Sometimes, an Emacs Lisp program needs to specify a standard file
name for a particular use—typically, to hold configuration data
specified by the current user. Usually, such files should be located
in the directory specified by
user-emacs-directory, which is
~/.emacs.d by default (see Init File). For example, abbrev
definitions are stored by default in ~/.emacs.d/abbrev_defs.
The easiest way to specify such a file name is to use the function
This function returns an absolute file name for an Emacs-specific configuration or data file. The argument base-name should be a relative file name. The return value is the absolute name of a file in the directory specified by
user-emacs-directory; if that directory does not exist, this function creates it.
If the optional argument old-name is non-
nil, it specifies a file in the user's home directory, ~/old-name. If such a file exists, the return value is the absolute name of that file, instead of the file specified by base-name. This argument is intended to be used by Emacs packages to provide backward compatibility. For instance, prior to the introduction of
user-emacs-directory, the abbrev file was located in ~/.abbrev_defs. Here is the definition of
abbrev-file-name:(defcustom abbrev-file-name (locate-user-emacs-file "abbrev_defs" ".abbrev_defs") "Default name of file from which to read abbrevs." ... :type 'file)
A lower-level function for standardizing file names, which
locate-user-emacs-file uses as a subroutine, is
This function returns a file name based on filename, which fits the conventions of the current operating system.
On GNU and Unix systems, this simply returns filename. On other operating systems, it may enforce system-specific file name conventions; for example, on MS-DOS this function performs a variety of changes to enforce MS-DOS file name limitations, including converting any leading ‘.’ to ‘_’ and truncating to three characters after the ‘.’.
The recommended way to use this function is to specify a name which fits the conventions of GNU and Unix systems, and pass it to