0
+ − 1 @c -*-texinfo-*-
+ − 2 @c This is part of the XEmacs Lisp Reference Manual.
444
+ − 3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
0
+ − 4 @c See the file lispref.texi for copying conditions.
+ − 5 @setfilename ../../info/backups.info
+ − 6 @node Backups and Auto-Saving, Buffers, Files, Top
+ − 7 @chapter Backups and Auto-Saving
+ − 8
+ − 9 Backup files and auto-save files are two methods by which XEmacs tries
+ − 10 to protect the user from the consequences of crashes or of the user's
+ − 11 own errors. Auto-saving preserves the text from earlier in the current
+ − 12 editing session; backup files preserve file contents prior to the
+ − 13 current session.
+ − 14
+ − 15 @menu
+ − 16 * Backup Files:: How backup files are made; how their names are chosen.
+ − 17 * Auto-Saving:: How auto-save files are made; how their names are chosen.
+ − 18 * Reverting:: @code{revert-buffer}, and how to customize what it does.
+ − 19 @end menu
+ − 20
+ − 21 @node Backup Files
+ − 22 @section Backup Files
+ − 23 @cindex backup file
+ − 24
+ − 25 A @dfn{backup file} is a copy of the old contents of a file you are
+ − 26 editing. XEmacs makes a backup file the first time you save a buffer
+ − 27 into its visited file. Normally, this means that the backup file
+ − 28 contains the contents of the file as it was before the current editing
+ − 29 session. The contents of the backup file normally remain unchanged once
+ − 30 it exists.
+ − 31
+ − 32 Backups are usually made by renaming the visited file to a new name.
+ − 33 Optionally, you can specify that backup files should be made by copying
+ − 34 the visited file. This choice makes a difference for files with
+ − 35 multiple names; it also can affect whether the edited file remains owned
+ − 36 by the original owner or becomes owned by the user editing it.
+ − 37
+ − 38 By default, XEmacs makes a single backup file for each file edited.
+ − 39 You can alternatively request numbered backups; then each new backup
+ − 40 file gets a new name. You can delete old numbered backups when you
+ − 41 don't want them any more, or XEmacs can delete them automatically.
+ − 42
+ − 43 @menu
+ − 44 * Making Backups:: How XEmacs makes backup files, and when.
+ − 45 * Rename or Copy:: Two alternatives: renaming the old file or copying it.
+ − 46 * Numbered Backups:: Keeping multiple backups for each source file.
+ − 47 * Backup Names:: How backup file names are computed; customization.
+ − 48 @end menu
+ − 49
+ − 50 @node Making Backups
+ − 51 @subsection Making Backup Files
+ − 52
+ − 53 @defun backup-buffer
+ − 54 This function makes a backup of the file visited by the current
+ − 55 buffer, if appropriate. It is called by @code{save-buffer} before
+ − 56 saving the buffer the first time.
+ − 57 @end defun
+ − 58
+ − 59 @defvar buffer-backed-up
+ − 60 This buffer-local variable indicates whether this buffer's file has
+ − 61 been backed up on account of this buffer. If it is non-@code{nil}, then
+ − 62 the backup file has been written. Otherwise, the file should be backed
+ − 63 up when it is next saved (if backups are enabled). This is a
+ − 64 permanent local; @code{kill-local-variables} does not alter it.
+ − 65 @end defvar
+ − 66
+ − 67 @defopt make-backup-files
+ − 68 This variable determines whether or not to make backup files. If it
+ − 69 is non-@code{nil}, then XEmacs creates a backup of each file when it is
+ − 70 saved for the first time---provided that @code{backup-inhibited}
+ − 71 is @code{nil} (see below).
+ − 72
+ − 73 The following example shows how to change the @code{make-backup-files}
+ − 74 variable only in the @file{RMAIL} buffer and not elsewhere. Setting it
+ − 75 @code{nil} stops XEmacs from making backups of the @file{RMAIL} file,
+ − 76 which may save disk space. (You would put this code in your
+ − 77 @file{.emacs} file.)
+ − 78
+ − 79 @smallexample
+ − 80 @group
444
+ − 81 (add-hook 'rmail-mode-hook
0
+ − 82 (function (lambda ()
444
+ − 83 (make-local-variable
0
+ − 84 'make-backup-files)
+ − 85 (setq make-backup-files nil))))
+ − 86 @end group
+ − 87 @end smallexample
+ − 88 @end defopt
+ − 89
+ − 90 @defvar backup-enable-predicate
+ − 91 This variable's value is a function to be called on certain occasions to
+ − 92 decide whether a file should have backup files. The function receives
+ − 93 one argument, a file name to consider. If the function returns
+ − 94 @code{nil}, backups are disabled for that file. Otherwise, the other
+ − 95 variables in this section say whether and how to make backups.
+ − 96
+ − 97 The default value is this:
+ − 98
+ − 99 @example
+ − 100 (lambda (name)
+ − 101 (or (< (length name) 5)
+ − 102 (not (string-equal "/tmp/"
+ − 103 (substring name 0 5)))))
+ − 104 @end example
+ − 105 @end defvar
+ − 106
+ − 107 @defvar backup-inhibited
+ − 108 If this variable is non-@code{nil}, backups are inhibited. It records
+ − 109 the result of testing @code{backup-enable-predicate} on the visited file
+ − 110 name. It can also coherently be used by other mechanisms that inhibit
+ − 111 backups based on which file is visited. For example, VC sets this
+ − 112 variable non-@code{nil} to prevent making backups for files managed
+ − 113 with a version control system.
+ − 114
+ − 115 This is a permanent local, so that changing the major mode does not lose
+ − 116 its value. Major modes should not set this variable---they should set
+ − 117 @code{make-backup-files} instead.
+ − 118 @end defvar
+ − 119
+ − 120 @node Rename or Copy
+ − 121 @subsection Backup by Renaming or by Copying?
+ − 122 @cindex backup files, how to make them
+ − 123
444
+ − 124 There are two ways that XEmacs can make a backup file:
0
+ − 125
+ − 126 @itemize @bullet
+ − 127 @item
+ − 128 XEmacs can rename the original file so that it becomes a backup file, and
+ − 129 then write the buffer being saved into a new file. After this
+ − 130 procedure, any other names (i.e., hard links) of the original file now
+ − 131 refer to the backup file. The new file is owned by the user doing the
+ − 132 editing, and its group is the default for new files written by the user
+ − 133 in that directory.
+ − 134
+ − 135 @item
+ − 136 XEmacs can copy the original file into a backup file, and then overwrite
+ − 137 the original file with new contents. After this procedure, any other
+ − 138 names (i.e., hard links) of the original file still refer to the current
+ − 139 version of the file. The file's owner and group will be unchanged.
+ − 140 @end itemize
+ − 141
+ − 142 The first method, renaming, is the default.
+ − 143
+ − 144 The variable @code{backup-by-copying}, if non-@code{nil}, says to use
+ − 145 the second method, which is to copy the original file and overwrite it
+ − 146 with the new buffer contents. The variable @code{file-precious-flag},
+ − 147 if non-@code{nil}, also has this effect (as a sideline of its main
+ − 148 significance). @xref{Saving Buffers}.
+ − 149
+ − 150 @defvar backup-by-copying
+ − 151 If this variable is non-@code{nil}, XEmacs always makes backup files by
+ − 152 copying.
+ − 153 @end defvar
+ − 154
+ − 155 The following two variables, when non-@code{nil}, cause the second
+ − 156 method to be used in certain special cases. They have no effect on the
+ − 157 treatment of files that don't fall into the special cases.
+ − 158
+ − 159 @defvar backup-by-copying-when-linked
+ − 160 If this variable is non-@code{nil}, XEmacs makes backups by copying for
+ − 161 files with multiple names (hard links).
+ − 162
+ − 163 This variable is significant only if @code{backup-by-copying} is
+ − 164 @code{nil}, since copying is always used when that variable is
+ − 165 non-@code{nil}.
+ − 166 @end defvar
+ − 167
+ − 168 @defvar backup-by-copying-when-mismatch
+ − 169 If this variable is non-@code{nil}, XEmacs makes backups by copying in cases
+ − 170 where renaming would change either the owner or the group of the file.
+ − 171
+ − 172 The value has no effect when renaming would not alter the owner or
+ − 173 group of the file; that is, for files which are owned by the user and
+ − 174 whose group matches the default for a new file created there by the
+ − 175 user.
+ − 176
+ − 177 This variable is significant only if @code{backup-by-copying} is
+ − 178 @code{nil}, since copying is always used when that variable is
+ − 179 non-@code{nil}.
+ − 180 @end defvar
+ − 181
+ − 182 @node Numbered Backups
+ − 183 @subsection Making and Deleting Numbered Backup Files
+ − 184
+ − 185 If a file's name is @file{foo}, the names of its numbered backup
+ − 186 versions are @file{foo.~@var{v}~}, for various integers @var{v}, like
+ − 187 this: @file{foo.~1~}, @file{foo.~2~}, @file{foo.~3~}, @dots{},
+ − 188 @file{foo.~259~}, and so on.
+ − 189
+ − 190 @defopt version-control
+ − 191 This variable controls whether to make a single non-numbered backup
+ − 192 file or multiple numbered backups.
+ − 193
+ − 194 @table @asis
+ − 195 @item @code{nil}
+ − 196 Make numbered backups if the visited file already has numbered backups;
+ − 197 otherwise, do not.
+ − 198
+ − 199 @item @code{never}
+ − 200 Do not make numbered backups.
+ − 201
+ − 202 @item @var{anything else}
+ − 203 Make numbered backups.
+ − 204 @end table
+ − 205 @end defopt
+ − 206
+ − 207 The use of numbered backups ultimately leads to a large number of
+ − 208 backup versions, which must then be deleted. XEmacs can do this
+ − 209 automatically or it can ask the user whether to delete them.
+ − 210
+ − 211 @defopt kept-new-versions
+ − 212 The value of this variable is the number of newest versions to keep
+ − 213 when a new numbered backup is made. The newly made backup is included
+ − 214 in the count. The default value is 2.
+ − 215 @end defopt
+ − 216
+ − 217 @defopt kept-old-versions
+ − 218 The value of this variable is the number of oldest versions to keep
+ − 219 when a new numbered backup is made. The default value is 2.
+ − 220 @end defopt
+ − 221
+ − 222 If there are backups numbered 1, 2, 3, 5, and 7, and both of these
+ − 223 variables have the value 2, then the backups numbered 1 and 2 are kept
+ − 224 as old versions and those numbered 5 and 7 are kept as new versions;
+ − 225 backup version 3 is excess. The function @code{find-backup-file-name}
+ − 226 (@pxref{Backup Names}) is responsible for determining which backup
+ − 227 versions to delete, but does not delete them itself.
+ − 228
359
+ − 229 @defopt delete-old-versions
0
+ − 230 If this variable is non-@code{nil}, then saving a file deletes excess
+ − 231 backup versions silently. Otherwise, it asks the user whether to delete
+ − 232 them.
+ − 233 @end defopt
+ − 234
+ − 235 @defopt dired-kept-versions
+ − 236 This variable specifies how many of the newest backup versions to keep
+ − 237 in the Dired command @kbd{.} (@code{dired-clean-directory}). That's the
+ − 238 same thing @code{kept-new-versions} specifies when you make a new backup
+ − 239 file. The default value is 2.
+ − 240 @end defopt
+ − 241
+ − 242 @node Backup Names
+ − 243 @subsection Naming Backup Files
+ − 244
+ − 245 The functions in this section are documented mainly because you can
+ − 246 customize the naming conventions for backup files by redefining them.
+ − 247 If you change one, you probably need to change the rest.
+ − 248
+ − 249 @defun backup-file-name-p filename
+ − 250 This function returns a non-@code{nil} value if @var{filename} is a
+ − 251 possible name for a backup file. A file with the name @var{filename}
+ − 252 need not exist; the function just checks the name.
+ − 253
+ − 254 @smallexample
+ − 255 @group
+ − 256 (backup-file-name-p "foo")
+ − 257 @result{} nil
+ − 258 @end group
+ − 259 @group
+ − 260 (backup-file-name-p "foo~")
+ − 261 @result{} 3
+ − 262 @end group
+ − 263 @end smallexample
+ − 264
+ − 265 The standard definition of this function is as follows:
+ − 266
+ − 267 @smallexample
+ − 268 @group
+ − 269 (defun backup-file-name-p (file)
+ − 270 "Return non-nil if FILE is a backup file \
+ − 271 name (numeric or not)..."
+ − 272 (string-match "~$" file))
+ − 273 @end group
+ − 274 @end smallexample
+ − 275
+ − 276 @noindent
+ − 277 Thus, the function returns a non-@code{nil} value if the file name ends
+ − 278 with a @samp{~}. (We use a backslash to split the documentation
+ − 279 string's first line into two lines in the text, but produce just one
+ − 280 line in the string itself.)
+ − 281
+ − 282 This simple expression is placed in a separate function to make it easy
+ − 283 to redefine for customization.
+ − 284 @end defun
+ − 285
+ − 286 @defun make-backup-file-name filename
+ − 287 This function returns a string that is the name to use for a
+ − 288 non-numbered backup file for file @var{filename}. On Unix, this is just
+ − 289 @var{filename} with a tilde appended.
+ − 290
+ − 291 The standard definition of this function is as follows:
+ − 292
+ − 293 @smallexample
+ − 294 @group
+ − 295 (defun make-backup-file-name (file)
+ − 296 "Create the non-numeric backup file name for FILE.
+ − 297 @dots{}"
+ − 298 (concat file "~"))
+ − 299 @end group
+ − 300 @end smallexample
+ − 301
+ − 302 You can change the backup-file naming convention by redefining this
+ − 303 function. The following example redefines @code{make-backup-file-name}
+ − 304 to prepend a @samp{.} in addition to appending a tilde:
+ − 305
+ − 306 @smallexample
+ − 307 @group
+ − 308 (defun make-backup-file-name (filename)
+ − 309 (concat "." filename "~"))
+ − 310 @end group
+ − 311
+ − 312 @group
+ − 313 (make-backup-file-name "backups.texi")
+ − 314 @result{} ".backups.texi~"
+ − 315 @end group
+ − 316 @end smallexample
+ − 317 @end defun
+ − 318
+ − 319 @defun find-backup-file-name filename
+ − 320 This function computes the file name for a new backup file for
+ − 321 @var{filename}. It may also propose certain existing backup files for
+ − 322 deletion. @code{find-backup-file-name} returns a list whose @sc{car} is
+ − 323 the name for the new backup file and whose @sc{cdr} is a list of backup
+ − 324 files whose deletion is proposed.
+ − 325
+ − 326 Two variables, @code{kept-old-versions} and @code{kept-new-versions},
+ − 327 determine which backup versions should be kept. This function keeps
+ − 328 those versions by excluding them from the @sc{cdr} of the value.
+ − 329 @xref{Numbered Backups}.
+ − 330
+ − 331 In this example, the value says that @file{~rms/foo.~5~} is the name
+ − 332 to use for the new backup file, and @file{~rms/foo.~3~} is an ``excess''
+ − 333 version that the caller should consider deleting now.
+ − 334
+ − 335 @smallexample
+ − 336 @group
+ − 337 (find-backup-file-name "~rms/foo")
+ − 338 @result{} ("~rms/foo.~5~" "~rms/foo.~3~")
+ − 339 @end group
+ − 340 @end smallexample
+ − 341 @end defun
+ − 342
+ − 343 @c Emacs 19 feature
+ − 344 @defun file-newest-backup filename
+ − 345 This function returns the name of the most recent backup file for
+ − 346 @var{filename}, or @code{nil} if that file has no backup files.
+ − 347
+ − 348 Some file comparison commands use this function so that they can
+ − 349 automatically compare a file with its most recent backup.
444
+ − 350 @end defun
0
+ − 351
+ − 352 @node Auto-Saving
+ − 353 @section Auto-Saving
+ − 354 @cindex auto-saving
+ − 355
+ − 356 XEmacs periodically saves all files that you are visiting; this is
+ − 357 called @dfn{auto-saving}. Auto-saving prevents you from losing more
+ − 358 than a limited amount of work if the system crashes. By default,
+ − 359 auto-saves happen every 300 keystrokes, or after around 30 seconds of
1288
+ − 360 idle time. @xref{Auto Save, Auto-Save, Auto-Saving: Protection Against
+ − 361 Disasters, xemacs, The XEmacs User's Manual}, for information on
446
+ − 362 auto-save for users. Here we describe the functions used to implement
+ − 363 auto-saving and the variables that control them.
0
+ − 364
+ − 365 @defvar buffer-auto-save-file-name
+ − 366 This buffer-local variable is the name of the file used for
+ − 367 auto-saving the current buffer. It is @code{nil} if the buffer
+ − 368 should not be auto-saved.
+ − 369
+ − 370 @example
+ − 371 @group
+ − 372 buffer-auto-save-file-name
+ − 373 => "/xcssun/users/rms/lewis/#files.texi#"
+ − 374 @end group
+ − 375 @end example
+ − 376 @end defvar
+ − 377
+ − 378 @deffn Command auto-save-mode arg
+ − 379 When used interactively without an argument, this command is a toggle
+ − 380 switch: it turns on auto-saving of the current buffer if it is off, and
+ − 381 vice-versa. With an argument @var{arg}, the command turns auto-saving
+ − 382 on if the value of @var{arg} is @code{t}, a nonempty list, or a positive
+ − 383 integer. Otherwise, it turns auto-saving off.
+ − 384 @end deffn
+ − 385
+ − 386 @defun auto-save-file-name-p filename
+ − 387 This function returns a non-@code{nil} value if @var{filename} is a
+ − 388 string that could be the name of an auto-save file. It works based on
+ − 389 knowledge of the naming convention for auto-save files: a name that
+ − 390 begins and ends with hash marks (@samp{#}) is a possible auto-save file
+ − 391 name. The argument @var{filename} should not contain a directory part.
+ − 392
+ − 393 @example
+ − 394 @group
+ − 395 (make-auto-save-file-name)
+ − 396 @result{} "/xcssun/users/rms/lewis/#files.texi#"
+ − 397 @end group
+ − 398 @group
+ − 399 (auto-save-file-name-p "#files.texi#")
+ − 400 @result{} 0
+ − 401 @end group
+ − 402 @group
+ − 403 (auto-save-file-name-p "files.texi")
+ − 404 @result{} nil
+ − 405 @end group
+ − 406 @end example
+ − 407
+ − 408 The standard definition of this function is as follows:
+ − 409
+ − 410 @example
+ − 411 @group
+ − 412 (defun auto-save-file-name-p (filename)
+ − 413 "Return non-nil if FILENAME can be yielded by..."
+ − 414 (string-match "^#.*#$" filename))
+ − 415 @end group
+ − 416 @end example
+ − 417
+ − 418 This function exists so that you can customize it if you wish to
+ − 419 change the naming convention for auto-save files. If you redefine it,
+ − 420 be sure to redefine the function @code{make-auto-save-file-name}
+ − 421 correspondingly.
+ − 422 @end defun
+ − 423
444
+ − 424 @defun make-auto-save-file-name &optional filename
0
+ − 425 This function returns the file name to use for auto-saving the current
+ − 426 buffer. This is just the file name with hash marks (@samp{#}) appended
+ − 427 and prepended to it. This function does not look at the variable
+ − 428 @code{auto-save-visited-file-name} (described below); you should check
+ − 429 that before calling this function.
+ − 430
+ − 431 @example
+ − 432 @group
+ − 433 (make-auto-save-file-name)
+ − 434 @result{} "/xcssun/users/rms/lewis/#backup.texi#"
+ − 435 @end group
+ − 436 @end example
+ − 437
+ − 438 The standard definition of this function is as follows:
+ − 439
+ − 440 @example
+ − 441 @group
+ − 442 (defun make-auto-save-file-name ()
+ − 443 "Return file name to use for auto-saves \
+ − 444 of current buffer.
+ − 445 @dots{}"
+ − 446 (if buffer-file-name
+ − 447 @end group
+ − 448 @group
+ − 449 (concat
+ − 450 (file-name-directory buffer-file-name)
+ − 451 "#"
+ − 452 (file-name-nondirectory buffer-file-name)
+ − 453 "#")
+ − 454 (expand-file-name
+ − 455 (concat "#%" (buffer-name) "#"))))
+ − 456 @end group
+ − 457 @end example
+ − 458
+ − 459 This exists as a separate function so that you can redefine it to
+ − 460 customize the naming convention for auto-save files. Be sure to
+ − 461 change @code{auto-save-file-name-p} in a corresponding way.
+ − 462 @end defun
+ − 463
+ − 464 @defvar auto-save-visited-file-name
+ − 465 If this variable is non-@code{nil}, XEmacs auto-saves buffers in
+ − 466 the files they are visiting. That is, the auto-save is done in the same
+ − 467 file that you are editing. Normally, this variable is @code{nil}, so
+ − 468 auto-save files have distinct names that are created by
+ − 469 @code{make-auto-save-file-name}.
+ − 470
+ − 471 When you change the value of this variable, the value does not take
+ − 472 effect until the next time auto-save mode is reenabled in any given
+ − 473 buffer. If auto-save mode is already enabled, auto-saves continue to go
+ − 474 in the same file name until @code{auto-save-mode} is called again.
+ − 475 @end defvar
+ − 476
+ − 477 @defun recent-auto-save-p
+ − 478 This function returns @code{t} if the current buffer has been
+ − 479 auto-saved since the last time it was read in or saved.
+ − 480 @end defun
+ − 481
+ − 482 @defun set-buffer-auto-saved
+ − 483 This function marks the current buffer as auto-saved. The buffer will
+ − 484 not be auto-saved again until the buffer text is changed again. The
+ − 485 function returns @code{nil}.
+ − 486 @end defun
+ − 487
+ − 488 @defopt auto-save-interval
+ − 489 The value of this variable is the number of characters that XEmacs
+ − 490 reads from the keyboard between auto-saves. Each time this many more
+ − 491 characters are read, auto-saving is done for all buffers in which it is
+ − 492 enabled.
+ − 493 @end defopt
+ − 494
+ − 495 @defopt auto-save-timeout
+ − 496 The value of this variable is the number of seconds of idle time that
+ − 497 should cause auto-saving. Each time the user pauses for this long,
+ − 498 XEmacs auto-saves any buffers that need it. (Actually, the specified
+ − 499 timeout is multiplied by a factor depending on the size of the current
+ − 500 buffer.)
+ − 501 @end defopt
+ − 502
+ − 503 @defvar auto-save-hook
+ − 504 This normal hook is run whenever an auto-save is about to happen.
+ − 505 @end defvar
+ − 506
+ − 507 @defopt auto-save-default
+ − 508 If this variable is non-@code{nil}, buffers that are visiting files
+ − 509 have auto-saving enabled by default. Otherwise, they do not.
+ − 510 @end defopt
+ − 511
+ − 512 @deffn Command do-auto-save &optional no-message current-only
+ − 513 This function auto-saves all buffers that need to be auto-saved. It
+ − 514 saves all buffers for which auto-saving is enabled and that have been
+ − 515 changed since the previous auto-save.
+ − 516
+ − 517 Normally, if any buffers are auto-saved, a message that says
+ − 518 @samp{Auto-saving...} is displayed in the echo area while auto-saving is
+ − 519 going on. However, if @var{no-message} is non-@code{nil}, the message
+ − 520 is inhibited.
+ − 521
+ − 522 If @var{current-only} is non-@code{nil}, only the current buffer
+ − 523 is auto-saved.
+ − 524 @end deffn
+ − 525
+ − 526 @defun delete-auto-save-file-if-necessary
+ − 527 This function deletes the current buffer's auto-save file if
+ − 528 @code{delete-auto-save-files} is non-@code{nil}. It is called every
+ − 529 time a buffer is saved.
+ − 530 @end defun
+ − 531
+ − 532 @defvar delete-auto-save-files
+ − 533 This variable is used by the function
+ − 534 @code{delete-auto-save-file-if-necessary}. If it is non-@code{nil},
+ − 535 Emacs deletes auto-save files when a true save is done (in the visited
+ − 536 file). This saves disk space and unclutters your directory.
+ − 537 @end defvar
+ − 538
+ − 539 @defun rename-auto-save-file
+ − 540 This function adjusts the current buffer's auto-save file name if the
+ − 541 visited file name has changed. It also renames an existing auto-save
+ − 542 file. If the visited file name has not changed, this function does
+ − 543 nothing.
+ − 544 @end defun
+ − 545
+ − 546 @defvar buffer-saved-size
+ − 547 The value of this buffer-local variable is the length of the current
+ − 548 buffer as of the last time it was read in, saved, or auto-saved. This is
+ − 549 used to detect a substantial decrease in size, and turn off auto-saving
+ − 550 in response.
+ − 551
+ − 552 If it is -1, that means auto-saving is temporarily shut off in this
+ − 553 buffer due to a substantial deletion. Explicitly saving the buffer
+ − 554 stores a positive value in this variable, thus reenabling auto-saving.
+ − 555 Turning auto-save mode off or on also alters this variable.
+ − 556 @end defvar
+ − 557
+ − 558 @defvar auto-save-list-file-name
+ − 559 This variable (if non-@code{nil}) specifies a file for recording the
+ − 560 names of all the auto-save files. Each time XEmacs does auto-saving, it
+ − 561 writes two lines into this file for each buffer that has auto-saving
+ − 562 enabled. The first line gives the name of the visited file (it's empty
+ − 563 if the buffer has none), and the second gives the name of the auto-save
+ − 564 file.
+ − 565
+ − 566 If XEmacs exits normally, it deletes this file. If XEmacs crashes, you
+ − 567 can look in the file to find all the auto-save files that might contain
+ − 568 work that was otherwise lost. The @code{recover-session} command uses
+ − 569 these files.
+ − 570
+ − 571 The default name for this file is in your home directory and starts with
+ − 572 @samp{.saves-}. It also contains the XEmacs process @sc{id} and the host
+ − 573 name.
+ − 574 @end defvar
+ − 575
+ − 576 @node Reverting
+ − 577 @section Reverting
+ − 578
+ − 579 If you have made extensive changes to a file and then change your mind
+ − 580 about them, you can get rid of them by reading in the previous version
+ − 581 of the file with the @code{revert-buffer} command. @xref{Reverting, ,
1710
+ − 582 Reverting a Buffer, xemacs, The XEmacs User's Manual}.
0
+ − 583
444
+ − 584 @deffn Command revert-buffer &optional check-auto-save noconfirm preserve-modes
0
+ − 585 This command replaces the buffer text with the text of the visited
+ − 586 file on disk. This action undoes all changes since the file was visited
+ − 587 or saved.
+ − 588
+ − 589 If the argument @var{check-auto-save} is non-@code{nil}, and the
+ − 590 latest auto-save file is more recent than the visited file,
+ − 591 @code{revert-buffer} asks the user whether to use that instead.
+ − 592 Otherwise, it always uses the text of the visited file itself.
+ − 593 Interactively, @var{check-auto-save} is set if there is a numeric prefix
+ − 594 argument.
+ − 595
+ − 596 Normally, @code{revert-buffer} asks for confirmation before it changes
+ − 597 the buffer; but if the argument @var{noconfirm} is non-@code{nil},
+ − 598 @code{revert-buffer} does not ask for confirmation.
+ − 599
444
+ − 600 Optional third argument @var{preserve-modes} non-@code{nil} means don't
+ − 601 alter the files modes. Normally we reinitialize them using
+ − 602 @code{normal-mode}.
+ − 603
0
+ − 604 Reverting tries to preserve marker positions in the buffer by using the
+ − 605 replacement feature of @code{insert-file-contents}. If the buffer
+ − 606 contents and the file contents are identical before the revert
+ − 607 operation, reverting preserves all the markers. If they are not
+ − 608 identical, reverting does change the buffer; then it preserves the
+ − 609 markers in the unchanged text (if any) at the beginning and end of the
+ − 610 buffer. Preserving any additional markers would be problematical.
+ − 611 @end deffn
+ − 612
+ − 613 You can customize how @code{revert-buffer} does its work by setting
+ − 614 these variables---typically, as buffer-local variables.
+ − 615
+ − 616 @defvar revert-buffer-function
+ − 617 The value of this variable is the function to use to revert this buffer.
+ − 618 If non-@code{nil}, it is called as a function with no arguments to do
+ − 619 the work of reverting. If the value is @code{nil}, reverting works the
+ − 620 usual way.
+ − 621
+ − 622 Modes such as Dired mode, in which the text being edited does not
+ − 623 consist of a file's contents but can be regenerated in some other
+ − 624 fashion, give this variable a buffer-local value that is a function to
+ − 625 regenerate the contents.
+ − 626 @end defvar
+ − 627
+ − 628 @defvar revert-buffer-insert-file-contents-function
+ − 629 The value of this variable, if non-@code{nil}, is the function to use to
+ − 630 insert the updated contents when reverting this buffer. The function
+ − 631 receives two arguments: first the file name to use; second, @code{t} if
+ − 632 the user has asked to read the auto-save file.
+ − 633 @end defvar
+ − 634
+ − 635 @defvar before-revert-hook
+ − 636 This normal hook is run by @code{revert-buffer} before actually
+ − 637 inserting the modified contents---but only if
+ − 638 @code{revert-buffer-function} is @code{nil}.
+ − 639
+ − 640 Font Lock mode uses this hook to record that the buffer contents are no
+ − 641 longer fontified.
+ − 642 @end defvar
+ − 643
+ − 644 @defvar after-revert-hook
+ − 645 This normal hook is run by @code{revert-buffer} after actually inserting
+ − 646 the modified contents---but only if @code{revert-buffer-function} is
+ − 647 @code{nil}.
+ − 648
+ − 649 Font Lock mode uses this hook to recompute the fonts for the updated
+ − 650 buffer contents.
+ − 651 @end defvar
+ − 652
