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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
b3d90e46 GM |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1999, 2001, 2002, 2003, |
4 | @c 2004, 2005, 2006, 2007 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 | |
1db203ff EZ |
9 | @cindex backups and auto-saving |
10 | @cindex back up and auto save | |
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11 | |
12 | Backup files and auto-save files are two methods by which Emacs tries | |
13 | to protect the user from the consequences of crashes or of the user's | |
14 | own errors. Auto-saving preserves the text from earlier in the current | |
15 | editing session; backup files preserve file contents prior to the | |
16 | current session. | |
17 | ||
18 | @menu | |
19 | * Backup Files:: How backup files are made; how their names are chosen. | |
20 | * Auto-Saving:: How auto-save files are made; how their names are chosen. | |
21 | * Reverting:: @code{revert-buffer}, and how to customize what it does. | |
22 | @end menu | |
23 | ||
0680592c | 24 | @node Backup Files |
b1b12a8e RS |
25 | @section Backup Files |
26 | @cindex backup file | |
27 | ||
28 | A @dfn{backup file} is a copy of the old contents of a file you are | |
29 | editing. Emacs makes a backup file the first time you save a buffer | |
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30 | into its visited file. Thus, normally, the backup file contains the |
31 | contents of the file as it was before the current editing session. | |
32 | The contents of the backup file normally remain unchanged once it | |
33 | exists. | |
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34 | |
35 | Backups are usually made by renaming the visited file to a new name. | |
36 | Optionally, you can specify that backup files should be made by copying | |
37 | the visited file. This choice makes a difference for files with | |
38 | multiple names; it also can affect whether the edited file remains owned | |
39 | by the original owner or becomes owned by the user editing it. | |
40 | ||
41 | By default, Emacs makes a single backup file for each file edited. | |
42 | You can alternatively request numbered backups; then each new backup | |
43 | file gets a new name. You can delete old numbered backups when you | |
44 | don't want them any more, or Emacs can delete them automatically. | |
45 | ||
46 | @menu | |
47 | * Making Backups:: How Emacs makes backup files, and when. | |
48 | * Rename or Copy:: Two alternatives: renaming the old file or copying it. | |
49 | * Numbered Backups:: Keeping multiple backups for each source file. | |
50 | * Backup Names:: How backup file names are computed; customization. | |
51 | @end menu | |
52 | ||
0680592c | 53 | @node Making Backups |
b1b12a8e RS |
54 | @subsection Making Backup Files |
55 | ||
56 | @defun backup-buffer | |
57 | This function makes a backup of the file visited by the current | |
58 | buffer, if appropriate. It is called by @code{save-buffer} before | |
59 | saving the buffer the first time. | |
ab19c39b LT |
60 | |
61 | If a backup was made by renaming, the return value is a cons cell of | |
62 | the form (@var{modes} . @var{backupname}), where @var{modes} are the | |
63 | mode bits of the original file, as returned by @code{file-modes} | |
64 | (@pxref{File Attributes,, Other Information about Files}), and | |
65 | @var{backupname} is the name of the backup. In all other cases, that | |
66 | is, if a backup was made by copying or if no backup was made, this | |
67 | function returns @code{nil}. | |
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68 | @end defun |
69 | ||
70 | @defvar buffer-backed-up | |
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71 | This buffer-local variable says whether this buffer's file has |
72 | been backed up on account of this buffer. If it is non-@code{nil}, | |
b1b12a8e | 73 | the backup file has been written. Otherwise, the file should be backed |
2e00781a | 74 | up when it is next saved (if backups are enabled). This is a |
997b849e | 75 | permanent local; @code{kill-all-local-variables} does not alter@tie{}it. |
b1b12a8e RS |
76 | @end defvar |
77 | ||
78 | @defopt make-backup-files | |
bfe721d1 | 79 | This variable determines whether or not to make backup files. If it |
b1b12a8e | 80 | is non-@code{nil}, then Emacs creates a backup of each file when it is |
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81 | saved for the first time---provided that @code{backup-inhibited} |
82 | is @code{nil} (see below). | |
b1b12a8e | 83 | |
bfe721d1 | 84 | The following example shows how to change the @code{make-backup-files} |
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85 | variable only in the Rmail buffers and not elsewhere. Setting it |
86 | @code{nil} stops Emacs from making backups of these files, which may | |
a40d4712 | 87 | save disk space. (You would put this code in your init file.) |
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88 | |
89 | @smallexample | |
90 | @group | |
177c0ea7 | 91 | (add-hook 'rmail-mode-hook |
b1b12a8e | 92 | (function (lambda () |
177c0ea7 | 93 | (make-local-variable |
b1b12a8e RS |
94 | 'make-backup-files) |
95 | (setq make-backup-files nil)))) | |
96 | @end group | |
97 | @end smallexample | |
98 | @end defopt | |
99 | ||
2e00781a | 100 | @defvar backup-enable-predicate |
b1b12a8e | 101 | This variable's value is a function to be called on certain occasions to |
2e00781a | 102 | decide whether a file should have backup files. The function receives |
ab19c39b | 103 | one argument, an absolute file name to consider. If the function returns |
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104 | @code{nil}, backups are disabled for that file. Otherwise, the other |
105 | variables in this section say whether and how to make backups. | |
b1b12a8e | 106 | |
bae2aa40 DL |
107 | @findex normal-backup-enable-predicate |
108 | The default value is @code{normal-backup-enable-predicate}, which checks | |
109 | for files in @code{temporary-file-directory} and | |
110 | @code{small-temporary-file-directory}. | |
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111 | @end defvar |
112 | ||
113 | @defvar backup-inhibited | |
114 | If this variable is non-@code{nil}, backups are inhibited. It records | |
115 | the result of testing @code{backup-enable-predicate} on the visited file | |
116 | name. It can also coherently be used by other mechanisms that inhibit | |
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117 | backups based on which file is visited. For example, VC sets this |
118 | variable non-@code{nil} to prevent making backups for files managed | |
119 | with a version control system. | |
2e00781a | 120 | |
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121 | This is a permanent local, so that changing the major mode does not lose |
122 | its value. Major modes should not set this variable---they should set | |
2e00781a | 123 | @code{make-backup-files} instead. |
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124 | @end defvar |
125 | ||
bae2aa40 DL |
126 | @defvar backup-directory-alist |
127 | This variable's value is an alist of filename patterns and backup | |
128 | directory names. Each element looks like | |
129 | @smallexample | |
130 | (@var{regexp} . @var{directory}) | |
131 | @end smallexample | |
132 | ||
133 | @noindent | |
134 | Backups of files with names matching @var{regexp} will be made in | |
135 | @var{directory}. @var{directory} may be relative or absolute. If it is | |
136 | absolute, so that all matching files are backed up into the same | |
137 | directory, the file names in this directory will be the full name of the | |
138 | file backed up with all directory separators changed to @samp{!} to | |
139 | prevent clashes. This will not work correctly if your filesystem | |
140 | truncates the resulting name. | |
141 | ||
142 | For the common case of all backups going into one directory, the alist | |
143 | should contain a single element pairing @samp{"."} with the appropriate | |
144 | directory name. | |
145 | ||
146 | If this variable is @code{nil}, or it fails to match a filename, the | |
147 | backup is made in the original file's directory. | |
148 | ||
149 | On MS-DOS filesystems without long names this variable is always | |
150 | ignored. | |
151 | @end defvar | |
152 | ||
153 | @defvar make-backup-file-name-function | |
9a8dc0d3 RS |
154 | This variable's value is a function to use for making backups instead |
155 | of the default @code{make-backup-file-name}. A value of @code{nil} | |
f3b11af5 | 156 | gives the default @code{make-backup-file-name} behavior. |
ab19c39b | 157 | @xref{Backup Names,, Naming Backup Files}. |
bae2aa40 | 158 | |
5bf6f93d | 159 | This could be buffer-local to do something special for specific |
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160 | files. If you define it, you may need to change |
161 | @code{backup-file-name-p} and @code{file-name-sans-versions} too. | |
162 | @end defvar | |
163 | ||
164 | ||
0680592c | 165 | @node Rename or Copy |
b1b12a8e RS |
166 | @subsection Backup by Renaming or by Copying? |
167 | @cindex backup files, how to make them | |
168 | ||
177c0ea7 | 169 | There are two ways that Emacs can make a backup file: |
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170 | |
171 | @itemize @bullet | |
172 | @item | |
173 | Emacs can rename the original file so that it becomes a backup file, and | |
174 | then write the buffer being saved into a new file. After this | |
175 | procedure, any other names (i.e., hard links) of the original file now | |
176 | refer to the backup file. The new file is owned by the user doing the | |
177 | editing, and its group is the default for new files written by the user | |
178 | in that directory. | |
179 | ||
180 | @item | |
181 | Emacs can copy the original file into a backup file, and then overwrite | |
182 | the original file with new contents. After this procedure, any other | |
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183 | names (i.e., hard links) of the original file continue to refer to the |
184 | current (updated) version of the file. The file's owner and group will | |
185 | be unchanged. | |
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186 | @end itemize |
187 | ||
188 | The first method, renaming, is the default. | |
189 | ||
190 | The variable @code{backup-by-copying}, if non-@code{nil}, says to use | |
191 | the second method, which is to copy the original file and overwrite it | |
192 | with the new buffer contents. The variable @code{file-precious-flag}, | |
193 | if non-@code{nil}, also has this effect (as a sideline of its main | |
194 | significance). @xref{Saving Buffers}. | |
195 | ||
ab19c39b | 196 | @defopt backup-by-copying |
b1b12a8e RS |
197 | If this variable is non-@code{nil}, Emacs always makes backup files by |
198 | copying. | |
ab19c39b | 199 | @end defopt |
b1b12a8e | 200 | |
fe4c5da1 | 201 | The following three variables, when non-@code{nil}, cause the second |
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202 | method to be used in certain special cases. They have no effect on the |
203 | treatment of files that don't fall into the special cases. | |
204 | ||
ab19c39b | 205 | @defopt backup-by-copying-when-linked |
b1b12a8e RS |
206 | If this variable is non-@code{nil}, Emacs makes backups by copying for |
207 | files with multiple names (hard links). | |
208 | ||
209 | This variable is significant only if @code{backup-by-copying} is | |
210 | @code{nil}, since copying is always used when that variable is | |
211 | non-@code{nil}. | |
ab19c39b | 212 | @end defopt |
b1b12a8e | 213 | |
ab19c39b | 214 | @defopt backup-by-copying-when-mismatch |
b1b12a8e RS |
215 | If this variable is non-@code{nil}, Emacs makes backups by copying in cases |
216 | where renaming would change either the owner or the group of the file. | |
217 | ||
218 | The value has no effect when renaming would not alter the owner or | |
219 | group of the file; that is, for files which are owned by the user and | |
220 | whose group matches the default for a new file created there by the | |
221 | user. | |
222 | ||
223 | This variable is significant only if @code{backup-by-copying} is | |
224 | @code{nil}, since copying is always used when that variable is | |
225 | non-@code{nil}. | |
ab19c39b | 226 | @end defopt |
b1b12a8e | 227 | |
ab19c39b | 228 | @defopt backup-by-copying-when-privileged-mismatch |
8241495d RS |
229 | This variable, if non-@code{nil}, specifies the same behavior as |
230 | @code{backup-by-copying-when-mismatch}, but only for certain user-id | |
231 | values: namely, those less than or equal to a certain number. You set | |
232 | this variable to that number. | |
233 | ||
234 | Thus, if you set @code{backup-by-copying-when-privileged-mismatch} | |
235 | to 0, backup by copying is done for the superuser only, | |
236 | when necessary to prevent a change in the owner of the file. | |
237 | ||
238 | The default is 200. | |
ab19c39b | 239 | @end defopt |
8241495d | 240 | |
0680592c | 241 | @node Numbered Backups |
b1b12a8e RS |
242 | @subsection Making and Deleting Numbered Backup Files |
243 | ||
244 | If a file's name is @file{foo}, the names of its numbered backup | |
245 | versions are @file{foo.~@var{v}~}, for various integers @var{v}, like | |
246 | this: @file{foo.~1~}, @file{foo.~2~}, @file{foo.~3~}, @dots{}, | |
247 | @file{foo.~259~}, and so on. | |
248 | ||
249 | @defopt version-control | |
250 | This variable controls whether to make a single non-numbered backup | |
251 | file or multiple numbered backups. | |
252 | ||
253 | @table @asis | |
254 | @item @code{nil} | |
255 | Make numbered backups if the visited file already has numbered backups; | |
fe4c5da1 | 256 | otherwise, do not. This is the default. |
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257 | |
258 | @item @code{never} | |
259 | Do not make numbered backups. | |
260 | ||
261 | @item @var{anything else} | |
2e00781a | 262 | Make numbered backups. |
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263 | @end table |
264 | @end defopt | |
265 | ||
266 | The use of numbered backups ultimately leads to a large number of | |
267 | backup versions, which must then be deleted. Emacs can do this | |
2e00781a | 268 | automatically or it can ask the user whether to delete them. |
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269 | |
270 | @defopt kept-new-versions | |
2e00781a | 271 | The value of this variable is the number of newest versions to keep |
b1b12a8e | 272 | when a new numbered backup is made. The newly made backup is included |
997b849e | 273 | in the count. The default value is@tie{}2. |
b1b12a8e RS |
274 | @end defopt |
275 | ||
276 | @defopt kept-old-versions | |
277 | The value of this variable is the number of oldest versions to keep | |
997b849e | 278 | when a new numbered backup is made. The default value is@tie{}2. |
b1b12a8e RS |
279 | @end defopt |
280 | ||
281 | If there are backups numbered 1, 2, 3, 5, and 7, and both of these | |
282 | variables have the value 2, then the backups numbered 1 and 2 are kept | |
283 | as old versions and those numbered 5 and 7 are kept as new versions; | |
2e00781a | 284 | backup version 3 is excess. The function @code{find-backup-file-name} |
b1b12a8e RS |
285 | (@pxref{Backup Names}) is responsible for determining which backup |
286 | versions to delete, but does not delete them itself. | |
287 | ||
f9f59935 | 288 | @defopt delete-old-versions |
29b677db RS |
289 | If this variable is @code{t}, then saving a file deletes excess |
290 | backup versions silently. If it is @code{nil}, that means | |
291 | to ask for confirmation before deleting excess backups. | |
292 | Otherwise, they are not deleted at all. | |
b1b12a8e RS |
293 | @end defopt |
294 | ||
295 | @defopt dired-kept-versions | |
296 | This variable specifies how many of the newest backup versions to keep | |
297 | in the Dired command @kbd{.} (@code{dired-clean-directory}). That's the | |
2e00781a | 298 | same thing @code{kept-new-versions} specifies when you make a new backup |
997b849e | 299 | file. The default is@tie{}2. |
b1b12a8e RS |
300 | @end defopt |
301 | ||
0680592c | 302 | @node Backup Names |
b1b12a8e RS |
303 | @subsection Naming Backup Files |
304 | ||
305 | The functions in this section are documented mainly because you can | |
306 | customize the naming conventions for backup files by redefining them. | |
307 | If you change one, you probably need to change the rest. | |
308 | ||
309 | @defun backup-file-name-p filename | |
310 | This function returns a non-@code{nil} value if @var{filename} is a | |
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311 | possible name for a backup file. It just checks the name, not whether |
312 | a file with the name @var{filename} exists. | |
b1b12a8e RS |
313 | |
314 | @smallexample | |
315 | @group | |
316 | (backup-file-name-p "foo") | |
317 | @result{} nil | |
318 | @end group | |
319 | @group | |
320 | (backup-file-name-p "foo~") | |
321 | @result{} 3 | |
322 | @end group | |
323 | @end smallexample | |
324 | ||
325 | The standard definition of this function is as follows: | |
326 | ||
327 | @smallexample | |
328 | @group | |
329 | (defun backup-file-name-p (file) | |
330 | "Return non-nil if FILE is a backup file \ | |
331 | name (numeric or not)..." | |
29b677db | 332 | (string-match "~\\'" file)) |
b1b12a8e RS |
333 | @end group |
334 | @end smallexample | |
335 | ||
336 | @noindent | |
337 | Thus, the function returns a non-@code{nil} value if the file name ends | |
338 | with a @samp{~}. (We use a backslash to split the documentation | |
339 | string's first line into two lines in the text, but produce just one | |
340 | line in the string itself.) | |
341 | ||
342 | This simple expression is placed in a separate function to make it easy | |
343 | to redefine for customization. | |
344 | @end defun | |
345 | ||
346 | @defun make-backup-file-name filename | |
2e00781a | 347 | This function returns a string that is the name to use for a |
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348 | non-numbered backup file for file @var{filename}. On Unix, this is just |
349 | @var{filename} with a tilde appended. | |
350 | ||
a9f0a989 RS |
351 | The standard definition of this function, on most operating systems, is |
352 | as follows: | |
b1b12a8e RS |
353 | |
354 | @smallexample | |
355 | @group | |
356 | (defun make-backup-file-name (file) | |
29b677db | 357 | "Create the non-numeric backup file name for FILE..." |
b1b12a8e RS |
358 | (concat file "~")) |
359 | @end group | |
360 | @end smallexample | |
361 | ||
2e00781a | 362 | You can change the backup-file naming convention by redefining this |
b1b12a8e | 363 | function. The following example redefines @code{make-backup-file-name} |
2e00781a | 364 | to prepend a @samp{.} in addition to appending a tilde: |
b1b12a8e RS |
365 | |
366 | @smallexample | |
367 | @group | |
368 | (defun make-backup-file-name (filename) | |
a9f0a989 RS |
369 | (expand-file-name |
370 | (concat "." (file-name-nondirectory filename) "~") | |
371 | (file-name-directory filename))) | |
b1b12a8e RS |
372 | @end group |
373 | ||
374 | @group | |
375 | (make-backup-file-name "backups.texi") | |
376 | @result{} ".backups.texi~" | |
377 | @end group | |
378 | @end smallexample | |
a9f0a989 RS |
379 | |
380 | Some parts of Emacs, including some Dired commands, assume that backup | |
381 | file names end with @samp{~}. If you do not follow that convention, it | |
382 | will not cause serious problems, but these commands may give | |
383 | less-than-desirable results. | |
b1b12a8e RS |
384 | @end defun |
385 | ||
386 | @defun find-backup-file-name filename | |
387 | This function computes the file name for a new backup file for | |
388 | @var{filename}. It may also propose certain existing backup files for | |
389 | deletion. @code{find-backup-file-name} returns a list whose @sc{car} is | |
390 | the name for the new backup file and whose @sc{cdr} is a list of backup | |
ab19c39b LT |
391 | files whose deletion is proposed. The value can also be @code{nil}, |
392 | which means not to make a backup. | |
b1b12a8e RS |
393 | |
394 | Two variables, @code{kept-old-versions} and @code{kept-new-versions}, | |
395 | determine which backup versions should be kept. This function keeps | |
396 | those versions by excluding them from the @sc{cdr} of the value. | |
397 | @xref{Numbered Backups}. | |
398 | ||
399 | In this example, the value says that @file{~rms/foo.~5~} is the name | |
400 | to use for the new backup file, and @file{~rms/foo.~3~} is an ``excess'' | |
401 | version that the caller should consider deleting now. | |
402 | ||
403 | @smallexample | |
404 | @group | |
405 | (find-backup-file-name "~rms/foo") | |
406 | @result{} ("~rms/foo.~5~" "~rms/foo.~3~") | |
407 | @end group | |
408 | @end smallexample | |
409 | @end defun | |
410 | ||
411 | @c Emacs 19 feature | |
412 | @defun file-newest-backup filename | |
413 | This function returns the name of the most recent backup file for | |
2e00781a | 414 | @var{filename}, or @code{nil} if that file has no backup files. |
b1b12a8e | 415 | |
2e00781a RS |
416 | Some file comparison commands use this function so that they can |
417 | automatically compare a file with its most recent backup. | |
177c0ea7 | 418 | @end defun |
b1b12a8e | 419 | |
0680592c | 420 | @node Auto-Saving |
b1b12a8e RS |
421 | @section Auto-Saving |
422 | @cindex auto-saving | |
423 | ||
424 | Emacs periodically saves all files that you are visiting; this is | |
425 | called @dfn{auto-saving}. Auto-saving prevents you from losing more | |
426 | than a limited amount of work if the system crashes. By default, | |
427 | auto-saves happen every 300 keystrokes, or after around 30 seconds of | |
333c5fc5 | 428 | idle time. @xref{Auto Save, Auto Save, Auto-Saving: Protection Against |
b1b12a8e RS |
429 | Disasters, emacs, The GNU Emacs Manual}, for information on auto-save |
430 | for users. Here we describe the functions used to implement auto-saving | |
431 | and the variables that control them. | |
432 | ||
433 | @defvar buffer-auto-save-file-name | |
434 | This buffer-local variable is the name of the file used for | |
435 | auto-saving the current buffer. It is @code{nil} if the buffer | |
436 | should not be auto-saved. | |
437 | ||
438 | @example | |
439 | @group | |
440 | buffer-auto-save-file-name | |
29b677db | 441 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" |
b1b12a8e RS |
442 | @end group |
443 | @end example | |
444 | @end defvar | |
445 | ||
446 | @deffn Command auto-save-mode arg | |
447 | When used interactively without an argument, this command is a toggle | |
448 | switch: it turns on auto-saving of the current buffer if it is off, and | |
29b677db | 449 | vice versa. With an argument @var{arg}, the command turns auto-saving |
b1b12a8e RS |
450 | on if the value of @var{arg} is @code{t}, a nonempty list, or a positive |
451 | integer. Otherwise, it turns auto-saving off. | |
452 | @end deffn | |
453 | ||
454 | @defun auto-save-file-name-p filename | |
455 | This function returns a non-@code{nil} value if @var{filename} is a | |
8241495d RS |
456 | string that could be the name of an auto-save file. It assumes |
457 | the usual naming convention for auto-save files: a name that | |
b1b12a8e RS |
458 | begins and ends with hash marks (@samp{#}) is a possible auto-save file |
459 | name. The argument @var{filename} should not contain a directory part. | |
460 | ||
461 | @example | |
462 | @group | |
463 | (make-auto-save-file-name) | |
29b677db | 464 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" |
b1b12a8e RS |
465 | @end group |
466 | @group | |
29b677db | 467 | (auto-save-file-name-p "#backups.texi#") |
b1b12a8e RS |
468 | @result{} 0 |
469 | @end group | |
470 | @group | |
29b677db | 471 | (auto-save-file-name-p "backups.texi") |
b1b12a8e RS |
472 | @result{} nil |
473 | @end group | |
474 | @end example | |
475 | ||
476 | The standard definition of this function is as follows: | |
477 | ||
478 | @example | |
479 | @group | |
480 | (defun auto-save-file-name-p (filename) | |
481 | "Return non-nil if FILENAME can be yielded by..." | |
482 | (string-match "^#.*#$" filename)) | |
483 | @end group | |
484 | @end example | |
485 | ||
486 | This function exists so that you can customize it if you wish to | |
487 | change the naming convention for auto-save files. If you redefine it, | |
488 | be sure to redefine the function @code{make-auto-save-file-name} | |
489 | correspondingly. | |
490 | @end defun | |
491 | ||
492 | @defun make-auto-save-file-name | |
493 | This function returns the file name to use for auto-saving the current | |
86494bd5 KH |
494 | buffer. This is just the file name with hash marks (@samp{#}) prepended |
495 | and appended to it. This function does not look at the variable | |
8241495d RS |
496 | @code{auto-save-visited-file-name} (described below); callers of this |
497 | function should check that variable first. | |
b1b12a8e RS |
498 | |
499 | @example | |
500 | @group | |
501 | (make-auto-save-file-name) | |
29b677db | 502 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" |
b1b12a8e RS |
503 | @end group |
504 | @end example | |
505 | ||
fe4c5da1 RS |
506 | Here is a simplified version of the standard definition of this |
507 | function: | |
b1b12a8e RS |
508 | |
509 | @example | |
510 | @group | |
511 | (defun make-auto-save-file-name () | |
512 | "Return file name to use for auto-saves \ | |
29b677db | 513 | of current buffer.." |
b1b12a8e RS |
514 | (if buffer-file-name |
515 | @end group | |
516 | @group | |
517 | (concat | |
518 | (file-name-directory buffer-file-name) | |
519 | "#" | |
520 | (file-name-nondirectory buffer-file-name) | |
521 | "#") | |
522 | (expand-file-name | |
523 | (concat "#%" (buffer-name) "#")))) | |
524 | @end group | |
525 | @end example | |
526 | ||
527 | This exists as a separate function so that you can redefine it to | |
528 | customize the naming convention for auto-save files. Be sure to | |
529 | change @code{auto-save-file-name-p} in a corresponding way. | |
530 | @end defun | |
531 | ||
ab19c39b | 532 | @defopt auto-save-visited-file-name |
b1b12a8e RS |
533 | If this variable is non-@code{nil}, Emacs auto-saves buffers in |
534 | the files they are visiting. That is, the auto-save is done in the same | |
2e00781a | 535 | file that you are editing. Normally, this variable is @code{nil}, so |
b1b12a8e RS |
536 | auto-save files have distinct names that are created by |
537 | @code{make-auto-save-file-name}. | |
538 | ||
8241495d RS |
539 | When you change the value of this variable, the new value does not take |
540 | effect in an existing buffer until the next time auto-save mode is | |
541 | reenabled in it. If auto-save mode is already enabled, auto-saves | |
542 | continue to go in the same file name until @code{auto-save-mode} is | |
543 | called again. | |
ab19c39b | 544 | @end defopt |
b1b12a8e RS |
545 | |
546 | @defun recent-auto-save-p | |
547 | This function returns @code{t} if the current buffer has been | |
548 | auto-saved since the last time it was read in or saved. | |
549 | @end defun | |
550 | ||
551 | @defun set-buffer-auto-saved | |
552 | This function marks the current buffer as auto-saved. The buffer will | |
553 | not be auto-saved again until the buffer text is changed again. The | |
554 | function returns @code{nil}. | |
555 | @end defun | |
556 | ||
557 | @defopt auto-save-interval | |
8241495d RS |
558 | The value of this variable specifies how often to do auto-saving, in |
559 | terms of number of input events. Each time this many additional input | |
560 | events are read, Emacs does auto-saving for all buffers in which that is | |
ab19c39b LT |
561 | enabled. Setting this to zero disables autosaving based on the |
562 | number of characters typed. | |
b1b12a8e RS |
563 | @end defopt |
564 | ||
565 | @defopt auto-save-timeout | |
566 | The value of this variable is the number of seconds of idle time that | |
567 | should cause auto-saving. Each time the user pauses for this long, | |
29b677db RS |
568 | Emacs does auto-saving for all buffers in which that is enabled. (If |
569 | the current buffer is large, the specified timeout is multiplied by a | |
080a57ba | 570 | factor that increases as the size increases; for a million-byte |
29b677db RS |
571 | buffer, the factor is almost 4.) |
572 | ||
9a8dc0d3 RS |
573 | If the value is zero or @code{nil}, then auto-saving is not done as a |
574 | result of idleness, only after a certain number of input events as | |
575 | specified by @code{auto-save-interval}. | |
b1b12a8e RS |
576 | @end defopt |
577 | ||
578 | @defvar auto-save-hook | |
579 | This normal hook is run whenever an auto-save is about to happen. | |
580 | @end defvar | |
581 | ||
582 | @defopt auto-save-default | |
583 | If this variable is non-@code{nil}, buffers that are visiting files | |
584 | have auto-saving enabled by default. Otherwise, they do not. | |
585 | @end defopt | |
586 | ||
bfe721d1 | 587 | @deffn Command do-auto-save &optional no-message current-only |
b1b12a8e RS |
588 | This function auto-saves all buffers that need to be auto-saved. It |
589 | saves all buffers for which auto-saving is enabled and that have been | |
590 | changed since the previous auto-save. | |
591 | ||
920fc480 RS |
592 | If any buffers are auto-saved, @code{do-auto-save} normally displays a |
593 | message saying @samp{Auto-saving...} in the echo area while | |
594 | auto-saving is going on. However, if @var{no-message} is | |
595 | non-@code{nil}, the message is inhibited. | |
bfe721d1 KH |
596 | |
597 | If @var{current-only} is non-@code{nil}, only the current buffer | |
598 | is auto-saved. | |
b1b12a8e RS |
599 | @end deffn |
600 | ||
ab19c39b | 601 | @defun delete-auto-save-file-if-necessary &optional force |
b1b12a8e RS |
602 | This function deletes the current buffer's auto-save file if |
603 | @code{delete-auto-save-files} is non-@code{nil}. It is called every | |
604 | time a buffer is saved. | |
ab19c39b LT |
605 | |
606 | Unless @var{force} is non-@code{nil}, this function only deletes the | |
607 | file if it was written by the current Emacs session since the last | |
608 | true save. | |
b1b12a8e RS |
609 | @end defun |
610 | ||
ab19c39b | 611 | @defopt delete-auto-save-files |
b1b12a8e RS |
612 | This variable is used by the function |
613 | @code{delete-auto-save-file-if-necessary}. If it is non-@code{nil}, | |
614 | Emacs deletes auto-save files when a true save is done (in the visited | |
615 | file). This saves disk space and unclutters your directory. | |
ab19c39b | 616 | @end defopt |
b1b12a8e RS |
617 | |
618 | @defun rename-auto-save-file | |
619 | This function adjusts the current buffer's auto-save file name if the | |
620 | visited file name has changed. It also renames an existing auto-save | |
ab19c39b LT |
621 | file, if it was made in the current Emacs session. If the visited |
622 | file name has not changed, this function does nothing. | |
b1b12a8e RS |
623 | @end defun |
624 | ||
0680592c | 625 | @defvar buffer-saved-size |
2e00781a | 626 | The value of this buffer-local variable is the length of the current |
8241495d | 627 | buffer, when it was last read in, saved, or auto-saved. This is |
2e00781a RS |
628 | used to detect a substantial decrease in size, and turn off auto-saving |
629 | in response. | |
0680592c | 630 | |
8241495d RS |
631 | If it is @minus{}1, that means auto-saving is temporarily shut off in |
632 | this buffer due to a substantial decrease in size. Explicitly saving | |
633 | the buffer stores a positive value in this variable, thus reenabling | |
634 | auto-saving. Turning auto-save mode off or on also updates this | |
635 | variable, so that the substantial decrease in size is forgotten. | |
0680592c RS |
636 | @end defvar |
637 | ||
9589417c RS |
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 | |
bfe721d1 KH |
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 | ||
8241495d | 646 | When Emacs exits normally, it deletes this file; if Emacs crashes, you |
bfe721d1 KH |
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 | |
8241495d | 649 | this file to find them. |
9589417c | 650 | |
8241495d | 651 | The default name for this file specifies your home directory and starts |
ad800164 | 652 | with @samp{.saves-}. It also contains the Emacs process @acronym{ID} and the |
8241495d | 653 | host name. |
9589417c RS |
654 | @end defvar |
655 | ||
29b677db | 656 | @defvar auto-save-list-file-prefix |
29b677db RS |
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}. | |
662 | @end defvar | |
663 | ||
0680592c | 664 | @node Reverting |
b1b12a8e RS |
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 | ||
ab19c39b | 672 | @deffn Command revert-buffer &optional ignore-auto noconfirm preserve-modes |
b1b12a8e RS |
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 | ||
1911e6e5 | 677 | By default, if the latest auto-save file is more recent than the visited |
b581dd19 | 678 | file, and the argument @var{ignore-auto} is @code{nil}, |
8241495d RS |
679 | @code{revert-buffer} asks the user whether to use that auto-save |
680 | instead. When you invoke this command interactively, @var{ignore-auto} | |
b581dd19 GM |
681 | is @code{t} if there is no numeric prefix argument; thus, the |
682 | interactive default is not to check the auto-save file. | |
b1b12a8e RS |
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 | ||
5a31f3ff | 688 | Normally, this command reinitializes the buffer's major and minor modes |
ab19c39b LT |
689 | using @code{normal-mode}. But if @var{preserve-modes} is |
690 | non-@code{nil}, the modes remain unchanged. | |
691 | ||
b1b12a8e | 692 | Reverting tries to preserve marker positions in the buffer by using the |
2e00781a RS |
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 | |
8241495d RS |
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. | |
b1b12a8e RS |
699 | @end deffn |
700 | ||
2e00781a | 701 | You can customize how @code{revert-buffer} does its work by setting |
29b677db | 702 | the variables described in the rest of this section. |
2e00781a | 703 | |
ab19c39b | 704 | @defopt revert-without-query |
1911e6e5 | 705 | This variable holds a list of files that should be reverted without |
8241495d RS |
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. | |
ab19c39b | 710 | @end defopt |
1911e6e5 | 711 | |
29b677db RS |
712 | Some major modes customize @code{revert-buffer} by making |
713 | buffer-local bindings for these variables: | |
714 | ||
b1b12a8e | 715 | @defvar revert-buffer-function |
7baeca0c | 716 | @anchor{Definition of revert-buffer-function} |
ab19c39b LT |
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. | |
2e00781a RS |
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 | |
29b677db | 726 | fashion, can give this variable a buffer-local value that is a function to |
2e00781a | 727 | regenerate the contents. |
b1b12a8e RS |
728 | @end defvar |
729 | ||
730 | @defvar revert-buffer-insert-file-contents-function | |
8241495d | 731 | The value of this variable, if non-@code{nil}, specifies the function to use to |
bfe721d1 KH |
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. | |
29b677db RS |
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. | |
b1b12a8e RS |
741 | @end defvar |
742 | ||
743 | @defvar before-revert-hook | |
8241495d | 744 | This normal hook is run by @code{revert-buffer} before |
b1b12a8e RS |
745 | inserting the modified contents---but only if |
746 | @code{revert-buffer-function} is @code{nil}. | |
b1b12a8e RS |
747 | @end defvar |
748 | ||
749 | @defvar after-revert-hook | |
8241495d | 750 | This normal hook is run by @code{revert-buffer} after inserting |
b1b12a8e RS |
751 | the modified contents---but only if @code{revert-buffer-function} is |
752 | @code{nil}. | |
b1b12a8e | 753 | @end defvar |
ab5796a9 MB |
754 | |
755 | @ignore | |
756 | arch-tag: 295a6321-e5ab-46d5-aef5-0bb4f447a67f | |
757 | @end ignore |