@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1999
-@c Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1999, 2002, 2003, 2004,
+@c 2005, 2006 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/backups
@node Backups and Auto-Saving, Buffers, Files, Top
This function makes a backup of the file visited by the current
buffer, if appropriate. It is called by @code{save-buffer} before
saving the buffer the first time.
+
+If a backup was made by renaming, the return value is a cons cell of
+the form (@var{modes} . @var{backupname}), where @var{modes} are the
+mode bits of the original file, as returned by @code{file-modes}
+(@pxref{File Attributes,, Other Information about Files}), and
+@var{backupname} is the name of the backup. In all other cases, that
+is, if a backup was made by copying or if no backup was made, this
+function returns @code{nil}.
@end defun
@defvar buffer-backed-up
@defvar backup-enable-predicate
This variable's value is a function to be called on certain occasions to
decide whether a file should have backup files. The function receives
-one argument, a file name to consider. If the function returns
+one argument, an absolute file name to consider. If the function returns
@code{nil}, backups are disabled for that file. Otherwise, the other
variables in this section say whether and how to make backups.
@defvar make-backup-file-name-function
@tindex make-backup-file-name-function
-This variable's value is a function to use for making backups instead of
-the default @code{make-backup-file-name}. A value of nil gives the
-default @code{make-backup-file-name} behaviour.
+This variable's value is a function to use for making backups instead
+of the default @code{make-backup-file-name}. A value of @code{nil}
+gives the default @code{make-backup-file-name} behavior.
+@xref{Backup Names,, Naming Backup Files}.
This could be buffer-local to do something special for specific
files. If you define it, you may need to change
if non-@code{nil}, also has this effect (as a sideline of its main
significance). @xref{Saving Buffers}.
-@defvar backup-by-copying
+@defopt backup-by-copying
If this variable is non-@code{nil}, Emacs always makes backup files by
copying.
-@end defvar
+@end defopt
- The following two variables, when non-@code{nil}, cause the second
+ The following three variables, when non-@code{nil}, cause the second
method to be used in certain special cases. They have no effect on the
treatment of files that don't fall into the special cases.
-@defvar backup-by-copying-when-linked
+@defopt backup-by-copying-when-linked
If this variable is non-@code{nil}, Emacs makes backups by copying for
files with multiple names (hard links).
This variable is significant only if @code{backup-by-copying} is
@code{nil}, since copying is always used when that variable is
non-@code{nil}.
-@end defvar
+@end defopt
-@defvar backup-by-copying-when-mismatch
+@defopt backup-by-copying-when-mismatch
If this variable is non-@code{nil}, Emacs makes backups by copying in cases
where renaming would change either the owner or the group of the file.
This variable is significant only if @code{backup-by-copying} is
@code{nil}, since copying is always used when that variable is
non-@code{nil}.
-@end defvar
+@end defopt
-@defvar backup-by-copying-when-privileged-mismatch
+@defopt backup-by-copying-when-privileged-mismatch
This variable, if non-@code{nil}, specifies the same behavior as
@code{backup-by-copying-when-mismatch}, but only for certain user-id
values: namely, those less than or equal to a certain number. You set
when necessary to prevent a change in the owner of the file.
The default is 200.
-@end defvar
+@end defopt
@node Numbered Backups
@subsection Making and Deleting Numbered Backup Files
@table @asis
@item @code{nil}
Make numbered backups if the visited file already has numbered backups;
-otherwise, do not.
+otherwise, do not. This is the default.
@item @code{never}
Do not make numbered backups.
@var{filename}. It may also propose certain existing backup files for
deletion. @code{find-backup-file-name} returns a list whose @sc{car} is
the name for the new backup file and whose @sc{cdr} is a list of backup
-files whose deletion is proposed.
+files whose deletion is proposed. The value can also be @code{nil},
+which means not to make a backup.
Two variables, @code{kept-old-versions} and @code{kept-new-versions},
determine which backup versions should be kept. This function keeps
called @dfn{auto-saving}. Auto-saving prevents you from losing more
than a limited amount of work if the system crashes. By default,
auto-saves happen every 300 keystrokes, or after around 30 seconds of
-idle time. @xref{Auto-Save, Auto-Save, Auto-Saving: Protection Against
+idle time. @xref{Auto Save, Auto Save, Auto-Saving: Protection Against
Disasters, emacs, The GNU Emacs Manual}, for information on auto-save
for users. Here we describe the functions used to implement auto-saving
and the variables that control them.
@end group
@end example
-The standard definition of this function is as follows:
+Here is a simplified version of the standard definition of this
+function:
@example
@group
change @code{auto-save-file-name-p} in a corresponding way.
@end defun
-@defvar auto-save-visited-file-name
+@defopt auto-save-visited-file-name
If this variable is non-@code{nil}, Emacs auto-saves buffers in
the files they are visiting. That is, the auto-save is done in the same
file that you are editing. Normally, this variable is @code{nil}, so
reenabled in it. If auto-save mode is already enabled, auto-saves
continue to go in the same file name until @code{auto-save-mode} is
called again.
-@end defvar
+@end defopt
@defun recent-auto-save-p
This function returns @code{t} if the current buffer has been
The value of this variable specifies how often to do auto-saving, in
terms of number of input events. Each time this many additional input
events are read, Emacs does auto-saving for all buffers in which that is
-enabled.
+enabled. Setting this to zero disables autosaving based on the
+number of characters typed.
@end defopt
@defopt auto-save-timeout
factor that increases as the size increases; for a million-byte
buffer, the factor is almost 4.)
-If the value is zero or nil, then auto-saving is not done as a result
-of idleness, only after a certain number of input events
-as specified by @code{auto-save-interval}.
+If the value is zero or @code{nil}, then auto-saving is not done as a
+result of idleness, only after a certain number of input events as
+specified by @code{auto-save-interval}.
@end defopt
@defvar auto-save-hook
saves all buffers for which auto-saving is enabled and that have been
changed since the previous auto-save.
-Normally, if any buffers are auto-saved, a message that says
-@samp{Auto-saving...} is displayed in the echo area while auto-saving is
-going on. However, if @var{no-message} is non-@code{nil}, the message
-is inhibited.
+If any buffers are auto-saved, @code{do-auto-save} normally displays a
+message saying @samp{Auto-saving...} in the echo area while
+auto-saving is going on. However, if @var{no-message} is
+non-@code{nil}, the message is inhibited.
If @var{current-only} is non-@code{nil}, only the current buffer
is auto-saved.
@end deffn
-@defun delete-auto-save-file-if-necessary
+@defun delete-auto-save-file-if-necessary &optional force
This function deletes the current buffer's auto-save file if
@code{delete-auto-save-files} is non-@code{nil}. It is called every
time a buffer is saved.
+
+Unless @var{force} is non-@code{nil}, this function only deletes the
+file if it was written by the current Emacs session since the last
+true save.
@end defun
-@defvar delete-auto-save-files
+@defopt delete-auto-save-files
This variable is used by the function
@code{delete-auto-save-file-if-necessary}. If it is non-@code{nil},
Emacs deletes auto-save files when a true save is done (in the visited
file). This saves disk space and unclutters your directory.
-@end defvar
+@end defopt
@defun rename-auto-save-file
This function adjusts the current buffer's auto-save file name if the
visited file name has changed. It also renames an existing auto-save
-file. If the visited file name has not changed, this function does
-nothing.
+file, if it was made in the current Emacs session. If the visited
+file name has not changed, this function does nothing.
@end defun
@defvar buffer-saved-size
this file to find them.
The default name for this file specifies your home directory and starts
-with @samp{.saves-}. It also contains the Emacs process @sc{id} and the
+with @samp{.saves-}. It also contains the Emacs process @acronym{ID} and the
host name.
@end defvar
of the file with the @code{revert-buffer} command. @xref{Reverting, ,
Reverting a Buffer, emacs, The GNU Emacs Manual}.
-@deffn Command revert-buffer &optional ignore-auto noconfirm
+@deffn Command revert-buffer &optional ignore-auto noconfirm preserve-modes
This command replaces the buffer text with the text of the visited
file on disk. This action undoes all changes since the file was visited
or saved.
the buffer; but if the argument @var{noconfirm} is non-@code{nil},
@code{revert-buffer} does not ask for confirmation.
+Normally, this command reinitializes the file's major and minor modes
+using @code{normal-mode}. But if @var{preserve-modes} is
+non-@code{nil}, the modes remain unchanged.
+
Reverting tries to preserve marker positions in the buffer by using the
replacement feature of @code{insert-file-contents}. If the buffer
contents and the file contents are identical before the revert
You can customize how @code{revert-buffer} does its work by setting
the variables described in the rest of this section.
-@defvar revert-without-query
+@defopt revert-without-query
This variable holds a list of files that should be reverted without
query. The value is a list of regular expressions. If the visited file
name matches one of these regular expressions, and the file has changed
on disk but the buffer is not modified, then @code{revert-buffer}
reverts the file without asking the user for confirmation.
-@end defvar
+@end defopt
Some major modes customize @code{revert-buffer} by making
buffer-local bindings for these variables:
@defvar revert-buffer-function
-The value of this variable is the function to use to revert this buffer.
-If non-@code{nil}, it is called as a function with no arguments to do
-the work of reverting. If the value is @code{nil}, reverting works the
-usual way.
+@anchor{Definition of revert-buffer-function}
+The value of this variable is the function to use to revert this
+buffer. If non-@code{nil}, it should be a function with two optional
+arguments to do the work of reverting. The two optional arguments,
+@var{ignore-auto} and @var{noconfirm}, are the arguments that
+@code{revert-buffer} received. If the value is @code{nil}, reverting
+works the usual way.
Modes such as Dired mode, in which the text being edited does not
consist of a file's contents but can be regenerated in some other
the modified contents---but only if @code{revert-buffer-function} is
@code{nil}.
@end defvar
+
+@ignore
+ arch-tag: 295a6321-e5ab-46d5-aef5-0bb4f447a67f
+@end ignore