the display of detailed file information, for those archive types where it won't fit in a single line. Operations such as renaming a subfile, or changing its mode or owner, are supported only for some of the archive formats.

Unlike Tar mode, Archive mode runs the archiving programs to unpack and repack archives. However, you don't need these programs to look at the archive table of contents, only to extract or manipulate the subfiles in the archive. Details of the program names and their options can be set in the ‘Archive’ Customize group.

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18.14 Remote Files

You can refer to files on other machines using a special file name syntax: 

     /host:filename
     /user@host:filename
     /user@host#port:filename
     /method:user@host:filename
     /method:user@host#port:filename

To carry out this request, Emacs uses a remote-login program such as ftp, ssh, rlogin, or telnet. You can always specify in the file name which method to use—for example, /ftp:user@host:filename uses FTP, whereas /ssh:user@host:filename uses ssh. When you don't specify a method in the file name, Emacs chooses the method as follows:

  1. If the host name starts with ‘ftp.’ (with dot), Emacs uses FTP.
  2. If the user name is ‘ftp’ or ‘anonymous’, Emacs uses FTP.
  3. If the variable tramp-default-method is set to ‘ftp’, Emacs uses FTP.
  4. If ssh-agent is running, Emacs uses scp.
  5. Otherwise, Emacs uses ssh.

You can entirely turn off the remote file name feature by setting the variable tramp-mode to nil. You can turn off the feature in individual cases by quoting the file name with ‘/:’ (see Quoted File Names).

Remote file access through FTP is handled by the Ange-FTP package, which is documented in the following. Remote file access through the other methods is handled by the Tramp package, which has its own manual. See The Tramp Manual.

When the Ange-FTP package is used, Emacs logs in through FTP using the name user, if that is specified in the remote file name. If user is unspecified, Emacs logs in using your user name on the local system; but if you set the variable ange-ftp-default-user to a string, that string is used instead. When logging in, Emacs may also ask for a password.

For performance reasons, Emacs does not make backup files for files accessed via FTP by default. To make it do so, change the variable ange-ftp-make-backup-files to a non-nil value.

By default, auto-save files for remote files are made in the temporary file directory on the local machine, as specified by the variable auto-save-file-name-transforms. See Auto Save Files.

To visit files accessible by anonymous FTP, you use special user names ‘anonymous’ or ‘ftp’. Passwords for these user names are handled specially. The variable ange-ftp-generate-anonymous-password controls what happens: if the value of this variable is a string, then that string is used as the password; if non-nil (the default), then the value of user-mail-address is used; if nil, then Emacs prompts you for a password as usual (see Passwords).

Sometimes you may be unable to access files on a remote machine because a firewall in between blocks the connection for security reasons. If you can log in on a gateway machine from which the target files are accessible, and whose FTP server supports gatewaying features, you can still use remote file names; all you have to do is specify the name of the gateway machine by setting the variable ange-ftp-gateway-host, and set ange-ftp-smart-gateway to t. Otherwise you may be able to make remote file names work, but the procedure is complex. You can read the instructions by typing M-x finder-commentary <RET> ange-ftp <RET>.

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18.15 Quoted File Names

You can quote an absolute file name to prevent special characters and syntax in it from having their special effects. The way to do this is to add ‘/:’ at the beginning.

For example, you can quote a local file name which appears remote, to prevent it from being treated as a remote file name. Thus, if you have a directory named /foo: and a file named bar in it, you can refer to that file in Emacs as ‘/:/foo:/bar’.

‘/:’ can also prevent ‘~’ from being treated as a special character for a user's home directory. For example, /:/tmp/~hack refers to a file whose name is ~hack in directory /tmp.

Quoting with ‘/:’ is also a way to enter in the minibuffer a file name that contains ‘$’. In order for this to work, the ‘/:’ must be at the beginning of the minibuffer contents. (You can also double each ‘$’; see File Names with $.)

You can also quote wildcard characters with ‘/:’, for visiting. For example, /:/tmp/foo*bar visits the file /tmp/foo*bar.

Another method of getting the same result is to enter /tmp/foo[*]bar, which is a wildcard specification that matches only /tmp/foo*bar. However, in many cases there is no need to quote the wildcard characters because even unquoted they give the right result. For example, if the only file name in /tmp that starts with ‘foo’ and ends with ‘bar’ is foo*bar, then specifying /tmp/foo*bar will visit only /tmp/foo*bar.

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18.16 File Name Cache

You can use the file name cache to make it easy to locate a file by name, without having to remember exactly where it is located. When typing a file name in the minibuffer, C-<tab> (file-cache-minibuffer-complete) completes it using the file name cache. If you repeat C-<tab>, that cycles through the possible completions of what you had originally typed. (However, note that the C-<tab> character cannot be typed on most text terminals.)

The file name cache does not fill up automatically. Instead, you load file names into the cache using these commands:

M-x file-cache-add-directory <RET> directory <RET>
Add each file name in directory to the file name cache.
M-x file-cache-add-directory-using-find <RET> directory <RET>
Add each file name in directory and all of its nested subdirectories to the file name cache.
M-x file-cache-add-directory-using-locate <RET> directory <RET>
Add each file name in directory and all of its nested subdirectories to the file name cache, using locate to find them all.
M-x file-cache-add-directory-list <RET> variable <RET>
Add each file name in each directory listed in variable to the file name cache. variable should be a Lisp variable whose value is a list of directory names, like load-path.
M-x file-cache-clear-cache <RET>
Clear the cache; that is, remove all file names from it.

The file name cache is not persistent: it is kept and maintained only for the duration of the Emacs session. You can view the contents of the cache with the file-cache-display command.

Next: , Previous: File Name Cache, Up: Files

18.17 Convenience Features for Finding Files

In this section, we introduce some convenient facilities for finding recently-opened files, reading file names from a buffer, and viewing image files.

If you enable Recentf mode, with M-x recentf-mode, the ‘File’ menu includes a submenu containing a list of recently opened files. M-x recentf-save-list saves the current recent-file-list to a file, and M-x recentf-edit-list edits it.

The M-x ffap command generalizes find-file with more powerful heuristic defaults (see FFAP), often based on the text at point. Partial Completion mode offers other features extending find-file, which can be used with ffap. See Completion Options.

Visiting image files automatically selects Image mode. In this major mode, you can type C-c C-c (image-toggle-display) to toggle between displaying the file as an image in the Emacs buffer, and displaying its underlying text (or raw byte) representation. Displaying the file as an image works only if Emacs is compiled with support for displaying such images. If the displayed image is wider or taller than the frame, the usual point motion keys (C-f, C-p, and so forth) cause different parts of the image to be displayed. If the image can be animated, the command RET (image-toggle-animation) starts or stops the animation. Animation plays once, unless the option image-animate-loop is non-nil. Currently, Emacs only supports animation in GIF files.

If Emacs was compiled with support for the ImageMagick library, it can use ImageMagick to render a wide variety of images. The variable imagemagick-enabled-types lists the image types that Emacs may render using ImageMagick; each element in the list should be an internal ImageMagick name for an image type, as a symbol or an equivalent string (e.g., BMP for .bmp images). To enable ImageMagick for all possible image types, change imagemagick-enabled-types to t. The variable imagemagick-types-inhibit lists the image types which should never be rendered using ImageMagick, regardless of the value of imagemagick-enabled-types (the default list includes types like C and HTML, which ImageMagick can render as an “image” but Emacs should not). To disable ImageMagick entirely, change imagemagick-types-inhibit to t.

The Image-Dired package can also be used to view images as thumbnails. See Image-Dired.

Previous: File Conveniences, Up: Files

18.18 Filesets

If you regularly edit a certain group of files, you can define them as a fileset. This lets you perform certain operations, such as visiting, query-replace, and shell commands on all the files at once. To make use of filesets, you must first add the expression (filesets-init) to your init file (see Init File). This adds a ‘Filesets’ menu to the menu bar.

The simplest way to define a fileset is by adding files to it one at a time. To add a file to fileset name, visit the file and type M-x filesets-add-buffer RET name RET. If there is no fileset name, this creates a new one, which initially contains only the current file. The command M-x filesets-remove-buffer removes the current file from a fileset.

You can also edit the list of filesets directly, with M-x filesets-edit (or by choosing ‘Edit Filesets’ from the ‘Filesets’ menu). The editing is performed in a Customize buffer (see Easy Customization). Normally, a fileset is a simple list of files, but you can also define a fileset as a regular expression matching file names. Some examples of these more complicated filesets are shown in the Customize buffer. Remember to select ‘Save for future sessions’ if you want to use the same filesets in future Emacs sessions.

You can use the command M-x filesets-open to visit all the files in a fileset, and M-x filesets-close to close them. Use M-x filesets-run-cmd to run a shell command on all the files in a fileset. These commands are also available from the ‘Filesets’ menu, where each existing fileset is represented by a submenu.

See Version Control, for a different concept of “filesets”: groups of files bundled together for version control operations. Filesets of that type are unnamed, and do not persist across Emacs sessions.

Next: , Previous: Files, Up: Top

19 Using Multiple Buffers

The text you are editing in Emacs resides in an object called a buffer. Each time you visit a file, a buffer is used to hold the file's text. Each time you invoke Dired, a buffer is used to hold the directory listing. If you send a message with C-x m, a buffer is used to hold the text of the message. When you ask for a command's documentation, that appears in a buffer named *Help*.

Each buffer has a unique name, which can be of any length. When a buffer is displayed in a window, its name is shown in the mode line (see Mode Line). The distinction between upper and lower case matters in buffer names. Most buffers are made by visiting files, and their names are derived from the files' names; however, you can also create an empty buffer with any name you want. A newly started Emacs has several buffers, including one named *scratch*, which can be used for evaluating Lisp expressions and is not associated with any file (see Lisp Interaction).

At any time, one and only one buffer is selected; we call it the current buffer. We sometimes say that a command operates on “the buffer”; this really means that it operates on the current buffer. When there is only one Emacs window, the buffer displayed in that window is current. When there are multiple windows, the buffer displayed in the selected window is current. See Windows.

Aside from its textual contents, each buffer records several pieces of information, such as what file it is visiting (if any), whether it is modified, and what major mode and minor modes are in effect (see Modes). These are stored in buffer-local variables—variables that can have a different value in each buffer. See Locals.

A buffer's size cannot be larger than some maximum, which is defined by the largest buffer position representable by Emacs integers. This is because Emacs tracks buffer positions using that data type. For typical 64-bit machines, this maximum buffer size is 2^61 - 2 bytes, or about 2 EiB. For typical 32-bit machines, the maximum is usually 2^29 - 2 bytes, or about 512 MiB. Buffer sizes are also limited by the amount of memory in the system.

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19.1 Creating and Selecting Buffers

C-x b buffer <RET>
Select or create a buffer named buffer (switch-to-buffer).
C-x 4 b buffer <RET>
Similar, but select buffer in another window (switch-to-buffer-other-window).
C-x 5 b buffer <RET>
Similar, but select buffer in a separate frame (switch-to-buffer-other-frame).
C-x <LEFT>
Select the previous buffer in the buffer list (previous-buffer).
C-x <RIGHT>
Select the next buffer in the buffer list (next-buffer).
C-u M-g M-g
C-u M-g g
Read a number n and move to line n in the most recently selected buffer other than the current buffer.

The C-x b (switch-to-buffer) command reads a buffer name using the minibuffer. Then it makes that buffer current, and displays it in the currently-selected window. An empty input specifies the buffer that was current most recently among those not now displayed in any window.

While entering the buffer name, you can use the usual completion and history commands (see Minibuffer). Note that C-x b, and related commands, use “permissive completion with confirmation” for minibuffer completion: if you type <RET> immediately after completing up to a nonexistent buffer name, Emacs prints ‘[Confirm]’ and you must type a second <RET> to submit that buffer name. See Completion Exit, for details.

If you specify a buffer that does not exist, C-x b creates a new, empty buffer that is not visiting any file, and selects it for editing. The default value of the variable major-mode determines the new buffer's major mode; the default value is Fundamental mode. See Major Modes. One reason to create a new buffer is to use it for making temporary notes. If you try to save it, Emacs asks for the file name to use, and the buffer's major mode is re-established taking that file name into account (see Choosing Modes).

For conveniently switching between a few buffers, use the commands C-x <LEFT> and C-x <RIGHT>. C-x <LEFT> (previous-buffer) selects the previous buffer (following the order of most recent selection in the current frame), while C-x <RIGHT> (next-buffer) moves through buffers in the reverse direction.

To select a buffer in a window other than the current one, type C-x 4 b (switch-to-buffer-other-window). This prompts for a buffer name using the minibuffer, displays that buffer in another window, and selects that window.

Similarly, C-x 5 b (switch-to-buffer-other-frame) prompts for a buffer name, displays that buffer in another frame, and selects that frame. If the buffer is already being shown in a window on another frame, Emacs selects that window and frame instead of creating a new frame.

See Displaying Buffers, for how the C-x 4 b and C-x 5 b commands get the window and/or frame to display in.

In addition, C-x C-f, and any other command for visiting a file, can also be used to switch to an existing file-visiting buffer. See Visiting.

C-u M-g M-g, that is goto-line with a plain prefix argument, reads a number n using the minibuffer, selects the most recently selected buffer other than the current buffer in another window, and then moves point to the beginning of line number n in that buffer. This is mainly useful in a buffer that refers to line numbers in another buffer: if point is on or just after a number, goto-line uses that number as the default for n. Note that prefix arguments other than just C-u behave differently. C-u 4 M-g M-g goes to line 4 in the current buffer, without reading a number from the minibuffer. (Remember that M-g M-g without prefix argument reads a number n and then moves to line number n in the current buffer. See Moving Point.)

Emacs uses buffer names that start with a space for internal purposes. It treats these buffers specially in minor ways—for example, by default they do not record undo information. It is best to avoid using such buffer names yourself.

Next: , Previous: Select Buffer, Up: Buffers

19.2 Listing Existing Buffers

C-x C-b
List the existing buffers (list-buffers).

To display a list of existing buffers, type C-x C-b. Each line in the list shows one buffer's name, major mode and visited file. The buffers are listed in the order that they were current; the buffers that were current most recently come first.

‘.’ in the first field of a line indicates that the buffer is current. ‘%’ indicates a read-only buffer. ‘*’ indicates that the buffer is “modified”. If several buffers are modified, it may be time to save some with C-x s (see Save Commands). Here is an example of a buffer list: 

     CRM Buffer                Size  Mode              File
     . * .emacs                3294  Emacs-Lisp        ~/.emacs
      %  *Help*                 101  Help
         search.c             86055  C                 ~/cvs/emacs/src/search.c
      %  src                  20959  Dired by name     ~/cvs/emacs/src/
       * *mail*                  42  Mail
      %  HELLO                 1607  Fundamental       ~/cvs/emacs/etc/HELLO
      %  NEWS                481184  Outline           ~/cvs/emacs/etc/NEWS
         *scratch*              191  Lisp Interaction
       * *Messages*            1554  Fundamental

The buffer *Help* was made by a help request (see Help); it is not visiting any file. The buffer src was made by Dired on the directory ~/cvs/emacs/src/. You can list only buffers that are visiting files by giving the command a prefix argument, as in C-u C-x C-b.

list-buffers omits buffers whose names begin with a space, unless they visit files: such buffers are used internally by Emacs.

Next: , Previous: List Buffers, Up: Buffers

19.3 Miscellaneous Buffer Operations

C-x C-q
Toggle read-only status of buffer (read-only-mode).
M-x rename-buffer <RET> name <RET>
Change the name of the current buffer.
M-x rename-uniquely
Rename the current buffer by adding ‘<number>’ to the end.
M-x view-buffer <RET> buffer <RET>
Scroll through buffer buffer. See View Mode.

A buffer can be read-only, which means that commands to change its contents are not allowed. The mode line indicates read-only buffers with ‘%%’ or ‘%*’ near the left margin. Read-only buffers are usually made by subsystems such as Dired and Rmail that have special commands to operate on the text; also by visiting a file whose access control says you cannot write it.

The command C-x C-q (read-only-mode) makes a read-only buffer writable, and makes a writable buffer read-only. This works by setting the variable buffer-read-only, which has a local value in each buffer and makes the buffer read-only if its value is non-nil. If you change the option view-read-only to a non-nil value, making the buffer read-only with C-x C-q also enables View mode in the buffer (see View Mode).

M-x rename-buffer changes the name of the current buffer. You specify the new name as a minibuffer argument; there is no default. If you specify a name that is in use for some other buffer, an error happens and no renaming is done.

M-x rename-uniquely renames the current buffer to a similar name with a numeric suffix added to make it both different and unique. This command does not need an argument. It is useful for creating multiple shell buffers: if you rename the *shell* buffer, then do M-x shell again, it makes a new shell buffer named *shell*; meanwhile, the old shell buffer continues to exist under its new name. This method is also good for mail buffers, compilation buffers, and most Emacs features that create special buffers with particular names. (With some of these features, such as M-x compile, M-x grep, you need to switch to some other buffer before using the command again, otherwise it will reuse the current buffer despite the name change.)

The commands M-x append-to-buffer and M-x insert-buffer can also be used to copy text from one buffer to another. See Accumulating Text.

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19.4 Killing Buffers

If you continue an Emacs session for a while, you may accumulate a large number of buffers. You may then find it convenient to kill the buffers you no longer need. On most operating systems, killing a buffer releases its space back to the operating system so that other programs can use it. Here are some commands for killing buffers:

C-x k bufname <RET>
Kill buffer bufname (kill-buffer).
M-x kill-some-buffers
Offer to kill each buffer, one by one.
M-x kill-matching-buffers
Offer to kill all buffers matching a regular expression.

C-x k (kill-buffer) kills one buffer, whose name you specify in the minibuffer. The default, used if you type just <RET> in the minibuffer, is to kill the current buffer. If you kill the current buffer, another buffer becomes current: one that was current in the recent past but is not displayed in any window now. If you ask to kill a file-visiting buffer that is modified, then you must confirm with yes before the buffer is killed.

The command M-x kill-some-buffers asks about each buffer, one by one. An answer of y means to kill the buffer, just like kill-buffer. This command ignores buffers whose names begin with a space, which are used internally by Emacs.

The command M-x kill-matching-buffers prompts for a regular expression and kills all buffers whose names match that expression. See Regexps. Like kill-some-buffers, it asks for confirmation before each kill. This command normally ignores buffers whose names begin with a space, which are used internally by Emacs. To kill internal buffers as well, call kill-matching-buffers with a prefix argument.

The Buffer Menu feature is also convenient for killing various buffers. See Several Buffers.

If you want to do something special every time a buffer is killed, you can add hook functions to the hook kill-buffer-hook (see Hooks).

If you run one Emacs session for a period of days, as many people do, it can fill up with buffers that you used several days ago. The command M-x clean-buffer-list is a convenient way to purge them; it kills all the unmodified buffers that you have not used for a long time. An ordinary buffer is killed if it has not been displayed for three days; however, you can specify certain buffers that should never be killed automatically, and others that should be killed if they have been unused for a mere hour.

You can also have this buffer purging done for you, once a day, by enabling Midnight mode. Midnight mode operates each day at midnight; at that time, it runs clean-buffer-list, or whichever functions you have placed in the normal hook midnight-hook (see Hooks). To enable Midnight mode, use the Customization buffer to set the variable midnight-mode to t. See Easy Customization.

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19.5 Operating on Several Buffers

M-x buffer-menu
Begin editing a buffer listing all Emacs buffers.
M-x buffer-menu-other-window.
Similar, but do it in another window.

The Buffer Menu opened by C-x C-b (see List Buffers) does not merely list buffers. It also allows you to perform various operations on buffers, through an interface similar to Dired (see Dired). You can save buffers, kill them (here called deleting them, for consistency with Dired), or display them.

To use the Buffer Menu, type C-x C-b and switch to the window displaying the *Buffer List* buffer. You can also type M-x buffer-menu to open the Buffer Menu in the selected window. Alternatively, the command M-x buffer-menu-other-window opens the Buffer Menu in another window, and selects that window.

The Buffer Menu is a read-only buffer, and can be changed only through the special commands described in this section. The usual cursor motion commands can be used in this buffer. The following commands apply to the buffer described on the current line:

d
Flag the buffer for deletion (killing), then move point to the next line (Buffer-menu-delete). The deletion flag is indicated by the character ‘D’ on the line, before the buffer name. The deletion occurs only when you type the x command (see below).
C-d
Like d, but move point up instead of down (Buffer-menu-delete-backwards).
s
Flag the buffer for saving (Buffer-menu-save). The save flag is indicated by the character ‘S’ on the line, before the buffer name. The saving occurs only when you type x. You may request both saving and deletion for the same buffer.
x
Perform all flagged deletions and saves (Buffer-menu-execute).
u
Remove all flags from the current line, and move down (Buffer-menu-unmark).
<DEL>
Move to the previous line and remove all flags on that line (Buffer-menu-backup-unmark).

The commands for adding or removing flags, d, C-d, s and u, all accept a numeric argument as a repeat count.

The following commands operate immediately on the buffer listed on the current line. They also accept a numeric argument as a repeat count.

~
Mark the buffer as unmodified (Buffer-menu-not-modified). See Save Commands.
%
Toggle the buffer's read-only status (Buffer-menu-toggle-read-only). See Misc Buffer.
t
Visit the buffer as a tags table (Buffer-menu-visit-tags-table). See Select Tags Table.

The following commands are used to select another buffer or buffers:

q
Quit the Buffer Menu (quit-window). The most recent formerly visible buffer is displayed in its place.
<RET>
f
Select this line's buffer, replacing the *Buffer List* buffer in its window (Buffer-menu-this-window).
o
Select this line's buffer in another window, as if by C-x 4 b, leaving *Buffer List* visible (Buffer-menu-other-window).
C-o
Display this line's buffer in another window, without selecting it (Buffer-menu-switch-other-window).
1
Select this line's buffer in a full-frame window (Buffer-menu-1-window).
2
Set up two windows on the current frame, with this line's buffer selected in one, and a previously current buffer (aside from *Buffer List*) in the other (Buffer-menu-2-window).
b
Bury this line's buffer (Buffer-menu-bury).
m
Mark this line's buffer to be displayed in another window if you exit with the v command (Buffer-menu-mark). The display flag is indicated by the character ‘>’ at the beginning of the line. (A single buffer may not have both deletion and display flags.)
v
Select this line's buffer, and also display in other windows any buffers flagged with the m command (Buffer-menu-select). If you have not flagged any buffers, this command is equivalent to 1.

The following commands affect the entire buffer list:

S
Sort the Buffer Menu entries according to their values in the column at point. With a numeric prefix argument n, sort according to the n-th column (tabulated-list-sort).
T
Delete, or reinsert, lines for non-file buffers Buffer-menu-toggle-files-only). This command toggles the inclusion of such buffers in the buffer list.

Normally, the buffer *Buffer List* is not updated automatically when buffers are created and killed; its contents are just text. If you have created, deleted or renamed buffers, the way to update *Buffer List* to show what you have done is to type g (revert-buffer). You can make this happen regularly every auto-revert-interval seconds if you enable Auto Revert mode in this buffer, as long as it is not marked modified. Global Auto Revert mode applies to the *Buffer List* buffer only if global-auto-revert-non-file-buffers is non-nil. See global-auto-revert-non-file-buffers, for details.

Next: , Previous: Several Buffers, Up: Buffers

19.6 Indirect Buffers

An indirect buffer shares the text of some other buffer, which is called the base buffer of the indirect buffer. In some ways it is a buffer analogue of a symbolic link between files.

M-x make-indirect-buffer <RET> base-buffer <RET> indirect-name <RET>
Create an indirect buffer named indirect-name with base buffer base-buffer.
M-x clone-indirect-buffer <RET>
Create an indirect buffer that is a twin copy of the current buffer.
C-x 4 c
Create an indirect buffer that is a twin copy of the current buffer, and select it in another window (clone-indirect-buffer-other-window).

The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. But in all other respects, the indirect buffer and its base buffer are completely separate. They can have different names, different values of point, different narrowing, different markers, different major modes, and different local variables.

An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually works by saving the base buffer. Killing the base buffer effectively kills the indirect buffer, but killing an indirect buffer has no effect on its base buffer.

One way to use indirect buffers is to display multiple views of an outline. See Outline Views.

A quick and handy way to make an indirect buffer is with the command M-x clone-indirect-buffer. It creates and selects an indirect buffer whose base buffer is the current buffer. With a numeric argument, it prompts for the name of the indirect buffer; otherwise it uses the name of the current buffer, with a ‘<n>’ suffix added. C-x 4 c (clone-indirect-buffer-other-window) works like M-x clone-indirect-buffer, but it selects the new buffer in another window. These functions run the hook clone-indirect-buffer-hook after creating the indirect buffer.

The more general way to make an indirect buffer is with the command M-x make-indirect-buffer. It creates an indirect buffer named indirect-name from a buffer base-buffer, prompting for both using the minibuffer.

Previous: Indirect Buffers, Up: Buffers

19.7 Convenience Features and Customization of Buffer Handling

This section describes several modes and features that make it more convenient to switch between buffers.

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19.7.1 Making Buffer Names Unique

When several buffers visit identically-named files, Emacs must give the buffers distinct names. The usual method for making buffer names unique adds ‘<2>’, ‘<3>’, etc. to the end of the buffer names (all but one of them).

Other methods work by adding parts of each file's directory to the buffer name. To select one, load the library uniquify (e.g., using (require 'uniquify)), and customize the variable uniquify-buffer-name-style (see Easy Customization).

To begin with, the forward naming method includes part of the file's directory name at the beginning of the buffer name; using this method, buffers visiting the files /u/rms/tmp/Makefile and /usr/projects/zaphod/Makefile would be named ‘tmp/Makefile’ and ‘zaphod/Makefile’, respectively (instead of ‘Makefile’ and ‘Makefile<2>’).

In contrast, the post-forward naming method would call the buffers ‘Makefile|tmp’ and ‘Makefile|zaphod’, and the reverse naming method would call them ‘Makefile\tmp’ and ‘Makefile\zaphod’. The nontrivial difference between post-forward and reverse occurs when just one directory name is not enough to distinguish two files; then reverse puts the directory names in reverse order, so that /top/middle/file becomes ‘file\middle\top’, while post-forward puts them in forward order after the file name, as in ‘file|top/middle’.

Which rule to follow for putting the directory names in the buffer name is not very important if you are going to look at the buffer names before you type one. But as an experienced user, if you know the rule, you won't have to look. And then you may find that one rule or another is easier for you to remember and apply quickly.

Next: , Previous: Uniquify, Up: Buffer Convenience

19.7.2 Switching Between Buffers using Substrings

Iswitchb global minor mode provides convenient switching between buffers using substrings of their names. It replaces the normal definitions of C-x b, C-x 4 b, C-x 5 b, and C-x 4 C-o with alternative commands that are somewhat “smarter”.

When one of these commands prompts you for a buffer name, you can type in just a substring of the name you want to choose. As you enter the substring, Iswitchb mode continuously displays a list of buffers that match the substring you have typed.

At any time, you can type <RET> to select the first buffer in the list. So the way to select a particular buffer is to make it the first in the list. There are two ways to do this. You can type more of the buffer name and thus narrow down the list, excluding unwanted buffers above the desired one. Alternatively, you can use C-s and C-r to rotate the list until the desired buffer is first.

<TAB> while entering the buffer name performs completion on the string you have entered, based on the displayed list of buffers.

To enable Iswitchb mode, type M-x iswitchb-mode, or customize the variable iswitchb-mode to t (see Easy Customization).

Previous: Iswitchb, Up: Buffer Convenience

19.7.3 Customizing Buffer Menus

M-x bs-show
Make a list of buffers similarly to M-x list-buffers but customizable.

M-x bs-show pops up a buffer list similar to the one normally displayed by C-x C-b but which you can customize. If you prefer this to the usual buffer list, you can bind this command to C-x C-b. To customize this buffer list, use the bs Custom group (see Easy Customization).

MSB global minor mode (“MSB” stands for “mouse select buffer”) provides a different and customizable mouse buffer menu which you may prefer. It replaces the bindings of mouse-buffer-menu, normally on C-Down-Mouse-1, and the menu bar buffer menu. You can customize the menu in the msb Custom group.

Next: , Previous: Buffers, Up: Top

20 Multiple Windows

Emacs can split a frame into two or many windows. Multiple windows can display parts of different buffers, or different parts of one buffer. Multiple frames always imply multiple windows, because each frame has its own set of windows. Each window belongs to one and only one frame.

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20.1 Concepts of Emacs Windows

Each Emacs window displays one Emacs buffer at any time. A single buffer may appear in more than one window; if it does, any changes in its text are displayed in all the windows where it appears. But these windows can show different parts of the buffer, because each window has its own value of point.

At any time, one Emacs window is the selected window; the buffer this window is displaying is the current buffer. On graphical displays, the point is indicated by a solid blinking cursor in the selected window, and by a hollow box in non-selected windows. On text terminals, the cursor is drawn only in the selected window. See Cursor Display.

Commands to move point affect the value of point for the selected Emacs window only. They do not change the value of point in other Emacs windows, even those showing the same buffer. The same is true for buffer-switching commands such as C-x b; they do not affect other windows at all. However, there are other commands such as C-x 4 b that select a different window and switch buffers in it. Also, all commands that display information in a window, including (for example) C-h f (describe-function) and C-x C-b (list-buffers), work by switching buffers in a nonselected window without affecting the selected window.

When multiple windows show the same buffer, they can have different regions, because they can have different values of point. However, they all have the same value for the mark, because each buffer has only one mark position.

Each window has its own mode line, which displays the buffer name, modification status and major and minor modes of the buffer that is displayed in the window. The selected window's mode line appears in a different color. See Mode Line, for details.

Next: , Previous: Basic Window, Up: Windows

20.2 Splitting Windows

C-x 2
Split the selected window into two windows, one above the other (split-window-below).
C-x 3
Split the selected window into two windows, positioned side by side (split-window-right).
C-Mouse-2
In the mode line of a window, split that window.

C-x 2 (split-window-below) splits the selected window into two windows, one above the other. After splitting, the selected window is the upper one, and the newly split-off window is below. Both windows have the same value of point as before, and display the same portion of the buffer (or as close to it as possible). If necessary, the windows are scrolled to keep point on-screen. By default, the two windows each get half the height of the original window. A positive numeric argument specifies how many lines to give to the top window; a negative numeric argument specifies how many lines to give to the bottom window.

If you change the variable split-window-keep-point to nil, C-x 2 instead adjusts the portion of the buffer displayed by the two windows, as well as the value of point in each window, in order to keep the text on the screen as close as possible to what it was before; furthermore, if point was in the lower half of the original window, the bottom window is selected instead of the upper one.

C-x 3 (split-window-right) splits the selected window into two side-by-side windows. The left window is the selected one; the right window displays the same portion of the same buffer, and has the same value of point. A positive numeric argument specifies how many columns to give the left window; a negative numeric argument specifies how many columns to give the right window.

When you split a window with C-x 3, each resulting window occupies less than the full width of the frame. If it becomes too narrow, the buffer may be difficult to read if continuation lines are in use (see Continuation Lines). Therefore, Emacs automatically switches to line truncation if the window width becomes narrower than 50 columns. This truncation occurs regardless of the value of the variable truncate-lines (see Line Truncation); it is instead controlled by the variable truncate-partial-width-windows. If the value of this variable is a positive integer (the default is 50), that specifies the minimum width for a partial-width window before automatic line truncation occurs; if the value is nil, automatic line truncation is disabled; and for any other non-nil value, Emacs truncates lines in every partial-width window regardless of its width.

On text terminals, side-by-side windows are separated by a vertical divider which is drawn using the vertical-border face.

If you click C-Mouse-2 in the mode line of a window, that splits the window, putting a vertical divider where you click. Depending on how Emacs is compiled, you can also split a window by clicking C-Mouse-2 in the scroll bar, which puts a horizontal divider where you click (this feature does not work when Emacs uses GTK+ scroll bars).

Next: , Previous: Split Window, Up: Windows

20.3 Using Other Windows

C-x o
Select another window (other-window).
C-M-v
Scroll the next window (scroll-other-window).
Mouse-1
Mouse-1, in the text area of a window, selects the window and moves point to the position clicked. Clicking in the mode line selects the window without moving point in it.

With the keyboard, you can switch windows by typing C-x o (other-window). That is an o, for “other”, not a zero. When there are more than two windows, this command moves through all the windows in a cyclic order, generally top to bottom and left to right. After the rightmost and bottommost window, it goes back to the one at the upper left corner. A numeric argument means to move several steps in the cyclic order of windows. A negative argument moves around the cycle in the opposite order. When the minibuffer is active, the minibuffer is the last window in the cycle; you can switch from the minibuffer window to one of the other windows, and later switch back and finish supplying the minibuffer argument that is requested. See Minibuffer Edit.

The usual scrolling commands (see Display) apply to the selected window only, but there is one command to scroll the next window. C-M-v (scroll-other-window) scrolls the window that C-x o would select. It takes arguments, positive and negative, like C-v. (In the minibuffer, C-M-v scrolls the help window associated with the minibuffer, if any, rather than the next window in the standard cyclic order; see Minibuffer Edit.)

If you set mouse-autoselect-window to a non-nil value, moving the mouse over a different window selects that window. This feature is off by default.

Next: , Previous: Other Window, Up: Windows

20.4 Displaying in Another Window

C-x 4 is a prefix key for a variety of commands that switch to a buffer in a different window—either another existing window, or a new window created by splitting the selected window. See Window Choice, for how Emacs picks or creates the window to use.

C-x 4 b bufname <RET>
Select buffer bufname in another window (switch-to-buffer-other-window).


C-x 4 C-o bufname <RET>
Display buffer bufname in some window, without trying to select it (display-buffer). See Displaying Buffers, for details about how the window is chosen.


C-x 4 f filename <RET>
Visit file filename and select its buffer in another window (find-file-other-window). See Visiting.


C-x 4 d directory <RET>
Select a Dired buffer for directory directory in another window (dired-other-window). See Dired.


C-x 4 m
Start composing a mail message, similar to C-x m (see Sending Mail), but in another window (mail-other-window).


C-x 4 .
Find a tag in the current tags table, similar to M-. (see Tags), but in another window (find-tag-other-window).
C-x 4 r filename <RET>
Visit file filename read-only, and select its buffer in another window (find-file-read-only-other-window). See Visiting.

Next: , Previous: Pop Up Window, Up: Windows

20.5 Deleting and Rearranging Windows

C-x 0
Delete the selected window (delete-window).
C-x 1
Delete all windows in the selected frame except the selected window (delete-other-windows).
C-x 4 0
Delete the selected window and kill the buffer that was showing in it (kill-buffer-and-window). The last character in this key sequence is a zero.
C-x ^
Make selected window taller (enlarge-window).
C-x }
Make selected window wider (enlarge-window-horizontally).
C-x {
Make selected window narrower (shrink-window-horizontally).
C-x -
Shrink this window if its buffer doesn't need so many lines (shrink-window-if-larger-than-buffer).
C-x +
Make all windows the same height (balance-windows).

To delete the selected window, type C-x 0 (delete-window). (That is a zero.) Once a window is deleted, the space that it occupied is given to an adjacent window (but not the minibuffer window, even if that is active at the time). Deleting the window has no effect on the buffer it used to display; the buffer continues to exist, and you can still switch to with C-x b.

C-x 4 0 (kill-buffer-and-window) is a stronger command than C-x 0; it kills the current buffer and then deletes the selected window.

C-x 1 (delete-other-windows) deletes all the windows, except the selected one; the selected window expands to use the whole frame. (This command cannot be used while the minibuffer window is active; attempting to do so signals an error.)

The command C-x ^ (enlarge-window) makes the selected window one line taller, taking space from a vertically adjacent window without changing the height of the frame. With a positive numeric argument, this command increases the window height by that many lines; with a negative argument, it reduces the height by that many lines. If there are no vertically adjacent windows (i.e., the window is at the full frame height), that signals an error. The command also signals an error if you attempt to reduce the height of any window below a certain minimum number of lines, specified by the variable window-min-height (the default is 4).

Similarly, C-x } (enlarge-window-horizontally) makes the selected window wider, and C-x { (shrink-window-horizontally) makes it narrower. These commands signal an error if you attempt to reduce the width of any window below a certain minimum number of columns, specified by the variable window-min-width (the default is 10).

C-x - (shrink-window-if-larger-than-buffer) reduces the height of the selected window, if it is taller than necessary to show the whole text of the buffer it is displaying. It gives the extra lines to other windows in the frame.

You can also use C-x + (balance-windows) to even out the heights of all the windows in the selected frame.

Mouse clicks on the mode line provide another way to change window heights and to delete windows. See Mode Line Mouse.

Next: , Previous: Change Window, Up: Windows

20.6 Displaying a Buffer in a Window

It is a common Emacs operation to display or “pop up” some buffer in response to a user command. There are several different ways in which commands do this.

Many commands, like C-x C-f (find-file), display the buffer by “taking over” the selected window, expecting that the user's attention will be diverted to that buffer. These commands usually work by calling switch-to-buffer internally (see Select Buffer).

Some commands try to display “intelligently”, trying not to take over the selected window, e.g., by splitting off a new window and displaying the desired buffer there. Such commands, which include the various help commands (see Help), work by calling display-buffer internally. See Window Choice, for details.

Other commands do the same as display-buffer, and additionally select the displaying window so that you can begin editing its buffer. The command C-x ` (next-error) is one example (see Compilation Mode). Such commands work by calling the function pop-to-buffer internally. See Switching to a Buffer in a Window.

Commands with names ending in -other-window behave like display-buffer, except that they never display in the selected window. Several of these commands are bound in the C-x 4 prefix key (see Pop Up Window).

Commands with names ending in -other-frame behave like display-buffer, except that they (i) never display in the selected window and (ii) prefer to create a new frame to display the desired buffer instead of splitting a window—as though the variable pop-up-frames is set to t (see Window Choice). Several of these commands are bound in the C-x 5 prefix key.

Up: Displaying Buffers

20.6.1 How display-buffer works

The display-buffer command (as well as commands that call it internally) chooses a window to display by following the steps given below. See Choosing a Window for Display, for details about how to alter this sequence of steps.

Previous: Displaying Buffers, Up: Windows

20.7 Convenience Features for Window Handling

Winner mode is a global minor mode that records the changes in the window configuration (i.e., how the frames are partitioned into windows), so that you can “undo” them. You can toggle Winner mode with M-x winner-mode, or by customizing the variable winner-mode. When the mode is enabled, C-c left (winner-undo) undoes the last window configuration change. If you change your mind while undoing, you can redo the changes you had undone using C-c right (M-x winner-redo).

Follow mode (M-x follow-mode) synchronizes several windows on the same buffer so that they always display adjacent sections of that buffer. See Follow Mode.

The Windmove package defines commands for moving directionally between neighboring windows in a frame. M-x windmove-right selects the window immediately to the right of the currently selected one, and similarly for the “left”, “up”, and “down” counterparts. M-x windmove-default-keybindings binds these commands to S-right etc.; doing so disables shift selection for those keys (see Shift Selection).

The command M-x compare-windows lets you compare the text shown in different windows. See Comparing Files.

Scroll All mode (M-x scroll-all-mode) is a global minor mode that causes scrolling commands and point motion commands to apply to every single window.

Next: , Previous: Windows, Up: Top

21 Frames and Graphical Displays

When Emacs is started on a graphical display, e.g., on the X Window System, it occupies a graphical system-level “window”. In this manual, we call this a frame, reserving the word “window” for the part of the frame used for displaying a buffer. A frame initially contains one window, but it can be subdivided into multiple windows (see Windows). A frame normally also contains a menu bar, tool bar, and echo area.

You can also create additional frames (see Creating Frames). All frames created in the same Emacs session have access to the same underlying buffers and other data. For instance, if a buffer is being shown in more than one frame, any changes made to it in one frame show up immediately in the other frames too.

Typing C-x C-c closes all the frames on the current display, and ends the Emacs session if it has no frames open on any other displays (see Exiting). To close just the selected frame, type C-x 5 0 (that is zero, not o).

This chapter describes Emacs features specific to graphical displays (particularly mouse commands), and features for managing multiple frames. On text terminals, many of these features are unavailable. However, it is still possible to create multiple “frames” on text terminals; such frames are displayed one at a time, filling the entire terminal screen (see Non-Window Terminals). It is also possible to use the mouse on some text terminals (see Text-Only Mouse, for doing so on GNU and Unix systems; and see MS-DOS Mouse, for doing so on MS-DOS).

Next: , Up: Frames

21.1 Mouse Commands for Editing

Mouse-1
Move point to where you click (mouse-set-point).
Drag-Mouse-1
Activate the region around the text selected by dragging, and put the text in the primary selection (mouse-set-region).
Mouse-2
Move point to where you click, and insert the contents of the primary selection there (mouse-yank-primary).
Mouse-3
If the region is active, move the nearer end of the region to the click position; otherwise, set mark at the current value of point and point at the click position. Save the resulting region in the kill ring; on a second click, kill it (mouse-save-then-kill).

The most basic mouse command is mouse-set-point, which is invoked by clicking with the left mouse button, Mouse-1, in the text area of a window. This moves point to the position where you clicked. If that window was not the selected window, it becomes the selected window.

Normally, if the frame you clicked in was not the selected frame, it is made the selected frame, in addition to selecting the window and setting the cursor. On the X Window System, you can change this by setting the variable x-mouse-click-focus-ignore-position to t. In that case, the initial click on an unselected frame just selects the frame, without doing anything else; clicking again selects the window and sets the cursor position.

Holding down Mouse-1 and “dragging” the mouse over a stretch of text activates the region around that text (mouse-set-region), placing the mark where you started holding down the mouse button, and point where you release it (see Mark). In addition, the text in the region becomes the primary selection (see Primary Selection).

If you change the variable mouse-drag-copy-region to a non-nil value, dragging the mouse over a stretch of text also adds the text to the kill ring. The default is nil.

If you move the mouse off the top or bottom of the window while dragging, the window scrolls at a steady rate until you move the mouse back into the window. This way, you can select regions that don't fit entirely on the screen. The number of lines scrolled per step depends on how far away from the window edge the mouse has gone; the variable mouse-scroll-min-lines specifies a minimum step size.

Clicking with the middle mouse button, Mouse-2, moves point to the position where you clicked and inserts the contents of the primary selection (mouse-yank-primary). See Primary Selection. This behavior is consistent with other X applications. Alternatively, you can rebind Mouse-2 to mouse-yank-at-click, which performs a yank at point.

If you change the variable mouse-yank-at-point to a non-nil value, Mouse-2 does not move point; it inserts the text at point, regardless of where you clicked or even which of the frame's windows you clicked on. This variable affects both mouse-yank-primary and mouse-yank-at-click.

Clicking with the right mouse button, Mouse-3, runs the command mouse-save-then-kill. This performs several actions depending on where you click and the status of the region:

The mouse-save-then-kill command also obeys the variable mouse-drag-copy-region (described above). If the value is non-nil, then whenever the command sets or adjusts the active region, the text in the region is also added to the kill ring. If the latest kill ring entry had been added the same way, that entry is replaced rather than making a new entry.

Whenever you set the region using any of the mouse commands described above, the mark will be deactivated by any subsequent unshifted cursor motion command, in addition to the usual ways of deactivating the mark. See Shift Selection.

Some mice have a “wheel” which can be used for scrolling. Emacs supports scrolling windows with the mouse wheel, by default, on most graphical displays. To toggle this feature, use M-x mouse-wheel-mode. The variables mouse-wheel-follow-mouse and mouse-wheel-scroll-amount determine where and by how much buffers are scrolled. The variable mouse-wheel-progressive-speed determines whether the scroll speed is linked to how fast you move the wheel.

Next: , Previous: Mouse Commands, Up: Frames

21.2 Mouse Commands for Words and Lines

These variants of Mouse-1 select entire words or lines at a time. Emacs activates the region around the selected text, which is also copied to the kill ring.

Double-Mouse-1
Select the text around the word which you click on.

Double-clicking on a character with “symbol” syntax (such as underscore, in C mode) selects the symbol surrounding that character. Double-clicking on a character with open- or close-parenthesis syntax selects the parenthetical grouping which that character starts or ends. Double-clicking on a character with string-delimiter syntax (such as a single-quote or double-quote in C) selects the string constant (Emacs uses heuristics to figure out whether that character is the beginning or the end of it).

Double-Drag-Mouse-1
Select the text you drag across, in the form of whole words.
Triple-Mouse-1
Select the line you click on.
Triple-Drag-Mouse-1
Select the text you drag across, in the form of whole lines.

Next: , Previous: Word and Line Mouse, Up: Frames

21.3 Following References with the Mouse

Some Emacs buffers include buttons, or hyperlinks: pieces of text that perform some action (e.g., following a reference) when activated (e.g., by clicking on them). Usually, a button's text is visually highlighted: it is underlined, or a box is drawn around it. If you move the mouse over a button, the shape of the mouse cursor changes and the button lights up. If you change the variable mouse-highlight to nil, Emacs disables this highlighting.

You can activate a button by moving point to it and typing <RET>, or by clicking either Mouse-1 or Mouse-2 on the button. For example, in a Dired buffer, each file name is a button; activating it causes Emacs to visit that file (see Dired). In a *Compilation* buffer, each error message is a button, and activating it visits the source code for that error (see Compilation).

Although clicking Mouse-1 on a button usually activates the button, if you hold the mouse button down for a period of time before releasing it (specifically, for more than 450 milliseconds), then Emacs moves point where you clicked, without activating the button. In this way, you can use the mouse to move point over a button without activating it. Dragging the mouse over or onto a button has its usual behavior of setting the region, and does not activate the button.

You can change how Mouse-1 applies to buttons by customizing the variable mouse-1-click-follows-link. If the value is a positive integer, that determines how long you need to hold the mouse button down for, in milliseconds, to cancel button activation; the default is 450, as described in the previous paragraph. If the value is nil, Mouse-1 just sets point where you clicked, and does not activate buttons. If the value is double, double clicks activate buttons but single clicks just set point.

Normally, Mouse-1 on a button activates the button even if it is in a non-selected window. If you change the variable mouse-1-click-in-non-selected-windows to nil, Mouse-1 on a button in an unselected window moves point to the clicked position and selects that window, without activating the button.

Next: , Previous: Mouse References, Up: Frames

21.4 Mouse Clicks for Menus

Several mouse clicks with the <CTRL> and <SHIFT> modifiers bring up menus.

C-Mouse-1
This menu is for selecting a buffer.

The MSB (“mouse select buffer”) global minor mode makes this menu smarter and more customizable. See Buffer Menus.

C-Mouse-2
This menu contains entries for examining faces and other text properties, and well as for setting them (the latter is mainly useful when editing enriched text; see Enriched Text).
C-Mouse-3
This menu is mode-specific. For most modes if Menu-bar mode is on, this menu has the same items as all the mode-specific menu-bar menus put together. Some modes may specify a different menu for this button. If Menu Bar mode is off, this menu contains all the items which would be present in the menu bar—not just the mode-specific ones—so that you can access them without having to display the menu bar.
S-Mouse-1
This menu is for changing the default face within the window's buffer. See Text Scale.

Some graphical applications use Mouse-3 for a mode-specific menu. If you prefer Mouse-3 in Emacs to bring up such a menu instead of running the mouse-save-then-kill command, rebind Mouse-3 by adding the following line to your init file (see Init Rebinding): 

     (global-set-key [mouse-3] 'mouse-popup-menubar-stuff)

Next: , Previous: Menu Mouse Clicks, Up: Frames

21.5 Mode Line Mouse Commands

You can use mouse clicks on window mode lines to select and manipulate windows.

Some areas of the mode line, such as the buffer name, and major and minor mode names, have their own special mouse bindings. These areas are highlighted when you hold the mouse over them, and information about the special bindings will be displayed (see Tooltips). This section's commands do not apply in those areas.

Mouse-1
Mouse-1 on a mode line selects the window it belongs to. By dragging Mouse-1 on the mode line, you can move it, thus changing the height of the windows above and below. Changing heights with the mouse in this way never deletes windows, it just refuses to make any window smaller than the minimum height.
Mouse-2
Mouse-2 on a mode line expands that window to fill its frame.
Mouse-3
Mouse-3 on a mode line deletes the window it belongs to. If the frame has only one window, it does nothing.
C-Mouse-2
C-Mouse-2 on a mode line splits that window, producing two side-by-side windows with the boundary running through the click position (see Split Window).

Furthermore, by clicking and dragging Mouse-1 on the divider between two side-by-side mode lines, you can move the vertical boundary to the left or right.

Next: , Previous: Mode Line Mouse, Up: Frames

21.6 Creating Frames

The prefix key C-x 5 is analogous to C-x 4. Whereas each C-x 4 command pops up a buffer in a different window in the selected frame (see Pop Up Window), the C-x 5 commands use a different frame. If an existing visible or iconified (“minimized”) frame already displays the requested buffer, that frame is raised and deiconified (“un-minimized”); otherwise, a new frame is created on the current display terminal.

The various C-x 5 commands differ in how they find or create the buffer to select:

C-x 5 2
Create a new frame (make-frame-command).
C-x 5 b bufname <RET>
Select buffer bufname in another frame. This runs switch-to-buffer-other-frame.
C-x 5 f filename <RET>
Visit file filename and select its buffer in another frame. This runs find-file-other-frame. See Visiting.
C-x 5 d directory <RET>
Select a Dired buffer for directory directory in another frame. This runs dired-other-frame. See Dired.
C-x 5 m
Start composing a mail message in another frame. This runs mail-other-frame. It is the other-frame variant of C-x m. See Sending Mail.
C-x 5 .
Find a tag in the current tag table in another frame. This runs find-tag-other-frame, the multiple-frame variant of M-.. See Tags.
C-x 5 r filename <RET>
Visit file filename read-only, and select its buffer in another frame. This runs find-file-read-only-other-frame. See Visiting.

You can control the appearance and behavior of the newly-created frames by specifying frame parameters. See Frame Parameters.

Next: , Previous: Creating Frames, Up: Frames

21.7 Frame Commands

The following commands are used to delete and operate on frames:

C-x 5 0
Delete the selected frame (delete-frame). This signals an error if there is only one frame.
C-z
Minimize (or “iconify) the selected Emacs frame (suspend-frame). See Exiting.
C-x 5 o
Select another frame, and raise it. If you repeat this command, it cycles through all the frames on your terminal.
C-x 5 1
Delete all frames on the current terminal, except the selected one.

The C-x 5 0 (delete-frame) command deletes the selected frame. However, it will refuse to delete the last frame in an Emacs session, to prevent you from losing the ability to interact with the Emacs session. Note that when Emacs is run as a daemon (see Emacs Server), there is always a “virtual frame” that remains after all the ordinary, interactive frames are deleted. In this case, C-x 5 0 can delete the last interactive frame; you can use emacsclient to reconnect to the Emacs session.

The C-x 5 1 (delete-other-frames) command deletes all other frames on the current terminal (this terminal refers to either a graphical display, or a text terminal; see Non-Window Terminals). If the Emacs session has frames open on other graphical displays or text terminals, those are not deleted.

The C-x 5 o (other-frame) command selects the next frame on the current terminal. If you are using Emacs on the X Window System with a window manager that selects (or gives focus to) whatever frame the mouse cursor is over, you have to change the variable focus-follows-mouse to t in order for this command to work properly. Then invoking C-x 5 o will also warp the mouse cursor to the chosen frame.

Next: , Previous: Frame Commands, Up: Frames

21.8 Fonts

By default, Emacs displays text on graphical displays using a 12-point monospace font. There are several different ways to specify a different font:

To check what font you're currently using, the C-u C-x = command can be helpful. It describes the character at point, and names the font that it's rendered in.

On X, there are four different ways to express a “font name”. The first is to use a Fontconfig pattern. Fontconfig patterns have the following form: 

     fontname[-fontsize][:name1=values1][:name2=values2]...

Within this format, any of the elements in braces may be omitted. Here, fontname is the family name of the font, such as ‘Monospace’ or ‘DejaVu Sans Mono’; fontsize is the point size of the font (one printer's point is about 1/72 of an inch); and the ‘name=values’ entries specify settings such as the slant and weight of the font. Each values may be a single value, or a list of values separated by commas. In addition, some property values are valid with only one kind of property name, in which case the ‘name=’ part may be omitted.

Here is a list of common font properties:

‘slant’
One of ‘italic’, ‘oblique’, or ‘roman’.
‘weight’
One of ‘light’, ‘medium’, ‘demibold’, ‘bold’ or ‘black’.
‘style’
Some fonts define special styles which are a combination of slant and weight. For instance, ‘Dejavu Sans’ defines the ‘book’ style, which overrides the slant and weight properties.
‘width’
One of ‘condensed’, ‘normal’, or ‘expanded’.
‘spacing’
One of ‘monospace’, ‘proportional’, ‘dual-width’, or ‘charcell’.

Here are some examples of Fontconfig patterns: 

     Monospace
     Monospace-12
     Monospace-12:bold
     DejaVu Sans Mono:bold:italic
     Monospace-12:weight=bold:slant=italic

For a more detailed description of Fontconfig patterns, see the Fontconfig manual, which is distributed with Fontconfig and available online at http://fontconfig.org/fontconfig-user.html.

The second way to specify a font is to use a GTK font pattern. These have the syntax 

     fontname [properties] [fontsize]

where fontname is the family name, properties is a list of property values separated by spaces, and fontsize is the point size. The properties that you may specify for GTK font patterns are as follows:

Here are some examples of GTK font patterns: 

     Monospace 12
     Monospace Bold Italic 12

The third way to specify a font is to use an XLFD (X Logical Font Description). This is the traditional method for specifying fonts under X. Each XLFD consists of fourteen words or numbers, separated by dashes, like this: 

     -misc-fixed-medium-r-semicondensed--13-*-*-*-c-60-iso8859-1

A wildcard character (‘*’) in an XLFD matches any sequence of characters (including none), and ‘?’ matches any single character. However, matching is implementation-dependent, and can be inaccurate when wildcards match dashes in a long name. For reliable results, supply all 14 dashes and use wildcards only within a field. Case is insignificant in an XLFD. The syntax for an XLFD is as follows: 

     -maker-family-weight-slant-widthtype-style...
     ...-pixels-height-horiz-vert-spacing-width-registry-encoding

The entries have the following meanings:

maker
The name of the font manufacturer.
family
The name of the font family (e.g., ‘courier’).
weight
The font weight—normally either ‘bold’, ‘medium’ or ‘light’. Some font names support other values.
slant
The font slant—normally ‘r’ (roman), ‘i’ (italic), ‘o’ (oblique), ‘ri’ (reverse italic), or ‘ot’ (other). Some font names support other values.
widthtype
The font width—normally ‘normal’, ‘condensed’, ‘semicondensed’, or ‘extended’. Some font names support other values.
style
An optional additional style name. Usually it is empty—most XLFDs have two hyphens in a row at this point.
pixels
The font height, in pixels.
height
The font height on the screen, measured in tenths of a printer's point. This is the point size of the font, times ten. For a given vertical resolution, height and pixels are proportional; therefore, it is common to specify just one of them and use ‘*’ for the other.
horiz
The horizontal resolution, in pixels per inch, of the screen for which the font is intended.
vert
The vertical resolution, in pixels per inch, of the screen for which the font is intended. Normally the resolution of the fonts on your system is the right value for your screen; therefore, you normally specify ‘*’ for this and horiz.
spacing
This is ‘m’ (monospace), ‘p’ (proportional) or ‘c’ (character cell).
width
The average character width, in pixels, multiplied by ten.
registry
encoding
The X font character set that the font depicts. (X font character sets are not the same as Emacs character sets, but they are similar.) You can use the xfontsel program to check which choices you have. Normally you should use ‘iso8859’ for registry and ‘1’ for encoding.

The fourth and final method of specifying a font is to use a “font nickname”. Certain fonts have shorter nicknames, which you can use instead of a normal font specification. For instance, ‘6x13’ is equivalent to 

     -misc-fixed-medium-r-semicondensed--13-*-*-*-c-60-iso8859-1

On X, Emacs recognizes two types of fonts: client-side fonts, which are provided by the Xft and Fontconfig libraries, and server-side fonts, which are provided by the X server itself. Most client-side fonts support advanced font features such as antialiasing and subpixel hinting, while server-side fonts do not. Fontconfig and GTK patterns match only client-side fonts.

You will probably want to use a fixed-width default font—that is, a font in which all characters have the same width. For Xft and Fontconfig fonts, you can use the fc-list command to list the available fixed-width fonts, like this: 

     fc-list :spacing=mono fc-list :spacing=charcell

For server-side X fonts, you can use the xlsfonts program to list the available fixed-width fonts, like this: 

     xlsfonts -fn '*x*' | egrep "^[0-9]+x[0-9]+"
     xlsfonts -fn '*-*-*-*-*-*-*-*-*-*-*-m*'
     xlsfonts -fn '*-*-*-*-*-*-*-*-*-*-*-c*'

Any font with ‘m’ or ‘c’ in the spacing field of the XLFD is a fixed-width font. To see what a particular font looks like, use the xfd command. For example: 

     xfd -fn 6x13

displays the entire font ‘6x13’.

While running Emacs, you can also set the font of a specific kind of text (see Faces), or a particular frame (see Frame Parameters).

Next: , Previous: Fonts, Up: Frames

21.9 Speedbar Frames

The speedbar is a special frame for conveniently navigating in or operating on another frame. The speedbar, when it exists, is always associated with a specific frame, called its attached frame; all speedbar operations act on that frame.

Type M-x speedbar to create the speedbar and associate it with the current frame. To dismiss the speedbar, type M-x speedbar again, or select the speedbar and type q. (You can also delete the speedbar frame like any other Emacs frame.) If you wish to associate the speedbar with a different frame, dismiss it and call M-x speedbar from that frame.

The speedbar can operate in various modes. Its default mode is File Display mode, which shows the files in the current directory of the selected window of the attached frame, one file per line. Clicking on a file name visits that file in the selected window of the attached frame, and clicking on a directory name shows that directory in the speedbar (see Mouse References). Each line also has a box, ‘[+]’ or ‘<+>’, that you can click on to expand the contents of that item. Expanding a directory adds the contents of that directory to the speedbar display, underneath the directory's own line. Expanding an ordinary file adds a list of the tags in that file to the speedbar display; you can click on a tag name to jump to that tag in the selected window of the attached frame. When a file or directory is expanded, the ‘[+]’ changes to ‘[-]’; you can click on that box to contract the item, hiding its contents.

You navigate through the speedbar using the keyboard, too. Typing RET while point is on a line in the speedbar is equivalent to clicking the item on the current line, and SPC expands or contracts the item. U displays the parent directory of the current directory. To copy, delete, or rename the file on the current line, type C, D, and R respectively. To create a new directory, type M.

Another general-purpose speedbar mode is Buffer Display mode; in this mode, the speedbar displays a list of Emacs buffers. To switch to this mode, type b in the speedbar. To return to File Display mode, type f. You can also change the display mode by clicking mouse-3 anywhere in the speedbar window (or mouse-1 on the mode-line) and selecting ‘Displays’ in the pop-up menu.

Some major modes, including Rmail mode, Info, and GUD, have specialized ways of putting useful items into the speedbar for you to select. For example, in Rmail mode, the speedbar shows a list of Rmail files, and lets you move the current message to another Rmail file by clicking on its ‘<M>’ box.

For more details on using and programming the speedbar, See Speedbar.

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21.10 Multiple Displays

A single Emacs can talk to more than one X display. Initially, Emacs uses just one display—the one specified with the DISPLAY environment variable or with the ‘--display’ option (see Initial Options). To connect to another display, use the command make-frame-on-display:

M-x make-frame-on-display <RET> display <RET>
Create a new frame on display display.

A single X server can handle more than one screen. When you open frames on two screens belonging to one server, Emacs knows they share a single keyboard, and it treats all the commands arriving from these screens as a single stream of input.

When you open frames on different X servers, Emacs makes a separate input stream for each server. Each server also has its own selected frame. The commands you enter with a particular X server apply to that server's selected frame.

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21.11 Frame Parameters

You can control the default appearance and behavior of all frames by specifying a default list of frame parameters in the variable default-frame-alist. Its value should be a list of entries, each specifying a parameter name and a value for that parameter. These entries take effect whenever Emacs creates a new frame, including the initial frame.

For example, you can add the following lines to your init file (see Init File) to set the default frame width to 90 character columns, the default frame height to 40 character rows, and the default font to ‘Monospace-10’: 

     (add-to-list 'default-frame-alist '(width  . 90))
     (add-to-list 'default-frame-alist '(height . 40))
     (add-to-list 'default-frame-alist '(font . "Monospace-10"))

For a list of frame parameters and their effects, see Frame Parameters.

You can also specify a list of frame parameters which apply to just the initial frame, by customizing the variable initial-frame-alist.

If Emacs is compiled to use an X toolkit, frame parameters that specify colors and fonts don't affect menus and the menu bar, since those are drawn by the toolkit and not directly by Emacs.

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21.12 Scroll Bars

On graphical displays, there is a scroll bar on the side of each Emacs window. Clicking Mouse-1 on the scroll bar's up and down buttons scrolls the window by one line at a time. Clicking Mouse-1 above or below the scroll bar's inner box scrolls the window by nearly the entire height of the window, like M-v and C-v respectively (see Moving Point). Dragging the inner box scrolls continuously.

If Emacs is compiled on the X Window System without X toolkit support, the scroll bar behaves differently. Clicking Mouse-1 anywhere on the scroll bar scrolls forward like C-v, while Mouse-3 scrolls backward like M-v. Clicking Mouse-2 in the scroll bar lets you drag the inner box up and down.

To toggle the use of scroll bars, type M-x scroll-bar-mode. This command applies to all frames, including frames yet to be created. To toggle scroll bars for just the selected frame, use the command M-x toggle-scroll-bar.

To control the use of scroll bars at startup, customize the variable scroll-bar-mode. Its value should be either right (put scroll bars on the right side of windows), left (put them on the left), or nil (disable scroll bars). By default, Emacs puts scroll bars on the right if it was compiled with GTK+ support on the X Window System, and on MS-Windows or Mac OS; Emacs puts scroll bars on the left if compiled on the X Window System without GTK+ support (following the old convention for X applications).

You can also use the X resource ‘verticalScrollBars’ to enable or disable the scroll bars (see Resources). To control the scroll bar width, change the scroll-bar-width frame parameter (see Frame Parameters).

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21.13 Drag and Drop

In most graphical desktop environments, Emacs has basic support for drag and drop operations. For instance, dropping text onto an Emacs frame inserts the text where it is dropped. Dropping a file onto an Emacs frame visits that file. As a special case, dropping the file on a Dired buffer moves or copies the file (according to the conventions of the application it came from) into the directory displayed in that buffer.

Dropping a file normally visits it in the window you drop it on. If you prefer to visit the file in a new window in such cases, customize the variable dnd-open-file-other-window.

The XDND and Motif drag and drop protocols, and the old KDE 1.x protocol, are currently supported.

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21.14 Menu Bars

You can toggle the use of menu bars with M-x menu-bar-mode. With no argument, this command toggles Menu Bar mode, a global minor mode. With an argument, the command turns Menu Bar mode on if the argument is positive, off if the argument is not positive. To control the use of menu bars at startup, customize the variable menu-bar-mode.

Expert users often turn off the menu bar, especially on text terminals, where this makes one additional line available for text. If the menu bar is off, you can still pop up a menu of its contents with C-Mouse-3 on a display which supports pop-up menus. See Menu Mouse Clicks.

See Menu Bar, for information on how to invoke commands with the menu bar. See X Resources, for how to customize the menu bar menus' visual appearance.

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21.15 Tool Bars

On graphical displays, Emacs puts a tool bar at the top of each frame, just below the menu bar. This is a row of icons which you can click on with the mouse to invoke various commands.

The global (default) tool bar contains general commands. Some major modes define their own tool bars; whenever a buffer with such a major mode is current, the mode's tool bar replaces the global tool bar.

To toggle the use of tool bars, type M-x tool-bar-mode. This command applies to all frames, including frames yet to be created. To control the use of tool bars at startup, customize the variable tool-bar-mode.

When Emacs is compiled with GTK+ support, each tool bar item can consist of an image, or a text label, or both. By default, Emacs follows the Gnome desktop's tool bar style setting; if none is defined, it displays tool bar items as just images. To impose a specific tool bar style, customize the variable tool-bar-style.

You can also control the placement of the tool bar for the GTK+ tool bar with the frame parameter tool-bar-position. See Frame Parameters.

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21.16 Using Dialog Boxes

A dialog box is a special kind of menu for asking you a yes-or-no question or some other special question. Many Emacs commands use a dialog box to ask a yes-or-no question, if you used the mouse to invoke the command that led to the question.

To disable the use of dialog boxes, change the variable use-dialog-box to nil. In that case, Emacs always performs yes-or-no prompts using the echo area and keyboard input. This variable also controls whether to use file selection windows (but those are not supported on all platforms).

A file selection window is a special kind of dialog box for asking for file names. You can customize the variable use-file-dialog to suppress the use of file selection windows, even if you still want other kinds of dialogs. This variable has no effect if you have suppressed all dialog boxes with the variable use-dialog-box.

When Emacs is compiled with GTK+ support, it uses the GTK+ “file chooser” dialog. Emacs adds an additional toggle button to this dialog, which you can use to enable or disable the display of hidden files (files starting with a dot) in that dialog. If you want this toggle to be activated by default, change the variable x-gtk-show-hidden-files to t. In addition, Emacs adds help text to the GTK+ file chooser dialog; to disable this help text, change the variable x-gtk-file-dialog-help-text to nil.

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21.17 Tooltips

Tooltips are small windows that display text information at the current mouse position. They activate when there is a pause in mouse movement over some significant piece of text in a window, or the mode line, or some other part of the Emacs frame such as a tool bar button or menu item.

You can toggle the use of tooltips with the command M-x tooltip-mode. When Tooltip mode is disabled, the help text is displayed in the echo area instead. To control the use of tooltips at startup, customize the variable tooltip-mode.

The variables tooltip-delay specifies how long Emacs should wait before displaying a tooltip. For additional customization options for displaying tooltips, use M-x customize-group <RET> tooltip <RET>.

If Emacs is built with GTK+ support, it displays tooltips via GTK+, using the default appearance of GTK+ tooltips. To disable this, change the variable x-gtk-use-system-tooltips to nil. If you do this, or if Emacs is built without GTK+ support, most attributes of the tooltip text are specified by the tooltip face, and by X resources (see X Resources).

GUD tooltips are special tooltips that show the values of variables when debugging a program with GUD. See Debugger Operation.

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21.18 Mouse Avoidance

On graphical terminals, the mouse pointer may obscure the text in the Emacs frame. Emacs provides two methods to avoid this problem.

Firstly, Emacs hides the mouse pointer each time you type a self-inserting character, if the pointer lies inside an Emacs frame; moving the mouse pointer makes it visible again. To disable this feature, set the variable make-pointer-invisible to nil.

Secondly, you can use Mouse Avoidance mode, a minor mode, to keep the mouse pointer away from point. To use Mouse Avoidance mode, customize the variable mouse-avoidance-mode. You can set this to various values to move the mouse in several ways:

banish
Move the pointer to a corner of the frame on any key-press. You can customize the variable mouse-avoidance-banish-position to specify where the pointer goes when it is banished.
exile
Banish the pointer only if the cursor gets too close, and allow it to return once the cursor is out of the way.
jump
If the cursor gets too close to the pointer, displace the pointer by a random distance and direction.
animate
As jump, but shows steps along the way for illusion of motion.
cat-and-mouse
The same as animate.
proteus
As animate, but changes the shape of the mouse pointer too.

You can also use the command M-x mouse-avoidance-mode to enable the mode. Whenever Mouse Avoidance mode moves the mouse, it also raises the frame.

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21.19 Non-Window Terminals

On a text terminal, Emacs can display only one Emacs frame at a time. However, you can still create multiple Emacs frames, and switch between them. Switching frames on these terminals is much like switching between different window configurations.

Use C-x 5 2 to create a new frame and switch to it; use C-x 5 o to cycle through the existing frames; use C-x 5 0 to delete the current frame.

Each frame has a number to distinguish it. If your terminal can display only one frame at a time, the selected frame's number n appears near the beginning of the mode line, in the form ‘Fn’.

‘Fn’ is in fact the frame's initial name. You can give frames more meaningful names if you wish, and you can select a frame by its name. Use the command M-x set-frame-name <RET> name <RET> to specify a new name for the selected frame, and use M-x select-frame-by-name <RET> name <RET> to select a frame according to its name. The name you specify appears in the mode line when the frame is selected.

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21.20 Using a Mouse in Text Terminals

Some text terminals support mouse clicks in the terminal window.

In a terminal emulator which is compatible with xterm, you can use M-x xterm-mouse-mode to give Emacs control over simple uses of the mouse—basically, only non-modified single clicks are supported. The normal xterm mouse functionality for such clicks is still available by holding down the SHIFT key when you press the mouse button. Xterm Mouse mode is a global minor mode (see Minor Modes). Repeating the command turns the mode off again.

In the console on GNU/Linux, you can use M-x gpm-mouse-mode to enable mouse support. You must have the gpm server installed and running on your system in order for this to work.

See MS-DOS Mouse, for information about mouse support on MS-DOS.

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22 International Character Set Support

Emacs supports a wide variety of international character sets, including European and Vietnamese variants of the Latin alphabet, as well as Cyrillic, Devanagari (for Hindi and Marathi), Ethiopic, Greek, Han (for Chinese and Japanese), Hangul (for Korean), Hebrew, IPA, Kannada, Lao, Malayalam, Tamil, Thai, Tibetan, and Vietnamese scripts. Emacs also supports various encodings of these characters that are used by other internationalized software, such as word processors and mailers.

Emacs allows editing text with international characters by supporting all the related activities:

The rest of this chapter describes these issues in detail.

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22.1 Introduction to International Character Sets

The users of international character sets and scripts have established many more-or-less standard coding systems for storing files. These coding systems are typically multibyte, meaning that sequences of two or more bytes are used to represent individual non-ASCII characters.

Internally, Emacs uses its own multibyte character encoding, which is a superset of the Unicode standard. This internal encoding allows characters from almost every known script to be intermixed in a single buffer or string. Emacs translates between the multibyte character encoding and various other coding systems when reading and writing files, and when exchanging data with subprocesses.

The command C-h h (view-hello-file) displays the file etc/HELLO, which illustrates various scripts by showing how to say “hello” in many languages. If some characters can't be displayed on your terminal, they appear as ‘?’ or as hollow boxes (see Undisplayable Characters).

Keyboards, even in the countries where these character sets are used, generally don't have keys for all the characters in them. You can insert characters that your keyboard does not support, using C-q (quoted-insert) or C-x 8 <RET> (insert-char). See Inserting Text. Emacs also supports various input methods, typically one for each script or language, which make it easier to type characters in the script. See Input Methods.

The prefix key C-x <RET> is used for commands that pertain to multibyte characters, coding systems, and input methods.

The command C-x = (what-cursor-position) shows information about the character at point. In addition to the character position, which was described in Position Info, this command displays how the character is encoded. For instance, it displays the following line in the echo area for the character ‘c’: 

     Char: c (99, #o143, #x63) point=28062 of 36168 (78%) column=53

The four values after ‘Char:’ describe the character that follows point, first by showing it and then by giving its character code in decimal, octal and hex. For a non-ASCII multibyte character, these are followed by ‘file’ and the character's representation, in hex, in the buffer's coding system, if that coding system encodes the character safely and with a single byte (see Coding Systems). If the character's encoding is longer than one byte, Emacs shows ‘file ...’.

As a special case, if the character lies in the range 128 (0200 octal) through 159 (0237 octal), it stands for a “raw” byte that does not correspond to any specific displayable character. Such a “character” lies within the eight-bit-control character set, and is displayed as an escaped octal character code. In this case, C-x = shows ‘part of display ...’ instead of ‘file’.

With a prefix argument (C-u C-x =), this command displays a detailed description of the character in a window:

Here's an example showing the Latin-1 character A with grave accent, in a buffer whose coding system is utf-8-unix: 

                  position: 1 of 1 (0%), column: 0
                 character: À (displayed as À) (codepoint 192, #o300, #xc0)
         preferred charset: unicode (Unicode (ISO10646))
     code point in charset: 0xC0
                    syntax: w       which means: word
                  category: .:Base, L:Left-to-right (strong),
                            j:Japanese, l:Latin, v:Viet
               buffer code: #xC3 #x80
                 file code: not encodable by coding system undecided-unix
                   display: by this font (glyph code)
         xft:-unknown-DejaVu Sans Mono-normal-normal-
             normal-*-13-*-*-*-m-0-iso10646-1 (#x82)
     
     Character code properties: customize what to show
       name: LATIN CAPITAL LETTER A WITH GRAVE
       old-name: LATIN CAPITAL LETTER A GRAVE
       general-category: Lu (Letter, Uppercase)
       decomposition: (65 768) ('A' '`')

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22.2 Disabling Multibyte Characters

By default, Emacs starts in multibyte mode: it stores the contents of buffers and strings using an internal encoding that represents non-ASCII characters using multi-byte sequences. Multibyte mode allows you to use all the supported languages and scripts without limitations.

Under very special circumstances, you may want to disable multibyte character support, for a specific buffer. When multibyte characters are disabled in a buffer, we call that unibyte mode. In unibyte mode, each character in the buffer has a character code ranging from 0 through 255 (0377 octal); 0 through 127 (0177 octal) represent ASCII characters, and 128 (0200 octal) through 255 (0377 octal) represent non-ASCII characters.

To edit a particular file in unibyte representation, visit it using find-file-literally. See Visiting. You can convert a multibyte buffer to unibyte by saving it to a file, killing the buffer, and visiting the file again with find-file-literally. Alternatively, you can use C-x <RET> c (universal-coding-system-argument) and specify ‘raw-text’ as the coding system with which to visit or save a file. See Text Coding. Unlike find-file-literally, finding a file as ‘raw-text’ doesn't disable format conversion, uncompression, or auto mode selection.

Emacs normally loads Lisp files as multibyte. This includes the Emacs initialization file, .emacs, and the initialization files of packages such as Gnus. However, you can specify unibyte loading for a particular Lisp file, by adding an entry ‘coding: raw-text’ in a file local variables section. See Specify Coding. Then that file is always loaded as unibyte text. You can also load a Lisp file as unibyte, on any one occasion, by typing C-x <RET> c raw-text <RET> immediately before loading it.

The buffer-local variable enable-multibyte-characters is non-nil in multibyte buffers, and nil in unibyte ones. The mode line also indicates whether a buffer is multibyte or not. See Mode Line. With a graphical display, in a multibyte buffer, the portion of the mode line that indicates the character set has a tooltip that (amongst other things) says that the buffer is multibyte. In a unibyte buffer, the character set indicator is absent. Thus, in a unibyte buffer (when using a graphical display) there is normally nothing before the indication of the visited file's end-of-line convention (colon, backslash, etc.), unless you are using an input method.

You can turn off multibyte support in a specific buffer by invoking the command toggle-enable-multibyte-characters in that buffer.

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22.3 Language Environments

All supported character sets are supported in Emacs buffers whenever multibyte characters are enabled; there is no need to select a particular language in order to display its characters. However, it is important to select a language environment in order to set various defaults. Roughly speaking, the language environment represents a choice of preferred script rather than a choice of language.

The language environment controls which coding systems to recognize when reading text (see Recognize Coding). This applies to files, incoming mail, and any other text you read into Emacs. It may also specify the default coding system to use when you create a file. Each language environment also specifies a default input method.

To select a language environment, customize current-language-environment or use the command M-x set-language-environment. It makes no difference which buffer is current when you use this command, because the effects apply globally to the Emacs session. The supported language environments (see the variable language-info-alist) include:

ASCII, Belarusian, Bengali, Brazilian Portuguese, Bulgarian, Cham, Chinese-BIG5, Chinese-CNS, Chinese-EUC-TW, Chinese-GB, Chinese-GBK, Chinese-GB18030, Croatian, Cyrillic-ALT, Cyrillic-ISO, Cyrillic-KOI8, Czech, Devanagari, Dutch, English, Esperanto, Ethiopic, French, Georgian, German, Greek, Gujarati, Hebrew, IPA, Italian, Japanese, Kannada, Khmer, Korean, Lao, Latin-1, Latin-2, Latin-3, Latin-4, Latin-5, Latin-6, Latin-7, Latin-8 (Celtic), Latin-9 (updated Latin-1 with the Euro sign), Latvian, Lithuanian, Malayalam, Oriya, Polish, Punjabi, Romanian, Russian, Sinhala, Slovak, Slovenian, Spanish, Swedish, TaiViet, Tajik, Tamil, Telugu, Thai, Tibetan, Turkish, UTF-8 (for a setup which prefers Unicode characters and files encoded in UTF-8), Ukrainian, Vietnamese, Welsh, and Windows-1255 (for a setup which prefers Cyrillic characters and files encoded in Windows-1255).

To display the script(s) used by your language environment on a graphical display, you need to have suitable fonts. See Fontsets, for more details about setting up your fonts.

Some operating systems let you specify the character-set locale you are using by setting the locale environment variables LC_ALL, LC_CTYPE, or LANG. (If more than one of these is set, the first one that is nonempty specifies your locale for this purpose.) During startup, Emacs looks up your character-set locale's name in the system locale alias table, matches its canonical name against entries in the value of the variables locale-charset-language-names and locale-language-names (the former overrides the latter), and selects the corresponding language environment if a match is found. It also adjusts the display table and terminal coding system, the locale coding system, the preferred coding system as needed for the locale, and—last but not least—the way Emacs decodes non-ASCII characters sent by your keyboard.

If you modify the LC_ALL, LC_CTYPE, or LANG environment variables while running Emacs (by using M-x setenv), you may want to invoke the set-locale-environment function afterwards to readjust the language environment from the new locale.

The set-locale-environment function normally uses the preferred coding system established by the language environment to decode system messages. But if your locale matches an entry in the variable locale-preferred-coding-systems, Emacs uses the corresponding coding system instead. For example, if the locale ‘ja_JP.PCK’ matches japanese-shift-jis in locale-preferred-coding-systems, Emacs uses that encoding even though it might normally use japanese-iso-8bit.

You can override the language environment chosen at startup with explicit use of the command set-language-environment, or with customization of current-language-environment in your init file.

To display information about the effects of a certain language environment lang-env, use the command C-h L lang-env <RET> (describe-language-environment). This tells you which languages this language environment is useful for, and lists the character sets, coding systems, and input methods that go with it. It also shows some sample text to illustrate scripts used in this language environment. If you give an empty input for lang-env, this command describes the chosen language environment. You can customize any language environment with the normal hook set-language-environment-hook. The command set-language-environment runs that hook after setting up the new language environment. The hook functions can test for a specific language environment by checking the variable current-language-environment. This hook is where you should put non-default settings for specific language environments, such as coding systems for keyboard input and terminal output, the default input method, etc.

Before it starts to set up the new language environment, set-language-environment first runs the hook exit-language-environment-hook. This hook is useful for undoing customizations that were made with set-language-environment-hook. For instance, if you set up a special key binding in a specific language environment using set-language-environment-hook, you should set up exit-language-environment-hook to restore the normal binding for that key.

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22.4 Input Methods

An input method is a kind of character conversion designed specifically for interactive input. In Emacs, typically each language has its own input method; sometimes several languages that use the same characters can share one input method. A few languages support several input methods.

The simplest kind of input method works by mapping ASCII letters into another alphabet; this allows you to use one other alphabet instead of ASCII. The Greek and Russian input methods work this way.

A more powerful technique is composition: converting sequences of characters into one letter. Many European input methods use composition to produce a single non-ASCII letter from a sequence that consists of a letter followed by accent characters (or vice versa). For example, some methods convert the sequence o ^ into a single accented letter. These input methods have no special commands of their own; all they do is compose sequences of printing characters.

The input methods for syllabic scripts typically use mapping followed by composition. The input methods for Thai and Korean work this way. First, letters are mapped into symbols for particular sounds or tone marks; then, sequences of these that make up a whole syllable are mapped into one syllable sign.

Chinese and Japanese require more complex methods. In Chinese input methods, first you enter the phonetic spelling of a Chinese word (in input method chinese-py, among others), or a sequence of portions of the character (input methods chinese-4corner and chinese-sw, and others). One input sequence typically corresponds to many possible Chinese characters. You select the one you mean using keys such as C-f, C-b, C-n, C-p (or the arrow keys), and digits, which have special meanings in this situation.

The possible characters are conceptually arranged in several rows, with each row holding up to 10 alternatives. Normally, Emacs displays just one row at a time, in the echo area; (i/j) appears at the beginning, to indicate that this is the ith row out of a total of j rows. Type C-n or C-p to display the next row or the previous row.

Type C-f and C-b to move forward and backward among the alternatives in the current row. As you do this, Emacs highlights the current alternative with a special color; type C-<SPC> to select the current alternative and use it as input. The alternatives in the row are also numbered; the number appears before the alternative. Typing a number selects the associated alternative of the current row and uses it as input.

<TAB> in these Chinese input methods displays a buffer showing all the possible characters at once; then clicking Mouse-2 on one of them selects that alternative. The keys C-f, C-b, C-n, C-p, and digits continue to work as usual, but they do the highlighting in the buffer showing the possible characters, rather than in the echo area.

In Japanese input methods, first you input a whole word using phonetic spelling; then, after the word is in the buffer, Emacs converts it into one or more characters using a large dictionary. One phonetic spelling corresponds to a number of different Japanese words; to select one of them, use C-n and C-p to cycle through the alternatives.

Sometimes it is useful to cut off input method processing so that the characters you have just entered will not combine with subsequent characters. For example, in input method latin-1-postfix, the sequence o ^ combines to form an ‘o’ with an accent. What if you want to enter them as separate characters?

One way is to type the accent twice; this is a special feature for entering the separate letter and accent. For example, o ^ ^ gives you the two characters ‘o^’. Another way is to type another letter after the o—something that won't combine with that—and immediately delete it. For example, you could type o o <DEL> ^ to get separate ‘o’ and ‘^’.

Another method, more general but not quite as easy to type, is to use C-\ C-\ between two characters to stop them from combining. This is the command C-\ (toggle-input-method) used twice. See Select Input Method.

C-\ C-\ is especially useful inside an incremental search, because it stops waiting for more characters to combine, and starts searching for what you have already entered.

To find out how to input the character after point using the current input method, type C-u C-x =. See Position Info.

The variables input-method-highlight-flag and input-method-verbose-flag control how input methods explain what is happening. If input-method-highlight-flag is non-nil, the partial sequence is highlighted in the buffer (for most input methods—some disable this feature). If input-method-verbose-flag is non-nil, the list of possible characters to type next is displayed in the echo area (but not when you are in the minibuffer).

Another facility for typing characters not on your keyboard is by using C-x 8 <RET> (insert-char) to insert a single character based on its Unicode name or code-point; see Inserting Text.

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22.5 Selecting an Input Method

C-\
Enable or disable use of the selected input method (toggle-input-method).
C-x <RET> C-\ method <RET>
Select a new input method for the current buffer (set-input-method).
C-h I method <RET>
C-h C-\ method <RET>
Describe the input method method (describe-input-method). By default, it describes the current input method (if any). This description should give you the full details of how to use any particular input method.
M-x list-input-methods
Display a list of all the supported input methods.

To choose an input method for the current buffer, use C-x <RET> C-\ (set-input-method). This command reads the input method name from the minibuffer; the name normally starts with the language environment that it is meant to be used with. The variable current-input-method records which input method is selected.

Input methods use various sequences of ASCII characters to stand for non-ASCII characters. Sometimes it is useful to turn off the input method temporarily. To do this, type C-\ (toggle-input-method). To reenable the input method, type C-\ again.

If you type C-\ and you have not yet selected an input method, it prompts you to specify one. This has the same effect as using C-x <RET> C-\ to specify an input method.

When invoked with a numeric argument, as in C-u C-\, toggle-input-method always prompts you for an input method, suggesting the most recently selected one as the default.

Selecting a language environment specifies a default input method for use in various buffers. When you have a default input method, you can select it in the current buffer by typing C-\. The variable default-input-method specifies the default input method (nil means there is none).

In some language environments, which support several different input methods, you might want to use an input method different from the default chosen by set-language-environment. You can instruct Emacs to select a different default input method for a certain language environment, if you wish, by using set-language-environment-hook (see set-language-environment-hook). For example: 

     (defun my-chinese-setup ()
       "Set up my private Chinese environment."
       (if (equal current-language-environment "Chinese-GB")
           (setq default-input-method "chinese-tonepy")))
     (add-hook 'set-language-environment-hook 'my-chinese-setup)

This sets the default input method to be chinese-tonepy whenever you choose a Chinese-GB language environment.

You can instruct Emacs to activate a certain input method automatically. For example: 

     (add-hook 'text-mode-hook
       (lambda () (set-input-method "german-prefix")))

This automatically activates the input method “german-prefix” in Text mode.

Some input methods for alphabetic scripts work by (in effect) remapping the keyboard to emulate various keyboard layouts commonly used for those scripts. How to do this remapping properly depends on your actual keyboard layout. To specify which layout your keyboard has, use the command M-x quail-set-keyboard-layout.

You can use the command M-x quail-show-key to show what key (or key sequence) to type in order to input the character following point, using the selected keyboard layout. The command C-u C-x = also shows that information, in addition to other information about the character.

M-x list-input-methods displays a list of all the supported input methods. The list gives information about each input method, including the string that stands for it in the mode line.

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22.6 Coding Systems

Users of various languages have established many more-or-less standard coding systems for representing them. Emacs does not use these coding systems internally; instead, it converts from various coding systems to its own system when reading data, and converts the internal coding system to other coding systems when writing data. Conversion is possible in reading or writing files, in sending or receiving from the terminal, and in exchanging data with subprocesses.

Emacs assigns a name to each coding system. Most coding systems are used for one language, and the name of the coding system starts with the language name. Some coding systems are used for several languages; their names usually start with ‘iso’. There are also special coding systems, such as no-conversion, raw-text, and emacs-internal.

A special class of coding systems, collectively known as codepages, is designed to support text encoded by MS-Windows and MS-DOS software. The names of these coding systems are cpnnnn, where nnnn is a 3- or 4-digit number of the codepage. You can use these encodings just like any other coding system; for example, to visit a file encoded in codepage 850, type C-x <RET> c cp850 <RET> C-x C-f filename <RET>.

In addition to converting various representations of non-ASCII characters, a coding system can perform end-of-line conversion. Emacs handles three different conventions for how to separate lines in a file: newline (“unix”), carriage-return linefeed (“dos”), and just carriage-return (“mac”).

C-h C coding <RET>
Describe coding system coding (describe-coding-system).
C-h C <RET>
Describe the coding systems currently in use.
M-x list-coding-systems
Display a list of all the supported coding systems.

The command C-h C (describe-coding-system) displays information about particular coding systems, including the end-of-line conversion specified by those coding systems. You can specify a coding system name as the argument; alternatively, with an empty argument, it describes the coding systems currently selected for various purposes, both in the current buffer and as the defaults, and the priority list for recognizing coding systems (see Recognize Coding).

To display a list of all the supported coding systems, type M-x list-coding-systems. The list gives information about each coding system, including the letter that stands for it in the mode line (see Mode Line).

Each of the coding systems that appear in this list—except for no-conversion, which means no conversion of any kind—specifies how and whether to convert printing characters, but leaves the choice of end-of-line conversion to be decided based on the contents of each file. For example, if the file appears to use the sequence carriage-return linefeed to separate lines, DOS end-of-line conversion will be used.

Each of the listed coding systems has three variants, which specify exactly what to do for end-of-line conversion:

...-unix
Don't do any end-of-line conversion; assume the file uses newline to separate lines. (This is the convention normally used on Unix and GNU systems, and Mac OS X.)
...-dos
Assume the file uses carriage-return linefeed to separate lines, and do the appropriate conversion. (This is the convention normally used on Microsoft systems.7)
...-mac
Assume the file uses carriage-return to separate lines, and do the appropriate conversion. (This was the convention used on the Macintosh system prior to OS X.)

These variant coding systems are omitted from the list-coding-systems display for brevity, since they are entirely predictable. For example, the coding system iso-latin-1 has variants iso-latin-1-unix, iso-latin-1-dos and iso-latin-1-mac.

The coding systems unix, dos, and mac are aliases for undecided-unix, undecided-dos, and undecided-mac, respectively. These coding systems specify only the end-of-line conversion, and leave the character code conversion to be deduced from the text itself.

The coding system raw-text is good for a file which is mainly ASCII text, but may contain byte values above 127 that are not meant to encode non-ASCII characters. With raw-text, Emacs copies those byte values unchanged, and sets enable-multibyte-characters to nil in the current buffer so that they will be interpreted properly. raw-text handles end-of-line conversion in the usual way, based on the data encountered, and has the usual three variants to specify the kind of end-of-line conversion to use.

In contrast, the coding system no-conversion specifies no character code conversion at all—none for non-ASCII byte values and none for end of line. This is useful for reading or writing binary files, tar files, and other files that must be examined verbatim. It, too, sets enable-multibyte-characters to nil.

The easiest way to edit a file with no conversion of any kind is with the M-x find-file-literally command. This uses no-conversion, and also suppresses other Emacs features that might convert the file contents before you see them. See Visiting.

The coding system emacs-internal (or utf-8-emacs, which is equivalent) means that the file contains non-ASCII characters stored with the internal Emacs encoding. This coding system handles end-of-line conversion based on the data encountered, and has the usual three variants to specify the kind of end-of-line conversion.

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22.7 Recognizing Coding Systems

Whenever Emacs reads a given piece of text, it tries to recognize which coding system to use. This applies to files being read, output from subprocesses, text from X selections, etc. Emacs can select the right coding system automatically most of the time—once you have specified your preferences.

Some coding systems can be recognized or distinguished by which byte sequences appear in the data. However, there are coding systems that cannot be distinguished, not even potentially. For example, there is no way to distinguish between Latin-1 and Latin-2; they use the same byte values with different meanings.

Emacs handles this situation by means of a priority list of coding systems. Whenever Emacs reads a file, if you do not specify the coding system to use, Emacs checks the data against each coding system, starting with the first in priority and working down the list, until it finds a coding system that fits the data. Then it converts the file contents assuming that they are represented in this coding system.

The priority list of coding systems depends on the selected language environment (see Language Environments). For example, if you use French, you probably want Emacs to prefer Latin-1 to Latin-2; if you use Czech, you probably want Latin-2 to be preferred. This is one of the reasons to specify a language environment.

However, you can alter the coding system priority list in detail with the command M-x prefer-coding-system. This command reads the name of a coding system from the minibuffer, and adds it to the front of the priority list, so that it is preferred to all others. If you use this command several times, each use adds one element to the front of the priority list.

If you use a coding system that specifies the end-of-line conversion type, such as iso-8859-1-dos, what this means is that Emacs should attempt to recognize iso-8859-1 with priority, and should use DOS end-of-line conversion when it does recognize iso-8859-1.

Sometimes a file name indicates which coding system to use for the file. The variable file-coding-system-alist specifies this correspondence. There is a special function modify-coding-system-alist for adding elements to this list. For example, to read and write all ‘.txt’ files using the coding system chinese-iso-8bit, you can execute this Lisp expression: 

     (modify-coding-system-alist 'file "\\.txt\\'" 'chinese-iso-8bit)

The first argument should be file, the second argument should be a regular expression that determines which files this applies to, and the third argument says which coding system to use for these files.

Emacs recognizes which kind of end-of-line conversion to use based on the contents of the file: if it sees only carriage-returns, or only carriage-return linefeed sequences, then it chooses the end-of-line conversion accordingly. You can inhibit the automatic use of end-of-line conversion by setting the variable inhibit-eol-conversion to non-nil. If you do that, DOS-style files will be displayed with the ‘^M’ characters visible in the buffer; some people prefer this to the more subtle ‘(DOS)’ end-of-line type indication near the left edge of the mode line (see eol-mnemonic).

By default, the automatic detection of coding system is sensitive to escape sequences. If Emacs sees a sequence of characters that begin with an escape character, and the sequence is valid as an ISO-2022 code, that tells Emacs to use one of the ISO-2022 encodings to decode the file.

However, there may be cases that you want to read escape sequences in a file as is. In such a case, you can set the variable inhibit-iso-escape-detection to non-nil. Then the code detection ignores any escape sequences, and never uses an ISO-2022 encoding. The result is that all escape sequences become visible in the buffer.

The default value of inhibit-iso-escape-detection is nil. We recommend that you not change it permanently, only for one specific operation. That's because some Emacs Lisp source files in the Emacs distribution contain non-ASCII characters encoded in the coding system iso-2022-7bit, and they won't be decoded correctly when you visit those files if you suppress the escape sequence detection.

The variables auto-coding-alist and auto-coding-regexp-alist are the strongest way to specify the coding system for certain patterns of file names, or for files containing certain patterns, respectively. These variables even override ‘-*-coding:-*-’ tags in the file itself (see Specify Coding). For example, Emacs uses auto-coding-alist for tar and archive files, to prevent it from being confused by a ‘-*-coding:-*-’ tag in a member of the archive and thinking it applies to the archive file as a whole.

Another way to specify a coding system is with the variable auto-coding-functions. For example, one of the builtin auto-coding-functions detects the encoding for XML files. Unlike the previous two, this variable does not override any ‘-*-coding:-*-’ tag.

When you get new mail in Rmail, each message is translated automatically from the coding system it is written in, as if it were a separate file. This uses the priority list of coding systems that you have specified. If a MIME message specifies a character set, Rmail obeys that specification. For reading and saving Rmail files themselves, Emacs uses the coding system specified by the variable rmail-file-coding-system. The default value is nil, which means that Rmail files are not translated (they are read and written in the Emacs internal character code).

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22.8 Specifying a File's Coding System

If Emacs recognizes the encoding of a file incorrectly, you can reread the file using the correct coding system with C-x <RET> r (revert-buffer-with-coding-system). This command prompts for the coding system to use. To see what coding system Emacs actually used to decode the file, look at the coding system mnemonic letter near the left edge of the mode line (see Mode Line), or type C-h C (describe-coding-system).

You can specify the coding system for a particular file in the file itself, using the ‘-*-...-*-’ construct at the beginning, or a local variables list at the end (see File Variables). You do this by defining a value for the “variable” named coding. Emacs does not really have a variable coding; instead of setting a variable, this uses the specified coding system for the file. For example, ‘-*-mode: C; coding: latin-1;-*-’ specifies use of the Latin-1 coding system, as well as C mode. When you specify the coding explicitly in the file, that overrides file-coding-system-alist.

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22.9 Choosing Coding Systems for Output

Once Emacs has chosen a coding system for a buffer, it stores that coding system in buffer-file-coding-system. That makes it the default for operations that write from this buffer into a file, such as save-buffer and write-region. You can specify a different coding system for further file output from the buffer using set-buffer-file-coding-system (see Text Coding).

You can insert any character Emacs supports into any Emacs buffer, but most coding systems can only handle a subset of these characters. Therefore, it's possible that the characters you insert cannot be encoded with the coding system that will be used to save the buffer. For example, you could visit a text file in Polish, encoded in iso-8859-2, and add some Russian words to it. When you save that buffer, Emacs cannot use the current value of buffer-file-coding-system, because the characters you added cannot be encoded by that coding system.

When that happens, Emacs tries the most-preferred coding system (set by M-x prefer-coding-system or M-x set-language-environment). If that coding system can safely encode all of the characters in the buffer, Emacs uses it, and stores its value in buffer-file-coding-system. Otherwise, Emacs displays a list of coding systems suitable for encoding the buffer's contents, and asks you to choose one of those coding systems.

If you insert the unsuitable characters in a mail message, Emacs behaves a bit differently. It additionally checks whether the most-preferred coding system is recommended for use in MIME messages; if not, it informs you of this fact and prompts you for another coding system. This is so you won't inadvertently send a message encoded in a way that your recipient's mail software will have difficulty decoding. (You can still use an unsuitable coding system if you enter its name at the prompt.)

When you send a mail message (see Sending Mail), Emacs has four different ways to determine the coding system to use for encoding the message text. It tries the buffer's own value of buffer-file-coding-system, if that is non-nil. Otherwise, it uses the value of sendmail-coding-system, if that is non-nil. The third way is to use the default coding system for new files, which is controlled by your choice of language environment, if that is non-nil. If all of these three values are nil, Emacs encodes outgoing mail using the Latin-1 coding system.

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22.10 Specifying a Coding System for File Text

In cases where Emacs does not automatically choose the right coding system for a file's contents, you can use these commands to specify one:

C-x <RET> f coding <RET>
Use coding system coding to save or revisit the file in the current buffer (set-buffer-file-coding-system).
C-x <RET> c coding <RET>
Specify coding system coding for the immediately following command (universal-coding-system-argument).
C-x <RET> r coding <RET>
Revisit the current file using the coding system coding (revert-buffer-with-coding-system).
M-x recode-region <RET> right <RET> wrong <RET>
Convert a region that was decoded using coding system wrong, decoding it using coding system right instead.

The command C-x <RET> f (set-buffer-file-coding-system) sets the file coding system for the current buffer (i.e., the coding system to use when saving or reverting the file). You specify which coding system using the minibuffer. You can also invoke this command by clicking with Mouse-3 on the coding system indicator in the mode line (see Mode Line).

If you specify a coding system that cannot handle all the characters in the buffer, Emacs will warn you about the troublesome characters, and ask you to choose another coding system, when you try to save the buffer (see Output Coding).

You can also use this command to specify the end-of-line conversion (see end-of-line conversion) for encoding the current buffer. For example, C-x <RET> f dos <RET> will cause Emacs to save the current buffer's text with DOS-style carriage-return linefeed line endings.

Another way to specify the coding system for a file is when you visit the file. First use the command C-x <RET> c (universal-coding-system-argument); this command uses the minibuffer to read a coding system name. After you exit the minibuffer, the specified coding system is used for the immediately following command.

So if the immediately following command is C-x C-f, for example, it reads the file using that coding system (and records the coding system for when you later save the file). Or if the immediately following command is C-x C-w, it writes the file using that coding system. When you specify the coding system for saving in this way, instead of with C-x <RET> f, there is no warning if the buffer contains characters that the coding system cannot handle.

Other file commands affected by a specified coding system include C-x i and C-x C-v, as well as the other-window variants of C-x C-f. C-x <RET> c also affects commands that start subprocesses, including M-x shell (see Shell). If the immediately following command does not use the coding system, then C-x <RET> c ultimately has no effect.

An easy way to visit a file with no conversion is with the M-x find-file-literally command. See Visiting.

The default value of the variable buffer-file-coding-system specifies the choice of coding system to use when you create a new file. It applies when you find a new file, and when you create a buffer and then save it in a file. Selecting a language environment typically sets this variable to a good choice of default coding system for that language environment.

If you visit a file with a wrong coding system, you can correct this with C-x <RET> r (revert-buffer-with-coding-system). This visits the current file again, using a coding system you specify.

If a piece of text has already been inserted into a buffer using the wrong coding system, you can redo the decoding of it using M-x recode-region. This prompts you for the proper coding system, then for the wrong coding system that was actually used, and does the conversion. It first encodes the region using the wrong coding system, then decodes it again using the proper coding system.

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22.11 Coding Systems for Interprocess Communication

This section explains how to specify coding systems for use in communication with other processes.

C-x <RET> x coding <RET>
Use coding system coding for transferring selections to and from other graphical applications (set-selection-coding-system).
C-x <RET> X coding <RET>
Use coding system coding for transferring one selection—the next one—to or from another graphical application (set-next-selection-coding-system).
C-x <RET> p input-coding <RET> output-coding <RET>
Use coding systems input-coding and output-coding for subprocess input and output in the current buffer (set-buffer-process-coding-system).

The command C-x <RET> x (set-selection-coding-system) specifies the coding system for sending selected text to other windowing applications, and for receiving the text of selections made in other applications. This command applies to all subsequent selections, until you override it by using the command again. The command C-x <RET> X (set-next-selection-coding-system) specifies the coding system for the next selection made in Emacs or read by Emacs.

The variable x-select-request-type specifies the data type to request from the X Window System for receiving text selections from other applications. If the value is nil (the default), Emacs tries UTF8_STRING and COMPOUND_TEXT, in this order, and uses various heuristics to choose the more appropriate of the two results; if none of these succeed, Emacs falls back on STRING. If the value of x-select-request-type is one of the symbols COMPOUND_TEXT, UTF8_STRING, STRING, or TEXT, Emacs uses only that request type. If the value is a list of some of these symbols, Emacs tries only the request types in the list, in order, until one of them succeeds, or until the list is exhausted.

The command C-x <RET> p (set-buffer-process-coding-system) specifies the coding system for input and output to a subprocess. This command applies to the current buffer; normally, each subprocess has its own buffer, and thus you can use this command to specify translation to and from a particular subprocess by giving the command in the corresponding buffer.

You can also use C-x <RET> c (universal-coding-system-argument) just before the command that runs or starts a subprocess, to specify the coding system for communicating with that subprocess. See Text Coding.

The default for translation of process input and output depends on the current language environment.

The variable locale-coding-system specifies a coding system to use when encoding and decoding system strings such as system error messages and format-time-string formats and time stamps. That coding system is also used for decoding non-ASCII keyboard input on the X Window System. You should choose a coding system that is compatible with the underlying system's text representation, which is normally specified by one of the environment variables LC_ALL, LC_CTYPE, and LANG. (The first one, in the order specified above, whose value is nonempty is the one that determines the text representation.)

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22.12 Coding Systems for File Names

C-x <RET> F coding <RET>
Use coding system coding for encoding and decoding file names (set-file-name-coding-system).

The command C-x <RET> F (set-file-name-coding-system) specifies a coding system to use for encoding file names. It has no effect on reading and writing the contents of files.

In fact, all this command does is set the value of the variable file-name-coding-system. If you set the variable to a coding system name (as a Lisp symbol or a string), Emacs encodes file names using that coding system for all file operations. This makes it possible to use non-ASCII characters in file names—or, at least, those non-ASCII characters that the specified coding system can encode.

If file-name-coding-system is nil, Emacs uses a default coding system determined by the selected language environment, and stored in the default-file-name-coding-system variable. In the default language environment, non-ASCII characters in file names are not encoded specially; they appear in the file system using the internal Emacs representation.

Warning: if you change file-name-coding-system (or the language environment) in the middle of an Emacs session, problems can result if you have already visited files whose names were encoded using the earlier coding system and cannot be encoded (or are encoded differently) under the new coding system. If you try to save one of these buffers under the visited file name, saving may use the wrong file name, or it may encounter an error. If such a problem happens, use C-x C-w to specify a new file name for that buffer.

If a mistake occurs when encoding a file name, use the command M-x recode-file-name to change the file name's coding system. This prompts for an existing file name, its old coding system, and the coding system to which you wish to convert.

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22.13 Coding Systems for Terminal I/O

C-x <RET> t coding <RET>
Use coding system coding for terminal output (set-terminal-coding-system).
C-x <RET> k coding <RET>
Use coding system coding for keyboard input (set-keyboard-coding-system).

The command C-x <RET> t (set-terminal-coding-system) specifies the coding system for terminal output. If you specify a character code for terminal output, all characters output to the terminal are translated into that coding system.

This feature is useful for certain character-only terminals built to support specific languages or character sets—for example, European terminals that support one of the ISO Latin character sets. You need to specify the terminal coding system when using multibyte text, so that Emacs knows which characters the terminal can actually handle.

By default, output to the terminal is not translated at all, unless Emacs can deduce the proper coding system from your terminal type or your locale specification (see Language Environments).

The command C-x <RET> k (set-keyboard-coding-system), or the variable keyboard-coding-system, specifies the coding system for keyboard input. Character-code translation of keyboard input is useful for terminals with keys that send non-ASCII graphic characters—for example, some terminals designed for ISO Latin-1 or subsets of it.

By default, keyboard input is translated based on your system locale setting. If your terminal does not really support the encoding implied by your locale (for example, if you find it inserts a non-ASCII character if you type M-i), you will need to set keyboard-coding-system to nil to turn off encoding. You can do this by putting 

     (set-keyboard-coding-system nil)

in your init file.

There is a similarity between using a coding system translation for keyboard input, and using an input method: both define sequences of keyboard input that translate into single characters. However, input methods are designed to be convenient for interactive use by humans, and the sequences that are translated are typically sequences of ASCII printing characters. Coding systems typically translate sequences of non-graphic characters.

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22.14 Fontsets

A font typically defines shapes for a single alphabet or script. Therefore, displaying the entire range of scripts that Emacs supports requires a collection of many fonts. In Emacs, such a collection is called a fontset. A fontset is defined by a list of font specifications, each assigned to handle a range of character codes, and may fall back on another fontset for characters that are not covered by the fonts it specifies.

Each fontset has a name, like a font. However, while fonts are stored in the system and the available font names are defined by the system, fontsets are defined within Emacs itself. Once you have defined a fontset, you can use it within Emacs by specifying its name, anywhere that you could use a single font. Of course, Emacs fontsets can use only the fonts that the system supports. If some characters appear on the screen as empty boxes or hex codes, this means that the fontset in use for them has no font for those characters. In this case, or if the characters are shown, but not as well as you would like, you may need to install extra fonts. Your operating system may have optional fonts that you can install; or you can install the GNU Intlfonts package, which includes fonts for most supported scripts.8

Emacs creates three fontsets automatically: the standard fontset, the startup fontset and the default fontset. The default fontset is most likely to have fonts for a wide variety of non-ASCII characters, and is the default fallback for the other two fontsets, and if you set a default font rather than fontset. However, it does not specify font family names, so results can be somewhat random if you use it directly. You can specify use of a particular fontset by starting Emacs with the ‘-fn’ option. For example, 

     emacs -fn fontset-standard

You can also specify a fontset with the ‘Font’ resource (see X Resources).

If no fontset is specified for use, then Emacs uses an ASCII font, with ‘fontset-default’ as a fallback for characters the font does not cover. The standard fontset is only used if explicitly requested, despite its name.

A fontset does not necessarily specify a font for every character code. If a fontset specifies no font for a certain character, or if it specifies a font that does not exist on your system, then it cannot display that character properly. It will display that character as a hex code or thin space or an empty box instead. (See glyphless characters, for details.)

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22.15 Defining fontsets

When running on X, Emacs creates a standard fontset automatically according to the value of standard-fontset-spec. This fontset's name is 

     -*-fixed-medium-r-normal-*-16-*-*-*-*-*-fontset-standard

or just ‘fontset-standard’ for short.

On GNUstep and Mac OS X, the standard fontset is created using the value of ns-standard-fontset-spec, and on MS Windows it is created using the value of w32-standard-fontset-spec.

Bold, italic, and bold-italic variants of the standard fontset are created automatically. Their names have ‘bold’ instead of ‘medium’, or ‘i’ instead of ‘r’, or both.

Emacs generates a fontset automatically, based on any default ASCII font that you specify with the ‘Font’ resource or the ‘-fn’ argument, or the default font that Emacs found when it started. This is the startup fontset and its name is fontset-startup. It does this by replacing the charset_registry field with ‘fontset’, and replacing charset_encoding field with ‘startup’, then using the resulting string to specify a fontset.

For instance, if you start Emacs with a font of this form, 

     emacs -fn "*courier-medium-r-normal--14-140-*-iso8859-1"

Emacs generates the following fontset and uses it for the initial X window frame: 

     -*-courier-medium-r-normal-*-14-140-*-*-*-*-fontset-startup

The startup fontset will use the font that you specify, or a variant with a different registry and encoding, for all the characters that are supported by that font, and fallback on ‘fontset-default’ for other characters.

With the X resource ‘Emacs.Font’, you can specify a fontset name just like an actual font name. But be careful not to specify a fontset name in a wildcard resource like ‘Emacs*Font’—that wildcard specification matches various other resources, such as for menus, and menus cannot handle fontsets. See X Resources.

You can specify additional fontsets using X resources named ‘Fontset-n’, where n is an integer starting from 0. The resource value should have this form: 

     fontpattern, [charset:font]...

fontpattern should have the form of a standard X font name (see the previous fontset-startup example), except for the last two fields. They should have the form ‘fontset-alias’.

The fontset has two names, one long and one short. The long name is fontpattern. The short name is ‘fontset-alias’. You can refer to the fontset by either name.

The construct ‘charset:font’ specifies which font to use (in this fontset) for one particular character set. Here, charset is the name of a character set, and font is the font to use for that character set. You can use this construct any number of times in defining one fontset.

For the other character sets, Emacs chooses a font based on fontpattern. It replaces ‘fontset-alias’ with values that describe the character set. For the ASCII character font, ‘fontset-alias’ is replaced with ‘ISO8859-1’.

In addition, when several consecutive fields are wildcards, Emacs collapses them into a single wildcard. This is to prevent use of auto-scaled fonts. Fonts made by scaling larger fonts are not usable for editing, and scaling a smaller font is not also useful, because it is better to use the smaller font in its own size, which is what Emacs does.

Thus if fontpattern is this, 

     -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24

the font specification for ASCII characters would be this: 

     -*-fixed-medium-r-normal-*-24-*-ISO8859-1

and the font specification for Chinese GB2312 characters would be this: 

     -*-fixed-medium-r-normal-*-24-*-gb2312*-*

You may not have any Chinese font matching the above font specification. Most X distributions include only Chinese fonts that have ‘song ti’ or ‘fangsong ti’ in the family field. In such a case, ‘Fontset-n’ can be specified as: 

     Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
             chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*

Then, the font specifications for all but Chinese GB2312 characters have ‘fixed’ in the family field, and the font specification for Chinese GB2312 characters has a wild card ‘*’ in the family field.

The function that processes the fontset resource value to create the fontset is called create-fontset-from-fontset-spec. You can also call this function explicitly to create a fontset.

See Fonts, for more information about font naming.

Next: , Previous: Defining Fontsets, Up: International

22.16 Modifying Fontsets

Fontsets do not always have to be created from scratch. If only minor changes are required it may be easier to modify an existing fontset. Modifying ‘fontset-default’ will also affect other fontsets that use it as a fallback, so can be an effective way of fixing problems with the fonts that Emacs chooses for a particular script.

Fontsets can be modified using the function set-fontset-font, specifying a character, a charset, a script, or a range of characters to modify the font for, and a font specification for the font to be used. Some examples are: 

     ;; Use Liberation Mono for latin-3 charset.
     (set-fontset-font "fontset-default" 'iso-8859-3
                       "Liberation Mono")
     
     ;; Prefer a big5 font for han characters
     (set-fontset-font "fontset-default"
                       'han (font-spec :registry "big5")
                       nil 'prepend)
     
     ;; Use DejaVu Sans Mono as a fallback in fontset-startup
     ;; before resorting to fontset-default.
     (set-fontset-font "fontset-startup" nil "DejaVu Sans Mono"
                       nil 'append)
     
     ;; Use MyPrivateFont for the Unicode private use area.
     (set-fontset-font "fontset-default"  '(#xe000 . #xf8ff)
                       "MyPrivateFont")

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22.17 Undisplayable Characters

There may be some non-ASCII characters that your terminal cannot display. Most text terminals support just a single character set (use the variable default-terminal-coding-system to tell Emacs which one, Terminal Coding); characters that can't be encoded in that coding system are displayed as ‘?’ by default.

Graphical displays can display a broader range of characters, but you may not have fonts installed for all of them; characters that have no font appear as a hollow box.

If you use Latin-1 characters but your terminal can't display Latin-1, you can arrange to display mnemonic ASCII sequences instead, e.g., ‘"o’ for o-umlaut. Load the library iso-ascii to do this.

If your terminal can display Latin-1, you can display characters from other European character sets using a mixture of equivalent Latin-1 characters and ASCII mnemonics. Customize the variable latin1-display to enable this. The mnemonic ASCII sequences mostly correspond to those of the prefix input methods.

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22.18 Unibyte Editing Mode

The ISO 8859 Latin-n character sets define character codes in the range 0240 to 0377 octal (160 to 255 decimal) to handle the accented letters and punctuation needed by various European languages (and some non-European ones). Note that Emacs considers bytes with codes in this range as raw bytes, not as characters, even in a unibyte buffer, i.e., if you disable multibyte characters. However, Emacs can still handle these character codes as if they belonged to one of the single-byte character sets at a time. To specify which of these codes to use, invoke M-x set-language-environment and specify a suitable language environment such as ‘Latin-n’.

For more information about unibyte operation, see Disabling Multibyte.

Emacs can also display bytes in the range 160 to 255 as readable characters, provided the terminal or font in use supports them. This works automatically. On a graphical display, Emacs can also display single-byte characters through fontsets, in effect by displaying the equivalent multibyte characters according to the current language environment. To request this, set the variable unibyte-display-via-language-environment to a non-nil value. Note that setting this only affects how these bytes are displayed, but does not change the fundamental fact that Emacs treats them as raw bytes, not as characters.

If your terminal does not support display of the Latin-1 character set, Emacs can display these characters as ASCII sequences which at least give you a clear idea of what the characters are. To do this, load the library iso-ascii. Similar libraries for other Latin-n character sets could be implemented, but have not been so far.

Normally non-ISO-8859 characters (decimal codes between 128 and 159 inclusive) are displayed as octal escapes. You can change this for non-standard “extended” versions of ISO-8859 character sets by using the function standard-display-8bit in the disp-table library.

There are two ways to input single-byte non-ASCII characters:

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22.19 Charsets

In Emacs, charset is short for “character set”. Emacs supports most popular charsets (such as ascii, iso-8859-1, cp1250, big5, and unicode), in addition to some charsets of its own (such as emacs, unicode-bmp, and eight-bit). All supported characters belong to one or more charsets.

Emacs normally “does the right thing” with respect to charsets, so that you don't have to worry about them. However, it is sometimes helpful to know some of the underlying details about charsets.

One example is font selection (see Fonts). Each language environment (see Language Environments) defines a “priority list” for the various charsets. When searching for a font, Emacs initially attempts to find one that can display the highest-priority charsets. For instance, in the Japanese language environment, the charset japanese-jisx0208 has the highest priority, so Emacs tries to use a font whose registry property is ‘JISX0208.1983-0’.

There are two commands that can be used to obtain information about charsets. The command M-x list-charset-chars prompts for a charset name, and displays all the characters in that character set. The command M-x describe-character-set prompts for a charset name, and displays information about that charset, including its internal representation within Emacs.

M-x list-character-sets displays a list of all supported charsets. The list gives the names of charsets and additional information to identity each charset; see the International Register of Coded Character Sets for more details. In this list, charsets are divided into two categories: normal charsets are listed first, followed by supplementary charsets. A supplementary charset is one that is used to define another charset (as a parent or a subset), or to provide backward-compatibility for older Emacs versions.

To find out which charset a character in the buffer belongs to, put point before it and type C-u C-x = (see International Chars).

Previous: Charsets, Up: International

22.20 Bidirectional Editing

Emacs supports editing text written in scripts, such as Arabic and Hebrew, whose natural ordering of horizontal text for display is from right to left. However, digits and Latin text embedded in these scripts are still displayed left to right. It is also not uncommon to have small portions of text in Arabic or Hebrew embedded in an otherwise Latin document; e.g., as comments and strings in a program source file. For these reasons, text that uses these scripts is actually bidirectional: a mixture of runs of left-to-right and right-to-left characters.

This section describes the facilities and options provided by Emacs for editing bidirectional text.

Emacs stores right-to-left and bidirectional text in the so-called logical (or reading) order: the buffer or string position of the first character you read precedes that of the next character. Reordering of bidirectional text into the visual order happens at display time. As result, character positions no longer increase monotonically with their positions on display. Emacs implements the Unicode Bidirectional Algorithm described in the Unicode Standard Annex #9, for reordering of bidirectional text for display.

The buffer-local variable bidi-display-reordering controls whether text in the buffer is reordered for display. If its value is non-nil, Emacs reorders characters that have right-to-left directionality when they are displayed. The default value is t.

Each paragraph of bidirectional text can have its own base direction, either right-to-left or left-to-right. (Paragraph boundaries are empty lines, i.e., lines consisting entirely of whitespace characters.) Text in left-to-right paragraphs begins on the screen at the left margin of the window and is truncated or continued when it reaches the right margin. By contrast, text in right-to-left paragraphs is displayed starting at the right margin and is continued or truncated at the left margin.

Emacs determines the base direction of each paragraph dynamically, based on the text at the beginning of the paragraph. However, sometimes a buffer may need to force a certain base direction for its paragraphs. The variable bidi-paragraph-direction, if non-nil, disables the dynamic determination of the base direction, and instead forces all paragraphs in the buffer to have the direction specified by its buffer-local value. The value can be either right-to-left or left-to-right. Any other value is interpreted as nil.

Alternatively, you can control the base direction of a paragraph by inserting special formatting characters in front of the paragraph. The special character RIGHT-TO-LEFT MARK, or rlm, forces the right-to-left direction on the following paragraph, while LEFT-TO-RIGHT MARK, or lrm forces the left-to-right direction. (You can use C-x 8 RET to insert these characters.) In a GUI session, the lrm and rlm characters display as very thin blank characters; on text terminals they display as blanks.

Because characters are reordered for display, Emacs commands that operate in the logical order or on stretches of buffer positions may produce unusual effects. For example, C-f and C-b commands move point in the logical order, so the cursor will sometimes jump when point traverses reordered bidirectional text. Similarly, a highlighted region covering a contiguous range of character positions may look discontinuous if the region spans reordered text. This is normal and similar to the behavior of other programs that support bidirectional text.

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23 Major and Minor Modes

Emacs contains many editing modes that alter its basic behavior in useful ways. These are divided into major modes and minor modes.

Major modes provide specialized facilities for working on a particular file type, such as a C source file (see Programs), or a particular type of non-file buffer, such as a shell buffer (see Shell). Major modes are mutually exclusive; each buffer has one and only one major mode at any time.

Minor modes are optional features which you can turn on or off, not necessarily specific to a type of file or buffer. For example, Auto Fill mode is a minor mode in which <SPC> breaks lines between words as you type (see Auto Fill). Minor modes are independent of one another, and of the selected major mode.

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23.1 Major Modes

Every buffer possesses a major mode, which determines the editing behavior of Emacs while that buffer is current. The mode line normally shows the name of the current major mode, in parentheses (see Mode Line).

The least specialized major mode is called Fundamental mode. This mode has no mode-specific redefinitions or variable settings, so that each Emacs command behaves in its most general manner, and each user option variable is in its default state.

For editing text of a specific type that Emacs knows about, such as Lisp code or English text, you typically use a more specialized major mode, such as Lisp mode or Text mode. Most major modes fall into three major groups. The first group contains modes for normal text, either plain or with mark-up. It includes Text mode, HTML mode, SGML mode, TeX mode and Outline mode. The second group contains modes for specific programming languages. These include Lisp mode (which has several variants), C mode, Fortran mode, and others. The third group consists of major modes that are not associated directly with files; they are used in buffers created for specific purposes by Emacs, such as Dired mode for buffers made by Dired (see Dired), Message mode for buffers made by C-x m (see Sending Mail), and Shell mode for buffers used to communicate with an inferior shell process (see Interactive Shell).

Usually, the major mode is automatically set by Emacs, when you first visit a file or create a buffer (see Choosing Modes). You can explicitly select a new major mode by using an M-x command. Take the name of the mode and add -mode to get the name of the command to select that mode (e.g., M-x lisp-mode enters Lisp mode).

The value of the buffer-local variable major-mode is a symbol with the same name as the major mode command (e.g., lisp-mode). This variable is set automatically; you should not change it yourself.

The default value of major-mode determines the major mode to use for files that do not specify a major mode, and for new buffers created with C-x b. Normally, this default value is the symbol fundamental-mode, which specifies Fundamental mode. You can change this default value via the Customization interface (see Easy Customization), or by adding a line like this to your init file (see Init File): 

     (setq-default major-mode 'text-mode)

If the default value of major-mode is nil, the major mode is taken from the previously current buffer.

Specialized major modes often change the meanings of certain keys to do something more suitable for the mode. For instance, programming language modes bind <TAB> to indent the current line according to the rules of the language (see Indentation). The keys that are commonly changed are <TAB>, <DEL>, and C-j. Many modes also define special commands of their own, usually bound in the prefix key C-c. Major modes can also alter user options and variables; for instance, programming language modes typically set a buffer-local value for the variable comment-start, which determines how source code comments are delimited (see Comments).

To view the documentation for the current major mode, including a list of its key bindings, type C-h m (describe-mode).

Every major mode, apart from Fundamental mode, defines a mode hook, a customizable list of Lisp functions to run each time the mode is enabled in a buffer. See Hooks, for more information about hooks. Each mode hook is named after its major mode, e.g., Fortran mode has fortran-mode-hook. Furthermore, all text-based major modes run text-mode-hook, and all programming language modes run prog-mode-hook, prior to running their own mode hooks. Hook functions can look at the value of the variable major-mode to see which mode is actually being entered.

Mode hooks are commonly used to enable minor modes (see Minor Modes). For example, you can put the following lines in your init file to enable Flyspell minor mode in all text-based major modes (see Spelling), and Eldoc minor mode in Emacs Lisp mode (see Lisp Doc): 

     (add-hook 'text-mode-hook 'flyspell-mode)
     (add-hook 'emacs-lisp-mode-hook 'eldoc-mode)

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23.2 Minor Modes

A minor mode is an optional editing mode that alters the behavior of Emacs in some well-defined way. Unlike major modes, any number of minor modes can be in effect at any time. Some minor modes are buffer-local, and can be turned on (enabled) in certain buffers and off (disabled) in others. Other minor modes are global: while enabled, they affect everything you do in the Emacs session, in all buffers. Most minor modes are disabled by default, but a few are enabled by default.

Most buffer-local minor modes say in the mode line when they are enabled, just after the major mode indicator. For example, ‘Fill’ in the mode line means that Auto Fill mode is enabled. See Mode Line.

Like major modes, each minor mode is associated with a mode command, whose name consists of the mode name followed by ‘-mode’. For instance, the mode command for Auto Fill mode is auto-fill-mode. But unlike a major mode command, which simply enables the mode, the mode command for a minor mode can either enable or disable it:

Most minor modes also have a mode variable, with the same name as the mode command. Its value is non-nil if the mode is enabled, and nil if it is disabled. In general, you should not try to enable or disable the mode by changing the value of the mode variable directly in Lisp; you should run the mode command instead. However, setting the mode variable through the Customize interface (see Easy Customization) will always properly enable or disable the mode, since Customize automatically runs the mode command for you.

The following is a list of some buffer-local minor modes:

And here are some useful global minor modes:

Previous: Minor Modes, Up: Modes

23.3 Choosing File Modes

When you visit a file, Emacs chooses a major mode automatically. Normally, it makes the choice based on the file name—for example, files whose names end in ‘.c’ are normally edited in C mode—but sometimes it chooses the major mode based on special text in the file. This special text can also be used to enable buffer-local minor modes.

Here is the exact procedure:

First, Emacs checks whether the file contains file-local mode variables. See File Variables. If there is a file-local variable that specifies a major mode, then Emacs uses that major mode, ignoring all other criteria. There are several methods to specify a major mode using a file-local variable; the simplest is to put the mode name in the first nonblank line, preceded and followed by ‘-*-’. Other text may appear on the line as well. For example, 

     ; -*-Lisp-*-

tells Emacs to use Lisp mode. Note how the semicolon is used to make Lisp treat this line as a comment. You could equivalently write 

     ; -*- mode: Lisp;-*-

You can also use file-local variables to specify buffer-local minor modes, by using eval specifications. For example, this first nonblank line puts the buffer in Lisp mode and enables Auto-Fill mode: 

     ; -*- mode: Lisp; eval: (auto-fill-mode 1); -*-

Note, however, that it is usually inappropriate to enable minor modes this way, since most minor modes represent individual user preferences. If you personally want to use a minor mode for a particular file type, it is better to enable the minor mode via a major mode hook (see Major Modes).

Second, if there is no file variable specifying a major mode, Emacs checks whether the file's contents begin with ‘#!’. If so, that indicates that the file can serve as an executable shell command, which works by running an interpreter named on the file's first line (the rest of the file is used as input to the interpreter). Therefore, Emacs tries to use the interpreter name to choose a mode. For instance, a file that begins with ‘#!/usr/bin/perl’ is opened in Perl mode. The variable interpreter-mode-alist specifies the correspondence between interpreter program names and major modes.

When the first line starts with ‘#!’, you usually cannot use the ‘-*-’ feature on the first line, because the system would get confused when running the interpreter. So Emacs looks for ‘-*-’ on the second line in such files as well as on the first line. The same is true for man pages which start with the magic string ‘'\"’ to specify a list of troff preprocessors.

Third, Emacs tries to determine the major mode by looking at the text at the start of the buffer, based on the variable magic-mode-alist. By default, this variable is nil (an empty list), so Emacs skips this step; however, you can customize it in your init file (see Init File). The value should be a list of elements of the form 

     (regexp . mode-function)

where regexp is a regular expression (see Regexps), and mode-function is a major mode command. If the text at the beginning of the file matches regexp, Emacs chooses the major mode specified by mode-function.

Alternatively, an element of magic-mode-alist may have the form 

     (match-function . mode-function)

where match-function is a Lisp function that is called at the beginning of the buffer; if the function returns non-nil, Emacs set the major mode with mode-function.

Fourth—if Emacs still hasn't found a suitable major mode—it looks at the file's name. The correspondence between file names and major modes is controlled by the variable auto-mode-alist. Its value is a list in which each element has this form, 

     (regexp . mode-function)

or this form, 

     (regexp mode-function flag)

For example, one element normally found in the list has the form ("\\.c\\'" . c-mode), and it is responsible for selecting C mode for files whose names end in .c. (Note that ‘\\’ is needed in Lisp syntax to include a ‘\’ in the string, which must be used to suppress the special meaning of ‘.’ in regexps.) If the element has the form (regexp mode-function flag) and flag is non-nil, then after calling mode-function, Emacs discards the suffix that matched regexp and searches the list again for another match.

On GNU/Linux and other systems with case-sensitive file names, Emacs performs a case-sensitive search through auto-mode-alist; if this search fails, it performs a second case-insensitive search through the alist. To suppress the second search, change the variable auto-mode-case-fold to nil. On systems with case-insensitive file names, such as Microsoft Windows, Emacs performs a single case-insensitive search through auto-mode-alist.

Finally, if Emacs still hasn't found a major mode to use, it compares the text at the start of the buffer to the variable magic-fallback-mode-alist. This variable works like magic-mode-alist, described above, except that is consulted only after auto-mode-alist. By default, magic-fallback-mode-alist contains forms that check for image files, HTML/XML/SGML files, and PostScript files.

If you have changed the major mode of a buffer, you can return to the major mode Emacs would have chosen automatically, by typing M-x normal-mode. This is the same function that find-file calls to choose the major mode. It also processes the file's ‘-*-’ line or local variables list (if any). See File Variables.

The commands C-x C-w and set-visited-file-name change to a new major mode if the new file name implies a mode (see Saving). (C-x C-s does this too, if the buffer wasn't visiting a file.) However, this does not happen if the buffer contents specify a major mode, and certain “special” major modes do not allow the mode to change. You can turn off this mode-changing feature by setting change-major-mode-with-file-name to nil.

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24 Indentation

Indentation refers to inserting or adjusting whitespace characters (space and/or tab characters) at the beginning of a line of text. This chapter documents indentation commands and options which are common to Text mode and related modes, as well as programming language modes. See Program Indent, for additional documentation about indenting in programming modes.

The simplest way to perform indentation is the <TAB> key. In most major modes, this runs the command indent-for-tab-command. (In C and related modes, <TAB> runs the command c-indent-line-or-region, which behaves similarly).

<TAB>
Insert whitespace, or indent the current line, in a mode-appropriate way (indent-for-tab-command). If the region is active, indent all the lines within it.

The exact behavior of <TAB> depends on the major mode. In Text mode and related major modes, <TAB> normally inserts some combination of space and tab characters to advance point to the next tab stop (see Tab Stops). For this purpose, the position of the first non-whitespace character on the preceding line is treated as an additional tab stop, so you can use <TAB> to “align” point with the preceding line. If the region is active (see Using Region), <TAB> acts specially: it indents each line in the region so that its first non-whitespace character is aligned with the preceding line.

In programming modes, <TAB> indents the current line of code in a way that makes sense given the code in the preceding lines. If the region is active, all the lines in the region are indented this way. If point was initially within the current line's indentation, it is repositioned to the first non-whitespace character on the line.

If you just want to insert a tab character in the buffer, type C-q <TAB> (see Inserting Text).

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24.1 Indentation Commands

Apart from the <TAB> (indent-for-tab-command) command, Emacs provides a variety of commands to perform indentation in other ways.

C-j
Perform <RET> followed by <TAB> (newline-and-indent).
C-M-o
Split the current line at point (split-line). The text on the line after point becomes a new line, indented to the same column where point is located. This command first moves point forward over any spaces and tabs. Afterward, point is positioned before the inserted newline.


M-m
Move (forward or back) to the first non-whitespace character on the current line (back-to-indentation). If there are no non-whitespace characters on the line, move to the end of the line.
M-i
Indent whitespace at point, up to the next tab stop (tab-to-tab-stop). See Tab Stops.


M-x indent-relative
Insert whitespace at point, until point is aligned with the first non-whitespace character on the previous line (actually, the last non-blank line). If point is already farther right than that, run tab-to-tab-stop instead—unless called with a numeric argument, in which case do nothing.
M-^
Merge the previous and the current line (delete-indentation). This “joins” the two lines cleanly, by replacing any indentation at the front of the current line, together with the line boundary, with a single space.

As a special case (useful for Lisp code), the single space is omitted if the characters to be joined are consecutive opening and closing parentheses, or if the junction follows another newline.

If there is a fill prefix, M-^ deletes the fill prefix if it appears after the newline that is deleted. See Fill Prefix.

C-M-\
Indent all the lines in the region, as though you had typed <TAB> at the beginning of each line (indent-region).

If a numeric argument is supplied, indent every line in the region to that column number.

C-x <TAB>
Shift each line in the region by a fixed distance, to the right or left (indent-rigidly). The distance to move is determined by the numeric argument (positive to move rightward, negative to move leftward).

This command can be used to remove all indentation from the lines in the region, by invoking it with a large negative argument, e.g., C-u -1000 C-x <TAB>.

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24.2 Tab Stops

Emacs defines certain column numbers to be tab stops. These are used as stopping points by <TAB> when inserting whitespace in Text mode and related modes (see Indentation), and by commands like M-i (see Indentation Commands). By default, tab stops are located every 8 columns. These positions are stored in the variable tab-stop-list, whose value is a list of column numbers in increasing order.

Instead of customizing the variable tab-stop-list directly, a convenient way to view and set tab stops is via the command M-x edit-tab-stops. This switches to a buffer containing a description of the tab stop settings, which looks like this: 

             :       :       :       :       :       :
     0         1         2         3         4
     0123456789012345678901234567890123456789012345678
     To install changes, type C-c C-c

The first line contains a colon at each tab stop. The numbers on the next two lines are present just to indicate where the colons are.

You can edit this buffer to specify different tab stops by placing colons on the desired columns. The buffer uses Overwrite mode (see Minor Modes). When you are done, type C-c C-c to make the new tab stops take effect. Normally, the new tab stop settings apply to all buffers. However, if you have made the tab-stop-list variable local to the buffer where you called M-x edit-tab-stops (see Locals), then the new tab stop settings apply only to that buffer. To save the tab stop settings for future Emacs sessions, use the Customize interface to save the value of tab-stop-list (see Easy Customization).

Note that the tab stops discussed in this section have nothing to do with how tab characters are displayed in the buffer. Tab characters are always displayed as empty spaces extending to the next display tab stop. See Text Display.

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24.3 Tabs vs. Spaces

Normally, indentation commands insert (or remove) an optimal mix of space characters and tab characters to align to the desired column. Tab characters are displayed as a stretch of empty space extending to the next display tab stop. By default, there is one display tab stop every tab-width columns (the default is 8). See Text Display.

If you prefer, all indentation can be made from spaces only. To request this, set the buffer-local variable indent-tabs-mode to nil. See Locals, for information about setting buffer-local variables. Note, however, that C-q <TAB> always inserts a tab character, regardless of the value of indent-tabs-mode.

One reason to set indent-tabs-mode to nil is that not all editors display tab characters in the same way. Emacs users, too, may have different customized values of tab-width. By using spaces only, you can make sure that your file always looks the same. If you only care about how it looks within Emacs, another way to tackle this problem is to set the tab-width variable in a file-local variable (see File Variables).

There are also commands to convert tabs to spaces or vice versa, always preserving the columns of all non-whitespace text. M-x tabify scans the region for sequences of spaces, and converts sequences of at least two spaces to tabs if that can be done without changing indentation. M-x untabify changes all tabs in the region to appropriate numbers of spaces.

Previous: Just Spaces, Up: Indentation

24.4 Convenience Features for Indentation

The variable tab-always-indent tweaks the behavior of the <TAB> (indent-for-tab-command) command. The default value, t, gives the behavior described in Indentation. If you change the value to the symbol complete, then <TAB> first tries to indent the current line, and if the line was already indented, it tries to complete the text at point (see Symbol Completion). If the value is nil, then <TAB> indents the current line only if point is at the left margin or in the line's indentation; otherwise, it inserts a tab character.

Electric Indent mode is a global minor mode that automatically indents the line after every <RET> you type. To toggle this minor mode, type M-x electric-indent-mode.

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25 Commands for Human Languages

This chapter describes Emacs commands that act on text, by which we mean sequences of characters in a human language (as opposed to, say, a computer programming language). These commands act in ways that take into account the syntactic and stylistic conventions of human languages: conventions involving words, sentences, paragraphs, and capital letters. There are also commands for filling, which means rearranging the lines of a paragraph to be approximately equal in length. These commands, while intended primarily for editing text, are also often useful for editing programs.

Emacs has several major modes for editing human-language text. If the file contains ordinary text, use Text mode, which customizes Emacs in small ways for the syntactic conventions of text. Outline mode provides special commands for operating on text with an outline structure. Org mode extends Outline mode and turn Emacs into a full-fledged organizer: you can manage TODO lists, store notes and publish them in many formats.

Emacs has other major modes for text which contains “embedded” commands, such as TeX and LaTeX (see TeX Mode); HTML and SGML (see HTML Mode); XML (see the nXML mode Info manual, which is distributed with Emacs); and Groff and Nroff (see Nroff Mode).

If you need to edit pictures made out of text characters (commonly referred to as “ASCII art”), use Picture mode, a special major mode for editing such pictures. See Picture Mode.

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25.1 Words

Emacs defines several commands for moving over or operating on words:

M-f
Move forward over a word (forward-word).
M-b
Move backward over a word (backward-word).
M-d
Kill up to the end of a word (kill-word).
M-<DEL>
Kill back to the beginning of a word (backward-kill-word).
M-@
Mark the end of the next word (mark-word).
M-t
Transpose two words or drag a word across others (transpose-words).

Notice how these keys form a series that parallels the character-based C-f, C-b, C-d, <DEL> and C-t. M-@ is cognate to C-@, which is an alias for C-<SPC>.

The commands M-f (forward-word) and M-b (backward-word) move forward and backward over words. These <Meta>-based key sequences are analogous to the key sequences C-f and C-b, which move over single characters. The analogy extends to numeric arguments, which serve as repeat counts. M-f with a negative argument moves backward, and M-b with a negative argument moves forward. Forward motion stops right after the last letter of the word, while backward motion stops right before the first letter.

M-d (kill-word) kills the word after point. To be precise, it kills everything from point to the place M-f would move to. Thus, if point is in the middle of a word, M-d kills just the part after point. If some punctuation comes between point and the next word, it is killed along with the word. (If you wish to kill only the next word but not the punctuation before it, simply do M-f to get the end, and kill the word backwards with M-<DEL>.) M-d takes arguments just like M-f.

M-<DEL> (backward-kill-word) kills the word before point. It kills everything from point back to where M-b would move to. For instance, if point is after the space in ‘FOO, BAR’, it kills ‘FOO, ’. If you wish to kill just ‘FOO’, and not the comma and the space, use M-b M-d instead of M-<DEL>.

M-t (transpose-words) exchanges the word before or containing point with the following word. The delimiter characters between the words do not move. For example, ‘FOO, BAR’ transposes into ‘BAR, FOO’ rather than ‘BAR FOO,’. See Transpose, for more on transposition.

To operate on words with an operation which acts on the region, use the command M-@ (mark-word). This command sets the mark where M-f would move to. See Marking Objects, for more information about this command.

The word commands' understanding of word boundaries is controlled by the syntax table. Any character can, for example, be declared to be a word delimiter. See Syntax Tables.

In addition, see Position Info for the M-= (count-words-region) and M-x count-words commands, which count and report the number of words in the region or buffer.

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25.2 Sentences

The Emacs commands for manipulating sentences and paragraphs are mostly on Meta keys, like the word-handling commands.

M-a
Move back to the beginning of the sentence (backward-sentence).
M-e
Move forward to the end of the sentence (forward-sentence).
M-k
Kill forward to the end of the sentence (kill-sentence).
C-x <DEL>
Kill back to the beginning of the sentence (backward-kill-sentence).

The commands M-a (backward-sentence) and M-e (forward-sentence) move to the beginning and end of the current sentence, respectively. Their bindings were chosen to resemble C-a and C-e, which move to the beginning and end of a line. Unlike them, M-a and M-e move over successive sentences if repeated.

Moving backward over a sentence places point just before the first character of the sentence; moving forward places point right after the punctuation that ends the sentence. Neither one moves over the whitespace at the sentence boundary.

Just as C-a and C-e have a kill command, C-k, to go with them, M-a and M-e have a corresponding kill command: M-k (kill-sentence) kills from point to the end of the sentence. With a positive numeric argument n, it kills the next n sentences; with a negative argument −n, it kills back to the beginning of the nth preceding sentence.

The C-x <DEL> (backward-kill-sentence) kills back to the beginning of a sentence.

The sentence commands assume that you follow the American typist's convention of putting two spaces at the end of a sentence. That is, a sentence ends wherever there is a ‘.’, ‘?’ or ‘!’ followed by the end of a line or two spaces, with any number of ‘)’, ‘]’, ‘'’, or ‘"’ characters allowed in between. A sentence also begins or ends wherever a paragraph begins or ends. It is useful to follow this convention, because it allows the Emacs sentence commands to distinguish between periods that end a sentence and periods that indicate abbreviations.

If you want to use just one space between sentences, you can set the variable sentence-end-double-space to nil to make the sentence commands stop for single spaces. However, this has a drawback: there is no way to distinguish between periods that end sentences and those that indicate abbreviations. For convenient and reliable editing, we therefore recommend you follow the two-space convention. The variable sentence-end-double-space also affects filling (see Fill Commands).

The variable sentence-end controls how to recognize the end of a sentence. If non-nil, its value should be a regular expression, which is used to match the last few characters of a sentence, together with the whitespace following the sentence (see Regexps). If the value is nil, the default, then Emacs computes sentence ends according to various criteria such as the value of sentence-end-double-space.

Some languages, such as Thai, do not use periods to indicate the end of a sentence. Set the variable sentence-end-without-period to t in such cases.

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25.3 Paragraphs

The Emacs commands for manipulating paragraphs are also on Meta keys.

M-{
Move back to previous paragraph beginning (backward-paragraph).
M-}
Move forward to next paragraph end (forward-paragraph).
M-h
Put point and mark around this or next paragraph (mark-paragraph).

M-{ (backward-paragraph) moves to the beginning of the current or previous paragraph (see below for the definition of a paragraph). M-} (forward-paragraph) moves to the end of the current or next paragraph. If there is a blank line before the paragraph, M-{ moves to the blank line.

When you wish to operate on a paragraph, type M-h (mark-paragraph) to set the region around it. For example, M-h C-w kills the paragraph around or after point. M-h puts point at the beginning and mark at the end of the paragraph point was in. If point is between paragraphs (in a run of blank lines, or at a boundary), M-h sets the region around the paragraph following point. If there are blank lines preceding the first line of the paragraph, one of these blank lines is included in the region. If the region is already active, the command sets the mark without changing point, and each subsequent M-h further advances the mark by one paragraph.

The definition of a paragraph depends on the major mode. In Fundamental mode, as well as Text mode and related modes, a paragraph is separated each neighboring paragraph another by one or more blank lines—lines that are either empty, or consist solely of space, tab and/or formfeed characters. In programming language modes, paragraphs are usually defined in a similar way, so that you can use the paragraph commands even though there are no paragraphs as such in a program.

Note that an indented line is not itself a paragraph break in Text mode. If you want indented lines to separate paragraphs, use Paragraph-Indent Text mode instead. See Text Mode.

If you set a fill prefix, then paragraphs are delimited by all lines which don't start with the fill prefix. See Filling.

The precise definition of a paragraph boundary is controlled by the variables paragraph-separate and paragraph-start. The value of paragraph-start is a regular expression that should match lines that either start or separate paragraphs (see Regexps). The value of paragraph-separate is another regular expression that should match lines that separate paragraphs without being part of any paragraph (for example, blank lines). Lines that start a new paragraph and are contained in it must match only paragraph-start, not paragraph-separate. For example, in Fundamental mode, paragraph-start is "\f\\|[ \t]*$", and paragraph-separate is "[ \t\f]*$".

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25.4 Pages

Within some text files, text is divided into pages delimited by the formfeed character (ASCII code 12, also denoted as <control-L>), which is displayed in Emacs as the escape sequence ‘^L’ (see Text Display). Traditionally, when such text files are printed to hardcopy, each formfeed character forces a page break. Most Emacs commands treat it just like any other character, so you can insert it with C-q C-l, delete it with <DEL>, etc. In addition, Emacs provides commands to move over pages and operate on them.

M-x what-page
Display the page number of point, and the line number within that page.
C-x [
Move point to previous page boundary (backward-page).
C-x ]
Move point to next page boundary (forward-page).
C-x C-p
Put point and mark around this page (or another page) (mark-page).
C-x l
Count the lines in this page (count-lines-page).

M-x what-page counts pages from the beginning of the file, and counts lines within the page, showing both numbers in the echo area.

The C-x [ (backward-page) command moves point to immediately after the previous page delimiter. If point is already right after a page delimiter, it skips that one and stops at the previous one. A numeric argument serves as a repeat count. The C-x ] (forward-page) command moves forward past the next page delimiter.

The C-x C-p command (mark-page) puts point at the beginning of the current page (after that page delimiter at the front), and the mark at the end of the page (after the page delimiter at the end).

C-x C-p C-w is a handy way to kill a page to move it elsewhere. If you move to another page delimiter with C-x [ and C-x ], then yank the killed page, all the pages will be properly delimited once again. The reason C-x C-p includes only the following page delimiter in the region is to ensure that.

A numeric argument to C-x C-p specifies which page to go to, relative to the current one. Zero means the current page, one the next page, and −1 the previous one.

The C-x l command (count-lines-page) is good for deciding where to break a page in two. It displays in the echo area the total number of lines in the current page, and then divides it up into those preceding the current line and those following, as in 

     Page has 96 (72+25) lines

Notice that the sum is off by one; this is correct if point is not at the beginning of a line.

The variable page-delimiter controls where pages begin. Its value is a regular expression that matches the beginning of a line that separates pages (see Regexps). The normal value of this variable is "^\f", which matches a formfeed character at the beginning of a line.

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25.5 Filling Text

Filling text means breaking it up into lines that fit a specified width. Emacs does filling in two ways. In Auto Fill mode, inserting text with self-inserting characters also automatically fills it. There are also explicit fill commands that you can use when editing text.

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25.5.1 Auto Fill Mode

Auto Fill mode is a buffer-local minor mode (see Minor Modes) in which lines are broken automatically when they become too wide. Breaking happens only when you type a <SPC> or <RET>.

M-x auto-fill-mode
Enable or disable Auto Fill mode.
<SPC>
<RET>
In Auto Fill mode, break lines when appropriate.

The mode command M-x auto-fill-mode toggles Auto Fill mode in the current buffer. With a positive numeric argument, it enables Auto Fill mode, and with a negative argument it disables it. If auto-fill-mode is called from Lisp with an omitted or nil argument, it enables Auto Fill mode. To enable Auto Fill mode automatically in certain major modes, add auto-fill-mode to the mode hooks (see Major Modes). When Auto Fill mode is enabled, the mode indicator ‘Fill’ appears in the mode line (see Mode Line).

Auto Fill mode breaks lines automatically at spaces whenever they get longer than the desired width. This line breaking occurs only when you type <SPC> or <RET>. If you wish to insert a space or newline without permitting line-breaking, type C-q <SPC> or C-q C-j respectively. Also, C-o inserts a newline without line breaking.

When Auto Fi