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A file can specify local variable values for use when you edit the file with Emacs. Visiting the file checks for local variable specifications; it automatically makes these variables local to the buffer, and sets them to the values specified in the file.
There are two ways to specify local variable values: in the first line, or with a local variables list. Here's how to specify them in the first line:
-*- mode: modename; var: value; ... -*-
You can specify any number of variables/value pairs in this way, each
pair with a colon and semicolon as shown above. mode:
modename; specifies the major mode; this should come first in the
line. The values are not evaluated; they are used literally.
Here is an example that specifies Lisp mode and sets two variables with
numeric values:
;; -*-mode: Lisp; fill-column: 75; comment-column: 50; -*-
You can also specify the coding system for a file in this way: just
specify a value for the "variable" named coding. The "value"
must be a coding system name that Emacs recognizes. See section Coding Systems.
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. If a file has both a local variables list and a `-*-' line, Emacs processes everything in the `-*-' line first, and everything in the local variables list afterward.
Here is an example of a local variables list:
;;; Local Variables: *** ;;; mode:lisp *** ;;; comment-column:0 *** ;;; comment-start: ";;; " *** ;;; comment-end:"***" *** ;;; End: ***
As you see, each line starts with the prefix `;;; ' and each line ends with the suffix ` ***'. Emacs recognizes these as the prefix and suffix based on the first line of the list, by finding them surrounding the magic string `Local Variables:'; then it automatically discards them from the other lines of the list.
The usual reason for using a prefix and/or suffix is to embed the
local variables list in a comment, so it won't confuse other programs
that the file is intended as input for. The example above is for a
language where comment lines start with `;;; ' and end with
`***'; the local values for comment-start and
comment-end customize the rest of Emacs for this unusual syntax.
Don't use a prefix (or a suffix) if you don't need one.
Two "variable names" have special meanings in a local variables
list: a value for the variable mode really sets the major mode,
and a value for the variable eval is simply evaluated as an
expression and the value is ignored. mode and eval are
not real variables; setting variables named mode and eval
in any other context has no special meaning. If mode is used to
set a major mode, it should be the first "variable" in the list.
You can use the mode "variable" to set minor modes as well as
major modes; in fact, you can use it more than once, first to set the
major mode and then to set minor modes which are specific to particular
buffers. But most minor modes should not be specified in the file in
any fashion, because they represent user preferences.
For example, you may be tempted to try to turn on Auto Fill mode with a local variable list. That is a mistake. The choice of Auto Fill mode or not is a matter of individual taste, not a matter of the contents of particular files. If you want to use Auto Fill, set up major mode hooks with your `.emacs' file to turn it on (when appropriate) for you alone (see section The Init File, `~/.emacs'). Don't use a local variable list to impose your taste on everyone.
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 of this rule is so that a stray `Local Variables:' not in the last page does not confuse Emacs, and so that visiting a long file that is all one page and has no local variables list need not take the time to search the whole file.
Use the command normal-mode to reset the local variables and
major mode of a buffer according to the file name and contents,
including the local variables list if any. See section How Major Modes are Chosen.
The variable enable-local-variables controls whether to process
local variables in files, and thus gives you a chance to override them.
Its default value is t, which means do process local variables in
files. If you set the value to nil, Emacs simply ignores local
variables in files. Any other value says to query you about each file
that has local variables, showing you the local variable specifications
so you can judge.
The eval "variable," and certain actual variables, create a
special risk; when you visit someone else's file, local variable
specifications for these could affect your Emacs in arbitrary ways.
Therefore, the option enable-local-eval controls whether Emacs
processes eval variables, as well variables with names that end
in `-hook', `-hooks', `-function' or `-functions',
and certain other variables. The three possibilities for the option's
value are t, nil, and anything else, just as for
enable-local-variables. The default is maybe, which is
neither t nor nil, so normally Emacs does ask for
confirmation about file settings for these variables.
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