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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. | |
4 | @c See the file elisp.texi for copying conditions. | |
5 | @setfilename ../info/backups | |
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 Emacs 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 | ||
0680592c | 21 | @node Backup Files |
b1b12a8e RS |
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. Emacs 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, Emacs 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 Emacs can delete them automatically. | |
42 | ||
43 | @menu | |
44 | * Making Backups:: How Emacs 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 | ||
0680592c | 50 | @node Making Backups |
b1b12a8e RS |
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 | |
2e00781a | 63 | up when it is next saved (if backups are enabled). This is a |
b1b12a8e RS |
64 | permanent local; @code{kill-local-variables} does not alter it. |
65 | @end defvar | |
66 | ||
67 | @defopt make-backup-files | |
bfe721d1 | 68 | This variable determines whether or not to make backup files. If it |
b1b12a8e | 69 | is non-@code{nil}, then Emacs creates a backup of each file when it is |
bfe721d1 KH |
70 | saved for the first time---provided that @code{backup-inhibited} |
71 | is @code{nil} (see below). | |
b1b12a8e | 72 | |
bfe721d1 | 73 | The following example shows how to change the @code{make-backup-files} |
b1b12a8e RS |
74 | variable only in the @file{RMAIL} buffer and not elsewhere. Setting it |
75 | @code{nil} stops Emacs 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 | |
81 | (add-hook 'rmail-mode-hook | |
82 | (function (lambda () | |
83 | (make-local-variable | |
84 | 'make-backup-files) | |
85 | (setq make-backup-files nil)))) | |
86 | @end group | |
87 | @end smallexample | |
88 | @end defopt | |
89 | ||
2e00781a | 90 | @defvar backup-enable-predicate |
b1b12a8e | 91 | This variable's value is a function to be called on certain occasions to |
2e00781a RS |
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. | |
b1b12a8e RS |
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 | |
bfe721d1 KH |
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. | |
2e00781a | 114 | |
bfe721d1 KH |
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 | |
2e00781a | 117 | @code{make-backup-files} instead. |
b1b12a8e RS |
118 | @end defvar |
119 | ||
0680592c | 120 | @node Rename or Copy |
b1b12a8e RS |
121 | @subsection Backup by Renaming or by Copying? |
122 | @cindex backup files, how to make them | |
123 | ||
124 | There are two ways that Emacs can make a backup file: | |
125 | ||
126 | @itemize @bullet | |
127 | @item | |
128 | Emacs 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 | Emacs 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}, Emacs 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}, Emacs 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}, Emacs 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 | ||
0680592c | 182 | @node Numbered Backups |
b1b12a8e RS |
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} | |
2e00781a | 203 | Make numbered backups. |
b1b12a8e RS |
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. Emacs can do this | |
2e00781a | 209 | automatically or it can ask the user whether to delete them. |
b1b12a8e RS |
210 | |
211 | @defopt kept-new-versions | |
2e00781a | 212 | The value of this variable is the number of newest versions to keep |
b1b12a8e RS |
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; | |
2e00781a | 225 | backup version 3 is excess. The function @code{find-backup-file-name} |
b1b12a8e RS |
226 | (@pxref{Backup Names}) is responsible for determining which backup |
227 | versions to delete, but does not delete them itself. | |
228 | ||
229 | @defopt trim-versions-without-asking | |
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 | |
2e00781a | 238 | same thing @code{kept-new-versions} specifies when you make a new backup |
b1b12a8e RS |
239 | file. The default value is 2. |
240 | @end defopt | |
241 | ||
0680592c | 242 | @node Backup Names |
b1b12a8e RS |
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 | |
2e00781a | 287 | This function returns a string that is the name to use for a |
b1b12a8e RS |
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 | ||
2e00781a | 302 | You can change the backup-file naming convention by redefining this |
b1b12a8e | 303 | function. The following example redefines @code{make-backup-file-name} |
2e00781a | 304 | to prepend a @samp{.} in addition to appending a tilde: |
b1b12a8e RS |
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 | |
2e00781a | 346 | @var{filename}, or @code{nil} if that file has no backup files. |
b1b12a8e | 347 | |
2e00781a RS |
348 | Some file comparison commands use this function so that they can |
349 | automatically compare a file with its most recent backup. | |
b1b12a8e RS |
350 | @end defun |
351 | ||
0680592c | 352 | @node Auto-Saving |
b1b12a8e RS |
353 | @section Auto-Saving |
354 | @cindex auto-saving | |
355 | ||
356 | Emacs 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 | |
360 | idle time. @xref{Auto-Save, Auto-Save, Auto-Saving: Protection Against | |
361 | Disasters, emacs, The GNU Emacs Manual}, for information on auto-save | |
362 | for users. Here we describe the functions used to implement auto-saving | |
363 | and the variables that control them. | |
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 | ||
424 | @defun make-auto-save-file-name | |
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 | |
2e00781a RS |
428 | @code{auto-save-visited-file-name} (described below); you should check |
429 | that before calling this function. | |
b1b12a8e RS |
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}, Emacs auto-saves buffers in | |
466 | the files they are visiting. That is, the auto-save is done in the same | |
2e00781a | 467 | file that you are editing. Normally, this variable is @code{nil}, so |
b1b12a8e RS |
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 Emacs | |
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 | Emacs 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 | ||
bfe721d1 | 512 | @deffn Command do-auto-save &optional no-message current-only |
b1b12a8e RS |
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. | |
bfe721d1 KH |
521 | |
522 | If @var{current-only} is non-@code{nil}, only the current buffer | |
523 | is auto-saved. | |
b1b12a8e RS |
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 | ||
0680592c | 546 | @defvar buffer-saved-size |
2e00781a RS |
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. | |
0680592c RS |
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 | |
bfe721d1 | 554 | stores a positive value in this variable, thus reenabling auto-saving. |
2e00781a | 555 | Turning auto-save mode off or on also alters this variable. |
0680592c RS |
556 | @end defvar |
557 | ||
9589417c RS |
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 Emacs does auto-saving, it | |
bfe721d1 KH |
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 Emacs exits normally, it deletes this file. If Emacs 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. | |
9589417c RS |
570 | |
571 | The default name for this file is in your home directory and starts with | |
572 | @samp{.saves-}. It also contains the Emacs process @sc{id} and the host | |
573 | name. | |
574 | @end defvar | |
575 | ||
0680592c | 576 | @node Reverting |
b1b12a8e RS |
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, , | |
582 | Reverting a Buffer, emacs, The GNU Emacs Manual}. | |
583 | ||
584 | @deffn Command revert-buffer &optional check-auto-save noconfirm | |
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 | ||
600 | Reverting tries to preserve marker positions in the buffer by using the | |
2e00781a RS |
601 | replacement feature of @code{insert-file-contents}. If the buffer |
602 | contents and the file contents are identical before the revert | |
603 | operation, reverting preserves all the markers. If they are not | |
604 | identical, reverting does change the buffer; then it preserves the | |
605 | markers in the unchanged text (if any) at the beginning and end of the | |
606 | buffer. Preserving any additional markers would be problematical. | |
b1b12a8e RS |
607 | @end deffn |
608 | ||
2e00781a RS |
609 | You can customize how @code{revert-buffer} does its work by setting |
610 | these variables---typically, as buffer-local variables. | |
611 | ||
b1b12a8e | 612 | @defvar revert-buffer-function |
2e00781a RS |
613 | The value of this variable is the function to use to revert this buffer. |
614 | If non-@code{nil}, it is called as a function with no arguments to do | |
615 | the work of reverting. If the value is @code{nil}, reverting works the | |
616 | usual way. | |
617 | ||
618 | Modes such as Dired mode, in which the text being edited does not | |
619 | consist of a file's contents but can be regenerated in some other | |
620 | fashion, give this variable a buffer-local value that is a function to | |
621 | regenerate the contents. | |
b1b12a8e RS |
622 | @end defvar |
623 | ||
624 | @defvar revert-buffer-insert-file-contents-function | |
2e00781a | 625 | The value of this variable, if non-@code{nil}, is the function to use to |
bfe721d1 KH |
626 | insert the updated contents when reverting this buffer. The function |
627 | receives two arguments: first the file name to use; second, @code{t} if | |
628 | the user has asked to read the auto-save file. | |
b1b12a8e RS |
629 | @end defvar |
630 | ||
631 | @defvar before-revert-hook | |
632 | This normal hook is run by @code{revert-buffer} before actually | |
633 | inserting the modified contents---but only if | |
634 | @code{revert-buffer-function} is @code{nil}. | |
635 | ||
636 | Font Lock mode uses this hook to record that the buffer contents are no | |
637 | longer fontified. | |
638 | @end defvar | |
639 | ||
640 | @defvar after-revert-hook | |
641 | This normal hook is run by @code{revert-buffer} after actually inserting | |
642 | the modified contents---but only if @code{revert-buffer-function} is | |
643 | @code{nil}. | |
644 | ||
645 | Font Lock mode uses this hook to recompute the fonts for the updated | |
646 | buffer contents. | |
647 | @end defvar | |
648 |