When you edit a file in Emacs, you are actually working on a buffer that is visiting that file—that is, the contents of the file are copied into the buffer and the copy is what you edit. Changes to the buffer do not change the file until you save the buffer, which means copying the contents of the buffer into the file.
This function saves the contents of the current buffer in its visited file if the buffer has been modified since it was last visited or saved. Otherwise it does nothing.
save-buffer is responsible for making backup files. Normally,
save-buffer makes a backup
file only if this is the first save since visiting the file. Other
values for backup-option request the making of backup files in
save-bufferfunction marks this version of the file to be backed up when the buffer is next saved.
save-bufferfunction unconditionally backs up the previous version of the file before saving it.
This command saves some modified file-visiting buffers. Normally it
asks the user about each buffer. But if save-silently-p is
nil, it saves all the file-visiting buffers without querying
The optional pred argument controls which buffers to ask about
(or to save silently if save-silently-p is non-
If it is
nil, that means to ask only about file-visiting buffers.
If it is
t, that means also offer to save certain other non-file
buffers—those that have a non-
nil buffer-local value of
buffer-offer-save (see Killing Buffers). A user who says
‘yes’ to saving a non-file buffer is asked to specify the file
name to use. The
save-buffers-kill-emacs function passes the
t for pred.
If pred is neither
nil, then it should be
a function of no arguments. It will be called in each buffer to decide
whether to offer to save that buffer. If it returns a non-
value in a certain buffer, that means do offer to save that buffer.
This function writes the current buffer into file filename, makes
the buffer visit that file, and marks it not modified. Then it renames
the buffer based on filename, appending a string like ‘<2>’
if necessary to make a unique buffer name. It does most of this work by
set-visited-file-name (see Buffer File Name) and
If confirm is non-
nil, that means to ask for confirmation
before overwriting an existing file. Interactively, confirmation is
required, unless the user supplies a prefix argument.
If filename is an existing directory, or a symbolic link to one,
write-file uses the name of the visited file, in directory
filename. If the buffer is not visiting a file, it uses the
buffer name instead.
Saving a buffer runs several hooks. It also performs format conversion (see Format Conversion).
The value of this variable is a list of functions to be called before
writing out a buffer to its visited file. If one of them returns
nil, the file is considered already written and the rest of
the functions are not called, nor is the usual code for writing the file
If a function in
write-file-functions returns non-
is responsible for making a backup file (if that is appropriate).
To do so, execute the following code:
(or buffer-backed-up (backup-buffer))
You might wish to save the file modes value returned by
backup-buffer and use that (if non-
nil) to set the mode
bits of the file that you write. This is what
normally does. See Making Backup Files.
The hook functions in
write-file-functions are also responsible
for encoding the data (if desired): they must choose a suitable coding
system and end-of-line conversion (see Lisp and Coding Systems),
perform the encoding (see Explicit Encoding), and set
last-coding-system-used to the coding system that was used
(see Encoding and I/O).
If you set this hook locally in a buffer, it is assumed to be
associated with the file or the way the contents of the buffer were
obtained. Thus the variable is marked as a permanent local, so that
changing the major mode does not alter a buffer-local value. On the
other hand, calling
set-visited-file-name will reset it.
If this is not what you want, you might like to use
Even though this is not a normal hook, you can use
remove-hook to manipulate the list. See Hooks.
This works just like
write-file-functions, but it is intended
for hooks that pertain to the buffer’s contents, not to the particular
visited file or its location. Such hooks are usually set up by major
modes, as buffer-local bindings for this variable. This variable
automatically becomes buffer-local whenever it is set; switching to a
new major mode always resets this variable, but calling
set-visited-file-name does not.
If any of the functions in this hook returns non-
nil, the file
is considered already written and the rest are not called and neither
are the functions in
This normal hook runs before a buffer is saved in its visited file, regardless of whether that is done normally or by one of the hooks described above. For instance, the copyright.el program uses this hook to make sure the file you are saving has the current year in its copyright notice.
This normal hook runs after a buffer has been saved in its visited file. One use of this hook is in Fast Lock mode; it uses this hook to save the highlighting information in a cache file.
If this variable is non-
against I/O errors while saving by writing the new file to a temporary
name instead of the name it is supposed to have, and then renaming it to
the intended name after it is clear there are no errors. This procedure
prevents problems such as a lack of disk space from resulting in an
As a side effect, backups are necessarily made by copying. See Rename or Copy. Yet, at the same time, saving a precious file always breaks all hard links between the file you save and other file names.
Some modes give this variable a non-
nil buffer-local value
in particular buffers.
This variable determines whether files may be written out that do
not end with a newline. If the value of the variable is
save-buffer silently adds a newline at the end
of the buffer whenever it does not already end in one. If the value
visit, Emacs adds a missing newline just after it visits the
file. If the value is
visit-save, Emacs adds a missing newline
both on visiting and on saving. For any other non-
save-buffer asks the user whether to add a newline each time
the case arises.
If the value of the variable is
doesn’t add newlines at all.
nil is the default value, but a few
major modes set it to
t in particular buffers.
See also the function
set-visited-file-name (see Buffer File Name).