22.3.1 Loading Libraries
`M-x load-file FILE'
Load the file FILE of Lisp code.
`M-x load-library LIBRARY'
Load the library named LIBRARY.
`M-x locate-library LIBRARY &optional NOSUFFIX'
Show the full path name of Emacs library LIBRARY.
To execute a file of Emacs Lisp, use `M-x load-file'. This command
reads the file name you provide in the minibuffer, then executes the
contents of that file as Lisp code. It is not necessary to visit the
file first; in fact, this command reads the file as found on disk, not
the 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.
The three names are: first, the specified name with `.elc' appended;
second, the name with `.el' appended; third, the specified name alone.
A `.elc' file would be the result of compiling the Lisp file into byte
code; if possible, it is loaded in preference to the Lisp file itself
because the compiled file loads and runs faster.
Because the argument to `load-library' is usually not in itself a
valid file name, file name completion is not available. In fact, when
using this command, you usually do not know exactly what file name will
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 elements of this list may not begin with "`~'",
so you must call `expand-file-name' on them before adding them to the
list. 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 to
`load-path'. `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 start wishing that `nil' were in the list, you should probably
use `M-x load-file' for this case.
The variable is initialized by the EMACSLOADPATH environment
variable. If no value is specified, the variable takes the default value
specified in the file `paths.h' when Emacs was built. If a path isn't
specified in `paths.h', a default value is obtained from the file
system, near the directory in which the Emacs executable resides.
Like `M-x load-library', `M-x locate-library' searches the
directories in `load-path' to find the file that `M-x load-library'
would load. If the optional second argument NOSUFFIX is non-`nil', the
suffixes `.elc' or `.el' are not added to the specified name LIBRARY
(like calling `load' instead of `load-library').
You often 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. Running any of those commands causes `load' to be called to
load the library; this replaces the autoload definitions with the real
ones from the library.
If autoloading a file does not finish, either because of an error or
because of a `C-g' quit, all function definitions made by the file are
undone automatically. So are any calls to `provide'. As a
consequence, the entire file is loaded a second time if you use one of
the autoloadable commands again. This prevents problems when the
command is no longer autoloading but is working incorrectly because the
file was only partially loaded. Function definitions are undone only
for autoloading; explicit calls to `load' do not undo anything if
loading is not completed.
The variable `after-load-alist' takes an alist of expressions to be
evaluated when particular files are loaded. Each element has the form
`(FILENAME forms...)'. When `load' is run and the filename argument is
FILENAME, the forms in the corresponding element are executed at the
end of loading.
FILENAME must match exactly. Normally FILENAME is the name of a
library, with no directory specified, since that is how load is
normally called. An error in `forms' does not undo the load, but it
does prevent execution of the rest of the `forms'.
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