1 This is ../info/lispref.info, produced by makeinfo version 4.0 from
4 INFO-DIR-SECTION XEmacs Editor
6 * Lispref: (lispref). XEmacs Lisp Reference Manual.
11 GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU
12 Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid
13 Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994
14 XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995
15 GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp
16 Programmer's Manual (for 19.13) Third Edition, July 1995 XEmacs Lisp
17 Reference Manual (for 19.14 and 20.0) v3.1, March 1996 XEmacs Lisp
18 Reference Manual (for 19.15 and 20.1, 20.2, 20.3) v3.2, April, May,
19 November 1997 XEmacs Lisp Reference Manual (for 21.0) v3.3, April 1998
21 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software
22 Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc.
23 Copyright (C) 1995, 1996 Ben Wing.
25 Permission is granted to make and distribute verbatim copies of this
26 manual provided the copyright notice and this permission notice are
27 preserved on all copies.
29 Permission is granted to copy and distribute modified versions of
30 this manual under the conditions for verbatim copying, provided that the
31 entire resulting derived work is distributed under the terms of a
32 permission notice identical to this one.
34 Permission is granted to copy and distribute translations of this
35 manual into another language, under the above conditions for modified
36 versions, except that this permission notice may be stated in a
37 translation approved by the Foundation.
39 Permission is granted to copy and distribute modified versions of
40 this manual under the conditions for verbatim copying, provided also
41 that the section entitled "GNU General Public License" is included
42 exactly as in the original, and provided that the entire resulting
43 derived work is distributed under the terms of a permission notice
44 identical to this one.
46 Permission is granted to copy and distribute translations of this
47 manual into another language, under the above conditions for modified
48 versions, except that the section entitled "GNU General Public License"
49 may be included in a translation approved by the Free Software
50 Foundation instead of in the original English.
53 File: lispref.info, Node: User Name Completion, Prev: File Name Completion, Up: File Names
58 This section describes low-level subroutines for completing a user
59 name. For other completion functions, see *Note Completion::.
61 - Function: user-name-all-completions partial-username
62 This function returns a list of all possible completions for a user
63 whose name starts with PARTIAL-USERNAME. The order of the
64 completions is unpredictable and conveys no useful information.
66 The argument PARTIAL-USERNAME must be a partial user name
67 containing no tilde character and no slash.
69 - Function: user-name-completion username
70 This function completes the user name USERNAME. It returns the
71 longest prefix common to all user names that start with USERNAME.
73 If only one match exists and USERNAME matches it exactly, the
74 function returns `t'. The function returns `nil' if no user name
75 starting with USERNAME exists.
77 - Function: user-name-completion-1 username
78 This function completes the user name USERNAME, like
79 `user-name-completion', differing only in the return value. This
80 function returns the cons of the completion returned by
81 `user-name-completion', and a boolean indicating whether that
82 completion was unique.
85 File: lispref.info, Node: Contents of Directories, Next: Create/Delete Dirs, Prev: File Names, Up: Files
87 Contents of Directories
88 =======================
90 A directory is a kind of file that contains other files entered under
91 various names. Directories are a feature of the file system.
93 XEmacs can list the names of the files in a directory as a Lisp list,
94 or display the names in a buffer using the `ls' shell command. In the
95 latter case, it can optionally display information about each file,
96 depending on the value of switches passed to the `ls' command.
98 - Function: directory-files directory &optional full-name match-regexp
100 This function returns a list of the names of the files in the
101 directory DIRECTORY. By default, the list is in alphabetical
104 If FULL-NAME is non-`nil', the function returns the files'
105 absolute file names. Otherwise, it returns just the names
106 relative to the specified directory.
108 If MATCH-REGEXP is non-`nil', this function returns only those
109 file names that contain that regular expression--the other file
110 names are discarded from the list.
112 If NOSORT is non-`nil', `directory-files' does not sort the list,
113 so you get the file names in no particular order. Use this if you
114 want the utmost possible speed and don't care what order the files
115 are processed in. If the order of processing is visible to the
116 user, then the user will probably be happier if you do sort the
119 If FILES-ONLY is the symbol `t', then only the "files" in the
120 directory will be returned; subdirectories will be excluded. If
121 FILES-ONLY is not `nil' and not `t', then only the subdirectories
122 will be returned. Otherwise, if FILES-ONLY is `nil' (the default)
123 then both files and subdirectories will be returned.
125 (directory-files "~lewis")
126 => ("#foo#" "#foo.el#" "." ".."
127 "dired-mods.el" "files.texi"
130 An error is signaled if DIRECTORY is not the name of a directory
133 - Function: insert-directory file switches &optional wildcard
135 This function inserts (in the current buffer) a directory listing
136 for directory FILE, formatted with `ls' according to SWITCHES. It
137 leaves point after the inserted text.
139 The argument FILE may be either a directory name or a file
140 specification including wildcard characters. If WILDCARD is
141 non-`nil', that means treat FILE as a file specification with
144 If FULL-DIRECTORY-P is non-`nil', that means FILE is a directory
145 and switches do not contain `-d', so that the listing should show
146 the full contents of the directory. (The `-d' option to `ls' says
147 to describe a directory itself rather than its contents.)
149 This function works by running a directory listing program whose
150 name is in the variable `insert-directory-program'. If WILDCARD is
151 non-`nil', it also runs the shell specified by `shell-file-name',
152 to expand the wildcards.
154 - Variable: insert-directory-program
155 This variable's value is the program to run to generate a
156 directory listing for the function `insert-directory'.
159 File: lispref.info, Node: Create/Delete Dirs, Next: Magic File Names, Prev: Contents of Directories, Up: Files
161 Creating and Deleting Directories
162 =================================
164 Most XEmacs Lisp file-manipulation functions get errors when used on
165 files that are directories. For example, you cannot delete a directory
166 with `delete-file'. These special functions exist to create and delete
169 - Command: make-directory dirname &optional parents
170 This function creates a directory named DIRNAME. Interactively,
171 the default choice of directory to create is the current default
172 directory for file names. That is useful when you have visited a
173 file in a nonexistent directory.
175 Non-interactively, optional argument PARENTS says whether to
176 create parent directories if they don't exist. (Interactively, this
179 - Command: delete-directory dirname
180 This function deletes the directory named DIRNAME. The function
181 `delete-file' does not work for files that are directories; you
182 must use `delete-directory' in that case.
185 File: lispref.info, Node: Magic File Names, Next: Partial Files, Prev: Create/Delete Dirs, Up: Files
187 Making Certain File Names "Magic"
188 =================================
190 You can implement special handling for certain file names. This is
191 called making those names "magic". You must supply a regular
192 expression to define the class of names (all those that match the
193 regular expression), plus a handler that implements all the primitive
194 XEmacs file operations for file names that do match.
196 The variable `file-name-handler-alist' holds a list of handlers,
197 together with regular expressions that determine when to apply each
198 handler. Each element has this form:
202 All the XEmacs primitives for file access and file name transformation
203 check the given file name against `file-name-handler-alist'. If the
204 file name matches REGEXP, the primitives handle that file by calling
207 The first argument given to HANDLER is the name of the primitive;
208 the remaining arguments are the arguments that were passed to that
209 operation. (The first of these arguments is typically the file name
210 itself.) For example, if you do this:
212 (file-exists-p FILENAME)
214 and FILENAME has handler HANDLER, then HANDLER is called like this:
216 (funcall HANDLER 'file-exists-p FILENAME)
218 Here are the operations that a magic file name handler gets to
221 `add-name-to-file', `copy-file', `delete-directory', `delete-file',
222 `diff-latest-backup-file', `directory-file-name', `directory-files',
223 `dired-compress-file', `dired-uncache', `expand-file-name',
224 `file-accessible-directory-p', `file-attributes', `file-directory-p',
225 `file-executable-p', `file-exists-p', `file-local-copy', `file-modes',
226 `file-name-all-completions', `file-name-as-directory',
227 `file-name-completion', `file-name-directory', `file-name-nondirectory',
228 `file-name-sans-versions', `file-newer-than-file-p', `file-readable-p',
229 `file-regular-p', `file-symlink-p', `file-truename', `file-writable-p',
230 `get-file-buffer', `insert-directory', `insert-file-contents', `load',
231 `make-directory', `make-symbolic-link', `rename-file', `set-file-modes',
232 `set-visited-file-modtime', `unhandled-file-name-directory',
233 `verify-visited-file-modtime', `write-region'.
235 Handlers for `insert-file-contents' typically need to clear the
236 buffer's modified flag, with `(set-buffer-modified-p nil)', if the
237 VISIT argument is non-`nil'. This also has the effect of unlocking the
238 buffer if it is locked.
240 The handler function must handle all of the above operations, and
241 possibly others to be added in the future. It need not implement all
242 these operations itself--when it has nothing special to do for a
243 certain operation, it can reinvoke the primitive, to handle the
244 operation "in the usual way". It should always reinvoke the primitive
245 for an operation it does not recognize. Here's one way to do this:
247 (defun my-file-handler (operation &rest args)
248 ;; First check for the specific operations
249 ;; that we have special handling for.
250 (cond ((eq operation 'insert-file-contents) ...)
251 ((eq operation 'write-region) ...)
253 ;; Handle any operation we don't know about.
254 (t (let ((inhibit-file-name-handlers
255 (cons 'my-file-handler
256 (and (eq inhibit-file-name-operation operation)
257 inhibit-file-name-handlers)))
258 (inhibit-file-name-operation operation))
259 (apply operation args)))))
261 When a handler function decides to call the ordinary Emacs primitive
262 for the operation at hand, it needs to prevent the primitive from
263 calling the same handler once again, thus leading to an infinite
264 recursion. The example above shows how to do this, with the variables
265 `inhibit-file-name-handlers' and `inhibit-file-name-operation'. Be
266 careful to use them exactly as shown above; the details are crucial for
267 proper behavior in the case of multiple handlers, and for operations
268 that have two file names that may each have handlers.
270 - Variable: inhibit-file-name-handlers
271 This variable holds a list of handlers whose use is presently
272 inhibited for a certain operation.
274 - Variable: inhibit-file-name-operation
275 The operation for which certain handlers are presently inhibited.
277 - Function: find-file-name-handler file operation
278 This function returns the handler function for file name FILE, or
279 `nil' if there is none. The argument OPERATION should be the
280 operation to be performed on the file--the value you will pass to
281 the handler as its first argument when you call it. The operation
282 is needed for comparison with `inhibit-file-name-operation'.
284 - Function: file-local-copy filename
285 This function copies file FILENAME to an ordinary non-magic file,
286 if it isn't one already.
288 If FILENAME specifies a "magic" file name, which programs outside
289 Emacs cannot directly read or write, this copies the contents to
290 an ordinary file and returns that file's name.
292 If FILENAME is an ordinary file name, not magic, then this function
293 does nothing and returns `nil'.
295 - Function: unhandled-file-name-directory filename
296 This function returns the name of a directory that is not magic.
297 It uses the directory part of FILENAME if that is not magic.
298 Otherwise, it asks the handler what to do.
300 This is useful for running a subprocess; every subprocess must
301 have a non-magic directory to serve as its current directory, and
302 this function is a good way to come up with one.
305 File: lispref.info, Node: Partial Files, Next: Format Conversion, Prev: Magic File Names, Up: Files
312 * Intro to Partial Files::
313 * Creating a Partial File::
314 * Detached Partial Files::
317 File: lispref.info, Node: Intro to Partial Files, Next: Creating a Partial File, Up: Partial Files
319 Intro to Partial Files
320 ----------------------
322 A "partial file" is a section of a buffer (called the "master
323 buffer") that is placed in its own buffer and treated as its own file.
324 Changes made to the partial file are not reflected in the master buffer
325 until the partial file is "saved" using the standard buffer save
326 commands. Partial files can be "reverted" (from the master buffer)
327 just like normal files. When a file part is active on a master buffer,
328 that section of the master buffer is marked as read-only. Two file
329 parts on the same master buffer are not allowed to overlap. Partial
330 file buffers are indicated by the words `File Part' in the modeline.
332 The master buffer knows about all the partial files that are active
333 on it, and thus killing or reverting the master buffer will be handled
334 properly. When the master buffer is saved, if there are any unsaved
335 partial files active on it then the user will be given the opportunity
336 to first save these files.
338 When a partial file buffer is first modified, the master buffer is
339 automatically marked as modified so that saving the master buffer will
343 File: lispref.info, Node: Creating a Partial File, Next: Detached Partial Files, Prev: Intro to Partial Files, Up: Partial Files
345 Creating a Partial File
346 -----------------------
348 - Function: make-file-part &optional start end name buffer
349 Make a file part on buffer BUFFER out of the region. Call it
350 NAME. This command creates a new buffer containing the contents
351 of the region and marks the buffer as referring to the specified
352 buffer, called the "master buffer". When the file-part buffer is
353 saved, its changes are integrated back into the master buffer.
354 When the master buffer is deleted, all file parts are deleted with
357 When called from a function, expects four arguments, START, END,
358 NAME, and BUFFER, all of which are optional and default to the
359 beginning of BUFFER, the end of BUFFER, a name generated from
360 BUFFER name, and the current buffer, respectively.
363 File: lispref.info, Node: Detached Partial Files, Prev: Creating a Partial File, Up: Partial Files
365 Detached Partial Files
366 ----------------------
368 Every partial file has an extent in the master buffer associated
369 with it (called the "master extent"), marking where in the master
370 buffer the partial file begins and ends. If the text in master buffer
371 that is contained by the extent is deleted, then the extent becomes
372 "detached", meaning that it no longer refers to a specific region of
373 the master buffer. This can happen either when the text is deleted
374 directly or when the master buffer is reverted. Neither of these should
375 happen in normal usage because the master buffer should generally not be
378 Before doing any operation that references a partial file's master
379 extent, XEmacs checks to make sure that the extent is not detached. If
380 this is the case, XEmacs warns the user of this and the master extent is
381 deleted out of the master buffer, disconnecting the file part. The file
382 part's filename is cleared and thus must be explicitly specified if the
383 detached file part is to be saved.
386 File: lispref.info, Node: Format Conversion, Next: Files and MS-DOS, Prev: Partial Files, Up: Files
388 File Format Conversion
389 ======================
391 The variable `format-alist' defines a list of "file formats", which
392 describe textual representations used in files for the data (text,
393 text-properties, and possibly other information) in an Emacs buffer.
394 Emacs performs format conversion if appropriate when reading and writing
397 - Variable: format-alist
398 This list contains one format definition for each defined file
401 Each format definition is a list of this form:
403 (NAME DOC-STRING REGEXP FROM-FN TO-FN MODIFY MODE-FN)
405 Here is what the elements in a format definition mean:
408 The name of this format.
411 A documentation string for the format.
414 A regular expression which is used to recognize files represented
418 A function to call to decode data in this format (to convert file
419 data into the usual Emacs data representation).
421 The FROM-FN is called with two args, BEGIN and END, which specify
422 the part of the buffer it should convert. It should convert the
423 text by editing it in place. Since this can change the length of
424 the text, FROM-FN should return the modified end position.
426 One responsibility of FROM-FN is to make sure that the beginning
427 of the file no longer matches REGEXP. Otherwise it is likely to
431 A function to call to encode data in this format (to convert the
432 usual Emacs data representation into this format).
434 The TO-FN is called with two args, BEGIN and END, which specify
435 the part of the buffer it should convert. There are two ways it
436 can do the conversion:
438 * By editing the buffer in place. In this case, TO-FN should
439 return the end-position of the range of text, as modified.
441 * By returning a list of annotations. This is a list of
442 elements of the form `(POSITION . STRING)', where POSITION is
443 an integer specifying the relative position in the text to be
444 written, and STRING is the annotation to add there. The list
445 must be sorted in order of position when TO-FN returns it.
447 When `write-region' actually writes the text from the buffer
448 to the file, it intermixes the specified annotations at the
449 corresponding positions. All this takes place without
450 modifying the buffer.
453 A flag, `t' if the encoding function modifies the buffer, and
454 `nil' if it works by returning a list of annotations.
457 A mode function to call after visiting a file converted from this
460 The function `insert-file-contents' automatically recognizes file
461 formats when it reads the specified file. It checks the text of the
462 beginning of the file against the regular expressions of the format
463 definitions, and if it finds a match, it calls the decoding function for
464 that format. Then it checks all the known formats over again. It
465 keeps checking them until none of them is applicable.
467 Visiting a file, with `find-file-noselect' or the commands that use
468 it, performs conversion likewise (because it calls
469 `insert-file-contents'); it also calls the mode function for each
470 format that it decodes. It stores a list of the format names in the
471 buffer-local variable `buffer-file-format'.
473 - Variable: buffer-file-format
474 This variable states the format of the visited file. More
475 precisely, this is a list of the file format names that were
476 decoded in the course of visiting the current buffer's file. It
477 is always local in all buffers.
479 When `write-region' writes data into a file, it first calls the
480 encoding functions for the formats listed in `buffer-file-format', in
481 the order of appearance in the list.
483 - Function: format-write-file file format
484 This command writes the current buffer contents into the file FILE
485 in format FORMAT, and makes that format the default for future
486 saves of the buffer. The argument FORMAT is a list of format
489 - Function: format-find-file file format
490 This command finds the file FILE, converting it according to
491 format FORMAT. It also makes FORMAT the default if the buffer is
494 The argument FORMAT is a list of format names. If FORMAT is
495 `nil', no conversion takes place. Interactively, typing just
496 <RET> for FORMAT specifies `nil'.
498 - Function: format-insert-file file format &optional beg end
499 This command inserts the contents of file FILE, converting it
500 according to format FORMAT. If BEG and END are non-`nil', they
501 specify which part of the file to read, as in
502 `insert-file-contents' (*note Reading from Files::).
504 The return value is like what `insert-file-contents' returns: a
505 list of the absolute file name and the length of the data inserted
508 The argument FORMAT is a list of format names. If FORMAT is
509 `nil', no conversion takes place. Interactively, typing just
510 <RET> for FORMAT specifies `nil'.
512 - Function: format-find-file file format
513 This command finds the file FILE, converting it according to
514 format FORMAT. It also makes FORMAT the default if the buffer is
517 The argument FORMAT is a list of format names. If FORMAT is
518 `nil', no conversion takes place. Interactively, typing just
519 <RET> for FORMAT specifies `nil'.
521 - Function: format-insert-file file format &optional beg end
522 This command inserts the contents of file FILE, converting it
523 according to format FORMAT. If BEG and END are non-`nil', they
524 specify which part of the file to read, as in
525 `insert-file-contents' (*note Reading from Files::).
527 The return value is like what `insert-file-contents' returns: a
528 list of the absolute file name and the length of the data inserted
531 The argument FORMAT is a list of format names. If FORMAT is
532 `nil', no conversion takes place. Interactively, typing just
533 <RET> for FORMAT specifies `nil'.
535 - Variable: auto-save-file-format
536 This variable specifies the format to use for auto-saving. Its
537 value is a list of format names, just like the value of
538 `buffer-file-format'; but it is used instead of
539 `buffer-file-format' for writing auto-save files. This variable
540 is always local in all buffers.
543 File: lispref.info, Node: Files and MS-DOS, Prev: Format Conversion, Up: Files
548 Emacs on MS-DOS makes a distinction between text files and binary
549 files. This is necessary because ordinary text files on MS-DOS use a
550 two character sequence between lines: carriage-return and linefeed
551 (CRLF). Emacs expects just a newline character (a linefeed) between
552 lines. When Emacs reads or writes a text file on MS-DOS, it needs to
553 convert the line separators. This means it needs to know which files
554 are text files and which are binary. It makes this decision when
555 visiting a file, and records the decision in the variable
556 `buffer-file-type' for use when the file is saved.
558 *Note MS-DOS Subprocesses::, for a related feature for subprocesses.
560 - Variable: buffer-file-type
561 This variable, automatically local in each buffer, records the
562 file type of the buffer's visited file. The value is `nil' for
563 text, `t' for binary.
565 - Function: find-buffer-file-type filename
566 This function determines whether file FILENAME is a text file or a
567 binary file. It returns `nil' for text, `t' for binary.
569 - User Option: file-name-buffer-file-type-alist
570 This variable holds an alist for distinguishing text files from
571 binary files. Each element has the form (REGEXP . TYPE), where
572 REGEXP is matched against the file name, and TYPE may be is `nil'
573 for text, `t' for binary, or a function to call to compute which.
574 If it is a function, then it is called with a single argument (the
575 file name) and should return `t' or `nil'.
577 - User Option: default-buffer-file-type
578 This variable specifies the default file type for files whose names
579 don't indicate anything in particular. Its value should be `nil'
580 for text, or `t' for binary.
582 - Command: find-file-text filename
583 Like `find-file', but treat the file as text regardless of its
586 - Command: find-file-binary filename
587 Like `find-file', but treat the file as binary regardless of its
591 File: lispref.info, Node: Backups and Auto-Saving, Next: Buffers, Prev: Files, Up: Top
593 Backups and Auto-Saving
594 ***********************
596 Backup files and auto-save files are two methods by which XEmacs
597 tries to protect the user from the consequences of crashes or of the
598 user's own errors. Auto-saving preserves the text from earlier in the
599 current editing session; backup files preserve file contents prior to
604 * Backup Files:: How backup files are made; how their names are chosen.
605 * Auto-Saving:: How auto-save files are made; how their names are chosen.
606 * Reverting:: `revert-buffer', and how to customize what it does.
609 File: lispref.info, Node: Backup Files, Next: Auto-Saving, Up: Backups and Auto-Saving
614 A "backup file" is a copy of the old contents of a file you are
615 editing. XEmacs makes a backup file the first time you save a buffer
616 into its visited file. Normally, this means that the backup file
617 contains the contents of the file as it was before the current editing
618 session. The contents of the backup file normally remain unchanged once
621 Backups are usually made by renaming the visited file to a new name.
622 Optionally, you can specify that backup files should be made by copying
623 the visited file. This choice makes a difference for files with
624 multiple names; it also can affect whether the edited file remains owned
625 by the original owner or becomes owned by the user editing it.
627 By default, XEmacs makes a single backup file for each file edited.
628 You can alternatively request numbered backups; then each new backup
629 file gets a new name. You can delete old numbered backups when you
630 don't want them any more, or XEmacs can delete them automatically.
634 * Making Backups:: How XEmacs makes backup files, and when.
635 * Rename or Copy:: Two alternatives: renaming the old file or copying it.
636 * Numbered Backups:: Keeping multiple backups for each source file.
637 * Backup Names:: How backup file names are computed; customization.
640 File: lispref.info, Node: Making Backups, Next: Rename or Copy, Up: Backup Files
645 - Function: backup-buffer
646 This function makes a backup of the file visited by the current
647 buffer, if appropriate. It is called by `save-buffer' before
648 saving the buffer the first time.
650 - Variable: buffer-backed-up
651 This buffer-local variable indicates whether this buffer's file has
652 been backed up on account of this buffer. If it is non-`nil', then
653 the backup file has been written. Otherwise, the file should be
654 backed up when it is next saved (if backups are enabled). This is
655 a permanent local; `kill-local-variables' does not alter it.
657 - User Option: make-backup-files
658 This variable determines whether or not to make backup files. If
659 it is non-`nil', then XEmacs creates a backup of each file when it
660 is saved for the first time--provided that `backup-inhibited' is
663 The following example shows how to change the `make-backup-files'
664 variable only in the `RMAIL' buffer and not elsewhere. Setting it
665 `nil' stops XEmacs from making backups of the `RMAIL' file, which
666 may save disk space. (You would put this code in your `.emacs'
669 (add-hook 'rmail-mode-hook
673 (setq make-backup-files nil))))
675 - Variable: backup-enable-predicate
676 This variable's value is a function to be called on certain
677 occasions to decide whether a file should have backup files. The
678 function receives one argument, a file name to consider. If the
679 function returns `nil', backups are disabled for that file.
680 Otherwise, the other variables in this section say whether and how
683 The default value is this:
686 (or (< (length name) 5)
687 (not (string-equal "/tmp/"
688 (substring name 0 5)))))
690 - Variable: backup-inhibited
691 If this variable is non-`nil', backups are inhibited. It records
692 the result of testing `backup-enable-predicate' on the visited file
693 name. It can also coherently be used by other mechanisms that
694 inhibit backups based on which file is visited. For example, VC
695 sets this variable non-`nil' to prevent making backups for files
696 managed with a version control system.
698 This is a permanent local, so that changing the major mode does
699 not lose its value. Major modes should not set this
700 variable--they should set `make-backup-files' instead.
703 File: lispref.info, Node: Rename or Copy, Next: Numbered Backups, Prev: Making Backups, Up: Backup Files
705 Backup by Renaming or by Copying?
706 ---------------------------------
708 There are two ways that XEmacs can make a backup file:
710 * XEmacs can rename the original file so that it becomes a backup
711 file, and then write the buffer being saved into a new file.
712 After this procedure, any other names (i.e., hard links) of the
713 original file now refer to the backup file. The new file is owned
714 by the user doing the editing, and its group is the default for
715 new files written by the user in that directory.
717 * XEmacs can copy the original file into a backup file, and then
718 overwrite the original file with new contents. After this
719 procedure, any other names (i.e., hard links) of the original file
720 still refer to the current version of the file. The file's owner
721 and group will be unchanged.
723 The first method, renaming, is the default.
725 The variable `backup-by-copying', if non-`nil', says to use the
726 second method, which is to copy the original file and overwrite it with
727 the new buffer contents. The variable `file-precious-flag', if
728 non-`nil', also has this effect (as a sideline of its main
729 significance). *Note Saving Buffers::.
731 - Variable: backup-by-copying
732 If this variable is non-`nil', XEmacs always makes backup files by
735 The following two variables, when non-`nil', cause the second method
736 to be used in certain special cases. They have no effect on the
737 treatment of files that don't fall into the special cases.
739 - Variable: backup-by-copying-when-linked
740 If this variable is non-`nil', XEmacs makes backups by copying for
741 files with multiple names (hard links).
743 This variable is significant only if `backup-by-copying' is `nil',
744 since copying is always used when that variable is non-`nil'.
746 - Variable: backup-by-copying-when-mismatch
747 If this variable is non-`nil', XEmacs makes backups by copying in
748 cases where renaming would change either the owner or the group of
751 The value has no effect when renaming would not alter the owner or
752 group of the file; that is, for files which are owned by the user
753 and whose group matches the default for a new file created there
756 This variable is significant only if `backup-by-copying' is `nil',
757 since copying is always used when that variable is non-`nil'.
760 File: lispref.info, Node: Numbered Backups, Next: Backup Names, Prev: Rename or Copy, Up: Backup Files
762 Making and Deleting Numbered Backup Files
763 -----------------------------------------
765 If a file's name is `foo', the names of its numbered backup versions
766 are `foo.~V~', for various integers V, like this: `foo.~1~', `foo.~2~',
767 `foo.~3~', ..., `foo.~259~', and so on.
769 - User Option: version-control
770 This variable controls whether to make a single non-numbered backup
771 file or multiple numbered backups.
774 Make numbered backups if the visited file already has
775 numbered backups; otherwise, do not.
778 Do not make numbered backups.
781 Make numbered backups.
783 The use of numbered backups ultimately leads to a large number of
784 backup versions, which must then be deleted. XEmacs can do this
785 automatically or it can ask the user whether to delete them.
787 - User Option: kept-new-versions
788 The value of this variable is the number of newest versions to keep
789 when a new numbered backup is made. The newly made backup is
790 included in the count. The default value is 2.
792 - User Option: kept-old-versions
793 The value of this variable is the number of oldest versions to keep
794 when a new numbered backup is made. The default value is 2.
796 If there are backups numbered 1, 2, 3, 5, and 7, and both of these
797 variables have the value 2, then the backups numbered 1 and 2 are kept
798 as old versions and those numbered 5 and 7 are kept as new versions;
799 backup version 3 is excess. The function `find-backup-file-name'
800 (*note Backup Names::) is responsible for determining which backup
801 versions to delete, but does not delete them itself.
803 - User Option: delete-old-versions
804 If this variable is non-`nil', then saving a file deletes excess
805 backup versions silently. Otherwise, it asks the user whether to
808 - User Option: dired-kept-versions
809 This variable specifies how many of the newest backup versions to
810 keep in the Dired command `.' (`dired-clean-directory'). That's
811 the same thing `kept-new-versions' specifies when you make a new
812 backup file. The default value is 2.
815 File: lispref.info, Node: Backup Names, Prev: Numbered Backups, Up: Backup Files
820 The functions in this section are documented mainly because you can
821 customize the naming conventions for backup files by redefining them.
822 If you change one, you probably need to change the rest.
824 - Function: backup-file-name-p filename
825 This function returns a non-`nil' value if FILENAME is a possible
826 name for a backup file. A file with the name FILENAME need not
827 exist; the function just checks the name.
829 (backup-file-name-p "foo")
831 (backup-file-name-p "foo~")
834 The standard definition of this function is as follows:
836 (defun backup-file-name-p (file)
837 "Return non-nil if FILE is a backup file \
838 name (numeric or not)..."
839 (string-match "~$" file))
841 Thus, the function returns a non-`nil' value if the file name ends
842 with a `~'. (We use a backslash to split the documentation
843 string's first line into two lines in the text, but produce just
844 one line in the string itself.)
846 This simple expression is placed in a separate function to make it
847 easy to redefine for customization.
849 - Function: make-backup-file-name filename
850 This function returns a string that is the name to use for a
851 non-numbered backup file for file FILENAME. On Unix, this is just
852 FILENAME with a tilde appended.
854 The standard definition of this function is as follows:
856 (defun make-backup-file-name (file)
857 "Create the non-numeric backup file name for FILE.
861 You can change the backup-file naming convention by redefining this
862 function. The following example redefines `make-backup-file-name'
863 to prepend a `.' in addition to appending a tilde:
865 (defun make-backup-file-name (filename)
866 (concat "." filename "~"))
868 (make-backup-file-name "backups.texi")
871 - Function: find-backup-file-name filename
872 This function computes the file name for a new backup file for
873 FILENAME. It may also propose certain existing backup files for
874 deletion. `find-backup-file-name' returns a list whose CAR is the
875 name for the new backup file and whose CDR is a list of backup
876 files whose deletion is proposed.
878 Two variables, `kept-old-versions' and `kept-new-versions',
879 determine which backup versions should be kept. This function
880 keeps those versions by excluding them from the CDR of the value.
881 *Note Numbered Backups::.
883 In this example, the value says that `~rms/foo.~5~' is the name to
884 use for the new backup file, and `~rms/foo.~3~' is an "excess"
885 version that the caller should consider deleting now.
887 (find-backup-file-name "~rms/foo")
888 => ("~rms/foo.~5~" "~rms/foo.~3~")
890 - Function: file-newest-backup filename
891 This function returns the name of the most recent backup file for
892 FILENAME, or `nil' if that file has no backup files.
894 Some file comparison commands use this function so that they can
895 automatically compare a file with its most recent backup.
898 File: lispref.info, Node: Auto-Saving, Next: Reverting, Prev: Backup Files, Up: Backups and Auto-Saving
903 XEmacs periodically saves all files that you are visiting; this is
904 called "auto-saving". Auto-saving prevents you from losing more than a
905 limited amount of work if the system crashes. By default, auto-saves
906 happen every 300 keystrokes, or after around 30 seconds of idle time.
907 *Note Auto-Save: (emacs)Auto-Save, for information on auto-save for
908 users. Here we describe the functions used to implement auto-saving
909 and the variables that control them.
911 - Variable: buffer-auto-save-file-name
912 This buffer-local variable is the name of the file used for
913 auto-saving the current buffer. It is `nil' if the buffer should
916 buffer-auto-save-file-name
917 => "/xcssun/users/rms/lewis/#files.texi#"
919 - Command: auto-save-mode arg
920 When used interactively without an argument, this command is a
921 toggle switch: it turns on auto-saving of the current buffer if it
922 is off, and vice-versa. With an argument ARG, the command turns
923 auto-saving on if the value of ARG is `t', a nonempty list, or a
924 positive integer. Otherwise, it turns auto-saving off.
926 - Function: auto-save-file-name-p filename
927 This function returns a non-`nil' value if FILENAME is a string
928 that could be the name of an auto-save file. It works based on
929 knowledge of the naming convention for auto-save files: a name that
930 begins and ends with hash marks (`#') is a possible auto-save file
931 name. The argument FILENAME should not contain a directory part.
933 (make-auto-save-file-name)
934 => "/xcssun/users/rms/lewis/#files.texi#"
935 (auto-save-file-name-p "#files.texi#")
937 (auto-save-file-name-p "files.texi")
940 The standard definition of this function is as follows:
942 (defun auto-save-file-name-p (filename)
943 "Return non-nil if FILENAME can be yielded by..."
944 (string-match "^#.*#$" filename))
946 This function exists so that you can customize it if you wish to
947 change the naming convention for auto-save files. If you redefine
948 it, be sure to redefine the function `make-auto-save-file-name'
951 - Function: make-auto-save-file-name
952 This function returns the file name to use for auto-saving the
953 current buffer. This is just the file name with hash marks (`#')
954 appended and prepended to it. This function does not look at the
955 variable `auto-save-visited-file-name' (described below); you
956 should check that before calling this function.
958 (make-auto-save-file-name)
959 => "/xcssun/users/rms/lewis/#backup.texi#"
961 The standard definition of this function is as follows:
963 (defun make-auto-save-file-name ()
964 "Return file name to use for auto-saves \
969 (file-name-directory buffer-file-name)
971 (file-name-nondirectory buffer-file-name)
974 (concat "#%" (buffer-name) "#"))))
976 This exists as a separate function so that you can redefine it to
977 customize the naming convention for auto-save files. Be sure to
978 change `auto-save-file-name-p' in a corresponding way.
980 - Variable: auto-save-visited-file-name
981 If this variable is non-`nil', XEmacs auto-saves buffers in the
982 files they are visiting. That is, the auto-save is done in the
983 same file that you are editing. Normally, this variable is `nil',
984 so auto-save files have distinct names that are created by
985 `make-auto-save-file-name'.
987 When you change the value of this variable, the value does not take
988 effect until the next time auto-save mode is reenabled in any given
989 buffer. If auto-save mode is already enabled, auto-saves continue
990 to go in the same file name until `auto-save-mode' is called again.
992 - Function: recent-auto-save-p
993 This function returns `t' if the current buffer has been
994 auto-saved since the last time it was read in or saved.
996 - Function: set-buffer-auto-saved
997 This function marks the current buffer as auto-saved. The buffer
998 will not be auto-saved again until the buffer text is changed
999 again. The function returns `nil'.
1001 - User Option: auto-save-interval
1002 The value of this variable is the number of characters that XEmacs
1003 reads from the keyboard between auto-saves. Each time this many
1004 more characters are read, auto-saving is done for all buffers in
1005 which it is enabled.
1007 - User Option: auto-save-timeout
1008 The value of this variable is the number of seconds of idle time
1009 that should cause auto-saving. Each time the user pauses for this
1010 long, XEmacs auto-saves any buffers that need it. (Actually, the
1011 specified timeout is multiplied by a factor depending on the size
1012 of the current buffer.)
1014 - Variable: auto-save-hook
1015 This normal hook is run whenever an auto-save is about to happen.
1017 - User Option: auto-save-default
1018 If this variable is non-`nil', buffers that are visiting files
1019 have auto-saving enabled by default. Otherwise, they do not.
1021 - Command: do-auto-save &optional no-message current-only
1022 This function auto-saves all buffers that need to be auto-saved.
1023 It saves all buffers for which auto-saving is enabled and that
1024 have been changed since the previous auto-save.
1026 Normally, if any buffers are auto-saved, a message that says
1027 `Auto-saving...' is displayed in the echo area while auto-saving is
1028 going on. However, if NO-MESSAGE is non-`nil', the message is
1031 If CURRENT-ONLY is non-`nil', only the current buffer is
1034 - Function: delete-auto-save-file-if-necessary
1035 This function deletes the current buffer's auto-save file if
1036 `delete-auto-save-files' is non-`nil'. It is called every time a
1039 - Variable: delete-auto-save-files
1040 This variable is used by the function
1041 `delete-auto-save-file-if-necessary'. If it is non-`nil', Emacs
1042 deletes auto-save files when a true save is done (in the visited
1043 file). This saves disk space and unclutters your directory.
1045 - Function: rename-auto-save-file
1046 This function adjusts the current buffer's auto-save file name if
1047 the visited file name has changed. It also renames an existing
1048 auto-save file. If the visited file name has not changed, this
1049 function does nothing.
1051 - Variable: buffer-saved-size
1052 The value of this buffer-local variable is the length of the
1053 current buffer as of the last time it was read in, saved, or
1054 auto-saved. This is used to detect a substantial decrease in
1055 size, and turn off auto-saving in response.
1057 If it is -1, that means auto-saving is temporarily shut off in this
1058 buffer due to a substantial deletion. Explicitly saving the buffer
1059 stores a positive value in this variable, thus reenabling
1060 auto-saving. Turning auto-save mode off or on also alters this
1063 - Variable: auto-save-list-file-name
1064 This variable (if non-`nil') specifies a file for recording the
1065 names of all the auto-save files. Each time XEmacs does
1066 auto-saving, it writes two lines into this file for each buffer
1067 that has auto-saving enabled. The first line gives the name of
1068 the visited file (it's empty if the buffer has none), and the
1069 second gives the name of the auto-save file.
1071 If XEmacs exits normally, it deletes this file. If XEmacs
1072 crashes, you can look in the file to find all the auto-save files
1073 that might contain work that was otherwise lost. The
1074 `recover-session' command uses these files.
1076 The default name for this file is in your home directory and
1077 starts with `.saves-'. It also contains the XEmacs process ID and
1081 File: lispref.info, Node: Reverting, Prev: Auto-Saving, Up: Backups and Auto-Saving
1086 If you have made extensive changes to a file and then change your
1087 mind about them, you can get rid of them by reading in the previous
1088 version of the file with the `revert-buffer' command. *Note Reverting
1089 a Buffer: (emacs)Reverting.
1091 - Command: revert-buffer &optional check-auto-save noconfirm
1092 This command replaces the buffer text with the text of the visited
1093 file on disk. This action undoes all changes since the file was
1096 If the argument CHECK-AUTO-SAVE is non-`nil', and the latest
1097 auto-save file is more recent than the visited file,
1098 `revert-buffer' asks the user whether to use that instead.
1099 Otherwise, it always uses the text of the visited file itself.
1100 Interactively, CHECK-AUTO-SAVE is set if there is a numeric prefix
1103 Normally, `revert-buffer' asks for confirmation before it changes
1104 the buffer; but if the argument NOCONFIRM is non-`nil',
1105 `revert-buffer' does not ask for confirmation.
1107 Reverting tries to preserve marker positions in the buffer by
1108 using the replacement feature of `insert-file-contents'. If the
1109 buffer contents and the file contents are identical before the
1110 revert operation, reverting preserves all the markers. If they
1111 are not identical, reverting does change the buffer; then it
1112 preserves the markers in the unchanged text (if any) at the
1113 beginning and end of the buffer. Preserving any additional
1114 markers would be problematical.
1116 You can customize how `revert-buffer' does its work by setting these
1117 variables--typically, as buffer-local variables.
1119 - Variable: revert-buffer-function
1120 The value of this variable is the function to use to revert this
1121 buffer. If non-`nil', it is called as a function with no
1122 arguments to do the work of reverting. If the value is `nil',
1123 reverting works the usual way.
1125 Modes such as Dired mode, in which the text being edited does not
1126 consist of a file's contents but can be regenerated in some other
1127 fashion, give this variable a buffer-local value that is a
1128 function to regenerate the contents.
1130 - Variable: revert-buffer-insert-file-contents-function
1131 The value of this variable, if non-`nil', is the function to use to
1132 insert the updated contents when reverting this buffer. The
1133 function receives two arguments: first the file name to use;
1134 second, `t' if the user has asked to read the auto-save file.
1136 - Variable: before-revert-hook
1137 This normal hook is run by `revert-buffer' before actually
1138 inserting the modified contents--but only if
1139 `revert-buffer-function' is `nil'.
1141 Font Lock mode uses this hook to record that the buffer contents
1142 are no longer fontified.
1144 - Variable: after-revert-hook
1145 This normal hook is run by `revert-buffer' after actually inserting
1146 the modified contents--but only if `revert-buffer-function' is
1149 Font Lock mode uses this hook to recompute the fonts for the
1150 updated buffer contents.
1153 File: lispref.info, Node: Buffers, Next: Windows, Prev: Backups and Auto-Saving, Up: Top
1158 A "buffer" is a Lisp object containing text to be edited. Buffers
1159 are used to hold the contents of files that are being visited; there may
1160 also be buffers that are not visiting files. While several buffers may
1161 exist at one time, exactly one buffer is designated the "current
1162 buffer" at any time. Most editing commands act on the contents of the
1163 current buffer. Each buffer, including the current buffer, may or may
1164 not be displayed in any windows.
1168 * Buffer Basics:: What is a buffer?
1169 * Current Buffer:: Designating a buffer as current
1170 so primitives will access its contents.
1171 * Buffer Names:: Accessing and changing buffer names.
1172 * Buffer File Name:: The buffer file name indicates which file is visited.
1173 * Buffer Modification:: A buffer is "modified" if it needs to be saved.
1174 * Modification Time:: Determining whether the visited file was changed
1175 ``behind XEmacs's back''.
1176 * Read Only Buffers:: Modifying text is not allowed in a read-only buffer.
1177 * The Buffer List:: How to look at all the existing buffers.
1178 * Creating Buffers:: Functions that create buffers.
1179 * Killing Buffers:: Buffers exist until explicitly killed.
1180 * Indirect Buffers:: An indirect buffer shares text with some other buffer.