2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2004
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. If any of the
408 functions in this hook returns non-@code{nil}, @code{write-file-functions}
411 This variable automatically becomes buffer-local whenever it is set;
412 switching to a new major mode always resets this variable, but
413 calling @code{set-visited-file-name} does not.
416 @defopt before-save-hook
417 This normal hook runs before a buffer is saved in its visited file,
418 regardless of whether that is done normally or by one of the hooks
419 described above. One use of this hook is for the Copyright package;
420 it uses this hook to make sure the file has the current year in the
425 @defopt after-save-hook
426 This normal hook runs after a buffer has been saved in its visited file.
427 One use of this hook is in Fast Lock mode; it uses this hook to save the
428 highlighting information in a cache file.
431 @defvar file-precious-flag
432 If this variable is non-@code{nil}, then @code{save-buffer} protects
433 against I/O errors while saving by writing the new file to a temporary
434 name instead of the name it is supposed to have, and then renaming it to
435 the intended name after it is clear there are no errors. This procedure
436 prevents problems such as a lack of disk space from resulting in an
439 As a side effect, backups are necessarily made by copying. @xref{Rename
440 or Copy}. Yet, at the same time, saving a precious file always breaks
441 all hard links between the file you save and other file names.
443 Some modes give this variable a non-@code{nil} buffer-local value
444 in particular buffers.
447 @defopt require-final-newline
448 This variable determines whether files may be written out that do
449 @emph{not} end with a newline. If the value of the variable is
450 @code{t}, then @code{save-buffer} silently adds a newline at the end of
451 the file whenever the buffer being saved does not already end in one.
452 If the value of the variable is non-@code{nil}, but not @code{t}, then
453 @code{save-buffer} asks the user whether to add a newline each time the
456 If the value of the variable is @code{nil}, then @code{save-buffer}
457 doesn't add newlines at all. @code{nil} is the default value, but a few
458 major modes set it to @code{t} in particular buffers.
461 See also the function @code{set-visited-file-name} (@pxref{Buffer File
464 @node Reading from Files
465 @comment node-name, next, previous, up
466 @section Reading from Files
468 You can copy a file from the disk and insert it into a buffer
469 using the @code{insert-file-contents} function. Don't use the user-level
470 command @code{insert-file} in a Lisp program, as that sets the mark.
472 @defun insert-file-contents filename &optional visit beg end replace
473 This function inserts the contents of file @var{filename} into the
474 current buffer after point. It returns a list of the absolute file name
475 and the length of the data inserted. An error is signaled if
476 @var{filename} is not the name of a file that can be read.
478 The function @code{insert-file-contents} checks the file contents
479 against the defined file formats, and converts the file contents if
480 appropriate. @xref{Format Conversion}. It also calls the functions in
481 the list @code{after-insert-file-functions}; see @ref{Saving
482 Properties}. Normally, one of the functions in the
483 @code{after-insert-file-functions} list determines the coding system
484 (@pxref{Coding Systems}) used for decoding the file's contents.
486 If @var{visit} is non-@code{nil}, this function additionally marks the
487 buffer as unmodified and sets up various fields in the buffer so that it
488 is visiting the file @var{filename}: these include the buffer's visited
489 file name and its last save file modtime. This feature is used by
490 @code{find-file-noselect} and you probably should not use it yourself.
492 If @var{beg} and @var{end} are non-@code{nil}, they should be integers
493 specifying the portion of the file to insert. In this case, @var{visit}
494 must be @code{nil}. For example,
497 (insert-file-contents filename nil 0 500)
501 inserts the first 500 characters of a file.
503 If the argument @var{replace} is non-@code{nil}, it means to replace the
504 contents of the buffer (actually, just the accessible portion) with the
505 contents of the file. This is better than simply deleting the buffer
506 contents and inserting the whole file, because (1) it preserves some
507 marker positions and (2) it puts less data in the undo list.
509 It is possible to read a special file (such as a FIFO or an I/O device)
510 with @code{insert-file-contents}, as long as @var{replace} and
511 @var{visit} are @code{nil}.
514 @defun insert-file-contents-literally filename &optional visit beg end replace
515 This function works like @code{insert-file-contents} except that it does
516 not do format decoding (@pxref{Format Conversion}), does not do
517 character code conversion (@pxref{Coding Systems}), does not run
518 @code{find-file-hook}, does not perform automatic uncompression, and so
522 If you want to pass a file name to another process so that another
523 program can read the file, use the function @code{file-local-copy}; see
524 @ref{Magic File Names}.
526 @node Writing to Files
527 @comment node-name, next, previous, up
528 @section Writing to Files
530 You can write the contents of a buffer, or part of a buffer, directly
531 to a file on disk using the @code{append-to-file} and
532 @code{write-region} functions. Don't use these functions to write to
533 files that are being visited; that could cause confusion in the
534 mechanisms for visiting.
536 @deffn Command append-to-file start end filename
537 This function appends the contents of the region delimited by
538 @var{start} and @var{end} in the current buffer to the end of file
539 @var{filename}. If that file does not exist, it is created. This
540 function returns @code{nil}.
542 An error is signaled if @var{filename} specifies a nonwritable file,
543 or a nonexistent file in a directory where files cannot be created.
546 @deffn Command write-region start end filename &optional append visit lockname mustbenew
547 This function writes the region delimited by @var{start} and @var{end}
548 in the current buffer into the file specified by @var{filename}.
551 If @var{start} is a string, then @code{write-region} writes or appends
552 that string, rather than text from the buffer. @var{end} is ignored in
555 If @var{append} is non-@code{nil}, then the specified text is appended
556 to the existing file contents (if any). Starting in Emacs 21, if
557 @var{append} is an integer, then @code{write-region} seeks to that byte
558 offset from the start of the file and writes the data from there.
560 If @var{mustbenew} is non-@code{nil}, then @code{write-region} asks
561 for confirmation if @var{filename} names an existing file.
562 Starting in Emacs 21, if @var{mustbenew} is the symbol @code{excl},
563 then @code{write-region} does not ask for confirmation, but instead
564 it signals an error @code{file-already-exists} if the file already
567 The test for an existing file, when @var{mustbenew} is @code{excl}, uses
568 a special system feature. At least for files on a local disk, there is
569 no chance that some other program could create a file of the same name
570 before Emacs does, without Emacs's noticing.
572 If @var{visit} is @code{t}, then Emacs establishes an association
573 between the buffer and the file: the buffer is then visiting that file.
574 It also sets the last file modification time for the current buffer to
575 @var{filename}'s modtime, and marks the buffer as not modified. This
576 feature is used by @code{save-buffer}, but you probably should not use
580 If @var{visit} is a string, it specifies the file name to visit. This
581 way, you can write the data to one file (@var{filename}) while recording
582 the buffer as visiting another file (@var{visit}). The argument
583 @var{visit} is used in the echo area message and also for file locking;
584 @var{visit} is stored in @code{buffer-file-name}. This feature is used
585 to implement @code{file-precious-flag}; don't use it yourself unless you
586 really know what you're doing.
588 The optional argument @var{lockname}, if non-@code{nil}, specifies the
589 file name to use for purposes of locking and unlocking, overriding
590 @var{filename} and @var{visit} for that purpose.
592 The function @code{write-region} converts the data which it writes to
593 the appropriate file formats specified by @code{buffer-file-format}.
594 @xref{Format Conversion}. It also calls the functions in the list
595 @code{write-region-annotate-functions}; see @ref{Saving Properties}.
597 Normally, @code{write-region} displays the message @samp{Wrote
598 @var{filename}} in the echo area. If @var{visit} is neither @code{t}
599 nor @code{nil} nor a string, then this message is inhibited. This
600 feature is useful for programs that use files for internal purposes,
601 files that the user does not need to know about.
604 @defmac with-temp-file file body...
605 The @code{with-temp-file} macro evaluates the @var{body} forms with a
606 temporary buffer as the current buffer; then, at the end, it writes the
607 buffer contents into file @var{file}. It kills the temporary buffer
608 when finished, restoring the buffer that was current before the
609 @code{with-temp-file} form. Then it returns the value of the last form
612 The current buffer is restored even in case of an abnormal exit via
613 @code{throw} or error (@pxref{Nonlocal Exits}).
615 See also @code{with-temp-buffer} in @ref{Current Buffer}.
622 When two users edit the same file at the same time, they are likely to
623 interfere with each other. Emacs tries to prevent this situation from
624 arising by recording a @dfn{file lock} when a file is being modified.
625 Emacs can then detect the first attempt to modify a buffer visiting a
626 file that is locked by another Emacs job, and ask the user what to do.
627 The file lock is really a file, a symbolic link with a special name,
628 stored in the same directory as the file you are editing.
630 When you access files using NFS, there may be a small probability that
631 you and another user will both lock the same file ``simultaneously''.
632 If this happens, it is possible for the two users to make changes
633 simultaneously, but Emacs will still warn the user who saves second.
634 Also, the detection of modification of a buffer visiting a file changed
635 on disk catches some cases of simultaneous editing; see
636 @ref{Modification Time}.
638 @defun file-locked-p filename
639 This function returns @code{nil} if the file @var{filename} is not
640 locked. It returns @code{t} if it is locked by this Emacs process, and
641 it returns the name of the user who has locked it if it is locked by
646 (file-locked-p "foo")
652 @defun lock-buffer &optional filename
653 This function locks the file @var{filename}, if the current buffer is
654 modified. The argument @var{filename} defaults to the current buffer's
655 visited file. Nothing is done if the current buffer is not visiting a
656 file, or is not modified.
660 This function unlocks the file being visited in the current buffer,
661 if the buffer is modified. If the buffer is not modified, then
662 the file should not be locked, so this function does nothing. It also
663 does nothing if the current buffer is not visiting a file.
666 File locking is not supported on some systems. On systems that do not
667 support it, the functions @code{lock-buffer}, @code{unlock-buffer} and
668 @code{file-locked-p} do nothing and return @code{nil}.
670 @defun ask-user-about-lock file other-user
671 This function is called when the user tries to modify @var{file}, but it
672 is locked by another user named @var{other-user}. The default
673 definition of this function asks the user to say what to do. The value
674 this function returns determines what Emacs does next:
678 A value of @code{t} says to grab the lock on the file. Then
679 this user may edit the file and @var{other-user} loses the lock.
682 A value of @code{nil} says to ignore the lock and let this
683 user edit the file anyway.
687 This function may instead signal a @code{file-locked} error, in which
688 case the change that the user was about to make does not take place.
690 The error message for this error looks like this:
693 @error{} File is locked: @var{file} @var{other-user}
697 where @code{file} is the name of the file and @var{other-user} is the
698 name of the user who has locked the file.
701 If you wish, you can replace the @code{ask-user-about-lock} function
702 with your own version that makes the decision in another way. The code
703 for its usual definition is in @file{userlock.el}.
706 @node Information about Files
707 @section Information about Files
709 The functions described in this section all operate on strings that
710 designate file names. All the functions have names that begin with the
711 word @samp{file}. These functions all return information about actual
712 files or directories, so their arguments must all exist as actual files
713 or directories unless otherwise noted.
716 * Testing Accessibility:: Is a given file readable? Writable?
717 * Kinds of Files:: Is it a directory? A symbolic link?
718 * Truenames:: Eliminating symbolic links from a file name.
719 * File Attributes:: How large is it? Any other names? Etc.
722 @node Testing Accessibility
723 @comment node-name, next, previous, up
724 @subsection Testing Accessibility
725 @cindex accessibility of a file
726 @cindex file accessibility
728 These functions test for permission to access a file in specific ways.
730 @defun file-exists-p filename
731 This function returns @code{t} if a file named @var{filename} appears
732 to exist. This does not mean you can necessarily read the file, only
733 that you can find out its attributes. (On Unix and GNU/Linux, this is
734 true if the file exists and you have execute permission on the
735 containing directories, regardless of the protection of the file
738 If the file does not exist, or if fascist access control policies
739 prevent you from finding the attributes of the file, this function
742 Directories are files, so @code{file-exists-p} returns @code{t} when
743 given a directory name. However, symbolic links are treated
744 specially; @code{file-exists-p} returns @code{t} for a symbolic link
745 name only if the target file exists.
748 @defun file-readable-p filename
749 This function returns @code{t} if a file named @var{filename} exists
750 and you can read it. It returns @code{nil} otherwise.
754 (file-readable-p "files.texi")
758 (file-exists-p "/usr/spool/mqueue")
762 (file-readable-p "/usr/spool/mqueue")
769 @defun file-executable-p filename
770 This function returns @code{t} if a file named @var{filename} exists and
771 you can execute it. It returns @code{nil} otherwise. On Unix and
772 GNU/Linux, if the file is a directory, execute permission means you can
773 check the existence and attributes of files inside the directory, and
774 open those files if their modes permit.
777 @defun file-writable-p filename
778 This function returns @code{t} if the file @var{filename} can be written
779 or created by you, and @code{nil} otherwise. A file is writable if the
780 file exists and you can write it. It is creatable if it does not exist,
781 but the specified directory does exist and you can write in that
784 In the third example below, @file{foo} is not writable because the
785 parent directory does not exist, even though the user could create such
790 (file-writable-p "~/foo")
794 (file-writable-p "/foo")
798 (file-writable-p "~/no-such-dir/foo")
805 @defun file-accessible-directory-p dirname
806 This function returns @code{t} if you have permission to open existing
807 files in the directory whose name as a file is @var{dirname}; otherwise
808 (or if there is no such directory), it returns @code{nil}. The value
809 of @var{dirname} may be either a directory name or the file name of a
810 file which is a directory.
812 Example: after the following,
815 (file-accessible-directory-p "/foo")
820 we can deduce that any attempt to read a file in @file{/foo/} will
824 @defun access-file filename string
825 This function opens file @var{filename} for reading, then closes it and
826 returns @code{nil}. However, if the open fails, it signals an error
827 using @var{string} as the error message text.
830 @defun file-ownership-preserved-p filename
831 This function returns @code{t} if deleting the file @var{filename} and
832 then creating it anew would keep the file's owner unchanged.
835 @defun file-newer-than-file-p filename1 filename2
837 @cindex file modification time
838 This function returns @code{t} if the file @var{filename1} is
839 newer than file @var{filename2}. If @var{filename1} does not
840 exist, it returns @code{nil}. If @var{filename2} does not exist,
843 In the following example, assume that the file @file{aug-19} was written
844 on the 19th, @file{aug-20} was written on the 20th, and the file
845 @file{no-file} doesn't exist at all.
849 (file-newer-than-file-p "aug-19" "aug-20")
853 (file-newer-than-file-p "aug-20" "aug-19")
857 (file-newer-than-file-p "aug-19" "no-file")
861 (file-newer-than-file-p "no-file" "aug-19")
866 You can use @code{file-attributes} to get a file's last modification
867 time as a list of two numbers. @xref{File Attributes}.
871 @comment node-name, next, previous, up
872 @subsection Distinguishing Kinds of Files
874 This section describes how to distinguish various kinds of files, such
875 as directories, symbolic links, and ordinary files.
877 @defun file-symlink-p filename
878 @cindex file symbolic links
879 If the file @var{filename} is a symbolic link, the
880 @code{file-symlink-p} function returns the link target as a string.
881 (Determining the file name that the link points to from the target is
884 If the file @var{filename} is not a symbolic link (or there is no such file),
885 @code{file-symlink-p} returns @code{nil}.
889 (file-symlink-p "foo")
893 (file-symlink-p "sym-link")
897 (file-symlink-p "sym-link2")
901 (file-symlink-p "/bin")
906 @c !!! file-symlink-p: should show output of ls -l for comparison
909 @defun file-directory-p filename
910 This function returns @code{t} if @var{filename} is the name of an
911 existing directory, @code{nil} otherwise.
915 (file-directory-p "~rms")
919 (file-directory-p "~rms/lewis/files.texi")
923 (file-directory-p "~rms/lewis/no-such-file")
927 (file-directory-p "$HOME")
932 (substitute-in-file-name "$HOME"))
938 @defun file-regular-p filename
939 This function returns @code{t} if the file @var{filename} exists and is
940 a regular file (not a directory, named pipe, terminal, or
945 @subsection Truenames
946 @cindex truename (of file)
949 The @dfn{truename} of a file is the name that you get by following
950 symbolic links at all levels until none remain, then simplifying away
951 @samp{.}@: and @samp{..}@: appearing as name components. This results
952 in a sort of canonical name for the file. A file does not always have a
953 unique truename; the number of distinct truenames a file has is equal to
954 the number of hard links to the file. However, truenames are useful
955 because they eliminate symbolic links as a cause of name variation.
957 @defun file-truename filename
958 The function @code{file-truename} returns the truename of the file
959 @var{filename}. The argument must be an absolute file name.
962 @defun file-chase-links filename &optional limit
963 This function follows symbolic links, starting with @var{filename},
964 until it finds a file name which is not the name of a symbolic link.
965 Then it returns that file name. If you specify a number for
966 @var{limit}, then after chasing through that many links, the function
967 just returns what it as even if that is still a symbolic link.
970 To illustrate the difference between @code{file-chase-links} and
971 @code{file-truename}, suppose that @file{/usr/foo} is a symbolic link to
972 the directory @file{/home/foo}, and @file{/home/foo/hello} is an
973 ordinary file (or at least, not a symbolic link) or nonexistent. Then
977 (file-chase-links "/usr/foo/hello")
978 ;; @r{This does not follow the links in the parent directories.}
979 @result{} "/usr/foo/hello"
980 (file-truename "/usr/foo/hello")
981 ;; @r{Assuming that @file{/home} is not a symbolic link.}
982 @result{} "/home/foo/hello"
985 @xref{Buffer File Name}, for related information.
987 @node File Attributes
988 @comment node-name, next, previous, up
989 @subsection Other Information about Files
991 This section describes the functions for getting detailed information
992 about a file, other than its contents. This information includes the
993 mode bits that control access permission, the owner and group numbers,
994 the number of names, the inode number, the size, and the times of access
997 @defun file-modes filename
999 @cindex file attributes
1000 This function returns the mode bits of @var{filename}, as an integer.
1001 The mode bits are also called the file permissions, and they specify
1002 access control in the usual Unix fashion. If the low-order bit is 1,
1003 then the file is executable by all users, if the second-lowest-order bit
1004 is 1, then the file is writable by all users, etc.
1006 The highest value returnable is 4095 (7777 octal), meaning that
1007 everyone has read, write, and execute permission, that the @acronym{SUID} bit
1008 is set for both others and group, and that the sticky bit is set.
1012 (file-modes "~/junk/diffs")
1013 @result{} 492 ; @r{Decimal integer.}
1017 @result{} "754" ; @r{Convert to octal.}
1021 (set-file-modes "~/junk/diffs" 438)
1027 @result{} "666" ; @r{Convert to octal.}
1032 -rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs
1037 @defun file-nlinks filename
1038 This functions returns the number of names (i.e., hard links) that
1039 file @var{filename} has. If the file does not exist, then this function
1040 returns @code{nil}. Note that symbolic links have no effect on this
1041 function, because they are not considered to be names of the files they
1047 -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo
1048 -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo1
1056 (file-nlinks "doesnt-exist")
1062 @defun file-attributes filename &optional id-format
1063 This function returns a list of attributes of file @var{filename}. If
1064 the specified file cannot be opened, it returns @code{nil}.
1065 The optional parameter @var{id-format} specifies the preferred format
1066 of attributes @acronym{UID} and @acronym{GID} (see below)---the
1067 valid values are @code{'string} and @code{'integer}. The latter is
1068 the default, but we plan to change that, so you should specify a
1069 non-@code{nil} value for @var{id-format} if you use the returned
1070 @acronym{UID} or @acronym{GID}.
1072 The elements of the list, in order, are:
1076 @code{t} for a directory, a string for a symbolic link (the name
1077 linked to), or @code{nil} for a text file.
1079 @c Wordy so as to prevent an overfull hbox. --rjc 15mar92
1081 The number of names the file has. Alternate names, also known as hard
1082 links, can be created by using the @code{add-name-to-file} function
1083 (@pxref{Changing Files}).
1086 The file's @acronym{UID} as a string or an integer. If a string
1087 value cannot be looked up, the integer value is returned.
1090 The file's @acronym{GID} likewise.
1093 The time of last access, as a list of two integers.
1094 The first integer has the high-order 16 bits of time,
1095 the second has the low 16 bits. (This is similar to the
1096 value of @code{current-time}; see @ref{Time of Day}.)
1099 The time of last modification as a list of two integers (as above).
1102 The time of last status change as a list of two integers (as above).
1105 The size of the file in bytes. If the size is too large to fit in a
1106 Lisp integer, this is a floating point number.
1109 The file's modes, as a string of ten letters or dashes,
1113 @code{t} if the file's @acronym{GID} would change if file were
1114 deleted and recreated; @code{nil} otherwise.
1117 The file's inode number. If possible, this is an integer. If the inode
1118 number is too large to be represented as an integer in Emacs Lisp, then
1119 the value has the form @code{(@var{high} . @var{low})}, where @var{low}
1120 holds the low 16 bits.
1123 The file system number of the file system that the file is in.
1124 Depending on the magnitude of the value, this can be either an integer
1125 or a cons cell, in the same manner as the inode number. This element
1126 and the file's inode number together give enough information to
1127 distinguish any two files on the system---no two files can have the same
1128 values for both of these numbers.
1131 For example, here are the file attributes for @file{files.texi}:
1135 (file-attributes "files.texi" 'string)
1136 @result{} (nil 1 "lh" "users"
1146 and here is how the result is interpreted:
1150 is neither a directory nor a symbolic link.
1153 has only one name (the name @file{files.texi} in the current default
1157 is owned by the user with name "lh".
1160 is in the group with name "users".
1163 was last accessed on Aug 19 00:09.
1166 was last modified on Aug 19 00:09.
1169 last had its inode changed on Aug 19 00:09.
1172 is 14906 bytes long. (It may not contain 14906 characters, though,
1173 if some of the bytes belong to multibyte sequences.)
1176 has a mode of read and write access for the owner, group, and world.
1179 would retain the same @acronym{GID} if it were recreated.
1182 has an inode number of 129500.
1184 is on file system number -32252.
1188 @node Changing Files
1189 @section Changing File Names and Attributes
1190 @cindex renaming files
1191 @cindex copying files
1192 @cindex deleting files
1193 @cindex linking files
1194 @cindex setting modes of files
1196 The functions in this section rename, copy, delete, link, and set the
1199 In the functions that have an argument @var{newname}, if a file by the
1200 name of @var{newname} already exists, the actions taken depend on the
1201 value of the argument @var{ok-if-already-exists}:
1205 Signal a @code{file-already-exists} error if
1206 @var{ok-if-already-exists} is @code{nil}.
1209 Request confirmation if @var{ok-if-already-exists} is a number.
1212 Replace the old file without confirmation if @var{ok-if-already-exists}
1216 @defun add-name-to-file oldname newname &optional ok-if-already-exists
1217 @cindex file with multiple names
1218 @cindex file hard link
1219 This function gives the file named @var{oldname} the additional name
1220 @var{newname}. This means that @var{newname} becomes a new ``hard
1221 link'' to @var{oldname}.
1223 In the first part of the following example, we list two files,
1224 @file{foo} and @file{foo3}.
1229 81908 -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo
1230 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
1234 Now we create a hard link, by calling @code{add-name-to-file}, then list
1235 the files again. This shows two names for one file, @file{foo} and
1240 (add-name-to-file "foo" "foo2")
1246 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo
1247 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2
1248 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
1252 Finally, we evaluate the following:
1255 (add-name-to-file "foo" "foo3" t)
1259 and list the files again. Now there are three names
1260 for one file: @file{foo}, @file{foo2}, and @file{foo3}. The old
1261 contents of @file{foo3} are lost.
1265 (add-name-to-file "foo1" "foo3")
1271 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo
1272 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2
1273 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3
1277 This function is meaningless on operating systems where multiple names
1278 for one file are not allowed. Some systems implement multiple names
1279 by copying the file instead.
1281 See also @code{file-nlinks} in @ref{File Attributes}.
1284 @deffn Command rename-file filename newname &optional ok-if-already-exists
1285 This command renames the file @var{filename} as @var{newname}.
1287 If @var{filename} has additional names aside from @var{filename}, it
1288 continues to have those names. In fact, adding the name @var{newname}
1289 with @code{add-name-to-file} and then deleting @var{filename} has the
1290 same effect as renaming, aside from momentary intermediate states.
1292 In an interactive call, this function prompts for @var{filename} and
1293 @var{newname} in the minibuffer; also, it requests confirmation if
1294 @var{newname} already exists.
1297 @deffn Command copy-file oldname newname &optional ok-if-exists time
1298 This command copies the file @var{oldname} to @var{newname}. An
1299 error is signaled if @var{oldname} does not exist. If @var{newname}
1300 names a directory, it copies @var{oldname} into that directory,
1301 preserving its final name component.
1303 If @var{time} is non-@code{nil}, then this function gives the new file
1304 the same last-modified time that the old one has. (This works on only
1305 some operating systems.) If setting the time gets an error,
1306 @code{copy-file} signals a @code{file-date-error} error.
1308 This function copies the file modes, too.
1310 In an interactive call, this function prompts for @var{filename} and
1311 @var{newname} in the minibuffer; also, it requests confirmation if
1312 @var{newname} already exists.
1315 @deffn Command delete-file filename
1317 This command deletes the file @var{filename}, like the shell command
1318 @samp{rm @var{filename}}. If the file has multiple names, it continues
1319 to exist under the other names.
1321 A suitable kind of @code{file-error} error is signaled if the file does
1322 not exist, or is not deletable. (On Unix and GNU/Linux, a file is
1323 deletable if its directory is writable.)
1325 See also @code{delete-directory} in @ref{Create/Delete Dirs}.
1328 @deffn Command make-symbolic-link filename newname &optional ok-if-exists
1330 @kindex file-already-exists
1331 This command makes a symbolic link to @var{filename}, named
1332 @var{newname}. This is like the shell command @samp{ln -s
1333 @var{filename} @var{newname}}.
1335 In an interactive call, this function prompts for @var{filename} and
1336 @var{newname} in the minibuffer; also, it requests confirmation if
1337 @var{newname} already exists.
1339 This function is not available on systems that don't support symbolic
1343 @defun define-logical-name varname string
1344 This function defines the logical name @var{name} to have the value
1345 @var{string}. It is available only on VMS.
1348 @defun set-file-modes filename mode
1349 This function sets mode bits of @var{filename} to @var{mode} (which must
1350 be an integer). Only the low 12 bits of @var{mode} are used.
1354 @defun set-default-file-modes mode
1356 This function sets the default file protection for new files created by
1357 Emacs and its subprocesses. Every file created with Emacs initially has
1358 this protection, or a subset of it (@code{write-region} will not give a
1359 file execute permission even if the default file protection allows
1360 execute permission). On Unix and GNU/Linux, the default protection is
1361 the bitwise complement of the ``umask'' value.
1363 The argument @var{mode} must be an integer. On most systems, only the
1364 low 9 bits of @var{mode} are meaningful. You can use the Lisp construct
1365 for octal character codes to enter @var{mode}; for example,
1368 (set-default-file-modes ?\644)
1371 Saving a modified version of an existing file does not count as creating
1372 the file; it preserves the existing file's mode, whatever that is. So
1373 the default file protection has no effect.
1376 @defun default-file-modes
1377 This function returns the current default protection value.
1380 @cindex MS-DOS and file modes
1381 @cindex file modes and MS-DOS
1382 On MS-DOS, there is no such thing as an ``executable'' file mode bit.
1383 So Emacs considers a file executable if its name ends in one of the
1384 standard executable extensions, such as @file{.com}, @file{.bat},
1385 @file{.exe}, and some others. Files that begin with the Unix-standard
1386 @samp{#!} signature, such as shell and Perl scripts, are also considered
1387 as executable files. This is reflected in the values returned by
1388 @code{file-modes} and @code{file-attributes}. Directories are also
1389 reported with executable bit set, for compatibility with Unix.
1395 Files are generally referred to by their names, in Emacs as elsewhere.
1396 File names in Emacs are represented as strings. The functions that
1397 operate on a file all expect a file name argument.
1399 In addition to operating on files themselves, Emacs Lisp programs
1400 often need to operate on file names; i.e., to take them apart and to use
1401 part of a name to construct related file names. This section describes
1402 how to manipulate file names.
1404 The functions in this section do not actually access files, so they
1405 can operate on file names that do not refer to an existing file or
1408 On MS-DOS and MS-Windows, these functions (like the function that
1409 actually operate on files) accept MS-DOS or MS-Windows file-name syntax,
1410 where backslashes separate the components, as well as Unix syntax; but
1411 they always return Unix syntax. On VMS, these functions (and the ones
1412 that operate on files) understand both VMS file-name syntax and Unix
1413 syntax. This enables Lisp programs to specify file names in Unix syntax
1414 and work properly on all systems without change.
1417 * File Name Components:: The directory part of a file name, and the rest.
1418 * Relative File Names:: Some file names are relative to a current directory.
1419 * Directory Names:: A directory's name as a directory
1420 is different from its name as a file.
1421 * File Name Expansion:: Converting relative file names to absolute ones.
1422 * Unique File Names:: Generating names for temporary files.
1423 * File Name Completion:: Finding the completions for a given file name.
1424 * Standard File Names:: If your package uses a fixed file name,
1425 how to handle various operating systems simply.
1428 @node File Name Components
1429 @subsection File Name Components
1430 @cindex directory part (of file name)
1431 @cindex nondirectory part (of file name)
1432 @cindex version number (in file name)
1434 The operating system groups files into directories. To specify a
1435 file, you must specify the directory and the file's name within that
1436 directory. Therefore, Emacs considers a file name as having two main
1437 parts: the @dfn{directory name} part, and the @dfn{nondirectory} part
1438 (or @dfn{file name within the directory}). Either part may be empty.
1439 Concatenating these two parts reproduces the original file name.
1441 On most systems, the directory part is everything up to and including
1442 the last slash (backslash is also allowed in input on MS-DOS or
1443 MS-Windows); the nondirectory part is the rest. The rules in VMS syntax
1446 For some purposes, the nondirectory part is further subdivided into
1447 the name proper and the @dfn{version number}. On most systems, only
1448 backup files have version numbers in their names. On VMS, every file
1449 has a version number, but most of the time the file name actually used
1450 in Emacs omits the version number, so that version numbers in Emacs are
1451 found mostly in directory lists.
1453 @defun file-name-directory filename
1454 This function returns the directory part of @var{filename}, as a
1455 directory name (@pxref{Directory Names}), or @code{nil} if
1456 @var{filename} does not include a directory part.
1458 On GNU and Unix systems, a string returned by this function always
1459 ends in a slash. On MSDOS it can also end in a colon. On VMS, it
1460 returns a string ending in one of the three characters @samp{:},
1461 @samp{]}, or @samp{>}.
1465 (file-name-directory "lewis/foo") ; @r{Unix example}
1469 (file-name-directory "foo") ; @r{Unix example}
1473 (file-name-directory "[X]FOO.TMP") ; @r{VMS example}
1479 @defun file-name-nondirectory filename
1480 This function returns the nondirectory part of @var{filename}.
1484 (file-name-nondirectory "lewis/foo")
1488 (file-name-nondirectory "foo")
1492 (file-name-nondirectory "lewis/")
1496 ;; @r{The following example is accurate only on VMS.}
1497 (file-name-nondirectory "[X]FOO.TMP")
1503 @defun file-name-extension filename &optional period
1504 This function returns @var{filename}'s final ``extension,'' if any,
1505 after applying @code{file-name-sans-versions} to remove any
1506 version/backup part. It returns @code{nil} for extensionless file
1507 names such as @file{foo}. If @var{period} is non-@code{nil}, then the
1508 returned value includes the period that delimits the extension, and if
1509 @var{filename} has no extension, the value is @code{""}. If the last
1510 component of a file name begins with a @samp{.}, that @samp{.} doesn't
1511 count as the beginning of an extension, so, for example,
1512 @file{.emacs}'s ``extension'' is @code{nil}, not @samp{.emacs}.
1515 @defun file-name-sans-versions filename &optional keep-backup-version
1516 This function returns @var{filename} with any file version numbers,
1517 backup version numbers, or trailing tildes discarded.
1519 If @var{keep-backup-version} is non-@code{nil}, then true file version
1520 numbers understood as such by the file system are discarded from the
1521 return value, but backup version numbers are kept.
1525 (file-name-sans-versions "~rms/foo.~1~")
1526 @result{} "~rms/foo"
1529 (file-name-sans-versions "~rms/foo~")
1530 @result{} "~rms/foo"
1533 (file-name-sans-versions "~rms/foo")
1534 @result{} "~rms/foo"
1537 ;; @r{The following example applies to VMS only.}
1538 (file-name-sans-versions "foo;23")
1544 @defun file-name-sans-extension filename
1545 This function returns @var{filename} minus its ``extension,'' if any.
1546 The extension, in a file name, is the part that starts with the last
1547 @samp{.} in the last name component, except if that @samp{.} is the
1548 first character of the file name's last component. For example,
1551 (file-name-sans-extension "foo.lose.c")
1552 @result{} "foo.lose"
1553 (file-name-sans-extension "big.hack/foo")
1554 @result{} "big.hack/foo"
1555 (file-name-sans-extension "/my/home/.emacs")
1556 @result{} "/my/home/.emacs"
1557 (file-name-sans-extension "/my/home/.emacs.el")
1558 @result{} "/my/home/.emacs"
1563 Andrew Innes says that this
1565 @c @defvar directory-sep-char
1566 @c @tindex directory-sep-char
1567 This variable holds the character that Emacs normally uses to separate
1568 file name components. The default value is @code{?/}, but on MS-Windows
1569 you can set it to @code{?\\}; then the functions that transform file names
1570 use backslashes in their output.
1572 File names using backslashes work as input to Lisp primitives even on
1573 MS-DOS and MS-Windows, even if @code{directory-sep-char} has its default
1578 @node Relative File Names
1579 @subsection Absolute and Relative File Names
1580 @cindex absolute file name
1581 @cindex relative file name
1583 All the directories in the file system form a tree starting at the
1584 root directory. A file name can specify all the directory names
1585 starting from the root of the tree; then it is called an @dfn{absolute}
1586 file name. Or it can specify the position of the file in the tree
1587 relative to a default directory; then it is called a @dfn{relative} file
1588 name. On Unix and GNU/Linux, an absolute file name starts with a slash
1589 or a tilde (@samp{~}), and a relative one does not. On MS-DOS and
1590 MS-Windows, an absolute file name starts with a slash or a backslash, or
1591 with a drive specification @samp{@var{x}:/}, where @var{x} is the
1592 @dfn{drive letter}. The rules on VMS are complicated.
1594 @defun file-name-absolute-p filename
1595 This function returns @code{t} if file @var{filename} is an absolute
1596 file name, @code{nil} otherwise. On VMS, this function understands both
1597 Unix syntax and VMS syntax.
1601 (file-name-absolute-p "~rms/foo")
1605 (file-name-absolute-p "rms/foo")
1609 (file-name-absolute-p "/user/rms/foo")
1615 @node Directory Names
1616 @comment node-name, next, previous, up
1617 @subsection Directory Names
1618 @cindex directory name
1619 @cindex file name of directory
1621 A @dfn{directory name} is the name of a directory. A directory is
1622 actually a kind of file, so it has a file name, which is related to
1623 the directory name but not identical to it. (This is not quite the
1624 same as the usual Unix terminology.) These two different names for
1625 the same entity are related by a syntactic transformation. On GNU and
1626 Unix systems, this is simple: a directory name ends in a slash (or
1627 backslash), whereas the directory's name as a file lacks that slash.
1628 On MSDOS and VMS, the relationship is more complicated.
1630 The difference between a directory name and its name as a file is
1631 subtle but crucial. When an Emacs variable or function argument is
1632 described as being a directory name, a file name of a directory is not
1633 acceptable. When @code{file-name-directory} returns a string, that is
1634 always a directory name.
1636 The following two functions convert between directory names and file
1637 names. They do nothing special with environment variable substitutions
1638 such as @samp{$HOME}, and the constructs @samp{~}, and @samp{..}.
1640 @defun file-name-as-directory filename
1641 This function returns a string representing @var{filename} in a form
1642 that the operating system will interpret as the name of a directory. On
1643 most systems, this means appending a slash to the string (if it does not
1644 already end in one). On VMS, the function converts a string of the form
1645 @file{[X]Y.DIR.1} to the form @file{[X.Y]}.
1649 (file-name-as-directory "~rms/lewis")
1650 @result{} "~rms/lewis/"
1655 @defun directory-file-name dirname
1656 This function returns a string representing @var{dirname} in a form that
1657 the operating system will interpret as the name of a file. On most
1658 systems, this means removing the final slash (or backslash) from the
1659 string. On VMS, the function converts a string of the form @file{[X.Y]}
1660 to @file{[X]Y.DIR.1}.
1664 (directory-file-name "~lewis/")
1670 Given a directory name, you can combine it with a relative file name
1671 using @code{concat}:
1674 (concat @var{dirname} @var{relfile})
1678 Be sure to verify that the file name is relative before doing that.
1679 If you use an absolute file name, the results could be syntactically
1680 invalid or refer to the wrong file.
1682 If you want to use a directory file name in making such a
1683 combination, you must first convert it to a directory name using
1684 @code{file-name-as-directory}:
1687 (concat (file-name-as-directory @var{dirfile}) @var{relfile})
1691 Don't try concatenating a slash by hand, as in
1695 (concat @var{dirfile} "/" @var{relfile})
1699 because this is not portable. Always use
1700 @code{file-name-as-directory}.
1702 @cindex directory name abbreviation
1703 Directory name abbreviations are useful for directories that are
1704 normally accessed through symbolic links. Sometimes the users recognize
1705 primarily the link's name as ``the name'' of the directory, and find it
1706 annoying to see the directory's ``real'' name. If you define the link
1707 name as an abbreviation for the ``real'' name, Emacs shows users the
1708 abbreviation instead.
1710 @defvar directory-abbrev-alist
1711 The variable @code{directory-abbrev-alist} contains an alist of
1712 abbreviations to use for file directories. Each element has the form
1713 @code{(@var{from} . @var{to})}, and says to replace @var{from} with
1714 @var{to} when it appears in a directory name. The @var{from} string is
1715 actually a regular expression; it should always start with @samp{^}.
1716 The function @code{abbreviate-file-name} performs these substitutions.
1718 You can set this variable in @file{site-init.el} to describe the
1719 abbreviations appropriate for your site.
1721 Here's an example, from a system on which file system @file{/home/fsf}
1722 and so on are normally accessed through symbolic links named @file{/fsf}
1726 (("^/home/fsf" . "/fsf")
1727 ("^/home/gp" . "/gp")
1728 ("^/home/gd" . "/gd"))
1732 To convert a directory name to its abbreviation, use this
1735 @defun abbreviate-file-name filename
1736 This function applies abbreviations from @code{directory-abbrev-alist}
1737 to its argument, and substitutes @samp{~} for the user's home
1738 directory. You can use it for directory names and for file names,
1739 because it recognizes abbreviations even as part of the name.
1742 @node File Name Expansion
1743 @subsection Functions that Expand Filenames
1744 @cindex expansion of file names
1746 @dfn{Expansion} of a file name means converting a relative file name
1747 to an absolute one. Since this is done relative to a default directory,
1748 you must specify the default directory name as well as the file name to
1749 be expanded. Expansion also simplifies file names by eliminating
1750 redundancies such as @file{./} and @file{@var{name}/../}.
1752 @defun expand-file-name filename &optional directory
1753 This function converts @var{filename} to an absolute file name. If
1754 @var{directory} is supplied, it is the default directory to start with
1755 if @var{filename} is relative. (The value of @var{directory} should
1756 itself be an absolute directory name; it may start with @samp{~}.)
1757 Otherwise, the current buffer's value of @code{default-directory} is
1762 (expand-file-name "foo")
1763 @result{} "/xcssun/users/rms/lewis/foo"
1766 (expand-file-name "../foo")
1767 @result{} "/xcssun/users/rms/foo"
1770 (expand-file-name "foo" "/usr/spool/")
1771 @result{} "/usr/spool/foo"
1774 (expand-file-name "$HOME/foo")
1775 @result{} "/xcssun/users/rms/lewis/$HOME/foo"
1779 Filenames containing @samp{.} or @samp{..} are simplified to their
1784 (expand-file-name "bar/../foo")
1785 @result{} "/xcssun/users/rms/lewis/foo"
1789 Note that @code{expand-file-name} does @emph{not} expand environment
1790 variables; only @code{substitute-in-file-name} does that.
1794 @defun file-relative-name filename &optional directory
1795 This function does the inverse of expansion---it tries to return a
1796 relative name that is equivalent to @var{filename} when interpreted
1797 relative to @var{directory}. If @var{directory} is omitted or
1798 @code{nil}, it defaults to the current buffer's default directory.
1800 On some operating systems, an absolute file name begins with a device
1801 name. On such systems, @var{filename} has no relative equivalent based
1802 on @var{directory} if they start with two different device names. In
1803 this case, @code{file-relative-name} returns @var{filename} in absolute
1807 (file-relative-name "/foo/bar" "/foo/")
1809 (file-relative-name "/foo/bar" "/hack/")
1810 @result{} "../foo/bar"
1814 @defvar default-directory
1815 The value of this buffer-local variable is the default directory for the
1816 current buffer. It should be an absolute directory name; it may start
1817 with @samp{~}. This variable is buffer-local in every buffer.
1819 @code{expand-file-name} uses the default directory when its second
1820 argument is @code{nil}.
1822 Aside from VMS, the value is always a string ending with a slash.
1827 @result{} "/user/lewis/manual/"
1832 @defun substitute-in-file-name filename
1833 This function replaces environment variables references in
1834 @var{filename} with the environment variable values. Following
1835 standard Unix shell syntax, @samp{$} is the prefix to substitute an
1836 environment variable value. If the input contains @samp{$$}, that is
1837 converted to @samp{$}; this gives the user a way to ``quote'' a
1840 The environment variable name is the series of alphanumeric characters
1841 (including underscores) that follow the @samp{$}. If the character following
1842 the @samp{$} is a @samp{@{}, then the variable name is everything up to the
1845 Calling @code{substitute-in-file-name} on output produced by
1846 @code{substitute-in-file-name} tends to give incorrect results. For
1847 instance, use of @samp{$$} to quote a single @samp{$} won't work
1848 properly, and @samp{$} in an environment variable's value could lead
1849 to repeated substitution. Therefore, programs that call this function
1850 and put the output where it will be passed to this function need to
1851 double all @samp{$} characters to prevent subsequent incorrect
1854 @c Wordy to avoid overfull hbox. --rjc 15mar92
1855 Here we assume that the environment variable @code{HOME}, which holds
1856 the user's home directory name, has value @samp{/xcssun/users/rms}.
1860 (substitute-in-file-name "$HOME/foo")
1861 @result{} "/xcssun/users/rms/foo"
1865 After substitution, if a @samp{~} or a @samp{/} appears following a
1866 @samp{/}, everything before the following @samp{/} is discarded:
1870 (substitute-in-file-name "bar/~/foo")
1874 (substitute-in-file-name "/usr/local/$HOME/foo")
1875 @result{} "/xcssun/users/rms/foo"
1876 ;; @r{@file{/usr/local/} has been discarded.}
1880 On VMS, @samp{$} substitution is not done, so this function does nothing
1881 on VMS except discard superfluous initial components as shown above.
1884 @node Unique File Names
1885 @subsection Generating Unique File Names
1887 Some programs need to write temporary files. Here is the usual way to
1888 construct a name for such a file, starting in Emacs 21:
1891 (make-temp-file @var{name-of-application})
1895 The job of @code{make-temp-file} is to prevent two different users or
1896 two different jobs from trying to use the exact same file name.
1898 @defun make-temp-file prefix &optional dir-flag
1899 @tindex make-temp-file
1900 This function creates a temporary file and returns its name.
1901 The name starts with @var{prefix}; it also contains a number that is
1902 different in each Emacs job. If @var{prefix} is a relative file name,
1903 it is expanded against @code{temporary-file-directory}.
1907 (make-temp-file "foo")
1908 @result{} "/tmp/foo232J6v"
1912 When @code{make-temp-file} returns, the file has been created and is
1913 empty. At that point, you should write the intended contents into the
1916 If @var{dir-flag} is non-@code{nil}, @code{make-temp-file} creates
1917 an empty directory instead of an empty file.
1919 To prevent conflicts among different libraries running in the same
1920 Emacs, each Lisp program that uses @code{make-temp-file} should have its
1921 own @var{prefix}. The number added to the end of @var{prefix}
1922 distinguishes between the same application running in different Emacs
1923 jobs. Additional added characters permit a large number of distinct
1924 names even in one Emacs job.
1927 The default directory for temporary files is controlled by the
1928 variable @code{temporary-file-directory}. This variable gives the user
1929 a uniform way to specify the directory for all temporary files. Some
1930 programs use @code{small-temporary-file-directory} instead, if that is
1931 non-@code{nil}. To use it, you should expand the prefix against
1932 the proper directory before calling @code{make-temp-file}.
1934 In older Emacs versions where @code{make-temp-file} does not exist,
1935 you should use @code{make-temp-name} instead:
1939 (expand-file-name @var{name-of-application}
1940 temporary-file-directory))
1943 @defun make-temp-name string
1944 This function generates a string that can be used as a unique file name.
1945 The name starts with @var{string}, and contains a number that is
1946 different in each Emacs job. It is like @code{make-temp-file} except
1947 that it just constructs a name, and does not create a file. On MS-DOS,
1948 the @var{string} prefix can be truncated to fit into the 8+3 file-name
1952 @defvar temporary-file-directory
1953 @cindex @code{TMPDIR} environment variable
1954 @cindex @code{TMP} environment variable
1955 @cindex @code{TEMP} environment variable
1956 This variable specifies the directory name for creating temporary files.
1957 Its value should be a directory name (@pxref{Directory Names}), but it
1958 is good for Lisp programs to cope if the value is a directory's file
1959 name instead. Using the value as the second argument to
1960 @code{expand-file-name} is a good way to achieve that.
1962 The default value is determined in a reasonable way for your operating
1963 system; it is based on the @code{TMPDIR}, @code{TMP} and @code{TEMP}
1964 environment variables, with a fall-back to a system-dependent name if
1965 none of these variables is defined.
1967 Even if you do not use @code{make-temp-name} to choose the temporary
1968 file's name, you should still use this variable to decide which
1969 directory to put the file in. However, if you expect the file to be
1970 small, you should use @code{small-temporary-file-directory} first if
1971 that is non-@code{nil}.
1974 @tindex small-temporary-file-directory
1975 @defvar small-temporary-file-directory
1976 This variable (new in Emacs 21) specifies the directory name for
1977 creating certain temporary files, which are likely to be small.
1979 If you want to write a temporary file which is likely to be small, you
1980 should compute the directory like this:
1984 (expand-file-name @var{prefix}
1985 (or small-temporary-file-directory
1986 temporary-file-directory)))
1990 @node File Name Completion
1991 @subsection File Name Completion
1992 @cindex file name completion subroutines
1993 @cindex completion, file name
1995 This section describes low-level subroutines for completing a file
1996 name. For other completion functions, see @ref{Completion}.
1998 @defun file-name-all-completions partial-filename directory
1999 This function returns a list of all possible completions for a file
2000 whose name starts with @var{partial-filename} in directory
2001 @var{directory}. The order of the completions is the order of the files
2002 in the directory, which is unpredictable and conveys no useful
2005 The argument @var{partial-filename} must be a file name containing no
2006 directory part and no slash (or backslash on some systems). The current
2007 buffer's default directory is prepended to @var{directory}, if
2008 @var{directory} is not absolute.
2010 In the following example, suppose that @file{~rms/lewis} is the current
2011 default directory, and has five files whose names begin with @samp{f}:
2012 @file{foo}, @file{file~}, @file{file.c}, @file{file.c.~1~}, and
2013 @file{file.c.~2~}.@refill
2017 (file-name-all-completions "f" "")
2018 @result{} ("foo" "file~" "file.c.~2~"
2019 "file.c.~1~" "file.c")
2023 (file-name-all-completions "fo" "")
2029 @defun file-name-completion filename directory
2030 This function completes the file name @var{filename} in directory
2031 @var{directory}. It returns the longest prefix common to all file names
2032 in directory @var{directory} that start with @var{filename}.
2034 If only one match exists and @var{filename} matches it exactly, the
2035 function returns @code{t}. The function returns @code{nil} if directory
2036 @var{directory} contains no name starting with @var{filename}.
2038 In the following example, suppose that the current default directory
2039 has five files whose names begin with @samp{f}: @file{foo},
2040 @file{file~}, @file{file.c}, @file{file.c.~1~}, and
2041 @file{file.c.~2~}.@refill
2045 (file-name-completion "fi" "")
2050 (file-name-completion "file.c.~1" "")
2051 @result{} "file.c.~1~"
2055 (file-name-completion "file.c.~1~" "")
2060 (file-name-completion "file.c.~3" "")
2066 @defopt completion-ignored-extensions
2067 @code{file-name-completion} usually ignores file names that end in any
2068 string in this list. It does not ignore them when all the possible
2069 completions end in one of these suffixes or when a buffer showing all
2070 possible completions is displayed.@refill
2072 A typical value might look like this:
2076 completion-ignored-extensions
2077 @result{} (".o" ".elc" "~" ".dvi")
2081 If an element of @code{completion-ignored-extensions} ends in a slash
2082 @samp{/}, it signals a directory. The elements which do @emph{not} end
2083 in a slash will never match a directory; thus, the above value will not
2084 filter out a directory named @file{foo.elc}.
2087 @node Standard File Names
2088 @subsection Standard File Names
2090 Most of the file names used in Lisp programs are entered by the user.
2091 But occasionally a Lisp program needs to specify a standard file name
2092 for a particular use---typically, to hold customization information
2093 about each user. For example, abbrev definitions are stored (by
2094 default) in the file @file{~/.abbrev_defs}; the @code{completion}
2095 package stores completions in the file @file{~/.completions}. These are
2096 two of the many standard file names used by parts of Emacs for certain
2099 Various operating systems have their own conventions for valid file
2100 names and for which file names to use for user profile data. A Lisp
2101 program which reads a file using a standard file name ought to use, on
2102 each type of system, a file name suitable for that system. The function
2103 @code{convert-standard-filename} makes this easy to do.
2105 @defun convert-standard-filename filename
2106 This function alters the file name @var{filename} to fit the conventions
2107 of the operating system in use, and returns the result as a new string.
2110 The recommended way to specify a standard file name in a Lisp program
2111 is to choose a name which fits the conventions of GNU and Unix systems,
2112 usually with a nondirectory part that starts with a period, and pass it
2113 to @code{convert-standard-filename} instead of using it directly. Here
2114 is an example from the @code{completion} package:
2117 (defvar save-completions-file-name
2118 (convert-standard-filename "~/.completions")
2119 "*The file name to save completions to.")
2122 On GNU and Unix systems, and on some other systems as well,
2123 @code{convert-standard-filename} returns its argument unchanged. On
2124 some other systems, it alters the name to fit the system's conventions.
2126 For example, on MS-DOS the alterations made by this function include
2127 converting a leading @samp{.} to @samp{_}, converting a @samp{_} in the
2128 middle of the name to @samp{.} if there is no other @samp{.}, inserting
2129 a @samp{.} after eight characters if there is none, and truncating to
2130 three characters after the @samp{.}. (It makes other changes as well.)
2131 Thus, @file{.abbrev_defs} becomes @file{_abbrev.def}, and
2132 @file{.completions} becomes @file{_complet.ion}.
2134 @node Contents of Directories
2135 @section Contents of Directories
2136 @cindex directory-oriented functions
2137 @cindex file names in directory
2139 A directory is a kind of file that contains other files entered under
2140 various names. Directories are a feature of the file system.
2142 Emacs can list the names of the files in a directory as a Lisp list,
2143 or display the names in a buffer using the @code{ls} shell command. In
2144 the latter case, it can optionally display information about each file,
2145 depending on the options passed to the @code{ls} command.
2147 @defun directory-files directory &optional full-name match-regexp nosort
2148 This function returns a list of the names of the files in the directory
2149 @var{directory}. By default, the list is in alphabetical order.
2151 If @var{full-name} is non-@code{nil}, the function returns the files'
2152 absolute file names. Otherwise, it returns the names relative to
2153 the specified directory.
2155 If @var{match-regexp} is non-@code{nil}, this function returns only
2156 those file names that contain a match for that regular expression---the
2157 other file names are excluded from the list.
2160 If @var{nosort} is non-@code{nil}, @code{directory-files} does not sort
2161 the list, so you get the file names in no particular order. Use this if
2162 you want the utmost possible speed and don't care what order the files
2163 are processed in. If the order of processing is visible to the user,
2164 then the user will probably be happier if you do sort the names.
2168 (directory-files "~lewis")
2169 @result{} ("#foo#" "#foo.el#" "." ".."
2170 "dired-mods.el" "files.texi"
2175 An error is signaled if @var{directory} is not the name of a directory
2179 @defun directory-files-and-attributes directory &optional full-name match-regexp nosort
2180 This is similar to @code{directory-files} in deciding which files
2181 to report on and how to report their names. However, instead
2182 of returning a list of file names, it returns for each file a
2183 list @code{(@var{filename} . @var{attributes})}, where @var{attributes}
2184 is what @code{file-attributes} would return for that file.
2187 @defun file-name-all-versions file dirname
2188 This function returns a list of all versions of the file named
2189 @var{file} in directory @var{dirname}.
2192 @tindex file-expand-wildcards
2193 @defun file-expand-wildcards pattern &optional full
2194 This function expands the wildcard pattern @var{pattern}, returning
2195 a list of file names that match it.
2197 If @var{pattern} is written as an absolute file name,
2198 the values are absolute also.
2200 If @var{pattern} is written as a relative file name, it is interpreted
2201 relative to the current default directory. The file names returned are
2202 normally also relative to the current default directory. However, if
2203 @var{full} is non-@code{nil}, they are absolute.
2206 @defun insert-directory file switches &optional wildcard full-directory-p
2207 This function inserts (in the current buffer) a directory listing for
2208 directory @var{file}, formatted with @code{ls} according to
2209 @var{switches}. It leaves point after the inserted text.
2211 The argument @var{file} may be either a directory name or a file
2212 specification including wildcard characters. If @var{wildcard} is
2213 non-@code{nil}, that means treat @var{file} as a file specification with
2216 If @var{full-directory-p} is non-@code{nil}, that means the directory
2217 listing is expected to show the full contents of a directory. You
2218 should specify @code{t} when @var{file} is a directory and switches do
2219 not contain @samp{-d}. (The @samp{-d} option to @code{ls} says to
2220 describe a directory itself as a file, rather than showing its
2223 On most systems, this function works by running a directory listing
2224 program whose name is in the variable @code{insert-directory-program}.
2225 If @var{wildcard} is non-@code{nil}, it also runs the shell specified by
2226 @code{shell-file-name}, to expand the wildcards.
2228 MS-DOS and MS-Windows systems usually lack the standard Unix program
2229 @code{ls}, so this function emulates the standard Unix program @code{ls}
2233 @defvar insert-directory-program
2234 This variable's value is the program to run to generate a directory listing
2235 for the function @code{insert-directory}. It is ignored on systems
2236 which generate the listing with Lisp code.
2239 @node Create/Delete Dirs
2240 @section Creating and Deleting Directories
2241 @c Emacs 19 features
2243 Most Emacs Lisp file-manipulation functions get errors when used on
2244 files that are directories. For example, you cannot delete a directory
2245 with @code{delete-file}. These special functions exist to create and
2248 @defun make-directory dirname &optional parents
2249 This function creates a directory named @var{dirname}.
2250 If @var{parents} is non-@code{nil}, that means to create
2251 the parent directories first, if they don't already exist.
2254 @defun delete-directory dirname
2255 This function deletes the directory named @var{dirname}. The function
2256 @code{delete-file} does not work for files that are directories; you
2257 must use @code{delete-directory} for them. If the directory contains
2258 any files, @code{delete-directory} signals an error.
2261 @node Magic File Names
2262 @section Making Certain File Names ``Magic''
2263 @cindex magic file names
2266 You can implement special handling for certain file names. This is
2267 called making those names @dfn{magic}. The principal use for this
2268 feature is in implementing remote file names (@pxref{Remote Files,,
2269 Remote Files, emacs, The GNU Emacs Manual}).
2271 To define a kind of magic file name, you must supply a regular
2272 expression to define the class of names (all those that match the
2273 regular expression), plus a handler that implements all the primitive
2274 Emacs file operations for file names that do match.
2276 The variable @code{file-name-handler-alist} holds a list of handlers,
2277 together with regular expressions that determine when to apply each
2278 handler. Each element has this form:
2281 (@var{regexp} . @var{handler})
2285 All the Emacs primitives for file access and file name transformation
2286 check the given file name against @code{file-name-handler-alist}. If
2287 the file name matches @var{regexp}, the primitives handle that file by
2288 calling @var{handler}.
2290 The first argument given to @var{handler} is the name of the primitive;
2291 the remaining arguments are the arguments that were passed to that
2292 primitive. (The first of these arguments is most often the file name
2293 itself.) For example, if you do this:
2296 (file-exists-p @var{filename})
2300 and @var{filename} has handler @var{handler}, then @var{handler} is
2304 (funcall @var{handler} 'file-exists-p @var{filename})
2307 When a function takes two or more arguments that must be file names,
2308 it checks each of those names for a handler. For example, if you do
2312 (expand-file-name @var{filename} @var{dirname})
2316 then it checks for a handler for @var{filename} and then for a handler
2317 for @var{dirname}. In either case, the @var{handler} is called like
2321 (funcall @var{handler} 'expand-file-name @var{filename} @var{dirname})
2325 The @var{handler} then needs to figure out whether to handle
2326 @var{filename} or @var{dirname}.
2328 If the specified file name matches more than one handler, the one
2329 whose match starts last in the file name gets precedence. This rule
2330 is chosen so that handlers for jobs such as uncompression are handled
2331 first, before handlers for jobs such as remote file access.
2333 Here are the operations that a magic file name handler gets to handle:
2337 @code{access-file}, @code{add-name-to-file},
2338 @code{byte-compiler-base-file-name},@*
2339 @code{copy-file}, @code{delete-directory},
2341 @code{diff-latest-backup-file},
2342 @code{directory-file-name},
2343 @code{directory-files},
2344 @code{directory-files-and-attributes},
2345 @code{dired-call-process},
2346 @code{dired-compress-file}, @code{dired-uncache},@*
2347 @code{expand-file-name},
2348 @code{file-accessible-directory-p},
2349 @code{file-attributes},
2350 @code{file-directory-p},
2351 @code{file-executable-p}, @code{file-exists-p},
2352 @code{file-local-copy},
2353 @code{file-modes}, @code{file-name-all-completions},
2354 @code{file-name-as-directory},
2355 @code{file-name-completion},
2356 @code{file-name-directory},
2357 @code{file-name-nondirectory},
2358 @code{file-name-sans-versions}, @code{file-newer-than-file-p},
2359 @code{file-ownership-preserved-p},
2360 @code{file-readable-p}, @code{file-regular-p}, @code{file-symlink-p},
2361 @code{file-truename}, @code{file-writable-p},
2362 @code{find-backup-file-name},
2363 @code{find-file-noselect},@*
2364 @code{get-file-buffer},
2365 @code{insert-directory},
2366 @code{insert-file-contents},@*
2367 @code{load}, @code{make-directory},
2368 @code{make-directory-internal},
2369 @code{make-symbolic-link},@*
2370 @code{rename-file}, @code{set-file-modes},
2371 @code{set-visited-file-modtime}, @code{shell-command},
2372 @code{substitute-in-file-name},@*
2373 @code{unhandled-file-name-directory},
2374 @code{vc-registered},
2375 @code{verify-visited-file-modtime},@*
2376 @code{write-region}.
2381 @code{access-file}, @code{add-name-to-file},
2382 @code{byte-com@discretionary{}{}{}piler-base-file-name},
2383 @code{copy-file}, @code{delete-directory},
2385 @code{diff-latest-backup-file},
2386 @code{directory-file-name},
2387 @code{directory-files},
2388 @code{directory-files-and-at@discretionary{}{}{}tributes},
2389 @code{dired-call-process},
2390 @code{dired-compress-file}, @code{dired-uncache},
2391 @code{expand-file-name},
2392 @code{file-accessible-direc@discretionary{}{}{}tory-p},
2393 @code{file-attributes},
2394 @code{file-direct@discretionary{}{}{}ory-p},
2395 @code{file-executable-p}, @code{file-exists-p},
2396 @code{file-local-copy},
2397 @code{file-modes}, @code{file-name-all-completions},
2398 @code{file-name-as-directory},
2399 @code{file-name-completion},
2400 @code{file-name-directory},
2401 @code{file-name-nondirec@discretionary{}{}{}tory},
2402 @code{file-name-sans-versions}, @code{file-newer-than-file-p},
2403 @code{file-ownership-pre@discretionary{}{}{}served-p},
2404 @code{file-readable-p}, @code{file-regular-p}, @code{file-symlink-p},
2405 @code{file-truename}, @code{file-writable-p},
2406 @code{find-backup-file-name},
2407 @code{find-file-noselect},
2408 @code{get-file-buffer},
2409 @code{insert-directory},
2410 @code{insert-file-contents},
2411 @code{load}, @code{make-direc@discretionary{}{}{}tory},
2412 @code{make-direc@discretionary{}{}{}tory-internal},
2413 @code{make-symbolic-link},
2414 @code{rename-file}, @code{set-file-modes},
2415 @code{set-visited-file-modtime}, @code{shell-command},
2416 @code{substitute-in-file-name},
2417 @code{unhandled-file-name-directory},
2418 @code{vc-regis@discretionary{}{}{}tered},
2419 @code{verify-visited-file-modtime},
2420 @code{write-region}.
2424 Handlers for @code{insert-file-contents} typically need to clear the
2425 buffer's modified flag, with @code{(set-buffer-modified-p nil)}, if the
2426 @var{visit} argument is non-@code{nil}. This also has the effect of
2427 unlocking the buffer if it is locked.
2429 The handler function must handle all of the above operations, and
2430 possibly others to be added in the future. It need not implement all
2431 these operations itself---when it has nothing special to do for a
2432 certain operation, it can reinvoke the primitive, to handle the
2433 operation ``in the usual way''. It should always reinvoke the primitive
2434 for an operation it does not recognize. Here's one way to do this:
2437 (defun my-file-handler (operation &rest args)
2438 ;; @r{First check for the specific operations}
2439 ;; @r{that we have special handling for.}
2440 (cond ((eq operation 'insert-file-contents) @dots{})
2441 ((eq operation 'write-region) @dots{})
2443 ;; @r{Handle any operation we don't know about.}
2444 (t (let ((inhibit-file-name-handlers
2445 (cons 'my-file-handler
2446 (and (eq inhibit-file-name-operation operation)
2447 inhibit-file-name-handlers)))
2448 (inhibit-file-name-operation operation))
2449 (apply operation args)))))
2452 When a handler function decides to call the ordinary Emacs primitive for
2453 the operation at hand, it needs to prevent the primitive from calling
2454 the same handler once again, thus leading to an infinite recursion. The
2455 example above shows how to do this, with the variables
2456 @code{inhibit-file-name-handlers} and
2457 @code{inhibit-file-name-operation}. Be careful to use them exactly as
2458 shown above; the details are crucial for proper behavior in the case of
2459 multiple handlers, and for operations that have two file names that may
2462 @kindex safe-magic (@r{property})
2463 Handlers that don't really do anything special for actual access to the
2464 file---such as the ones that implement completion of host names for
2465 remote file names---should have a non-@code{nil} @code{safe-magic}
2466 property. For instance, Emacs normally ``protects'' directory names
2467 it finds in @code{PATH} from becoming magic, if they look like magic
2468 file names, by prefixing them with @samp{/:}. But if the handler that
2469 would be used for them has a non-@code{nil} @code{safe-magic}
2470 property, the @samp{/:} is not added.
2472 @defvar inhibit-file-name-handlers
2473 This variable holds a list of handlers whose use is presently inhibited
2474 for a certain operation.
2477 @defvar inhibit-file-name-operation
2478 The operation for which certain handlers are presently inhibited.
2481 @defun find-file-name-handler file operation
2482 This function returns the handler function for file name @var{file}, or
2483 @code{nil} if there is none. The argument @var{operation} should be the
2484 operation to be performed on the file---the value you will pass to the
2485 handler as its first argument when you call it. The operation is needed
2486 for comparison with @code{inhibit-file-name-operation}.
2489 @defun file-local-copy filename
2490 This function copies file @var{filename} to an ordinary non-magic file
2491 on the local machine, if it isn't on the local machine already. Magic
2492 file names should handle the @code{file-local-copy} operation if they
2493 refer to files on other machines. A magic file name that is used for
2494 other purposes than remote file access should not handle
2495 @code{file-local-copy}; then this function will treat the file as
2498 If @var{filename} is local, whether magic or not, this function does
2499 nothing and returns @code{nil}. Otherwise it returns the file name
2500 of the local copy file.
2503 @defun file-remote-p filename
2504 This functions return @code{t} if @var{filename} is a remote file---that is,
2505 a magic file name that handles @code{file-local-copy}.
2508 @defun unhandled-file-name-directory filename
2509 This function returns the name of a directory that is not magic. It
2510 uses the directory part of @var{filename} if that is not magic. For a
2511 magic file name, it invokes the file name handler, which therefore
2512 decides what value to return.
2514 This is useful for running a subprocess; every subprocess must have a
2515 non-magic directory to serve as its current directory, and this function
2516 is a good way to come up with one.
2519 @node Format Conversion
2520 @section File Format Conversion
2522 @cindex file format conversion
2523 @cindex encoding file formats
2524 @cindex decoding file formats
2525 The variable @code{format-alist} defines a list of @dfn{file formats},
2526 which describe textual representations used in files for the data (text,
2527 text-properties, and possibly other information) in an Emacs buffer.
2528 Emacs performs format conversion if appropriate when reading and writing
2531 @defvar format-alist
2532 This list contains one format definition for each defined file format.
2535 @cindex format definition
2536 Each format definition is a list of this form:
2539 (@var{name} @var{doc-string} @var{regexp} @var{from-fn} @var{to-fn} @var{modify} @var{mode-fn})
2542 Here is what the elements in a format definition mean:
2546 The name of this format.
2549 A documentation string for the format.
2552 A regular expression which is used to recognize files represented in
2556 A shell command or function to decode data in this format (to convert
2557 file data into the usual Emacs data representation).
2559 A shell command is represented as a string; Emacs runs the command as a
2560 filter to perform the conversion.
2562 If @var{from-fn} is a function, it is called with two arguments, @var{begin}
2563 and @var{end}, which specify the part of the buffer it should convert.
2564 It should convert the text by editing it in place. Since this can
2565 change the length of the text, @var{from-fn} should return the modified
2568 One responsibility of @var{from-fn} is to make sure that the beginning
2569 of the file no longer matches @var{regexp}. Otherwise it is likely to
2573 A shell command or function to encode data in this format---that is, to
2574 convert the usual Emacs data representation into this format.
2576 If @var{to-fn} is a string, it is a shell command; Emacs runs the
2577 command as a filter to perform the conversion.
2579 If @var{to-fn} is a function, it is called with two arguments, @var{begin}
2580 and @var{end}, which specify the part of the buffer it should convert.
2581 There are two ways it can do the conversion:
2585 By editing the buffer in place. In this case, @var{to-fn} should
2586 return the end-position of the range of text, as modified.
2589 By returning a list of annotations. This is a list of elements of the
2590 form @code{(@var{position} . @var{string})}, where @var{position} is an
2591 integer specifying the relative position in the text to be written, and
2592 @var{string} is the annotation to add there. The list must be sorted in
2593 order of position when @var{to-fn} returns it.
2595 When @code{write-region} actually writes the text from the buffer to the
2596 file, it intermixes the specified annotations at the corresponding
2597 positions. All this takes place without modifying the buffer.
2601 A flag, @code{t} if the encoding function modifies the buffer, and
2602 @code{nil} if it works by returning a list of annotations.
2605 A minor-mode function to call after visiting a file converted from this
2606 format. The function is called with one argument, the integer 1;
2607 that tells a minor-mode function to enable the mode.
2610 The function @code{insert-file-contents} automatically recognizes file
2611 formats when it reads the specified file. It checks the text of the
2612 beginning of the file against the regular expressions of the format
2613 definitions, and if it finds a match, it calls the decoding function for
2614 that format. Then it checks all the known formats over again.
2615 It keeps checking them until none of them is applicable.
2617 Visiting a file, with @code{find-file-noselect} or the commands that use
2618 it, performs conversion likewise (because it calls
2619 @code{insert-file-contents}); it also calls the mode function for each
2620 format that it decodes. It stores a list of the format names in the
2621 buffer-local variable @code{buffer-file-format}.
2623 @defvar buffer-file-format
2624 This variable states the format of the visited file. More precisely,
2625 this is a list of the file format names that were decoded in the course
2626 of visiting the current buffer's file. It is always buffer-local in all
2630 When @code{write-region} writes data into a file, it first calls the
2631 encoding functions for the formats listed in @code{buffer-file-format},
2632 in the order of appearance in the list.
2634 @deffn Command format-write-file file format
2635 This command writes the current buffer contents into the file @var{file}
2636 in format @var{format}, and makes that format the default for future
2637 saves of the buffer. The argument @var{format} is a list of format
2641 @deffn Command format-find-file file format
2642 This command finds the file @var{file}, converting it according to
2643 format @var{format}. It also makes @var{format} the default if the
2644 buffer is saved later.
2646 The argument @var{format} is a list of format names. If @var{format} is
2647 @code{nil}, no conversion takes place. Interactively, typing just
2648 @key{RET} for @var{format} specifies @code{nil}.
2651 @deffn Command format-insert-file file format &optional beg end
2652 This command inserts the contents of file @var{file}, converting it
2653 according to format @var{format}. If @var{beg} and @var{end} are
2654 non-@code{nil}, they specify which part of the file to read, as in
2655 @code{insert-file-contents} (@pxref{Reading from Files}).
2657 The return value is like what @code{insert-file-contents} returns: a
2658 list of the absolute file name and the length of the data inserted
2661 The argument @var{format} is a list of format names. If @var{format} is
2662 @code{nil}, no conversion takes place. Interactively, typing just
2663 @key{RET} for @var{format} specifies @code{nil}.
2666 @defvar auto-save-file-format
2667 This variable specifies the format to use for auto-saving. Its value is
2668 a list of format names, just like the value of
2669 @code{buffer-file-format}; however, it is used instead of
2670 @code{buffer-file-format} for writing auto-save files. This variable is
2671 always buffer-local in all buffers.
2675 arch-tag: 141f74ce-6ae3-40dc-a6c4-ef83fc4ec35c