| 1 | @c -*-texinfo-*- |
| 2 | @c This is part of the GNU Emacs Lisp Reference Manual. |
| 3 | @c Copyright (C) 1990-1995, 1999, 2001-2012 Free Software Foundation, Inc. |
| 4 | @c See the file elisp.texi for copying conditions. |
| 5 | @node Backups and Auto-Saving |
| 6 | @chapter Backups and Auto-Saving |
| 7 | @cindex backups and auto-saving |
| 8 | |
| 9 | Backup files and auto-save files are two methods by which Emacs tries |
| 10 | to protect the user from the consequences of crashes or of the user's |
| 11 | own errors. Auto-saving preserves the text from earlier in the current |
| 12 | editing session; backup files preserve file contents prior to the |
| 13 | current session. |
| 14 | |
| 15 | @menu |
| 16 | * Backup Files:: How backup files are made; how their names are chosen. |
| 17 | * Auto-Saving:: How auto-save files are made; how their names are chosen. |
| 18 | * Reverting:: @code{revert-buffer}, and how to customize what it does. |
| 19 | @end menu |
| 20 | |
| 21 | @node Backup Files |
| 22 | @section Backup Files |
| 23 | @cindex backup file |
| 24 | |
| 25 | A @dfn{backup file} is a copy of the old contents of a file you are |
| 26 | editing. Emacs makes a backup file the first time you save a buffer |
| 27 | into its visited file. Thus, normally, the backup file contains the |
| 28 | contents of the file as it was before the current editing session. |
| 29 | The contents of the backup file normally remain unchanged once it |
| 30 | exists. |
| 31 | |
| 32 | Backups are usually made by renaming the visited file to a new name. |
| 33 | Optionally, you can specify that backup files should be made by copying |
| 34 | the visited file. This choice makes a difference for files with |
| 35 | multiple names; it also can affect whether the edited file remains owned |
| 36 | by the original owner or becomes owned by the user editing it. |
| 37 | |
| 38 | By default, Emacs makes a single backup file for each file edited. |
| 39 | You can alternatively request numbered backups; then each new backup |
| 40 | file gets a new name. You can delete old numbered backups when you |
| 41 | don't want them any more, or Emacs can delete them automatically. |
| 42 | |
| 43 | @menu |
| 44 | * Making Backups:: How Emacs makes backup files, and when. |
| 45 | * Rename or Copy:: Two alternatives: renaming the old file or copying it. |
| 46 | * Numbered Backups:: Keeping multiple backups for each source file. |
| 47 | * Backup Names:: How backup file names are computed; customization. |
| 48 | @end menu |
| 49 | |
| 50 | @node Making Backups |
| 51 | @subsection Making Backup Files |
| 52 | |
| 53 | @defun backup-buffer |
| 54 | This function makes a backup of the file visited by the current |
| 55 | buffer, if appropriate. It is called by @code{save-buffer} before |
| 56 | saving the buffer the first time. |
| 57 | |
| 58 | If a backup was made by renaming, the return value is a cons cell of |
| 59 | the form (@var{modes} @var{context} @var{backupname}), where |
| 60 | @var{modes} are the mode bits of the original file, as returned by |
| 61 | @code{file-modes} (@pxref{File Attributes,, Other Information about |
| 62 | Files}), @var{context} is a list describing the original file's |
| 63 | SELinux context (@pxref{File Attributes}), and @var{backupname} is the |
| 64 | name of the backup. In all other cases, that is, if a backup was made |
| 65 | by copying or if no backup was made, this 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 |
| 90 | (lambda () |
| 91 | (set (make-local-variable 'make-backup-files) nil))) |
| 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 | |
| 122 | @defopt backup-directory-alist |
| 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} (the default), or it fails to match a |
| 143 | filename, the backup is made in the original file's directory. |
| 144 | |
| 145 | On MS-DOS filesystems without long names this variable is always |
| 146 | ignored. |
| 147 | @end defopt |
| 148 | |
| 149 | @defopt make-backup-file-name-function |
| 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. |
| 158 | @end defopt |
| 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. The default is @code{nil}. |
| 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). The default is @code{nil}. |
| 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} (the default), Emacs makes backups |
| 212 | by copying in cases where renaming would change either the owner or |
| 213 | the group of the file. |
| 214 | |
| 215 | The value has no effect when renaming would not alter the owner or |
| 216 | group of the file; that is, for files which are owned by the user and |
| 217 | whose group matches the default for a new file created there by the |
| 218 | user. |
| 219 | |
| 220 | This variable is significant only if @code{backup-by-copying} is |
| 221 | @code{nil}, since copying is always used when that variable is |
| 222 | non-@code{nil}. |
| 223 | @end defopt |
| 224 | |
| 225 | @defopt backup-by-copying-when-privileged-mismatch |
| 226 | This variable, if non-@code{nil}, specifies the same behavior as |
| 227 | @code{backup-by-copying-when-mismatch}, but only for certain user-id |
| 228 | values: namely, those less than or equal to a certain number. You set |
| 229 | this variable to that number. |
| 230 | |
| 231 | Thus, if you set @code{backup-by-copying-when-privileged-mismatch} |
| 232 | to 0, backup by copying is done for the superuser only, |
| 233 | when necessary to prevent a change in the owner of the file. |
| 234 | |
| 235 | The default is 200. |
| 236 | @end defopt |
| 237 | |
| 238 | @node Numbered Backups |
| 239 | @subsection Making and Deleting Numbered Backup Files |
| 240 | |
| 241 | If a file's name is @file{foo}, the names of its numbered backup |
| 242 | versions are @file{foo.~@var{v}~}, for various integers @var{v}, like |
| 243 | this: @file{foo.~1~}, @file{foo.~2~}, @file{foo.~3~}, @dots{}, |
| 244 | @file{foo.~259~}, and so on. |
| 245 | |
| 246 | @defopt version-control |
| 247 | This variable controls whether to make a single non-numbered backup |
| 248 | file or multiple numbered backups. |
| 249 | |
| 250 | @table @asis |
| 251 | @item @code{nil} |
| 252 | Make numbered backups if the visited file already has numbered backups; |
| 253 | otherwise, do not. This is the default. |
| 254 | |
| 255 | @item @code{never} |
| 256 | Do not make numbered backups. |
| 257 | |
| 258 | @item @var{anything else} |
| 259 | Make numbered backups. |
| 260 | @end table |
| 261 | @end defopt |
| 262 | |
| 263 | The use of numbered backups ultimately leads to a large number of |
| 264 | backup versions, which must then be deleted. Emacs can do this |
| 265 | automatically or it can ask the user whether to delete them. |
| 266 | |
| 267 | @defopt kept-new-versions |
| 268 | The value of this variable is the number of newest versions to keep |
| 269 | when a new numbered backup is made. The newly made backup is included |
| 270 | in the count. The default value is@tie{}2. |
| 271 | @end defopt |
| 272 | |
| 273 | @defopt kept-old-versions |
| 274 | The value of this variable is the number of oldest versions to keep |
| 275 | when a new numbered backup is made. The default value is@tie{}2. |
| 276 | @end defopt |
| 277 | |
| 278 | If there are backups numbered 1, 2, 3, 5, and 7, and both of these |
| 279 | variables have the value 2, then the backups numbered 1 and 2 are kept |
| 280 | as old versions and those numbered 5 and 7 are kept as new versions; |
| 281 | backup version 3 is excess. The function @code{find-backup-file-name} |
| 282 | (@pxref{Backup Names}) is responsible for determining which backup |
| 283 | versions to delete, but does not delete them itself. |
| 284 | |
| 285 | @defopt delete-old-versions |
| 286 | If this variable is @code{t}, then saving a file deletes excess |
| 287 | backup versions silently. If it is @code{nil}, that means |
| 288 | to ask for confirmation before deleting excess backups. |
| 289 | Otherwise, they are not deleted at all. |
| 290 | @end defopt |
| 291 | |
| 292 | @defopt dired-kept-versions |
| 293 | This variable specifies how many of the newest backup versions to keep |
| 294 | in the Dired command @kbd{.} (@code{dired-clean-directory}). That's the |
| 295 | same thing @code{kept-new-versions} specifies when you make a new backup |
| 296 | file. The default is@tie{}2. |
| 297 | @end defopt |
| 298 | |
| 299 | @node Backup Names |
| 300 | @subsection Naming Backup Files |
| 301 | |
| 302 | The functions in this section are documented mainly because you can |
| 303 | customize the naming conventions for backup files by redefining them. |
| 304 | If you change one, you probably need to change the rest. |
| 305 | |
| 306 | @defun backup-file-name-p filename |
| 307 | This function returns a non-@code{nil} value if @var{filename} is a |
| 308 | possible name for a backup file. It just checks the name, not whether |
| 309 | a file with the name @var{filename} exists. |
| 310 | |
| 311 | @smallexample |
| 312 | @group |
| 313 | (backup-file-name-p "foo") |
| 314 | @result{} nil |
| 315 | @end group |
| 316 | @group |
| 317 | (backup-file-name-p "foo~") |
| 318 | @result{} 3 |
| 319 | @end group |
| 320 | @end smallexample |
| 321 | |
| 322 | The standard definition of this function is as follows: |
| 323 | |
| 324 | @smallexample |
| 325 | @group |
| 326 | (defun backup-file-name-p (file) |
| 327 | "Return non-nil if FILE is a backup file \ |
| 328 | name (numeric or not)..." |
| 329 | (string-match "~\\'" file)) |
| 330 | @end group |
| 331 | @end smallexample |
| 332 | |
| 333 | @noindent |
| 334 | Thus, the function returns a non-@code{nil} value if the file name ends |
| 335 | with a @samp{~}. (We use a backslash to split the documentation |
| 336 | string's first line into two lines in the text, but produce just one |
| 337 | line in the string itself.) |
| 338 | |
| 339 | This simple expression is placed in a separate function to make it easy |
| 340 | to redefine for customization. |
| 341 | @end defun |
| 342 | |
| 343 | @defun make-backup-file-name filename |
| 344 | This function returns a string that is the name to use for a |
| 345 | non-numbered backup file for file @var{filename}. On Unix, this is just |
| 346 | @var{filename} with a tilde appended. |
| 347 | |
| 348 | The standard definition of this function, on most operating systems, is |
| 349 | as follows: |
| 350 | |
| 351 | @smallexample |
| 352 | @group |
| 353 | (defun make-backup-file-name (file) |
| 354 | "Create the non-numeric backup file name for FILE..." |
| 355 | (concat file "~")) |
| 356 | @end group |
| 357 | @end smallexample |
| 358 | |
| 359 | You can change the backup-file naming convention by redefining this |
| 360 | function. The following example redefines @code{make-backup-file-name} |
| 361 | to prepend a @samp{.} in addition to appending a tilde: |
| 362 | |
| 363 | @smallexample |
| 364 | @group |
| 365 | (defun make-backup-file-name (filename) |
| 366 | (expand-file-name |
| 367 | (concat "." (file-name-nondirectory filename) "~") |
| 368 | (file-name-directory filename))) |
| 369 | @end group |
| 370 | |
| 371 | @group |
| 372 | (make-backup-file-name "backups.texi") |
| 373 | @result{} ".backups.texi~" |
| 374 | @end group |
| 375 | @end smallexample |
| 376 | |
| 377 | Some parts of Emacs, including some Dired commands, assume that backup |
| 378 | file names end with @samp{~}. If you do not follow that convention, it |
| 379 | will not cause serious problems, but these commands may give |
| 380 | less-than-desirable results. |
| 381 | @end defun |
| 382 | |
| 383 | @defun find-backup-file-name filename |
| 384 | This function computes the file name for a new backup file for |
| 385 | @var{filename}. It may also propose certain existing backup files for |
| 386 | deletion. @code{find-backup-file-name} returns a list whose @sc{car} is |
| 387 | the name for the new backup file and whose @sc{cdr} is a list of backup |
| 388 | files whose deletion is proposed. The value can also be @code{nil}, |
| 389 | which means not to make a backup. |
| 390 | |
| 391 | Two variables, @code{kept-old-versions} and @code{kept-new-versions}, |
| 392 | determine which backup versions should be kept. This function keeps |
| 393 | those versions by excluding them from the @sc{cdr} of the value. |
| 394 | @xref{Numbered Backups}. |
| 395 | |
| 396 | In this example, the value says that @file{~rms/foo.~5~} is the name |
| 397 | to use for the new backup file, and @file{~rms/foo.~3~} is an ``excess'' |
| 398 | version that the caller should consider deleting now. |
| 399 | |
| 400 | @smallexample |
| 401 | @group |
| 402 | (find-backup-file-name "~rms/foo") |
| 403 | @result{} ("~rms/foo.~5~" "~rms/foo.~3~") |
| 404 | @end group |
| 405 | @end smallexample |
| 406 | @end defun |
| 407 | |
| 408 | @c Emacs 19 feature |
| 409 | @defun file-newest-backup filename |
| 410 | This function returns the name of the most recent backup file for |
| 411 | @var{filename}, or @code{nil} if that file has no backup files. |
| 412 | |
| 413 | Some file comparison commands use this function so that they can |
| 414 | automatically compare a file with its most recent backup. |
| 415 | @end defun |
| 416 | |
| 417 | @node Auto-Saving |
| 418 | @section Auto-Saving |
| 419 | @c @cindex auto-saving Lots of symbols starting with auto-save here. |
| 420 | |
| 421 | Emacs periodically saves all files that you are visiting; this is |
| 422 | called @dfn{auto-saving}. Auto-saving prevents you from losing more |
| 423 | than a limited amount of work if the system crashes. By default, |
| 424 | auto-saves happen every 300 keystrokes, or after around 30 seconds of |
| 425 | idle time. @xref{Auto Save, Auto Save, Auto-Saving: Protection Against |
| 426 | Disasters, emacs, The GNU Emacs Manual}, for information on auto-save |
| 427 | for users. Here we describe the functions used to implement auto-saving |
| 428 | and the variables that control them. |
| 429 | |
| 430 | @defvar buffer-auto-save-file-name |
| 431 | This buffer-local variable is the name of the file used for |
| 432 | auto-saving the current buffer. It is @code{nil} if the buffer |
| 433 | should not be auto-saved. |
| 434 | |
| 435 | @example |
| 436 | @group |
| 437 | buffer-auto-save-file-name |
| 438 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" |
| 439 | @end group |
| 440 | @end example |
| 441 | @end defvar |
| 442 | |
| 443 | @deffn Command auto-save-mode arg |
| 444 | This is the mode command for Auto Save mode, a buffer-local minor |
| 445 | mode. When Auto Save mode is enabled, auto-saving is enabled in the |
| 446 | buffer. The calling convention is the same as for other minor mode |
| 447 | commands (@pxref{Minor Mode Conventions}). |
| 448 | |
| 449 | Unlike most minor modes, there is no @code{auto-save-mode} variable. |
| 450 | Auto Save mode is enabled if @code{buffer-auto-save-file-name} is |
| 451 | non-@code{nil} and @code{buffer-saved-size} (see below) is non-zero. |
| 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 |
| 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 |
| 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) |
| 464 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" |
| 465 | @end group |
| 466 | @group |
| 467 | (auto-save-file-name-p "#backups.texi#") |
| 468 | @result{} 0 |
| 469 | @end group |
| 470 | @group |
| 471 | (auto-save-file-name-p "backups.texi") |
| 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 |
| 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 |
| 496 | @code{auto-save-visited-file-name} (described below); callers of this |
| 497 | function should check that variable first. |
| 498 | |
| 499 | @example |
| 500 | @group |
| 501 | (make-auto-save-file-name) |
| 502 | @result{} "/xcssun/users/rms/lewis/#backups.texi#" |
| 503 | @end group |
| 504 | @end example |
| 505 | |
| 506 | Here is a simplified version of the standard definition of this |
| 507 | function: |
| 508 | |
| 509 | @example |
| 510 | @group |
| 511 | (defun make-auto-save-file-name () |
| 512 | "Return file name to use for auto-saves \ |
| 513 | of current buffer.." |
| 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 | |
| 532 | @defopt auto-save-visited-file-name |
| 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 |
| 535 | file that you are editing. Normally, this variable is @code{nil}, so |
| 536 | auto-save files have distinct names that are created by |
| 537 | @code{make-auto-save-file-name}. |
| 538 | |
| 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. |
| 544 | @end defopt |
| 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 |
| 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 |
| 561 | enabled. Setting this to zero disables autosaving based on the |
| 562 | number of characters typed. |
| 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, |
| 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 |
| 570 | factor that increases as the size increases; for a million-byte |
| 571 | buffer, the factor is almost 4.) |
| 572 | |
| 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}. |
| 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 | |
| 587 | @deffn Command do-auto-save &optional no-message current-only |
| 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 | |
| 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. |
| 596 | |
| 597 | If @var{current-only} is non-@code{nil}, only the current buffer |
| 598 | is auto-saved. |
| 599 | @end deffn |
| 600 | |
| 601 | @defun delete-auto-save-file-if-necessary &optional force |
| 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. |
| 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. |
| 609 | @end defun |
| 610 | |
| 611 | @defopt delete-auto-save-files |
| 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. |
| 616 | @end defopt |
| 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 |
| 621 | file, if it was made in the current Emacs session. If the visited |
| 622 | file name has not changed, this function does nothing. |
| 623 | @end defun |
| 624 | |
| 625 | @defvar buffer-saved-size |
| 626 | The value of this buffer-local variable is the length of the current |
| 627 | buffer, when it was last read in, saved, or auto-saved. This is |
| 628 | used to detect a substantial decrease in size, and turn off auto-saving |
| 629 | in response. |
| 630 | |
| 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. |
| 636 | |
| 637 | If it is @minus{}2, that means this buffer should disregard changes in |
| 638 | buffer size; in particular, it should not shut off auto-saving |
| 639 | temporarily due to changes in buffer size. |
| 640 | @end defvar |
| 641 | |
| 642 | @defvar auto-save-list-file-name |
| 643 | This variable (if non-@code{nil}) specifies a file for recording the |
| 644 | names of all the auto-save files. Each time Emacs does auto-saving, it |
| 645 | writes two lines into this file for each buffer that has auto-saving |
| 646 | enabled. The first line gives the name of the visited file (it's empty |
| 647 | if the buffer has none), and the second gives the name of the auto-save |
| 648 | file. |
| 649 | |
| 650 | When Emacs exits normally, it deletes this file; if Emacs crashes, you |
| 651 | can look in the file to find all the auto-save files that might contain |
| 652 | work that was otherwise lost. The @code{recover-session} command uses |
| 653 | this file to find them. |
| 654 | |
| 655 | The default name for this file specifies your home directory and starts |
| 656 | with @samp{.saves-}. It also contains the Emacs process @acronym{ID} and the |
| 657 | host name. |
| 658 | @end defvar |
| 659 | |
| 660 | @defopt auto-save-list-file-prefix |
| 661 | After Emacs reads your init file, it initializes |
| 662 | @code{auto-save-list-file-name} (if you have not already set it |
| 663 | non-@code{nil}) based on this prefix, adding the host name and process |
| 664 | ID. If you set this to @code{nil} in your init file, then Emacs does |
| 665 | not initialize @code{auto-save-list-file-name}. |
| 666 | @end defopt |
| 667 | |
| 668 | @node Reverting |
| 669 | @section Reverting |
| 670 | |
| 671 | If you have made extensive changes to a file and then change your mind |
| 672 | about them, you can get rid of them by reading in the previous version |
| 673 | of the file with the @code{revert-buffer} command. @xref{Reverting, , |
| 674 | Reverting a Buffer, emacs, The GNU Emacs Manual}. |
| 675 | |
| 676 | @deffn Command revert-buffer &optional ignore-auto noconfirm preserve-modes |
| 677 | This command replaces the buffer text with the text of the visited |
| 678 | file on disk. This action undoes all changes since the file was visited |
| 679 | or saved. |
| 680 | |
| 681 | By default, if the latest auto-save file is more recent than the visited |
| 682 | file, and the argument @var{ignore-auto} is @code{nil}, |
| 683 | @code{revert-buffer} asks the user whether to use that auto-save |
| 684 | instead. When you invoke this command interactively, @var{ignore-auto} |
| 685 | is @code{t} if there is no numeric prefix argument; thus, the |
| 686 | interactive default is not to check the auto-save file. |
| 687 | |
| 688 | Normally, @code{revert-buffer} asks for confirmation before it changes |
| 689 | the buffer; but if the argument @var{noconfirm} is non-@code{nil}, |
| 690 | @code{revert-buffer} does not ask for confirmation. |
| 691 | |
| 692 | Normally, this command reinitializes the buffer's major and minor modes |
| 693 | using @code{normal-mode}. But if @var{preserve-modes} is |
| 694 | non-@code{nil}, the modes remain unchanged. |
| 695 | |
| 696 | Reverting tries to preserve marker positions in the buffer by using the |
| 697 | replacement feature of @code{insert-file-contents}. If the buffer |
| 698 | contents and the file contents are identical before the revert |
| 699 | operation, reverting preserves all the markers. If they are not |
| 700 | identical, reverting does change the buffer; in that case, it preserves |
| 701 | the markers in the unchanged text (if any) at the beginning and end of |
| 702 | the buffer. Preserving any additional markers would be problematical. |
| 703 | @end deffn |
| 704 | |
| 705 | @defvar revert-buffer-in-progress-p |
| 706 | @code{revert-buffer} binds this variable to a non-@code{nil} value |
| 707 | while it is working. |
| 708 | @end defvar |
| 709 | |
| 710 | You can customize how @code{revert-buffer} does its work by setting |
| 711 | the variables described in the rest of this section. |
| 712 | |
| 713 | @defopt revert-without-query |
| 714 | This variable holds a list of files that should be reverted without |
| 715 | query. The value is a list of regular expressions. If the visited file |
| 716 | name matches one of these regular expressions, and the file has changed |
| 717 | on disk but the buffer is not modified, then @code{revert-buffer} |
| 718 | reverts the file without asking the user for confirmation. |
| 719 | @end defopt |
| 720 | |
| 721 | Some major modes customize @code{revert-buffer} by making |
| 722 | buffer-local bindings for these variables: |
| 723 | |
| 724 | @defvar revert-buffer-function |
| 725 | @anchor{Definition of revert-buffer-function} |
| 726 | The value of this variable is the function to use to revert this |
| 727 | buffer. If non-@code{nil}, it should be a function with two optional |
| 728 | arguments to do the work of reverting. The two optional arguments, |
| 729 | @var{ignore-auto} and @var{noconfirm}, are the arguments that |
| 730 | @code{revert-buffer} received. If the value is @code{nil}, reverting |
| 731 | works the usual way. |
| 732 | |
| 733 | Modes such as Dired mode, in which the text being edited does not |
| 734 | consist of a file's contents but can be regenerated in some other |
| 735 | fashion, can give this variable a buffer-local value that is a function to |
| 736 | regenerate the contents. |
| 737 | @end defvar |
| 738 | |
| 739 | @defvar revert-buffer-insert-file-contents-function |
| 740 | The value of this variable, if non-@code{nil}, specifies the function to use to |
| 741 | insert the updated contents when reverting this buffer. The function |
| 742 | receives two arguments: first the file name to use; second, @code{t} if |
| 743 | the user has asked to read the auto-save file. |
| 744 | |
| 745 | The reason for a mode to set this variable instead of |
| 746 | @code{revert-buffer-function} is to avoid duplicating or replacing the |
| 747 | rest of what @code{revert-buffer} does: asking for confirmation, |
| 748 | clearing the undo list, deciding the proper major mode, and running the |
| 749 | hooks listed below. |
| 750 | @end defvar |
| 751 | |
| 752 | @defvar before-revert-hook |
| 753 | This normal hook is run by @code{revert-buffer} before |
| 754 | inserting the modified contents---but only if |
| 755 | @code{revert-buffer-function} is @code{nil}. |
| 756 | @end defvar |
| 757 | |
| 758 | @defvar after-revert-hook |
| 759 | This normal hook is run by @code{revert-buffer} after inserting |
| 760 | the modified contents---but only if @code{revert-buffer-function} is |
| 761 | @code{nil}. |
| 762 | @end defvar |
| 763 | |
| 764 | @c FIXME? Move this section from arevert-xtra to here? |
| 765 | @defvar buffer-stale-function |
| 766 | The value of this variable, if non-@code{nil}, specifies a function |
| 767 | to call to check whether a non-file buffer needs reverting |
| 768 | @iftex |
| 769 | (@pxref{Supporting additional buffers,,, emacs-xtra, Specialized Emacs Features}). |
| 770 | @end iftex |
| 771 | @ifnottex |
| 772 | (@pxref{Supporting additional buffers,,, emacs}). |
| 773 | @end ifnottex |
| 774 | @end defvar |
| 775 | |