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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
fd897522 | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1999 |
177c0ea7 | 4 | @c Free Software Foundation, Inc. |
b1b12a8e RS |
5 | @c See the file elisp.texi for copying conditions. |
6 | @setfilename ../info/backups | |
7 | @node Backups and Auto-Saving, Buffers, Files, Top | |
8 | @chapter 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 | ||
0680592c | 22 | @node Backup Files |
b1b12a8e RS |
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. Normally, this means that the backup file | |
29 | contains the contents of the file as it was before the current editing | |
30 | session. The contents of the backup file normally remain unchanged once | |
31 | it 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 | ||
0680592c | 51 | @node Making Backups |
b1b12a8e RS |
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 | @end defun | |
59 | ||
60 | @defvar buffer-backed-up | |
61 | This buffer-local variable indicates whether this buffer's file has | |
62 | been backed up on account of this buffer. If it is non-@code{nil}, then | |
63 | the backup file has been written. Otherwise, the file should be backed | |
2e00781a | 64 | up when it is next saved (if backups are enabled). This is a |
29b677db | 65 | permanent local; @code{kill-all-local-variables} does not alter it. |
b1b12a8e RS |
66 | @end defvar |
67 | ||
68 | @defopt make-backup-files | |
bfe721d1 | 69 | This variable determines whether or not to make backup files. If it |
b1b12a8e | 70 | is non-@code{nil}, then Emacs creates a backup of each file when it is |
bfe721d1 KH |
71 | saved for the first time---provided that @code{backup-inhibited} |
72 | is @code{nil} (see below). | |
b1b12a8e | 73 | |
bfe721d1 | 74 | The following example shows how to change the @code{make-backup-files} |
f9f59935 RS |
75 | variable only in the Rmail buffers and not elsewhere. Setting it |
76 | @code{nil} stops Emacs from making backups of these files, which may | |
a40d4712 | 77 | save disk space. (You would put this code in your init file.) |
b1b12a8e RS |
78 | |
79 | @smallexample | |
80 | @group | |
177c0ea7 | 81 | (add-hook 'rmail-mode-hook |
b1b12a8e | 82 | (function (lambda () |
177c0ea7 | 83 | (make-local-variable |
b1b12a8e RS |
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 | 96 | |
bae2aa40 DL |
97 | @findex normal-backup-enable-predicate |
98 | The default value is @code{normal-backup-enable-predicate}, which checks | |
99 | for files in @code{temporary-file-directory} and | |
100 | @code{small-temporary-file-directory}. | |
b1b12a8e RS |
101 | @end defvar |
102 | ||
103 | @defvar backup-inhibited | |
104 | If this variable is non-@code{nil}, backups are inhibited. It records | |
105 | the result of testing @code{backup-enable-predicate} on the visited file | |
106 | name. It can also coherently be used by other mechanisms that inhibit | |
bfe721d1 KH |
107 | backups based on which file is visited. For example, VC sets this |
108 | variable non-@code{nil} to prevent making backups for files managed | |
109 | with a version control system. | |
2e00781a | 110 | |
bfe721d1 KH |
111 | This is a permanent local, so that changing the major mode does not lose |
112 | its value. Major modes should not set this variable---they should set | |
2e00781a | 113 | @code{make-backup-files} instead. |
b1b12a8e RS |
114 | @end defvar |
115 | ||
bae2aa40 | 116 | @defvar backup-directory-alist |
87b3b129 | 117 | @tindex backup-directory-alist |
bae2aa40 DL |
118 | This variable's value is an alist of filename patterns and backup |
119 | directory names. Each element looks like | |
120 | @smallexample | |
121 | (@var{regexp} . @var{directory}) | |
122 | @end smallexample | |
123 | ||
124 | @noindent | |
125 | Backups of files with names matching @var{regexp} will be made in | |
126 | @var{directory}. @var{directory} may be relative or absolute. If it is | |
127 | absolute, so that all matching files are backed up into the same | |
128 | directory, the file names in this directory will be the full name of the | |
129 | file backed up with all directory separators changed to @samp{!} to | |
130 | prevent clashes. This will not work correctly if your filesystem | |
131 | truncates the resulting name. | |
132 | ||
133 | For the common case of all backups going into one directory, the alist | |
134 | should contain a single element pairing @samp{"."} with the appropriate | |
135 | directory name. | |
136 | ||
137 | If this variable is @code{nil}, or it fails to match a filename, the | |
138 | backup is made in the original file's directory. | |
139 | ||
140 | On MS-DOS filesystems without long names this variable is always | |
141 | ignored. | |
142 | @end defvar | |
143 | ||
144 | @defvar make-backup-file-name-function | |
87b3b129 | 145 | @tindex make-backup-file-name-function |
9a8dc0d3 RS |
146 | This variable's value is a function to use for making backups instead |
147 | of the default @code{make-backup-file-name}. A value of @code{nil} | |
148 | gives the default @code{make-backup-file-name} behaviour. | |
bae2aa40 | 149 | |
5bf6f93d | 150 | This could be buffer-local to do something special for specific |
bae2aa40 DL |
151 | files. If you define it, you may need to change |
152 | @code{backup-file-name-p} and @code{file-name-sans-versions} too. | |
153 | @end defvar | |
154 | ||
155 | ||
0680592c | 156 | @node Rename or Copy |
b1b12a8e RS |
157 | @subsection Backup by Renaming or by Copying? |
158 | @cindex backup files, how to make them | |
159 | ||
177c0ea7 | 160 | There are two ways that Emacs can make a backup file: |
b1b12a8e RS |
161 | |
162 | @itemize @bullet | |
163 | @item | |
164 | Emacs can rename the original file so that it becomes a backup file, and | |
165 | then write the buffer being saved into a new file. After this | |
166 | procedure, any other names (i.e., hard links) of the original file now | |
167 | refer to the backup file. The new file is owned by the user doing the | |
168 | editing, and its group is the default for new files written by the user | |
169 | in that directory. | |
170 | ||
171 | @item | |
172 | Emacs can copy the original file into a backup file, and then overwrite | |
173 | the original file with new contents. After this procedure, any other | |
f9f59935 RS |
174 | names (i.e., hard links) of the original file continue to refer to the |
175 | current (updated) version of the file. The file's owner and group will | |
176 | be unchanged. | |
b1b12a8e RS |
177 | @end itemize |
178 | ||
179 | The first method, renaming, is the default. | |
180 | ||
181 | The variable @code{backup-by-copying}, if non-@code{nil}, says to use | |
182 | the second method, which is to copy the original file and overwrite it | |
183 | with the new buffer contents. The variable @code{file-precious-flag}, | |
184 | if non-@code{nil}, also has this effect (as a sideline of its main | |
185 | significance). @xref{Saving Buffers}. | |
186 | ||
187 | @defvar backup-by-copying | |
188 | If this variable is non-@code{nil}, Emacs always makes backup files by | |
189 | copying. | |
190 | @end defvar | |
191 | ||
192 | The following two variables, when non-@code{nil}, cause the second | |
193 | method to be used in certain special cases. They have no effect on the | |
194 | treatment of files that don't fall into the special cases. | |
195 | ||
196 | @defvar backup-by-copying-when-linked | |
197 | If this variable is non-@code{nil}, Emacs makes backups by copying for | |
198 | files with multiple names (hard links). | |
199 | ||
200 | This variable is significant only if @code{backup-by-copying} is | |
201 | @code{nil}, since copying is always used when that variable is | |
202 | non-@code{nil}. | |
203 | @end defvar | |
204 | ||
205 | @defvar backup-by-copying-when-mismatch | |
206 | If this variable is non-@code{nil}, Emacs makes backups by copying in cases | |
207 | where renaming would change either the owner or the group of the file. | |
208 | ||
209 | The value has no effect when renaming would not alter the owner or | |
210 | group of the file; that is, for files which are owned by the user and | |
211 | whose group matches the default for a new file created there by the | |
212 | user. | |
213 | ||
214 | This variable is significant only if @code{backup-by-copying} is | |
215 | @code{nil}, since copying is always used when that variable is | |
216 | non-@code{nil}. | |
217 | @end defvar | |
218 | ||
8241495d RS |
219 | @defvar backup-by-copying-when-privileged-mismatch |
220 | This variable, if non-@code{nil}, specifies the same behavior as | |
221 | @code{backup-by-copying-when-mismatch}, but only for certain user-id | |
222 | values: namely, those less than or equal to a certain number. You set | |
223 | this variable to that number. | |
224 | ||
225 | Thus, if you set @code{backup-by-copying-when-privileged-mismatch} | |
226 | to 0, backup by copying is done for the superuser only, | |
227 | when necessary to prevent a change in the owner of the file. | |
228 | ||
229 | The default is 200. | |
230 | @end defvar | |
231 | ||
0680592c | 232 | @node Numbered Backups |
b1b12a8e RS |
233 | @subsection Making and Deleting Numbered Backup Files |
234 | ||
235 | If a file's name is @file{foo}, the names of its numbered backup | |
236 | versions are @file{foo.~@var{v}~}, for various integers @var{v}, like | |
237 | this: @file{foo.~1~}, @file{foo.~2~}, @file{foo.~3~}, @dots{}, | |
238 | @file{foo.~259~}, and so on. | |
239 | ||
240 | @defopt version-control | |
241 | This variable controls whether to make a single non-numbered backup | |
242 | file or multiple numbered backups. | |
243 | ||
244 | @table @asis | |
245 | @item @code{nil} | |
246 | Make numbered backups if the visited file already has numbered backups; | |
247 | otherwise, do not. | |
248 | ||
249 | @item @code{never} | |
250 | Do not make numbered backups. | |
251 | ||
252 | @item @var{anything else} | |
2e00781a | 253 | Make numbered backups. |
b1b12a8e RS |
254 | @end table |
255 | @end defopt | |
256 | ||
257 | The use of numbered backups ultimately leads to a large number of | |
258 | backup versions, which must then be deleted. Emacs can do this | |
2e00781a | 259 | automatically or it can ask the user whether to delete them. |
b1b12a8e RS |
260 | |
261 | @defopt kept-new-versions | |
2e00781a | 262 | The value of this variable is the number of newest versions to keep |
b1b12a8e RS |
263 | when a new numbered backup is made. The newly made backup is included |
264 | in the count. The default value is 2. | |
265 | @end defopt | |
266 | ||
267 | @defopt kept-old-versions | |
268 | The value of this variable is the number of oldest versions to keep | |
269 | when a new numbered backup is made. The default value is 2. | |
270 | @end defopt | |
271 | ||
272 | If there are backups numbered 1, 2, 3, 5, and 7, and both of these | |
273 | variables have the value 2, then the backups numbered 1 and 2 are kept | |
274 | as old versions and those numbered 5 and 7 are kept as new versions; | |
2e00781a | 275 | backup version 3 is excess. The function @code{find-backup-file-name} |
b1b12a8e RS |
276 | (@pxref{Backup Names}) is responsible for determining which backup |
277 | versions to delete, but does not delete them itself. | |
278 | ||
f9f59935 | 279 | @defopt delete-old-versions |
29b677db RS |
280 | If this variable is @code{t}, then saving a file deletes excess |
281 | backup versions silently. If it is @code{nil}, that means | |
282 | to ask for confirmation before deleting excess backups. | |
283 | Otherwise, they are not deleted at all. | |
b1b12a8e RS |
284 | @end defopt |
285 | ||
286 | @defopt dired-kept-versions | |
287 | This variable specifies how many of the newest backup versions to keep | |
288 | in the Dired command @kbd{.} (@code{dired-clean-directory}). That's the | |
2e00781a | 289 | same thing @code{kept-new-versions} specifies when you make a new backup |
b1b12a8e RS |
290 | file. The default value is 2. |
291 | @end defopt | |
292 | ||
0680592c | 293 | @node Backup Names |
b1b12a8e RS |
294 | @subsection Naming Backup Files |
295 | ||
296 | The functions in this section are documented mainly because you can | |
297 | customize the naming conventions for backup files by redefining them. | |
298 | If you change one, you probably need to change the rest. | |
299 | ||
300 | @defun backup-file-name-p filename | |
301 | This function returns a non-@code{nil} value if @var{filename} is a | |
302 | possible name for a backup file. A file with the name @var{filename} | |
303 | need not exist; the function just checks the name. | |
304 | ||
305 | @smallexample | |
306 | @group | |
307 | (backup-file-name-p "foo") | |
308 | @result{} nil | |
309 | @end group | |
310 | @group | |
311 | (backup-file-name-p "foo~") | |
312 | @result{} 3 | |
313 | @end group | |
314 | @end smallexample | |
315 | ||
316 | The standard definition of this function is as follows: | |
317 | ||
318 | @smallexample | |
319 | @group | |
320 | (defun backup-file-name-p (file) | |
321 | "Return non-nil if FILE is a backup file \ | |
322 | name (numeric or not)..." | |
29b677db | 323 | (string-match "~\\'" file)) |
b1b12a8e RS |
324 | @end group |
325 | @end smallexample | |
326 | ||
327 | @noindent | |
328 | Thus, the function returns a non-@code{nil} value if the file name ends | |
329 | with a @samp{~}. (We use a backslash to split the documentation | |
330 | string's first line into two lines in the text, but produce just one | |
331 | line in the string itself.) | |
332 | ||
333 | This simple expression is placed in a separate function to make it easy | |
334 | to redefine for customization. | |
335 | @end defun | |
336 | ||
337 | @defun make-backup-file-name filename | |
2e00781a | 338 | This function returns a string that is the name to use for a |
b1b12a8e RS |
339 | non-numbered backup file for file @var{filename}. On Unix, this is just |
340 | @var{filename} with a tilde appended. | |
341 | ||
a9f0a989 RS |
342 | The standard definition of this function, on most operating systems, is |
343 | as follows: | |
b1b12a8e RS |
344 | |
345 | @smallexample | |
346 | @group | |
347 | (defun make-backup-file-name (file) | |
29b677db | 348 | "Create the non-numeric backup file name for FILE..." |
b1b12a8e RS |
349 | (concat file "~")) |
350 | @end group | |
351 | @end smallexample | |
352 | ||
2e00781a | 353 | You can change the backup-file naming convention by redefining this |
b1b12a8e | 354 | function. The following example redefines @code{make-backup-file-name} |
2e00781a | 355 | to prepend a @samp{.} in addition to appending a tilde: |
b1b12a8e RS |
356 | |
357 | @smallexample | |
358 | @group | |
359 | (defun make-backup-file-name (filename) | |
a9f0a989 RS |
360 | (expand-file-name |
361 | (concat "." (file-name-nondirectory filename) "~") | |
362 | (file-name-directory filename))) | |
b1b12a8e RS |
363 | @end group |
364 | ||
365 | @group | |
366 | (make-backup-file-name "backups.texi") | |
367 | @result{} ".backups.texi~" | |
368 | @end group | |
369 | @end smallexample | |
a9f0a989 RS |
370 | |
371 | Some parts of Emacs, including some Dired commands, assume that backup | |
372 | file names end with @samp{~}. If you do not follow that convention, it | |
373 | will not cause serious problems, but these commands may give | |
374 | less-than-desirable results. | |
b1b12a8e RS |
375 | @end defun |
376 | ||
377 | @defun find-backup-file-name filename | |
378 | This function computes the file name for a new backup file for | |
379 | @var{filename}. It may also propose certain existing backup files for | |
380 | deletion. @code{find-backup-file-name} returns a list whose @sc{car} is | |
381 | the name for the new backup file and whose @sc{cdr} is a list of backup | |
382 | files whose deletion is proposed. | |
383 | ||
384 | Two variables, @code{kept-old-versions} and @code{kept-new-versions}, | |
385 | determine which backup versions should be kept. This function keeps | |
386 | those versions by excluding them from the @sc{cdr} of the value. | |
387 | @xref{Numbered Backups}. | |
388 | ||
389 | In this example, the value says that @file{~rms/foo.~5~} is the name | |
390 | to use for the new backup file, and @file{~rms/foo.~3~} is an ``excess'' | |
391 | version that the caller should consider deleting now. | |
392 | ||
393 | @smallexample | |
394 | @group | |
395 | (find-backup-file-name "~rms/foo") | |
396 | @result{} ("~rms/foo.~5~" "~rms/foo.~3~") | |
397 | @end group | |
398 | @end smallexample | |
399 | @end defun | |
400 | ||
401 | @c Emacs 19 feature | |
402 | @defun file-newest-backup filename | |
403 | This function returns the name of the most recent backup file for | |
2e00781a | 404 | @var{filename}, or @code{nil} if that file has no backup files. |
b1b12a8e | 405 | |
2e00781a RS |
406 | Some file comparison commands use this function so that they can |
407 | automatically compare a file with its most recent backup. | |
177c0ea7 | 408 | @end defun |
b1b12a8e | 409 | |
0680592c | 410 | @node Auto-Saving |
b1b12a8e RS |
411 | @section Auto-Saving |
412 | @cindex auto-saving | |
413 | ||
414 | Emacs periodically saves all files that you are visiting; this is | |
415 | called @dfn{auto-saving}. Auto-saving prevents you from losing more | |
416 | than a limited amount of work if the system crashes. By default, | |
417 | auto-saves happen every 300 keystrokes, or after around 30 seconds of | |
333c5fc5 | 418 | idle time. @xref{Auto Save, Auto Save, Auto-Saving: Protection Against |
b1b12a8e RS |
419 | Disasters, emacs, The GNU Emacs Manual}, for information on auto-save |
420 | for users. Here we describe the functions used to implement auto-saving | |
421 | and the variables that control them. | |
422 | ||
423 | @defvar buffer-auto-save-file-name | |
424 | This buffer-local variable is the name of the file used for | |
425 | auto-saving the current buffer. It is @code{nil} if the buffer | |
426 | should not be auto-saved. | |
427 | ||
428 | @example | |
429 | @group | |
430 | buffer-auto-save-file-name | |
29b677db | 431 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" |
b1b12a8e RS |
432 | @end group |
433 | @end example | |
434 | @end defvar | |
435 | ||
436 | @deffn Command auto-save-mode arg | |
437 | When used interactively without an argument, this command is a toggle | |
438 | switch: it turns on auto-saving of the current buffer if it is off, and | |
29b677db | 439 | vice versa. With an argument @var{arg}, the command turns auto-saving |
b1b12a8e RS |
440 | on if the value of @var{arg} is @code{t}, a nonempty list, or a positive |
441 | integer. Otherwise, it turns auto-saving off. | |
442 | @end deffn | |
443 | ||
444 | @defun auto-save-file-name-p filename | |
445 | This function returns a non-@code{nil} value if @var{filename} is a | |
8241495d RS |
446 | string that could be the name of an auto-save file. It assumes |
447 | the usual naming convention for auto-save files: a name that | |
b1b12a8e RS |
448 | begins and ends with hash marks (@samp{#}) is a possible auto-save file |
449 | name. The argument @var{filename} should not contain a directory part. | |
450 | ||
451 | @example | |
452 | @group | |
453 | (make-auto-save-file-name) | |
29b677db | 454 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" |
b1b12a8e RS |
455 | @end group |
456 | @group | |
29b677db | 457 | (auto-save-file-name-p "#backups.texi#") |
b1b12a8e RS |
458 | @result{} 0 |
459 | @end group | |
460 | @group | |
29b677db | 461 | (auto-save-file-name-p "backups.texi") |
b1b12a8e RS |
462 | @result{} nil |
463 | @end group | |
464 | @end example | |
465 | ||
466 | The standard definition of this function is as follows: | |
467 | ||
468 | @example | |
469 | @group | |
470 | (defun auto-save-file-name-p (filename) | |
471 | "Return non-nil if FILENAME can be yielded by..." | |
472 | (string-match "^#.*#$" filename)) | |
473 | @end group | |
474 | @end example | |
475 | ||
476 | This function exists so that you can customize it if you wish to | |
477 | change the naming convention for auto-save files. If you redefine it, | |
478 | be sure to redefine the function @code{make-auto-save-file-name} | |
479 | correspondingly. | |
480 | @end defun | |
481 | ||
482 | @defun make-auto-save-file-name | |
483 | This function returns the file name to use for auto-saving the current | |
86494bd5 KH |
484 | buffer. This is just the file name with hash marks (@samp{#}) prepended |
485 | and appended to it. This function does not look at the variable | |
8241495d RS |
486 | @code{auto-save-visited-file-name} (described below); callers of this |
487 | function should check that variable first. | |
b1b12a8e RS |
488 | |
489 | @example | |
490 | @group | |
491 | (make-auto-save-file-name) | |
29b677db | 492 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" |
b1b12a8e RS |
493 | @end group |
494 | @end example | |
495 | ||
496 | The standard definition of this function is as follows: | |
497 | ||
498 | @example | |
499 | @group | |
500 | (defun make-auto-save-file-name () | |
501 | "Return file name to use for auto-saves \ | |
29b677db | 502 | of current buffer.." |
b1b12a8e RS |
503 | (if buffer-file-name |
504 | @end group | |
505 | @group | |
506 | (concat | |
507 | (file-name-directory buffer-file-name) | |
508 | "#" | |
509 | (file-name-nondirectory buffer-file-name) | |
510 | "#") | |
511 | (expand-file-name | |
512 | (concat "#%" (buffer-name) "#")))) | |
513 | @end group | |
514 | @end example | |
515 | ||
516 | This exists as a separate function so that you can redefine it to | |
517 | customize the naming convention for auto-save files. Be sure to | |
518 | change @code{auto-save-file-name-p} in a corresponding way. | |
519 | @end defun | |
520 | ||
521 | @defvar auto-save-visited-file-name | |
522 | If this variable is non-@code{nil}, Emacs auto-saves buffers in | |
523 | the files they are visiting. That is, the auto-save is done in the same | |
2e00781a | 524 | file that you are editing. Normally, this variable is @code{nil}, so |
b1b12a8e RS |
525 | auto-save files have distinct names that are created by |
526 | @code{make-auto-save-file-name}. | |
527 | ||
8241495d RS |
528 | When you change the value of this variable, the new value does not take |
529 | effect in an existing buffer until the next time auto-save mode is | |
530 | reenabled in it. If auto-save mode is already enabled, auto-saves | |
531 | continue to go in the same file name until @code{auto-save-mode} is | |
532 | called again. | |
b1b12a8e RS |
533 | @end defvar |
534 | ||
535 | @defun recent-auto-save-p | |
536 | This function returns @code{t} if the current buffer has been | |
537 | auto-saved since the last time it was read in or saved. | |
538 | @end defun | |
539 | ||
540 | @defun set-buffer-auto-saved | |
541 | This function marks the current buffer as auto-saved. The buffer will | |
542 | not be auto-saved again until the buffer text is changed again. The | |
543 | function returns @code{nil}. | |
544 | @end defun | |
545 | ||
546 | @defopt auto-save-interval | |
8241495d RS |
547 | The value of this variable specifies how often to do auto-saving, in |
548 | terms of number of input events. Each time this many additional input | |
549 | events are read, Emacs does auto-saving for all buffers in which that is | |
b1b12a8e RS |
550 | enabled. |
551 | @end defopt | |
552 | ||
553 | @defopt auto-save-timeout | |
554 | The value of this variable is the number of seconds of idle time that | |
555 | should cause auto-saving. Each time the user pauses for this long, | |
29b677db RS |
556 | Emacs does auto-saving for all buffers in which that is enabled. (If |
557 | the current buffer is large, the specified timeout is multiplied by a | |
080a57ba | 558 | factor that increases as the size increases; for a million-byte |
29b677db RS |
559 | buffer, the factor is almost 4.) |
560 | ||
9a8dc0d3 RS |
561 | If the value is zero or @code{nil}, then auto-saving is not done as a |
562 | result of idleness, only after a certain number of input events as | |
563 | specified by @code{auto-save-interval}. | |
b1b12a8e RS |
564 | @end defopt |
565 | ||
566 | @defvar auto-save-hook | |
567 | This normal hook is run whenever an auto-save is about to happen. | |
568 | @end defvar | |
569 | ||
570 | @defopt auto-save-default | |
571 | If this variable is non-@code{nil}, buffers that are visiting files | |
572 | have auto-saving enabled by default. Otherwise, they do not. | |
573 | @end defopt | |
574 | ||
bfe721d1 | 575 | @deffn Command do-auto-save &optional no-message current-only |
b1b12a8e RS |
576 | This function auto-saves all buffers that need to be auto-saved. It |
577 | saves all buffers for which auto-saving is enabled and that have been | |
578 | changed since the previous auto-save. | |
579 | ||
580 | Normally, if any buffers are auto-saved, a message that says | |
581 | @samp{Auto-saving...} is displayed in the echo area while auto-saving is | |
582 | going on. However, if @var{no-message} is non-@code{nil}, the message | |
583 | is inhibited. | |
bfe721d1 KH |
584 | |
585 | If @var{current-only} is non-@code{nil}, only the current buffer | |
586 | is auto-saved. | |
b1b12a8e RS |
587 | @end deffn |
588 | ||
589 | @defun delete-auto-save-file-if-necessary | |
590 | This function deletes the current buffer's auto-save file if | |
591 | @code{delete-auto-save-files} is non-@code{nil}. It is called every | |
592 | time a buffer is saved. | |
593 | @end defun | |
594 | ||
595 | @defvar delete-auto-save-files | |
596 | This variable is used by the function | |
597 | @code{delete-auto-save-file-if-necessary}. If it is non-@code{nil}, | |
598 | Emacs deletes auto-save files when a true save is done (in the visited | |
599 | file). This saves disk space and unclutters your directory. | |
600 | @end defvar | |
601 | ||
602 | @defun rename-auto-save-file | |
603 | This function adjusts the current buffer's auto-save file name if the | |
604 | visited file name has changed. It also renames an existing auto-save | |
605 | file. If the visited file name has not changed, this function does | |
606 | nothing. | |
607 | @end defun | |
608 | ||
0680592c | 609 | @defvar buffer-saved-size |
2e00781a | 610 | The value of this buffer-local variable is the length of the current |
8241495d | 611 | buffer, when it was last read in, saved, or auto-saved. This is |
2e00781a RS |
612 | used to detect a substantial decrease in size, and turn off auto-saving |
613 | in response. | |
0680592c | 614 | |
8241495d RS |
615 | If it is @minus{}1, that means auto-saving is temporarily shut off in |
616 | this buffer due to a substantial decrease in size. Explicitly saving | |
617 | the buffer stores a positive value in this variable, thus reenabling | |
618 | auto-saving. Turning auto-save mode off or on also updates this | |
619 | variable, so that the substantial decrease in size is forgotten. | |
0680592c RS |
620 | @end defvar |
621 | ||
9589417c RS |
622 | @defvar auto-save-list-file-name |
623 | This variable (if non-@code{nil}) specifies a file for recording the | |
624 | names of all the auto-save files. Each time Emacs does auto-saving, it | |
bfe721d1 KH |
625 | writes two lines into this file for each buffer that has auto-saving |
626 | enabled. The first line gives the name of the visited file (it's empty | |
627 | if the buffer has none), and the second gives the name of the auto-save | |
628 | file. | |
629 | ||
8241495d | 630 | When Emacs exits normally, it deletes this file; if Emacs crashes, you |
bfe721d1 KH |
631 | can look in the file to find all the auto-save files that might contain |
632 | work that was otherwise lost. The @code{recover-session} command uses | |
8241495d | 633 | this file to find them. |
9589417c | 634 | |
8241495d RS |
635 | The default name for this file specifies your home directory and starts |
636 | with @samp{.saves-}. It also contains the Emacs process @sc{id} and the | |
637 | host name. | |
9589417c RS |
638 | @end defvar |
639 | ||
29b677db RS |
640 | @defvar auto-save-list-file-prefix |
641 | @tindex auto-save-list-file-prefix | |
642 | After Emacs reads your init file, it initializes | |
643 | @code{auto-save-list-file-name} (if you have not already set it | |
644 | non-@code{nil}) based on this prefix, adding the host name and process | |
645 | ID. If you set this to @code{nil} in your init file, then Emacs does | |
646 | not initialize @code{auto-save-list-file-name}. | |
647 | @end defvar | |
648 | ||
0680592c | 649 | @node Reverting |
b1b12a8e RS |
650 | @section Reverting |
651 | ||
652 | If you have made extensive changes to a file and then change your mind | |
653 | about them, you can get rid of them by reading in the previous version | |
654 | of the file with the @code{revert-buffer} command. @xref{Reverting, , | |
655 | Reverting a Buffer, emacs, The GNU Emacs Manual}. | |
656 | ||
1911e6e5 | 657 | @deffn Command revert-buffer &optional ignore-auto noconfirm |
b1b12a8e RS |
658 | This command replaces the buffer text with the text of the visited |
659 | file on disk. This action undoes all changes since the file was visited | |
660 | or saved. | |
661 | ||
1911e6e5 | 662 | By default, if the latest auto-save file is more recent than the visited |
b581dd19 | 663 | file, and the argument @var{ignore-auto} is @code{nil}, |
8241495d RS |
664 | @code{revert-buffer} asks the user whether to use that auto-save |
665 | instead. When you invoke this command interactively, @var{ignore-auto} | |
b581dd19 GM |
666 | is @code{t} if there is no numeric prefix argument; thus, the |
667 | interactive default is not to check the auto-save file. | |
b1b12a8e RS |
668 | |
669 | Normally, @code{revert-buffer} asks for confirmation before it changes | |
670 | the buffer; but if the argument @var{noconfirm} is non-@code{nil}, | |
671 | @code{revert-buffer} does not ask for confirmation. | |
672 | ||
673 | Reverting tries to preserve marker positions in the buffer by using the | |
2e00781a RS |
674 | replacement feature of @code{insert-file-contents}. If the buffer |
675 | contents and the file contents are identical before the revert | |
676 | operation, reverting preserves all the markers. If they are not | |
8241495d RS |
677 | identical, reverting does change the buffer; in that case, it preserves |
678 | the markers in the unchanged text (if any) at the beginning and end of | |
679 | the buffer. Preserving any additional markers would be problematical. | |
b1b12a8e RS |
680 | @end deffn |
681 | ||
2e00781a | 682 | You can customize how @code{revert-buffer} does its work by setting |
29b677db | 683 | the variables described in the rest of this section. |
2e00781a | 684 | |
1911e6e5 RS |
685 | @defvar revert-without-query |
686 | This variable holds a list of files that should be reverted without | |
8241495d RS |
687 | query. The value is a list of regular expressions. If the visited file |
688 | name matches one of these regular expressions, and the file has changed | |
689 | on disk but the buffer is not modified, then @code{revert-buffer} | |
690 | reverts the file without asking the user for confirmation. | |
1911e6e5 RS |
691 | @end defvar |
692 | ||
29b677db RS |
693 | Some major modes customize @code{revert-buffer} by making |
694 | buffer-local bindings for these variables: | |
695 | ||
b1b12a8e | 696 | @defvar revert-buffer-function |
2e00781a RS |
697 | The value of this variable is the function to use to revert this buffer. |
698 | If non-@code{nil}, it is called as a function with no arguments to do | |
699 | the work of reverting. If the value is @code{nil}, reverting works the | |
700 | usual way. | |
701 | ||
702 | Modes such as Dired mode, in which the text being edited does not | |
703 | consist of a file's contents but can be regenerated in some other | |
29b677db | 704 | fashion, can give this variable a buffer-local value that is a function to |
2e00781a | 705 | regenerate the contents. |
b1b12a8e RS |
706 | @end defvar |
707 | ||
708 | @defvar revert-buffer-insert-file-contents-function | |
8241495d | 709 | The value of this variable, if non-@code{nil}, specifies the function to use to |
bfe721d1 KH |
710 | insert the updated contents when reverting this buffer. The function |
711 | receives two arguments: first the file name to use; second, @code{t} if | |
712 | the user has asked to read the auto-save file. | |
29b677db RS |
713 | |
714 | The reason for a mode to set this variable instead of | |
715 | @code{revert-buffer-function} is to avoid duplicating or replacing the | |
716 | rest of what @code{revert-buffer} does: asking for confirmation, | |
717 | clearing the undo list, deciding the proper major mode, and running the | |
718 | hooks listed below. | |
b1b12a8e RS |
719 | @end defvar |
720 | ||
721 | @defvar before-revert-hook | |
8241495d | 722 | This normal hook is run by @code{revert-buffer} before |
b1b12a8e RS |
723 | inserting the modified contents---but only if |
724 | @code{revert-buffer-function} is @code{nil}. | |
b1b12a8e RS |
725 | @end defvar |
726 | ||
727 | @defvar after-revert-hook | |
8241495d | 728 | This normal hook is run by @code{revert-buffer} after inserting |
b1b12a8e RS |
729 | the modified contents---but only if @code{revert-buffer-function} is |
730 | @code{nil}. | |
b1b12a8e | 731 | @end defvar |