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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
f9f59935 | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc. |
b1b12a8e RS |
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 |
29b677db | 64 | permanent local; @code{kill-all-local-variables} does not alter it. |
b1b12a8e RS |
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} |
f9f59935 RS |
74 | variable only in the Rmail buffers and not elsewhere. Setting it |
75 | @code{nil} stops Emacs from making backups of these files, which may | |
a40d4712 | 76 | save disk space. (You would put this code in your init file.) |
b1b12a8e RS |
77 | |
78 | @smallexample | |
79 | @group | |
80 | (add-hook 'rmail-mode-hook | |
81 | (function (lambda () | |
82 | (make-local-variable | |
83 | 'make-backup-files) | |
84 | (setq make-backup-files nil)))) | |
85 | @end group | |
86 | @end smallexample | |
87 | @end defopt | |
88 | ||
2e00781a | 89 | @defvar backup-enable-predicate |
b1b12a8e | 90 | This variable's value is a function to be called on certain occasions to |
2e00781a RS |
91 | decide whether a file should have backup files. The function receives |
92 | one argument, a file name to consider. If the function returns | |
93 | @code{nil}, backups are disabled for that file. Otherwise, the other | |
94 | variables in this section say whether and how to make backups. | |
b1b12a8e RS |
95 | |
96 | The default value is this: | |
97 | ||
98 | @example | |
99 | (lambda (name) | |
100 | (or (< (length name) 5) | |
101 | (not (string-equal "/tmp/" | |
102 | (substring name 0 5))))) | |
103 | @end example | |
104 | @end defvar | |
105 | ||
106 | @defvar backup-inhibited | |
107 | If this variable is non-@code{nil}, backups are inhibited. It records | |
108 | the result of testing @code{backup-enable-predicate} on the visited file | |
109 | name. It can also coherently be used by other mechanisms that inhibit | |
bfe721d1 KH |
110 | backups based on which file is visited. For example, VC sets this |
111 | variable non-@code{nil} to prevent making backups for files managed | |
112 | with a version control system. | |
2e00781a | 113 | |
bfe721d1 KH |
114 | This is a permanent local, so that changing the major mode does not lose |
115 | its value. Major modes should not set this variable---they should set | |
2e00781a | 116 | @code{make-backup-files} instead. |
b1b12a8e RS |
117 | @end defvar |
118 | ||
0680592c | 119 | @node Rename or Copy |
b1b12a8e RS |
120 | @subsection Backup by Renaming or by Copying? |
121 | @cindex backup files, how to make them | |
122 | ||
123 | There are two ways that Emacs can make a backup file: | |
124 | ||
125 | @itemize @bullet | |
126 | @item | |
127 | Emacs can rename the original file so that it becomes a backup file, and | |
128 | then write the buffer being saved into a new file. After this | |
129 | procedure, any other names (i.e., hard links) of the original file now | |
130 | refer to the backup file. The new file is owned by the user doing the | |
131 | editing, and its group is the default for new files written by the user | |
132 | in that directory. | |
133 | ||
134 | @item | |
135 | Emacs can copy the original file into a backup file, and then overwrite | |
136 | the original file with new contents. After this procedure, any other | |
f9f59935 RS |
137 | names (i.e., hard links) of the original file continue to refer to the |
138 | current (updated) version of the file. The file's owner and group will | |
139 | be unchanged. | |
b1b12a8e RS |
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 | ||
8241495d RS |
182 | @defvar backup-by-copying-when-privileged-mismatch |
183 | This variable, if non-@code{nil}, specifies the same behavior as | |
184 | @code{backup-by-copying-when-mismatch}, but only for certain user-id | |
185 | values: namely, those less than or equal to a certain number. You set | |
186 | this variable to that number. | |
187 | ||
188 | Thus, if you set @code{backup-by-copying-when-privileged-mismatch} | |
189 | to 0, backup by copying is done for the superuser only, | |
190 | when necessary to prevent a change in the owner of the file. | |
191 | ||
192 | The default is 200. | |
193 | @end defvar | |
194 | ||
0680592c | 195 | @node Numbered Backups |
b1b12a8e RS |
196 | @subsection Making and Deleting Numbered Backup Files |
197 | ||
198 | If a file's name is @file{foo}, the names of its numbered backup | |
199 | versions are @file{foo.~@var{v}~}, for various integers @var{v}, like | |
200 | this: @file{foo.~1~}, @file{foo.~2~}, @file{foo.~3~}, @dots{}, | |
201 | @file{foo.~259~}, and so on. | |
202 | ||
203 | @defopt version-control | |
204 | This variable controls whether to make a single non-numbered backup | |
205 | file or multiple numbered backups. | |
206 | ||
207 | @table @asis | |
208 | @item @code{nil} | |
209 | Make numbered backups if the visited file already has numbered backups; | |
210 | otherwise, do not. | |
211 | ||
212 | @item @code{never} | |
213 | Do not make numbered backups. | |
214 | ||
215 | @item @var{anything else} | |
2e00781a | 216 | Make numbered backups. |
b1b12a8e RS |
217 | @end table |
218 | @end defopt | |
219 | ||
220 | The use of numbered backups ultimately leads to a large number of | |
221 | backup versions, which must then be deleted. Emacs can do this | |
2e00781a | 222 | automatically or it can ask the user whether to delete them. |
b1b12a8e RS |
223 | |
224 | @defopt kept-new-versions | |
2e00781a | 225 | The value of this variable is the number of newest versions to keep |
b1b12a8e RS |
226 | when a new numbered backup is made. The newly made backup is included |
227 | in the count. The default value is 2. | |
228 | @end defopt | |
229 | ||
230 | @defopt kept-old-versions | |
231 | The value of this variable is the number of oldest versions to keep | |
232 | when a new numbered backup is made. The default value is 2. | |
233 | @end defopt | |
234 | ||
235 | If there are backups numbered 1, 2, 3, 5, and 7, and both of these | |
236 | variables have the value 2, then the backups numbered 1 and 2 are kept | |
237 | as old versions and those numbered 5 and 7 are kept as new versions; | |
2e00781a | 238 | backup version 3 is excess. The function @code{find-backup-file-name} |
b1b12a8e RS |
239 | (@pxref{Backup Names}) is responsible for determining which backup |
240 | versions to delete, but does not delete them itself. | |
241 | ||
f9f59935 RS |
242 | @tindex delete-old-versions |
243 | @defopt delete-old-versions | |
29b677db RS |
244 | If this variable is @code{t}, then saving a file deletes excess |
245 | backup versions silently. If it is @code{nil}, that means | |
246 | to ask for confirmation before deleting excess backups. | |
247 | Otherwise, they are not deleted at all. | |
b1b12a8e RS |
248 | @end defopt |
249 | ||
250 | @defopt dired-kept-versions | |
251 | This variable specifies how many of the newest backup versions to keep | |
252 | in the Dired command @kbd{.} (@code{dired-clean-directory}). That's the | |
2e00781a | 253 | same thing @code{kept-new-versions} specifies when you make a new backup |
b1b12a8e RS |
254 | file. The default value is 2. |
255 | @end defopt | |
256 | ||
0680592c | 257 | @node Backup Names |
b1b12a8e RS |
258 | @subsection Naming Backup Files |
259 | ||
260 | The functions in this section are documented mainly because you can | |
261 | customize the naming conventions for backup files by redefining them. | |
262 | If you change one, you probably need to change the rest. | |
263 | ||
264 | @defun backup-file-name-p filename | |
265 | This function returns a non-@code{nil} value if @var{filename} is a | |
266 | possible name for a backup file. A file with the name @var{filename} | |
267 | need not exist; the function just checks the name. | |
268 | ||
269 | @smallexample | |
270 | @group | |
271 | (backup-file-name-p "foo") | |
272 | @result{} nil | |
273 | @end group | |
274 | @group | |
275 | (backup-file-name-p "foo~") | |
276 | @result{} 3 | |
277 | @end group | |
278 | @end smallexample | |
279 | ||
280 | The standard definition of this function is as follows: | |
281 | ||
282 | @smallexample | |
283 | @group | |
284 | (defun backup-file-name-p (file) | |
285 | "Return non-nil if FILE is a backup file \ | |
286 | name (numeric or not)..." | |
29b677db | 287 | (string-match "~\\'" file)) |
b1b12a8e RS |
288 | @end group |
289 | @end smallexample | |
290 | ||
291 | @noindent | |
292 | Thus, the function returns a non-@code{nil} value if the file name ends | |
293 | with a @samp{~}. (We use a backslash to split the documentation | |
294 | string's first line into two lines in the text, but produce just one | |
295 | line in the string itself.) | |
296 | ||
297 | This simple expression is placed in a separate function to make it easy | |
298 | to redefine for customization. | |
299 | @end defun | |
300 | ||
301 | @defun make-backup-file-name filename | |
2e00781a | 302 | This function returns a string that is the name to use for a |
b1b12a8e RS |
303 | non-numbered backup file for file @var{filename}. On Unix, this is just |
304 | @var{filename} with a tilde appended. | |
305 | ||
a9f0a989 RS |
306 | The standard definition of this function, on most operating systems, is |
307 | as follows: | |
b1b12a8e RS |
308 | |
309 | @smallexample | |
310 | @group | |
311 | (defun make-backup-file-name (file) | |
29b677db | 312 | "Create the non-numeric backup file name for FILE..." |
b1b12a8e RS |
313 | (concat file "~")) |
314 | @end group | |
315 | @end smallexample | |
316 | ||
2e00781a | 317 | You can change the backup-file naming convention by redefining this |
b1b12a8e | 318 | function. The following example redefines @code{make-backup-file-name} |
2e00781a | 319 | to prepend a @samp{.} in addition to appending a tilde: |
b1b12a8e RS |
320 | |
321 | @smallexample | |
322 | @group | |
323 | (defun make-backup-file-name (filename) | |
a9f0a989 RS |
324 | (expand-file-name |
325 | (concat "." (file-name-nondirectory filename) "~") | |
326 | (file-name-directory filename))) | |
b1b12a8e RS |
327 | @end group |
328 | ||
329 | @group | |
330 | (make-backup-file-name "backups.texi") | |
331 | @result{} ".backups.texi~" | |
332 | @end group | |
333 | @end smallexample | |
a9f0a989 RS |
334 | |
335 | Some parts of Emacs, including some Dired commands, assume that backup | |
336 | file names end with @samp{~}. If you do not follow that convention, it | |
337 | will not cause serious problems, but these commands may give | |
338 | less-than-desirable results. | |
b1b12a8e RS |
339 | @end defun |
340 | ||
341 | @defun find-backup-file-name filename | |
342 | This function computes the file name for a new backup file for | |
343 | @var{filename}. It may also propose certain existing backup files for | |
344 | deletion. @code{find-backup-file-name} returns a list whose @sc{car} is | |
345 | the name for the new backup file and whose @sc{cdr} is a list of backup | |
346 | files whose deletion is proposed. | |
347 | ||
348 | Two variables, @code{kept-old-versions} and @code{kept-new-versions}, | |
349 | determine which backup versions should be kept. This function keeps | |
350 | those versions by excluding them from the @sc{cdr} of the value. | |
351 | @xref{Numbered Backups}. | |
352 | ||
353 | In this example, the value says that @file{~rms/foo.~5~} is the name | |
354 | to use for the new backup file, and @file{~rms/foo.~3~} is an ``excess'' | |
355 | version that the caller should consider deleting now. | |
356 | ||
357 | @smallexample | |
358 | @group | |
359 | (find-backup-file-name "~rms/foo") | |
360 | @result{} ("~rms/foo.~5~" "~rms/foo.~3~") | |
361 | @end group | |
362 | @end smallexample | |
363 | @end defun | |
364 | ||
365 | @c Emacs 19 feature | |
366 | @defun file-newest-backup filename | |
367 | This function returns the name of the most recent backup file for | |
2e00781a | 368 | @var{filename}, or @code{nil} if that file has no backup files. |
b1b12a8e | 369 | |
2e00781a RS |
370 | Some file comparison commands use this function so that they can |
371 | automatically compare a file with its most recent backup. | |
b1b12a8e RS |
372 | @end defun |
373 | ||
0680592c | 374 | @node Auto-Saving |
b1b12a8e RS |
375 | @section Auto-Saving |
376 | @cindex auto-saving | |
377 | ||
378 | Emacs periodically saves all files that you are visiting; this is | |
379 | called @dfn{auto-saving}. Auto-saving prevents you from losing more | |
380 | than a limited amount of work if the system crashes. By default, | |
381 | auto-saves happen every 300 keystrokes, or after around 30 seconds of | |
382 | idle time. @xref{Auto-Save, Auto-Save, Auto-Saving: Protection Against | |
383 | Disasters, emacs, The GNU Emacs Manual}, for information on auto-save | |
384 | for users. Here we describe the functions used to implement auto-saving | |
385 | and the variables that control them. | |
386 | ||
387 | @defvar buffer-auto-save-file-name | |
388 | This buffer-local variable is the name of the file used for | |
389 | auto-saving the current buffer. It is @code{nil} if the buffer | |
390 | should not be auto-saved. | |
391 | ||
392 | @example | |
393 | @group | |
394 | buffer-auto-save-file-name | |
29b677db | 395 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" |
b1b12a8e RS |
396 | @end group |
397 | @end example | |
398 | @end defvar | |
399 | ||
400 | @deffn Command auto-save-mode arg | |
401 | When used interactively without an argument, this command is a toggle | |
402 | switch: it turns on auto-saving of the current buffer if it is off, and | |
29b677db | 403 | vice versa. With an argument @var{arg}, the command turns auto-saving |
b1b12a8e RS |
404 | on if the value of @var{arg} is @code{t}, a nonempty list, or a positive |
405 | integer. Otherwise, it turns auto-saving off. | |
406 | @end deffn | |
407 | ||
408 | @defun auto-save-file-name-p filename | |
409 | This function returns a non-@code{nil} value if @var{filename} is a | |
8241495d RS |
410 | string that could be the name of an auto-save file. It assumes |
411 | the usual naming convention for auto-save files: a name that | |
b1b12a8e RS |
412 | begins and ends with hash marks (@samp{#}) is a possible auto-save file |
413 | name. The argument @var{filename} should not contain a directory part. | |
414 | ||
415 | @example | |
416 | @group | |
417 | (make-auto-save-file-name) | |
29b677db | 418 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" |
b1b12a8e RS |
419 | @end group |
420 | @group | |
29b677db | 421 | (auto-save-file-name-p "#backups.texi#") |
b1b12a8e RS |
422 | @result{} 0 |
423 | @end group | |
424 | @group | |
29b677db | 425 | (auto-save-file-name-p "backups.texi") |
b1b12a8e RS |
426 | @result{} nil |
427 | @end group | |
428 | @end example | |
429 | ||
430 | The standard definition of this function is as follows: | |
431 | ||
432 | @example | |
433 | @group | |
434 | (defun auto-save-file-name-p (filename) | |
435 | "Return non-nil if FILENAME can be yielded by..." | |
436 | (string-match "^#.*#$" filename)) | |
437 | @end group | |
438 | @end example | |
439 | ||
440 | This function exists so that you can customize it if you wish to | |
441 | change the naming convention for auto-save files. If you redefine it, | |
442 | be sure to redefine the function @code{make-auto-save-file-name} | |
443 | correspondingly. | |
444 | @end defun | |
445 | ||
446 | @defun make-auto-save-file-name | |
447 | This function returns the file name to use for auto-saving the current | |
86494bd5 KH |
448 | buffer. This is just the file name with hash marks (@samp{#}) prepended |
449 | and appended to it. This function does not look at the variable | |
8241495d RS |
450 | @code{auto-save-visited-file-name} (described below); callers of this |
451 | function should check that variable first. | |
b1b12a8e RS |
452 | |
453 | @example | |
454 | @group | |
455 | (make-auto-save-file-name) | |
29b677db | 456 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" |
b1b12a8e RS |
457 | @end group |
458 | @end example | |
459 | ||
460 | The standard definition of this function is as follows: | |
461 | ||
462 | @example | |
463 | @group | |
464 | (defun make-auto-save-file-name () | |
465 | "Return file name to use for auto-saves \ | |
29b677db | 466 | of current buffer.." |
b1b12a8e RS |
467 | (if buffer-file-name |
468 | @end group | |
469 | @group | |
470 | (concat | |
471 | (file-name-directory buffer-file-name) | |
472 | "#" | |
473 | (file-name-nondirectory buffer-file-name) | |
474 | "#") | |
475 | (expand-file-name | |
476 | (concat "#%" (buffer-name) "#")))) | |
477 | @end group | |
478 | @end example | |
479 | ||
480 | This exists as a separate function so that you can redefine it to | |
481 | customize the naming convention for auto-save files. Be sure to | |
482 | change @code{auto-save-file-name-p} in a corresponding way. | |
483 | @end defun | |
484 | ||
485 | @defvar auto-save-visited-file-name | |
486 | If this variable is non-@code{nil}, Emacs auto-saves buffers in | |
487 | the files they are visiting. That is, the auto-save is done in the same | |
2e00781a | 488 | file that you are editing. Normally, this variable is @code{nil}, so |
b1b12a8e RS |
489 | auto-save files have distinct names that are created by |
490 | @code{make-auto-save-file-name}. | |
491 | ||
8241495d RS |
492 | When you change the value of this variable, the new value does not take |
493 | effect in an existing buffer until the next time auto-save mode is | |
494 | reenabled in it. If auto-save mode is already enabled, auto-saves | |
495 | continue to go in the same file name until @code{auto-save-mode} is | |
496 | called again. | |
b1b12a8e RS |
497 | @end defvar |
498 | ||
499 | @defun recent-auto-save-p | |
500 | This function returns @code{t} if the current buffer has been | |
501 | auto-saved since the last time it was read in or saved. | |
502 | @end defun | |
503 | ||
504 | @defun set-buffer-auto-saved | |
505 | This function marks the current buffer as auto-saved. The buffer will | |
506 | not be auto-saved again until the buffer text is changed again. The | |
507 | function returns @code{nil}. | |
508 | @end defun | |
509 | ||
510 | @defopt auto-save-interval | |
8241495d RS |
511 | The value of this variable specifies how often to do auto-saving, in |
512 | terms of number of input events. Each time this many additional input | |
513 | events are read, Emacs does auto-saving for all buffers in which that is | |
b1b12a8e RS |
514 | enabled. |
515 | @end defopt | |
516 | ||
517 | @defopt auto-save-timeout | |
518 | The value of this variable is the number of seconds of idle time that | |
519 | should cause auto-saving. Each time the user pauses for this long, | |
29b677db RS |
520 | Emacs does auto-saving for all buffers in which that is enabled. (If |
521 | the current buffer is large, the specified timeout is multiplied by a | |
522 | factor that depends increases as the size increases; for a million-byte | |
523 | buffer, the factor is almost 4.) | |
524 | ||
525 | If the value is zero or nil, then auto-saving is not done as a result | |
526 | of idleness, only after a certain number of input events | |
527 | as specified by @code{auto-save-interval}. | |
b1b12a8e RS |
528 | @end defopt |
529 | ||
530 | @defvar auto-save-hook | |
531 | This normal hook is run whenever an auto-save is about to happen. | |
532 | @end defvar | |
533 | ||
534 | @defopt auto-save-default | |
535 | If this variable is non-@code{nil}, buffers that are visiting files | |
536 | have auto-saving enabled by default. Otherwise, they do not. | |
537 | @end defopt | |
538 | ||
bfe721d1 | 539 | @deffn Command do-auto-save &optional no-message current-only |
b1b12a8e RS |
540 | This function auto-saves all buffers that need to be auto-saved. It |
541 | saves all buffers for which auto-saving is enabled and that have been | |
542 | changed since the previous auto-save. | |
543 | ||
544 | Normally, if any buffers are auto-saved, a message that says | |
545 | @samp{Auto-saving...} is displayed in the echo area while auto-saving is | |
546 | going on. However, if @var{no-message} is non-@code{nil}, the message | |
547 | is inhibited. | |
bfe721d1 KH |
548 | |
549 | If @var{current-only} is non-@code{nil}, only the current buffer | |
550 | is auto-saved. | |
b1b12a8e RS |
551 | @end deffn |
552 | ||
553 | @defun delete-auto-save-file-if-necessary | |
554 | This function deletes the current buffer's auto-save file if | |
555 | @code{delete-auto-save-files} is non-@code{nil}. It is called every | |
556 | time a buffer is saved. | |
557 | @end defun | |
558 | ||
559 | @defvar delete-auto-save-files | |
560 | This variable is used by the function | |
561 | @code{delete-auto-save-file-if-necessary}. If it is non-@code{nil}, | |
562 | Emacs deletes auto-save files when a true save is done (in the visited | |
563 | file). This saves disk space and unclutters your directory. | |
564 | @end defvar | |
565 | ||
566 | @defun rename-auto-save-file | |
567 | This function adjusts the current buffer's auto-save file name if the | |
568 | visited file name has changed. It also renames an existing auto-save | |
569 | file. If the visited file name has not changed, this function does | |
570 | nothing. | |
571 | @end defun | |
572 | ||
0680592c | 573 | @defvar buffer-saved-size |
2e00781a | 574 | The value of this buffer-local variable is the length of the current |
8241495d | 575 | buffer, when it was last read in, saved, or auto-saved. This is |
2e00781a RS |
576 | used to detect a substantial decrease in size, and turn off auto-saving |
577 | in response. | |
0680592c | 578 | |
8241495d RS |
579 | If it is @minus{}1, that means auto-saving is temporarily shut off in |
580 | this buffer due to a substantial decrease in size. Explicitly saving | |
581 | the buffer stores a positive value in this variable, thus reenabling | |
582 | auto-saving. Turning auto-save mode off or on also updates this | |
583 | variable, so that the substantial decrease in size is forgotten. | |
0680592c RS |
584 | @end defvar |
585 | ||
9589417c RS |
586 | @defvar auto-save-list-file-name |
587 | This variable (if non-@code{nil}) specifies a file for recording the | |
588 | names of all the auto-save files. Each time Emacs does auto-saving, it | |
bfe721d1 KH |
589 | writes two lines into this file for each buffer that has auto-saving |
590 | enabled. The first line gives the name of the visited file (it's empty | |
591 | if the buffer has none), and the second gives the name of the auto-save | |
592 | file. | |
593 | ||
8241495d | 594 | When Emacs exits normally, it deletes this file; if Emacs crashes, you |
bfe721d1 KH |
595 | can look in the file to find all the auto-save files that might contain |
596 | work that was otherwise lost. The @code{recover-session} command uses | |
8241495d | 597 | this file to find them. |
9589417c | 598 | |
8241495d RS |
599 | The default name for this file specifies your home directory and starts |
600 | with @samp{.saves-}. It also contains the Emacs process @sc{id} and the | |
601 | host name. | |
9589417c RS |
602 | @end defvar |
603 | ||
29b677db RS |
604 | @defvar auto-save-list-file-prefix |
605 | @tindex auto-save-list-file-prefix | |
606 | After Emacs reads your init file, it initializes | |
607 | @code{auto-save-list-file-name} (if you have not already set it | |
608 | non-@code{nil}) based on this prefix, adding the host name and process | |
609 | ID. If you set this to @code{nil} in your init file, then Emacs does | |
610 | not initialize @code{auto-save-list-file-name}. | |
611 | @end defvar | |
612 | ||
0680592c | 613 | @node Reverting |
b1b12a8e RS |
614 | @section Reverting |
615 | ||
616 | If you have made extensive changes to a file and then change your mind | |
617 | about them, you can get rid of them by reading in the previous version | |
618 | of the file with the @code{revert-buffer} command. @xref{Reverting, , | |
619 | Reverting a Buffer, emacs, The GNU Emacs Manual}. | |
620 | ||
1911e6e5 | 621 | @deffn Command revert-buffer &optional ignore-auto noconfirm |
b1b12a8e RS |
622 | This command replaces the buffer text with the text of the visited |
623 | file on disk. This action undoes all changes since the file was visited | |
624 | or saved. | |
625 | ||
1911e6e5 | 626 | By default, if the latest auto-save file is more recent than the visited |
b581dd19 | 627 | file, and the argument @var{ignore-auto} is @code{nil}, |
8241495d RS |
628 | @code{revert-buffer} asks the user whether to use that auto-save |
629 | instead. When you invoke this command interactively, @var{ignore-auto} | |
b581dd19 GM |
630 | is @code{t} if there is no numeric prefix argument; thus, the |
631 | interactive default is not to check the auto-save file. | |
b1b12a8e RS |
632 | |
633 | Normally, @code{revert-buffer} asks for confirmation before it changes | |
634 | the buffer; but if the argument @var{noconfirm} is non-@code{nil}, | |
635 | @code{revert-buffer} does not ask for confirmation. | |
636 | ||
637 | Reverting tries to preserve marker positions in the buffer by using the | |
2e00781a RS |
638 | replacement feature of @code{insert-file-contents}. If the buffer |
639 | contents and the file contents are identical before the revert | |
640 | operation, reverting preserves all the markers. If they are not | |
8241495d RS |
641 | identical, reverting does change the buffer; in that case, it preserves |
642 | the markers in the unchanged text (if any) at the beginning and end of | |
643 | the buffer. Preserving any additional markers would be problematical. | |
b1b12a8e RS |
644 | @end deffn |
645 | ||
2e00781a | 646 | You can customize how @code{revert-buffer} does its work by setting |
29b677db | 647 | the variables described in the rest of this section. |
2e00781a | 648 | |
1911e6e5 RS |
649 | @defvar revert-without-query |
650 | This variable holds a list of files that should be reverted without | |
8241495d RS |
651 | query. The value is a list of regular expressions. If the visited file |
652 | name matches one of these regular expressions, and the file has changed | |
653 | on disk but the buffer is not modified, then @code{revert-buffer} | |
654 | reverts the file without asking the user for confirmation. | |
1911e6e5 RS |
655 | @end defvar |
656 | ||
29b677db RS |
657 | Some major modes customize @code{revert-buffer} by making |
658 | buffer-local bindings for these variables: | |
659 | ||
b1b12a8e | 660 | @defvar revert-buffer-function |
2e00781a RS |
661 | The value of this variable is the function to use to revert this buffer. |
662 | If non-@code{nil}, it is called as a function with no arguments to do | |
663 | the work of reverting. If the value is @code{nil}, reverting works the | |
664 | usual way. | |
665 | ||
666 | Modes such as Dired mode, in which the text being edited does not | |
667 | consist of a file's contents but can be regenerated in some other | |
29b677db | 668 | fashion, can give this variable a buffer-local value that is a function to |
2e00781a | 669 | regenerate the contents. |
b1b12a8e RS |
670 | @end defvar |
671 | ||
672 | @defvar revert-buffer-insert-file-contents-function | |
8241495d | 673 | The value of this variable, if non-@code{nil}, specifies the function to use to |
bfe721d1 KH |
674 | insert the updated contents when reverting this buffer. The function |
675 | receives two arguments: first the file name to use; second, @code{t} if | |
676 | the user has asked to read the auto-save file. | |
29b677db RS |
677 | |
678 | The reason for a mode to set this variable instead of | |
679 | @code{revert-buffer-function} is to avoid duplicating or replacing the | |
680 | rest of what @code{revert-buffer} does: asking for confirmation, | |
681 | clearing the undo list, deciding the proper major mode, and running the | |
682 | hooks listed below. | |
b1b12a8e RS |
683 | @end defvar |
684 | ||
685 | @defvar before-revert-hook | |
8241495d | 686 | This normal hook is run by @code{revert-buffer} before |
b1b12a8e RS |
687 | inserting the modified contents---but only if |
688 | @code{revert-buffer-function} is @code{nil}. | |
b1b12a8e RS |
689 | @end defvar |
690 | ||
691 | @defvar after-revert-hook | |
8241495d | 692 | This normal hook is run by @code{revert-buffer} after inserting |
b1b12a8e RS |
693 | the modified contents---but only if @code{revert-buffer-function} is |
694 | @code{nil}. | |
b1b12a8e | 695 | @end defvar |