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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
73b0cd50 | 3 | @c Copyright (C) 1990-1995, 1999, 2001-2011 Free Software Foundation, Inc. |
b8d4c8d0 | 4 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 5 | @setfilename ../../info/backups |
b8d4c8d0 GM |
6 | @node Backups and Auto-Saving, Buffers, Files, Top |
7 | @chapter Backups and Auto-Saving | |
8 | @cindex backups and auto-saving | |
9 | ||
10 | Backup files and auto-save files are two methods by which Emacs tries | |
11 | to protect the user from the consequences of crashes or of the user's | |
12 | own errors. Auto-saving preserves the text from earlier in the current | |
13 | editing session; backup files preserve file contents prior to the | |
14 | current session. | |
15 | ||
16 | @menu | |
17 | * Backup Files:: How backup files are made; how their names are chosen. | |
18 | * Auto-Saving:: How auto-save files are made; how their names are chosen. | |
19 | * Reverting:: @code{revert-buffer}, and how to customize what it does. | |
20 | @end menu | |
21 | ||
22 | @node Backup Files | |
23 | @section Backup Files | |
24 | @cindex backup file | |
25 | ||
26 | A @dfn{backup file} is a copy of the old contents of a file you are | |
27 | editing. Emacs makes a backup file the first time you save a buffer | |
28 | into its visited file. Thus, normally, the backup file contains the | |
29 | contents of the file as it was before the current editing session. | |
30 | The contents of the backup file normally remain unchanged once it | |
31 | exists. | |
32 | ||
33 | Backups are usually made by renaming the visited file to a new name. | |
34 | Optionally, you can specify that backup files should be made by copying | |
35 | the visited file. This choice makes a difference for files with | |
36 | multiple names; it also can affect whether the edited file remains owned | |
37 | by the original owner or becomes owned by the user editing it. | |
38 | ||
39 | By default, Emacs makes a single backup file for each file edited. | |
40 | You can alternatively request numbered backups; then each new backup | |
41 | file gets a new name. You can delete old numbered backups when you | |
42 | don't want them any more, or Emacs can delete them automatically. | |
43 | ||
44 | @menu | |
45 | * Making Backups:: How Emacs makes backup files, and when. | |
46 | * Rename or Copy:: Two alternatives: renaming the old file or copying it. | |
47 | * Numbered Backups:: Keeping multiple backups for each source file. | |
48 | * Backup Names:: How backup file names are computed; customization. | |
49 | @end menu | |
50 | ||
51 | @node Making Backups | |
52 | @subsection Making Backup Files | |
53 | ||
54 | @defun backup-buffer | |
55 | This function makes a backup of the file visited by the current | |
56 | buffer, if appropriate. It is called by @code{save-buffer} before | |
57 | saving the buffer the first time. | |
58 | ||
59 | If a backup was made by renaming, the return value is a cons cell of | |
60 | the form (@var{modes} . @var{backupname}), where @var{modes} are the | |
61 | mode bits of the original file, as returned by @code{file-modes} | |
62 | (@pxref{File Attributes,, Other Information about Files}), and | |
63 | @var{backupname} is the name of the backup. In all other cases, that | |
64 | is, if a backup was made by copying or if no backup was made, this | |
65 | function returns @code{nil}. | |
66 | @end defun | |
67 | ||
68 | @defvar buffer-backed-up | |
69 | This buffer-local variable says whether this buffer's file has | |
70 | been backed up on account of this buffer. If it is non-@code{nil}, | |
71 | the backup file has been written. Otherwise, the file should be backed | |
72 | up when it is next saved (if backups are enabled). This is a | |
73 | permanent local; @code{kill-all-local-variables} does not alter@tie{}it. | |
74 | @end defvar | |
75 | ||
76 | @defopt make-backup-files | |
77 | This variable determines whether or not to make backup files. If it | |
78 | is non-@code{nil}, then Emacs creates a backup of each file when it is | |
79 | saved for the first time---provided that @code{backup-inhibited} | |
80 | is @code{nil} (see below). | |
81 | ||
82 | The following example shows how to change the @code{make-backup-files} | |
83 | variable only in the Rmail buffers and not elsewhere. Setting it | |
84 | @code{nil} stops Emacs from making backups of these files, which may | |
85 | save disk space. (You would put this code in your init file.) | |
86 | ||
87 | @smallexample | |
88 | @group | |
89 | (add-hook 'rmail-mode-hook | |
769741e3 SM |
90 | (lambda () |
91 | (set (make-local-variable 'make-backup-files) nil))) | |
b8d4c8d0 GM |
92 | @end group |
93 | @end smallexample | |
94 | @end defopt | |
95 | ||
96 | @defvar backup-enable-predicate | |
97 | This variable's value is a function to be called on certain occasions to | |
98 | decide whether a file should have backup files. The function receives | |
99 | one argument, an absolute file name to consider. If the function returns | |
100 | @code{nil}, backups are disabled for that file. Otherwise, the other | |
101 | variables in this section say whether and how to make backups. | |
102 | ||
103 | @findex normal-backup-enable-predicate | |
104 | The default value is @code{normal-backup-enable-predicate}, which checks | |
105 | for files in @code{temporary-file-directory} and | |
106 | @code{small-temporary-file-directory}. | |
107 | @end defvar | |
108 | ||
109 | @defvar backup-inhibited | |
110 | If this variable is non-@code{nil}, backups are inhibited. It records | |
111 | the result of testing @code{backup-enable-predicate} on the visited file | |
112 | name. It can also coherently be used by other mechanisms that inhibit | |
113 | backups based on which file is visited. For example, VC sets this | |
114 | variable non-@code{nil} to prevent making backups for files managed | |
115 | with a version control system. | |
116 | ||
117 | This is a permanent local, so that changing the major mode does not lose | |
118 | its value. Major modes should not set this variable---they should set | |
119 | @code{make-backup-files} instead. | |
120 | @end defvar | |
121 | ||
01f17ae2 | 122 | @defopt backup-directory-alist |
b8d4c8d0 GM |
123 | This variable's value is an alist of filename patterns and backup |
124 | directory names. Each element looks like | |
125 | @smallexample | |
126 | (@var{regexp} . @var{directory}) | |
127 | @end smallexample | |
128 | ||
129 | @noindent | |
130 | Backups of files with names matching @var{regexp} will be made in | |
131 | @var{directory}. @var{directory} may be relative or absolute. If it is | |
132 | absolute, so that all matching files are backed up into the same | |
133 | directory, the file names in this directory will be the full name of the | |
134 | file backed up with all directory separators changed to @samp{!} to | |
135 | prevent clashes. This will not work correctly if your filesystem | |
136 | truncates the resulting name. | |
137 | ||
138 | For the common case of all backups going into one directory, the alist | |
139 | should contain a single element pairing @samp{"."} with the appropriate | |
140 | directory name. | |
141 | ||
142 | If this variable is @code{nil}, or it fails to match a filename, the | |
143 | backup is made in the original file's directory. | |
144 | ||
145 | On MS-DOS filesystems without long names this variable is always | |
146 | ignored. | |
01f17ae2 | 147 | @end defopt |
b8d4c8d0 | 148 | |
01f17ae2 | 149 | @defopt make-backup-file-name-function |
b8d4c8d0 GM |
150 | This variable's value is a function to use for making backups instead |
151 | of the default @code{make-backup-file-name}. A value of @code{nil} | |
152 | gives the default @code{make-backup-file-name} behavior. | |
153 | @xref{Backup Names,, Naming Backup Files}. | |
154 | ||
155 | This could be buffer-local to do something special for specific | |
156 | files. If you define it, you may need to change | |
157 | @code{backup-file-name-p} and @code{file-name-sans-versions} too. | |
01f17ae2 | 158 | @end defopt |
b8d4c8d0 GM |
159 | |
160 | ||
161 | @node Rename or Copy | |
162 | @subsection Backup by Renaming or by Copying? | |
163 | @cindex backup files, rename or copy | |
164 | ||
165 | There are two ways that Emacs can make a backup file: | |
166 | ||
167 | @itemize @bullet | |
168 | @item | |
169 | Emacs can rename the original file so that it becomes a backup file, and | |
170 | then write the buffer being saved into a new file. After this | |
171 | procedure, any other names (i.e., hard links) of the original file now | |
172 | refer to the backup file. The new file is owned by the user doing the | |
173 | editing, and its group is the default for new files written by the user | |
174 | in that directory. | |
175 | ||
176 | @item | |
177 | Emacs can copy the original file into a backup file, and then overwrite | |
178 | the original file with new contents. After this procedure, any other | |
179 | names (i.e., hard links) of the original file continue to refer to the | |
180 | current (updated) version of the file. The file's owner and group will | |
181 | be unchanged. | |
182 | @end itemize | |
183 | ||
184 | The first method, renaming, is the default. | |
185 | ||
186 | The variable @code{backup-by-copying}, if non-@code{nil}, says to use | |
187 | the second method, which is to copy the original file and overwrite it | |
188 | with the new buffer contents. The variable @code{file-precious-flag}, | |
189 | if non-@code{nil}, also has this effect (as a sideline of its main | |
190 | significance). @xref{Saving Buffers}. | |
191 | ||
192 | @defopt backup-by-copying | |
193 | If this variable is non-@code{nil}, Emacs always makes backup files by | |
194 | copying. | |
195 | @end defopt | |
196 | ||
197 | The following three variables, when non-@code{nil}, cause the second | |
198 | method to be used in certain special cases. They have no effect on the | |
199 | treatment of files that don't fall into the special cases. | |
200 | ||
201 | @defopt backup-by-copying-when-linked | |
202 | If this variable is non-@code{nil}, Emacs makes backups by copying for | |
203 | files with multiple names (hard links). | |
204 | ||
205 | This variable is significant only if @code{backup-by-copying} is | |
206 | @code{nil}, since copying is always used when that variable is | |
207 | non-@code{nil}. | |
208 | @end defopt | |
209 | ||
210 | @defopt backup-by-copying-when-mismatch | |
211 | If this variable is non-@code{nil}, Emacs makes backups by copying in cases | |
212 | where renaming would change either the owner or the group of the file. | |
213 | ||
214 | The value has no effect when renaming would not alter the owner or | |
215 | group of the file; that is, for files which are owned by the user and | |
216 | whose group matches the default for a new file created there by the | |
217 | user. | |
218 | ||
219 | This variable is significant only if @code{backup-by-copying} is | |
220 | @code{nil}, since copying is always used when that variable is | |
221 | non-@code{nil}. | |
222 | @end defopt | |
223 | ||
224 | @defopt backup-by-copying-when-privileged-mismatch | |
225 | This variable, if non-@code{nil}, specifies the same behavior as | |
226 | @code{backup-by-copying-when-mismatch}, but only for certain user-id | |
227 | values: namely, those less than or equal to a certain number. You set | |
228 | this variable to that number. | |
229 | ||
230 | Thus, if you set @code{backup-by-copying-when-privileged-mismatch} | |
231 | to 0, backup by copying is done for the superuser only, | |
232 | when necessary to prevent a change in the owner of the file. | |
233 | ||
234 | The default is 200. | |
235 | @end defopt | |
236 | ||
237 | @node Numbered Backups | |
238 | @subsection Making and Deleting Numbered Backup Files | |
239 | ||
240 | If a file's name is @file{foo}, the names of its numbered backup | |
241 | versions are @file{foo.~@var{v}~}, for various integers @var{v}, like | |
242 | this: @file{foo.~1~}, @file{foo.~2~}, @file{foo.~3~}, @dots{}, | |
243 | @file{foo.~259~}, and so on. | |
244 | ||
245 | @defopt version-control | |
246 | This variable controls whether to make a single non-numbered backup | |
247 | file or multiple numbered backups. | |
248 | ||
249 | @table @asis | |
250 | @item @code{nil} | |
251 | Make numbered backups if the visited file already has numbered backups; | |
252 | otherwise, do not. This is the default. | |
253 | ||
254 | @item @code{never} | |
255 | Do not make numbered backups. | |
256 | ||
257 | @item @var{anything else} | |
258 | Make numbered backups. | |
259 | @end table | |
260 | @end defopt | |
261 | ||
262 | The use of numbered backups ultimately leads to a large number of | |
263 | backup versions, which must then be deleted. Emacs can do this | |
264 | automatically or it can ask the user whether to delete them. | |
265 | ||
266 | @defopt kept-new-versions | |
267 | The value of this variable is the number of newest versions to keep | |
268 | when a new numbered backup is made. The newly made backup is included | |
269 | in the count. The default value is@tie{}2. | |
270 | @end defopt | |
271 | ||
272 | @defopt kept-old-versions | |
273 | The value of this variable is the number of oldest versions to keep | |
274 | when a new numbered backup is made. The default value is@tie{}2. | |
275 | @end defopt | |
276 | ||
277 | If there are backups numbered 1, 2, 3, 5, and 7, and both of these | |
278 | variables have the value 2, then the backups numbered 1 and 2 are kept | |
279 | as old versions and those numbered 5 and 7 are kept as new versions; | |
280 | backup version 3 is excess. The function @code{find-backup-file-name} | |
281 | (@pxref{Backup Names}) is responsible for determining which backup | |
282 | versions to delete, but does not delete them itself. | |
283 | ||
284 | @defopt delete-old-versions | |
285 | If this variable is @code{t}, then saving a file deletes excess | |
286 | backup versions silently. If it is @code{nil}, that means | |
287 | to ask for confirmation before deleting excess backups. | |
288 | Otherwise, they are not deleted at all. | |
289 | @end defopt | |
290 | ||
291 | @defopt dired-kept-versions | |
292 | This variable specifies how many of the newest backup versions to keep | |
293 | in the Dired command @kbd{.} (@code{dired-clean-directory}). That's the | |
294 | same thing @code{kept-new-versions} specifies when you make a new backup | |
295 | file. The default is@tie{}2. | |
296 | @end defopt | |
297 | ||
298 | @node Backup Names | |
299 | @subsection Naming Backup Files | |
300 | ||
301 | The functions in this section are documented mainly because you can | |
302 | customize the naming conventions for backup files by redefining them. | |
303 | If you change one, you probably need to change the rest. | |
304 | ||
305 | @defun backup-file-name-p filename | |
306 | This function returns a non-@code{nil} value if @var{filename} is a | |
307 | possible name for a backup file. It just checks the name, not whether | |
308 | a file with the name @var{filename} exists. | |
309 | ||
310 | @smallexample | |
311 | @group | |
312 | (backup-file-name-p "foo") | |
313 | @result{} nil | |
314 | @end group | |
315 | @group | |
316 | (backup-file-name-p "foo~") | |
317 | @result{} 3 | |
318 | @end group | |
319 | @end smallexample | |
320 | ||
321 | The standard definition of this function is as follows: | |
322 | ||
323 | @smallexample | |
324 | @group | |
325 | (defun backup-file-name-p (file) | |
326 | "Return non-nil if FILE is a backup file \ | |
327 | name (numeric or not)..." | |
328 | (string-match "~\\'" file)) | |
329 | @end group | |
330 | @end smallexample | |
331 | ||
332 | @noindent | |
333 | Thus, the function returns a non-@code{nil} value if the file name ends | |
334 | with a @samp{~}. (We use a backslash to split the documentation | |
335 | string's first line into two lines in the text, but produce just one | |
336 | line in the string itself.) | |
337 | ||
338 | This simple expression is placed in a separate function to make it easy | |
339 | to redefine for customization. | |
340 | @end defun | |
341 | ||
342 | @defun make-backup-file-name filename | |
343 | This function returns a string that is the name to use for a | |
344 | non-numbered backup file for file @var{filename}. On Unix, this is just | |
345 | @var{filename} with a tilde appended. | |
346 | ||
347 | The standard definition of this function, on most operating systems, is | |
348 | as follows: | |
349 | ||
350 | @smallexample | |
351 | @group | |
352 | (defun make-backup-file-name (file) | |
353 | "Create the non-numeric backup file name for FILE..." | |
354 | (concat file "~")) | |
355 | @end group | |
356 | @end smallexample | |
357 | ||
358 | You can change the backup-file naming convention by redefining this | |
359 | function. The following example redefines @code{make-backup-file-name} | |
360 | to prepend a @samp{.} in addition to appending a tilde: | |
361 | ||
362 | @smallexample | |
363 | @group | |
364 | (defun make-backup-file-name (filename) | |
365 | (expand-file-name | |
366 | (concat "." (file-name-nondirectory filename) "~") | |
367 | (file-name-directory filename))) | |
368 | @end group | |
369 | ||
370 | @group | |
371 | (make-backup-file-name "backups.texi") | |
372 | @result{} ".backups.texi~" | |
373 | @end group | |
374 | @end smallexample | |
375 | ||
376 | Some parts of Emacs, including some Dired commands, assume that backup | |
377 | file names end with @samp{~}. If you do not follow that convention, it | |
378 | will not cause serious problems, but these commands may give | |
379 | less-than-desirable results. | |
380 | @end defun | |
381 | ||
382 | @defun find-backup-file-name filename | |
383 | This function computes the file name for a new backup file for | |
384 | @var{filename}. It may also propose certain existing backup files for | |
385 | deletion. @code{find-backup-file-name} returns a list whose @sc{car} is | |
386 | the name for the new backup file and whose @sc{cdr} is a list of backup | |
387 | files whose deletion is proposed. The value can also be @code{nil}, | |
388 | which means not to make a backup. | |
389 | ||
390 | Two variables, @code{kept-old-versions} and @code{kept-new-versions}, | |
391 | determine which backup versions should be kept. This function keeps | |
392 | those versions by excluding them from the @sc{cdr} of the value. | |
393 | @xref{Numbered Backups}. | |
394 | ||
395 | In this example, the value says that @file{~rms/foo.~5~} is the name | |
396 | to use for the new backup file, and @file{~rms/foo.~3~} is an ``excess'' | |
397 | version that the caller should consider deleting now. | |
398 | ||
399 | @smallexample | |
400 | @group | |
401 | (find-backup-file-name "~rms/foo") | |
402 | @result{} ("~rms/foo.~5~" "~rms/foo.~3~") | |
403 | @end group | |
404 | @end smallexample | |
405 | @end defun | |
406 | ||
407 | @c Emacs 19 feature | |
408 | @defun file-newest-backup filename | |
409 | This function returns the name of the most recent backup file for | |
410 | @var{filename}, or @code{nil} if that file has no backup files. | |
411 | ||
412 | Some file comparison commands use this function so that they can | |
413 | automatically compare a file with its most recent backup. | |
414 | @end defun | |
415 | ||
416 | @node Auto-Saving | |
417 | @section Auto-Saving | |
418 | @c @cindex auto-saving Lots of symbols starting with auto-save here. | |
419 | ||
420 | Emacs periodically saves all files that you are visiting; this is | |
421 | called @dfn{auto-saving}. Auto-saving prevents you from losing more | |
422 | than a limited amount of work if the system crashes. By default, | |
423 | auto-saves happen every 300 keystrokes, or after around 30 seconds of | |
424 | idle time. @xref{Auto Save, Auto Save, Auto-Saving: Protection Against | |
425 | Disasters, emacs, The GNU Emacs Manual}, for information on auto-save | |
426 | for users. Here we describe the functions used to implement auto-saving | |
427 | and the variables that control them. | |
428 | ||
429 | @defvar buffer-auto-save-file-name | |
430 | This buffer-local variable is the name of the file used for | |
431 | auto-saving the current buffer. It is @code{nil} if the buffer | |
432 | should not be auto-saved. | |
433 | ||
434 | @example | |
435 | @group | |
436 | buffer-auto-save-file-name | |
437 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" | |
438 | @end group | |
439 | @end example | |
440 | @end defvar | |
441 | ||
442 | @deffn Command auto-save-mode arg | |
443 | When used interactively without an argument, this command is a toggle | |
444 | switch: it turns on auto-saving of the current buffer if it is off, and | |
445 | vice versa. With an argument @var{arg}, the command turns auto-saving | |
446 | on if the value of @var{arg} is @code{t}, a nonempty list, or a positive | |
447 | integer. Otherwise, it turns auto-saving off. | |
448 | @end deffn | |
449 | ||
450 | @defun auto-save-file-name-p filename | |
451 | This function returns a non-@code{nil} value if @var{filename} is a | |
452 | string that could be the name of an auto-save file. It assumes | |
453 | the usual naming convention for auto-save files: a name that | |
454 | begins and ends with hash marks (@samp{#}) is a possible auto-save file | |
455 | name. The argument @var{filename} should not contain a directory part. | |
456 | ||
457 | @example | |
458 | @group | |
459 | (make-auto-save-file-name) | |
460 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" | |
461 | @end group | |
462 | @group | |
463 | (auto-save-file-name-p "#backups.texi#") | |
464 | @result{} 0 | |
465 | @end group | |
466 | @group | |
467 | (auto-save-file-name-p "backups.texi") | |
468 | @result{} nil | |
469 | @end group | |
470 | @end example | |
471 | ||
472 | The standard definition of this function is as follows: | |
473 | ||
474 | @example | |
475 | @group | |
476 | (defun auto-save-file-name-p (filename) | |
477 | "Return non-nil if FILENAME can be yielded by..." | |
478 | (string-match "^#.*#$" filename)) | |
479 | @end group | |
480 | @end example | |
481 | ||
482 | This function exists so that you can customize it if you wish to | |
483 | change the naming convention for auto-save files. If you redefine it, | |
484 | be sure to redefine the function @code{make-auto-save-file-name} | |
485 | correspondingly. | |
486 | @end defun | |
487 | ||
488 | @defun make-auto-save-file-name | |
489 | This function returns the file name to use for auto-saving the current | |
490 | buffer. This is just the file name with hash marks (@samp{#}) prepended | |
491 | and appended to it. This function does not look at the variable | |
492 | @code{auto-save-visited-file-name} (described below); callers of this | |
493 | function should check that variable first. | |
494 | ||
495 | @example | |
496 | @group | |
497 | (make-auto-save-file-name) | |
498 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" | |
499 | @end group | |
500 | @end example | |
501 | ||
502 | Here is a simplified version of the standard definition of this | |
503 | function: | |
504 | ||
505 | @example | |
506 | @group | |
507 | (defun make-auto-save-file-name () | |
508 | "Return file name to use for auto-saves \ | |
509 | of current buffer.." | |
510 | (if buffer-file-name | |
511 | @end group | |
512 | @group | |
513 | (concat | |
514 | (file-name-directory buffer-file-name) | |
515 | "#" | |
516 | (file-name-nondirectory buffer-file-name) | |
517 | "#") | |
518 | (expand-file-name | |
519 | (concat "#%" (buffer-name) "#")))) | |
520 | @end group | |
521 | @end example | |
522 | ||
523 | This exists as a separate function so that you can redefine it to | |
524 | customize the naming convention for auto-save files. Be sure to | |
525 | change @code{auto-save-file-name-p} in a corresponding way. | |
526 | @end defun | |
527 | ||
528 | @defopt auto-save-visited-file-name | |
529 | If this variable is non-@code{nil}, Emacs auto-saves buffers in | |
530 | the files they are visiting. That is, the auto-save is done in the same | |
531 | file that you are editing. Normally, this variable is @code{nil}, so | |
532 | auto-save files have distinct names that are created by | |
533 | @code{make-auto-save-file-name}. | |
534 | ||
535 | When you change the value of this variable, the new value does not take | |
536 | effect in an existing buffer until the next time auto-save mode is | |
537 | reenabled in it. If auto-save mode is already enabled, auto-saves | |
538 | continue to go in the same file name until @code{auto-save-mode} is | |
539 | called again. | |
540 | @end defopt | |
541 | ||
542 | @defun recent-auto-save-p | |
543 | This function returns @code{t} if the current buffer has been | |
544 | auto-saved since the last time it was read in or saved. | |
545 | @end defun | |
546 | ||
547 | @defun set-buffer-auto-saved | |
548 | This function marks the current buffer as auto-saved. The buffer will | |
549 | not be auto-saved again until the buffer text is changed again. The | |
550 | function returns @code{nil}. | |
551 | @end defun | |
552 | ||
553 | @defopt auto-save-interval | |
554 | The value of this variable specifies how often to do auto-saving, in | |
555 | terms of number of input events. Each time this many additional input | |
556 | events are read, Emacs does auto-saving for all buffers in which that is | |
557 | enabled. Setting this to zero disables autosaving based on the | |
558 | number of characters typed. | |
559 | @end defopt | |
560 | ||
561 | @defopt auto-save-timeout | |
562 | The value of this variable is the number of seconds of idle time that | |
563 | should cause auto-saving. Each time the user pauses for this long, | |
564 | Emacs does auto-saving for all buffers in which that is enabled. (If | |
565 | the current buffer is large, the specified timeout is multiplied by a | |
566 | factor that increases as the size increases; for a million-byte | |
567 | buffer, the factor is almost 4.) | |
568 | ||
569 | If the value is zero or @code{nil}, then auto-saving is not done as a | |
570 | result of idleness, only after a certain number of input events as | |
571 | specified by @code{auto-save-interval}. | |
572 | @end defopt | |
573 | ||
574 | @defvar auto-save-hook | |
575 | This normal hook is run whenever an auto-save is about to happen. | |
576 | @end defvar | |
577 | ||
578 | @defopt auto-save-default | |
579 | If this variable is non-@code{nil}, buffers that are visiting files | |
580 | have auto-saving enabled by default. Otherwise, they do not. | |
581 | @end defopt | |
582 | ||
583 | @deffn Command do-auto-save &optional no-message current-only | |
584 | This function auto-saves all buffers that need to be auto-saved. It | |
585 | saves all buffers for which auto-saving is enabled and that have been | |
586 | changed since the previous auto-save. | |
587 | ||
588 | If any buffers are auto-saved, @code{do-auto-save} normally displays a | |
589 | message saying @samp{Auto-saving...} in the echo area while | |
590 | auto-saving is going on. However, if @var{no-message} is | |
591 | non-@code{nil}, the message is inhibited. | |
592 | ||
593 | If @var{current-only} is non-@code{nil}, only the current buffer | |
594 | is auto-saved. | |
595 | @end deffn | |
596 | ||
597 | @defun delete-auto-save-file-if-necessary &optional force | |
598 | This function deletes the current buffer's auto-save file if | |
599 | @code{delete-auto-save-files} is non-@code{nil}. It is called every | |
600 | time a buffer is saved. | |
601 | ||
602 | Unless @var{force} is non-@code{nil}, this function only deletes the | |
603 | file if it was written by the current Emacs session since the last | |
604 | true save. | |
605 | @end defun | |
606 | ||
607 | @defopt delete-auto-save-files | |
608 | This variable is used by the function | |
609 | @code{delete-auto-save-file-if-necessary}. If it is non-@code{nil}, | |
610 | Emacs deletes auto-save files when a true save is done (in the visited | |
611 | file). This saves disk space and unclutters your directory. | |
612 | @end defopt | |
613 | ||
614 | @defun rename-auto-save-file | |
615 | This function adjusts the current buffer's auto-save file name if the | |
616 | visited file name has changed. It also renames an existing auto-save | |
617 | file, if it was made in the current Emacs session. If the visited | |
618 | file name has not changed, this function does nothing. | |
619 | @end defun | |
620 | ||
621 | @defvar buffer-saved-size | |
622 | The value of this buffer-local variable is the length of the current | |
623 | buffer, when it was last read in, saved, or auto-saved. This is | |
624 | used to detect a substantial decrease in size, and turn off auto-saving | |
625 | in response. | |
626 | ||
627 | If it is @minus{}1, that means auto-saving is temporarily shut off in | |
628 | this buffer due to a substantial decrease in size. Explicitly saving | |
629 | the buffer stores a positive value in this variable, thus reenabling | |
630 | auto-saving. Turning auto-save mode off or on also updates this | |
631 | variable, so that the substantial decrease in size is forgotten. | |
137987ab RS |
632 | |
633 | If it is @minus{}2, that means this buffer should disregard changes in | |
634 | buffer size; in particular, it should not shut off auto-saving | |
635 | temporarily due to changes in buffer size. | |
b8d4c8d0 GM |
636 | @end defvar |
637 | ||
638 | @defvar auto-save-list-file-name | |
639 | This variable (if non-@code{nil}) specifies a file for recording the | |
640 | names of all the auto-save files. Each time Emacs does auto-saving, it | |
641 | writes two lines into this file for each buffer that has auto-saving | |
642 | enabled. The first line gives the name of the visited file (it's empty | |
643 | if the buffer has none), and the second gives the name of the auto-save | |
644 | file. | |
645 | ||
646 | When Emacs exits normally, it deletes this file; if Emacs crashes, you | |
647 | can look in the file to find all the auto-save files that might contain | |
648 | work that was otherwise lost. The @code{recover-session} command uses | |
649 | this file to find them. | |
650 | ||
651 | The default name for this file specifies your home directory and starts | |
652 | with @samp{.saves-}. It also contains the Emacs process @acronym{ID} and the | |
653 | host name. | |
654 | @end defvar | |
655 | ||
01f17ae2 | 656 | @defopt auto-save-list-file-prefix |
b8d4c8d0 GM |
657 | After Emacs reads your init file, it initializes |
658 | @code{auto-save-list-file-name} (if you have not already set it | |
659 | non-@code{nil}) based on this prefix, adding the host name and process | |
660 | ID. If you set this to @code{nil} in your init file, then Emacs does | |
661 | not initialize @code{auto-save-list-file-name}. | |
01f17ae2 | 662 | @end defopt |
b8d4c8d0 GM |
663 | |
664 | @node Reverting | |
665 | @section Reverting | |
666 | ||
667 | If you have made extensive changes to a file and then change your mind | |
668 | about them, you can get rid of them by reading in the previous version | |
669 | of the file with the @code{revert-buffer} command. @xref{Reverting, , | |
670 | Reverting a Buffer, emacs, The GNU Emacs Manual}. | |
671 | ||
672 | @deffn Command revert-buffer &optional ignore-auto noconfirm preserve-modes | |
673 | This command replaces the buffer text with the text of the visited | |
674 | file on disk. This action undoes all changes since the file was visited | |
675 | or saved. | |
676 | ||
677 | By default, if the latest auto-save file is more recent than the visited | |
678 | file, and the argument @var{ignore-auto} is @code{nil}, | |
679 | @code{revert-buffer} asks the user whether to use that auto-save | |
680 | instead. When you invoke this command interactively, @var{ignore-auto} | |
681 | is @code{t} if there is no numeric prefix argument; thus, the | |
682 | interactive default is not to check the auto-save file. | |
683 | ||
684 | Normally, @code{revert-buffer} asks for confirmation before it changes | |
685 | the buffer; but if the argument @var{noconfirm} is non-@code{nil}, | |
686 | @code{revert-buffer} does not ask for confirmation. | |
687 | ||
688 | Normally, this command reinitializes the buffer's major and minor modes | |
689 | using @code{normal-mode}. But if @var{preserve-modes} is | |
690 | non-@code{nil}, the modes remain unchanged. | |
691 | ||
692 | Reverting tries to preserve marker positions in the buffer by using the | |
693 | replacement feature of @code{insert-file-contents}. If the buffer | |
694 | contents and the file contents are identical before the revert | |
695 | operation, reverting preserves all the markers. If they are not | |
696 | identical, reverting does change the buffer; in that case, it preserves | |
697 | the markers in the unchanged text (if any) at the beginning and end of | |
698 | the buffer. Preserving any additional markers would be problematical. | |
699 | @end deffn | |
700 | ||
701 | You can customize how @code{revert-buffer} does its work by setting | |
702 | the variables described in the rest of this section. | |
703 | ||
704 | @defopt revert-without-query | |
705 | This variable holds a list of files that should be reverted without | |
706 | query. The value is a list of regular expressions. If the visited file | |
707 | name matches one of these regular expressions, and the file has changed | |
708 | on disk but the buffer is not modified, then @code{revert-buffer} | |
709 | reverts the file without asking the user for confirmation. | |
710 | @end defopt | |
711 | ||
712 | Some major modes customize @code{revert-buffer} by making | |
713 | buffer-local bindings for these variables: | |
714 | ||
715 | @defvar revert-buffer-function | |
716 | @anchor{Definition of revert-buffer-function} | |
717 | The value of this variable is the function to use to revert this | |
718 | buffer. If non-@code{nil}, it should be a function with two optional | |
719 | arguments to do the work of reverting. The two optional arguments, | |
720 | @var{ignore-auto} and @var{noconfirm}, are the arguments that | |
721 | @code{revert-buffer} received. If the value is @code{nil}, reverting | |
722 | works the usual way. | |
723 | ||
724 | Modes such as Dired mode, in which the text being edited does not | |
725 | consist of a file's contents but can be regenerated in some other | |
726 | fashion, can give this variable a buffer-local value that is a function to | |
727 | regenerate the contents. | |
728 | @end defvar | |
729 | ||
730 | @defvar revert-buffer-insert-file-contents-function | |
731 | The value of this variable, if non-@code{nil}, specifies the function to use to | |
732 | insert the updated contents when reverting this buffer. The function | |
733 | receives two arguments: first the file name to use; second, @code{t} if | |
734 | the user has asked to read the auto-save file. | |
735 | ||
736 | The reason for a mode to set this variable instead of | |
737 | @code{revert-buffer-function} is to avoid duplicating or replacing the | |
738 | rest of what @code{revert-buffer} does: asking for confirmation, | |
739 | clearing the undo list, deciding the proper major mode, and running the | |
740 | hooks listed below. | |
741 | @end defvar | |
742 | ||
743 | @defvar before-revert-hook | |
744 | This normal hook is run by @code{revert-buffer} before | |
745 | inserting the modified contents---but only if | |
746 | @code{revert-buffer-function} is @code{nil}. | |
747 | @end defvar | |
748 | ||
749 | @defvar after-revert-hook | |
750 | This normal hook is run by @code{revert-buffer} after inserting | |
751 | the modified contents---but only if @code{revert-buffer-function} is | |
752 | @code{nil}. | |
753 | @end defvar |