GNU Emacs uses newline characters to separate text lines. This is the convention used on GNU, Unix, and other Posix-compliant systems.
By contrast, MS-DOS and MS-Windows normally use carriage-return linefeed, a two-character sequence, to separate text lines. (Linefeed is the same character as newline.) Therefore, convenient editing of typical files with Emacs requires conversion of these end-of-line (EOL) sequences. And that is what Emacs normally does: it converts carriage-return linefeed into newline when reading files, and converts newline into carriage-return linefeed when writing files. The same mechanism that handles conversion of international character codes does this conversion also (see Coding Systems).
One consequence of this special format-conversion of most files is that character positions as reported by Emacs (see Position Info) do not agree with the file size information known to the operating system.
In addition, if Emacs recognizes from a file's contents that it uses newline rather than carriage-return linefeed as its line separator, it does not perform EOL conversion when reading or writing that file. Thus, you can read and edit files from GNU and Unix systems on MS-DOS with no special effort, and they will retain their Unix-style end-of-line convention after you edit them.
The mode line indicates whether end-of-line translation was used for the current buffer. If MS-DOS end-of-line translation is in use for the buffer, the MS-Windows build of Emacs displays a backslash ‘\’ after the coding system mnemonic near the beginning of the mode line (see Mode Line). If no EOL translation was performed, the string ‘(Unix)’ is displayed instead of the backslash, to alert you that the file's EOL format is not the usual carriage-return linefeed.
To visit a file and specify whether it uses DOS-style or Unix-style
end-of-line, specify a coding system (see Text Coding). For
example, C-x <RET> c unix <RET> C-x C-f foobar.txt
visits the file foobar.txt without converting the EOLs; if some
line ends with a carriage-return linefeed pair, Emacs will display
‘^M’ at the end of that line. Similarly, you can direct Emacs to
save a buffer in a specified EOL format with the C-x <RET> f
command. For example, to save a buffer with Unix EOL format, type
C-x <RET> f unix <RET> C-x C-s. If you visit a file
with DOS EOL conversion, then save it with Unix EOL format, that
effectively converts the file to Unix EOL style, like the
When you use NFS, Samba, or some other similar method to access file
systems that reside on computers using GNU or Unix systems, Emacs
should not perform end-of-line translation on any files in these file
systems—not even when you create a new file. To request this,
designate these file systems as untranslated file systems by
calling the function
add-untranslated-filesystem. It takes one
argument: the file system name, including a drive letter and
optionally a directory. For example,
designates drive Z as an untranslated file system, and
designates directory \foo on drive Z as an untranslated file system.
Most often you would use
add-untranslated-filesystem in your
.emacs file, or in site-start.el so that all the users at
your site get the benefit of it.
To countermand the effect of
remove-untranslated-filesystem. This function takes
one argument, which should be a string just like the one that was used
Designating a file system as untranslated does not affect character set conversion, only end-of-line conversion. Essentially, it directs Emacs to create new files with the Unix-style convention of using newline at the end of a line. See Coding Systems.