32.8 Libraries of Lisp Code for Emacs
Lisp code for Emacs editing commands is stored in files whose names
conventionally end in .el. This ending tells Emacs to edit them in
Emacs-Lisp mode (see Executing Lisp).
To execute a file of Emacs Lisp code, use M-x load-file. This
command reads a file name using the minibuffer and then executes the
contents of that file as Lisp code. It is not necessary to visit the
file first; in any case, this command reads the file as found on disk,
not text in an Emacs buffer.
Once a file of Lisp code is installed in the Emacs Lisp library
directories, users can load it using M-x load-library. Programs can
load it by calling
load-library, or with
load, a more primitive
function that is similar but accepts some additional arguments.
M-x load-library differs from M-x load-file in that it
searches a sequence of directories and tries three file names in each
directory. Suppose your argument is lib; the three names are
lib.elc, lib.el, and lastly just
lib. If lib.elc exists, it is by convention
the result of compiling lib.el; it is better to load the
compiled file, since it will load and run faster.
load-library finds that lib.el is newer than
lib.elc file, it issues a warning, because it's likely that
somebody made changes to the .el file and forgot to recompile
Because the argument to
load-library is usually not in itself
a valid file name, file name completion is not available. Indeed, when
using this command, you usually do not know exactly what file name
will be used.
The sequence of directories searched by M-x load-library is
specified by the variable
load-path, a list of strings that are
directory names. The default value of the list contains the directory where
the Lisp code for Emacs itself is stored. If you have libraries of
your own, put them in a single directory and add that directory
nil in this list stands for the current default
directory, but it is probably not a good idea to put
nil in the
list. If you find yourself wishing that
nil were in the list,
most likely what you really want to do is use M-x load-file
Often you do not have to give any command to load a library, because
the commands defined in the library are set up to autoload that
library. Trying to run any of those commands calls
load to load
the library; this replaces the autoload definitions with the real ones
from the library.
Emacs Lisp code can be compiled into byte-code which loads faster,
takes up less space when loaded, and executes faster. See Byte Compilation.
By convention, the compiled code for a library goes in a separate file
whose name consists of the library source file with ‘c’ appended.
Thus, the compiled code for foo.el goes in foo.elc.
load-library searches for ‘.elc’ files first.
By default, Emacs refuses to load compiled Lisp files which were
compiled with XEmacs, a modified versions of Emacs—they can cause
Emacs to crash. Set the variable
t if you want to try loading them.