@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994 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
been backed up on account of this buffer. If it is non-@code{nil}, then
the backup file has been written. Otherwise, the file should be backed
up when it is next saved (if backups are enabled). This is a
-permanent local; @code{kill-local-variables} does not alter it.
+permanent local; @code{kill-all-local-variables} does not alter it.
@end defvar
@defopt make-backup-files
- This variable determines whether or not to make backup files. If it
+This variable determines whether or not to make backup files. If it
is non-@code{nil}, then Emacs creates a backup of each file when it is
-saved for the first time.
+saved for the first time---provided that @code{backup-inhibited}
+is @code{nil} (see below).
- The following example shows how to change the @code{make-backup-files}
-variable only in the @file{RMAIL} buffer and not elsewhere. Setting it
-@code{nil} stops Emacs from making backups of the @file{RMAIL} file,
-which may save disk space. (You would put this code in your
-@file{.emacs} file.)
+The following example shows how to change the @code{make-backup-files}
+variable only in the Rmail buffers and not elsewhere. Setting it
+@code{nil} stops Emacs from making backups of these files, which may
+save disk space. (You would put this code in your init file.)
@smallexample
@group
-(add-hook 'rmail-mode-hook
+(add-hook 'rmail-mode-hook
(function (lambda ()
- (make-local-variable
+ (make-local-variable
'make-backup-files)
(setq make-backup-files nil))))
@end group
@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.
-The default value is this:
-
-@example
-(lambda (name)
- (or (< (length name) 5)
- (not (string-equal "/tmp/"
- (substring name 0 5)))))
-@end example
+@findex normal-backup-enable-predicate
+The default value is @code{normal-backup-enable-predicate}, which checks
+for files in @code{temporary-file-directory} and
+@code{small-temporary-file-directory}.
@end defvar
@defvar backup-inhibited
If this variable is non-@code{nil}, backups are inhibited. It records
the result of testing @code{backup-enable-predicate} on the visited file
name. It can also coherently be used by other mechanisms that inhibit
-backups based on which file is visited. This is a permanent local,
-so that changing the major mode does not lose its value.
+backups based on which file is visited. For example, VC sets this
+variable non-@code{nil} to prevent making backups for files managed
+with a version control system.
-Major modes should not set this variable---they should set
+This is a permanent local, so that changing the major mode does not lose
+its value. Major modes should not set this variable---they should set
@code{make-backup-files} instead.
@end defvar
+@defvar backup-directory-alist
+@tindex backup-directory-alist
+This variable's value is an alist of filename patterns and backup
+directory names. Each element looks like
+@smallexample
+(@var{regexp} . @var{directory})
+@end smallexample
+
+@noindent
+Backups of files with names matching @var{regexp} will be made in
+@var{directory}. @var{directory} may be relative or absolute. If it is
+absolute, so that all matching files are backed up into the same
+directory, the file names in this directory will be the full name of the
+file backed up with all directory separators changed to @samp{!} to
+prevent clashes. This will not work correctly if your filesystem
+truncates the resulting name.
+
+For the common case of all backups going into one directory, the alist
+should contain a single element pairing @samp{"."} with the appropriate
+directory name.
+
+If this variable is @code{nil}, or it fails to match a filename, the
+backup is made in the original file's directory.
+
+On MS-DOS filesystems without long names this variable is always
+ignored.
+@end defvar
+
+@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 @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
+@code{backup-file-name-p} and @code{file-name-sans-versions} too.
+@end defvar
+
+
@node Rename or Copy
@subsection Backup by Renaming or by Copying?
@cindex backup files, how to make them
- There are two ways that Emacs can make a backup file:
+ There are two ways that Emacs can make a backup file:
@itemize @bullet
@item
@item
Emacs can copy the original file into a backup file, and then overwrite
the original file with new contents. After this procedure, any other
-names (i.e., hard links) of the original file still refer to the current
-version of the file. The file's owner and group will be unchanged.
+names (i.e., hard links) of the original file continue to refer to the
+current (updated) version of the file. The file's owner and group will
+be unchanged.
@end itemize
The first method, renaming, is the default.
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
+
+@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
+this variable to that number.
+
+Thus, if you set @code{backup-by-copying-when-privileged-mismatch}
+to 0, backup by copying is done for the superuser only,
+when necessary to prevent a change in the owner of the file.
+
+The default is 200.
+@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.
(@pxref{Backup Names}) is responsible for determining which backup
versions to delete, but does not delete them itself.
-@defopt trim-versions-without-asking
-If this variable is non-@code{nil}, then saving a file deletes excess
-backup versions silently. Otherwise, it asks the user whether to delete
-them.
+@defopt delete-old-versions
+If this variable is @code{t}, then saving a file deletes excess
+backup versions silently. If it is @code{nil}, that means
+to ask for confirmation before deleting excess backups.
+Otherwise, they are not deleted at all.
@end defopt
@defopt dired-kept-versions
(defun backup-file-name-p (file)
"Return non-nil if FILE is a backup file \
name (numeric or not)..."
- (string-match "~$" file))
+ (string-match "~\\'" file))
@end group
@end smallexample
non-numbered backup file for file @var{filename}. On Unix, this is just
@var{filename} with a tilde appended.
-The standard definition of this function is as follows:
+The standard definition of this function, on most operating systems, is
+as follows:
@smallexample
@group
(defun make-backup-file-name (file)
- "Create the non-numeric backup file name for FILE.
-@dots{}"
+ "Create the non-numeric backup file name for FILE..."
(concat file "~"))
@end group
@end smallexample
@smallexample
@group
(defun make-backup-file-name (filename)
- (concat "." filename "~"))
+ (expand-file-name
+ (concat "." (file-name-nondirectory filename) "~")
+ (file-name-directory filename)))
@end group
@group
@result{} ".backups.texi~"
@end group
@end smallexample
+
+Some parts of Emacs, including some Dired commands, assume that backup
+file names end with @samp{~}. If you do not follow that convention, it
+will not cause serious problems, but these commands may give
+less-than-desirable results.
@end defun
@defun find-backup-file-name filename
@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
Some file comparison commands use this function so that they can
automatically compare a file with its most recent backup.
-@end defun
+@end defun
@node Auto-Saving
@section Auto-Saving
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.
@example
@group
buffer-auto-save-file-name
-=> "/xcssun/users/rms/lewis/#files.texi#"
+ @result{} "/xcssun/users/rms/lewis/#backups.texi#"
@end group
@end example
@end defvar
@deffn Command auto-save-mode arg
When used interactively without an argument, this command is a toggle
switch: it turns on auto-saving of the current buffer if it is off, and
-vice-versa. With an argument @var{arg}, the command turns auto-saving
+vice versa. With an argument @var{arg}, the command turns auto-saving
on if the value of @var{arg} is @code{t}, a nonempty list, or a positive
integer. Otherwise, it turns auto-saving off.
@end deffn
@defun auto-save-file-name-p filename
This function returns a non-@code{nil} value if @var{filename} is a
-string that could be the name of an auto-save file. It works based on
-knowledge of the naming convention for auto-save files: a name that
+string that could be the name of an auto-save file. It assumes
+the usual naming convention for auto-save files: a name that
begins and ends with hash marks (@samp{#}) is a possible auto-save file
name. The argument @var{filename} should not contain a directory part.
@example
@group
(make-auto-save-file-name)
- @result{} "/xcssun/users/rms/lewis/#files.texi#"
+ @result{} "/xcssun/users/rms/lewis/#backups.texi#"
@end group
@group
-(auto-save-file-name-p "#files.texi#")
+(auto-save-file-name-p "#backups.texi#")
@result{} 0
@end group
@group
-(auto-save-file-name-p "files.texi")
+(auto-save-file-name-p "backups.texi")
@result{} nil
@end group
@end example
@defun make-auto-save-file-name
This function returns the file name to use for auto-saving the current
-buffer. This is just the file name with hash marks (@samp{#}) appended
-and prepended to it. This function does not look at the variable
-@code{auto-save-visited-file-name} (described below); you should check
-that before calling this function.
+buffer. This is just the file name with hash marks (@samp{#}) prepended
+and appended to it. This function does not look at the variable
+@code{auto-save-visited-file-name} (described below); callers of this
+function should check that variable first.
@example
@group
(make-auto-save-file-name)
- @result{} "/xcssun/users/rms/lewis/#backup.texi#"
+ @result{} "/xcssun/users/rms/lewis/#backups.texi#"
@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
(defun make-auto-save-file-name ()
"Return file name to use for auto-saves \
-of current buffer.
-@dots{}"
+of current buffer.."
(if buffer-file-name
@end group
@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
auto-save files have distinct names that are created by
@code{make-auto-save-file-name}.
-When you change the value of this variable, the value does not take
-effect until the next time auto-save mode is reenabled in any given
-buffer. 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
+When you change the value of this variable, the new value does not take
+effect in an existing buffer until the next time auto-save mode is
+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 defopt
@defun recent-auto-save-p
This function returns @code{t} if the current buffer has been
@end defun
@defopt auto-save-interval
-The value of this variable is the number of characters that Emacs
-reads from the keyboard between auto-saves. Each time this many more
-characters are read, auto-saving is done for all buffers in which it is
-enabled.
+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. Setting this to zero disables autosaving based on the
+number of characters typed.
@end defopt
@defopt auto-save-timeout
The value of this variable is the number of seconds of idle time that
should cause auto-saving. Each time the user pauses for this long,
-Emacs auto-saves any buffers that need it. (Actually, the specified
-timeout is multiplied by a factor depending on the size of the current
-buffer.)
+Emacs does auto-saving for all buffers in which that is enabled. (If
+the current buffer is large, the specified timeout is multiplied by a
+factor that increases as the size increases; for a million-byte
+buffer, the factor is almost 4.)
+
+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
have auto-saving enabled by default. Otherwise, they do not.
@end defopt
-@deffn Command do-auto-save &optional no-message
+@deffn Command do-auto-save &optional no-message current-only
This function auto-saves all buffers that need to be auto-saved. It
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
The value of this buffer-local variable is the length of the current
-buffer as of the last time it was read in, saved, or auto-saved. This is
+buffer, when it was last read in, saved, or auto-saved. This is
used to detect a substantial decrease in size, and turn off auto-saving
in response.
-If it is -1, that means auto-saving is temporarily shut off in this
-buffer due to a substantial deletion. Explicitly saving the buffer
-stores a positive value in this variable, thus reenabling auto-save.
-Turning auto-save mode off or on also alters this variable.
+If it is @minus{}1, that means auto-saving is temporarily shut off in
+this buffer due to a substantial decrease in size. Explicitly saving
+the buffer stores a positive value in this variable, thus reenabling
+auto-saving. Turning auto-save mode off or on also updates this
+variable, so that the substantial decrease in size is forgotten.
@end defvar
@defvar auto-save-list-file-name
This variable (if non-@code{nil}) specifies a file for recording the
names of all the auto-save files. Each time Emacs does auto-saving, it
-writes into this file the names of all the auto-save files of all the
-buffers that have auto-save enabled. If Emacs crashes, you can look in
-this file to find all the auto-save files that might contain work that
-was otherwise lost. The @code{multi-replace} command uses these files.
-
-The default name for this file is in your home directory and starts with
-@samp{.saves-}. It also contains the Emacs process @sc{id} and the host
-name.
+writes two lines into this file for each buffer that has auto-saving
+enabled. The first line gives the name of the visited file (it's empty
+if the buffer has none), and the second gives the name of the auto-save
+file.
+
+When Emacs exits normally, it deletes this file; if Emacs crashes, you
+can look in the file to find all the auto-save files that might contain
+work that was otherwise lost. The @code{recover-session} command uses
+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 @acronym{ID} and the
+host name.
+@end defvar
+
+@defvar auto-save-list-file-prefix
+@tindex auto-save-list-file-prefix
+After Emacs reads your init file, it initializes
+@code{auto-save-list-file-name} (if you have not already set it
+non-@code{nil}) based on this prefix, adding the host name and process
+ID. If you set this to @code{nil} in your init file, then Emacs does
+not initialize @code{auto-save-list-file-name}.
@end defvar
@node Reverting
of the file with the @code{revert-buffer} command. @xref{Reverting, ,
Reverting a Buffer, emacs, The GNU Emacs Manual}.
-@deffn Command revert-buffer &optional check-auto-save 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.
-If the argument @var{check-auto-save} is non-@code{nil}, and the
-latest auto-save file is more recent than the visited file,
-@code{revert-buffer} asks the user whether to use that instead.
-Otherwise, it always uses the text of the visited file itself.
-Interactively, @var{check-auto-save} is set if there is a numeric prefix
-argument.
+By default, if the latest auto-save file is more recent than the visited
+file, and the argument @var{ignore-auto} is @code{nil},
+@code{revert-buffer} asks the user whether to use that auto-save
+instead. When you invoke this command interactively, @var{ignore-auto}
+is @code{t} if there is no numeric prefix argument; thus, the
+interactive default is not to check the auto-save file.
Normally, @code{revert-buffer} asks for confirmation before it changes
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
operation, reverting preserves all the markers. If they are not
-identical, reverting does change the buffer; then it preserves the
-markers in the unchanged text (if any) at the beginning and end of the
-buffer. Preserving any additional markers would be problematical.
+identical, reverting does change the buffer; in that case, it preserves
+the markers in the unchanged text (if any) at the beginning and end of
+the buffer. Preserving any additional markers would be problematical.
@end deffn
You can customize how @code{revert-buffer} does its work by setting
-these variables---typically, as buffer-local variables.
+the variables described in the rest of this section.
+
+@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 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
-fashion, give this variable a buffer-local value that is a function to
+fashion, can give this variable a buffer-local value that is a function to
regenerate the contents.
@end defvar
@defvar revert-buffer-insert-file-contents-function
-The value of this variable, if non-@code{nil}, is the function to use to
-insert contents when reverting this buffer. The function receives two
-arguments, first the file name to use; second, @code{t} if the user has
-asked to read the auto-save file.
+The value of this variable, if non-@code{nil}, specifies the function to use to
+insert the updated contents when reverting this buffer. The function
+receives two arguments: first the file name to use; second, @code{t} if
+the user has asked to read the auto-save file.
+
+The reason for a mode to set this variable instead of
+@code{revert-buffer-function} is to avoid duplicating or replacing the
+rest of what @code{revert-buffer} does: asking for confirmation,
+clearing the undo list, deciding the proper major mode, and running the
+hooks listed below.
@end defvar
@defvar before-revert-hook
-This normal hook is run by @code{revert-buffer} before actually
+This normal hook is run by @code{revert-buffer} before
inserting the modified contents---but only if
@code{revert-buffer-function} is @code{nil}.
-
-Font Lock mode uses this hook to record that the buffer contents are no
-longer fontified.
@end defvar
@defvar after-revert-hook
-This normal hook is run by @code{revert-buffer} after actually inserting
+This normal hook is run by @code{revert-buffer} after inserting
the modified contents---but only if @code{revert-buffer-function} is
@code{nil}.
-
-Font Lock mode uses this hook to recompute the fonts for the updated
-buffer contents.
@end defvar
-@deffn Command recover-file filename
-This function visits @var{filename}, but gets the contents from its
-last auto-save file. This is useful after the system has crashed, to
-resume editing the same file without losing all the work done in the
-previous session.
-
-An error is signaled if there is no auto-save file for @var{filename},
-or if @var{filename} is newer than its auto-save file. If
-@var{filename} does not exist, but its auto-save file does, then the
-auto-save file is read as usual. This last situation may occur if you
-visited a nonexistent file and never actually saved it.
-@end deffn
-
+@ignore
+ arch-tag: 295a6321-e5ab-46d5-aef5-0bb4f447a67f
+@end ignore