(emacs.info) File Variables
Local Variables in Files
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
-*- 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. 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
( Init File). 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. Choosing Modes.
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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