27.2.5 Local Variables in Files

A file can contain a local variables list, which specifies the values to use for certain Emacs variables when that file is edited. Visiting the file checks for a local variables list and makes each variable in the list local to the buffer in which the file is visited, with the value specified in the file.

A local variables list goes near the end of the file, in the last page. (It is often best to put it on a page by itself.) The local variables list starts with a line containing the string ‘Local Variables:’, and ends with a line containing the string ‘End:’. In between come the variable names and values, one set per line, as ‘variable: value’. The values are not evaluated; they are used literally.

The line which starts the local variables list does not have to say just ‘Local Variables:’. If there is other text before ‘Local Variables:’, that text is called the prefix, and if there is other text after, that is called the suffix. If a prefix or suffix are present, each entry in the local variables list should have the prefix before it and the suffix after it. This includes the ‘End:’ line. The prefix and suffix are included to disguise the local variables list as a comment so the compiler or text formatter will ignore it. If you do not need to disguise the local variables list as a comment in this way, there is no need to include a prefix or a suffix.

Two “variable” names are special in a local variables list: a value for the variable mode sets the major mode, and a value for the variable eval is simply evaluated as an expression and the value is ignored. These are not real variables; setting them in any other context does not have the same effect. If mode is used in a local variables list, it should be the first entry in the list.

Here is an example of a local variables list:

;;; Local Variables: ***
;;; mode:lisp ***
;;; comment-column:0 ***
;;; comment-start: ";;; "  ***
;;; comment-end:"***" ***
;;; End: ***

Note that the prefix is ‘;;; ’ and the suffix is ‘ ***’. Note also that comments in the file begin with and end with the same strings. Presumably the file contains code in a language which is enough like Lisp for Lisp mode to be useful but in which comments start and end differently. The prefix and suffix are used in the local variables list to make the list look like several lines of comments when the compiler or interpreter for that language reads the file.

The start of the local variables list must be no more than 3000 characters from the end of the file, and must be in the last page if the file is divided into pages. Otherwise, Emacs will not notice it is there. The purpose is twofold: a stray ‘Local Variables:’ not in the last page does not confuse Emacs, and Emacs never needs to search a long file that contains no page markers and has no local variables list.

You may be tempted to turn on Auto Fill mode with a local variable list. That is inappropriate. Whether you use Auto Fill mode or not is a matter of personal taste, not a matter of the contents of particular files. If you want to use Auto Fill, set up major mode hooks with your init file to turn it on (when appropriate) for you alone (see Init File). Don’t try to use a local variable list that would impose your taste on everyone working with the file.

SXEmacs allows you to specify local variables in the first line of a file, in addition to specifying them in the Local Variables section at the end of a file.

If the first line of a file contains two occurrences of `-*-', SXEmacs uses the information between them to determine what the major mode and variable settings should be. For example, these are all legal:

        ;;; -*- mode: emacs-lisp -*-
        ;;; -*- mode: postscript; version-control: never -*-
        ;;; -*- tags-file-name: "/foo/bar/TAGS" -*-

For historical reasons, the syntax `-*- modename -*-' is allowed as well; for example, you can use:

        ;;; -*- emacs-lisp -*-

The variable enable-local-variables controls the use of local variables lists in files you visit. The value can be t, nil, or something else. A value of t means local variables lists are obeyed; nil means they are ignored; anything else means query.

The command M-x normal-mode always obeys local variables lists and ignores this variable.