GNU Emacs Manual

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The Emacs Editor

Emacs is the extensible, customizable, self-documenting real-time display editor. This Info file describes how to edit with Emacs and some of how to customize it; it corresponds to GNU Emacs version 23.1.

For information on extending Emacs, see Emacs Lisp.

This is the Sixteenth edition of the GNU Emacs Manual,
updated for Emacs version 23.1.

Copyright © 1985, 1986, 1987, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 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.”

Indexes (each index contains a large menu)

Important General Concepts

Fundamental Editing Commands

Important Text-Changing Commands

Major Structures of Emacs

Advanced Features

Recovery from Problems

Appendices

--- The Detailed Node Listing --- ---------------------------------

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

The Organization of the Screen

Basic Editing Commands

The Minibuffer

Completion

Help

The Mark and the Region

Killing and Moving Text

Yanking

Registers

Controlling the Display

Searching and Replacement

Incremental Search

Replacement Commands

Commands for Fixing Typos

Keyboard Macros

File Handling

Saving Files

Backup Files

Auto Reverting Non-File Buffers

Auto-Saving: Protection Against Disasters

Using Multiple Buffers

Convenience Features and Customization of Buffer Handling

Multiple Windows

Frames and Graphical Displays

Killing and Yanking on Graphical Displays

International Character Set Support

Major Modes

Indentation

Commands for Human Languages

Filling Text

Outline Mode

TeX Mode

Editing Formatted Text

Editing Text-based Tables

Editing Programs

Top-Level Definitions, or Defuns

Indentation for Programs

Commands for Editing with Parentheses

Manipulating Comments

Documentation Lookup

C and Related Modes

Fortran Mode

Fortran Indentation

Compiling and Testing Programs

Running Debuggers Under Emacs

GDB Graphical Interface

Maintaining Large Programs

Version Control

Introduction to Version Control

Basic Editing under Version Control

The Secondary Commands of VC

VC Directory Mode

Multiple Branches of a File

Remote Repositories

Revision Tags

Miscellaneous Commands and Features of VC

Customizing VC

Change Logs

Tags Tables

Merging Files with Emerge

Abbrevs

Editing Pictures

Sending Mail

Mail Mode

Reading Mail with Rmail

Summaries

Dired, the Directory Editor

The Calendar and the Diary

Movement in the Calendar

Conversion To and From Other Calendars

The Diary

Customizing the Calendar and Diary

Document Viewing

Gnus

Running Shell Commands from Emacs

Shell Command History

Using Emacs as a Server

Printing Hard Copies

Hyperlinking and Navigation Features

Customization

Easy Customization Interface

Variables

Local Variables in Files

Customizing Key Bindings

The Init File, ~/.emacs

Dealing with Emacs Trouble

Reporting Bugs

Command Line Arguments for Emacs Invocation

Environment Variables

X Options and Resources

GTK resources

Emacs and Mac OS / GNUstep

Emacs and Microsoft Windows/MS-DOS

Emacs and 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 on 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.

You can also order copies of GNU Emacs from the Free Software Foundation. This is a convenient and reliable way to get a copy; it is also a good way to help fund our work. 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/. For further information, write to

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

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 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. If company policy is unsympathetic to the idea of donating to charity, you might instead suggest ordering a CD-ROM from the Foundation occasionally, or subscribing to periodic updates.


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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 text-only terminal, the Emacs display occupies the entire terminal screen. On a graphical display, such as on GNU/Linux using the X Window System, Emacs creates its own windows to use. We use the term frame to mean the entire terminal screen or graphical window used by Emacs. Emacs uses both kinds of frames, in the same way, to display your editing. Emacs normally starts out with just one frame, but you can create additional frames if you wish (see Frames).

The 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 a special echo area, where short 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. This is where Emacs displays the buffer: the text that you are editing. On a graphical display, the window possesses a scroll bar on one side, which you can use to display different parts of the buffer in the window. 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). In this manual, the word “window” refers to the initial large window if not subdivided, or any one of the multiple windows you have subdivided it into.

At any time, one window is the selected window. On graphical displays, the selected window normally shows a more prominent cursor (usually solid and blinking) while other windows show a weaker cursor (such as a hollow box). Text terminals have just one cursor, so it always appears 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 active cursor shows the location at which editing commands will 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.

While the cursor appears to be on a character, you should think of point as between two characters; it points before the character that appears 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.

Sometimes people speak of “the cursor” when they mean “point,” or speak of commands that move point as “cursor motion” commands.

If you are editing several files in Emacs, each in its own buffer, each buffer has its own point location. A buffer that is not currently displayed remembers its point location in case you display it again later. When Emacs displays multiple windows, each window has its own point location. If the same buffer appears in more than one window, each window has its own point position in that buffer.

On a graphical display, Emacs shows a cursor in each window; the selected window's cursor is solid and blinking, and the other cursors are hollow. On a text-only terminal, there is just one cursor, in the selected window; even though the unselected windows have their own point positions, they do not display a cursor. See Cursor Display, for customizable variables that control cursor display.


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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.

Echoing means displaying the characters that you type. Single-character commands, including most simple editing operations, are not echoed. Multi-character commands are echoed if you pause while typing them: if you pause for more than a second in the middle of a command, Emacs echoes all the characters of the command so far, to prompt you for the rest of the command. The echoed characters are displayed in the echo area. 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. See Display Custom.

If a command cannot do its job, it may display an error message. Error messages are also displayed in the echo area. They may be accompanied by beeping or by flashing the screen.

Some commands display informative messages in the echo area. Unlike error messages, these messages are not announced with a beep or flash. Sometimes the message tells you what the command has done, when this is not obvious from looking at the text being edited. Other times, the sole purpose of a command is to show you a message giving you specific information. For example, C-x = (hold down <CTRL> and type x, then let go of <CTRL> and type =) displays a message describing the character position of point in the text and its current column in the window. Commands that take a long time often display messages ending in ‘...’ while they are working, and add ‘done’ at the end when they are finished. They may also indicate progress with percentages.

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.

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 (usually ending with a colon); also, 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, and the mode line of the selected window has a brighter color than that of unselected windows to make it stand out. On a text-only terminal, the mode line is usually drawn in inverse video.

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

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

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

cs describes the character set of the buffer (see Coding Systems). If it is a dash (‘-’), that indicates the default state of affairs: no special character set handling, except for the end-of-line translations described in the next paragraph. ‘=’ means no conversion whatsoever. Letters represent various nontrivial coding systems—for example, ‘1’ represents ISO Latin-1. On a text-only terminal, cs is preceded by two additional characters that describe the coding system for keyboard input and the coding system for terminal output. Furthermore, if you are using an input method, cs is preceded by a string that identifies the input method, which takes the form ‘i>’, ‘i+’, or ‘i@’ (see Input Methods).

The character after cs is usually a colon. However, under some circumstances a different string is displayed, which indicates a nontrivial end-of-line convention. Usually, lines of text are separated by newline characters, but two other conventions are sometimes used. The MS-DOS convention is to use 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. The Macintosh end-of-line convention is to use a “carriage-return” character instead of a newline; when editing such files, the colon indicator 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-only 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 it is all 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, Rmail buffers display the current message number and the total number of messages. Compilation buffers and Shell buffers display the status of the subprocess.

minor is a list of some of the minor modes turned on in the buffer. Minor modes 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 through 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, not just one buffer, the square brackets appear in every window's mode line or not in any of them. 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. A right-arrow at the end 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 invoked 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 text-only terminals with no mouse, 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 also has an assigned letter or digit which designates that item; it is 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. The simplest characters that you can input into Emacs correspond to graphic symbols such as ‘a’, ‘B’, ‘3’, ‘=’, the space character (conventionally denoted as <SPC>), and so on. Entering these using the keyboard is straightforward. Certain characters found on non-English keyboards also fall into this category (see International).

In addition to these simple characters, Emacs recognizes control characters such as <RET>, <TAB>, <DEL>, <ESC>, <F1>, <Home>, <left>, etc. Most keyboards have special keys for entering these.

Emacs also recognizes control characters that are entered using modifier keys. Two commonly-used modifier keys are <Control> (which is usually labelled as <Ctrl>), and <Meta> (which is usually labeled as <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.

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-only terminals where the <Meta> key does not function reliably.

Modifier keys can apply not only to alphanumerical characters, but also to special input characters, such as the arrow keys and mouse buttons.

See Input Events, for the full Lisp-level details about keyboard and mouse input, which are collectively referred to as input events. If you are not doing Lisp programming, but simply want to redefine the meaning of some characters or non-character events, see Customization.

On graphical displays, the window manager is likely to block the character M-<TAB> before Emacs can see it. It may also block M-<SPC>, C-M-d and C-M-l. If you have these problems, we recommend that you customize your window manager to turn off those commands, or put them on key combinations that Emacs does not use.


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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. But Emacs also has commands that 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 is either a complete key or a prefix key.

A prefix key combines with the following input event to make a longer key sequence, which may itself be complete or a prefix. For example, C-x is a prefix key, so C-x and the next input event combine to make a two-event key sequence. This two-event key sequence 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 a key sequence, but in practice people rarely use sequences longer than three or four input events.

You can't add input events onto a complete key. For example, the two-event sequence C-f C-k is not a key, because the C-f is a complete key in itself, so C-f C-k cannot have an independent meaning as a command. 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 anything would become 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 displays a list of the 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. A command also has a function definition which is a Lisp program; this is how the command does its work. In Emacs Lisp, a command is a Lisp function with special properties that make it suitable for interactive use. For more information on commands and functions, 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 also 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 buffer contains some information about Emacs, and includes links to common tasks that might be useful to 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 specific 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 edit one file at a time: once you are done with that file, you exit the editor, and start it again the next time you need it.

Using Emacs in this way—starting it afresh each time you want to edit a file—is unnecessary and wasteful. Emacs can visit more than one file in a single editing session, and exiting the Emacs session loses valuable accumulated context, such as the kill ring, registers, undo history, and mark ring. These features, described later in the manual, are useful for performing edits across multiple files, or continuing edits to a single file.

The recommended way to use Emacs is to start it only once, just after you log in, and do all your editing in the same Emacs session. Each time you edit a file, visit it with the existing Emacs, which eventually has many files in it ready for editing. See Files, for more information on visiting more than one file.

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

Emacs accepts other command line arguments that tell it to load certain Lisp files, call certain functions, and so forth. These features exist mainly for advanced users. 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 can be either the name of the desired file or directory, or t, which means to display the ‘*scratch*’ buffer.


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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 (suspend-emacs); on a graphical display, iconify (or “minimize”) the selected frame (iconify-or-deiconify-frame).

Killing Emacs means terminating the Emacs program. To do this, type C-x C-c (save-buffers-kill-terminal). A two-character key 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.

You can “exit” Emacs in two other ways. On a graphical display, you can iconify (or minimize) an Emacs frame; depending on the window system, this either replaces the Emacs frame with a tiny “icon” or conceals the frame entirely (see Frames). On a text-only terminal, you can suspend Emacs; this means stopping the Emacs program temporarily, returning control to its parent process (usually a shell).

On a graphical display, C-z runs the command iconify-or-deiconify-frame, which iconifies the selected Emacs frame. On a text terminal, C-z runs the command suspend-emacs, which suspends Emacs.

After iconifying or suspending Emacs, you can return to it and continue editing wherever you left off. The way to do this depends on the window system or shell. In most common shells, you can resume Emacs after suspending it with the shell command %emacs.

On very old systems that don't support suspending programs, C-z starts an inferior shell that communicates directly with the terminal, and Emacs waits until you exit the subshell. (The way to exit the subshell is usually C-d or exit.) On these systems, you can only get back to the shell from which Emacs was run (to log out, for example) when you kill Emacs. Suspending can also fail if you run Emacs under a shell that doesn't support suspending jobs, even if the system itself does support it. In this case, you can set the variable cannot-suspend to a non-nil value to force C-z to start an inferior shell.

Text-only 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 Control-h t inside Emacs. (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>. This key may be labeled <Return> or <Enter> on your keyboard, but we refer to it as <RET> in this manual. Pressing it inserts a newline character in the buffer. If point is at the end of the line, this creates 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, if you turn on a minor mode called Auto Fill mode, Emacs can split lines automatically when they become too long (see Filling). If you turn on a minor mode called Overwrite mode, inserted characters 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 greater than 10, some letters starting with a serve as part of a character code, just like digits.

A numeric argument tells C-q how many copies of the quoted character to insert (see Arguments).

Instead of C-q, you can use C-x 8 <RET> (ucs-insert) to insert a character based on its Unicode name or code-point. This commands prompts for a character to insert, using the minibuffer; you can specify the character using either (i) the character's name in the Unicode standard, or (ii) the character's code-point in the Unicode standard.


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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, up and down respectively. These are equivalent to the commands <right>, <left>, <down>, and <up>, entered using the arrow keys present on many keyboards. Many Emacs users find that it is slower to use the arrow keys than the equivalent control keys. 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-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).
C-f
<right>
Move forward one character (forward-char).
C-b
<left>
Move backward one character (backward-char).
M-f
M-<right>
C-<right>
Move forward one word (forward-word).
M-b
M-<left>
C-<left>
Move backward one word (backward-word).
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.
M-r
Move point to left margin, vertically centered in the window (move-to-window-line). Text does not move on the screen. 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).
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. See Arguments, for more information on numeric arguments.
M->
Move to the end of the buffer (end-of-buffer).
C-v
<PageDown>
<next>
Scroll the display one screen forward, and move point if necessary to put it on the screen (scroll-up). If your keyboard has a <PageDown> key (sometimes labelled <next>), it does the same thing as <C-v>. Scrolling commands are described further in Scrolling.
M-v
<PageUp>
<prior>
Scroll one screen backward, and move point if necessary to put it on the screen (scroll-down). If your keyboard has a <PageUp> key (sometimes labelled <prior>), it does the same thing as M-v.
M-x goto-char
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.
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. Moving by logical lines was the default behavior prior to Emacs 23.1. 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 of 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 (delete-backward-char).
C-d
<Delete>
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 key <DEL> (delete-backward-char) removes the character before point, moving the cursor and all the characters after it backwards. On most keyboards, <DEL> is labelled <Backspace>, but we refer to it as <DEL> in this manual. Do not confuse <DEL> with another key, labelled <Delete>, that exists on many keyboards; we will discuss <Delete> momentarily.

Typing <DEL> when the cursor is at the beginning of a line deletes the preceding newline character, joining the line with the one before it.

On some text-only terminals, Emacs may not recognize the <DEL> key properly. If <DEL> does not do the right thing (e.g., if it deletes characters forwards), see DEL Does Not Delete.

The key C-d (delete-char) deletes the character after point, i.e., the character under the cursor. This shifts the rest of the text on the line to the left. If you type C-d at the end of a line, it joins that line with the following line. This command is also bound to the key labelled <Delete> on many keyboards.

To erase a larger amount of text, use the C-k key, which 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.

To learn more about killing text, see Killing.


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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. Files are named units of text which are stored by the operating system for you to retrieve later by name. To use the contents of a file in any way, including editing it with Emacs, you must specify the file name.

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 with the Help character, which is C-h (or <F1>, which is an alias for C-h). Type C-h k, followed by the key of interest; for example, C-h k C-n tells you what C-n does. C-h is a prefix key; C-h k is just one of its subcommands (the command describe-key). The other subcommands of C-h provide different kinds of help. Type C-h twice to get a description of all the help facilities. See Help.


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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-only 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-only 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 lines.

M-x what-page
Display the page number of point, and the line number within that page.
M-x what-line
Display the line number of point in the whole buffer.
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-x count-lines-region
Display the number of lines in the current region. Normally bound to M-=, except in a few specialist modes. See Mark, for information about the region.
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-x what-page counts pages from the beginning of the file, and counts lines within the page, showing both numbers in the echo area. See Pages.

Use M-x count-lines-region (normally bound to M-=) to display the number of lines in the region (see Mark). See Pages, for the command C-x l which counts the lines in the current page.

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 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” as well as “numeric argument,” to emphasize that you type these argument before the command, and to distinguish them from minibuffer arguments that come after 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.

When the minibuffer is in use, it appears in the echo area, with a cursor. The minibuffer display starts with a prompt in a distinct color, usually ending with a colon. The prompt states what kind of input is expected, and how it will be used.

The simplest way to enter a minibuffer argument is to type the text, then <RET> to submit the argument and exit the minibuffer. You can cancel the minibuffer, and the command that wants the argument, by typing C-g.

Sometimes, a default argument appears in the prompt, inside parentheses before the colon. The default will be used as the argument value 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.

Since the minibuffer appears in the echo area, it can conflict with other uses of the echo area. If an error occurs while the minibuffer is active, the error message hides the minibuffer for a few seconds, or until you type something; then the minibuffer comes back. If a command such as C-x = needs to display a message in the echo area, 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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8.1 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 by adding ..: for example, /u2/emacs/src/../lisp/simple.el is equivalent to /u2/emacs/lisp/simple.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 HOME on MS-DOS. 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.


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8.2 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 is defined to exit the minibuffer, you can't use it to insert a newline in the minibuffer. To do that, type C-o or C-q C-j. (The newline character is really the ASCII character control-J.)

Inside a minibuffer, the keys <TAB>, <SPC>, and <?> are often bound to commands that perform completion. See Completion. You can use C-q (quoted-insert) to insert a <TAB>, <SPC>, or <?> character. For example, C-q <TAB> inserts a <TAB> character. See Inserting Text.

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 accomodate 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.


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8.3 Completion

Sometimes, you can use a feature called completion to help you 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 you have typed so far.

When completion is available, certain keys (usually <TAB>, <RET>, and <SPC>) are rebound to complete the text in the minibuffer into a longer string chosen from a set of completion alternatives. The set of completion alternatives depends on the command that requested the argument, and on what you have typed so far. In addition, you can usually type ? to display a list of possible completions.

For example, 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. So, to run the command insert-buffer, you can type M-x ins <SPC> b <RET> instead of the full M-x insert-buffer <RET>.

Case is significant in completion when it is significant in the argument you are entering, such as command names. Thus, ‘insert-buffer’ is not a valid completion for ‘IN’. Completion ignores case distinctions for certain arguments in which case does not matter.


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8.3.1 Completion Example

A concrete example may help here. If you type M-x a u <TAB>, the <TAB> looks for 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’.

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. You have been able to enter ‘auto-fill-mode’ by typing just a u <TAB> - f <TAB>.


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8.3.2 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). <SPC> for completion is not available when entering a file name, since file names often include spaces.
<RET>
Submit the text in the minibuffer as the argument, possibly completing first as described in the next node (minibuffer-complete-and-exit). See Strict Completion.
?
Display a list of possible completions of the text before point (minibuffer-completion-help).

<TAB> (minibuffer-complete) is the most fundamental completion command. It searches for all possible completion alternatives that match the existing minibuffer text, and attempts to complete as much as it can. The matching of completion alternatives to the minibuffer text is performed according to somewhat intricate rules, which are designed so that plausible completions are offered under most circumstances. A valid completion alternative must satisfy the following criteria:

When performing these comparisons, a ‘*’ in the minibuffer text acts as a wildcard—it matches any character at the corresponding position in the completion alternative.

<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 possible completions (if there are any) in a separate window. You can choose a completion from this list using the following commands:

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


M-v
<PageUp>
<prior>
Typing M-v, while in the minibuffer, selects the window showing the completion list buffer (switch-to-completions). This paves the way for using the commands below. Typing <PageUp> or <prior> does the same, as does selecting that window in other ways.


<RET>
Typing <RET>, while in the completion list buffer, chooses the completion that point is in or next to (choose-completion). To use this command, you must first switch to the completion list window.


<Right>
Typing the right-arrow key <Right>, while in the completion list buffer, moves point to the following completion possibility (next-completion).


<Left>
Typing the left-arrow key <Left>, while in the completion list buffer, moves point to the previous completion possibility (previous-completion).


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8.3.3 Strict Completion

There are three different ways that <RET> can do completion, depending on how the argument will be used.

The completion commands display a list of all possible completions whenever they can't determine even one more character by completion. Also, typing ? explicitly requests such a list. You can scroll the list with C-M-v (see Other Window).


Previous: Strict Completion, Up: Completion

8.3.4 Completion Options

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> does the completion list buffer.

When completing file names, certain file names are usually ignored. The variable completion-ignored-extensions contains a list of strings; a file name ending in any of those strings is ignored as a completion candidate. The standard value of this variable 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’. Displaying a list of possible completions disregards completion-ignored-extensions; it shows them all.

If an element of completion-ignored-extensions ends in a slash (/), it's a subdirectory name; that directory and its contents are ignored. Elements of completion-ignored-extensions that do not end in a slash are ordinary file names.

When completing file names, Emacs ignores case differences 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, Emacs ignores case differences if read-buffer-completion-ignore-case is non-nil (the default value is nil).

You can customize the matching rules for completion alternatives using the variable completion-styles. Its value should be a list of symbols, each representing a completion style; valid style symbols are basic, partial-completion, emacs22, and emacs21. When completing, Emacs attempts to use the first completion style in the list; if this does not return any completion alternatives, it tries the next completion style in the list, and so on. The completion rules described in Completion Commands correspond to the default value of completion-styles, which is (basic partial-completion emacs22).

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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8.4 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, typing M-p or <Up> (previous-history-element) moves up 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. Similarly, typing M-n or <Down> (next-history-element) moves back down the history list, fetching later entries into the minibuffer. You can think of these commands as “backwards” and “forwards” through the history list.

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 argument: values that you are likely to enter. You can think of this as moving through the “future list” instead of the “history list”.

The input that M-p or M-n fetches into the minibuffer entirely replaces the existing contents of the minibuffer, so you can simply type <RET> to use it as an argument. You can also edit the text before you reuse it; this does not change the history element that you “moved” to, but your new argument does go at the end of the history list in its own right.

There are also commands to search forward or backward through the history; they search for history elements that match a regular expression. M-r (previous-matching-history-element) searches older elements in the history, while M-s (next-matching-history-element) searches newer elements. These commands are unusual: they use the minibuffer to read the regular expression even though they are invoked from the minibuffer. As with incremental searching, 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).

All uses of the minibuffer record your input on a history list, but there are separate history lists for different kinds of arguments. For example, there is a list for file names, used by all the commands that read file names. (As a special feature, this history list records the absolute file name, even if the name you entered was not absolute.)

There are several other specific history lists, including one for buffer names, one for arguments of commands like query-replace, one used by M-x for command names, and one used by compile for compilation commands. Finally, there is one “miscellaneous” history list that most minibuffer arguments use.

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 of history-length 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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8.5 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> is used to re-execute 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 understand Lisp syntax, 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 repeated command is added to the front of the command history unless it is identical to the most recently item.

Once inside the minibuffer for C-x <ESC> <ESC>, you can use the minibuffer history commands (M-p, M-n, M-r, M-s; see Minibuffer History) to move through the history list of saved entire commands. After finding the desired previous command, you can edit its expression as usual and then repeat 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 which 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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8.6 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, in a basic sense, 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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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 extensive help features, all accessible through the help character, C-h. This is a prefix key that is used for commands that display documentation; the next character you type should be a help option, to ask for a particular kind of help. You can cancel the C-h command with C-g. The function key <F1> is equivalent to C-h.

C-h itself is one of the help options; C-h C-h displays a list of help options, with a brief description of each one (help-for-help). You can scroll the list with <SPC> and <DEL>, then type the help option you want. To cancel, type C-g.

C-h or <F1> means “help” in various other contexts as well. For instance, you can type them after a prefix key to display 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.)

Most help buffers use a special major mode, Help mode, which lets you scroll conveniently with <SPC> and <DEL>. You can also follow hyperlinks to URLs, and to other facilities including Info nodes and customization buffers. 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 on-line Emacs manual, and displays 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. You can use the Info commands to browse it.
C-h p
This displays the available Emacs packages based on keywords. See Library Keywords.


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10.1 Help Summary

Here is a summary of the Emacs interactive help commands. (The character that follows C-h is the “help option.”) See Help Files, for other help commands that display fixed files of information.

C-h a topics <RET>
Display a list of commands whose names match topics (apropos-command; see Apropos).
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
Given a key sequence key, show the name of the command that it runs (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 complete Emacs manual is available on-line 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).
C-h r
Display the Emacs manual in Info (info-emacs-manual).
C-h s
Display the current contents of the syntax table, with an explanation of what they mean (describe-syntax). See Syntax.
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.)


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10.2 Documentation for a Key

The help commands to get information about a key sequence are C-h c and C-h k. 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’. Since command names are chosen to describe what the commands do, this gives you a very brief description of what key does.

C-h k key is similar but gives more information: it displays the documentation string of the command as well as its name. It displays this information in a window, since it may not fit in the echo area.

To find the documentation of a key sequence key, type C-h K key. This displays the appropriate manual section which contains the documentation of 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.


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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> will describe 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 definition, if you have the source files installed. (See Hyperlinking.) If you know Lisp (or C), this provides the ultimate documentation. If you don't know Lisp, you should learn it. (The Introduction to Emacs Lisp Programming, available from the FSF through fsf.org, is a good way to get started.) If Emacs feels you are just using it, treating it as an object program, its feelings may be hurt. For real intimacy, read the Emacs source code.

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.


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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 apropos command displays a list of items that match the pattern, in a separate buffer.

C-h a pattern <RET>
Search for commands whose names match pattern.
M-x apropos <RET> pattern <RET>
Search for functions and variables whose names match pattern. Both interactive functions (commands) and noninteractive functions can be found by this command.
M-x apropos-variable <RET> pattern <RET>
Search for user-option variables whose names match pattern.
M-x apropos-value <RET> pattern <RET>
Search for functions whose definitions match pattern, and variables whose values match pattern.
C-h d pattern <RET>
Search for functions and variables whose documentation strings match pattern.

The simplest kind of apropos pattern is one word. Anything which contains that word matches the pattern. Thus, to find the 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.

The a in C-h a stands for “Apropos”; C-h a runs the command apropos-command. This command normally checks only commands (interactive functions); if you specify a prefix argument, it checks noninteractive functions as well.

For more information about a function definition, variable or symbol property listed in the 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.

Use M-x apropos instead of C-h a to list all the Lisp symbols that match an apropos pattern, not just the symbols that are commands. This command does not list key bindings by default; specify a numeric argument if you want it to list them.

Use M-x apropos-variable to list user-customizable variables that match an apropos pattern. If you specify a prefix argument, it lists all matching variables.

The apropos-documentation command is like apropos except that it searches documentation strings instead of symbol names for matches.

The apropos-value command is like apropos except that it searches variables' values for matches for the apropos pattern. With a prefix argument, it also checks symbols' function definitions and property lists.

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, apropos lists the search results in alphabetical order. If the variable apropos-sort-by-scores is non-nil, the apropos commands try to guess the relevance of each result, and display the most relevant ones first.

By default, apropos lists the search results for apropos-documentation in order of relevance of the match. If the variable apropos-documentation-sort-by-scores is nil, apropos lists the symbols found in alphabetical order.


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10.5 Help Mode Commands

Help buffers provide the same commands as View mode (see Misc File Ops), plus a few special commands of their own.

<SPC>
Scroll forward.
<DEL>
Scroll backward.
<RET>
Follow a cross reference at point.
<TAB>
Move point forward to the next cross reference.
S-<TAB>
Move point back to the previous cross reference.
Mouse-1
Mouse-2
Follow a cross reference that you click on.
C-c C-c
Show all documentation about the symbol at point.

When a function name (see Running Commands by Name), variable name (see Variables), or face name (see Faces) appears in the documentation, it normally appears inside paired single-quotes. To view the documentation of that command, variable or face, you can click on the name with Mouse-1 or Mouse-2, or move point there and type <RET>. Use C-c C-b to retrace your steps.

You can follow cross references to URLs (web pages) also. This uses the browse-url command to view the page in the browser you choose. See Browse-URL.

There are convenient commands to move point to cross references in the help text. <TAB> (help-next-ref) moves point down to the next cross reference. S-<TAB> moves up to the previous cross reference (help-previous-ref).

To view all documentation about any symbol name that appears in the text, move point to the symbol name and type C-c C-c (help-follow-symbol). This shows all available documentation about the symbol as a variable, function and/or face. As above, use C-c C-b to retrace your steps.


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10.6 Keyword Search for Lisp Libraries

The C-h p command lets you search the standard Emacs Lisp libraries by topic keywords. Here is a partial list of keywords you can use:

abbrevabbreviation handling, typing shortcuts, macros.
bibcode related to the bib bibliography processor.
csupport for the C language and related languages.
calendarcalendar and time management support.
commcommunications, networking, remote access to files.
convenienceconvenience features for faster editing.
datasupport for editing files of data.
docssupport for Emacs documentation.
emulationsemulations of other editors.
extensionsEmacs Lisp language extensions.
facessupport for multiple fonts.
filessupport for editing and manipulating files.
framessupport for Emacs frames and window systems.
gamesgames, jokes and amusements.
hardwaresupport for interfacing with exotic hardware.
helpsupport for on-line help systems.
hypermediasupport for links between text or other media types.
i18ninternationalization and alternate character-set support.
internalcode for Emacs internals, build process, defaults.
languagesspecialized modes for editing programming languages.
lispLisp support, including Emacs Lisp.
localcode local to your site.
maintmaintenance aids for the Emacs development group.
mailmodes for electronic-mail handling.
matchingvarious sorts of searching and matching.
mousemouse support.
multimediaimages and sound support.
newssupport for netnews reading and posting.
oopsupport for object-oriented programming.
outlinessupport for hierarchical outlining.
processesprocess, subshell, compilation, and job control support.
terminalssupport for terminal types.
texsupporting code for the TeX formatter.
toolsprogramming tools.
unixfront-ends/assistants for, or emulators of, UNIX-like features.
wpword processing.


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10.7 Help for International Language Support

You can use the command C-h L (describe-language-environment) to get information about a specific language environment. See Language Environments. This tells you which languages this language environment supports. It also lists the character sets, coding systems, and input methods that work with this language environment, and finally shows some sample text to illustrate scripts.

The command C-h h (view-hello-file) displays the file etc/HELLO, which shows 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).

You can get a list of subcommands for a particular prefix key by typing C-h 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

The Emacs help commands described above display dynamic help based on the current state within Emacs, or refer to manuals. Other help commands display pre-written, static help files.

Except for C-h g, these commands all have the form C-h C-char; that is, C-h followed by a control character.

C-h C-c
Display the Emacs copying conditions (describe-copying). These are the rules under which you can copy and redistribute Emacs.
C-h C-d
Display how to debug Emacs problems (view-emacs-debugging).
C-h C-f
Display the Emacs frequently-answered-questions list (view-emacs-FAQ).
C-h g
Display general information about the GNU Project (describe-gnu-project).
C-h C-m
Display how to order printed copies of Emacs manuals (view-order-manuals).
C-h C-n
Display the Emacs “news” file, which lists new features in the most recent 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

When text on the screen is “active”, so that it does something special in response to mouse clicks or RET, it often has associated help text. For instance, most parts of the mode line have help text. On terminals that support mouse tracking, Emacs displays the help text as a “tooltip” (sometimes known as “balloon help”) or in the echo area, whenever you leave the mouse stationary over the active text. See Tooltips.

If your terminal doesn't support mouse-tracking, you can display the help text for active buffer text using the keyboard. C-h . (display-local-help) displays any help text associated with the character after point, using the echo area. To display help text automatically whenever it is available on the character after point, set the variable help-at-pt-display-when-idle to t.


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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, Emacs indicates the extent of the region 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).

This default behavior of the mark is known as Transient Mark mode. Disabling Transient Mark mode switches Emacs to an alternative behavior, in which the mark is always active, which was the default prior to Emacs 23. See Persistent 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.


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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 move point where the mark was (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 motion keys
Set the mark at point if the mark is inactive, then move point.

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 the beginning 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.

The command C-x C-x (exchange-point-and-mark) exchanges the positions of point and the mark, keeping the region unchanged. If the mark is inactive, Emacs first reactivates the mark wherever it was last set. 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.

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 while holding down this button, 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. Using the mouse to mark a region also copies the region into the kill ring (see Kill Ring). 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 referred to as shift-selection. This 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.

Whenever the mark is active, you can deactivate it by typing C-g (see Quitting). The mark is also automatically deactivated after certain non-motion commands.


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11.2 Commands to Mark Textual Objects

Here are the 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) puts the mark at the end of the next word, while C-M-@ (mark-sexp) puts it at the end of the next balanced expression (see Expressions). These commands handle arguments just like M-f and C-M-f.

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) moves point to the beginning of the paragraph that surrounds or follows point, and sets the mark at the end of that paragraph (see Paragraphs). As a special exception, repeated invocations of M-h extend the region to subsequent paragraphs. This is convenient for indenting, case-converting, or killing entire paragraphs.

The M-h command accepts prefix arguments. If the argument's value is positive, M-h marks that many paragraphs starting with the one surrounding point; therefore, C-u M-h is equivalent to M-h M-h M-h M-h. If the prefix argument is −n, M-h marks n paragraphs running back from the one surrounding point; in this case, point moves forward to the end of that paragraph, and the mark goes at the start of the region.

Similarly, C-M-h (mark-defun) sets mark and point around major top-level definitions (see Moving by Defuns), and C-x C-p (mark-page) does the same for pages (see Pages). These treat repeated invocations and prefix arguments similarly to mark-paragraph.

Finally, 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. (In some programs this is called “select all.”)


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11.3 Operating on the Region

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

Most commands that operate on the text in the region have the word region in their names.

Some commands have a default behavior when the mark is inactive, but operate on the text in 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 region 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.

If you enable Delete Selection mode, a minor mode, then inserting text while the mark is active causes the selected text to be deleted first. This also deactivates the mark. Many graphical applications follow this convention, but Emacs does not. To toggle Delete Selection mode on or off, type M-x delete-selection-mode. Another effect of this mode is that some keys, such as <DEL> and C-d, always kill the region if one exists.


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11.4 The Mark Ring

Aside from delimiting the region, the mark is also useful for remembering spots that you may want to go back to. Each buffer remembers 16 previous locations of the mark, in the mark ring. Commands that set the mark also push the old mark onto this ring.

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 Persistent 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. 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 the variable mark-even-if-inactive is nil, commands can only use the mark and the region when it is active. This variable is non-nil by default.

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, in any buffer, this is recorded in the global mark ring in addition to the current buffer's own mark ring.

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.


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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, newly introduced in Emacs 23, 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 extend 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 this does not disable setting the mark via mouse commands.


Previous: Shift Selection, Up: Mark

11.7 Persistent Marks

By default, the mark is activated by setting it, and deactivated by most non-motion commands (including all commands that change the text in the buffer). This behavior is called Transient Mark mode6.

Turning off Transient Mark mode switches Emacs to an alternative mode of operation, which was the default prior to Emacs 23. When Transient Mark mode is off, the mark is never deactivated, but it can be set to different locations using commands such as C-<SPC>. Emacs does not highlight the region, because that would be a nuisance. As a special exception, the region is temporarily highlighted if you set it with the mouse (see Setting Mark), or with shift-selection (see Shift Selection).

To turn off Transient Mark mode, type M-x transient-mark-mode. This command toggles the mode; you can use the same command to turn Transient Mark mode on again. You can also turn off Transient Mark mode using the menu bar: in the ‘Options’ menu, toggle the ‘Active Region Highlighting’ menu item.

Here are the details of how Emacs behaves when Transient Mark mode is off:

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
Activate the mark without changing it; enable Transient Mark mode just once, until the mark is 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.


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12 Killing and Moving Text

Killing means erasing text and copying it into the kill ring, from which you can bring it back into the buffer by yanking it. (Some applications use the terms “cutting” and “pasting” for similar operations.) This is the most common way of moving or copying text within Emacs. It is very versatile, because there are commands for killing many different types of syntactic units.

Most commands which erase text from the buffer save it in the kill ring. These are known as kill commands. The kill ring stores several recent kills, not just the last one, so killing is a very safe operation: when you make a new kill, you don't have to worry much about losing text that you previously killed.

You can yank text from the kill ring into any position in a buffer, including a position in a different buffer; the kill ring is shared by all buffers. The C-/ (undo) command can undo both kill and delete commands (see Undo); the importance of the kill ring is that you can yank the text in a different place.

Commands that erase text but do not save it in the kill ring are known as delete commands. 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. The commands' names and individual descriptions use the words ‘kill’ and ‘delete’ to say which kind of operation they perform.

Some specialized buffers contain read-only text, which cannot be modified and therefore cannot be killed. But some users like to use the kill commands to copy read-only text into the kill ring, without actually changing it. Therefore, 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, kill commands 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.

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


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12.1 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.

C-d
<Delete>
Delete next character (delete-char).
<DEL>
<Backspace>
Delete previous character (delete-backward-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 C-d (delete-char) and <DEL> (delete-backward-char). See Erasing.

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 after 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 after 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-^.


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12.2 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. If given at the beginning of a line, it kills all the text on the line7, leaving it blank. When used on a blank line, it kills the whole line including its newline.

More precisely, C-k kills from point up to the end of the line, unless it is at the end of a line. In that case it kills the newline following point, thus merging the next line into the current one. Spaces and tabs at the end of the line are ignored when deciding which case applies, so 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.

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


Previous: Killing by Lines, Up: Killing

12.3 Other Kill Commands

C-w
Kill region (kill-region). See Mark.
M-w
Save region as last killed text without actually killing it (kill-ring-save). Some programs call this “copying.”
M-d
Kill word (kill-word). See Words.
M-<DEL>
Kill word backwards (backward-kill-word).
C-x <DEL>
Kill back to beginning of sentence (backward-kill-sentence). See Sentences.
M-k
Kill to end of 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).

Apart from C-k, the most commonly-used kill command is C-w (kill-region), which kills the text in the region (i.e., between point and mark). See Mark. If the mark is inactive when you type C-w, it first reactivates the mark where it was last set. The mark is deactivated at the end of the command.

The command M-w (kill-ring-save) copies the region into the kill ring without removing it from the buffer. This is approximately equivalent to C-w followed by C-/, except that M-w does not alter the undo history.

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.


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13 Yanking

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

C-y
Yank last killed text (yank).
M-y
Replace text just yanked with an earlier batch of killed text (yank-pop).
C-M-w
Append next kill to last batch of killed text (append-next-kill).

On graphical displays with window systems, if there is a current selection in some other application, and you selected it more recently than you killed any text in Emacs, C-y copies the selection instead of text killed within Emacs.


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13.1 The Kill Ring

All killed text is recorded in the kill ring, a list of blocks of text that have been 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 file to another. (There are several other methods: for instance, you could store the text in a register. See Registers, for information about registers. See Accumulating Text, for some other ways to move text around.)

The command C-y (yank) reinserts the text of the most recent kill, leaving the cursor at the end of the text. It also adds the position of the beginning of the text to the mark ring, without activating the mark; this allows you to jump easily to that position with C-x C-x (see Setting Mark). With a plain prefix argument (C-u C-y), it instead leaves the cursor in front of the text, and adds the position of the end of the text to the mark ring. Using other sort of prefix argument specifies an earlier kill; for example, C-u 4 C-y reinserts the fourth most recent kill. See Earlier Kills.

The yank commands discard certain properties from the yanked text. These are properties that might lead to annoying results, such as causing the text to respond to the mouse or specifying key bindings. The list of properties to discard is stored in the variable yank-excluded-properties. Yanking of register contents and rectangles also discard these properties. See Text Properties, for more information about text properties.


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13.2 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.


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13.3 Yanking Earlier Kills

To recover killed text that is no longer the most recent kill, use the M-y command (yank-pop). It takes the text previously 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.

If you know how many M-y commands it would take to find the text you want, you can yank that text in one step using C-y with a numeric argument. C-y with an argument restores the text from the specified kill ring entry, counting back from the most recent as 1. Thus, C-u 2 C-y gets the next-to-the-last block of killed text—it is equivalent to C-y M-y. C-y with a numeric argument starts counting from the “last yank” pointer, and sets the “last yank” pointer to the entry that it yanks.

The length of the kill ring is controlled by the variable kill-ring-max; no more than that many blocks of killed text are saved.

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 the command C-h v kill-ring.


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14 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.


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15 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.

When you must specify a rectangle for a command to work on, you do it by putting the mark at one corner and point at the opposite corner. The rectangle thus specified is called the region-rectangle because you control it 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.

If point and the mark are in the same column, the rectangle they delimit is empty. If they are in the same line, the rectangle is one line high. This asymmetry between lines and columns comes about because point (and likewise the mark) is between two columns, but within a line.

C-x r k
Kill the text of the region-rectangle, saving its contents as the “last killed rectangle” (kill-rectangle).
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 rightward.
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 for deleting and inserting rectangles, and commands for blank rectangles.

There are two ways to get rid of the text in a rectangle: you can discard the text (delete it) or save it as the “last killed” rectangle. The commands for these two ways are C-x r d (delete-rectangle) and C-x r k (kill-rectangle). In either case, the portion of each line that falls inside the rectangle's boundaries is deleted, causing any following text on the line to move left into the gap.

Note that “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 can only record 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. It is hard to define yank-popping for rectangles, so we do not try.

To yank the last killed rectangle, type C-x r y (yank-rectangle). Yanking a rectangle is the opposite of killing one. Point specifies where to put the rectangle's upper left corner. The rectangle's first line is inserted there, the rectangle's second line is inserted at the same horizontal position, but one line vertically down, and so on. The number of lines affected is determined by the height of the saved rectangle.

You can convert single-column lists into double-column lists using rectangle killing and yanking; kill the second half of the list as a rectangle and then yank it beside the first line of the list. See Two-Column, for another way to edit multi-column text.

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) which blanks out existing text, and C-x r o (open-rectangle) which inserts a blank rectangle. Clearing a rectangle is equivalent to deleting it and then inserting a blank rectangle of the same size.

The command 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 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.


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16 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. C-x means cut (kill), C-c copy, C-v paste (yank), and C-z undo. Standard Emacs commands like C-x C-c still work, because C-x and C-c only take effect when the mark is active (and the region is highlighted). However, if you don't want to override these bindings in Emacs at all, set cua-enable-cua-keys to nil.

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.

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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17 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 enough in spirit to registers that they seem to belong in this chapter.


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17.1 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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17.2 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.
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.

C-x r i r inserts in the buffer the text from register r. Normally it leaves point before the text and places the mark after, but with a numeric argument (C-u) it puts point after the text and the mark before.


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17.3 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 command inserts a text string if the register contains one, and inserts a rectangle if the register contains one.

See also the command sort-columns, which you can think of as sorting a rectangle. See Sorting.


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17.4 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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17.5 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
Increment the number in register r by number (increment-register).
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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17.6 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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17.7 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 offers to save your bookmark values in your default bookmark file, ~/.emacs.bmk, if you have changed any bookmark values. You can also save the bookmarks at any time with the M-x bookmark-save command. 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.)

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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18 Controlling the Display

Since only part of a large buffer fits in the window, Emacs tries to show a part that is likely to be interesting. Display-control commands and variables allow you to specify which part of the text you want to see, and how to display it.


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18.1 Scrolling

If a buffer contains text that is too large to fit entirely within a window that is displaying the buffer, Emacs shows a contiguous portion of the text. The portion shown always contains point.

Scrolling means moving text up or down in the window so that different parts of the text are visible. Scrolling “forward” or “up” means that text moves up, and new text appears at the bottom. Scrolling “backward” or “down” moves text down, and new text appears at the top.

Scrolling happens automatically if you move point past the bottom or top of the window. You can also scroll explicitly with these commands:

C-l
Scroll the selected window to center point vertically within it and redisplay the screen (recenter-top-bottom).
C-v
<next>
<PageDown>
Scroll forward by nearly a full window (scroll-up).
M-v
<prior>
<PageUp>
Scroll backward (scroll-down).
C-M-l
Scroll heuristically to bring useful information onto the screen (reposition-window).

The most basic scrolling command is C-l (recenter-top-bottom). This 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. It also clears the screen and redisplays all windows; this is useful in case the screen becomes garbled for any reason (see Screen Garbled).

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 screen positions. (If you change the variable scroll-margin to a non-zero value n, Emacs leaves n screen lines between point and the top or bottom of the window. See Auto Scrolling.)

You can also supply C-l with a prefix argument. With a plain prefix argument, C-u C-l, Emacs simply recenters point. With a positive argument n, it scrolls to place 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. For example, C-u - 1 C-l puts point on the bottom line, and C-u - 5 C-l puts it five lines from the bottom. When given an argument, C-l does not clear the screen or cycle through different screen positions.

To read the buffer a windowful at a time, use C-v (scroll-up). This 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 at the new top of the window.

M-v (scroll-down) scrolls backward in a similar way.

The variable next-screen-context-lines controls the number of lines of overlap left by C-v or M-v; by default, it is 2. The function keys <next> and <prior>, or <PageDown> and <PageUp>, are equivalent to C-v and M-v respectively.

You can supply C-v or M-v with a numeric prefix argument n. This scrolls the window by n lines, while attempting 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.

The names of scroll commands are based on the direction that the text moves in the window. Thus, the command to scroll forward is called scroll-up because it moves the text upward on the screen. The keys <PageUp> and <PageDown> derive their names and customary meanings from a different convention that developed elsewhere; hence the strange result that <PageDown> runs scroll-up.

Some users like the full-screen scroll commands to keep point at the same screen position. To enable this behavior, set the variable scroll-preserve-screen-position to a non-nil value. Then, whenever a command scrolls the text around point offscreen (or within scroll-margin lines of the edge), Emacs moves point to keep it at the same vertical and horizontal position within the window. This mode is convenient for browsing through a file by scrolling by screenfuls; if you come back to the screen where you started, point goes back to the line where it started.

The C-M-l command (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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18.2 Automatic Scrolling

Emacs performs automatic scrolling when point moves out of the visible portion of the text.

Normally, this centers point vertically within the window. However, if you set scroll-conservatively to a small number n, then if you move point just a little off the screen (less than n lines), Emacs scrolls the text just far enough to bring point back on screen. By default, scroll-conservatively is 0.

When the window does scroll by a longer distance, you can control how aggressively it scrolls by setting the variables scroll-up-aggressively and scroll-down-aggressively. The value of scroll-up-aggressively should be either nil, or a fraction f between 0 and 1. A fraction specifies where on the screen to put point when scrolling upward: when a window scrolls up because point is above the window start, the new start position is chosen to put point f parts of the window height from the top. Thus, larger f means more aggressive scrolling. The default value, nil, is equivalent to 0.5.

Likewise, scroll-down-aggressively is used for scrolling down. The value specifies how far point should be placed from the bottom of the window; thus, as with scroll-up-aggressively, a larger value is more aggressive.

The variable scroll-margin restricts how close point can come to the top or bottom of a window. 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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18.3 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.

The variable hscroll-margin controls how close point can get to the window's edges before automatic scrolling occurs. It is measured in columns. 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 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.

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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18.4 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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18.5 Faces: Controlling Text Display Style

Emacs can display text in several different styles, which are called faces. Each face can specify various face attributes, such as the font, height, weight and slant, the foreground and background color, and underlining or overlining. A face does not have to specify all of these attributes; often it inherits most of them from another face.

On a text-only terminal, not all face attributes are meaningful. Some text-only terminals support inverse video, bold, and underline attributes; some support colors. Text-only terminals generally do not support changing the height, width or font.

Most major modes assign faces to the text automatically through the work of Font Lock mode. See Font Lock, for more information about Font Lock mode and syntactic highlighting. You can print the current buffer with the highlighting that appears on your screen using the command ps-print-buffer-with-faces. See PostScript.

Enriched mode, the mode for editing formatted text, provides commands and menus for specifying faces for text in the buffer. See Format Faces.

To alter the appearance of a face, use the customization buffer. See Face Customization. You can also use X resources to specify attributes of any particular face (see Resources). When displaying a character, any attribute that isn't specified by its face is taken from the default face, whose attributes reflect the default settings of the frame itself.

You can also change the foreground and background colors of a specific 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 name, with completion, and then set that face to use the specified color. See Face Customization, for information about color names. These commands affect the face colors on all frames, both existing and those to be created in the future. These changes do not, however, persist for future Emacs sessions; to make lasting changes, use the customization buffer (see Face Customization).

You can also set foreground and background colors for the current frame only; see Frame Parameters.

Emacs can display variable-width fonts, but some of the Emacs commands that calculate width and indentation do not know how to calculate variable widths. This can sometimes lead to incorrect results when you use variable-width fonts. In particular, indentation commands can give inconsistent results, so we recommend you avoid variable-width fonts, especially for editing program source code.


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18.6 Standard Faces

To see what faces are currently defined, and what they look like, type M-x list-faces-display. It's possible for a given face to look different in different frames; this command shows the appearance in the frame in which you type it. With a prefix argument, this prompts for a regular expression, and displays only faces with names matching that regular expression.

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.
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 highlighting portions of text, in various modes. For example, mouse-sensitive text is highlighted using this face.
isearch
This face is used for highlighting the current Isearch match (see Incremental Search).
query-replace
This face is used for highlighting the current Query Replace match (see Replace).
lazy-highlight
This face is used for lazy highlighting of Isearch and Query Replace matches other than the current one.
region
This face is used for displaying a selected region (see Mark).
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.
nobreak-space
The face for displaying the character “nobreak space.”
escape-glyph
The face for highlighting the ‘\’ or ‘^’ that indicates a control character. It's also used when ‘\’ indicates a nobreak space or nobreak (soft) hyphen.

These faces control the appearance of parts of the Emacs frame. They exist as faces to provide a consistent way to customize the appearance of these parts of the 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. By default this face inherits from the mode-line-inactive face on character terminals. On graphical displays the foreground color of this face is used for the vertical line between windows without scrollbars.
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.
scroll-bar
This face determines the visual appearance of the scroll bar. See Scroll Bars.
border
This face determines the color of the frame border.
cursor
This face determines the color of the cursor.
mouse
This face determines the color of the mouse pointer.
tool-bar
This face determines the color of tool bar icons. See Tool Bars.
tooltip
This face is used for tooltips. See Tooltips.
menu
This face determines the colors and font of Emacs's menus. See Menu Bars. This has no effect in Emacs built with GTK and in the MS-Windows/Mac ports; you need to use system-wide styles and options to change the appearance of GTK, Windows, or Mac menus. Setting the font of LessTif/Motif menus is currently not supported; attempts to set the font are ignored in this case.


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18.7 Temporary Face Changes

The following commands change the default face within a buffer.

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 height of the default face by the value of the variable text-scale-mode-step. As a special case, an argument of 0 removes any scaling currently active.

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 above commands automatically enable or disable the minor mode text-scale-mode, depending on whether the current font scaling is other than 1 or not.

To temporarily change the face in the current buffer to a variable-pitch (“proportional”) font, use the command M-x variable-pitch-mode to enable or disable the Variable Pitch minor mode.


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18.8 Font Lock mode

Font Lock mode is a minor mode, always local to a particular buffer, which highlights (or “fontifies”) the buffer contents according to the syntax of the text you are editing. It can recognize comments and strings in most programming languages; in several languages, it can also recognize and properly highlight various other important constructs, such as names of functions being defined or reserved keywords. Some special modes, such as Occur mode and Info mode, have completely specialized ways of assigning fonts for Font Lock mode.

Font Lock mode is turned on by default in all modes which support it. You can toggle font-lock for each buffer with the command M-x font-lock-mode. Using a positive argument unconditionally turns Font Lock mode on, and a negative or zero argument turns it off.

If you do not wish Font Lock mode to be turned on by default, customize the variable global-font-lock-mode using the Customize interface (see Easy Customization), or use the function global-font-lock-mode in your .emacs file, like this:

     (global-font-lock-mode 0)

This variable, like all the variables that control Font Lock mode, take effect whenever fontification is done; that is, potentially at any time.

If you have disabled Global Font Lock mode, you can still enable Font Lock for specific major modes by adding the function turn-on-font-lock 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 'turn-on-font-lock)

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.

The variable font-lock-maximum-decoration specifies the preferred level of fontification, for modes that provide multiple levels. Level 1 is the least amount of fontification; some modes support levels as high as 3. The normal default is “as high as possible.” You can specify an integer, which applies to all modes, or you can specify different numbers for particular major modes; for example, to use level 1 for C/C++ modes, and the default level otherwise, use this:

     (setq font-lock-maximum-decoration
           '((c-mode . 1) (c++-mode . 1)))

Fontification can be too slow for large buffers, so you can suppress it for buffers above a certain size. The variable font-lock-maximum-size specifies a buffer size, beyond which buffer fontification is suppressed.

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. (See Left Margin Paren.) If you don't follow this convention, Font Lock mode can misfontify the text that follows an open-parenthesis or open-brace in the leftmost column that is inside a string or comment.

The variable font-lock-beginning-of-syntax-function (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 many 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 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.


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18.9 Interactive Highlighting

Highlight Changes mode is a minor mode that highlights the parts of the buffer 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 history list. While being prompted for a face use M-p and M-n 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), t (highlight the patterns), 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 nil. 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.


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18.10 Window Fringes

On a graphical display, 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.

The most common use of the fringes is to indicate a continuation line, when one line of text is split into multiple lines on the screen. 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.”

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 empty lines, or where a program you are debugging is executing (see Debuggers).

You can enable and disable the fringes for all frames using M-x fringe-mode. To enable and disable the fringes for the selected frame, use M-x set-fringe-style.


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18.11 Displaying Boundaries

On a graphical display, Emacs can indicate the buffer boundaries in the fringes. It indicates the first line and the last line 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 up and down.

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)).

The value of the variable default-indicate-buffer-boundaries is the default value for indicate-buffer-boundaries in buffers that do not override it.


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18.12 Useless Whitespace

It is easy to leave unnecessary spaces at the end of a line, or empty lines at the end of a file, without realizing it. In most cases, this trailing whitespace has no effect, but there are special circumstances where it matters, and 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.

To delete all trailing whitespace within the buffer's accessible portion (see Narrowing), type M-x delete-trailing-whitespace <RET>. This command does not remove newline characters.

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 window lines that do not correspond to any buffer text. Blank lines at the end of the buffer then stand out because they do not have this image in the fringe.

To enable this feature, set the buffer-local variable indicate-empty-lines to a non-nil value. The default value of this variable is controlled by the variable default-indicate-empty-lines; by setting that variable, you can enable or disable this feature for all new buffers. (This feature currently doesn't work on text-only terminals.)


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18.13 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.


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18.14 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 usually appears after the buffer name, before the mode names and their parentheses. It 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 of running processes in the whole system recently. (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 a graphical display 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.

By default, the mode line is drawn on graphics displays with 3D-style highlighting, like that of a button when it is not being pressed. If you don't like this effect, you can disable the 3D highlighting of the mode line, by customizing the attributes of the mode-line face. 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.


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18.15 How Text Is Displayed

ASCII printing characters (octal codes 040 through 0176) in Emacs buffers are displayed with their graphics, as are non-ASCII multibyte printing characters (octal codes above 0400).

Some ASCII control characters are displayed in special ways. The newline character (octal code 012) is displayed by starting a new line. The tab character (octal code 011) is displayed by moving to the next tab stop column (normally every 8 columns). The number of spaces per tab is controlled by the variable tab-width, which must have an integer value between 1 and 1000, inclusive, and is made local by changing it. Note that how the tab character in the buffer is displayed has nothing to do with the definition of <TAB> as a command. The variable default-tab-width controls the default value of this variable for buffers where you have not set it locally.

Other ASCII control characters are normally displayed as a caret (‘^’) followed by the non-control version of the character; thus, control-A is displayed as ‘^A’. The caret appears in face escape-glyph.

Non-ASCII characters 0200 through 0237 (octal) are displayed with octal escape sequences; thus, character code 0230 (octal) is displayed as ‘\230’. The backslash appears in face escape-glyph.

If the variable ctl-arrow is nil, control characters in the buffer are displayed with octal escape sequences, except for newline and tab. Altering the value of ctl-arrow makes it local to the current buffer; until that time, the default value is in effect. The default is initially t.

The display of character codes 0240 through 0377 (octal) may be either as escape sequences or as graphics. They do not normally occur in multibyte buffers, but if they do, they are displayed as Latin-1 graphics. In unibyte mode, if you enable European display they are displayed using their graphics (assuming your terminal supports them), otherwise as escape sequences. See Unibyte Mode.

Some character sets define “no-break” versions of the space and hyphen characters, which are used where a line should not be broken. Emacs normally displays these characters with special faces (respectively, nobreak-space and escape-glyph) to distinguish them from ordinary spaces and hyphens. You can turn off this feature by setting the variable nobreak-char-display to nil. If you set the variable to any other value, that means to prefix these characters with an escape character.

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


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18.16 Displaying the Cursor

You can customize the cursor's color, and whether it blinks, using the cursor Custom group (see Easy Customization). On a graphical display, the command M-x blink-cursor-mode enables or disables the blinking of the cursor. (On text terminals, the terminal itself blinks the cursor, and Emacs has no control over it.) You can control how the cursor appears when it blinks off by setting the variable blink-cursor-alist.

Some text terminals offer two different cursors: the normal cursor and the very visible cursor, where the latter may be e.g. bigger or blinking. 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 doesn't switch, so it uses the normal cursor.

Normally, the cursor appears in non-selected windows without blinking, with the same appearance as when the blinking cursor blinks “off.” For a box cursor, this is a hollow box; for a bar cursor, this is a thinner bar. To turn off cursors in non-selected windows, customize the variable cursor-in-non-selected-windows and assign it a nil value.

On graphical displays, Emacs can optionally draw the block cursor as wide as the character under the cursor—for example, if the cursor is on a tab character, it would cover the full width occupied by that tab character. To enable this feature, set the variable x-stretch-cursor to a non-nil value.

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.


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18.17 Truncation of Lines

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-only terminals, ‘$’ appears in the first column when there is text truncated to the left, and in the last column when there is text truncated to the right.

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 is in effect. The default value is normally nil.

If the variable truncate-partial-width-windows is non-nil, it forces truncation rather than continuation in any window less than the full width of the screen or frame, regardless of the value of truncate-lines. See also Display.

If the variable overflow-newline-into-fringe is non-nil on a graphical display, then Emacs does not continue or truncate a line which is exactly as wide as the window. Instead, the newline overflows into the right fringe, and the cursor appears in the fringe when positioned on that newline.


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18.18 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.


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18.19 Customization of Display

This section describes variables (see Variables) that you can change to customize how Emacs displays. Beginning users can skip it.

If the variable inverse-video is non-nil, Emacs attempts to invert all the lines of the display from what they normally are.

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 someting to echo. See Echo Area.

The variable baud-rate holds the output speed of the terminal, as far as Emacs knows. Setting this variable does not change the speed of actual data transmission, but the value is used for calculations. On text-only terminals, it affects padding, and decisions about whether to scroll part of the screen or redraw it instead. It also affects the behavior of incremental search.

On graphical displays, baud-rate is only used to determine how frequently to look for pending input during display updating. A higher value of baud-rate means that check for pending input will be done less frequently.

On graphical displays, Emacs can optionally display the mouse pointer in a special shape to say that Emacs is busy. To turn this feature on or off, customize the group cursor. You can also control the amount of time Emacs must remain busy before the busy indicator is displayed, by setting the variable hourglass-delay.

On graphical displays, 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 value is 2.

On graphical displays, Emacs normally draws an underline at the baseline level of the font. If x-underline-at-descent-line is non-nil, Emacs draws the underline at the same height as the font's descent line.

On some text-only 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.

On a text-only terminal, when you reenter Emacs after suspending, Emacs normally clears the screen and redraws the entire display. On some terminals with more than one page of memory, it is possible to arrange the termcap entry so that the ‘ti’ and ‘te’ strings (output to the terminal when Emacs is entered and exited, respectively) switch between pages of memory so as to use one page for Emacs and another page for other output. On such terminals, you might want to set the variable no-redraw-on-reenter non-nil; this tells Emacs to assume, when resumed, that the screen page it is using still contains what Emacs last wrote there.


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19 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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19.1 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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19.1.1 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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19.1.2 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 terminate editing the string and search for it.


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19.1.3 Errors in Incremental Search

If your string is not found at all, the echo area says ‘Failing I-Search’. The cursor is after 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 customizable 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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19.1.4 Special Input for Incremental Search

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

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 keybindings. These keybindings are part of the keymap isearch-mode-map (see Keymaps).


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19.1.5 Isearch Yanking

Within incremental search, you can use C-w and C-y to grab text from the buffer into the search string. This makes it convenient to search for another occurrence of text at point.

C-w copies the character or word after point and adds it to the search string, advancing point over it. (The decision, whether to copy a character or a word, is heuristic.)

C-y is similar to C-w but copies all the rest of the current line into the search string. If point is already at the end of a line, it grabs the entire next line. If the search is currently case-insensitive, both C-y and C-w convert the text they copy to lower case, so that the search remains case-insensitive.

C-M-w and C-M-y modify the search string by only one character at a time: C-M-w deletes the last character from the search string and C-M-y copies the character after point to the end of the search string. An alternative method to add the character after point into the search string is to enter the minibuffer by M-e and to type C-f at the end of the search string in the minibuffer.

The character M-y copies text from the kill ring into the search string. It uses the same text that C-y would yank. Mouse-2 in the echo area does the same. See Yanking.


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19.1.6 Scrolling During Incremental Search

You can enable the use of vertical scrolling during incremental search (without exiting the search) by setting the customizable variable isearch-allow-scroll to a non-nil value. This applies to using the vertical scroll-bar and to certain keyboard commands such as <prior> (scroll-down), <next> (scroll-up) and C-l (recenter). You must run these commands via their key sequences to stay in the search—typing M-x will terminate 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 feature also affects some other commands, such as C-x 2 (split-window-vertically) and C-x ^ (enlarge-window) which don't exactly scroll but do affect where the text appears on the screen. In general, 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. (You type C-h c C-h l; it says view-lossage.) Then you can put the following line in your .emacs 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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19.1.7 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. Cancelling the search, with C-g, restores the contents of the minibuffer when you began the search.


Previous: Isearch Minibuffer, Up: Incremental Search

19.1.8 Slow Terminal Incremental Search

Incremental search on a slow terminal uses a modified style of display that is designed to take less time. Instead of redisplaying the buffer at each place the search gets to, it creates a new single-line window and uses that to display the line that the search has found. The single-line window comes into play as soon as point moves outside of the text that is already on the screen.

When you terminate the search, the single-line window is removed. Emacs then redisplays the window in which the search was done, to show its new position of point.

The slow terminal style of display is used when the terminal baud rate is less than or equal to the value of the variable search-slow-speed, initially 1200. See also the discussion of the variable baud-rate (see Customization of Display).

The number of lines to use in slow terminal search display is controlled by the variable search-slow-window-lines. Its normal value is 1.


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19.2 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 nonincremental search, search-forward, if the string you specify is empty. (Such an empty argument would otherwise be useless.) C-r <RET> does likewise, for a reverse incremental search.

Forward and backward nonincremental searches are implemented by the commands search-forward and search-backward. These commands may be bound to other keys in the usual manner.


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19.3 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.

A nonincremental word search differs slightly from the incremental version in the way it finds a match: the last word in the search string must be an exact match for a whole word. In an incremental word search, the last word in the search string can match part of a word; this allows the matching to proceed incrementally as you type.


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19.4 Regular Expression Search

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

If you type <SPC> in incremental regexp search, it matches any sequence of whitespace characters, including newlines. If you want to match just a space, type C-q <SPC>. You can control what a bare space matches by setting the variable search-whitespace-regexp to the desired regexp.

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 by the functions 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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19.5 Syntax of Regular Expressions

This manual describes regular expression features that users typically want to use. There are additional features that are mainly used in Lisp programs; see Regular Expressions.

Regular expressions have a syntax in which a few characters are special constructs and the rest are ordinary. An ordinary character is a simple regular expression which matches that same character and nothing else. The special characters are ‘$’, ‘^’, ‘.’, ‘*’, ‘+’, ‘?’, ‘[’, and ‘\’. 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.

As a simple example, we can concatenate the regular expressions ‘f’ and ‘o’ to get 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. Using concatenation, we can make regular expressions like ‘a.b’, which 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 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. So, for example, ‘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. For example, ‘ca?r’ matches ‘car’ or ‘cr’; nothing else.
*?, +?, ??
are non-greedy variants of the operators above. The normal operators ‘*’, ‘+’, ‘?’ are greedy in that they match as much as they can, as long as the overall regexp can still match. With a following ‘?’, they are non-greedy: 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 that specifies repetition n times—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 that specifies repetition between n and m times—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, which begins with ‘[’ and is 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), from which 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.

Note that the usual regexp special characters are not special inside a character set. A completely different set of special characters exists inside character sets: ‘]’, ‘-’ and ‘^’.

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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19.6 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.
\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.
\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).


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19.7 Regular Expression Example

Here is an example of a regexp—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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19.8 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’ are also considered a match. Regexps, and in particular character sets, are included: ‘[ab]’ would match ‘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 affects only the current buffer, but there is a default value in default-case-fold-search that you can also set. 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>.


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19.9 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 mark is active, they operate on the region 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).


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19.9.1 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. The argument's value doesn't matter.

See Replacement and Case, for details about case-sensitivity in replace commands.


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19.9.2 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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19.9.3 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.


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19.9.4 Query Replace

M-% string <RET> newstring <RET>
M-x query-replace <RET> string <RET> newstring <RET>
Replace some occurrences of string with newstring.
C-M-% regexp <RET> newstring <RET>
M-x query-replace-regexp <RET> 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 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 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.
^
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.


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19.10 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 occur <RET> regexp <RET>
Display a list showing each line in the buffer that contains a match for regexp. 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. Currently, occur can not correctly handle multiline matches.

The buffer ‘*Occur*’ containing the output serves as a menu for finding the occurrences in their original context. Click Mouse-2 on an occurrence listed in ‘*Occur*’, or position point there and type <RET>; this switches to the buffer that was searched and moves point to the original of the chosen occurrence. o and C-o display the match in another window; C-o does not select it.

After using M-x occur, you can use next-error to visit the occurrences found, one by one. Compilation Mode.


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 list-matching-lines
Synonym for M-x occur.
M-x multi-occur <RET> buffers <RET> regexp <RET>
This function 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 <RET> bufregexp <RET> regexp <RET>
This function 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 <RET> regexp <RET>
Print the number of matches for regexp that exist in the buffer after point. If the region is active, this operates on the region instead.
M-x flush-lines <RET> regexp <RET>
This command deletes each line that contains a match for regexp, operating on the text after point; it 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 <RET> regexp <RET>
This command deletes each line that does not contain a match for regexp, operating on the text after point; if point is not at the beginning of a line, it 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.


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20 Commands for Fixing Typos

In this chapter we describe the commands that are especially useful when you catch a mistake in your text after you have made it, or change your mind while composing text on the fly.

The most fundamental command for correcting erroneous editing is the undo command C-/ (which is 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 self-inserting characters. 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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20.1 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 as back its 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)8. 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.

On the other hand, 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 Persistent 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 records for a buffer becomes too large, Emacs discards the oldest undo records from time to time (during garbage collection). You can specify how much undo records 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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20.2 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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20.3 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.


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20.4 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. Aspell, Ispell or Hunspell are not part of Emacs, but one or the other is usually installed in GNU/Linux and other free operating systems. See Aspell.

M-$
Check and correct spelling of the active region or the word at point (ispell-word).
M-x ispell
Check and correct spelling in the active region or the entire buffer.
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 Persistent 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 Aspell/Ispell/Hunspell subprocess.
?
Show the list of options.

In Text mode and related modes, the command M-<TAB> (ispell-complete-word) shows a list of completions based on spelling correction. Insert the beginning of a word, and then type M-<TAB>; the command displays a completion list window. (If your window manager intercepts M-<TAB>, type <ESC> <TAB> or C-M-i.) To choose one of the completions listed, click Mouse-2 or Mouse-1 fast on it, or move the cursor there in the completions window and type <RET>. See Text Mode.

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 time except when you do spelling correction.

Ispell, Aspell and Hunspell use two dictionaries together for spell checking: the standard dictionary and your private dictionary. The standard dictionary is specified by ispell-local-dictionary or, if nil, by ispell-dictionary. If both are nil the default dictionary is selected. 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. Personal dictionary is specified by ispell-personal-dictionary. If nil, default value is used.

Set variable ispell-dictionary to select a specific default dictionary for all your documents. Set variable ispell-local-dictionary in the local variables section to select a specific dictionary for a given document.

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 fully-automatic way to check spelling as you edit in Emacs. It operates by checking words as you change or insert them. When it finds a word that it does not recognize, it highlights that word. This does not interfere with your editing, but when you see the highlighted word, you can move to it and fix it. Type M-x flyspell-mode to enable or disable this mode in the current buffer. To enable flyspell-mode in all text mode buffers, add turn-on-flyspell to text-mode-hook.

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.


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21 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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21.1 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 keybindings 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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21.2 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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21.3 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 RegNumbers. For most purposes, it is simpler to use a keyboard macro counter.


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21.4 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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21.5 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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21.6 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).


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21.7 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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22 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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22.1 File Names

Many Emacs commands that operate on a file require you to specify the file name, using the minibuffer (see Minibuffer). You can use completion to specify long file names (see Completion). Note that file name completion ignores file names whose extensions appear in the variable completion-ignored-extensions (see Completion Options).

For most operations, there is a default file name which is used if you type just <RET> to enter an empty argument. Normally, the default file name is the name of the file visited in the current buffer.

Each buffer has a default directory which is normally the same as the directory of the file visited in that buffer. For example, if the default file name is /u/rms/gnu/gnu.tasks, the default directory is normally /u/rms/gnu/. The default directory is kept in the variable default-directory, which has a separate value in every buffer. When a command reads a file name using the minibuffer, the default directory usually serves as the initial contents of the minibuffer. To inhibit the insertion of the default directory, set the variable insert-default-directory to nil.

If you enter a file name without a directory, that specifies a file in the default directory. If you specify a directory in a relative fashion, with a name that does not start with a slash, it is interpreted with respect to the default directory. For example, suppose the default directory is /u/rms/gnu/. 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, for more information about these shortcuts.

The command M-x pwd displays the default directory, and the command M-x cd sets it to a value read using the minibuffer. A buffer's default directory changes only when the cd command is used. A file-visiting buffer's default directory is initialized to the directory of the file it visits. If you create a buffer with C-x b, its default directory is copied from that of the buffer that was current at the time (see Select Buffer).

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 if you set the variable file-name-coding-system to a non-nil value. See File Name Coding.


Next: , Previous: File Names, Up: Files

22.2 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.

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.

Each window's mode line shows the name of the buffer that is being displayed in that window, so you can always tell what buffer you are editing. see Mode Line.

The changes you make with editing commands are made in the Emacs buffer. They do not take effect in the file that you visited, or any permanent place, 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.

To visit a file, type C-x C-f (find-file) and use the minibuffer to enter the name of the desired file. The usual defaulting and completion behavior is available in this minibuffer (see Minibuffer File). Note, also, that completion ignores certain file names (see Completion Options). While in the minibuffer, you can abort C-x C-f by typing C-g.

Your can tell that C-x C-f has completed successfully by the appearance of new text on the screen and a new buffer name in the mode line. If the specified file does not exist and you could not create it, or exists but you can't read it, an error message is displayed in the echo area.

If you visit a file that is already in Emacs, C-x C-f does not make another copy. It selects the existing buffer containing that file. However, before doing so, it checks whether the file itself has changed since you visited or saved it last. 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 around 256 megabytes on 32-bit machines (see Buffers). If you try, Emacs will display 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.

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.

What if you want to create a new file? Just visit it. Emacs displays ‘(New file)’ in the echo area, but in other respects behaves as if you had visited an existing empty file. If you make changes and save them, the file is created.

When <TAB> completion results in a nonexistent file name and you type <RET> immediately to visit it, Emacs asks for confirmation; this is because it's possible that you expected completion to go further and give you an existing file's name. The string ‘[Confirm]’ appears for a short time after the file name to indicate the need to confirm in this way. Type <RET> to confirm and visit the nonexistent file. The variable confirm-nonexistent-file-or-buffer controls whether Emacs asks for confirmation before visiting a new file. The default value, after-completion, gives the behavior we have just described. If the value is nil, Emacs never asks for confirmation; for any other non-nil value, Emacs always asks for confirmation. This variable also affects the switch-to-buffer command (see Select Buffer). See Completion, for more information about completion.

If you visit a nonexistent file unintentionally (because you typed the wrong file name), 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; this lets you “edit” the contents of the directory. 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 (toggle-read-only). 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 makes visible any existing frame showing the file you seek. This feature is available only when you are using a window system. See Frames.

Emacs recognizes from the contents of a file which end-of-line convention it uses to separate lines—newline (used on GNU/Linux and on Unix), carriage-return linefeed (used on Microsoft systems), or just carriage-return (used on the Macintosh)—and automatically converts the contents to the normal Emacs convention, which is that the newline character separates lines. This is a part of the general feature of coding system conversion (see Coding Systems), and makes it possible to edit files imported from different operating systems with equal convenience. If you change the text and save the file, Emacs performs the inverse conversion, changing newlines back into carriage-return linefeed or just carriage-return if appropriate.

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 Formatted Text), 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 the list find-file-not-found-functions; this variable holds a list of functions, and the functions 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 the list 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).


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22.3 Saving Files

Saving a buffer in Emacs means writing its contents back into the file that was visited in the buffer.


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22.3.1 Commands for Saving Files

These are the commands that relate to saving and writing files.

C-x C-s
Save the current buffer in its visited file on disk (save-buffer).
C-x s
Save any or all buffers in their visited 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 selected 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.


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22.3.2 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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22.3.2.1 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 %backup%~ in your home directory. 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 .emacs 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.


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22.3.2.2 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
22.3.2.3 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).

Having the owner change is usually a good idea, because then the owner always shows who last edited the file. Also, the owners of the backups show who produced those versions. Occasionally there is a file whose owner should not change; it is a good idea for such files to contain local variable lists to set backup-by-copying-when-mismatch locally (see File Variables).

The choice of renaming or copying is controlled by four variables. Renaming is the default choice. If the variable backup-by-copying is non-nil, copying is used. Otherwise, if the variable backup-by-copying-when-linked is non-nil, then copying is used for files that have multiple names, but renaming may still be used when the file being edited has only one name. If the variable backup-by-copying-when-mismatch is non-nil, then copying is used if renaming would cause the file's owner or group to change. backup-by-copying-when-mismatch is t by default if you start Emacs as the superuser. The fourth variable, backup-by-copying-when-privileged-mismatch, gives the highest numeric user-id for which backup-by-copying-when-mismatch will be forced on. This is useful when low-numbered user-ids are assigned to special system users, such as root, bin, daemon, etc., which must maintain ownership of files.

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.


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22.3.3 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, that means to add newlines both on visiting and on saving. If the value is nil, Emacs leaves the end of the file unchanged; if it's neither nil nor t, Emacs asks you whether to add a newline. The default is nil.

Many major modes are designed for specific kinds of files that are always supposed to end in newlines. These major modes set the variable require-final-newline according to mode-require-final-newline. 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, because it requires the disk to spin up each time you save a file. Setting write-region-inhibit-fsync to a non-nil value disables this synchronization. Be careful—this means increased risk of data loss.


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22.3.4 Protection against Simultaneous Editing

Simultaneous editing occurs when two users visit the same file, both make changes, and then both save them. If nobody were informed that this was happening, whichever user saved 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.

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.

Note that locking works on the basis of a file name; if a file has multiple names, Emacs does not realize that the two names are the same file and cannot prevent two users from editing it simultaneously under different names. However, basing locking on names means that Emacs can interlock the editing of new files that will not really exist until they are saved.

Some systems are not configured to allow Emacs to make locks, and there are cases where lock files cannot be written. In these cases, Emacs cannot detect trouble in advance, but it still can detect the collision when you try to save a file and overwrite someone else's changes. Every time Emacs saves a buffer, it first checks the last-modification date of the existing file on disk to verify that it has not changed since the file was last visited or saved. If the date does not match, it implies that changes were made in the file in some other way, and these changes are about to be lost if Emacs actually does save. To prevent this, Emacs displays a warning message and asks for confirmation before saving. Occasionally you will know why the file was changed and know that it does not matter; then you can answer yes and proceed. Otherwise, you should cancel the save with C-g and investigate the situation.

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.

The first thing you should do when notified that simultaneous editing has already taken place is to list the directory with C-u C-x C-d (see Directories). This shows the file's current author. You should attempt to contact him to warn him not to continue editing. Often the next step is to save the contents of your Emacs buffer under a different name, and use diff to compare the two files.


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22.3.5 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

22.3.6 Updating Time Stamps Automatically

You can arrange to put a time stamp in a file, so that it will be updated automatically each time you edit and save the file. The time stamp has to 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 hook function time-stamp to the hook before-save-hook; that hook function will automatically update the time stamp, inserting the current date and time when you save the file. 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 non-numeric fields in the time stamp are formatted according to your locale setting (see Environment).


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22.4 Reverting a Buffer

If you have made extensive changes to a file and then change your mind about them, you can get rid of them by reading in the previous version of the file. To do this, use M-x revert-buffer, which operates on the current buffer. Since reverting a buffer unintentionally could lose a lot of work, you must confirm this command with yes.

revert-buffer tries to position point in such a way that, if the file was edited only slightly, you will be at approximately the same piece of text after reverting as before. However, if you have made drastic changes, point may wind up in a totally different piece of text.

Reverting marks the buffer as “not modified”.

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.)

In addition, you can tell Emacs to periodically revert a buffer by typing M-x auto-revert-mode. This turns on Auto-Revert mode, a minor mode that makes Emacs automatically revert the current buffer every five seconds. You can change this interval through the variable auto-revert-interval. Typing M-x global-auto-revert-mode enables Global Auto-Revert mode, which does the same for all file buffers. Auto-Revert mode and Global Auto-Revert 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.

See VC Mode Line, for Auto Revert peculiarities in buffers that visit files under version control.


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22.5 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: enabling Auto Revert Mode in those buffers (using M-x auto-revert-mode); and setting global-auto-revert-non-file-buffers non-nil. 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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22.5.1 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.


Next: , Previous: Auto Reverting the Buffer Menu, Up: Autorevert

22.5.2 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

22.5.3 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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22.6 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.


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22.6.1 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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22.6.2 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 Entering Emacs). The default for this variable is t, so auto-saving is the usual practice for file-visiting buffers. Auto-saving can be turned on or off for any existing buffer with the command M-x auto-save-mode. Like other minor mode commands, M-x auto-save-mode turns auto-saving on with a positive argument, off with a zero or negative argument; with no argument, it toggles.

Emacs does auto-saving periodically based on counting how many characters you have typed since the last time auto-saving was done. 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. The variable auto-save-timeout says how many seconds Emacs should wait before it does an auto save (and perhaps also a garbage collection). (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 request an auto-save explicitly with the command M-x do-auto-save.


Previous: Auto Save Control, Up: Auto Save

22.6.3 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 for later recovery in files named ~/.emacs.d/auto-save-list/.saves-pid-hostname. The directory used, ~/.emacs.d/auto-save-list/, is determined by the variable auto-save-list-file-prefix. You can record sessions in a different place by customizing that variable. If you set auto-save-list-file-prefix to nil in your .emacs file, sessions are not recorded for recovery.


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22.7 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.


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22.8 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. It must be empty, or you get an error.

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, this signals an error. On systems that have a “Trash” or “Recycle Bin” feature, you can make this command move the specified directory to the Trash or Recycle Bin, 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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22.9 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 diff output formats.

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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22.10 Diff Mode

Diff mode is a major mode used for the output of M-x diff and other similar commands, as well as the output of the diff program. 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 diff 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).
M-p
Move to the previous hunk-start (diff-hunk-prev).
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.
M-x diff-show-trailing-whitespaces RET
Highlight trailing whitespace characters, except for those used by the patch syntax (see Useless Whitespace).


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22.11 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 view-file allows you to scan or read a file by sequential screenfuls. It reads a file name argument using the minibuffer. After reading the file into an Emacs buffer, view-file displays the beginning. You can then type <SPC> to scroll forward one windowful, or <DEL> to scroll backward. Various other commands are provided for moving around in the file, but none for changing it; type ? while viewing for a list of them. They are mostly the same as normal Emacs cursor motion commands. To exit from viewing, type q. The commands for viewing are defined by a special minor mode called View mode.

A related command, M-x view-buffer, views a buffer already present in Emacs. See Misc Buffer.

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 delete-file deletes the specified file, like the rm command in the shell. If you are deleting many files in one directory, it may be more convenient to use Dired rather than delete-file. See Dired.

On some systems, there is a facility called the “Trash” (or “Recycle Bin”); “deleting” a file normally means moving it into the Trash, and you can bring the file back from the Trash if you later change your mind. By default, Emacs does not use the Trash for file deletion—when Emacs deletes a file, it is gone forever. You can tell Emacs to use the Trash by changing the variable delete-by-moving-to-trash to t. This applies to file deletion via M-x delete-file, as well as M-x delete-directory (see Directories) and file deletion in Dired (see Dired Deletion). In addition, you can explicitly move a file into the Trash with the command M-x move-file-to-trash.

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.

The similar command M-x add-name-to-file is used to add 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 copy-file reads the file old and writes a new file named new with the same contents.

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.

Not all systems support symbolic links; on systems that don't support them, this command is not defined.

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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22.12 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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22.13 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. v extracts a file into a buffer in 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.

If your display supports colors and the mouse, moving the mouse pointer across a file name highlights that file name, indicating that you can click on it. Clicking Mouse-2 on the highlighted file name extracts the file into a buffer and displays that buffer.

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 archives produced by the programs arc, jar, lzh, zip, rar, and zoo, which have extensions corresponding to the program names. Archive mode also works for those 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 program to unpack and repack archives. Details of the program names and their options can be set in the ‘Archive’ Customize group. 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.


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22.14 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), then Emacs uses FTP.
  2. If the user name is ‘ftp’ or ‘anonymous’, then Emacs uses FTP.
  3. If the variable tramp-default-method is set to ‘ftp’, then Emacs uses FTP.
  4. If ssh-agent is running, then 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 your user name or the name user. It may ask you for a password from time to time (see Passwords); this is used for logging in on host. The form using port allows you to access servers running on a non-default TCP port.

If you want to disable backups for remote files, set the variable ange-ftp-make-backup-files to nil.

By default, the auto-save files (see Auto Save Files) for remote files are made in the temporary file directory on the local machine. This is achieved using the variable auto-save-file-name-transforms.

Normally, if you do not specify a user name in a remote file name, that means to use your own user name. But if you set the variable ange-ftp-default-user to a string, that string is used instead.

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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22.15 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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22.16 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-only 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 such as load-path or exec-path, whose value is a list of directory names.
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.


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22.17 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. This major mode allows you to toggle between displaying the file as an image in the Emacs buffer, and displaying its underlying text representation, using the command C-c C-c (image-toggle-display). This works only when Emacs can display the specific image type. 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.

See also the Image-Dired package (see Image-Dired) for viewing images as thumbnails.


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22.18 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 .emacs 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 creates 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). Filesets need not be a simple list of files—you can also define filesets using 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.

Emacs uses the concept of a fileset elsewhere see Version Control to describe sets of files to be treated as a group for purposes of version control operations. Those filesets are unnamed and do not persist across Emacs sessions.


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23 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 created to hold the file's text. Each time you invoke Dired, a buffer is created to hold the directory listing. If you send a message with C-x m, a buffer named ‘*mail*’ is used to hold the text of the message. When you ask for a command's documentation, that appears in a buffer called ‘*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 a buffer named ‘*scratch*’, which is not associated with any file and can be used for evaluating Lisp expressions in Emacs (see Lisp Interaction).

At any time, one and only one buffer is current. This is also called the selected buffer. We often say that a command operates on “the buffer”; this really means that the command operates on the current buffer (most commands do). When there is only one Emacs window, the buffer displayed in that window is current. When there are multiple windows present, the buffer displayed in the selected window is current. See Windows.

Each buffer records individually what file it is visiting (if any), whether it is modified, and what major mode and minor modes are in effect (see Major Modes). Any Emacs variable can be made local to a particular buffer, meaning its value in that buffer can be different from the value in other buffers. See Locals.

A buffer's size cannot be larger than some maximum, which is defined by the largest buffer position representable by the Emacs integer data type. This is because Emacs tracks buffer positions using that data type. For 32-bit machines, the largest buffer size is 256 megabytes.


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23.1 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 list of existing buffers.
C-x <RIGHT>
Select the next buffer in the list of existing buffers.
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.

To select the buffer named bufname, type C-x b bufname <RET>. This runs the command switch-to-buffer with argument bufname. While entering the buffer name, you can use the usual minibuffer completion and history commands (see Minibuffer). An empty argument to C-x b specifies the buffer that was current most recently among those not now displayed in any window.

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. First, however, Emacs might prompt you for confirmation, in case you entered the wrong buffer name. Emacs asks for confirmation only if the last key you typed, before submitting the minibuffer input with <RET>, was <TAB> (minibuffer-complete). This catches a common mistake, in which one types <RET> before realizing that <TAB> did not complete far enough to yield the desired buffer name (see Completion). Emacs asks for confirmation by putting the message ‘[Confirm]’ in the minibuffer; type <RET> again to confirm and visit the buffer.

The variable confirm-nonexistent-file-or-buffer controls whether Emacs asks for confirmation before visiting a buffer that did not previously exist. The default value, after-completion, gives the behavior we have just described. If the value is nil, Emacs never asks for confirmation; for any other non-nil value, Emacs always asks for confirmation. This variable also affects the find-file command (see Visiting).

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. The variable default-major-mode determines the new buffer's major mode; the default value is Fundamental mode. See Major Modes.

For conveniently switching between a few buffers, use the commands C-x <LEFT> and C-x <RIGHT>. C-x <RIGHT> (previous-buffer) selects the previous buffer (following the order of most recent selection in the current frame), while C-x <LEFT> (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. By default, if displaying the buffer causes two vertically adjacent windows to be displayed, the heights of those windows are evened out; to countermand that and preserve the window configuration, set the variable even-window-heights to nil.

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.

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.

You can control how certain buffers are handled by these commands by customizing the variables special-display-buffer-names, special-display-regexps, same-window-buffer-names, and same-window-regexps. See Force Same Window, and Special Buffer Frames, for more about these variables. In addition, if the value of display-buffer-reuse-frames is non-nil, and the buffer you want to switch to is already displayed in some frame, Emacs will just raise that frame.

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.


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23.2 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.


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23.3 Miscellaneous Buffer Operations

C-x C-q
Toggle read-only status of buffer (toggle-read-only).
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.

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.

If you wish to make changes in a read-only buffer, use the command C-x C-q (toggle-read-only). It 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 have files under version control, you may find it convenient to bind C-x C-q to vc-toggle-read-only instead. This will guard you against an operation that will confuse most modern version-conmtrol systems. See Version Control.

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 an M-x info, you need to switch to some other buffer before using the command, in order for it to make a different buffer.)

M-x view-buffer is much like M-x view-file (see Misc File Ops) except that it examines an already existing Emacs buffer. View mode provides commands for scrolling through the buffer conveniently but not for changing it. When you exit View mode with q, that switches back to the buffer (and the position) which was previously displayed in the window. Alternatively, if you exit View mode with e, the buffer and the value of point that resulted from your perusal remain in effect.

The commands M-x append-to-buffer and M-x insert-buffer can be used to copy text from one buffer to another. See Accumulating Text.


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23.4 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, every day at midnight, 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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23.5 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 Emacs cursor motion commands can be used in this buffer. The following commands apply to the buffer described on the current line:

d
Request to delete (kill) the buffer, then move down. The request shows as a ‘D’ on the line, before the buffer name. Requested deletions take place when you type the x command.
C-d
Like d but move up afterwards instead of down.
s
Request to save the buffer. The request shows as an ‘S’ on the line. Requested saves take place when you type the x command. You may request both saving and deletion for the same buffer.
x
Perform previously requested deletions and saves.
u
Remove any request made for the current line, and move down.
<DEL>
Move to previous line and remove any request made for that line.

The d, C-d, s and u commands to add or remove flags also move down (or up) one line. They accept a numeric argument as a repeat count.

These commands operate immediately on the buffer listed on the current line:

~
Mark the buffer “unmodified.” The command ~ does this immediately when you type it.
%
Toggle the buffer's read-only flag. The command % does this immediately when you type it.
t
Visit the buffer as a tags table. See Select Tags Table.

There are also commands to select another buffer or buffers:

q
Quit the buffer menu—immediately display the most recent formerly visible buffer in its place.
<RET>
f
Immediately select this line's buffer in place of the ‘*Buffer List*’ buffer.
o
Immediately select this line's buffer in another window as if by C-x 4 b, leaving ‘*Buffer List*’ visible.
C-o
Immediately display this line's buffer in another window, but don't select the window.
1
Immediately select this line's buffer in a full-screen window.
2
Immediately set up two windows, with this line's buffer selected in one, and the previously current buffer (aside from the buffer ‘*Buffer List*’) displayed in the other.
b
Bury the buffer listed on this line.
m
Mark this line's buffer to be displayed in another window if you exit with the v command. The request shows as a ‘>’ at the beginning of the line. (A single buffer may not have both a delete request and a display request.)
v
Immediately select this line's buffer, and also display in other windows any buffers previously marked with the m command. If you have not marked any buffers, this command is equivalent to 1.

There is also a command that affects the entire buffer list:

T
Delete, or reinsert, lines for non-file buffers. This command toggles the inclusion of such buffers in the buffer list.

What buffer-menu actually does is create and switch to a suitable buffer, and turn on Buffer Menu mode in it. Everything else described above is implemented by the special commands provided in Buffer Menu mode. One consequence of this is that you can switch from the ‘*Buffer List*’ buffer to another Emacs buffer, and edit there. You can reselect the ‘*Buffer List*’ buffer later, to perform the operations already requested, or you can kill it, or pay no further attention to it.

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.


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23.6 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 the analogue, for buffers, 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 whose base buffer is 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 from buffer base-buffer, under the name indirect-name. It prompts for both base-buffer and indirect-name using the minibuffer.


Previous: Indirect Buffers, Up: Buffers

23.7 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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23.7.1 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, 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

23.7.2 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

23.7.3 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

24 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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24.1 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. The terminal's cursor shows the location of point in this window. Each other window has a location of point as well. On text-only terminals, there is no way to show where those locations are, since the terminal has only one cursor. On a graphical display, the location of point in a non-selected window is indicated by a hollow box; the cursor in the selected window is blinking or solid.

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 commands such as C-x b to switch buffers in the selected window; 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 full details on the mode line.


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24.2 Splitting Windows

C-x 2
Split the selected window into two windows, one above the other (split-window-vertically).
C-x 3
Split the selected window into two windows positioned side by side (split-window-horizontally).
C-Mouse-2
In the mode line or scroll bar of a window, split that window.

The command C-x 2 (split-window-vertically) breaks the selected window into two windows, one above the other. Both windows start out displaying the same buffer, with the same value of point. By default the two windows each get half the height of the window that was split; a numeric argument specifies how many lines to give to the top window.

C-x 3 (split-window-horizontally) breaks the selected window into two side-by-side windows. A numeric argument specifies how many columns to give the one on the left. If you are not using scrollbars, a vertical line separates the two windows. You can customize its color with the face vertical-border. Windows that are not the full width of the screen have mode lines, but they are truncated. On terminals where Emacs does not support highlighting, truncated mode lines sometimes do not appear in inverse video.

You can split a window horizontally or vertically by clicking C-Mouse-2 in the mode line or the scroll bar. The line of splitting goes through the place where you click: if you click on the mode line, the new scroll bar goes above the spot; if you click in the scroll bar, the mode line of the split window is side by side with your click.

When a window occupies less than the full width of the frame, it may become too narrow for most of the text lines in its buffer. If most of its lines are continued (see Continuation Lines), the buffer may become difficult to read. Therefore, Emacs automatically truncates lines 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 truncate-partial-width-windows 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.

Horizontal scrolling is often used in side-by-side windows. See Horizontal Scrolling.

If split-window-keep-point is non-nil, the default, both of the windows resulting from C-x 2 inherit the value of point from the window that was split. This means that scrolling is inevitable. If this variable is nil, then C-x 2 tries to avoid scrolling the text currently visible on the screen, by putting point in each window at a position already visible in the window. It also selects whichever window contains the screen line that the cursor was previously on. Some users prefer that mode on slow terminals.


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24.3 Using Other Windows

C-x o
Select another window (other-window). That is o, not zero.
C-M-v
Scroll the next window (scroll-other-window).
M-x compare-windows
Find next place where the text in the selected window does not match the text in the next window.
Mouse-1
Mouse-1, in a window's mode line, selects that window but does not move point in it (mouse-select-window).

To select a different window, click with Mouse-1 on its mode line. 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 window that contains the minibuffer help display, if any, rather than the next window in the standard cyclic order.)

The command M-x compare-windows lets you compare two files or buffers visible in two windows, by moving through them to the next mismatch. See Comparing Files, for details.

If you set mouse-autoselect-window to a non-nil value, moving the mouse into a different window selects that window. This feature is off by default.


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24.4 Displaying in Another Window

C-x 4 is a prefix key for commands that select another window (splitting the window if there is only one) and select a buffer in that window. Different C-x 4 commands have different ways of finding the buffer to select.

C-x 4 b bufname <RET>
Select buffer bufname in another window. This runs switch-to-buffer-other-window.
C-x 4 C-o bufname <RET>
Display buffer bufname in another window, but don't select that buffer or that window. This runs display-buffer.
C-x 4 f filename <RET>
Visit file filename and select its buffer in another window. This runs find-file-other-window. See Visiting.
C-x 4 d directory <RET>
Select a Dired buffer for directory directory in another window. This runs dired-other-window. See Dired.
C-x 4 m
Start composing a mail message in another window. This runs mail-other-window; its same-window analogue is C-x m (see Sending Mail).
C-x 4 .
Find a tag in the current tags table, in another window. This runs find-tag-other-window, the multiple-window variant of M-. (see Tags).
C-x 4 r filename <RET>
Visit file filename read-only, and select its buffer in another window. This runs find-file-read-only-other-window. See Visiting.

By default, these commands split the window vertically when there is only one. You can customize the variables split-height-threshold and split-width-threshold to split the window horizontally instead.


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24.5 Forcing Display in the Same Window

Certain Emacs commands switch to a specific buffer with special contents. For example, M-x shell switches to a buffer named ‘*shell*’. By convention, all these commands are written to pop up the buffer in a separate window. But you can specify that certain of these buffers should appear in the selected window.

If you add a buffer name to the list same-window-buffer-names, the effect is that such commands display that particular buffer by switching to it in the selected window. For example, if you add the element "*grep*" to the list, the grep command will display its output buffer in the selected window.

The default value of same-window-buffer-names is not nil: it specifies buffer names ‘*info*’, ‘*mail*’ and ‘*shell*’ (as well as others used by more obscure Emacs packages). This is why M-x shell normally switches to the ‘*shell*’ buffer in the selected window. If you delete this element from the value of same-window-buffer-names, the behavior of M-x shell will change—it will pop up the buffer in another window instead.

You can specify these buffers more generally with the variable same-window-regexps. Set it to a list of regular expressions; then any buffer whose name matches one of those regular expressions is displayed by switching to it in the selected window. (Once again, this applies only to buffers that normally get displayed for you in a separate window.) The default value of this variable specifies Telnet and rlogin buffers.

An analogous feature lets you specify buffers which should be displayed in their own individual frames. See Special Buffer Frames.


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24.6 Deleting and Rearranging Windows

C-x 0
Delete the selected window (delete-window). The last character in this key sequence is a zero.
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 a window, type C-x 0 (delete-window). (That is a zero.) The space occupied by the deleted window is given to an adjacent window (but not the minibuffer window, even if that is active at the time). Once a window is deleted, its attributes are forgotten; only restoring a window configuration can bring it back. Deleting the window has no effect on the buffer it used to display; the buffer continues to exist, and you can select it in any window 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) is more powerful in a different way; it deletes all the windows except the selected one (and the minibuffer); the selected window expands to use the whole frame except for the echo area.

To readjust the division of space among vertically adjacent windows, use C-x ^ (enlarge-window). It makes the currently selected window one line bigger, or as many lines as is specified with a numeric argument. With a negative argument, it makes the selected window smaller. C-x } (enlarge-window-horizontally) makes the selected window wider by the specified number of columns. C-x { (shrink-window-horizontally) makes the selected window narrower by the specified number of columns.

When you make a window bigger, the space comes from its peers. If this makes any window too small, it is deleted and its space is given to an adjacent window. The minimum size is specified by the variables window-min-height and window-min-width.

The command 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.


Previous: Change Window, Up: Windows

24.7 Window Handling Convenience Features and Customization

M-x 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. To undo, use C-c left (winner-undo). If you change your mind while undoing, you can redo the changes you had undone using C-c right (M-x winner-redo). Another way to enable Winner mode is by customizing the variable winner-mode.

The Windmove commands move 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. (Not all terminals support shifted arrow keys, however.)

Follow minor 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.

M-x scroll-all-mode provides commands to scroll all visible windows together. You can also turn it on by customizing the variable scroll-all-mode. The commands provided are M-x scroll-all-scroll-down-all, M-x scroll-all-page-down-all and their corresponding “up” equivalents. To make this mode useful, you should bind these commands to appropriate keys.


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25 Frames and Graphical Displays

When using a graphical display, you can create multiple system-level “windows” in a single Emacs session. We refer to these system-level windows as frames. A frame initially contains a single Emacs window; however, you can subdivide this Emacs window into smaller windows, all fitting into the same frame. Each frame normally contains its own echo area and minibuffer.

To avoid confusion, we reserve the word “window” for the subdivisions that Emacs implements, and never use it to refer to a frame.

Any editing you do in one frame affects the other frames. For instance, if you put text in the kill ring in one frame, you can yank it in another frame. If you exit Emacs through C-x C-c in one frame, it terminates all the frames. To delete just one frame, use C-x 5 0 (that is zero, not o).

Emacs compiled for MS-DOS emulates some windowing functionality, so that you can use many of the features described in this chapter. See MS-DOS Mouse.


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25.1 Killing and Yanking on Graphical Displays

This section describes commands for selecting a region, killing, and yanking using the mouse.


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25.1.1 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 copy it to the kill ring (mouse-set-region).
Mouse-2
Yank the last killed text at the click position (mouse-yank-at-click).
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 called 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.

Normally, Emacs does not distinguish between ordinary mouse clicks and clicks that select a frame. When you click on a frame to select it, that also changes the selected window and cursor position according to the mouse click position. On the X window system, you can change this behavior by setting the variable x-mouse-click-focus-ignore-position to t. Then the first click selects the frame, but does not affect the selected window or cursor position. If you click again in the same place, that click will be in the selected frame, so it will change the window or cursor position.

Holding down Mouse-1 and “dragging” the mouse over a stretch of text activates the region around that text (mouse-set-region). See Mark. Emacs places the mark where you started holding down the mouse button, and point where you release it. In addition, the region is copied into the kill ring (see Kill Ring). If you don't want Emacs to copy the region, change the variable mouse-drag-copy-region to 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 performs a yank (mouse-yank-at-click). See Yanking. If you change the variable mouse-yank-at-point to a non-nil value, Mouse-2 does not move point. Then it does not matter where you click, or even which of the frame's windows you click on; the yank occurs at the existing point. This variable also affects yanking the primary and secondary selections (see Cut/Paste Other App).

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:

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. While the region remains active, typing <Backspace> or <Delete> deletes the text in that region and deactivates the mark; this behavior follows a convention established by other graphical programs, and it does not apply when you set the region any other way, including shift-selection (see Shift Selection).

Many graphical applications also follow the convention that insertion while text is selected deletes the selected text. You can make Emacs behave this way by enabling Delete Selection mode. See Using Region.


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25.1.2 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 singlequote or doublequote 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: Cut and Paste

25.1.3 Cut and Paste with Other Window Applications

When running Emacs under the X window system, you can easily transfer text between Emacs and other X applications using the primary selection (also called the X selection). This is not the same thing as the clipboard, which is a separate facility used on desktop environments such as Gnome, and on operating systems such as Microsoft Windows (see Clipboard).

Under X, whenever you select some text in Emacs by dragging or clicking the mouse (see Mouse Commands), it is also saved in the primary selection. You can then paste that text into any other X application, usually by clicking Mouse-2 in that application. Unlike the Emacs kill ring (see Kill Ring), the primary selection has no “memory”: each time you save something in the primary selection, either in Emacs or in another X application, the previous contents of the primary selection are lost.

Whenever you kill some text using a command such as C-w (kill-region), or copy it into the kill ring using a command such as M-w (kill-ring-save), that text is also saved in the primary selection. See Killing.

Whenever Emacs saves some text to the primary selection, it may also save it to the cut buffer. The cut buffer is an obsolete predecessor to the primary selection; most modern applications do not make use of it. Because saving text to the cut buffer is slow and inefficient, Emacs only does it if the text is shorter than the value of x-cut-buffer-max (the default is 20000 characters).

You can yank the primary selection into Emacs using the usual yank commands, such as C-y (yank) and Mouse-2 (mouse-yank-at-click). These commands actually check the primary selection before referring to the kill ring; if no primary selection is available, the kill ring contents are used. To prevent yank commands from accessing the primary selection, set the variable x-select-enable-primary to nil.

The standard coding system for the primary selection is compound-text-with-extensions. You may find that the pasted text is not what you expected. In such a case, you can specify another coding system for the selection by typing C-x <RET> x or C-x <RET> X. Alternatively, you can request a different data type by modifying the variable x-select-request-type. See Communication Coding.


Next: , Previous: Cut/Paste Other App, Up: Cut and Paste

25.1.4 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.


Previous: Secondary Selection, Up: Cut and Paste

25.1.5 Using the Clipboard

In desktop environments such as Gnome, and operating systems such as Microsoft Windows and Mac OS X, you can transfer data (usually text) between different applications using the clipboard. The clipboard is distinct from the primary selection and secondary selection discussed earlier. You can access the clipboard through the ‘Edit’ menu of the menu bar (see Menu Bar).

The command clipboard-kill-region, which is bound to the Cut menu item, kills the region and saves it in the clipboard.

The command clipboard-kill-ring-save, which is bound to the Copy menu item, copies the region to the kill ring and saves it in the clipboard.

The Paste menu item in the Edit menu yanks the contents of the clipboard at point (clipboard-yank).

You can customize the variable x-select-enable-clipboard to make the Emacs yank functions consult the clipboard before the primary selection, and to make the kill functions to store in the clipboard as well as the primary selection. Otherwise, these commands do not access the clipboard at all. Using the clipboard is the default on MS-Windows and Mac OS, but not on other systems.


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25.2 Following References with the Mouse

Some Emacs buffers include buttons. A button is a piece of text that performs some action when you activate it, such as following a reference. 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, typing <RET> or clicking on a file name in a Dired buffer visits that file (see Dired). Doing it on an error message in the ‘*Compilation*’ buffer goes to the source code for that error message (see Compilation). Doing it on a completion in the ‘*Completions*’ buffer chooses that completion (see Completion).

Although clicking Mouse-1 on a button usually activates that button, if you hold the mouse button down for a short period of time before releasing it (specifically, for more than 450 milliseconds), then Emacs moves point where you clicked instead. This behavior allows you to use the mouse to move point over a button without following it. Dragging—moving the mouse while it is held down—has its usual behavior of setting the region, even if you drag from or onto a button.

Normally, clicking Mouse-1 on a button activates the button even if it is in a nonselected window. If you change the variable mouse-1-click-in-non-selected-windows to nil, clicking Mouse-1 on a button in an un-selected window moves point to the clicked position and selects that window, without activating the button.

In Emacs versions before 22, only Mouse-2 activates buttons and Mouse-1 always sets point. If you prefer this older behavior, set the variable mouse-1-click-follows-link to nil. This variable also lets you choose various other alternatives for following links with the mouse. Type C-h v mouse-1-click-follows-link <RET> for more details.


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25.3 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 is for specifying faces and other text properties for editing formatted text. See Formatted 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.9 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 Temporary Face Changes.


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25.4 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 buries the current buffer instead, and switches to another buffer.
C-Mouse-2
C-Mouse-2 on a mode line splits the window above horizontally, above the place in the mode line where you click.

Using Mouse-1 on the divider between two side-by-side mode lines, you can move the vertical boundary left or right. Using C-Mouse-2 on a scroll bar splits the corresponding window vertically. See Split Window.


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25.5 Creating Frames

The prefix key C-x 5 is analogous to C-x 4, with parallel subcommands. The difference is that C-x 5 commands create a new frame rather than just a new window in the selected frame (see Pop Up Window). If an existing visible or iconified (“minimized”) frame already displays the requested material, these commands use the existing frame, after raising or deiconifying (“un-minimizing”) as necessary.

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 of new frames you create by setting the frame parameters in default-frame-alist. You can use the variable initial-frame-alist to specify parameters that affect only the initial frame. See Initial Parameters, for more information.

For instance, one way to specify the principal font for all your Emacs frames is to modify default-frame-alist to specify the font parameter (see Font X):

     (add-to-list 'default-frame-alist '(font . "10x20"))

Here's a similar example for specifying a foreground color:

     (add-to-list 'default-frame-alist '(foreground-color . "blue"))

By putting such customizations in your init file, you can control the appearance of all the frames Emacs creates, including the initial one. See Init File.


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25.6 Frame Commands

The following commands let you create, delete and operate on frames:

C-z
Iconify (“minimize”) the selected Emacs frame (iconify-or-deiconify-frame). See Exiting.
C-x 5 0
Delete the selected frame (delete-frame). This is not allowed if there is only one frame.
C-x 5 o
Select another frame, raise it, and warp the mouse to it. If you repeat this command, it cycles through all the frames on your terminal.
C-x 5 1
Delete all frames except the selected one.

To make the command C-x 5 o work properly, you should tell Emacs how the system (or the window manager) handles focus-switching between windows. There are two possibilities: either simply moving the mouse onto a window selects it (gives it focus), or you have to click on it to do so. On X, this focus policy also affects whether the focus is given to a frame that Emacs raises. Unfortunately there is no way Emacs can find out automatically which way the system handles this, so you have to explicitly say, by setting the variable focus-follows-mouse. If just moving the mouse onto a window selects it, that variable should be t; if a click is necessary, the variable should be nil. The default is t.

The window manager that is part of MS-Windows always gives focus to a frame that raises, so this variable has no effect in the native MS-Windows build of Emacs.


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25.7 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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25.8 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.

It is even possible to use this feature to let two or more users type simultaneously on the two displays, within the same Emacs job. In practice, however, the different users can easily interfere with each others' edits if they are not careful.


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25.9 Special Buffer Frames

You can make certain chosen buffers, which Emacs normally displays in “another window,” appear in special frames of their own. To do this, set the variable special-display-buffer-names to a list of buffer names; any buffer whose name is in that list automatically gets a special frame, when an Emacs command wants to display it “in another window.”

For example, if you set the variable this way,

     (setq special-display-buffer-names
           '("*Completions*" "*grep*" "*tex-shell*"))

then completion lists, grep output and the TeX mode shell buffer get individual frames of their own. These frames, and the windows in them, are never automatically split or reused for any other buffers. They continue to show the buffers they were created for, unless you alter them by hand. Killing the special buffer deletes its frame automatically.

More generally, you can set special-display-regexps to a list of regular expressions; then a buffer gets its own frame if its name matches any of those regular expressions. (Once again, this applies only to buffers that normally get displayed for you in “another window.”)

The variable special-display-frame-alist specifies the frame parameters for these frames. It has a default value, so you don't need to set it.

For those who know Lisp, an element of special-display-buffer-names or special-display-regexps can also be a list. Then the first element is the buffer name or regular expression; the rest of the list specifies how to create the frame. It can be an association list specifying frame parameter values; these values take precedence over parameter values specified in special-display-frame-alist. If you specify the symbol same-window as a “frame parameter” in this list, with a non-nil value, that means to use the selected window if possible. If you use the symbol same-frame as a “frame parameter” in this list, with a non-nil value, that means to use the selected frame if possible.

Alternatively, the value can have this form:

     (function args...)

where function is a symbol. Then the frame is constructed by calling function; its first argument is the buffer, and its remaining arguments are args.

An analogous feature lets you specify buffers which should be displayed in the selected window. See Force Same Window. The same-window feature takes precedence over the special-frame feature; therefore, if you add a buffer name to special-display-buffer-names and it has no effect, check to see whether that feature is also in use for the same buffer name.


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25.10 Setting Frame Parameters

These commands are available for controlling the window management behavior of the selected frame:

M-x auto-raise-mode
Toggle whether or not the selected frame should auto-raise. Auto-raise means that every time you move the mouse onto the frame, it raises the frame.

Some window managers also implement auto-raise. If you enable auto-raise for Emacs frames in your window manager, it will work, but it is beyond Emacs' control, so auto-raise-mode has no effect on it.


M-x auto-lower-mode
Toggle whether or not the selected frame should auto-lower. Auto-lower means that every time you move the mouse off the frame, the frame moves to the bottom of the stack on the screen.

The command auto-lower-mode has no effect on auto-lower implemented by the window manager. To control that, you must use the appropriate window manager features.

In Emacs versions that use an X toolkit, the color-setting and font-setting functions don't affect menus and the menu bar, since they are displayed by their own widget classes. To change the appearance of the menus and menu bar, you must use X resources (see Resources). See Colors, regarding colors. See Font X, regarding choice of font.

Colors, fonts, and other attributes of the frame's display can also be customized by setting frame parameters in the variable default-frame-alist (see Creating Frames). For a detailed description of frame parameters and customization, see Frame Parameters.


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25.11 Scroll Bars

On graphical displays, Emacs normally makes a scroll bar at the left of each Emacs window, running the height of the window.10

When Emacs is compiled with GTK+ support on the X window system, or in operating systems such as Microsoft Windows or Mac OS, you can use the scroll bar as you do in other graphical applications. If you click Mouse-1 on the scroll bar's up and down buttons, that 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 with Mouse-1 scrolls the window continuously.

If Emacs is compiled without GTK+ support on the X window system, the scroll bar behaves differently. The scroll bar's inner box is drawn to represent the portion of the buffer currently displayed, with the entire height of the scroll bar representing the entire length of the buffer. Mouse-1 anywhere on the scroll bar scrolls forward like C-v, and Mouse-3 scrolls backward like M-v. Clicking Mouse-2 in the scroll bar lets you move or drag the inner box up and down.

You can also click C-Mouse-2 in the scroll bar to split a window vertically. The split occurs on the line where you click.

You can toggle the use of the scroll bar with the command M-x scroll-bar-mode. With a prefix argument, this command turns use of scroll bars on if and only if the argument is positive. This command applies to all frames, including frames yet to be created. Customize the variable scroll-bar-mode to control the use of scroll bars at startup. You can use it to specify that they are placed at the right of windows if you prefer that. You have to set this variable through the ‘Customize’ interface (see Easy Customization), or it will not work properly. You can also use the X resource ‘verticalScrollBars’ to control the initial setting of Scroll Bar mode. See Resources.

To enable or disable scroll bars for just the selected frame, use the command M-x toggle-scroll-bar.

You can control the scroll bar width by changing the value of the scroll-bar-width frame parameter.


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25.12 Scrolling With “Wheeled” Mice

Some mice have a “wheel” instead of a third button. You can usually click the wheel to act as either Mouse-2 or Mouse-3, depending on the setup. You can also use the wheel to scroll windows instead of using the scroll bar or keyboard commands. Mouse wheel support only works if the system generates appropriate events; whenever possible, it is turned on by default. To toggle this feature, use M-x mouse-wheel-mode.

The two 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.


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25.13 Drag and Drop

Emacs supports drag and drop using the mouse. 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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25.14 Menu Bars

You can turn display of menu bars on or off with M-x menu-bar-mode or by customizing the variable menu-bar-mode. With no argument, this command toggles Menu Bar mode, a minor mode. With an argument, the command turns Menu Bar mode on if the argument is positive, off if the argument is not positive. You can use the X resource ‘menuBarLines’ to control the initial setting of Menu Bar mode. See Resources.

Expert users often turn off the menu bar, especially on text-only 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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25.15 Tool Bars

The tool bar is a line (or lines) of icons at the top of the Emacs window, just below the menu bar. You can click on these icons with the mouse to do various jobs.

The global tool bar contains general commands. Some major modes define their own tool bars to replace it. A few “special” modes that are not designed for ordinary editing remove some items from the global tool bar.

Tool bars work only on a graphical display. The tool bar uses colored XPM icons if Emacs was built with XPM support. Otherwise, the tool bar uses monochrome icons (PBM or XBM format).

You can turn display of tool bars on or off with M-x tool-bar-mode or by customizing the option tool-bar-mode.


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25.16 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.

In GTK+ versions 2.4 through 2.10, you can choose to use an older version of the GTK+ file dialog by setting the variable x-gtk-use-old-file-dialog to a non-nil value. If Emacs is built with a GTK+ version that has only one file dialog, this variable has no effect.


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25.17 Tooltips

Tooltips are small windows that display text information at the current mouse position. They activate when there is a pause in mouse movement. There are two types of tooltip: help tooltips and GUD tooltips.

Help tooltips typically display over text—including the mode line—but are also available for other parts of the Emacs frame, such as the tool bar and menu items.

You can toggle display of help tooltips (Tooltip mode) with the command M-x tooltip-mode. When Tooltip mode is disabled, the help text is displayed in the echo area instead.

GUD tooltips show values of variables. They are useful when you are debugging a program. See Debugger Operation.

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>. See X Resources, for information on customizing the windows that display tooltips.


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25.18 Mouse Avoidance

Mouse Avoidance mode keeps the mouse pointer away from point, to avoid obscuring text you want to edit. Whenever it moves the mouse, it also raises the frame. 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 mouse to the upper-right corner on any key-press;
exile
Move the mouse to the corner 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 mouse, displace the mouse a random distance & 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.


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25.19 Non-Window Terminals

On a text-only 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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25.20 Using a Mouse in Terminal Emulators

Some text-only 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 use 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 terminal mouse support. You must have the gpm package installed and running on your system in order for this to work.


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26 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 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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26.1 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 shows how to say “hello” in many languages. This illustrates various scripts. 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> (ucs-insert). 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:

             character: À (192, #o300, #xc0)
     preferred charset: unicode (Unicode (ISO10646))
            code point: 0xC0
                syntax: w 	which means: word
              category: j:Japanese l:Latin v:Vietnamese
           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
       general-category: Lu (Letter, Uppercase)
       decomposition: (65 768) ('A' '̀')
       old-name: LATIN CAPITAL LETTER A GRAVE
     
     There are text properties here:
       auto-composed        t


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26.2 Enabling 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, either for Emacs as a whole, or for a single 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.

To turn off multibyte character support by default, start Emacs with the ‘--unibyte’ option (see Initial Options), or set the environment variable EMACS_UNIBYTE. You can also customize enable-multibyte-characters or, equivalently, directly set the variable default-enable-multibyte-characters to nil in your init file to have basically the same effect as ‘--unibyte’. With ‘--unibyte’, multibyte strings are not created during initialization from the values of environment variables, /etc/passwd entries etc., even if those contain non-ASCII characters.

Emacs normally loads Lisp files as multibyte, regardless of whether you used ‘--unibyte’. This includes the Emacs initialization file, .emacs, and the initialization files of Emacs packages such as Gnus. However, you can specify unibyte loading for a particular Lisp file, by putting ‘-*-unibyte: t;-*- in a comment on the first line (see File Variables). Then that file is always loaded as unibyte text. The motivation for these conventions is that it is more reliable to always load any particular Lisp file in the same way. However, you can load a Lisp file as unibyte, on any one occasion, by typing C-x <RET> c raw-text <RET> immediately before loading it.

The mode line indicates whether multibyte character support is enabled in the current buffer. If it is, there are two or more characters (most often two dashes) near the beginning of the mode line, before the indication of the visited file's end-of-line convention (colon, backslash, etc.). When multibyte characters are not enabled, nothing precedes the colon except a single dash. See Mode Line, for more details about this.

To convert a unibyte session to a multibyte session, set default-enable-multibyte-characters to t. Buffers which were created in the unibyte session before you turn on multibyte support will stay unibyte. You can turn on multibyte support in a specific buffer by invoking the command toggle-enable-multibyte-characters in that buffer.


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26.3 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 in an Emacs buffer. 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 the variable 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 include:

ASCII, Belarusian, Bengali, Brazilian Portuguese, Bulgarian, 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 a suitable font. If some of the characters appear as empty boxes, you should install the GNU Intlfonts package, which includes fonts for most supported scripts.11 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.12 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, and selects the corresponding language environment if a match is found. (The former variable overrides the latter.) 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, 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 environment, 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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26.4 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 which 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 a' 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 which 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, 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 digit n selects the nth 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 e ' combines to form an ‘e’ 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, e ' ' gives you the two characters ‘e'’. Another way is to type another letter after the e—something that won't combine with that—and immediately delete it. For example, you could type e e <DEL> ' to get separate ‘e’ 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).


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26.5 Selecting an Input Method

C-\
Enable or disable use of the selected input method.
C-x <RET> C-\ method <RET>
Select a new input method for the current buffer.
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 for 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 activates the input method “german-prefix” automatically in the 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 the other information about the character.

To see a list of all the supported input methods, type M-x list-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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26.6 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, carriage-return linefeed, and just carriage-return.

C-h C coding <RET>
Describe coding system coding.
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.)
...-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.13)
...-mac
Assume the file uses carriage-return to separate lines, and do the appropriate conversion. (This is the convention normally used on the Macintosh system.)

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 which 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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26.7 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 many 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, auto-coding-regexp-alist and auto-coding-functions are the strongest way to specify the coding system for certain patterns of file names, or for files containing certain patterns; these variables even override ‘-*-coding:-*-’ tags in the file itself. 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. Likewise, Emacs uses auto-coding-regexp-alist to ensure that RMAIL files, whose names in general don't match any particular pattern, are decoded correctly. One of the builtin auto-coding-functions detects the encoding for XML files.

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, unless rmail-decode-mime-charset is nil. 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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26.8 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 by typing C-x <RET> r coding-system <RET>. 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 <RET>.

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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26.9 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, Emacs tells you that the most-preferred coding system is not recommended 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 type its name in response to the question.)

When you send a message with Mail mode (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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26.10 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 for saving or revisiting the visited file in the current buffer.
C-x <RET> c coding <RET>
Specify coding system coding for the immediately following command.
C-x <RET> r coding <RET>
Revisit the current file using the coding system coding.
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—in other words, it says which coding system to use when saving or reverting the visited file. You specify which coding system using the minibuffer. If you specify a coding system that cannot handle all of the characters in the buffer, Emacs warns you about the troublesome characters when you actually save the buffer.

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 CRLF 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 variable default-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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26.11 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 window-based applications.
C-x <RET> X coding <RET>
Use coding system coding for transferring one selection—the next one—to or from another window-based application.
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.
C-x <RET> c coding <RET>
Specify coding system coding for the immediately following command.

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 COMPOUND_TEXT and UTF8_STRING, 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 just before the command that runs or starts a subprocess, to specify the coding system to use for communication with that subprocess.

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 X Window systems. 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.)

The variable x-select-request-type specifies a selection data type of selection to request from the X server. The default value is nil, which means Emacs tries COMPOUND_TEXT and UTF8_STRING, and uses whichever result seems more appropriate. You can explicitly specify the data type by setting the variable to one of the symbols COMPOUND_TEXT, UTF8_STRING, STRING and TEXT.


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26.12 Coding Systems for File Names

C-x <RET> F coding <RET>
Use coding system coding for encoding and decoding file names.

The variable 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.

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 which the specified coding system can encode. Use C-x <RET> F (set-file-name-coding-system) to specify this interactively.

If file-name-coding-system is nil, Emacs uses a default coding system determined by the selected language environment. 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 get 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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26.13 Coding Systems for Terminal I/O

C-x <RET> k coding <RET>
Use coding system coding for keyboard input.
C-x <RET> t coding <RET>
Use coding system coding for terminal output.

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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26.14 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 specs, each assigned to handle a range of character codes, and may fall back on another fontset for characters which 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 certain characters appear on the screen as hollow boxes, this means that the fontset in use for them has no font for those characters.14

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 specific fontset 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 an empty box instead.


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26.15 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, fontset-standard is created using the value of ns-standard-fontset-spec, and on 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 this way,

     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 which 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.

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, 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 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 family field. In such a case, ‘Fontset-n’ can be specified as below:

     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 Font X, for more information about font naming in X.


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26.16 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-spec 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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26.17 Undisplayable Characters

There may be a some non-ASCII characters that your terminal cannot display. Most text-only terminals support just a single character set (use the variable default-terminal-coding-system (see Terminal Coding) to tell Emacs which one); characters which 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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26.18 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). If you disable multibyte characters, Emacs can still handle one of these character codes 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 Enabling Multibyte. Note particularly that you probably want to ensure that your initialization files are read as unibyte if they contain non-ASCII characters.

Emacs can also display those characters, provided the terminal or font in use supports them. This works automatically. Alternatively, 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.

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 we don't have them yet.

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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26.19 Charsets

Emacs defines most of popular character sets (e.g. ascii, iso-8859-1, cp1250, big5, unicode) as charsets and a few of its own charsets (e.g. emacs, unicode-bmp, eight-bit). All supported characters belong to one or more charsets. Usually you don't have to take care of “charset”, but knowing about it may help understanding the behavior of Emacs in some cases.

One example is a font selection. In each language environment, charsets have different priorities. Emacs, at first, tries to use a font that matches with charsets of higher priority. For instance, in Japanese language environment, the charset japanese-jisx0208 has the highest priority (see Describe Language Environment). So, Emacs tries to use a font whose registry property is “JISX0208.1983-0” for characters belonging to that charset.

Another example is a use of charset text property. When Emacs reads a file encoded in a coding systems that uses escape sequences to switch charsets (e.g. iso-2022-int-1), the buffer text keep the information of the original charset by charset text property. By using this information, Emacs can write the file with the same byte sequence as the original.

There are two commands for obtaining information about Emacs 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.

To display a list of all the supported charsets, type M-x list-character-sets. The list gives the names of charsets and additional information to identity each charset (see ISO/IEC's this page <http://www.itscj.ipsj.or.jp/ISO-IR/> for the detail). In the list, charsets are categorized into two; the normal charsets are listed first, and the supplementary charsets are listed last. A charset in the latter category is used for defining another charset (as a parent or a subset), or was used only in Emacs of the older versions.

To find out which charset a character in the buffer belongs to, put point before it and type C-u C-x =.


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27 Major Modes

Emacs provides many alternative major modes, each of which customizes Emacs for editing text of a particular sort. The major modes are mutually exclusive, and each buffer has one major mode at any time. 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 should switch to the appropriate major mode, such as Lisp mode or Text mode.

Selecting a major mode changes the meanings of a few keys to become more specifically adapted to the language being edited. The ones that are changed frequently are <TAB>, <DEL>, and C-j. The prefix key C-c normally contains mode-specific commands. In addition, the commands which handle comments use the mode to determine how comments are to be delimited. Many major modes redefine the syntactical properties of characters appearing in the buffer. See Syntax.

The 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 remaining major modes are not intended for use on users' files; they are used in buffers created for specific purposes by Emacs, such as Dired mode for buffers made by Dired (see Dired), Mail mode for buffers made by C-x m (see Sending Mail), and Shell mode for buffers used for communicating with an inferior shell process (see Interactive Shell).

Most programming-language major modes specify that only blank lines separate paragraphs. This is to make the paragraph commands useful. (See Paragraphs.) They also cause Auto Fill mode to use the definition of <TAB> to indent the new lines it creates. This is because most lines in a program are usually indented (see Indentation).


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27.1 How Major Modes are Chosen

You can select a major mode explicitly for the current buffer, but most of the time Emacs determines which mode to use based on the file name or on special text in the file.

To explicitly select a new major, you use an M-x command. Take the name of a major mode and add -mode to get the name of the command to select that mode. Thus, you can enter Lisp mode by executing M-x lisp-mode.

When you visit a file, Emacs usually chooses the right 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 the contents of the file. Here is the exact procedure:

First, Emacs checks whether the file contains a file-local variable that specifies the major mode. If so, it uses that major mode, ignoring all other criteria. See File Variables. 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. Alternatively, you could write

     ; -*- mode: Lisp;-*-

The latter format allows you to specify local variables as well, like this:

     ; -*- mode: Lisp; tab-width: 4; -*-

Second, 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 Lisp function that toggles a major mode. 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 wit 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 systems with case-insensitive file names, such as Microsoft Windows, Emacs performs a single case-insensitive search through auto-mode-alist. On other systems, Emacs normally performs a single case-sensitive search through the alist. However, if you change the variable auto-mode-case-fold to t, Emacs performs a second case-insensitive search if the first search fails.

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.

When you visit a file that does not specify a major mode to use, or when you create a new buffer with C-x b, the variable default-major-mode specifies which major mode to use. Normally its value is the symbol fundamental-mode, which specifies Fundamental mode. If default-major-mode is nil, the major mode is taken from the previously current buffer.

If you change the major mode of a buffer, you can go back to the major mode Emacs would choose automatically: use the command M-x normal-mode to do this. 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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28 Indentation

This chapter describes the Emacs commands that add, remove, or adjust indentation.

<TAB>
Indent the current line appropriately, in a mode-dependent fashion.
C-j
Perform <RET> followed by <TAB> (newline-and-indent).
M-^
Merge the previous and the current line (delete-indentation). This would cancel the effect of a preceding C-j.
C-M-o
Split the current line at point; text on the line after point becomes a new line indented to the same column where point is located (split-line).
M-m
Move (forward or back) to the first nonblank character on the current line (back-to-indentation).
C-M-\
Indent lines in the region to the same column (indent-region).
C-x <TAB>
Shift lines in the region rigidly right or left (indent-rigidly).
M-i
Indent from point to the next prespecified tab stop column (tab-to-tab-stop).
M-x indent-relative
Indent from point to under an indentation point in the previous line.

In most major modes, the <TAB> key runs the command indent-for-tab-command, which either performs indentation or inserts whitespace at point, depending on the situation.

In programming modes such as Lisp mode and C mode, <TAB> indents the current line if the region is inactive. If the region is active, it indents every line in the region (see Mark). Indentation means adding or removing some combination of space and tab characters (whitespace characters) at the start of the line, in a way that makes sense given the text in the preceding lines. Exactly how indentation is performed depends on the major mode. See Program Indent.

In text modes, <TAB> inserts some whitespace characters to advance point to the next tab stop (see Tab Stops). For the purposes of this command, the position of the first non-whitespace character on the preceding line is treated as an additional tab stop. You can therefore use <TAB> to “align” point with the preceding line. If the region is active, <TAB> performs this action on every line in the region.

Indentation is often performed with the help of tab characters (ASCII code 9), which are displayed as a stretch of empty space extending to the next display tab stop. By default, there is one display tab stop every eight columns; the number of columns is determined by the variable tab-width. You can insert a single tab character by typing C-q <TAB>. See Text Display.

The command M-i (tab-to-tab-stop) adjusts the whitespace characters around point, inserting just enough whitespace to advance point up to the next tab stop. By default, this involves deleting the existing whitespace and inserting a single tab character.

Normally, most of these indentation commands insert an optimal mix of tabs and spaces to align to the desired column. See Just Spaces, for how to disable use of tabs. However, C-q <TAB> always inserts a tab, even when tabs are disabled for the indentation commands.


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28.1 Indentation Commands and Techniques

To move over the indentation on a line, do M-m (back-to-indentation). This command, given anywhere on a line, positions point at the first nonblank character on the line, if any, or else at the end of the line.

To insert an indented line before the current line, do C-a C-o <TAB>. To make an indented line after the current line, use C-e C-j.

If you just want to insert a tab character in the buffer, type C-q <TAB>.

C-M-o (split-line) moves the text from point to the end of the line vertically down, so that the current line becomes two lines. C-M-o first moves point forward over any spaces and tabs. Then it inserts after point a newline and enough indentation to reach the same column point is on. Point remains before the inserted newline; in this regard, C-M-o resembles C-o.

To join two lines cleanly, use the M-^ (delete-indentation) command. It deletes the indentation at the front of the current line, and the line boundary as well, replacing them 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 open parentheses or closing parentheses, or if the junction follows another newline. To delete just the indentation of a line, go to the beginning of the line and use M-\ (delete-horizontal-space), which deletes all spaces and tabs around the cursor.

If you have a fill prefix, M-^ deletes the fill prefix if it appears after the newline that is deleted. See Fill Prefix.

There are also commands for changing the indentation of several lines at once. They apply to all the lines that begin in the region. C-M-\ (indent-region) indents each line in the “usual” way, as if you had typed <TAB> at the beginning of the line. A numeric argument specifies the column to indent to, and each line is shifted left or right so that its first nonblank character appears in that column. C-x <TAB> (indent-rigidly) moves all of the lines in the region right by its argument (left, for negative arguments). The whole group of lines moves rigidly sideways, which is how the command gets its name.

To remove all indentation from all of the lines in the region, invoke C-x <TAB> with a large negative argument, such as -1000.

M-x indent-relative indents at point based on the previous line (actually, the last nonempty line). It inserts whitespace at point, moving point, until it is underneath the next indentation point in the previous line. An indentation point is the end of a sequence of whitespace or the end of the line. If point is farther right than any indentation point in the previous line, indent-relative runs tab-to-tab-stop (see Tab Stops), unless it is called with a numeric argument, in which case it does nothing.

See Format Indentation, for another way of specifying the indentation for part of your text.


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28.2 Tab Stops

For typing in tables, you can use M-i (tab-to-tab-stop). This command inserts indentation before point, enough to reach the next tab stop column.

You can change the tab stops used by M-i and other indentation commands, so that they need not be spaced every eight characters, or even regularly spaced. The tab stops are stored in the variable tab-stop-list, as a list of column numbers in increasing order.

A convenient way to set the tab stops is with M-x edit-tab-stops, which creates and selects a buffer containing a description of the tab stop settings. You can edit this buffer to specify different tab stops, and then type C-c C-c to make those new tab stops take effect. The buffer uses Overwrite mode (see Minor Modes). edit-tab-stops records which buffer was current when you invoked it, and stores the tab stops back in that buffer; normally all buffers share the same tab stops and changing them in one buffer affects all, but if you happen to make tab-stop-list local in one buffer then edit-tab-stops in that buffer will edit the local settings.

Here is what the text representing the tab stops looks like for ordinary tab stops every eight columns.

             :       :       :       :       :       :
     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 remaining lines are present just to help you see where the colons are and know what to do.

Note that the tab stops that control tab-to-tab-stop 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, which occurs every tab-width columns regardless of the contents of tab-stop-list. See Text Display.


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28.3 Tabs vs. Spaces

Emacs normally uses both tabs and spaces to indent lines. If you prefer, all indentation can be made from spaces only. To request this, set indent-tabs-mode to nil. This is a per-buffer variable, so altering the variable affects only the current buffer, but there is a default value which you can change as well. See Locals.

A tab is not always displayed in the same way. By default, tabs are eight columns wide, but some people like to customize their editors to use a different tab width (e.g., by changing the variable tab-width in Emacs). By using spaces only, you can make sure that your file looks the same regardless of the tab width setting.

There are also commands to convert tabs to spaces or vice versa, always preserving the columns of all nonblank 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.


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29 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.

Emacs has other major modes for text which contains “embedded” commands, such as TeX and LaTeX (see TeX Mode); HTML, SGML, and XML (see HTML Mode); and Groff and Nroff (see Nroff Mode). In addition, you can edit formatted text in WYSIWYG style (“what you see is what you get”), using Enriched mode (see Formatted Text).

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.

The “automatic typing” features may be useful when writing text. see Top.


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29.1 Words

Emacs has commands for moving over or operating on words. By convention, the keys for them are all Meta characters.

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 the next n words with an operation which acts on the region, use the command M-@ (mark-word). This command does not move point, but sets the mark where M-f would move to. Once the mark is active, each additional M-@ advances the mark by one additional word. M-@ also accepts a numeric argument that says how many words to scan for the place to put the mark.

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.


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29.2 Sentences

The Emacs commands for manipulating sentences and paragraphs are mostly on Meta keys, so as to be 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 and M-e (backward-sentence and forward-sentence) move to the beginning and end of the current sentence, respectively. They 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; they consider a sentence to end 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 makes a distinction between periods that end a sentence and periods that indicate abbreviations; that enables the Emacs sentence commands to distinguish, too. These commands do not stop for 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) in related ways.

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 do not use periods to indicate the end of a sentence. For example, sentences in Thai end with a double space but without a period. Set the variable sentence-end-without-period to t in such cases.


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29.3 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-{ moves to the beginning of the current or previous paragraph, while M-} moves to the end of the current or next paragraph. Blank lines and text-formatter command lines separate paragraphs and are not considered part of any paragraph. If there is a blank line before the paragraph, M-{ moves to the blank line, because that is convenient in practice.

In Text mode, an indented line is not a paragraph break. If you want indented lines to have this effect, use Paragraph-Indent Text mode instead. See Text Mode.

In major modes for programs, paragraphs begin and end only at blank lines. This makes the paragraph commands useful, even though there are no paragraphs as such in a program.

When you have set a fill prefix, then paragraphs are delimited by all lines which don't start with the fill prefix. See Filling.

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), the paragraph following point is surrounded by point and mark. 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; furthermore, each subsequent M-h further advances the mark by one paragraph.

The precise definition of a paragraph boundary is controlled by the variables paragraph-separate and paragraph-start. The value of paragraph-start is a regexp that should match any line that either starts or separates paragraphs. The value of paragraph-separate is another regexp that should match only 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. Each regular expression must match at the left margin. For example, in Fundamental mode, paragraph-start is "\f\\|[ \t]*$", and paragraph-separate is "[ \t\f]*$".

Normally it is desirable for page boundaries to separate paragraphs. The default values of these variables recognize the usual separator for pages.


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29.4 Pages

Within some text files, text is divided into pages, which are delimited by the formfeed character (ASCII code 12, sometimes denoted as <control-L>). When you print hardcopy for a file, the formfeed character forces a page break: each page of the file goes on a separate page on paper. Most Emacs commands treat the formfeed character just like any other character: you can insert it with C-q C-l, and delete it with <DEL>. However, since pages are often meaningful divisions of the file, Emacs provides commands to move over them and operate on them.

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).

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 and the mark at the end. The page delimiter at the end is included (the mark follows it). The page delimiter at the front is excluded (point follows it).

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 means the next page, and −1 means 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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29.5 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 leaves it unfilled. When you edit formatted text, you can specify a style of filling for each portion of the text (see Formatted Text).


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29.5.1 Auto Fill Mode

Auto Fill mode is a minor mode 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.

M-x auto-fill-mode turns Auto Fill mode on if it was off, or off if it was on. With a positive numeric argument it always turns Auto Fill mode on, and with a negative argument always turns it off. You can see when Auto Fill mode is in effect by the presence of the word ‘Fill’ in the mode line, inside the parentheses. Auto Fill mode is a minor mode which is enabled or disabled for each buffer individually. See Minor Modes.

In Auto Fill mode, lines are broken automatically at spaces when they get longer than the desired width. Line breaking and rearrangement takes place 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 (recall that a newline is really a control-J). Also, C-o inserts a newline without line breaking.

Auto Fill mode works well with programming-language modes, because it indents new lines with <TAB>. If a line ending in a comment gets too long, the text of the comment is split into two comment lines. Optionally, new comment delimiters are inserted at the end of the first line and the beginning of the second so that each line is a separate comment; the variable comment-multi-line controls the choice (see Comments).

Adaptive filling (see Adaptive Fill) works for Auto Filling as well as for explicit fill commands. It takes a fill prefix automatically from the second or first line of a paragraph.

Auto Fill mode does not refill entire paragraphs; it can break lines but cannot merge lines. So editing in the middle of a paragraph can result in a paragraph that is not correctly filled. The easiest way to make the paragraph properly filled again is usually with the explicit fill commands. See Fill Commands.

Many users like Auto Fill mode and want to use it in all text files. The section on init files says how to arrange this permanently for yourself. See Init File.


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29.5.2 Explicit Fill Commands

M-q
Fill current paragraph (fill-paragraph).
C-x f
Set the fill column (set-fill-column).
M-x fill-region
Fill each paragraph in the region (fill-region).
M-x fill-region-as-paragraph
Fill the region, considering it as one paragraph.
M-o M-s
Center a line.

To refill a paragraph, use the command M-q (fill-paragraph). This operates on the paragraph that point is inside, or the one after point if point is between paragraphs. Refilling works by removing all the line-breaks, then inserting new ones where necessary. When there is an active region, this command operates on the text within the region like fill-region.

To refill many paragraphs, use M-x fill-region, which finds the paragraphs in the region and fills each of them.

M-q and fill-region use the same criteria as M-h for finding paragraph boundaries (see Paragraphs). For more control, you can use M-x fill-region-as-paragraph, which refills everything between point and mark as a single paragraph. This command deletes any blank lines within the region, so separate blocks of text end up combined into one block.

A numeric argument to M-q tells it to justify the text as well as filling it. This means that extra spaces are inserted to make the right margin line up exactly at the fill column. To remove the extra spaces, use M-q with no argument. (Likewise for fill-region.) Another way to control justification, and choose other styles of filling, is with the justification text property; see Format Justification.

The command M-o M-s (center-line) centers the current line within the current fill column. With an argument n, it centers n lines individually and moves past them. This binding is made by Text mode and is available only in that and related modes (see Text Mode).

The maximum line width for filling is in the variable fill-column. Altering the value of fill-column makes it local to the current buffer; until that time, the default value is in effect. The default is initially 70. See Locals. The easiest way to set fill-column is to use the command C-x f (set-fill-column). With a numeric argument, it uses that as the new fill column. With just C-u as argument, it sets fill-column to the current horizontal position of point.

Emacs commands normally consider a period followed by two spaces or by a newline as the end of a sentence; a period followed by just one space indicates an abbreviation and not the end of a sentence. To preserve the distinction between these two ways of using a period, the fill commands do not break a line after a period followed by just one space.

If the variable sentence-end-double-space is nil, the fill commands expect and leave just one space at the end of a sentence. Ordinarily this variable is t, so the fill commands insist on two spaces for the end of a sentence, as explained above. See Sentences.

If the variable colon-double-space is non-nil, the fill commands put two spaces after a colon.

The variable fill-nobreak-predicate is a hook (an abnormal hook, see Hooks) specifying additional conditions where line-breaking is not allowed. Each function is called with no arguments, with point at a place where Emacs is considering breaking the line. If a function returns a non-nil value, then that's a bad place to break the line. Two standard functions you can use are fill-single-word-nobreak-p (don't break after the first word of a sentence or before the last) and fill-french-nobreak-p (don't break after ‘(’ or before ‘)’, ‘:’ or ‘?’).


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29.5.3 The Fill Prefix

To fill a paragraph in which each line starts with a special marker (which might be a few spaces, giving an indented paragraph), you can use the fill prefix feature. The fill prefix is a string that Emacs expects every line to start with, and which is not included in filling. You can specify a fill prefix explicitly; Emacs can also deduce the fill prefix automatically (see Adaptive Fill).

C-x .
Set the fill prefix (set-fill-prefix).
M-q
Fill a paragraph using current fill prefix (fill-paragraph).
M-x fill-individual-paragraphs
Fill the region, considering each change of indentation as starting a new paragraph.
M-x fill-nonuniform-paragraphs
Fill the region, considering only paragraph-separator lines as starting a new paragraph.

To specify a fill prefix for the current buffer, move to a line that starts with the desired prefix, put point at the end of the prefix, and type C-x . (set-fill-prefix). (That's a period after the C-x.) To turn off the fill prefix, specify an empty prefix: type C-x . with point at the beginning of a line.

When a fill prefix is in effect, the fill commands remove the fill prefix from each line of the paragraph before filling and insert it on each line after filling. (The beginning of the first line of the paragraph is left unchanged, since often that is intentionally different.) Auto Fill mode also inserts the fill prefix automatically when it makes a new line. The C-o command inserts the fill prefix on new lines it creates, when you use it at the beginning of a line (see Blank Lines). Conversely, the command M-^ deletes the prefix (if it occurs) after the newline that it deletes (see Indentation).

For example, if fill-column is 40 and you set the fill prefix to ‘;; ’, then M-q in the following text

     ;; This is an
     ;; example of a paragraph
     ;; inside a Lisp-style comment.

produces this:

     ;; This is an example of a paragraph
     ;; inside a Lisp-style comment.

Lines that do not start with the fill prefix are considered to start paragraphs, both in M-q and the paragraph commands; this gives good results for paragraphs with hanging indentation (every line indented except the first one). Lines which are blank or indented once the prefix is removed also separate or start paragraphs; this is what you want if you are writing multi-paragraph comments with a comment delimiter on each line.

You can use M-x fill-individual-paragraphs to set the fill prefix for each paragraph automatically. This command divides the region into paragraphs, treating every change in the amount of indentation as the start of a new paragraph, and fills each of these paragraphs. Thus, all the lines in one “paragraph” have the same amount of indentation. That indentation serves as the fill prefix for that paragraph.

M-x fill-nonuniform-paragraphs is a similar command that divides the region into paragraphs in a different way. It considers only paragraph-separating lines (as defined by paragraph-separate) as starting a new paragraph. Since this means that the lines of one paragraph may have different amounts of indentation, the fill prefix used is the smallest amount of indentation of any of the lines of the paragraph. This gives good results with styles that indent a paragraph's first line more or less that the rest of the paragraph.

The fill prefix is stored in the variable fill-prefix. Its value is a string, or nil when there is no fill prefix. This is a per-buffer variable; altering the variable affects only the current buffer, but there is a default value which you can change as well. See Locals.

The indentation text property provides another way to control the amount of indentation paragraphs receive. See Format Indentation.


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29.5.4 Adaptive Filling

The fill commands can deduce the proper fill prefix for a paragraph automatically in certain cases: either whitespace or certain punctuation characters at the beginning of a line are propagated to all lines of the paragraph.

If the paragraph has two or more lines, the fill prefix is taken from the paragraph's second line, but only if it appears on the first line as well.

If a paragraph has just one line, fill commands may take a prefix from that line. The decision is complicated because there are three reasonable things to do in such a case:

All three of these styles of formatting are commonly used. So the fill commands try to determine what you would like, based on the prefix that appears and on the major mode. Here is how.

If the prefix found on the first line matches adaptive-fill-first-line-regexp, or if it appears to be a comment-starting sequence (this depends on the major mode), then the prefix found is used for filling the paragraph, provided it would not act as a paragraph starter on subsequent lines.

Otherwise, the prefix found is converted to an equivalent number of spaces, and those spaces are used as the fill prefix for the rest of the lines, provided they would not act as a paragraph starter on subsequent lines.

In Text mode, and other modes where only blank lines and page delimiters separate paragraphs, the prefix chosen by adaptive filling never acts as a paragraph starter, so it can always be used for filling.

The variable adaptive-fill-regexp determines what kinds of line beginnings can serve as a fill prefix: any characters at the start of the line that match this regular expression are used. If you set the variable adaptive-fill-mode to nil, the fill prefix is never chosen automatically.

You can specify more complex ways of choosing a fill prefix automatically by setting the variable adaptive-fill-function to a function. This function is called with point after the left margin of a line, and it should return the appropriate fill prefix based on that line. If it returns nil, adaptive-fill-regexp gets a chance to find a prefix.


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29.5.5 Refill Mode

Refill minor mode provides support for keeping paragraphs filled as you type or modify them in other ways. It provides an effect similar to typical word processor behavior. This works by running a paragraph-filling command at suitable times.

To toggle the use of Refill mode in the current buffer, type M-x refill-mode. When you are typing text, only characters which normally trigger auto filling, like the space character, will trigger refilling. This is to avoid making it too slow. Apart from self-inserting characters, other commands which modify the text cause refilling.

The current implementation is preliminary and not robust. You can get better “line wrapping” behavior using Longlines mode. See Longlines. However, Longlines mode has an important side-effect: the newlines that it inserts for you are not saved to disk, so the files that you make with Longlines mode will appear to be completely unfilled if you edit them without Longlines mode.


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29.5.6 Long Lines Mode

Sometimes, you may come across “unfilled” text files, which Emacs normally displays as a bunch of extremely long lines. Comfortably reading and editing such files normally requires “word wrap”, a feature that breaks up each long text line into multiple screen lines in a readable manner—by putting the breaks at word boundaries. Many text editors, such as those built into many web browsers, perform word wrapping by default.

There are two different minor modes in Emacs that perform word wrapping. The first is Visual Line mode, which does it by altering the behavior of screen line continuation. See Visual Line Mode, for information about Visual Line mode.

Instead of using Visual Line mode, you can use a minor mode called Long Lines mode. Long Lines mode wraps lines by inserting or deleting soft newlines as you type (see Hard and Soft Newlines). These soft newlines won't show up when you save the buffer into a file, or when you copy the text into the kill ring, clipboard, or a register. Unlike Visual Line mode, Lone Lines mode breaks long lines at the fill column (see Fill Commands), rather than the right window edge. To enable Long Lines mode, type M-x longlines-mode. If the text is full of long lines, this also immediately “wraps” them all.

The word wrap performed by Long Lines mode is not the same as ordinary filling (see Fill Commands). It does not contract multiple spaces into a single space, recognize fill prefixes (see Fill Prefix), or perform adaptive filling (see Adaptive Fill). The reason for this is that a wrapped line is still, conceptually, a single line. Each soft newline is equivalent to exactly one space in that long line, and vice versa. However, you can still call filling functions such as M-q, and these will work as expected, inserting soft newlines that won't show up on disk or when the text is copied. You can even rely entirely on the normal fill commands by turning off automatic line wrapping, with C-u M-x longlines-auto-wrap. To turn automatic line wrapping back on, type M-x longlines-auto-wrap.

Type RET to insert a hard newline, one which automatic refilling will not remove. If you want to see where all the hard newlines are, type M-x longlines-show-hard-newlines. This will mark each hard newline with a special symbol. The same command with a prefix argument turns this display off.

Long Lines mode does not change normal text files that are already filled, since the existing newlines are considered hard newlines. Before Long Lines can do anything, you need to transform each paragraph into a long line. One way is to set fill-column to a large number (e.g., C-u 9999 C-x f), re-fill all the paragraphs, and then set fill-column back to its original value.


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29.6 Case Conversion Commands

Emacs has commands for converting either a single word or any arbitrary range of text to upper case or to lower case.

M-l
Convert following word to lower case (downcase-word).
M-u
Convert following word to upper case (upcase-word).
M-c
Capitalize the following word (capitalize-word).
C-x C-l
Convert region to lower case (downcase-region).
C-x C-u
Convert region to upper case (upcase-region).

The word conversion commands are the most useful. M-l (downcase-word) converts the word after point to lower case, moving past it. Thus, repeating M-l converts successive words. M-u (upcase-word) converts to all capitals instead, while M-c (capitalize-word) puts the first letter of the word into upper case and the rest into lower case. All these commands convert several words at once if given an argument. They are especially convenient for converting a large amount of text from all upper case to mixed case, because you can move through the text using M-l, M-u or M-c on each word as appropriate, occasionally using M-f instead to skip a word.

When given a negative argument, the word case conversion commands apply to the appropriate number of words before point, but do not move point. This is convenient when you have just typed a word in the wrong case: you can give the case conversion command and continue typing.

If a word case conversion command is given in the middle of a word, it applies only to the part of the word which follows point. (This is comparable to what M-d (kill-word) does.) With a negative argument, case conversion applies only to the part of the word before point.

The other case conversion commands are C-x C-u (upcase-region) and C-x C-l (downcase-region), which convert everything between point and mark to the specified case. Point and mark do not move.

The region case conversion commands upcase-region and downcase-region are normally disabled. This means that they ask for confirmation if you try to use them. When you confirm, you may enable the command, which means it will not ask for confirmation again. See Disabling.


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29.7 Text Mode

When you edit files of text in a human language, it's more convenient to use Text mode rather than Fundamental mode. To enter Text mode, type M-x text-mode.

In Text mode, only blank lines and page delimiters separate paragraphs. As a result, paragraphs can be indented, and adaptive filling determines what indentation to use when filling a paragraph. See Adaptive Fill.

Text mode defines <TAB> to run indent-relative (see Indentation), so that you can conveniently indent a line like the previous line.

Text mode turns off the features concerned with comments except when you explicitly invoke them. It changes the syntax table so that single-quotes are considered part of words. However, if a word starts with single-quotes, these are treated as a prefix for purposes such as capitalization. That is, M-c will convert ‘'hello'’ into ‘'Hello'’, as expected.

If you indent the first lines of paragraphs, then you should use Paragraph-Indent Text mode rather than Text mode. In this mode, you do not need to have blank lines between paragraphs, because the first-line indentation is sufficient to start a paragraph; however paragraphs in which every line is indented are not supported. Use M-x paragraph-indent-text-mode to enter this mode. Use M-x paragraph-indent-minor-mode to enable an equivalent minor mode in situations where you can't change the major mode—in mail composition, for instance.

Text mode, and all the modes based on it, define M-<TAB> as the command ispell-complete-word, which performs completion of the partial word in the buffer before point, using the spelling dictionary as the space of possible words. See Spelling. If your window manager defines M-<TAB> to switch windows, you can type <ESC> <TAB> or C-M-i.

Entering Text mode runs the hook text-mode-hook. Other major modes related to Text mode also run this hook, followed by hooks of their own; this includes Paragraph-Indent Text mode, Nroff mode, TeX mode, Outline mode, and Mail mode. Hook functions on text-mode-hook can look at the value of major-mode to see which of these modes is actually being entered. See Hooks.


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29.8 Outline Mode

Outline mode is a major mode much like Text mode but intended for editing outlines. It allows you to make parts of the text temporarily invisible so that you can see the outline structure. Type M-x outline-mode to switch to Outline mode as the major mode of the current buffer.

When Outline mode makes a line invisible, the line does not appear on the screen. The screen appears exactly as if the invisible line were deleted, except that an ellipsis (three periods in a row) appears at the end of the previous visible line. (Multiple consecutive invisible lines produce just one ellipsis.)

Editing commands that operate on lines, such as C-n and C-p, treat the text of the invisible line as part of the previous visible line. Killing the ellipsis at the end of a visible line really kills all the following invisible lines.

Outline minor mode provides the same commands as the major mode, Outline mode, but you can use it in conjunction with other major modes. Type M-x outline-minor-mode to enable the Outline minor mode in the current buffer. You can also specify this in the text of a file, with a file local variable of the form ‘mode: outline-minor’ (see File Variables).

The major mode, Outline mode, provides special key bindings on the C-c prefix. Outline minor mode provides similar bindings with C-c @ as the prefix; this is to reduce the conflicts with the major mode's special commands. (The variable outline-minor-mode-prefix controls the prefix used.)

Entering Outline mode runs the hook text-mode-hook followed by the hook outline-mode-hook (see Hooks).


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29.8.1 Format of Outlines

Outline mode assumes that the lines in the buffer are of two types: heading lines and body lines. A heading line represents a topic in the outline. Heading lines start with one or more stars; the number of stars determines the depth of the heading in the outline structure. Thus, a heading line with one star is a major topic; all the heading lines with two stars between it and the next one-star heading are its subtopics; and so on. Any line that is not a heading line is a body line. Body lines belong with the preceding heading line. Here is an example:

     * Food
     This is the body,
     which says something about the topic of food.
     
     ** Delicious Food
     This is the body of the second-level header.
     
     ** Distasteful Food
     This could have
     a body too, with
     several lines.
     
     *** Dormitory Food
     
     * Shelter
     Another first-level topic with its header line.

A heading line together with all following body lines is called collectively an entry. A heading line together with all following deeper heading lines and their body lines is called a subtree.

You can customize the criterion for distinguishing heading lines by setting the variable outline-regexp. (The recommended ways to do this are in a major mode function or with a file local variable.) Any line whose beginning has a match for this regexp is considered a heading line. Matches that start within a line (not at the left margin) do not count.

The length of the matching text determines the level of the heading; longer matches make a more deeply nested level. Thus, for example, if a text formatter has commands ‘@chapter’, ‘@section’ and ‘@subsection’ to divide the document into chapters and sections, you could make those lines count as heading lines by setting outline-regexp to ‘"@chap\\|@\\(sub\\)*section"’. Note the trick: the two words ‘chapter’ and ‘section’ are equally long, but by defining the regexp to match only ‘chap’ we ensure that the length of the text matched on a chapter heading is shorter, so that Outline mode will know that sections are contained in chapters. This works as long as no other command starts with ‘@chap’.

You can explicitly specify a rule for calculating the level of a heading line by setting the variable outline-level. The value of outline-level should be a function that takes no arguments and returns the level of the current heading. The recommended ways to set this variable are in a major mode command or with a file local variable.


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29.8.2 Outline Motion Commands

Outline mode provides special motion commands that move backward and forward to heading lines.

C-c C-n
Move point to the next visible heading line (outline-next-visible-heading).
C-c C-p
Move point to the previous visible heading line (outline-previous-visible-heading).
C-c C-f
Move point to the next visible heading line at the same level as the one point is on (outline-forward-same-level).
C-c C-b
Move point to the previous visible heading line at the same level (outline-backward-same-level).
C-c C-u
Move point up to a lower-level (more inclusive) visible heading line (outline-up-heading).

C-c C-n (outline-next-visible-heading) moves down to the next heading line. C-c C-p (outline-previous-visible-heading) moves similarly backward. Both accept numeric arguments as repeat counts. The names emphasize that invisible headings are skipped, but this is not really a special feature. All editing commands that look for lines ignore the invisible lines automatically.

More powerful motion commands understand the level structure of headings. C-c C-f (outline-forward-same-level) and C-c C-b (outline-backward-same-level) move from one heading line to another visible heading at the same depth in the outline. C-c C-u (outline-up-heading) moves backward to another heading that is less deeply nested.


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29.8.3 Outline Visibility Commands

The other special commands of outline mode are used to make lines visible or invisible. Their names all start with hide or show. Most of them fall into pairs of opposites. They are not undoable; instead, you can undo right past them. Making lines visible or invisible is simply not recorded by the undo mechanism.

Many of these commands act on the “current” heading line. If point is on a heading line, that is the current heading line; if point is on a body line, the current heading line is the nearest preceding header line.

C-c C-c
Make the current heading line's body invisible (hide-entry).
C-c C-e
Make the current heading line's body visible (show-entry).
C-c C-d
Make everything under the current heading invisible, not including the heading itself (hide-subtree).
C-c C-s
Make everything under the current heading visible, including body, subheadings, and their bodies (show-subtree).
C-c C-l
Make the body of the current heading line, and of all its subheadings, invisible (hide-leaves).
C-c C-k
Make all subheadings of the current heading line, at all levels, visible (show-branches).
C-c C-i
Make immediate subheadings (one level down) of the current heading line visible (show-children).
C-c C-t
Make all body lines in the buffer invisible (hide-body).
C-c C-a
Make all lines in the buffer visible (show-all).
C-c C-q
Hide everything except the top n levels of heading lines (hide-sublevels).
C-c C-o
Hide everything except for the heading or body that point is in, plus the headings leading up from there to the top level of the outline (hide-other).

Two commands that are exact opposites are C-c C-c (hide-entry) and C-c C-e (show-entry). They apply to the body lines directly following the current heading line. Subheadings and their bodies are not affected.

Two more powerful opposites are C-c C-d (hide-subtree) and C-c C-s (show-subtree). Both apply to the current heading line's subtree: its body, all its subheadings, both direct and indirect, and all of their bodies. In other words, the subtree contains everything following the current heading line, up to and not including the next heading of the same or higher rank.

Intermediate between a visible subtree and an invisible one is having all the subheadings visible but none of the body. There are two commands for doing this, depending on whether you want to hide the bodies or make the subheadings visible. They are C-c C-l (hide-leaves) and C-c C-k (show-branches).

A little weaker than show-branches is C-c C-i (show-children). It makes just the direct subheadings visible—those one level down. Deeper subheadings remain invisible, if they were invisible.

Two commands have a blanket effect on the whole file. C-c C-t (hide-body) makes all body lines invisible, so that you see just the outline structure (as a special exception, it will not hide lines at the top of the file, preceding the first header line, even though these are technically body lines). C-c C-a (show-all) makes all lines visible. These commands can be thought of as a pair of opposites even though C-c C-a applies to more than just body lines.

The command C-c C-q (hide-sublevels) hides all but the top level headings. With a numeric argument n, it hides everything except the top n levels of heading lines.

The command C-c C-o (hide-other) hides everything except the heading and body text that point is in, plus its parents (the headers leading up from there to top level in the outline) and the top level headings.

When incremental search finds text that is hidden by Outline mode, it makes that part of the buffer visible. If you exit the search at that position, the text remains visible. You can also automatically make text visible as you navigate in it by using M-x reveal-mode.


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29.8.4 Viewing One Outline in Multiple Views

You can display two views of a single outline at the same time, in different windows. To do this, you must create an indirect buffer using M-x make-indirect-buffer. The first argument of this command is the existing outline buffer name, and its second argument is the name to use for the new indirect buffer. See Indirect Buffers.

Once the indirect buffer exists, you can display it in a window in the normal fashion, with C-x 4 b or other Emacs commands. The Outline mode commands to show and hide parts of the text operate on each buffer independently; as a result, each buffer can have its own view. If you want more than two views on the same outline, create additional indirect buffers.


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29.8.5 Folding Editing

The Foldout package extends Outline mode and Outline minor mode with “folding” commands. The idea of folding is that you zoom in on a nested portion of the outline, while hiding its relatives at higher levels.

Consider an Outline mode buffer with all the text and subheadings under level-1 headings hidden. To look at what is hidden under one of these headings, you could use C-c C-e (M-x show-entry) to expose the body, or C-c C-i to expose the child (level-2) headings.

With Foldout, you use C-c C-z (M-x foldout-zoom-subtree). This exposes the body and child subheadings, and narrows the buffer so that only the level-1 heading, the body and the level-2 headings are visible. Now to look under one of the level-2 headings, position the cursor on it and use C-c C-z again. This exposes the level-2 body and its level-3 child subheadings and narrows the buffer again. Zooming in on successive subheadings can be done as much as you like. A string in the mode line shows how deep you've gone.

When zooming in on a heading, to see only the child subheadings specify a numeric argument: C-u C-c C-z. The number of levels of children can be specified too (compare M-x show-children), e.g. M-2 C-c C-z exposes two levels of child subheadings. Alternatively, the body can be specified with a negative argument: M-- C-c C-z. The whole subtree can be expanded, similarly to C-c C-s (M-x show-subtree), by specifying a zero argument: M-0 C-c C-z.

While you're zoomed in, you can still use Outline mode's exposure and hiding functions without disturbing Foldout. Also, since the buffer is narrowed, “global” editing actions will only affect text under the zoomed-in heading. This is useful for restricting changes to a particular chapter or section of your document.

To unzoom (exit) a fold, use C-c C-x (M-x foldout-exit-fold). This hides all the text and subheadings under the top-level heading and returns you to the previous view of the buffer. Specifying a numeric argument exits that many levels of folds. Specifying a zero argument exits all folds.

To cancel the narrowing of a fold without hiding the text and subheadings, specify a negative argument. For example, M--2 C-c C-x exits two folds and leaves the text and subheadings exposed.

Foldout mode also provides mouse commands for entering and exiting folds, and for showing and hiding text:

C-M-Mouse-1 zooms in on the heading clicked on

C-M-Mouse-2 exposes text under the heading clicked on

C-M-Mouse-3 hides text under the heading clicked on or exits fold

You can specify different modifier keys (instead of Control-Meta-) by setting foldout-mouse-modifiers; but if you have already loaded the foldout.el library, you must reload it in order for this to take effect.

To use the Foldout package, you can type M-x load-library <RET> foldout <RET>; or you can arrange for to do that automatically by putting this in your .emacs file:

     (eval-after-load "outline" '(require 'foldout))


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29.9 TeX Mode

Emacs provides special major modes for editing files written in TeX and its related formats. TeX is a powerful text formatter written by Donald Knuth; like GNU Emacs, it is free software. LaTeX is a simplified input format for TeX, implemented using TeX macros. DocTeX is a special file format in which the LaTeX sources are written, combining sources with documentation. SliTeX is an obsolete special form of LaTeX.15

TeX mode has four variants: Plain TeX mode, LaTeX mode, DocTeX mode, and SliTeX mode. These distinct major modes differ only slightly, and are designed for editing the four different formats. Emacs selects the appropriate mode by looking at the contents of the buffer. (This is done by the tex-mode command, which is normally called automatically when you visit a TeX-like file. See Choosing Modes.) If the contents are insufficient to determine this, Emacs chooses the mode specified by the variable tex-default-mode; its default value is latex-mode. If Emacs does not guess right, you can select the correct variant of TeX mode using the command M-x plain-tex-mode, M-x latex-mode, M-x slitex-mode, or doctex-mode.

Emacs also provides BibTeX mode, a major mode for editing BibTeX files. BibTeX is a tool for storing and formatting bibliographic references, which is commonly used together with LaTeX. In addition, the RefTeX package provides a minor mode which can be used in conjunction with LaTeX mode to manage bibliographic references. see Top.


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29.9.1 TeX Editing Commands

"
Insert, according to context, either ‘``’ or ‘"’ or ‘''’ (tex-insert-quote).
C-j
Insert a paragraph break (two newlines) and check the previous paragraph for unbalanced braces or dollar signs (tex-terminate-paragraph).
M-x tex-validate-region
Check each paragraph in the region for unbalanced braces or dollar signs.
C-c {
Insert ‘{}’ and position point between them (tex-insert-braces).
C-c }
Move forward past the next unmatched close brace (up-list).

In TeX, the character ‘"’ is not normally used; instead, quotations begin with ‘``’ and end with ‘''’. For convenience, TeX mode overrides the normal meaning of the key " with a command that inserts a pair of single-quotes or backquotes (tex-insert-quote). To be precise, it inserts ‘``’ after whitespace or an open brace, ‘"’ after a backslash, and ‘''’ after any other character.

As a special exception, if you type " when the text before point is either ‘``’ or ‘''’, Emacs replaces that preceding text with a single ‘"’ character. You can therefore type "" to insert ‘"’, should you ever need to do so. (You can also use C-q " to insert this character.)

To disable the " expansion feature, eliminate that binding in the local map (see Key Bindings).

In TeX mode, ‘$’ has a special syntax code which attempts to understand the way TeX math mode delimiters match. When you insert a ‘$’ that is meant to exit math mode, the position of the matching ‘$’ that entered math mode is displayed for a second. This is the same feature that displays the open brace that matches a close brace that is inserted. However, there is no way to tell whether a ‘$’ enters math mode or leaves it; so when you insert a ‘$’ that enters math mode, the previous ‘$’ position is shown as if it were a match, even though they are actually unrelated.

TeX uses braces as delimiters that must match. Some users prefer to keep braces balanced at all times, rather than inserting them singly. Use C-c { (tex-insert-braces