2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999
4 @c Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @setfilename ../info/files
7 @node Files, Backups and Auto-Saving, Documentation, Top
8 @comment node-name, next, previous, up
11 In Emacs, you can find, create, view, save, and otherwise work with
12 files and file directories. This chapter describes most of the
13 file-related functions of Emacs Lisp, but a few others are described in
14 @ref{Buffers}, and those related to backups and auto-saving are
15 described in @ref{Backups and Auto-Saving}.
17 Many of the file functions take one or more arguments that are file
18 names. A file name is actually a string. Most of these functions
19 expand file name arguments by calling @code{expand-file-name}, so that
20 @file{~} is handled correctly, as are relative file names (including
21 @samp{../}). These functions don't recognize environment variable
22 substitutions such as @samp{$HOME}. @xref{File Name Expansion}.
24 When file I/O functions signal Lisp errors, they usually use the
25 condition @code{file-error} (@pxref{Handling Errors}). The error
26 message is in most cases obtained from the operating system, according
27 to locale @code{system-message-locale}, and decoded using coding system
28 @code{locale-coding-system} (@pxref{Locales}).
31 * Visiting Files:: Reading files into Emacs buffers for editing.
32 * Saving Buffers:: Writing changed buffers back into files.
33 * Reading from Files:: Reading files into buffers without visiting.
34 * Writing to Files:: Writing new files from parts of buffers.
35 * File Locks:: Locking and unlocking files, to prevent
36 simultaneous editing by two people.
37 * Information about Files:: Testing existence, accessibility, size of files.
38 * Changing Files:: Renaming files, changing protection, etc.
39 * File Names:: Decomposing and expanding file names.
40 * Contents of Directories:: Getting a list of the files in a directory.
41 * Create/Delete Dirs:: Creating and Deleting Directories.
42 * Magic File Names:: Defining "magic" special handling
43 for certain file names.
44 * Format Conversion:: Conversion to and from various file formats.
48 @section Visiting Files
50 @cindex visiting files
52 Visiting a file means reading a file into a buffer. Once this is
53 done, we say that the buffer is @dfn{visiting} that file, and call the
54 file ``the visited file'' of the buffer.
56 A file and a buffer are two different things. A file is information
57 recorded permanently in the computer (unless you delete it). A buffer,
58 on the other hand, is information inside of Emacs that will vanish at
59 the end of the editing session (or when you kill the buffer). Usually,
60 a buffer contains information that you have copied from a file; then we
61 say the buffer is visiting that file. The copy in the buffer is what
62 you modify with editing commands. Such changes to the buffer do not
63 change the file; therefore, to make the changes permanent, you must
64 @dfn{save} the buffer, which means copying the altered buffer contents
67 In spite of the distinction between files and buffers, people often
68 refer to a file when they mean a buffer and vice-versa. Indeed, we say,
69 ``I am editing a file,'' rather than, ``I am editing a buffer that I
70 will soon save as a file of the same name.'' Humans do not usually need
71 to make the distinction explicit. When dealing with a computer program,
72 however, it is good to keep the distinction in mind.
75 * Visiting Functions:: The usual interface functions for visiting.
76 * Subroutines of Visiting:: Lower-level subroutines that they use.
79 @node Visiting Functions
80 @subsection Functions for Visiting Files
82 This section describes the functions normally used to visit files.
83 For historical reasons, these functions have names starting with
84 @samp{find-} rather than @samp{visit-}. @xref{Buffer File Name}, for
85 functions and variables that access the visited file name of a buffer or
86 that find an existing buffer by its visited file name.
88 In a Lisp program, if you want to look at the contents of a file but
89 not alter it, the fastest way is to use @code{insert-file-contents} in a
90 temporary buffer. Visiting the file is not necessary and takes longer.
91 @xref{Reading from Files}.
93 @deffn Command find-file filename &optional wildcards
94 This command selects a buffer visiting the file @var{filename},
95 using an existing buffer if there is one, and otherwise creating a
96 new buffer and reading the file into it. It also returns that buffer.
98 The body of the @code{find-file} function is very simple and looks
102 (switch-to-buffer (find-file-noselect filename))
106 (See @code{switch-to-buffer} in @ref{Displaying Buffers}.)
108 If @var{wildcards} is non-@code{nil}, which is always true in an
109 interactive call, then @code{find-file} expands wildcard characters in
110 @var{filename} and visits all the matching files.
112 When @code{find-file} is called interactively, it prompts for
113 @var{filename} in the minibuffer.
116 @defun find-file-noselect filename &optional nowarn rawfile wildcards
117 This function is the guts of all the file-visiting functions. It finds
118 or creates a buffer visiting the file @var{filename}, and returns it.
119 It uses an existing buffer if there is one, and otherwise creates a new
120 buffer and reads the file into it. You may make the buffer current or
121 display it in a window if you wish, but this function does not do so.
123 If @var{wildcards} is non-@code{nil},
124 then @code{find-file-noselect} expands wildcard
125 characters in @var{filename} and visits all the matching files.
127 When @code{find-file-noselect} uses an existing buffer, it first
128 verifies that the file has not changed since it was last visited or
129 saved in that buffer. If the file has changed, then this function asks
130 the user whether to reread the changed file. If the user says
131 @samp{yes}, any changes previously made in the buffer are lost.
133 This function displays warning or advisory messages in various peculiar
134 cases, unless the optional argument @var{nowarn} is non-@code{nil}. For
135 example, if it needs to create a buffer, and there is no file named
136 @var{filename}, it displays the message @samp{(New file)} in the echo
137 area, and leaves the buffer empty.
139 The @code{find-file-noselect} function normally calls
140 @code{after-find-file} after reading the file (@pxref{Subroutines of
141 Visiting}). That function sets the buffer major mode, parses local
142 variables, warns the user if there exists an auto-save file more recent
143 than the file just visited, and finishes by running the functions in
144 @code{find-file-hook}.
146 If the optional argument @var{rawfile} is non-@code{nil}, then
147 @code{after-find-file} is not called, and the
148 @code{find-file-not-found-functions} are not run in case of failure. What's
149 more, a non-@code{nil} @var{rawfile} value suppresses coding system
150 conversion (@pxref{Coding Systems}) and format conversion (@pxref{Format
153 The @code{find-file-noselect} function usually returns the buffer that
154 is visiting the file @var{filename}. But, if wildcards are actually
155 used and expanded, it returns a list of buffers that are visiting the
160 (find-file-noselect "/etc/fstab")
161 @result{} #<buffer fstab>
166 @deffn Command find-file-other-window filename &optional wildcards
167 This command selects a buffer visiting the file @var{filename}, but
168 does so in a window other than the selected window. It may use another
169 existing window or split a window; see @ref{Displaying Buffers}.
171 When this command is called interactively, it prompts for
175 @deffn Command find-file-read-only filename &optional wildcards
176 This command selects a buffer visiting the file @var{filename}, like
177 @code{find-file}, but it marks the buffer as read-only. @xref{Read Only
178 Buffers}, for related functions and variables.
180 When this command is called interactively, it prompts for
184 @deffn Command view-file filename
185 This command visits @var{filename} using View mode, returning to the
186 previous buffer when you exit View mode. View mode is a minor mode that
187 provides commands to skim rapidly through the file, but does not let you
188 modify the text. Entering View mode runs the normal hook
189 @code{view-mode-hook}. @xref{Hooks}.
191 When @code{view-file} is called interactively, it prompts for
195 @tindex find-file-wildcards
196 @defvar find-file-wildcards
197 If this variable is non-@code{nil}, then the various @code{find-file}
198 commands check for wildcard characters and visit all the files that
199 match them. If this is @code{nil}, then wildcard characters are
200 not treated specially.
203 @defvar find-file-hook
204 The value of this variable is a list of functions to be called after a
205 file is visited. The file's local-variables specification (if any) will
206 have been processed before the hooks are run. The buffer visiting the
207 file is current when the hook functions are run.
209 This variable works just like a normal hook, but we think that renaming
210 it would not be advisable. @xref{Hooks}.
213 @defvar find-file-not-found-functions
214 The value of this variable is a list of functions to be called when
215 @code{find-file} or @code{find-file-noselect} is passed a nonexistent
216 file name. @code{find-file-noselect} calls these functions as soon as
217 it detects a nonexistent file. It calls them in the order of the list,
218 until one of them returns non-@code{nil}. @code{buffer-file-name} is
221 This is not a normal hook because the values of the functions are
222 used, and in many cases only some of the functions are called.
225 @node Subroutines of Visiting
226 @comment node-name, next, previous, up
227 @subsection Subroutines of Visiting
229 The @code{find-file-noselect} function uses two important subroutines
230 which are sometimes useful in user Lisp code: @code{create-file-buffer}
231 and @code{after-find-file}. This section explains how to use them.
233 @defun create-file-buffer filename
234 This function creates a suitably named buffer for visiting
235 @var{filename}, and returns it. It uses @var{filename} (sans directory)
236 as the name if that name is free; otherwise, it appends a string such as
237 @samp{<2>} to get an unused name. See also @ref{Creating Buffers}.
239 @strong{Please note:} @code{create-file-buffer} does @emph{not}
240 associate the new buffer with a file and does not select the buffer.
241 It also does not use the default major mode.
245 (create-file-buffer "foo")
246 @result{} #<buffer foo>
249 (create-file-buffer "foo")
250 @result{} #<buffer foo<2>>
253 (create-file-buffer "foo")
254 @result{} #<buffer foo<3>>
258 This function is used by @code{find-file-noselect}.
259 It uses @code{generate-new-buffer} (@pxref{Creating Buffers}).
262 @defun after-find-file &optional error warn noauto after-find-file-from-revert-buffer nomodes
263 This function sets the buffer major mode, and parses local variables
264 (@pxref{Auto Major Mode}). It is called by @code{find-file-noselect}
265 and by the default revert function (@pxref{Reverting}).
267 @cindex new file message
268 @cindex file open error
269 If reading the file got an error because the file does not exist, but
270 its directory does exist, the caller should pass a non-@code{nil} value
271 for @var{error}. In that case, @code{after-find-file} issues a warning:
272 @samp{(New file)}. For more serious errors, the caller should usually not
273 call @code{after-find-file}.
275 If @var{warn} is non-@code{nil}, then this function issues a warning
276 if an auto-save file exists and is more recent than the visited file.
278 If @var{noauto} is non-@code{nil}, that says not to enable or disable
279 Auto-Save mode. The mode remains enabled if it was enabled before.
281 If @var{after-find-file-from-revert-buffer} is non-@code{nil}, that
282 means this call was from @code{revert-buffer}. This has no direct
283 effect, but some mode functions and hook functions check the value
286 If @var{nomodes} is non-@code{nil}, that means don't alter the buffer's
287 major mode, don't process local variables specifications in the file,
288 and don't run @code{find-file-hook}. This feature is used by
289 @code{revert-buffer} in some cases.
291 The last thing @code{after-find-file} does is call all the functions
292 in the list @code{find-file-hook}.
296 @section Saving Buffers
298 When you edit a file in Emacs, you are actually working on a buffer
299 that is visiting that file---that is, the contents of the file are
300 copied into the buffer and the copy is what you edit. Changes to the
301 buffer do not change the file until you @dfn{save} the buffer, which
302 means copying the contents of the buffer into the file.
304 @deffn Command save-buffer &optional backup-option
305 This function saves the contents of the current buffer in its visited
306 file if the buffer has been modified since it was last visited or saved.
307 Otherwise it does nothing.
309 @code{save-buffer} is responsible for making backup files. Normally,
310 @var{backup-option} is @code{nil}, and @code{save-buffer} makes a backup
311 file only if this is the first save since visiting the file. Other
312 values for @var{backup-option} request the making of backup files in
317 With an argument of 4 or 64, reflecting 1 or 3 @kbd{C-u}'s, the
318 @code{save-buffer} function marks this version of the file to be
319 backed up when the buffer is next saved.
322 With an argument of 16 or 64, reflecting 2 or 3 @kbd{C-u}'s, the
323 @code{save-buffer} function unconditionally backs up the previous
324 version of the file before saving it.
328 @deffn Command save-some-buffers &optional save-silently-p pred
329 This command saves some modified file-visiting buffers. Normally it
330 asks the user about each buffer. But if @var{save-silently-p} is
331 non-@code{nil}, it saves all the file-visiting buffers without querying
334 The optional @var{pred} argument controls which buffers to ask about.
335 If it is @code{nil}, that means to ask only about file-visiting buffers.
336 If it is @code{t}, that means also offer to save certain other non-file
337 buffers---those that have a non-@code{nil} buffer-local value of
338 @code{buffer-offer-save}. (A user who says @samp{yes} to saving a
339 non-file buffer is asked to specify the file name to use.) The
340 @code{save-buffers-kill-emacs} function passes the value @code{t} for
343 If @var{pred} is neither @code{t} nor @code{nil}, then it should be
344 a function of no arguments. It will be called in each buffer to decide
345 whether to offer to save that buffer. If it returns a non-@code{nil}
346 value in a certain buffer, that means do offer to save that buffer.
349 @deffn Command write-file filename &optional confirm
350 This function writes the current buffer into file @var{filename}, makes
351 the buffer visit that file, and marks it not modified. Then it renames
352 the buffer based on @var{filename}, appending a string like @samp{<2>}
353 if necessary to make a unique buffer name. It does most of this work by
354 calling @code{set-visited-file-name} (@pxref{Buffer File Name}) and
357 If @var{confirm} is non-@code{nil}, that means to ask for confirmation
358 before overwriting an existing file.
361 Saving a buffer runs several hooks. It also performs format
362 conversion (@pxref{Format Conversion}), and may save text properties in
363 ``annotations'' (@pxref{Saving Properties}).
365 @defvar write-file-functions
366 The value of this variable is a list of functions to be called before
367 writing out a buffer to its visited file. If one of them returns
368 non-@code{nil}, the file is considered already written and the rest of
369 the functions are not called, nor is the usual code for writing the file
372 If a function in @code{write-file-functions} returns non-@code{nil}, it
373 is responsible for making a backup file (if that is appropriate).
374 To do so, execute the following code:
377 (or buffer-backed-up (backup-buffer))
380 You might wish to save the file modes value returned by
381 @code{backup-buffer} and use that to set the mode bits of the file that
382 you write. This is what @code{save-buffer} normally does.
384 The hook functions in @code{write-file-functions} are also responsible for
385 encoding the data (if desired): they must choose a suitable coding
386 system (@pxref{Lisp and Coding Systems}), perform the encoding
387 (@pxref{Explicit Encoding}), and set @code{last-coding-system-used} to
388 the coding system that was used (@pxref{Encoding and I/O}).
390 If you set this hook locally in a buffer, it is assumed to be
391 associated with the file or the way the contents of the buffer were
392 obtained. Thus the variable is marked as a permanent local, so that
393 changing the major mode does not alter a buffer-local value. On the
394 other hand, calling @code{set-visited-file-name} will reset it.
395 If this is not what you want, you might like to use
396 @code{write-contents-functions} instead.
398 Even though this is not a normal hook, you can use @code{add-hook} and
399 @code{remove-hook} to manipulate the list. @xref{Hooks}.
403 @defvar write-contents-functions
404 This works just like @code{write-file-functions}, but it is intended for
405 hooks that pertain to the contents of the file, as opposed to hooks that
406 pertain to where the file came from. Such hooks are usually set up by
407 major modes, as buffer-local bindings for this variable.
409 This variable automatically becomes buffer-local whenever it is set;
410 switching to a new major mode always resets this variable.
414 @defvar after-save-hook
415 This normal hook runs after a buffer has been saved in its visited file.
416 One use of this hook is in Fast Lock mode; it uses this hook to save the
417 highlighting information in a cache file.
420 @defvar file-precious-flag
421 If this variable is non-@code{nil}, then @code{save-buffer} protects
422 against I/O errors while saving by writing the new file to a temporary
423 name instead of the name it is supposed to have, and then renaming it to
424 the intended name after it is clear there are no errors. This procedure
425 prevents problems such as a lack of disk space from resulting in an
428 As a side effect, backups are necessarily made by copying. @xref{Rename
429 or Copy}. Yet, at the same time, saving a precious file always breaks
430 all hard links between the file you save and other file names.
432 Some modes give this variable a non-@code{nil} buffer-local value
433 in particular buffers.
436 @defopt require-final-newline
437 This variable determines whether files may be written out that do
438 @emph{not} end with a newline. If the value of the variable is
439 @code{t}, then @code{save-buffer} silently adds a newline at the end of
440 the file whenever the buffer being saved does not already end in one.
441 If the value of the variable is non-@code{nil}, but not @code{t}, then
442 @code{save-buffer} asks the user whether to add a newline each time the
445 If the value of the variable is @code{nil}, then @code{save-buffer}
446 doesn't add newlines at all. @code{nil} is the default value, but a few
447 major modes set it to @code{t} in particular buffers.
450 See also the function @code{set-visited-file-name} (@pxref{Buffer File
453 @node Reading from Files
454 @comment node-name, next, previous, up
455 @section Reading from Files
457 You can copy a file from the disk and insert it into a buffer
458 using the @code{insert-file-contents} function. Don't use the user-level
459 command @code{insert-file} in a Lisp program, as that sets the mark.
461 @defun insert-file-contents filename &optional visit beg end replace
462 This function inserts the contents of file @var{filename} into the
463 current buffer after point. It returns a list of the absolute file name
464 and the length of the data inserted. An error is signaled if
465 @var{filename} is not the name of a file that can be read.
467 The function @code{insert-file-contents} checks the file contents
468 against the defined file formats, and converts the file contents if
469 appropriate. @xref{Format Conversion}. It also calls the functions in
470 the list @code{after-insert-file-functions}; see @ref{Saving
471 Properties}. Normally, one of the functions in the
472 @code{after-insert-file-functions} list determines the coding system
473 (@pxref{Coding Systems}) used for decoding the file's contents.
475 If @var{visit} is non-@code{nil}, this function additionally marks the
476 buffer as unmodified and sets up various fields in the buffer so that it
477 is visiting the file @var{filename}: these include the buffer's visited
478 file name and its last save file modtime. This feature is used by
479 @code{find-file-noselect} and you probably should not use it yourself.
481 If @var{beg} and @var{end} are non-@code{nil}, they should be integers
482 specifying the portion of the file to insert. In this case, @var{visit}
483 must be @code{nil}. For example,
486 (insert-file-contents filename nil 0 500)
490 inserts the first 500 characters of a file.
492 If the argument @var{replace} is non-@code{nil}, it means to replace the
493 contents of the buffer (actually, just the accessible portion) with the
494 contents of the file. This is better than simply deleting the buffer
495 contents and inserting the whole file, because (1) it preserves some
496 marker positions and (2) it puts less data in the undo list.
498 It is possible to read a special file (such as a FIFO or an I/O device)
499 with @code{insert-file-contents}, as long as @var{replace} and
500 @var{visit} are @code{nil}.
503 @defun insert-file-contents-literally filename &optional visit beg end replace
504 This function works like @code{insert-file-contents} except that it does
505 not do format decoding (@pxref{Format Conversion}), does not do
506 character code conversion (@pxref{Coding Systems}), does not run
507 @code{find-file-hook}, does not perform automatic uncompression, and so
511 If you want to pass a file name to another process so that another
512 program can read the file, use the function @code{file-local-copy}; see
513 @ref{Magic File Names}.
515 @node Writing to Files
516 @comment node-name, next, previous, up
517 @section Writing to Files
519 You can write the contents of a buffer, or part of a buffer, directly
520 to a file on disk using the @code{append-to-file} and
521 @code{write-region} functions. Don't use these functions to write to
522 files that are being visited; that could cause confusion in the
523 mechanisms for visiting.
525 @deffn Command append-to-file start end filename
526 This function appends the contents of the region delimited by
527 @var{start} and @var{end} in the current buffer to the end of file
528 @var{filename}. If that file does not exist, it is created. This
529 function returns @code{nil}.
531 An error is signaled if @var{filename} specifies a nonwritable file,
532 or a nonexistent file in a directory where files cannot be created.
535 @deffn Command write-region start end filename &optional append visit lockname mustbenew
536 This function writes the region delimited by @var{start} and @var{end}
537 in the current buffer into the file specified by @var{filename}.
540 If @var{start} is a string, then @code{write-region} writes or appends
541 that string, rather than text from the buffer. @var{end} is ignored in
544 If @var{append} is non-@code{nil}, then the specified text is appended
545 to the existing file contents (if any). Starting in Emacs 21, if
546 @var{append} is an integer, then @code{write-region} seeks to that byte
547 offset from the start of the file and writes the data from there.
549 If @var{mustbenew} is non-@code{nil}, then @code{write-region} asks
550 for confirmation if @var{filename} names an existing file.
551 Starting in Emacs 21, if @var{mustbenew} is the symbol @code{excl},
552 then @code{write-region} does not ask for confirmation, but instead
553 it signals an error @code{file-already-exists} if the file already
556 The test for an existing file, when @var{mustbenew} is @code{excl}, uses
557 a special system feature. At least for files on a local disk, there is
558 no chance that some other program could create a file of the same name
559 before Emacs does, without Emacs's noticing.
561 If @var{visit} is @code{t}, then Emacs establishes an association
562 between the buffer and the file: the buffer is then visiting that file.
563 It also sets the last file modification time for the current buffer to
564 @var{filename}'s modtime, and marks the buffer as not modified. This
565 feature is used by @code{save-buffer}, but you probably should not use
569 If @var{visit} is a string, it specifies the file name to visit. This
570 way, you can write the data to one file (@var{filename}) while recording
571 the buffer as visiting another file (@var{visit}). The argument
572 @var{visit} is used in the echo area message and also for file locking;
573 @var{visit} is stored in @code{buffer-file-name}. This feature is used
574 to implement @code{file-precious-flag}; don't use it yourself unless you
575 really know what you're doing.
577 The optional argument @var{lockname}, if non-@code{nil}, specifies the
578 file name to use for purposes of locking and unlocking, overriding
579 @var{filename} and @var{visit} for that purpose.
581 The function @code{write-region} converts the data which it writes to
582 the appropriate file formats specified by @code{buffer-file-format}.
583 @xref{Format Conversion}. It also calls the functions in the list
584 @code{write-region-annotate-functions}; see @ref{Saving Properties}.
586 Normally, @code{write-region} displays the message @samp{Wrote
587 @var{filename}} in the echo area. If @var{visit} is neither @code{t}
588 nor @code{nil} nor a string, then this message is inhibited. This
589 feature is useful for programs that use files for internal purposes,
590 files that the user does not need to know about.
593 @defmac with-temp-file file body...
594 The @code{with-temp-file} macro evaluates the @var{body} forms with a
595 temporary buffer as the current buffer; then, at the end, it writes the
596 buffer contents into file @var{file}. It kills the temporary buffer
597 when finished, restoring the buffer that was current before the
598 @code{with-temp-file} form. Then it returns the value of the last form
601 The current buffer is restored even in case of an abnormal exit via
602 @code{throw} or error (@pxref{Nonlocal Exits}).
604 See also @code{with-temp-buffer} in @ref{Current Buffer}.
611 When two users edit the same file at the same time, they are likely to
612 interfere with each other. Emacs tries to prevent this situation from
613 arising by recording a @dfn{file lock} when a file is being modified.
614 Emacs can then detect the first attempt to modify a buffer visiting a
615 file that is locked by another Emacs job, and ask the user what to do.
616 The file lock is really a file, a symbolic link with a special name,
617 stored in the same directory as the file you are editing.
619 When you access files using NFS, there may be a small probability that
620 you and another user will both lock the same file ``simultaneously''.
621 If this happens, it is possible for the two users to make changes
622 simultaneously, but Emacs will still warn the user who saves second.
623 Also, the detection of modification of a buffer visiting a file changed
624 on disk catches some cases of simultaneous editing; see
625 @ref{Modification Time}.
627 @defun file-locked-p filename
628 This function returns @code{nil} if the file @var{filename} is not
629 locked. It returns @code{t} if it is locked by this Emacs process, and
630 it returns the name of the user who has locked it if it is locked by
635 (file-locked-p "foo")
641 @defun lock-buffer &optional filename
642 This function locks the file @var{filename}, if the current buffer is
643 modified. The argument @var{filename} defaults to the current buffer's
644 visited file. Nothing is done if the current buffer is not visiting a
645 file, or is not modified.
649 This function unlocks the file being visited in the current buffer,
650 if the buffer is modified. If the buffer is not modified, then
651 the file should not be locked, so this function does nothing. It also
652 does nothing if the current buffer is not visiting a file.
655 File locking is not supported on some systems. On systems that do not
656 support it, the functions @code{lock-buffer}, @code{unlock-buffer} and
657 @code{file-locked-p} do nothing and return @code{nil}.
659 @defun ask-user-about-lock file other-user
660 This function is called when the user tries to modify @var{file}, but it
661 is locked by another user named @var{other-user}. The default
662 definition of this function asks the user to say what to do. The value
663 this function returns determines what Emacs does next:
667 A value of @code{t} says to grab the lock on the file. Then
668 this user may edit the file and @var{other-user} loses the lock.
671 A value of @code{nil} says to ignore the lock and let this
672 user edit the file anyway.
676 This function may instead signal a @code{file-locked} error, in which
677 case the change that the user was about to make does not take place.
679 The error message for this error looks like this:
682 @error{} File is locked: @var{file} @var{other-user}
686 where @code{file} is the name of the file and @var{other-user} is the
687 name of the user who has locked the file.
690 If you wish, you can replace the @code{ask-user-about-lock} function
691 with your own version that makes the decision in another way. The code
692 for its usual definition is in @file{userlock.el}.
695 @node Information about Files
696 @section Information about Files
698 The functions described in this section all operate on strings that
699 designate file names. All the functions have names that begin with the
700 word @samp{file}. These functions all return information about actual
701 files or directories, so their arguments must all exist as actual files
702 or directories unless otherwise noted.
705 * Testing Accessibility:: Is a given file readable? Writable?
706 * Kinds of Files:: Is it a directory? A symbolic link?
707 * Truenames:: Eliminating symbolic links from a file name.
708 * File Attributes:: How large is it? Any other names? Etc.
711 @node Testing Accessibility
712 @comment node-name, next, previous, up
713 @subsection Testing Accessibility
714 @cindex accessibility of a file
715 @cindex file accessibility
717 These functions test for permission to access a file in specific ways.
719 @defun file-exists-p filename
720 This function returns @code{t} if a file named @var{filename} appears to
721 exist. This does not mean you can necessarily read the file, only that
722 you can find out its attributes. (On Unix and GNU/Linux, this is true
723 if the file exists and you have execute permission on the containing
724 directories, regardless of the protection of the file itself.)
726 If the file does not exist, or if fascist access control policies
727 prevent you from finding the attributes of the file, this function
731 @defun file-readable-p filename
732 This function returns @code{t} if a file named @var{filename} exists
733 and you can read it. It returns @code{nil} otherwise.
737 (file-readable-p "files.texi")
741 (file-exists-p "/usr/spool/mqueue")
745 (file-readable-p "/usr/spool/mqueue")
752 @defun file-executable-p filename
753 This function returns @code{t} if a file named @var{filename} exists and
754 you can execute it. It returns @code{nil} otherwise. On Unix and
755 GNU/Linux, if the file is a directory, execute permission means you can
756 check the existence and attributes of files inside the directory, and
757 open those files if their modes permit.
760 @defun file-writable-p filename
761 This function returns @code{t} if the file @var{filename} can be written
762 or created by you, and @code{nil} otherwise. A file is writable if the
763 file exists and you can write it. It is creatable if it does not exist,
764 but the specified directory does exist and you can write in that
767 In the third example below, @file{foo} is not writable because the
768 parent directory does not exist, even though the user could create such
773 (file-writable-p "~/foo")
777 (file-writable-p "/foo")
781 (file-writable-p "~/no-such-dir/foo")
788 @defun file-accessible-directory-p dirname
789 This function returns @code{t} if you have permission to open existing
790 files in the directory whose name as a file is @var{dirname}; otherwise
791 (or if there is no such directory), it returns @code{nil}. The value
792 of @var{dirname} may be either a directory name or the file name of a
793 file which is a directory.
795 Example: after the following,
798 (file-accessible-directory-p "/foo")
803 we can deduce that any attempt to read a file in @file{/foo/} will
807 @defun access-file filename string
808 This function opens file @var{filename} for reading, then closes it and
809 returns @code{nil}. However, if the open fails, it signals an error
810 using @var{string} as the error message text.
813 @defun file-ownership-preserved-p filename
814 This function returns @code{t} if deleting the file @var{filename} and
815 then creating it anew would keep the file's owner unchanged.
818 @defun file-newer-than-file-p filename1 filename2
820 @cindex file modification time
821 This function returns @code{t} if the file @var{filename1} is
822 newer than file @var{filename2}. If @var{filename1} does not
823 exist, it returns @code{nil}. If @var{filename2} does not exist,
826 In the following example, assume that the file @file{aug-19} was written
827 on the 19th, @file{aug-20} was written on the 20th, and the file
828 @file{no-file} doesn't exist at all.
832 (file-newer-than-file-p "aug-19" "aug-20")
836 (file-newer-than-file-p "aug-20" "aug-19")
840 (file-newer-than-file-p "aug-19" "no-file")
844 (file-newer-than-file-p "no-file" "aug-19")
849 You can use @code{file-attributes} to get a file's last modification
850 time as a list of two numbers. @xref{File Attributes}.
854 @comment node-name, next, previous, up
855 @subsection Distinguishing Kinds of Files
857 This section describes how to distinguish various kinds of files, such
858 as directories, symbolic links, and ordinary files.
860 @defun file-symlink-p filename
861 @cindex file symbolic links
862 If the file @var{filename} is a symbolic link, the @code{file-symlink-p}
863 function returns the file name to which it is linked. This may be the
864 name of a text file, a directory, or even another symbolic link, or it
865 may be a nonexistent file name.
867 If the file @var{filename} is not a symbolic link (or there is no such file),
868 @code{file-symlink-p} returns @code{nil}.
872 (file-symlink-p "foo")
876 (file-symlink-p "sym-link")
880 (file-symlink-p "sym-link2")
884 (file-symlink-p "/bin")
889 @c !!! file-symlink-p: should show output of ls -l for comparison
892 @defun file-directory-p filename
893 This function returns @code{t} if @var{filename} is the name of an
894 existing directory, @code{nil} otherwise.
898 (file-directory-p "~rms")
902 (file-directory-p "~rms/lewis/files.texi")
906 (file-directory-p "~rms/lewis/no-such-file")
910 (file-directory-p "$HOME")
915 (substitute-in-file-name "$HOME"))
921 @defun file-regular-p filename
922 This function returns @code{t} if the file @var{filename} exists and is
923 a regular file (not a directory, named pipe, terminal, or
928 @subsection Truenames
929 @cindex truename (of file)
932 The @dfn{truename} of a file is the name that you get by following
933 symbolic links at all levels until none remain, then simplifying away
934 @samp{.}@: and @samp{..}@: appearing as name components. This results
935 in a sort of canonical name for the file. A file does not always have a
936 unique truename; the number of distinct truenames a file has is equal to
937 the number of hard links to the file. However, truenames are useful
938 because they eliminate symbolic links as a cause of name variation.
940 @defun file-truename filename
941 The function @code{file-truename} returns the truename of the file
942 @var{filename}. The argument must be an absolute file name.
945 @defun file-chase-links filename
946 This function follows symbolic links, starting with @var{filename},
947 until it finds a file name which is not the name of a symbolic link.
948 Then it returns that file name.
951 To illustrate the difference between @code{file-chase-links} and
952 @code{file-truename}, suppose that @file{/usr/foo} is a symbolic link to
953 the directory @file{/home/foo}, and @file{/home/foo/hello} is an
954 ordinary file (or at least, not a symbolic link) or nonexistent. Then
958 (file-chase-links "/usr/foo/hello")
959 ;; @r{This does not follow the links in the parent directories.}
960 @result{} "/usr/foo/hello"
961 (file-truename "/usr/foo/hello")
962 ;; @r{Assuming that @file{/home} is not a symbolic link.}
963 @result{} "/home/foo/hello"
966 @xref{Buffer File Name}, for related information.
968 @node File Attributes
969 @comment node-name, next, previous, up
970 @subsection Other Information about Files
972 This section describes the functions for getting detailed information
973 about a file, other than its contents. This information includes the
974 mode bits that control access permission, the owner and group numbers,
975 the number of names, the inode number, the size, and the times of access
978 @defun file-modes filename
980 @cindex file attributes
981 This function returns the mode bits of @var{filename}, as an integer.
982 The mode bits are also called the file permissions, and they specify
983 access control in the usual Unix fashion. If the low-order bit is 1,
984 then the file is executable by all users, if the second-lowest-order bit
985 is 1, then the file is writable by all users, etc.
987 The highest value returnable is 4095 (7777 octal), meaning that
988 everyone has read, write, and execute permission, that the @sc{suid} bit
989 is set for both others and group, and that the sticky bit is set.
993 (file-modes "~/junk/diffs")
994 @result{} 492 ; @r{Decimal integer.}
998 @result{} "754" ; @r{Convert to octal.}
1002 (set-file-modes "~/junk/diffs" 438)
1008 @result{} "666" ; @r{Convert to octal.}
1013 -rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs
1018 @defun file-nlinks filename
1019 This functions returns the number of names (i.e., hard links) that
1020 file @var{filename} has. If the file does not exist, then this function
1021 returns @code{nil}. Note that symbolic links have no effect on this
1022 function, because they are not considered to be names of the files they
1028 -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo
1029 -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo1
1037 (file-nlinks "doesnt-exist")
1043 @defun file-attributes filename
1044 This function returns a list of attributes of file @var{filename}. If
1045 the specified file cannot be opened, it returns @code{nil}.
1047 The elements of the list, in order, are:
1051 @code{t} for a directory, a string for a symbolic link (the name
1052 linked to), or @code{nil} for a text file.
1054 @c Wordy so as to prevent an overfull hbox. --rjc 15mar92
1056 The number of names the file has. Alternate names, also known as hard
1057 links, can be created by using the @code{add-name-to-file} function
1058 (@pxref{Changing Files}).
1061 The file's @sc{uid}.
1064 The file's @sc{gid}.
1067 The time of last access, as a list of two integers.
1068 The first integer has the high-order 16 bits of time,
1069 the second has the low 16 bits. (This is similar to the
1070 value of @code{current-time}; see @ref{Time of Day}.)
1073 The time of last modification as a list of two integers (as above).
1076 The time of last status change as a list of two integers (as above).
1079 The size of the file in bytes. If the size is too large to fit in a
1080 Lisp integer, this is a floating point number.
1083 The file's modes, as a string of ten letters or dashes,
1087 @code{t} if the file's @sc{gid} would change if file were
1088 deleted and recreated; @code{nil} otherwise.
1091 The file's inode number. If possible, this is an integer. If the inode
1092 number is too large to be represented as an integer in Emacs Lisp, then
1093 the value has the form @code{(@var{high} . @var{low})}, where @var{low}
1094 holds the low 16 bits.
1097 The file system number of the file system that the file is in.
1098 Depending on the magnitude of the value, this can be either an integer
1099 or a cons cell, in the same manner as the inode number. This element
1100 and the file's inode number together give enough information to
1101 distinguish any two files on the system---no two files can have the same
1102 values for both of these numbers.
1105 For example, here are the file attributes for @file{files.texi}:
1109 (file-attributes "files.texi")
1110 @result{} (nil 1 2235 75
1120 and here is how the result is interpreted:
1124 is neither a directory nor a symbolic link.
1127 has only one name (the name @file{files.texi} in the current default
1131 is owned by the user with @sc{uid} 2235.
1134 is in the group with @sc{gid} 75.
1137 was last accessed on Aug 19 00:09.
1140 was last modified on Aug 19 00:09.
1143 last had its inode changed on Aug 19 00:09.
1146 is 14906 bytes long. (It may not contain 14906 characters, though,
1147 if some of the bytes belong to multibyte sequences.)
1150 has a mode of read and write access for the owner, group, and world.
1153 would retain the same @sc{gid} if it were recreated.
1156 has an inode number of 129500.
1158 is on file system number -32252.
1162 @node Changing Files
1163 @section Changing File Names and Attributes
1164 @cindex renaming files
1165 @cindex copying files
1166 @cindex deleting files
1167 @cindex linking files
1168 @cindex setting modes of files
1170 The functions in this section rename, copy, delete, link, and set the
1173 In the functions that have an argument @var{newname}, if a file by the
1174 name of @var{newname} already exists, the actions taken depend on the
1175 value of the argument @var{ok-if-already-exists}:
1179 Signal a @code{file-already-exists} error if
1180 @var{ok-if-already-exists} is @code{nil}.
1183 Request confirmation if @var{ok-if-already-exists} is a number.
1186 Replace the old file without confirmation if @var{ok-if-already-exists}
1190 @defun add-name-to-file oldname newname &optional ok-if-already-exists
1191 @cindex file with multiple names
1192 @cindex file hard link
1193 This function gives the file named @var{oldname} the additional name
1194 @var{newname}. This means that @var{newname} becomes a new ``hard
1195 link'' to @var{oldname}.
1197 In the first part of the following example, we list two files,
1198 @file{foo} and @file{foo3}.
1203 81908 -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo
1204 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
1208 Now we create a hard link, by calling @code{add-name-to-file}, then list
1209 the files again. This shows two names for one file, @file{foo} and
1214 (add-name-to-file "foo" "foo2")
1220 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo
1221 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2
1222 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
1226 Finally, we evaluate the following:
1229 (add-name-to-file "foo" "foo3" t)
1233 and list the files again. Now there are three names
1234 for one file: @file{foo}, @file{foo2}, and @file{foo3}. The old
1235 contents of @file{foo3} are lost.
1239 (add-name-to-file "foo1" "foo3")
1245 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo
1246 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2
1247 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3
1251 This function is meaningless on operating systems where multiple names
1252 for one file are not allowed. Some systems implement multiple names
1253 by copying the file instead.
1255 See also @code{file-nlinks} in @ref{File Attributes}.
1258 @deffn Command rename-file filename newname &optional ok-if-already-exists
1259 This command renames the file @var{filename} as @var{newname}.
1261 If @var{filename} has additional names aside from @var{filename}, it
1262 continues to have those names. In fact, adding the name @var{newname}
1263 with @code{add-name-to-file} and then deleting @var{filename} has the
1264 same effect as renaming, aside from momentary intermediate states.
1266 In an interactive call, this function prompts for @var{filename} and
1267 @var{newname} in the minibuffer; also, it requests confirmation if
1268 @var{newname} already exists.
1271 @deffn Command copy-file oldname newname &optional ok-if-exists time
1272 This command copies the file @var{oldname} to @var{newname}. An
1273 error is signaled if @var{oldname} does not exist.
1275 If @var{time} is non-@code{nil}, then this function gives the new file
1276 the same last-modified time that the old one has. (This works on only
1277 some operating systems.) If setting the time gets an error,
1278 @code{copy-file} signals a @code{file-date-error} error.
1280 In an interactive call, this function prompts for @var{filename} and
1281 @var{newname} in the minibuffer; also, it requests confirmation if
1282 @var{newname} already exists.
1285 @deffn Command delete-file filename
1287 This command deletes the file @var{filename}, like the shell command
1288 @samp{rm @var{filename}}. If the file has multiple names, it continues
1289 to exist under the other names.
1291 A suitable kind of @code{file-error} error is signaled if the file does
1292 not exist, or is not deletable. (On Unix and GNU/Linux, a file is
1293 deletable if its directory is writable.)
1295 See also @code{delete-directory} in @ref{Create/Delete Dirs}.
1298 @deffn Command make-symbolic-link filename newname &optional ok-if-exists
1300 @kindex file-already-exists
1301 This command makes a symbolic link to @var{filename}, named
1302 @var{newname}. This is like the shell command @samp{ln -s
1303 @var{filename} @var{newname}}.
1305 In an interactive call, this function prompts for @var{filename} and
1306 @var{newname} in the minibuffer; also, it requests confirmation if
1307 @var{newname} already exists.
1309 This function is not available on systems that don't support symbolic
1313 @defun define-logical-name varname string
1314 This function defines the logical name @var{name} to have the value
1315 @var{string}. It is available only on VMS.
1318 @defun set-file-modes filename mode
1319 This function sets mode bits of @var{filename} to @var{mode} (which must
1320 be an integer). Only the low 12 bits of @var{mode} are used.
1324 @defun set-default-file-modes mode
1325 This function sets the default file protection for new files created by
1326 Emacs and its subprocesses. Every file created with Emacs initially has
1327 this protection, or a subset of it (@code{write-region} will not give a
1328 file execute permission even if the default file protection allows
1329 execute permission). On Unix and GNU/Linux, the default protection is
1330 the bitwise complement of the ``umask'' value.
1332 The argument @var{mode} must be an integer. On most systems, only the
1333 low 9 bits of @var{mode} are meaningful. You can use the Lisp construct
1334 for octal character codes to enter @var{mode}; for example,
1337 (set-default-file-modes ?\644)
1340 Saving a modified version of an existing file does not count as creating
1341 the file; it preserves the existing file's mode, whatever that is. So
1342 the default file protection has no effect.
1345 @defun default-file-modes
1346 This function returns the current default protection value.
1349 @cindex MS-DOS and file modes
1350 @cindex file modes and MS-DOS
1351 On MS-DOS, there is no such thing as an ``executable'' file mode bit.
1352 So Emacs considers a file executable if its name ends in one of the
1353 standard executable extensions, such as @file{.com}, @file{.bat},
1354 @file{.exe}, and some others. Files that begin with the Unix-standard
1355 @samp{#!} signature, such as shell and Perl scripts, are also considered
1356 as executable files. This is reflected in the values returned by
1357 @code{file-modes} and @code{file-attributes}. Directories are also
1358 reported with executable bit set, for compatibility with Unix.
1364 Files are generally referred to by their names, in Emacs as elsewhere.
1365 File names in Emacs are represented as strings. The functions that
1366 operate on a file all expect a file name argument.
1368 In addition to operating on files themselves, Emacs Lisp programs
1369 often need to operate on file names; i.e., to take them apart and to use
1370 part of a name to construct related file names. This section describes
1371 how to manipulate file names.
1373 The functions in this section do not actually access files, so they
1374 can operate on file names that do not refer to an existing file or
1377 On MS-DOS and MS-Windows, these functions (like the function that
1378 actually operate on files) accept MS-DOS or MS-Windows file-name syntax,
1379 where backslashes separate the components, as well as Unix syntax; but
1380 they always return Unix syntax. On VMS, these functions (and the ones
1381 that operate on files) understand both VMS file-name syntax and Unix
1382 syntax. This enables Lisp programs to specify file names in Unix syntax
1383 and work properly on all systems without change.
1386 * File Name Components:: The directory part of a file name, and the rest.
1387 * Directory Names:: A directory's name as a directory
1388 is different from its name as a file.
1389 * Relative File Names:: Some file names are relative to a current directory.
1390 * File Name Expansion:: Converting relative file names to absolute ones.
1391 * Unique File Names:: Generating names for temporary files.
1392 * File Name Completion:: Finding the completions for a given file name.
1393 * Standard File Names:: If your package uses a fixed file name,
1394 how to handle various operating systems simply.
1397 @node File Name Components
1398 @subsection File Name Components
1399 @cindex directory part (of file name)
1400 @cindex nondirectory part (of file name)
1401 @cindex version number (in file name)
1403 The operating system groups files into directories. To specify a
1404 file, you must specify the directory and the file's name within that
1405 directory. Therefore, Emacs considers a file name as having two main
1406 parts: the @dfn{directory name} part, and the @dfn{nondirectory} part
1407 (or @dfn{file name within the directory}). Either part may be empty.
1408 Concatenating these two parts reproduces the original file name.
1410 On most systems, the directory part is everything up to and including
1411 the last slash (backslash is also allowed in input on MS-DOS or
1412 MS-Windows); the nondirectory part is the rest. The rules in VMS syntax
1415 For some purposes, the nondirectory part is further subdivided into
1416 the name proper and the @dfn{version number}. On most systems, only
1417 backup files have version numbers in their names. On VMS, every file
1418 has a version number, but most of the time the file name actually used
1419 in Emacs omits the version number, so that version numbers in Emacs are
1420 found mostly in directory lists.
1422 @defun file-name-directory filename
1423 This function returns the directory part of @var{filename} (or
1424 @code{nil} if @var{filename} does not include a directory part). On
1425 most systems, the function returns a string ending in a slash. On VMS,
1426 it returns a string ending in one of the three characters @samp{:},
1427 @samp{]}, or @samp{>}.
1431 (file-name-directory "lewis/foo") ; @r{Unix example}
1435 (file-name-directory "foo") ; @r{Unix example}
1439 (file-name-directory "[X]FOO.TMP") ; @r{VMS example}
1445 @defun file-name-nondirectory filename
1446 This function returns the nondirectory part of @var{filename}.
1450 (file-name-nondirectory "lewis/foo")
1454 (file-name-nondirectory "foo")
1458 ;; @r{The following example is accurate only on VMS.}
1459 (file-name-nondirectory "[X]FOO.TMP")
1465 @defun file-name-sans-versions filename &optional keep-backup-version
1466 This function returns @var{filename} with any file version numbers,
1467 backup version numbers, or trailing tildes discarded.
1469 If @var{keep-backup-version} is non-@code{nil}, then true file version
1470 numbers understood as such by the file system are discarded from the
1471 return value, but backup version numbers are kept.
1475 (file-name-sans-versions "~rms/foo.~1~")
1476 @result{} "~rms/foo"
1479 (file-name-sans-versions "~rms/foo~")
1480 @result{} "~rms/foo"
1483 (file-name-sans-versions "~rms/foo")
1484 @result{} "~rms/foo"
1487 ;; @r{The following example applies to VMS only.}
1488 (file-name-sans-versions "foo;23")
1494 @defun file-name-sans-extension filename
1495 This function returns @var{filename} minus its ``extension,'' if any.
1496 The extension, in a file name, is the part that starts with the last
1497 @samp{.} in the last name component, except if that @samp{.} is the
1498 first character of the file name's last component. For example,
1501 (file-name-sans-extension "foo.lose.c")
1502 @result{} "foo.lose"
1503 (file-name-sans-extension "big.hack/foo")
1504 @result{} "big.hack/foo"
1505 (file-name-sans-extension "/my/home/.emacs")
1506 @result{} "/my/home.emacs"
1507 (file-name-sans-extension "/my/home/.emacs.el")
1508 @result{} "/my/home/.emacs"
1513 Andrew Innes says that this
1515 @c @defvar directory-sep-char
1516 @c @tindex directory-sep-char
1517 This variable holds the character that Emacs normally uses to separate
1518 file name components. The default value is @code{?/}, but on MS-Windows
1519 you can set it to @code{?\\}; then the functions that transform file names
1520 use backslashes in their output.
1522 File names using backslashes work as input to Lisp primitives even on
1523 MS-DOS and MS-Windows, even if @code{directory-sep-char} has its default
1528 @defun file-name-extension filename &optional period
1529 This function returns @var{filename}'s final ``extension,'' if any,
1530 after applying @code{file-name-sans-versions} to remove any
1531 version/backup part. It returns @code{nil} for extensionless file
1532 names such as @file{foo}. If @var{period} is non-nil, then the
1533 returned value includes the period that delimits the extension, and if
1534 @var{filename} has no extension, the value is @code{""}. If the last
1535 component of a file name begins with a @samp{.}, that @samp{.} doesn't
1536 count as the beginning of an extension, so, for example,
1537 @file{.emacs}'s ``extension'' is @code{nil}, not @samp{.emacs}.
1540 @node Directory Names
1541 @comment node-name, next, previous, up
1542 @subsection Directory Names
1543 @cindex directory name
1544 @cindex file name of directory
1546 A @dfn{directory name} is the name of a directory. A directory is a
1547 kind of file, and it has a file name, which is related to the directory
1548 name but not identical to it. (This is not quite the same as the usual
1549 Unix terminology.) These two different names for the same entity are
1550 related by a syntactic transformation. On most systems, this is simple:
1551 a directory name ends in a slash (or backslash), whereas the directory's
1552 name as a file lacks that slash. On VMS, the relationship is more
1555 The difference between a directory name and its name as a file is
1556 subtle but crucial. When an Emacs variable or function argument is
1557 described as being a directory name, a file name of a directory is not
1560 The following two functions convert between directory names and file
1561 names. They do nothing special with environment variable substitutions
1562 such as @samp{$HOME}, and the constructs @samp{~}, and @samp{..}.
1564 @defun file-name-as-directory filename
1565 This function returns a string representing @var{filename} in a form
1566 that the operating system will interpret as the name of a directory. On
1567 most systems, this means appending a slash to the string (if it does not
1568 already end in one). On VMS, the function converts a string of the form
1569 @file{[X]Y.DIR.1} to the form @file{[X.Y]}.
1573 (file-name-as-directory "~rms/lewis")
1574 @result{} "~rms/lewis/"
1579 @defun directory-file-name dirname
1580 This function returns a string representing @var{dirname} in a form that
1581 the operating system will interpret as the name of a file. On most
1582 systems, this means removing the final slash (or backslash) from the
1583 string. On VMS, the function converts a string of the form @file{[X.Y]}
1584 to @file{[X]Y.DIR.1}.
1588 (directory-file-name "~lewis/")
1594 @cindex directory name abbreviation
1595 Directory name abbreviations are useful for directories that are
1596 normally accessed through symbolic links. Sometimes the users recognize
1597 primarily the link's name as ``the name'' of the directory, and find it
1598 annoying to see the directory's ``real'' name. If you define the link
1599 name as an abbreviation for the ``real'' name, Emacs shows users the
1600 abbreviation instead.
1602 @defvar directory-abbrev-alist
1603 The variable @code{directory-abbrev-alist} contains an alist of
1604 abbreviations to use for file directories. Each element has the form
1605 @code{(@var{from} . @var{to})}, and says to replace @var{from} with
1606 @var{to} when it appears in a directory name. The @var{from} string is
1607 actually a regular expression; it should always start with @samp{^}.
1608 The function @code{abbreviate-file-name} performs these substitutions.
1610 You can set this variable in @file{site-init.el} to describe the
1611 abbreviations appropriate for your site.
1613 Here's an example, from a system on which file system @file{/home/fsf}
1614 and so on are normally accessed through symbolic links named @file{/fsf}
1618 (("^/home/fsf" . "/fsf")
1619 ("^/home/gp" . "/gp")
1620 ("^/home/gd" . "/gd"))
1624 To convert a directory name to its abbreviation, use this
1627 @defun abbreviate-file-name dirname
1628 This function applies abbreviations from @code{directory-abbrev-alist}
1629 to its argument, and substitutes @samp{~} for the user's home
1633 @node Relative File Names
1634 @subsection Absolute and Relative File Names
1635 @cindex absolute file name
1636 @cindex relative file name
1638 All the directories in the file system form a tree starting at the
1639 root directory. A file name can specify all the directory names
1640 starting from the root of the tree; then it is called an @dfn{absolute}
1641 file name. Or it can specify the position of the file in the tree
1642 relative to a default directory; then it is called a @dfn{relative} file
1643 name. On Unix and GNU/Linux, an absolute file name starts with a slash
1644 or a tilde (@samp{~}), and a relative one does not. On MS-DOS and
1645 MS-Windows, an absolute file name starts with a slash or a backslash, or
1646 with a drive specification @samp{@var{x}:/}, where @var{x} is the
1647 @dfn{drive letter}. The rules on VMS are complicated.
1649 @defun file-name-absolute-p filename
1650 This function returns @code{t} if file @var{filename} is an absolute
1651 file name, @code{nil} otherwise. On VMS, this function understands both
1652 Unix syntax and VMS syntax.
1656 (file-name-absolute-p "~rms/foo")
1660 (file-name-absolute-p "rms/foo")
1664 (file-name-absolute-p "/user/rms/foo")
1670 @node File Name Expansion
1671 @subsection Functions that Expand Filenames
1672 @cindex expansion of file names
1674 @dfn{Expansion} of a file name means converting a relative file name
1675 to an absolute one. Since this is done relative to a default directory,
1676 you must specify the default directory name as well as the file name to
1677 be expanded. Expansion also simplifies file names by eliminating
1678 redundancies such as @file{./} and @file{@var{name}/../}.
1680 @defun expand-file-name filename &optional directory
1681 This function converts @var{filename} to an absolute file name. If
1682 @var{directory} is supplied, it is the default directory to start with
1683 if @var{filename} is relative. (The value of @var{directory} should
1684 itself be an absolute directory name; it may start with @samp{~}.)
1685 Otherwise, the current buffer's value of @code{default-directory} is
1690 (expand-file-name "foo")
1691 @result{} "/xcssun/users/rms/lewis/foo"
1694 (expand-file-name "../foo")
1695 @result{} "/xcssun/users/rms/foo"
1698 (expand-file-name "foo" "/usr/spool/")
1699 @result{} "/usr/spool/foo"
1702 (expand-file-name "$HOME/foo")
1703 @result{} "/xcssun/users/rms/lewis/$HOME/foo"
1707 Filenames containing @samp{.} or @samp{..} are simplified to their
1712 (expand-file-name "bar/../foo")
1713 @result{} "/xcssun/users/rms/lewis/foo"
1717 Note that @code{expand-file-name} does @emph{not} expand environment
1718 variables; only @code{substitute-in-file-name} does that.
1722 @defun file-relative-name filename &optional directory
1723 This function does the inverse of expansion---it tries to return a
1724 relative name that is equivalent to @var{filename} when interpreted
1725 relative to @var{directory}. If @var{directory} is omitted or
1726 @code{nil}, it defaults to the current buffer's default directory.
1728 On some operating systems, an absolute file name begins with a device
1729 name. On such systems, @var{filename} has no relative equivalent based
1730 on @var{directory} if they start with two different device names. In
1731 this case, @code{file-relative-name} returns @var{filename} in absolute
1735 (file-relative-name "/foo/bar" "/foo/")
1737 (file-relative-name "/foo/bar" "/hack/")
1738 @result{} "../foo/bar"
1742 @defvar default-directory
1743 The value of this buffer-local variable is the default directory for the
1744 current buffer. It should be an absolute directory name; it may start
1745 with @samp{~}. This variable is buffer-local in every buffer.
1747 @code{expand-file-name} uses the default directory when its second
1748 argument is @code{nil}.
1750 Aside from VMS, the value is always a string ending with a slash.
1755 @result{} "/user/lewis/manual/"
1760 @defun substitute-in-file-name filename
1761 This function replaces environment variables references in
1762 @var{filename} with the environment variable values. Following standard
1763 Unix shell syntax, @samp{$} is the prefix to substitute an environment
1766 The environment variable name is the series of alphanumeric characters
1767 (including underscores) that follow the @samp{$}. If the character following
1768 the @samp{$} is a @samp{@{}, then the variable name is everything up to the
1771 @c Wordy to avoid overfull hbox. --rjc 15mar92
1772 Here we assume that the environment variable @code{HOME}, which holds
1773 the user's home directory name, has value @samp{/xcssun/users/rms}.
1777 (substitute-in-file-name "$HOME/foo")
1778 @result{} "/xcssun/users/rms/foo"
1782 After substitution, if a @samp{~} or a @samp{/} appears following a
1783 @samp{/}, everything before the following @samp{/} is discarded:
1787 (substitute-in-file-name "bar/~/foo")
1791 (substitute-in-file-name "/usr/local/$HOME/foo")
1792 @result{} "/xcssun/users/rms/foo"
1793 ;; @r{@file{/usr/local/} has been discarded.}
1797 On VMS, @samp{$} substitution is not done, so this function does nothing
1798 on VMS except discard superfluous initial components as shown above.
1801 @node Unique File Names
1802 @subsection Generating Unique File Names
1804 Some programs need to write temporary files. Here is the usual way to
1805 construct a name for such a file, starting in Emacs 21:
1808 (make-temp-file @var{name-of-application})
1812 The job of @code{make-temp-file} is to prevent two different users or
1813 two different jobs from trying to use the exact same file name.
1815 @defun make-temp-file prefix &optional dir-flag
1816 @tindex make-temp-file
1817 This function creates a temporary file and returns its name.
1818 The name starts with @var{prefix}; it also contains a number that is
1819 different in each Emacs job. If @var{prefix} is a relative file name,
1820 it is expanded against @code{temporary-file-directory}.
1824 (make-temp-file "foo")
1825 @result{} "/tmp/foo232J6v"
1829 When @code{make-temp-file} returns, the file has been created and is
1830 empty. At that point, you should write the intended contents into the
1833 If @var{dir-flag} is non-@code{nil}, @code{make-temp-file} creates
1834 an empty directory instead of an empty file.
1836 To prevent conflicts among different libraries running in the same
1837 Emacs, each Lisp program that uses @code{make-temp-file} should have its
1838 own @var{prefix}. The number added to the end of @var{prefix}
1839 distinguishes between the same application running in different Emacs
1840 jobs. Additional added characters permit a large number of distinct
1841 names even in one Emacs job.
1844 The default directory for temporary files is controlled by the
1845 variable @code{temporary-file-directory}. This variable gives the user
1846 a uniform way to specify the directory for all temporary files. Some
1847 programs use @code{small-temporary-file-directory} instead, if that is
1848 non-@code{nil}. To use it, you should expand the prefix against
1849 the proper directory before calling @code{make-temp-file}.
1851 In older Emacs versions where @code{make-temp-file} does not exist,
1852 you should use @code{make-temp-name} instead:
1856 (expand-file-name @var{name-of-application}
1857 temporary-file-directory))
1860 @defun make-temp-name string
1861 This function generates a string that can be used as a unique file name.
1862 The name starts with @var{string}, and contains a number that is
1863 different in each Emacs job. It is like @code{make-temp-file} except
1864 that it just constructs a name, and does not create a file. On MS-DOS,
1865 the @var{string} prefix can be truncated to fit into the 8+3 file-name
1869 @defvar temporary-file-directory
1870 @cindex @code{TMPDIR} environment variable
1871 @cindex @code{TMP} environment variable
1872 @cindex @code{TEMP} environment variable
1873 This variable specifies the directory name for creating temporary files.
1874 Its value should be a directory name (@pxref{Directory Names}), but it
1875 is good for Lisp programs to cope if the value is a directory's file
1876 name instead. Using the value as the second argument to
1877 @code{expand-file-name} is a good way to achieve that.
1879 The default value is determined in a reasonable way for your operating
1880 system; it is based on the @code{TMPDIR}, @code{TMP} and @code{TEMP}
1881 environment variables, with a fall-back to a system-dependent name if
1882 none of these variables is defined.
1884 Even if you do not use @code{make-temp-name} to choose the temporary
1885 file's name, you should still use this variable to decide which
1886 directory to put the file in. However, if you expect the file to be
1887 small, you should use @code{small-temporary-file-directory} first if
1888 that is non-@code{nil}.
1891 @tindex small-temporary-file-directory
1892 @defvar small-temporary-file-directory
1893 This variable (new in Emacs 21) specifies the directory name for
1894 creating certain temporary files, which are likely to be small.
1896 If you want to write a temporary file which is likely to be small, you
1897 should compute the directory like this:
1901 (expand-file-name @var{prefix}
1902 (or small-temporary-file-directory
1903 temporary-file-directory)))
1907 @node File Name Completion
1908 @subsection File Name Completion
1909 @cindex file name completion subroutines
1910 @cindex completion, file name
1912 This section describes low-level subroutines for completing a file
1913 name. For other completion functions, see @ref{Completion}.
1915 @defun file-name-all-completions partial-filename directory
1916 This function returns a list of all possible completions for a file
1917 whose name starts with @var{partial-filename} in directory
1918 @var{directory}. The order of the completions is the order of the files
1919 in the directory, which is unpredictable and conveys no useful
1922 The argument @var{partial-filename} must be a file name containing no
1923 directory part and no slash (or backslash on some systems). The current
1924 buffer's default directory is prepended to @var{directory}, if
1925 @var{directory} is not absolute.
1927 In the following example, suppose that @file{~rms/lewis} is the current
1928 default directory, and has five files whose names begin with @samp{f}:
1929 @file{foo}, @file{file~}, @file{file.c}, @file{file.c.~1~}, and
1930 @file{file.c.~2~}.@refill
1934 (file-name-all-completions "f" "")
1935 @result{} ("foo" "file~" "file.c.~2~"
1936 "file.c.~1~" "file.c")
1940 (file-name-all-completions "fo" "")
1946 @defun file-name-completion filename directory
1947 This function completes the file name @var{filename} in directory
1948 @var{directory}. It returns the longest prefix common to all file names
1949 in directory @var{directory} that start with @var{filename}.
1951 If only one match exists and @var{filename} matches it exactly, the
1952 function returns @code{t}. The function returns @code{nil} if directory
1953 @var{directory} contains no name starting with @var{filename}.
1955 In the following example, suppose that the current default directory
1956 has five files whose names begin with @samp{f}: @file{foo},
1957 @file{file~}, @file{file.c}, @file{file.c.~1~}, and
1958 @file{file.c.~2~}.@refill
1962 (file-name-completion "fi" "")
1967 (file-name-completion "file.c.~1" "")
1968 @result{} "file.c.~1~"
1972 (file-name-completion "file.c.~1~" "")
1977 (file-name-completion "file.c.~3" "")
1983 @defopt completion-ignored-extensions
1984 @code{file-name-completion} usually ignores file names that end in any
1985 string in this list. It does not ignore them when all the possible
1986 completions end in one of these suffixes or when a buffer showing all
1987 possible completions is displayed.@refill
1989 A typical value might look like this:
1993 completion-ignored-extensions
1994 @result{} (".o" ".elc" "~" ".dvi")
1998 If an element of @code{completion-ignored-extensions} ends in a slash
1999 @samp{/}, it signals a directory. The elements which do @emph{not} end
2000 in a slash will never match a directory; thus, the above value will not
2001 filter out a directory named @file{foo.elc}.
2004 @node Standard File Names
2005 @subsection Standard File Names
2007 Most of the file names used in Lisp programs are entered by the user.
2008 But occasionally a Lisp program needs to specify a standard file name
2009 for a particular use---typically, to hold customization information
2010 about each user. For example, abbrev definitions are stored (by
2011 default) in the file @file{~/.abbrev_defs}; the @code{completion}
2012 package stores completions in the file @file{~/.completions}. These are
2013 two of the many standard file names used by parts of Emacs for certain
2016 Various operating systems have their own conventions for valid file
2017 names and for which file names to use for user profile data. A Lisp
2018 program which reads a file using a standard file name ought to use, on
2019 each type of system, a file name suitable for that system. The function
2020 @code{convert-standard-filename} makes this easy to do.
2022 @defun convert-standard-filename filename
2023 This function alters the file name @var{filename} to fit the conventions
2024 of the operating system in use, and returns the result as a new string.
2027 The recommended way to specify a standard file name in a Lisp program
2028 is to choose a name which fits the conventions of GNU and Unix systems,
2029 usually with a nondirectory part that starts with a period, and pass it
2030 to @code{convert-standard-filename} instead of using it directly. Here
2031 is an example from the @code{completion} package:
2034 (defvar save-completions-file-name
2035 (convert-standard-filename "~/.completions")
2036 "*The file name to save completions to.")
2039 On GNU and Unix systems, and on some other systems as well,
2040 @code{convert-standard-filename} returns its argument unchanged. On
2041 some other systems, it alters the name to fit the system's conventions.
2043 For example, on MS-DOS the alterations made by this function include
2044 converting a leading @samp{.} to @samp{_}, converting a @samp{_} in the
2045 middle of the name to @samp{.} if there is no other @samp{.}, inserting
2046 a @samp{.} after eight characters if there is none, and truncating to
2047 three characters after the @samp{.}. (It makes other changes as well.)
2048 Thus, @file{.abbrev_defs} becomes @file{_abbrev.def}, and
2049 @file{.completions} becomes @file{_complet.ion}.
2051 @node Contents of Directories
2052 @section Contents of Directories
2053 @cindex directory-oriented functions
2054 @cindex file names in directory
2056 A directory is a kind of file that contains other files entered under
2057 various names. Directories are a feature of the file system.
2059 Emacs can list the names of the files in a directory as a Lisp list,
2060 or display the names in a buffer using the @code{ls} shell command. In
2061 the latter case, it can optionally display information about each file,
2062 depending on the options passed to the @code{ls} command.
2064 @defun directory-files directory &optional full-name match-regexp nosort
2065 This function returns a list of the names of the files in the directory
2066 @var{directory}. By default, the list is in alphabetical order.
2068 If @var{full-name} is non-@code{nil}, the function returns the files'
2069 absolute file names. Otherwise, it returns the names relative to
2070 the specified directory.
2072 If @var{match-regexp} is non-@code{nil}, this function returns only
2073 those file names that contain a match for that regular expression---the
2074 other file names are excluded from the list.
2077 If @var{nosort} is non-@code{nil}, @code{directory-files} does not sort
2078 the list, so you get the file names in no particular order. Use this if
2079 you want the utmost possible speed and don't care what order the files
2080 are processed in. If the order of processing is visible to the user,
2081 then the user will probably be happier if you do sort the names.
2085 (directory-files "~lewis")
2086 @result{} ("#foo#" "#foo.el#" "." ".."
2087 "dired-mods.el" "files.texi"
2092 An error is signaled if @var{directory} is not the name of a directory
2096 @defun file-name-all-versions file dirname
2097 This function returns a list of all versions of the file named
2098 @var{file} in directory @var{dirname}.
2101 @tindex file-expand-wildcards
2102 @defun file-expand-wildcards pattern &optional full
2103 This function expands the wildcard pattern @var{pattern}, returning
2104 a list of file names that match it.
2106 If @var{pattern} is written as an absolute file name,
2107 the values are absolute also.
2109 If @var{pattern} is written as a relative file name, it is interpreted
2110 relative to the current default directory. The file names returned are
2111 normally also relative to the current default directory. However, if
2112 @var{full} is non-@code{nil}, they are absolute.
2115 @defun insert-directory file switches &optional wildcard full-directory-p
2116 This function inserts (in the current buffer) a directory listing for
2117 directory @var{file}, formatted with @code{ls} according to
2118 @var{switches}. It leaves point after the inserted text.
2120 The argument @var{file} may be either a directory name or a file
2121 specification including wildcard characters. If @var{wildcard} is
2122 non-@code{nil}, that means treat @var{file} as a file specification with
2125 If @var{full-directory-p} is non-@code{nil}, that means the directory
2126 listing is expected to show the full contents of a directory. You
2127 should specify @code{t} when @var{file} is a directory and switches do
2128 not contain @samp{-d}. (The @samp{-d} option to @code{ls} says to
2129 describe a directory itself as a file, rather than showing its
2132 On most systems, this function works by running a directory listing
2133 program whose name is in the variable @code{insert-directory-program}.
2134 If @var{wildcard} is non-@code{nil}, it also runs the shell specified by
2135 @code{shell-file-name}, to expand the wildcards.
2137 MS-DOS and MS-Windows systems usually lack the standard Unix program
2138 @code{ls}, so this function emulates the standard Unix program @code{ls}
2142 @defvar insert-directory-program
2143 This variable's value is the program to run to generate a directory listing
2144 for the function @code{insert-directory}. It is ignored on systems
2145 which generate the listing with Lisp code.
2148 @node Create/Delete Dirs
2149 @section Creating and Deleting Directories
2150 @c Emacs 19 features
2152 Most Emacs Lisp file-manipulation functions get errors when used on
2153 files that are directories. For example, you cannot delete a directory
2154 with @code{delete-file}. These special functions exist to create and
2157 @defun make-directory dirname &optional parents
2158 This function creates a directory named @var{dirname}.
2159 If @var{parents} is non-@code{nil}, that means to create
2160 the parent directories first, if they don't already exist.
2163 @defun delete-directory dirname
2164 This function deletes the directory named @var{dirname}. The function
2165 @code{delete-file} does not work for files that are directories; you
2166 must use @code{delete-directory} for them. If the directory contains
2167 any files, @code{delete-directory} signals an error.
2170 @node Magic File Names
2171 @section Making Certain File Names ``Magic''
2172 @cindex magic file names
2175 You can implement special handling for certain file names. This is
2176 called making those names @dfn{magic}. The principal use for this
2177 feature is in implementing remote file names (@pxref{Remote Files,,
2178 Remote Files, emacs, The GNU Emacs Manual}).
2180 To define a kind of magic file name, you must supply a regular
2181 expression to define the class of names (all those that match the
2182 regular expression), plus a handler that implements all the primitive
2183 Emacs file operations for file names that do match.
2185 The variable @code{file-name-handler-alist} holds a list of handlers,
2186 together with regular expressions that determine when to apply each
2187 handler. Each element has this form:
2190 (@var{regexp} . @var{handler})
2194 All the Emacs primitives for file access and file name transformation
2195 check the given file name against @code{file-name-handler-alist}. If
2196 the file name matches @var{regexp}, the primitives handle that file by
2197 calling @var{handler}.
2199 The first argument given to @var{handler} is the name of the primitive;
2200 the remaining arguments are the arguments that were passed to that
2201 primitive. (The first of these arguments is most often the file name
2202 itself.) For example, if you do this:
2205 (file-exists-p @var{filename})
2209 and @var{filename} has handler @var{handler}, then @var{handler} is
2213 (funcall @var{handler} 'file-exists-p @var{filename})
2216 When a function takes two or more arguments that must be file names,
2217 it checks each of those names for a handler. For example, if you do
2221 (expand-file-name @var{filename} @var{dirname})
2225 then it checks for a handler for @var{filename} and then for a handler
2226 for @var{dirname}. In either case, the @var{handler} is called like
2230 (funcall @var{handler} 'expand-file-name @var{filename} @var{dirname})
2234 The @var{handler} then needs to figure out whether to handle
2235 @var{filename} or @var{dirname}.
2237 Here are the operations that a magic file name handler gets to handle:
2241 @code{add-name-to-file}, @code{copy-file}, @code{delete-directory},
2243 @code{diff-latest-backup-file},
2244 @code{directory-file-name},
2245 @code{directory-files},
2246 @code{dired-call-process},
2247 @code{dired-compress-file}, @code{dired-uncache},
2248 @code{expand-file-name},
2249 @code{file-accessible-directory-p},@*
2250 @code{file-attributes},
2251 @code{file-directory-p},
2252 @code{file-executable-p}, @code{file-exists-p},@*
2253 @code{file-local-copy},
2254 @code{file-modes}, @code{file-name-all-completions},@*
2255 @code{file-name-as-directory},
2256 @code{file-name-completion},
2257 @code{file-name-directory},
2258 @code{file-name-nondirectory},
2259 @code{file-name-sans-versions}, @code{file-newer-than-file-p},
2260 @code{file-ownership-preserved-p},
2261 @code{file-readable-p}, @code{file-regular-p}, @code{file-symlink-p},
2262 @code{file-truename}, @code{file-writable-p},
2263 @code{find-backup-file-name},
2264 @code{get-file-buffer},@*
2265 @code{insert-directory},
2266 @code{insert-file-contents},
2267 @code{load}, @code{make-directory},
2268 @code{make-symbolic-link}, @code{rename-file}, @code{set-file-modes},
2269 @code{set-visited-file-modtime}, @code{shell-command},@*
2270 @code{unhandled-file-name-directory},
2271 @code{vc-registered},
2272 @code{verify-visited-file-modtime},@*
2273 @code{write-region}.
2278 @code{add-name-to-file}, @code{copy-file}, @code{delete-directory},
2280 @code{diff-latest-backup-file},
2281 @code{directory-file-name},
2282 @code{directory-files},
2283 @code{dired-call-process},
2284 @code{dired-compress-file}, @code{dired-uncache},
2285 @code{expand-file-name},
2286 @code{file-accessible-direc@discretionary{}{}{}tory-p},
2287 @code{file-attributes},
2288 @code{file-direct@discretionary{}{}{}ory-p},
2289 @code{file-executable-p}, @code{file-exists-p},
2290 @code{file-local-copy},
2291 @code{file-modes}, @code{file-name-all-completions},
2292 @code{file-name-as-directory},
2293 @code{file-name-completion},
2294 @code{file-name-directory},
2295 @code{file-name-nondirec@discretionary{}{}{}tory},
2296 @code{file-name-sans-versions}, @code{file-newer-than-file-p},
2297 @code{file-ownership-pre@discretionary{}{}{}served-p},
2298 @code{file-readable-p}, @code{file-regular-p}, @code{file-symlink-p},
2299 @code{file-truename}, @code{file-writable-p},
2300 @code{find-backup-file-name},
2301 @code{get-file-buffer},
2302 @code{insert-directory},
2303 @code{insert-file-contents},
2304 @code{load}, @code{make-direc@discretionary{}{}{}tory},
2305 @code{make-symbolic-link}, @code{rename-file}, @code{set-file-modes},
2306 @code{set-visited-file-modtime}, @code{shell-command},
2307 @code{unhandled-file-name-directory},
2308 @code{vc-regis@discretionary{}{}{}tered},
2309 @code{verify-visited-file-modtime},
2310 @code{write-region}.
2314 Handlers for @code{insert-file-contents} typically need to clear the
2315 buffer's modified flag, with @code{(set-buffer-modified-p nil)}, if the
2316 @var{visit} argument is non-@code{nil}. This also has the effect of
2317 unlocking the buffer if it is locked.
2319 The handler function must handle all of the above operations, and
2320 possibly others to be added in the future. It need not implement all
2321 these operations itself---when it has nothing special to do for a
2322 certain operation, it can reinvoke the primitive, to handle the
2323 operation ``in the usual way''. It should always reinvoke the primitive
2324 for an operation it does not recognize. Here's one way to do this:
2327 (defun my-file-handler (operation &rest args)
2328 ;; @r{First check for the specific operations}
2329 ;; @r{that we have special handling for.}
2330 (cond ((eq operation 'insert-file-contents) @dots{})
2331 ((eq operation 'write-region) @dots{})
2333 ;; @r{Handle any operation we don't know about.}
2334 (t (let ((inhibit-file-name-handlers
2335 (cons 'my-file-handler
2336 (and (eq inhibit-file-name-operation operation)
2337 inhibit-file-name-handlers)))
2338 (inhibit-file-name-operation operation))
2339 (apply operation args)))))
2342 When a handler function decides to call the ordinary Emacs primitive for
2343 the operation at hand, it needs to prevent the primitive from calling
2344 the same handler once again, thus leading to an infinite recursion. The
2345 example above shows how to do this, with the variables
2346 @code{inhibit-file-name-handlers} and
2347 @code{inhibit-file-name-operation}. Be careful to use them exactly as
2348 shown above; the details are crucial for proper behavior in the case of
2349 multiple handlers, and for operations that have two file names that may
2352 @defvar inhibit-file-name-handlers
2353 This variable holds a list of handlers whose use is presently inhibited
2354 for a certain operation.
2357 @defvar inhibit-file-name-operation
2358 The operation for which certain handlers are presently inhibited.
2361 @defun find-file-name-handler file operation
2362 This function returns the handler function for file name @var{file}, or
2363 @code{nil} if there is none. The argument @var{operation} should be the
2364 operation to be performed on the file---the value you will pass to the
2365 handler as its first argument when you call it. The operation is needed
2366 for comparison with @code{inhibit-file-name-operation}.
2369 @defun file-local-copy filename
2370 This function copies file @var{filename} to an ordinary non-magic file,
2371 if it isn't one already.
2373 If @var{filename} specifies a magic file name, which programs
2374 outside Emacs cannot directly read or write, this copies the contents to
2375 an ordinary file and returns that file's name.
2377 If @var{filename} is an ordinary file name, not magic, then this function
2378 does nothing and returns @code{nil}.
2381 @defun unhandled-file-name-directory filename
2382 This function returns the name of a directory that is not magic. It
2383 uses the directory part of @var{filename} if that is not magic. For a
2384 magic file name, it invokes the file name handler, which therefore
2385 decides what value to return.
2387 This is useful for running a subprocess; every subprocess must have a
2388 non-magic directory to serve as its current directory, and this function
2389 is a good way to come up with one.
2392 @node Format Conversion
2393 @section File Format Conversion
2395 @cindex file format conversion
2396 @cindex encoding file formats
2397 @cindex decoding file formats
2398 The variable @code{format-alist} defines a list of @dfn{file formats},
2399 which describe textual representations used in files for the data (text,
2400 text-properties, and possibly other information) in an Emacs buffer.
2401 Emacs performs format conversion if appropriate when reading and writing
2404 @defvar format-alist
2405 This list contains one format definition for each defined file format.
2408 @cindex format definition
2409 Each format definition is a list of this form:
2412 (@var{name} @var{doc-string} @var{regexp} @var{from-fn} @var{to-fn} @var{modify} @var{mode-fn})
2415 Here is what the elements in a format definition mean:
2419 The name of this format.
2422 A documentation string for the format.
2425 A regular expression which is used to recognize files represented in
2429 A shell command or function to decode data in this format (to convert
2430 file data into the usual Emacs data representation).
2432 A shell command is represented as a string; Emacs runs the command as a
2433 filter to perform the conversion.
2435 If @var{from-fn} is a function, it is called with two arguments, @var{begin}
2436 and @var{end}, which specify the part of the buffer it should convert.
2437 It should convert the text by editing it in place. Since this can
2438 change the length of the text, @var{from-fn} should return the modified
2441 One responsibility of @var{from-fn} is to make sure that the beginning
2442 of the file no longer matches @var{regexp}. Otherwise it is likely to
2446 A shell command or function to encode data in this format---that is, to
2447 convert the usual Emacs data representation into this format.
2449 If @var{to-fn} is a string, it is a shell command; Emacs runs the
2450 command as a filter to perform the conversion.
2452 If @var{to-fn} is a function, it is called with two arguments, @var{begin}
2453 and @var{end}, which specify the part of the buffer it should convert.
2454 There are two ways it can do the conversion:
2458 By editing the buffer in place. In this case, @var{to-fn} should
2459 return the end-position of the range of text, as modified.
2462 By returning a list of annotations. This is a list of elements of the
2463 form @code{(@var{position} . @var{string})}, where @var{position} is an
2464 integer specifying the relative position in the text to be written, and
2465 @var{string} is the annotation to add there. The list must be sorted in
2466 order of position when @var{to-fn} returns it.
2468 When @code{write-region} actually writes the text from the buffer to the
2469 file, it intermixes the specified annotations at the corresponding
2470 positions. All this takes place without modifying the buffer.
2474 A flag, @code{t} if the encoding function modifies the buffer, and
2475 @code{nil} if it works by returning a list of annotations.
2478 A minor-mode function to call after visiting a file converted from this
2479 format. The function is called with one argument, the integer 1;
2480 that tells a minor-mode function to enable the mode.
2483 The function @code{insert-file-contents} automatically recognizes file
2484 formats when it reads the specified file. It checks the text of the
2485 beginning of the file against the regular expressions of the format
2486 definitions, and if it finds a match, it calls the decoding function for
2487 that format. Then it checks all the known formats over again.
2488 It keeps checking them until none of them is applicable.
2490 Visiting a file, with @code{find-file-noselect} or the commands that use
2491 it, performs conversion likewise (because it calls
2492 @code{insert-file-contents}); it also calls the mode function for each
2493 format that it decodes. It stores a list of the format names in the
2494 buffer-local variable @code{buffer-file-format}.
2496 @defvar buffer-file-format
2497 This variable states the format of the visited file. More precisely,
2498 this is a list of the file format names that were decoded in the course
2499 of visiting the current buffer's file. It is always buffer-local in all
2503 When @code{write-region} writes data into a file, it first calls the
2504 encoding functions for the formats listed in @code{buffer-file-format},
2505 in the order of appearance in the list.
2507 @deffn Command format-write-file file format
2508 This command writes the current buffer contents into the file @var{file}
2509 in format @var{format}, and makes that format the default for future
2510 saves of the buffer. The argument @var{format} is a list of format
2514 @deffn Command format-find-file file format
2515 This command finds the file @var{file}, converting it according to
2516 format @var{format}. It also makes @var{format} the default if the
2517 buffer is saved later.
2519 The argument @var{format} is a list of format names. If @var{format} is
2520 @code{nil}, no conversion takes place. Interactively, typing just
2521 @key{RET} for @var{format} specifies @code{nil}.
2524 @deffn Command format-insert-file file format &optional beg end
2525 This command inserts the contents of file @var{file}, converting it
2526 according to format @var{format}. If @var{beg} and @var{end} are
2527 non-@code{nil}, they specify which part of the file to read, as in
2528 @code{insert-file-contents} (@pxref{Reading from Files}).
2530 The return value is like what @code{insert-file-contents} returns: a
2531 list of the absolute file name and the length of the data inserted
2534 The argument @var{format} is a list of format names. If @var{format} is
2535 @code{nil}, no conversion takes place. Interactively, typing just
2536 @key{RET} for @var{format} specifies @code{nil}.
2539 @defvar auto-save-file-format
2540 This variable specifies the format to use for auto-saving. Its value is
2541 a list of format names, just like the value of
2542 @code{buffer-file-format}; however, it is used instead of
2543 @code{buffer-file-format} for writing auto-save files. This variable is
2544 always buffer-local in all buffers.