In short local or file variables can be used to set certain aspects of Emacs local to a file. This might be useful for setting the indention level of a C program as well as setting the MajorMode to use for this file. This mechanism is regularly used in multi-document LaTeX projects where AUCTeX stores the information which file is the master document so it can compile the right one when the user invokes the LaTeX command (usually via C-c C-c).
Those variables are located at the end of your file and look like this:
# Local Variables: # mode: ksh # End:
That is there is a special keyword “Local Variables:” which starts the section and is surrounded by a prefix (”# “ in the above example) and a postfix (empty here). The keyword “End:” (with the same post- and prefixes) finishes that section. Obviously the prefix and postfixes are important to comment those lines according to the file-type.
For detailed documentation, see node “File Variables” in the Emacs Info file.
As of Emacs 24: Using “mode: MINOR-MODE” to enable a minor mode is deprecated. Instead, use “eval: (minor-mode 1)”.
If you create a file containing the following lines you won’t be able to open it:
-*- normal -*- ;; Local variables: ;; enable-local-eval: t ;; hack-local-variables-hook: save-buffers-kill-emacs ;; end:
AFAI remember that stems from an effect that in normal-mode the local variables are processed in a special way. Of course one could do severe damage with such a text file and I have a bad feeling towards this. If I am missing something here I’d be happy to learn what. – StefanKamphausen
Aborting the file open with C-g and then opening it with C-x C-f allows you to open the file (for some reason). Also, you can always open it with find-file-literally. – fledermaus
;; Turn off file variables ;; See: http://www.gnu.org/software/emacs/manual/html_node/emacs/Safe-File-Variables.html#Safe-File-Variables (setq enable-local-variables nil enable-local-eval nil)
This is actually using DirectoryVariables, but seems more useful to document here.
Directory Local Variables can be configured purely in elisp by configuring “directory classes” and specifying which classes apply to which directories.
There is no such mechanism for File Local Variables, but it turns out that we can successfully* apply directory classes to individual files. The only issue is that
file-name-as-directory on its argument, which prevents it from being matched, due to the trailing slash.
The following, therefore, is a way to configure directory local variables for a single file, without modifying the file itself, or affecting other files under the same parent directory.
* tested with Emacs 23.3.1