2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2011
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 Aside from some technical details, the body of the @code{find-file}
99 function is basically equivalent to:
102 (switch-to-buffer (find-file-noselect filename nil nil wildcards))
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
118 returns a buffer visiting the file @var{filename}. You may make the
119 buffer current or display it in a window if you wish, but this
120 function does not do so.
122 The function returns an existing buffer if there is one; otherwise it
123 creates a new buffer and reads the file into it. When
124 @code{find-file-noselect} uses an existing buffer, it first verifies
125 that the file has not changed since it was last visited or saved in
126 that buffer. If the file has changed, this function asks the user
127 whether to reread the changed file. If the user says @samp{yes}, any
128 edits previously made in the buffer are lost.
130 Reading the file involves decoding the file's contents (@pxref{Coding
131 Systems}), including end-of-line conversion, and format conversion
132 (@pxref{Format Conversion}). If @var{wildcards} is non-@code{nil},
133 then @code{find-file-noselect} expands wildcard characters in
134 @var{filename} and visits all the matching files.
136 This function displays warning or advisory messages in various peculiar
137 cases, unless the optional argument @var{nowarn} is non-@code{nil}. For
138 example, if it needs to create a buffer, and there is no file named
139 @var{filename}, it displays the message @samp{(New file)} in the echo
140 area, and leaves the buffer empty.
142 The @code{find-file-noselect} function normally calls
143 @code{after-find-file} after reading the file (@pxref{Subroutines of
144 Visiting}). That function sets the buffer major mode, parses local
145 variables, warns the user if there exists an auto-save file more recent
146 than the file just visited, and finishes by running the functions in
147 @code{find-file-hook}.
149 If the optional argument @var{rawfile} is non-@code{nil}, then
150 @code{after-find-file} is not called, and the
151 @code{find-file-not-found-functions} are not run in case of failure.
152 What's more, a non-@code{nil} @var{rawfile} value suppresses coding
153 system conversion and format conversion.
155 The @code{find-file-noselect} function usually returns the buffer that
156 is visiting the file @var{filename}. But, if wildcards are actually
157 used and expanded, it returns a list of buffers that are visiting the
162 (find-file-noselect "/etc/fstab")
163 @result{} #<buffer fstab>
168 @deffn Command find-file-other-window filename &optional wildcards
169 This command selects a buffer visiting the file @var{filename}, but
170 does so in a window other than the selected window. It may use another
171 existing window or split a window; see @ref{Displaying Buffers}.
173 When this command is called interactively, it prompts for
177 @deffn Command find-file-read-only filename &optional wildcards
178 This command selects a buffer visiting the file @var{filename}, like
179 @code{find-file}, but it marks the buffer as read-only. @xref{Read Only
180 Buffers}, for related functions and variables.
182 When this command is called interactively, it prompts for
186 @deffn Command view-file filename
187 This command visits @var{filename} using View mode, returning to the
188 previous buffer when you exit View mode. View mode is a minor mode that
189 provides commands to skim rapidly through the file, but does not let you
190 modify the text. Entering View mode runs the normal hook
191 @code{view-mode-hook}. @xref{Hooks}.
193 When @code{view-file} is called interactively, it prompts for
197 @defopt find-file-wildcards
198 If this variable is non-@code{nil}, then the various @code{find-file}
199 commands check for wildcard characters and visit all the files that
200 match them (when invoked interactively or when their @var{wildcards}
201 argument is non-@code{nil}). If this option is @code{nil}, then
202 the @code{find-file} commands ignore their @var{wildcards} argument
203 and never treat wildcard characters specially.
206 @defopt find-file-hook
207 The value of this variable is a list of functions to be called after a
208 file is visited. The file's local-variables specification (if any) will
209 have been processed before the hooks are run. The buffer visiting the
210 file is current when the hook functions are run.
212 This variable is a normal hook. @xref{Hooks}.
215 @defvar find-file-not-found-functions
216 The value of this variable is a list of functions to be called when
217 @code{find-file} or @code{find-file-noselect} is passed a nonexistent
218 file name. @code{find-file-noselect} calls these functions as soon as
219 it detects a nonexistent file. It calls them in the order of the list,
220 until one of them returns non-@code{nil}. @code{buffer-file-name} is
223 This is not a normal hook because the values of the functions are
224 used, and in many cases only some of the functions are called.
227 @node Subroutines of Visiting
228 @comment node-name, next, previous, up
229 @subsection Subroutines of Visiting
231 The @code{find-file-noselect} function uses two important subroutines
232 which are sometimes useful in user Lisp code: @code{create-file-buffer}
233 and @code{after-find-file}. This section explains how to use them.
235 @defun create-file-buffer filename
236 This function creates a suitably named buffer for visiting
237 @var{filename}, and returns it. It uses @var{filename} (sans directory)
238 as the name if that name is free; otherwise, it appends a string such as
239 @samp{<2>} to get an unused name. See also @ref{Creating Buffers}.
241 @strong{Please note:} @code{create-file-buffer} does @emph{not}
242 associate the new buffer with a file and does not select the buffer.
243 It also does not use the default major mode.
247 (create-file-buffer "foo")
248 @result{} #<buffer foo>
251 (create-file-buffer "foo")
252 @result{} #<buffer foo<2>>
255 (create-file-buffer "foo")
256 @result{} #<buffer foo<3>>
260 This function is used by @code{find-file-noselect}.
261 It uses @code{generate-new-buffer} (@pxref{Creating Buffers}).
264 @defun after-find-file &optional error warn noauto after-find-file-from-revert-buffer nomodes
265 This function sets the buffer major mode, and parses local variables
266 (@pxref{Auto Major Mode}). It is called by @code{find-file-noselect}
267 and by the default revert function (@pxref{Reverting}).
269 @cindex new file message
270 @cindex file open error
271 If reading the file got an error because the file does not exist, but
272 its directory does exist, the caller should pass a non-@code{nil} value
273 for @var{error}. In that case, @code{after-find-file} issues a warning:
274 @samp{(New file)}. For more serious errors, the caller should usually not
275 call @code{after-find-file}.
277 If @var{warn} is non-@code{nil}, then this function issues a warning
278 if an auto-save file exists and is more recent than the visited file.
280 If @var{noauto} is non-@code{nil}, that says not to enable or disable
281 Auto-Save mode. The mode remains enabled if it was enabled before.
283 If @var{after-find-file-from-revert-buffer} is non-@code{nil}, that
284 means this call was from @code{revert-buffer}. This has no direct
285 effect, but some mode functions and hook functions check the value
288 If @var{nomodes} is non-@code{nil}, that means don't alter the buffer's
289 major mode, don't process local variables specifications in the file,
290 and don't run @code{find-file-hook}. This feature is used by
291 @code{revert-buffer} in some cases.
293 The last thing @code{after-find-file} does is call all the functions
294 in the list @code{find-file-hook}.
298 @section Saving Buffers
299 @cindex saving buffers
301 When you edit a file in Emacs, you are actually working on a buffer
302 that is visiting that file---that is, the contents of the file are
303 copied into the buffer and the copy is what you edit. Changes to the
304 buffer do not change the file until you @dfn{save} the buffer, which
305 means copying the contents of the buffer into the file.
307 @deffn Command save-buffer &optional backup-option
308 This function saves the contents of the current buffer in its visited
309 file if the buffer has been modified since it was last visited or saved.
310 Otherwise it does nothing.
312 @code{save-buffer} is responsible for making backup files. Normally,
313 @var{backup-option} is @code{nil}, and @code{save-buffer} makes a backup
314 file only if this is the first save since visiting the file. Other
315 values for @var{backup-option} request the making of backup files in
320 With an argument of 4 or 64, reflecting 1 or 3 @kbd{C-u}'s, the
321 @code{save-buffer} function marks this version of the file to be
322 backed up when the buffer is next saved.
325 With an argument of 16 or 64, reflecting 2 or 3 @kbd{C-u}'s, the
326 @code{save-buffer} function unconditionally backs up the previous
327 version of the file before saving it.
330 With an argument of 0, unconditionally do @emph{not} make any backup file.
334 @deffn Command save-some-buffers &optional save-silently-p pred
335 @anchor{Definition of save-some-buffers}
336 This command saves some modified file-visiting buffers. Normally it
337 asks the user about each buffer. But if @var{save-silently-p} is
338 non-@code{nil}, it saves all the file-visiting buffers without querying
341 The optional @var{pred} argument controls which buffers to ask about
342 (or to save silently if @var{save-silently-p} is non-@code{nil}).
343 If it is @code{nil}, that means to ask only about file-visiting buffers.
344 If it is @code{t}, that means also offer to save certain other non-file
345 buffers---those that have a non-@code{nil} buffer-local value of
346 @code{buffer-offer-save} (@pxref{Killing Buffers}). A user who says
347 @samp{yes} to saving a non-file buffer is asked to specify the file
348 name to use. The @code{save-buffers-kill-emacs} function passes the
349 value @code{t} for @var{pred}.
351 If @var{pred} is neither @code{t} nor @code{nil}, then it should be
352 a function of no arguments. It will be called in each buffer to decide
353 whether to offer to save that buffer. If it returns a non-@code{nil}
354 value in a certain buffer, that means do offer to save that buffer.
357 @deffn Command write-file filename &optional confirm
358 @anchor{Definition of write-file}
359 This function writes the current buffer into file @var{filename}, makes
360 the buffer visit that file, and marks it not modified. Then it renames
361 the buffer based on @var{filename}, appending a string like @samp{<2>}
362 if necessary to make a unique buffer name. It does most of this work by
363 calling @code{set-visited-file-name} (@pxref{Buffer File Name}) and
366 If @var{confirm} is non-@code{nil}, that means to ask for confirmation
367 before overwriting an existing file. Interactively, confirmation is
368 required, unless the user supplies a prefix argument.
370 If @var{filename} is an existing directory, or a symbolic link to one,
371 @code{write-file} uses the name of the visited file, in directory
372 @var{filename}. If the buffer is not visiting a file, it uses the
376 Saving a buffer runs several hooks. It also performs format
377 conversion (@pxref{Format Conversion}).
379 @defvar write-file-functions
380 The value of this variable is a list of functions to be called before
381 writing out a buffer to its visited file. If one of them returns
382 non-@code{nil}, the file is considered already written and the rest of
383 the functions are not called, nor is the usual code for writing the file
386 If a function in @code{write-file-functions} returns non-@code{nil}, it
387 is responsible for making a backup file (if that is appropriate).
388 To do so, execute the following code:
391 (or buffer-backed-up (backup-buffer))
394 You might wish to save the file modes value returned by
395 @code{backup-buffer} and use that (if non-@code{nil}) to set the mode
396 bits of the file that you write. This is what @code{save-buffer}
397 normally does. @xref{Making Backups,, Making Backup Files}.
399 The hook functions in @code{write-file-functions} are also responsible
400 for encoding the data (if desired): they must choose a suitable coding
401 system and end-of-line conversion (@pxref{Lisp and Coding Systems}),
402 perform the encoding (@pxref{Explicit Encoding}), and set
403 @code{last-coding-system-used} to the coding system that was used
404 (@pxref{Encoding and I/O}).
406 If you set this hook locally in a buffer, it is assumed to be
407 associated with the file or the way the contents of the buffer were
408 obtained. Thus the variable is marked as a permanent local, so that
409 changing the major mode does not alter a buffer-local value. On the
410 other hand, calling @code{set-visited-file-name} will reset it.
411 If this is not what you want, you might like to use
412 @code{write-contents-functions} instead.
414 Even though this is not a normal hook, you can use @code{add-hook} and
415 @code{remove-hook} to manipulate the list. @xref{Hooks}.
419 @defvar write-contents-functions
420 This works just like @code{write-file-functions}, but it is intended
421 for hooks that pertain to the buffer's contents, not to the particular
422 visited file or its location. Such hooks are usually set up by major
423 modes, as buffer-local bindings for this variable. This variable
424 automatically becomes buffer-local whenever it is set; switching to a
425 new major mode always resets this variable, but calling
426 @code{set-visited-file-name} does not.
428 If any of the functions in this hook returns non-@code{nil}, the file
429 is considered already written and the rest are not called and neither
430 are the functions in @code{write-file-functions}.
433 @defopt before-save-hook
434 This normal hook runs before a buffer is saved in its visited file,
435 regardless of whether that is done normally or by one of the hooks
436 described above. For instance, the @file{copyright.el} program uses
437 this hook to make sure the file you are saving has the current year in
438 its copyright notice.
442 @defopt after-save-hook
443 This normal hook runs after a buffer has been saved in its visited file.
444 One use of this hook is in Fast Lock mode; it uses this hook to save the
445 highlighting information in a cache file.
448 @defopt file-precious-flag
449 If this variable is non-@code{nil}, then @code{save-buffer} protects
450 against I/O errors while saving by writing the new file to a temporary
451 name instead of the name it is supposed to have, and then renaming it to
452 the intended name after it is clear there are no errors. This procedure
453 prevents problems such as a lack of disk space from resulting in an
456 As a side effect, backups are necessarily made by copying. @xref{Rename
457 or Copy}. Yet, at the same time, saving a precious file always breaks
458 all hard links between the file you save and other file names.
460 Some modes give this variable a non-@code{nil} buffer-local value
461 in particular buffers.
464 @defopt require-final-newline
465 This variable determines whether files may be written out that do
466 @emph{not} end with a newline. If the value of the variable is
467 @code{t}, then @code{save-buffer} silently adds a newline at the end of
468 the file whenever the buffer being saved does not already end in one.
469 If the value of the variable is non-@code{nil}, but not @code{t}, then
470 @code{save-buffer} asks the user whether to add a newline each time the
473 If the value of the variable is @code{nil}, then @code{save-buffer}
474 doesn't add newlines at all. @code{nil} is the default value, but a few
475 major modes set it to @code{t} in particular buffers.
478 See also the function @code{set-visited-file-name} (@pxref{Buffer File
481 @node Reading from Files
482 @comment node-name, next, previous, up
483 @section Reading from Files
484 @cindex reading from files
486 You can copy a file from the disk and insert it into a buffer
487 using the @code{insert-file-contents} function. Don't use the user-level
488 command @code{insert-file} in a Lisp program, as that sets the mark.
490 @defun insert-file-contents filename &optional visit beg end replace
491 This function inserts the contents of file @var{filename} into the
492 current buffer after point. It returns a list of the absolute file name
493 and the length of the data inserted. An error is signaled if
494 @var{filename} is not the name of a file that can be read.
496 The function @code{insert-file-contents} checks the file contents
497 against the defined file formats, and converts the file contents if
498 appropriate and also calls the functions in
499 the list @code{after-insert-file-functions}. @xref{Format Conversion}.
500 Normally, one of the functions in the
501 @code{after-insert-file-functions} list determines the coding system
502 (@pxref{Coding Systems}) used for decoding the file's contents,
503 including end-of-line conversion. However, if the file contains null
504 bytes, it is by default visited without any code conversions; see
505 @ref{Lisp and Coding Systems, inhibit-null-byte-detection}, for how to
506 control this behavior.
508 If @var{visit} is non-@code{nil}, this function additionally marks the
509 buffer as unmodified and sets up various fields in the buffer so that it
510 is visiting the file @var{filename}: these include the buffer's visited
511 file name and its last save file modtime. This feature is used by
512 @code{find-file-noselect} and you probably should not use it yourself.
514 If @var{beg} and @var{end} are non-@code{nil}, they should be integers
515 specifying the portion of the file to insert. In this case, @var{visit}
516 must be @code{nil}. For example,
519 (insert-file-contents filename nil 0 500)
523 inserts the first 500 characters of a file.
525 If the argument @var{replace} is non-@code{nil}, it means to replace the
526 contents of the buffer (actually, just the accessible portion) with the
527 contents of the file. This is better than simply deleting the buffer
528 contents and inserting the whole file, because (1) it preserves some
529 marker positions and (2) it puts less data in the undo list.
531 It is possible to read a special file (such as a FIFO or an I/O device)
532 with @code{insert-file-contents}, as long as @var{replace} and
533 @var{visit} are @code{nil}.
536 @defun insert-file-contents-literally filename &optional visit beg end replace
537 This function works like @code{insert-file-contents} except that it does
538 not do format decoding (@pxref{Format Conversion}), does not do
539 character code conversion (@pxref{Coding Systems}), does not run
540 @code{find-file-hook}, does not perform automatic uncompression, and so
544 If you want to pass a file name to another process so that another
545 program can read the file, use the function @code{file-local-copy}; see
546 @ref{Magic File Names}.
548 @node Writing to Files
549 @comment node-name, next, previous, up
550 @section Writing to Files
551 @cindex writing to files
553 You can write the contents of a buffer, or part of a buffer, directly
554 to a file on disk using the @code{append-to-file} and
555 @code{write-region} functions. Don't use these functions to write to
556 files that are being visited; that could cause confusion in the
557 mechanisms for visiting.
559 @deffn Command append-to-file start end filename
560 This function appends the contents of the region delimited by
561 @var{start} and @var{end} in the current buffer to the end of file
562 @var{filename}. If that file does not exist, it is created. This
563 function returns @code{nil}.
565 An error is signaled if @var{filename} specifies a nonwritable file,
566 or a nonexistent file in a directory where files cannot be created.
568 When called from Lisp, this function is completely equivalent to:
571 (write-region start end filename t)
575 @deffn Command write-region start end filename &optional append visit lockname mustbenew
576 This function writes the region delimited by @var{start} and @var{end}
577 in the current buffer into the file specified by @var{filename}.
579 If @var{start} is @code{nil}, then the command writes the entire buffer
580 contents (@emph{not} just the accessible portion) to the file and
584 If @var{start} is a string, then @code{write-region} writes or appends
585 that string, rather than text from the buffer. @var{end} is ignored in
588 If @var{append} is non-@code{nil}, then the specified text is appended
589 to the existing file contents (if any). If @var{append} is an
590 integer, @code{write-region} seeks to that byte offset from the start
591 of the file and writes the data from there.
593 If @var{mustbenew} is non-@code{nil}, then @code{write-region} asks
594 for confirmation if @var{filename} names an existing file. If
595 @var{mustbenew} is the symbol @code{excl}, then @code{write-region}
596 does not ask for confirmation, but instead it signals an error
597 @code{file-already-exists} if the file already exists.
599 The test for an existing file, when @var{mustbenew} is @code{excl}, uses
600 a special system feature. At least for files on a local disk, there is
601 no chance that some other program could create a file of the same name
602 before Emacs does, without Emacs's noticing.
604 If @var{visit} is @code{t}, then Emacs establishes an association
605 between the buffer and the file: the buffer is then visiting that file.
606 It also sets the last file modification time for the current buffer to
607 @var{filename}'s modtime, and marks the buffer as not modified. This
608 feature is used by @code{save-buffer}, but you probably should not use
612 If @var{visit} is a string, it specifies the file name to visit. This
613 way, you can write the data to one file (@var{filename}) while recording
614 the buffer as visiting another file (@var{visit}). The argument
615 @var{visit} is used in the echo area message and also for file locking;
616 @var{visit} is stored in @code{buffer-file-name}. This feature is used
617 to implement @code{file-precious-flag}; don't use it yourself unless you
618 really know what you're doing.
620 The optional argument @var{lockname}, if non-@code{nil}, specifies the
621 file name to use for purposes of locking and unlocking, overriding
622 @var{filename} and @var{visit} for that purpose.
624 The function @code{write-region} converts the data which it writes to
625 the appropriate file formats specified by @code{buffer-file-format}
626 and also calls the functions in the list
627 @code{write-region-annotate-functions}.
628 @xref{Format Conversion}.
630 Normally, @code{write-region} displays the message @samp{Wrote
631 @var{filename}} in the echo area. If @var{visit} is neither @code{t}
632 nor @code{nil} nor a string, then this message is inhibited. This
633 feature is useful for programs that use files for internal purposes,
634 files that the user does not need to know about.
637 @defmac with-temp-file file body@dots{}
638 @anchor{Definition of with-temp-file}
639 The @code{with-temp-file} macro evaluates the @var{body} forms with a
640 temporary buffer as the current buffer; then, at the end, it writes the
641 buffer contents into file @var{file}. It kills the temporary buffer
642 when finished, restoring the buffer that was current before the
643 @code{with-temp-file} form. Then it returns the value of the last form
646 The current buffer is restored even in case of an abnormal exit via
647 @code{throw} or error (@pxref{Nonlocal Exits}).
649 See also @code{with-temp-buffer} in @ref{Definition of
650 with-temp-buffer,, The Current Buffer}.
658 When two users edit the same file at the same time, they are likely
659 to interfere with each other. Emacs tries to prevent this situation
660 from arising by recording a @dfn{file lock} when a file is being
661 modified. (File locks are not implemented on Microsoft systems.)
662 Emacs can then detect the first attempt to modify a buffer visiting a
663 file that is locked by another Emacs job, and ask the user what to do.
664 The file lock is really a file, a symbolic link with a special name,
665 stored in the same directory as the file you are editing.
667 When you access files using NFS, there may be a small probability that
668 you and another user will both lock the same file ``simultaneously.''
669 If this happens, it is possible for the two users to make changes
670 simultaneously, but Emacs will still warn the user who saves second.
671 Also, the detection of modification of a buffer visiting a file changed
672 on disk catches some cases of simultaneous editing; see
673 @ref{Modification Time}.
675 @defun file-locked-p filename
676 This function returns @code{nil} if the file @var{filename} is not
677 locked. It returns @code{t} if it is locked by this Emacs process, and
678 it returns the name of the user who has locked it if it is locked by
683 (file-locked-p "foo")
689 @defun lock-buffer &optional filename
690 This function locks the file @var{filename}, if the current buffer is
691 modified. The argument @var{filename} defaults to the current buffer's
692 visited file. Nothing is done if the current buffer is not visiting a
693 file, or is not modified, or if the system does not support locking.
697 This function unlocks the file being visited in the current buffer,
698 if the buffer is modified. If the buffer is not modified, then
699 the file should not be locked, so this function does nothing. It also
700 does nothing if the current buffer is not visiting a file, or if the
701 system does not support locking.
704 File locking is not supported on some systems. On systems that do not
705 support it, the functions @code{lock-buffer}, @code{unlock-buffer} and
706 @code{file-locked-p} do nothing and return @code{nil}.
708 @defun ask-user-about-lock file other-user
709 This function is called when the user tries to modify @var{file}, but it
710 is locked by another user named @var{other-user}. The default
711 definition of this function asks the user to say what to do. The value
712 this function returns determines what Emacs does next:
716 A value of @code{t} says to grab the lock on the file. Then
717 this user may edit the file and @var{other-user} loses the lock.
720 A value of @code{nil} says to ignore the lock and let this
721 user edit the file anyway.
725 This function may instead signal a @code{file-locked} error, in which
726 case the change that the user was about to make does not take place.
728 The error message for this error looks like this:
731 @error{} File is locked: @var{file} @var{other-user}
735 where @code{file} is the name of the file and @var{other-user} is the
736 name of the user who has locked the file.
739 If you wish, you can replace the @code{ask-user-about-lock} function
740 with your own version that makes the decision in another way. The code
741 for its usual definition is in @file{userlock.el}.
744 @node Information about Files
745 @section Information about Files
746 @cindex file, information about
748 The functions described in this section all operate on strings that
749 designate file names. With a few exceptions, all the functions have
750 names that begin with the word @samp{file}. These functions all
751 return information about actual files or directories, so their
752 arguments must all exist as actual files or directories unless
756 * Testing Accessibility:: Is a given file readable? Writable?
757 * Kinds of Files:: Is it a directory? A symbolic link?
758 * Truenames:: Eliminating symbolic links from a file name.
759 * File Attributes:: How large is it? Any other names? Etc.
760 * Locating Files:: How to find a file in standard places.
763 @node Testing Accessibility
764 @comment node-name, next, previous, up
765 @subsection Testing Accessibility
766 @cindex accessibility of a file
767 @cindex file accessibility
769 These functions test for permission to access a file in specific
770 ways. Unless explicitly stated otherwise, they recursively follow
771 symbolic links for their file name arguments, at all levels (at the
772 level of the file itself and at all levels of parent directories).
774 @defun file-exists-p filename
775 This function returns @code{t} if a file named @var{filename} appears
776 to exist. This does not mean you can necessarily read the file, only
777 that you can find out its attributes. (On Unix and GNU/Linux, this is
778 true if the file exists and you have execute permission on the
779 containing directories, regardless of the protection of the file
782 If the file does not exist, or if fascist access control policies
783 prevent you from finding the attributes of the file, this function
786 Directories are files, so @code{file-exists-p} returns @code{t} when
787 given a directory name. However, symbolic links are treated
788 specially; @code{file-exists-p} returns @code{t} for a symbolic link
789 name only if the target file exists.
792 @defun file-readable-p filename
793 This function returns @code{t} if a file named @var{filename} exists
794 and you can read it. It returns @code{nil} otherwise.
798 (file-readable-p "files.texi")
802 (file-exists-p "/usr/spool/mqueue")
806 (file-readable-p "/usr/spool/mqueue")
813 @defun file-executable-p filename
814 This function returns @code{t} if a file named @var{filename} exists and
815 you can execute it. It returns @code{nil} otherwise. On Unix and
816 GNU/Linux, if the file is a directory, execute permission means you can
817 check the existence and attributes of files inside the directory, and
818 open those files if their modes permit.
821 @defun file-writable-p filename
822 This function returns @code{t} if the file @var{filename} can be written
823 or created by you, and @code{nil} otherwise. A file is writable if the
824 file exists and you can write it. It is creatable if it does not exist,
825 but the specified directory does exist and you can write in that
828 In the third example below, @file{foo} is not writable because the
829 parent directory does not exist, even though the user could create such
834 (file-writable-p "~/foo")
838 (file-writable-p "/foo")
842 (file-writable-p "~/no-such-dir/foo")
849 @defun file-accessible-directory-p dirname
850 This function returns @code{t} if you have permission to open existing
851 files in the directory whose name as a file is @var{dirname};
852 otherwise (or if there is no such directory), it returns @code{nil}.
853 The value of @var{dirname} may be either a directory name (such as
854 @file{/foo/}) or the file name of a file which is a directory
855 (such as @file{/foo}, without the final slash).
857 Example: after the following,
860 (file-accessible-directory-p "/foo")
865 we can deduce that any attempt to read a file in @file{/foo/} will
869 @defun access-file filename string
870 This function opens file @var{filename} for reading, then closes it and
871 returns @code{nil}. However, if the open fails, it signals an error
872 using @var{string} as the error message text.
875 @defun file-ownership-preserved-p filename
876 This function returns @code{t} if deleting the file @var{filename} and
877 then creating it anew would keep the file's owner unchanged. It also
878 returns @code{t} for nonexistent files.
880 If @var{filename} is a symbolic link, then, unlike the other functions
881 discussed here, @code{file-ownership-preserved-p} does @emph{not}
882 replace @var{filename} with its target. However, it does recursively
883 follow symbolic links at all levels of parent directories.
886 @defun file-newer-than-file-p filename1 filename2
888 @cindex file modification time
889 This function returns @code{t} if the file @var{filename1} is
890 newer than file @var{filename2}. If @var{filename1} does not
891 exist, it returns @code{nil}. If @var{filename1} does exist, but
892 @var{filename2} does not, it returns @code{t}.
894 In the following example, assume that the file @file{aug-19} was written
895 on the 19th, @file{aug-20} was written on the 20th, and the file
896 @file{no-file} doesn't exist at all.
900 (file-newer-than-file-p "aug-19" "aug-20")
904 (file-newer-than-file-p "aug-20" "aug-19")
908 (file-newer-than-file-p "aug-19" "no-file")
912 (file-newer-than-file-p "no-file" "aug-19")
917 You can use @code{file-attributes} to get a file's last modification
918 time as a list of two numbers. @xref{File Attributes}.
922 @comment node-name, next, previous, up
923 @subsection Distinguishing Kinds of Files
925 This section describes how to distinguish various kinds of files, such
926 as directories, symbolic links, and ordinary files.
928 @defun file-symlink-p filename
929 @cindex file symbolic links
930 If the file @var{filename} is a symbolic link, the
931 @code{file-symlink-p} function returns the (non-recursive) link target
932 as a string. (Determining the file name that the link points to from
933 the target is nontrivial.) First, this function recursively follows
934 symbolic links at all levels of parent directories.
936 If the file @var{filename} is not a symbolic link (or there is no such file),
937 @code{file-symlink-p} returns @code{nil}.
941 (file-symlink-p "foo")
945 (file-symlink-p "sym-link")
949 (file-symlink-p "sym-link2")
953 (file-symlink-p "/bin")
958 @c !!! file-symlink-p: should show output of ls -l for comparison
961 The next two functions recursively follow symbolic links at
962 all levels for @var{filename}.
964 @defun file-directory-p filename
965 This function returns @code{t} if @var{filename} is the name of an
966 existing directory, @code{nil} otherwise.
970 (file-directory-p "~rms")
974 (file-directory-p "~rms/lewis/files.texi")
978 (file-directory-p "~rms/lewis/no-such-file")
982 (file-directory-p "$HOME")
987 (substitute-in-file-name "$HOME"))
993 @defun file-regular-p filename
994 This function returns @code{t} if the file @var{filename} exists and is
995 a regular file (not a directory, named pipe, terminal, or
1000 @subsection Truenames
1001 @cindex truename (of file)
1003 @c Emacs 19 features
1004 The @dfn{truename} of a file is the name that you get by following
1005 symbolic links at all levels until none remain, then simplifying away
1006 @samp{.}@: and @samp{..}@: appearing as name components. This results
1007 in a sort of canonical name for the file. A file does not always have a
1008 unique truename; the number of distinct truenames a file has is equal to
1009 the number of hard links to the file. However, truenames are useful
1010 because they eliminate symbolic links as a cause of name variation.
1012 @defun file-truename filename
1013 The function @code{file-truename} returns the truename of the file
1014 @var{filename}. The argument must be an absolute file name.
1016 This function does not expand environment variables. Only
1017 @code{substitute-in-file-name} does that. @xref{Definition of
1018 substitute-in-file-name}.
1020 If you may need to follow symbolic links preceding @samp{..}@:
1021 appearing as a name component, you should make sure to call
1022 @code{file-truename} without prior direct or indirect calls to
1023 @code{expand-file-name}, as otherwise the file name component
1024 immediately preceding @samp{..} will be ``simplified away'' before
1025 @code{file-truename} is called. To eliminate the need for a call to
1026 @code{expand-file-name}, @code{file-truename} handles @samp{~} in the
1027 same way that @code{expand-file-name} does. @xref{File Name
1028 Expansion,, Functions that Expand Filenames}.
1031 @defun file-chase-links filename &optional limit
1032 This function follows symbolic links, starting with @var{filename},
1033 until it finds a file name which is not the name of a symbolic link.
1034 Then it returns that file name. This function does @emph{not} follow
1035 symbolic links at the level of parent directories.
1037 If you specify a number for @var{limit}, then after chasing through
1038 that many links, the function just returns what it has even if that is
1039 still a symbolic link.
1042 To illustrate the difference between @code{file-chase-links} and
1043 @code{file-truename}, suppose that @file{/usr/foo} is a symbolic link to
1044 the directory @file{/home/foo}, and @file{/home/foo/hello} is an
1045 ordinary file (or at least, not a symbolic link) or nonexistent. Then
1049 (file-chase-links "/usr/foo/hello")
1050 ;; @r{This does not follow the links in the parent directories.}
1051 @result{} "/usr/foo/hello"
1052 (file-truename "/usr/foo/hello")
1053 ;; @r{Assuming that @file{/home} is not a symbolic link.}
1054 @result{} "/home/foo/hello"
1057 @xref{Buffer File Name}, for related information.
1059 @node File Attributes
1060 @comment node-name, next, previous, up
1061 @subsection Other Information about Files
1063 This section describes the functions for getting detailed information
1064 about a file, other than its contents. This information includes the
1065 mode bits that control access permission, the owner and group numbers,
1066 the number of names, the inode number, the size, and the times of access
1069 @defun file-modes filename
1071 @cindex file attributes
1072 This function returns the mode bits of @var{filename}, as an integer.
1073 The mode bits are also called the file permissions, and they specify
1074 access control in the usual Unix fashion. If the low-order bit is 1,
1075 then the file is executable by all users, if the second-lowest-order bit
1076 is 1, then the file is writable by all users, etc.
1078 The highest value returnable is 4095 (7777 octal), meaning that
1079 everyone has read, write, and execute permission, that the @acronym{SUID} bit
1080 is set for both others and group, and that the sticky bit is set.
1082 If @var{filename} does not exist, @code{file-modes} returns @code{nil}.
1084 This function recursively follows symbolic links at all levels.
1088 (file-modes "~/junk/diffs")
1089 @result{} 492 ; @r{Decimal integer.}
1093 @result{} "754" ; @r{Convert to octal.}
1097 (set-file-modes "~/junk/diffs" 438)
1103 @result{} "666" ; @r{Convert to octal.}
1108 -rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs
1113 If the @var{filename} argument to the next two functions is a symbolic
1114 link, then these function do @emph{not} replace it with its target.
1115 However, they both recursively follow symbolic links at all levels of
1118 @defun file-nlinks filename
1119 This functions returns the number of names (i.e., hard links) that
1120 file @var{filename} has. If the file does not exist, then this function
1121 returns @code{nil}. Note that symbolic links have no effect on this
1122 function, because they are not considered to be names of the files they
1128 -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo
1129 -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo1
1137 (file-nlinks "doesnt-exist")
1143 @defun file-attributes filename &optional id-format
1144 @anchor{Definition of file-attributes}
1145 This function returns a list of attributes of file @var{filename}. If
1146 the specified file cannot be opened, it returns @code{nil}.
1147 The optional parameter @var{id-format} specifies the preferred format
1148 of attributes @acronym{UID} and @acronym{GID} (see below)---the
1149 valid values are @code{'string} and @code{'integer}. The latter is
1150 the default, but we plan to change that, so you should specify a
1151 non-@code{nil} value for @var{id-format} if you use the returned
1152 @acronym{UID} or @acronym{GID}.
1154 The elements of the list, in order, are:
1158 @code{t} for a directory, a string for a symbolic link (the name
1159 linked to), or @code{nil} for a text file.
1161 @c Wordy so as to prevent an overfull hbox. --rjc 15mar92
1163 The number of names the file has. Alternate names, also known as hard
1164 links, can be created by using the @code{add-name-to-file} function
1165 (@pxref{Changing Files}).
1168 The file's @acronym{UID}, normally as a string. However, if it does
1169 not correspond to a named user, the value is an integer or a floating
1173 The file's @acronym{GID}, likewise.
1176 The time of last access, as a list of two integers.
1177 The first integer has the high-order 16 bits of time,
1178 the second has the low 16 bits. (This is similar to the
1179 value of @code{current-time}; see @ref{Time of Day}.) Note that on
1180 some FAT-based filesystems, only the date of last access is recorded,
1181 so this time will always hold the midnight of the day of last access.
1183 @cindex modification time of file
1185 The time of last modification as a list of two integers (as above).
1186 This is the last time when the file's contents were modified.
1189 The time of last status change as a list of two integers (as above).
1190 This is the time of the last change to the file's access mode bits,
1191 its owner and group, and other information recorded in the filesystem
1192 for the file, beyond the file's contents.
1195 The size of the file in bytes. If the size is too large to fit in a
1196 Lisp integer, this is a floating point number.
1199 The file's modes, as a string of ten letters or dashes,
1203 @code{t} if the file's @acronym{GID} would change if file were
1204 deleted and recreated; @code{nil} otherwise.
1207 The file's inode number. If possible, this is an integer. If the
1208 inode number is too large to be represented as an integer in Emacs
1209 Lisp, but still fits into a 32-bit integer, then the value has the
1210 form @code{(@var{high} . @var{low})}, where @var{low} holds the low 16
1211 bits. If the inode is wider than 32 bits, the value is of the form
1212 @code{(@var{high} @var{middle} . @var{low})}, where @code{high} holds
1213 the high 24 bits, @var{middle} the next 24 bits, and @var{low} the low
1217 The filesystem number of the device that the file is on. Depending on
1218 the magnitude of the value, this can be either an integer or a cons
1219 cell, in the same manner as the inode number. This element and the
1220 file's inode number together give enough information to distinguish
1221 any two files on the system---no two files can have the same values
1222 for both of these numbers.
1225 For example, here are the file attributes for @file{files.texi}:
1229 (file-attributes "files.texi" 'string)
1230 @result{} (nil 1 "lh" "users"
1235 nil (5888 2 . 43978)
1241 and here is how the result is interpreted:
1245 is neither a directory nor a symbolic link.
1248 has only one name (the name @file{files.texi} in the current default
1252 is owned by the user with name "lh".
1255 is in the group with name "users".
1258 was last accessed on Oct 5 2009, at 10:01:37.
1261 last had its contents modified on Oct 2 2009, at 13:49:12.
1264 last had its status changed on Feb 2 2008, at 12:19:00.
1267 is 122295 bytes long. (It may not contain 122295 characters, though,
1268 if some of the bytes belong to multibyte sequences, and also if the
1269 end-of-line format is CR-LF.)
1272 has a mode of read and write access for the owner, group, and world.
1275 would retain the same @acronym{GID} if it were recreated.
1277 @item (5888 2 . 43978)
1278 has an inode number of 6473924464520138.
1280 @item (15479 . 46724)
1281 is on the file-system device whose number is 1014478468.
1285 @cindex MS-DOS and file modes
1286 @cindex file modes and MS-DOS
1287 On MS-DOS, there is no such thing as an ``executable'' file mode bit.
1288 So Emacs considers a file executable if its name ends in one of the
1289 standard executable extensions, such as @file{.com}, @file{.bat},
1290 @file{.exe}, and some others. Files that begin with the Unix-standard
1291 @samp{#!} signature, such as shell and Perl scripts, are also considered
1292 as executable files. This is reflected in the values returned by
1293 @code{file-modes} and @code{file-attributes}. Directories are also
1294 reported with executable bit set, for compatibility with Unix.
1296 @node Locating Files
1297 @subsection How to Locate Files in Standard Places
1298 @cindex locate file in path
1299 @cindex find file in path
1301 This section explains how to search for a file in a list of
1302 directories (a @dfn{path}). One example is when you need to look for
1303 a program's executable file, e.g., to find out whether a given program
1304 is installed on the user's system. Another example is the search for
1305 Lisp libraries (@pxref{Library Search}). Such searches generally need
1306 to try various possible file name extensions, in addition to various
1307 possible directories. Emacs provides a function for such a
1308 generalized search for a file.
1310 @defun locate-file filename path &optional suffixes predicate
1311 This function searches for a file whose name is @var{filename} in a
1312 list of directories given by @var{path}, trying the suffixes in
1313 @var{suffixes}. If it finds such a file, it returns the full
1314 @dfn{absolute file name} of the file (@pxref{Relative File Names});
1315 otherwise it returns @code{nil}.
1317 The optional argument @var{suffixes} gives the list of file-name
1318 suffixes to append to @var{filename} when searching.
1319 @code{locate-file} tries each possible directory with each of these
1320 suffixes. If @var{suffixes} is @code{nil}, or @code{("")}, then there
1321 are no suffixes, and @var{filename} is used only as-is. Typical
1322 values of @var{suffixes} are @code{exec-suffixes} (@pxref{Subprocess
1323 Creation, exec-suffixes}), @code{load-suffixes},
1324 @code{load-file-rep-suffixes} and the return value of the function
1325 @code{get-load-suffixes} (@pxref{Load Suffixes}).
1327 Typical values for @var{path} are @code{exec-path} (@pxref{Subprocess
1328 Creation, exec-path}) when looking for executable programs or
1329 @code{load-path} (@pxref{Library Search, load-path}) when looking for
1330 Lisp files. If @var{filename} is absolute, @var{path} has no effect,
1331 but the suffixes in @var{suffixes} are still tried.
1333 The optional argument @var{predicate}, if non-@code{nil}, specifies
1334 the predicate function to use for testing whether a candidate file is
1335 suitable. The predicate function is passed the candidate file name as
1336 its single argument. If @var{predicate} is @code{nil} or unspecified,
1337 @code{locate-file} uses @code{file-readable-p} as the default
1338 predicate. Useful non-default predicates include
1339 @code{file-executable-p}, @code{file-directory-p}, and other
1340 predicates described in @ref{Kinds of Files}.
1342 For compatibility, @var{predicate} can also be one of the symbols
1343 @code{executable}, @code{readable}, @code{writable}, @code{exists}, or
1344 a list of one or more of these symbols.
1347 @defun executable-find program
1348 This function searches for the executable file of the named
1349 @var{program} and returns the full absolute name of the executable,
1350 including its file-name extensions, if any. It returns @code{nil} if
1351 the file is not found. The functions searches in all the directories
1352 in @code{exec-path} and tries all the file-name extensions in
1353 @code{exec-suffixes}.
1356 @node Changing Files
1357 @section Changing File Names and Attributes
1358 @c @cindex renaming files Duplicates rename-file
1359 @cindex copying files
1360 @cindex deleting files
1361 @cindex linking files
1362 @cindex setting modes of files
1364 The functions in this section rename, copy, delete, link, and set the
1367 In the functions that have an argument @var{newname}, if a file by the
1368 name of @var{newname} already exists, the actions taken depend on the
1369 value of the argument @var{ok-if-already-exists}:
1373 Signal a @code{file-already-exists} error if
1374 @var{ok-if-already-exists} is @code{nil}.
1377 Request confirmation if @var{ok-if-already-exists} is a number.
1380 Replace the old file without confirmation if @var{ok-if-already-exists}
1384 The next four commands all recursively follow symbolic links at all
1385 levels of parent directories for their first argument, but, if that
1386 argument is itself a symbolic link, then only @code{copy-file}
1387 replaces it with its (recursive) target.
1389 @deffn Command add-name-to-file oldname newname &optional ok-if-already-exists
1390 @cindex file with multiple names
1391 @cindex file hard link
1392 This function gives the file named @var{oldname} the additional name
1393 @var{newname}. This means that @var{newname} becomes a new ``hard
1394 link'' to @var{oldname}.
1396 In the first part of the following example, we list two files,
1397 @file{foo} and @file{foo3}.
1402 81908 -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo
1403 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
1407 Now we create a hard link, by calling @code{add-name-to-file}, then list
1408 the files again. This shows two names for one file, @file{foo} and
1413 (add-name-to-file "foo" "foo2")
1419 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo
1420 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2
1421 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
1425 Finally, we evaluate the following:
1428 (add-name-to-file "foo" "foo3" t)
1432 and list the files again. Now there are three names
1433 for one file: @file{foo}, @file{foo2}, and @file{foo3}. The old
1434 contents of @file{foo3} are lost.
1438 (add-name-to-file "foo1" "foo3")
1444 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo
1445 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2
1446 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3
1450 This function is meaningless on operating systems where multiple names
1451 for one file are not allowed. Some systems implement multiple names
1452 by copying the file instead.
1454 See also @code{file-nlinks} in @ref{File Attributes}.
1457 @deffn Command rename-file filename newname &optional ok-if-already-exists
1458 This command renames the file @var{filename} as @var{newname}.
1460 If @var{filename} has additional names aside from @var{filename}, it
1461 continues to have those names. In fact, adding the name @var{newname}
1462 with @code{add-name-to-file} and then deleting @var{filename} has the
1463 same effect as renaming, aside from momentary intermediate states.
1466 @deffn Command copy-file oldname newname &optional ok-if-exists time preserve-uid-gid
1467 This command copies the file @var{oldname} to @var{newname}. An
1468 error is signaled if @var{oldname} does not exist. If @var{newname}
1469 names a directory, it copies @var{oldname} into that directory,
1470 preserving its final name component.
1472 If @var{time} is non-@code{nil}, then this function gives the new file
1473 the same last-modified time that the old one has. (This works on only
1474 some operating systems.) If setting the time gets an error,
1475 @code{copy-file} signals a @code{file-date-error} error. In an
1476 interactive call, a prefix argument specifies a non-@code{nil} value
1479 This function copies the file modes, too.
1481 If argument @var{preserve-uid-gid} is @code{nil}, we let the operating
1482 system decide the user and group ownership of the new file (this is
1483 usually set to the user running Emacs). If @var{preserve-uid-gid} is
1484 non-@code{nil}, we attempt to copy the user and group ownership of the
1485 file. This works only on some operating systems, and only if you have
1486 the correct permissions to do so.
1489 @deffn Command make-symbolic-link filename newname &optional ok-if-exists
1491 @kindex file-already-exists
1492 This command makes a symbolic link to @var{filename}, named
1493 @var{newname}. This is like the shell command @samp{ln -s
1494 @var{filename} @var{newname}}.
1496 This function is not available on systems that don't support symbolic
1500 @deffn Command delete-file filename
1502 This command deletes the file @var{filename}, like the shell command
1503 @samp{rm @var{filename}}. If the file has multiple names, it continues
1504 to exist under the other names.
1506 A suitable kind of @code{file-error} error is signaled if the file does
1507 not exist, or is not deletable. (On Unix and GNU/Linux, a file is
1508 deletable if its directory is writable.)
1510 If @var{filename} is a symbolic link, @code{delete-file} does not
1511 replace it with its target, but it does follow symbolic links at all
1512 levels of parent directories.
1514 See also @code{delete-directory} in @ref{Create/Delete Dirs}.
1517 @deffn Command set-file-modes filename mode
1518 This function sets mode bits of @var{filename} to @var{mode} (which
1519 must be an integer when the function is called non-interactively).
1520 Only the low 12 bits of @var{mode} are used.
1522 Interactively, @var{mode} is read from the minibuffer using
1523 @code{read-file-modes}, which accepts mode bits either as a number or
1524 as a character string representing the mode bits symbolically. See
1525 the description of @code{read-file-modes} below for the supported
1526 forms of symbolic notation for mode bits.
1528 This function recursively follows symbolic links at all levels for
1533 @defun set-default-file-modes mode
1535 This function sets the default file protection for new files created by
1536 Emacs and its subprocesses. Every file created with Emacs initially has
1537 this protection, or a subset of it (@code{write-region} will not give a
1538 file execute permission even if the default file protection allows
1539 execute permission). On Unix and GNU/Linux, the default protection is
1540 the bitwise complement of the ``umask'' value.
1542 The argument @var{mode} must be an integer. On most systems, only the
1543 low 9 bits of @var{mode} are meaningful. You can use the Lisp construct
1544 for octal character codes to enter @var{mode}; for example,
1547 (set-default-file-modes ?\644)
1550 Saving a modified version of an existing file does not count as creating
1551 the file; it preserves the existing file's mode, whatever that is. So
1552 the default file protection has no effect.
1555 @defun default-file-modes
1556 This function returns the current default protection value.
1559 @defun read-file-modes &optional prompt base-file
1560 This function reads file mode bits from the minibuffer. The optional
1561 argument @var{prompt} specifies a non-default prompt. Second optional
1562 argument @var{base-file} is the name of a file on whose permissions to
1563 base the mode bits that this function returns, if what the user types
1564 specifies mode bits relative to permissions of an existing file.
1566 If user input represents an octal number, this function returns that
1567 number. If it is a complete symbolic specification of mode bits, as
1568 in @code{"u=rwx"}, the function converts it to the equivalent numeric
1569 value using @code{file-modes-symbolic-to-number} and returns the
1570 result. If the specification is relative, as in @code{"o+g"}, then
1571 the permissions on which the specification is based are taken from the
1572 mode bits of @var{base-file}. If @var{base-file} is omitted or
1573 @code{nil}, the function uses @code{0} as the base mode bits. The
1574 complete and relative specifications can be combined, as in
1575 @code{"u+r,g+rx,o+r,g-w"}. @xref{File Permissions,,, coreutils, The
1576 @sc{gnu} @code{Coreutils} Manual}, for detailed description of
1577 symbolic mode bits specifications.
1580 @defun file-modes-symbolic-to-number modes &optional base-modes
1581 This subroutine converts a symbolic specification of file mode bits in
1582 @var{modes} into the equivalent numeric value. If the symbolic
1583 specification is based on an existing file, that file's mode bits are
1584 taken from the optional argument @var{base-modes}; if that argument is
1585 omitted or @code{nil}, it defaults to zero, i.e.@: no access rights at
1589 @defun set-file-times filename &optional time
1590 This function sets the access and modification times of @var{filename}
1591 to @var{time}. The return value is @code{t} if the times are successfully
1592 set, otherwise it is @code{nil}. @var{time} defaults to the current
1593 time and must be in the format returned by @code{current-time}
1594 (@pxref{Time of Day}).
1601 Files are generally referred to by their names, in Emacs as elsewhere.
1602 File names in Emacs are represented as strings. The functions that
1603 operate on a file all expect a file name argument.
1605 In addition to operating on files themselves, Emacs Lisp programs
1606 often need to operate on file names; i.e., to take them apart and to use
1607 part of a name to construct related file names. This section describes
1608 how to manipulate file names.
1610 The functions in this section do not actually access files, so they
1611 can operate on file names that do not refer to an existing file or
1614 On MS-DOS and MS-Windows, these functions (like the function that
1615 actually operate on files) accept MS-DOS or MS-Windows file-name syntax,
1616 where backslashes separate the components, as well as Unix syntax; but
1617 they always return Unix syntax. This enables Lisp programs to specify
1618 file names in Unix syntax and work properly on all systems without
1622 * File Name Components:: The directory part of a file name, and the rest.
1623 * Relative File Names:: Some file names are relative to a current directory.
1624 * Directory Names:: A directory's name as a directory
1625 is different from its name as a file.
1626 * File Name Expansion:: Converting relative file names to absolute ones.
1627 * Unique File Names:: Generating names for temporary files.
1628 * File Name Completion:: Finding the completions for a given file name.
1629 * Standard File Names:: If your package uses a fixed file name,
1630 how to handle various operating systems simply.
1633 @node File Name Components
1634 @subsection File Name Components
1635 @cindex directory part (of file name)
1636 @cindex nondirectory part (of file name)
1637 @cindex version number (in file name)
1639 The operating system groups files into directories. To specify a
1640 file, you must specify the directory and the file's name within that
1641 directory. Therefore, Emacs considers a file name as having two main
1642 parts: the @dfn{directory name} part, and the @dfn{nondirectory} part
1643 (or @dfn{file name within the directory}). Either part may be empty.
1644 Concatenating these two parts reproduces the original file name.
1646 On most systems, the directory part is everything up to and including
1647 the last slash (backslash is also allowed in input on MS-DOS or
1648 MS-Windows); the nondirectory part is the rest.
1650 For some purposes, the nondirectory part is further subdivided into
1651 the name proper and the @dfn{version number}. On most systems, only
1652 backup files have version numbers in their names.
1654 @defun file-name-directory filename
1655 This function returns the directory part of @var{filename}, as a
1656 directory name (@pxref{Directory Names}), or @code{nil} if
1657 @var{filename} does not include a directory part.
1659 On GNU and Unix systems, a string returned by this function always
1660 ends in a slash. On MS-DOS it can also end in a colon.
1664 (file-name-directory "lewis/foo") ; @r{Unix example}
1668 (file-name-directory "foo") ; @r{Unix example}
1674 @defun file-name-nondirectory filename
1675 This function returns the nondirectory part of @var{filename}.
1679 (file-name-nondirectory "lewis/foo")
1683 (file-name-nondirectory "foo")
1687 (file-name-nondirectory "lewis/")
1693 @defun file-name-sans-versions filename &optional keep-backup-version
1694 This function returns @var{filename} with any file version numbers,
1695 backup version numbers, or trailing tildes discarded.
1697 If @var{keep-backup-version} is non-@code{nil}, then true file version
1698 numbers understood as such by the file system are discarded from the
1699 return value, but backup version numbers are kept.
1703 (file-name-sans-versions "~rms/foo.~1~")
1704 @result{} "~rms/foo"
1707 (file-name-sans-versions "~rms/foo~")
1708 @result{} "~rms/foo"
1711 (file-name-sans-versions "~rms/foo")
1712 @result{} "~rms/foo"
1717 @defun file-name-extension filename &optional period
1718 This function returns @var{filename}'s final ``extension,'' if any,
1719 after applying @code{file-name-sans-versions} to remove any
1720 version/backup part. The extension, in a file name, is the part that
1721 follows the last @samp{.} in the last name component (minus any
1722 version/backup part).
1724 This function returns @code{nil} for extensionless file names such as
1725 @file{foo}. It returns @code{""} for null extensions, as in
1726 @file{foo.}. If the last component of a file name begins with a
1727 @samp{.}, that @samp{.} doesn't count as the beginning of an
1728 extension. Thus, @file{.emacs}'s ``extension'' is @code{nil}, not
1731 If @var{period} is non-@code{nil}, then the returned value includes
1732 the period that delimits the extension, and if @var{filename} has no
1733 extension, the value is @code{""}.
1736 @defun file-name-sans-extension filename
1737 This function returns @var{filename} minus its extension, if any. The
1738 version/backup part, if present, is only removed if the file has an
1739 extension. For example,
1742 (file-name-sans-extension "foo.lose.c")
1743 @result{} "foo.lose"
1744 (file-name-sans-extension "big.hack/foo")
1745 @result{} "big.hack/foo"
1746 (file-name-sans-extension "/my/home/.emacs")
1747 @result{} "/my/home/.emacs"
1748 (file-name-sans-extension "/my/home/.emacs.el")
1749 @result{} "/my/home/.emacs"
1750 (file-name-sans-extension "~/foo.el.~3~")
1752 (file-name-sans-extension "~/foo.~3~")
1753 @result{} "~/foo.~3~"
1756 Note that the @samp{.~3~} in the two last examples is the backup part,
1761 @node Relative File Names
1762 @subsection Absolute and Relative File Names
1763 @cindex absolute file name
1764 @cindex relative file name
1766 All the directories in the file system form a tree starting at the
1767 root directory. A file name can specify all the directory names
1768 starting from the root of the tree; then it is called an @dfn{absolute}
1769 file name. Or it can specify the position of the file in the tree
1770 relative to a default directory; then it is called a @dfn{relative} file
1771 name. On Unix and GNU/Linux, an absolute file name starts with a slash
1772 or a tilde (@samp{~}), and a relative one does not. On MS-DOS and
1773 MS-Windows, an absolute file name starts with a slash or a backslash, or
1774 with a drive specification @samp{@var{x}:/}, where @var{x} is the
1777 @defun file-name-absolute-p filename
1778 This function returns @code{t} if file @var{filename} is an absolute
1779 file name, @code{nil} otherwise.
1783 (file-name-absolute-p "~rms/foo")
1787 (file-name-absolute-p "rms/foo")
1791 (file-name-absolute-p "/user/rms/foo")
1797 Given a possibly relative file name, you can convert it to an
1798 absolute name using @code{expand-file-name} (@pxref{File Name
1799 Expansion}). This function converts absolute file names to relative
1802 @defun file-relative-name filename &optional directory
1803 This function tries to return a relative name that is equivalent to
1804 @var{filename}, assuming the result will be interpreted relative to
1805 @var{directory} (an absolute directory name or directory file name).
1806 If @var{directory} is omitted or @code{nil}, it defaults to the
1807 current buffer's default directory.
1809 On some operating systems, an absolute file name begins with a device
1810 name. On such systems, @var{filename} has no relative equivalent based
1811 on @var{directory} if they start with two different device names. In
1812 this case, @code{file-relative-name} returns @var{filename} in absolute
1816 (file-relative-name "/foo/bar" "/foo/")
1818 (file-relative-name "/foo/bar" "/hack/")
1819 @result{} "../foo/bar"
1823 @node Directory Names
1824 @comment node-name, next, previous, up
1825 @subsection Directory Names
1826 @cindex directory name
1827 @cindex file name of directory
1829 A @dfn{directory name} is the name of a directory. A directory is
1830 actually a kind of file, so it has a file name, which is related to
1831 the directory name but not identical to it. (This is not quite the
1832 same as the usual Unix terminology.) These two different names for
1833 the same entity are related by a syntactic transformation. On GNU and
1834 Unix systems, this is simple: a directory name ends in a slash,
1835 whereas the directory's name as a file lacks that slash. On MS-DOS
1836 the relationship is more complicated.
1838 The difference between a directory name and its name as a file is
1839 subtle but crucial. When an Emacs variable or function argument is
1840 described as being a directory name, a file name of a directory is not
1841 acceptable. When @code{file-name-directory} returns a string, that is
1842 always a directory name.
1844 The following two functions convert between directory names and file
1845 names. They do nothing special with environment variable substitutions
1846 such as @samp{$HOME}, and the constructs @samp{~}, @samp{.} and @samp{..}.
1848 @defun file-name-as-directory filename
1849 This function returns a string representing @var{filename} in a form
1850 that the operating system will interpret as the name of a directory. On
1851 most systems, this means appending a slash to the string (if it does not
1852 already end in one).
1856 (file-name-as-directory "~rms/lewis")
1857 @result{} "~rms/lewis/"
1862 @defun directory-file-name dirname
1863 This function returns a string representing @var{dirname} in a form that
1864 the operating system will interpret as the name of a file. On most
1865 systems, this means removing the final slash (or backslash) from the
1870 (directory-file-name "~lewis/")
1876 Given a directory name, you can combine it with a relative file name
1877 using @code{concat}:
1880 (concat @var{dirname} @var{relfile})
1884 Be sure to verify that the file name is relative before doing that.
1885 If you use an absolute file name, the results could be syntactically
1886 invalid or refer to the wrong file.
1888 If you want to use a directory file name in making such a
1889 combination, you must first convert it to a directory name using
1890 @code{file-name-as-directory}:
1893 (concat (file-name-as-directory @var{dirfile}) @var{relfile})
1897 Don't try concatenating a slash by hand, as in
1901 (concat @var{dirfile} "/" @var{relfile})
1905 because this is not portable. Always use
1906 @code{file-name-as-directory}.
1908 To convert a directory name to its abbreviation, use this
1911 @defun abbreviate-file-name filename
1912 @anchor{Definition of abbreviate-file-name}
1913 This function returns an abbreviated form of @var{filename}. It
1914 applies the abbreviations specified in @code{directory-abbrev-alist}
1915 (@pxref{File Aliases,,File Aliases, emacs, The GNU Emacs Manual}),
1916 then substitutes @samp{~} for the user's home directory if the
1917 argument names a file in the home directory or one of its
1918 subdirectories. If the home directory is a root directory, it is not
1919 replaced with @samp{~}, because this does not make the result shorter
1922 You can use this function for directory names and for file names,
1923 because it recognizes abbreviations even as part of the name.
1926 @node File Name Expansion
1927 @subsection Functions that Expand Filenames
1928 @cindex expansion of file names
1930 @dfn{Expansion} of a file name means converting a relative file name
1931 to an absolute one. Since this is done relative to a default directory,
1932 you must specify the default directory name as well as the file name to
1933 be expanded. Expansion also simplifies file names by eliminating
1934 redundancies such as @file{./} and @file{@var{name}/../}.
1936 @defun expand-file-name filename &optional directory
1937 This function converts @var{filename} to an absolute file name. If
1938 @var{directory} is supplied, it is the default directory to start with
1939 if @var{filename} is relative. (The value of @var{directory} should
1940 itself be an absolute directory name or directory file name; it may
1941 start with @samp{~}.) Otherwise, the current buffer's value of
1942 @code{default-directory} is used. For example:
1946 (expand-file-name "foo")
1947 @result{} "/xcssun/users/rms/lewis/foo"
1950 (expand-file-name "../foo")
1951 @result{} "/xcssun/users/rms/foo"
1954 (expand-file-name "foo" "/usr/spool/")
1955 @result{} "/usr/spool/foo"
1958 (expand-file-name "$HOME/foo")
1959 @result{} "/xcssun/users/rms/lewis/$HOME/foo"
1963 If the part of the combined file name before the first slash is
1964 @samp{~}, it expands to the value of the @env{HOME} environment
1965 variable (usually your home directory). If the part before the first
1966 slash is @samp{~@var{user}} and if @var{user} is a valid login name,
1967 it expands to @var{user}'s home directory.
1969 Filenames containing @samp{.} or @samp{..} are simplified to their
1974 (expand-file-name "bar/../foo")
1975 @result{} "/xcssun/users/rms/lewis/foo"
1979 In some cases, a leading @samp{..} component can remain in the output:
1983 (expand-file-name "../home" "/")
1984 @result{} "/../home"
1989 This is for the sake of filesystems that have the concept of a
1990 ``superroot'' above the root directory @file{/}. On other filesystems,
1991 @file{/../} is interpreted exactly the same as @file{/}.
1993 Note that @code{expand-file-name} does @emph{not} expand environment
1994 variables; only @code{substitute-in-file-name} does that.
1996 Note also that @code{expand-file-name} does not follow symbolic links
1997 at any level. This results in a difference between the way
1998 @code{file-truename} and @code{expand-file-name} treat @samp{..}.
1999 Assuming that @samp{/tmp/bar} is a symbolic link to the directory
2000 @samp{/tmp/foo/bar} we get:
2004 (file-truename "/tmp/bar/../myfile")
2005 @result{} "/tmp/foo/myfile"
2008 (expand-file-name "/tmp/bar/../myfile")
2009 @result{} "/tmp/myfile"
2013 If you may need to follow symbolic links preceding @samp{..}, you
2014 should make sure to call @code{file-truename} without prior direct or
2015 indirect calls to @code{expand-file-name}. @xref{Truenames}.
2018 @defvar default-directory
2019 The value of this buffer-local variable is the default directory for the
2020 current buffer. It should be an absolute directory name; it may start
2021 with @samp{~}. This variable is buffer-local in every buffer.
2023 @code{expand-file-name} uses the default directory when its second
2024 argument is @code{nil}.
2026 The value is always a string ending with a slash.
2031 @result{} "/user/lewis/manual/"
2036 @defun substitute-in-file-name filename
2037 @anchor{Definition of substitute-in-file-name}
2038 This function replaces environment variable references in
2039 @var{filename} with the environment variable values. Following
2040 standard Unix shell syntax, @samp{$} is the prefix to substitute an
2041 environment variable value. If the input contains @samp{$$}, that is
2042 converted to @samp{$}; this gives the user a way to ``quote'' a
2045 The environment variable name is the series of alphanumeric characters
2046 (including underscores) that follow the @samp{$}. If the character following
2047 the @samp{$} is a @samp{@{}, then the variable name is everything up to the
2050 Calling @code{substitute-in-file-name} on output produced by
2051 @code{substitute-in-file-name} tends to give incorrect results. For
2052 instance, use of @samp{$$} to quote a single @samp{$} won't work
2053 properly, and @samp{$} in an environment variable's value could lead
2054 to repeated substitution. Therefore, programs that call this function
2055 and put the output where it will be passed to this function need to
2056 double all @samp{$} characters to prevent subsequent incorrect
2059 @c Wordy to avoid overfull hbox. --rjc 15mar92
2060 Here we assume that the environment variable @code{HOME}, which holds
2061 the user's home directory name, has value @samp{/xcssun/users/rms}.
2065 (substitute-in-file-name "$HOME/foo")
2066 @result{} "/xcssun/users/rms/foo"
2070 After substitution, if a @samp{~} or a @samp{/} appears immediately
2071 after another @samp{/}, the function discards everything before it (up
2072 through the immediately preceding @samp{/}).
2076 (substitute-in-file-name "bar/~/foo")
2080 (substitute-in-file-name "/usr/local/$HOME/foo")
2081 @result{} "/xcssun/users/rms/foo"
2082 ;; @r{@file{/usr/local/} has been discarded.}
2088 @node Unique File Names
2089 @subsection Generating Unique File Names
2091 Some programs need to write temporary files. Here is the usual way to
2092 construct a name for such a file:
2095 (make-temp-file @var{name-of-application})
2099 The job of @code{make-temp-file} is to prevent two different users or
2100 two different jobs from trying to use the exact same file name.
2102 @defun make-temp-file prefix &optional dir-flag suffix
2103 This function creates a temporary file and returns its name. Emacs
2104 creates the temporary file's name by adding to @var{prefix} some
2105 random characters that are different in each Emacs job. The result is
2106 guaranteed to be a newly created empty file. On MS-DOS, this function
2107 can truncate the @var{string} prefix to fit into the 8+3 file-name
2108 limits. If @var{prefix} is a relative file name, it is expanded
2109 against @code{temporary-file-directory}.
2113 (make-temp-file "foo")
2114 @result{} "/tmp/foo232J6v"
2118 When @code{make-temp-file} returns, the file has been created and is
2119 empty. At that point, you should write the intended contents into the
2122 If @var{dir-flag} is non-@code{nil}, @code{make-temp-file} creates an
2123 empty directory instead of an empty file. It returns the file name,
2124 not the directory name, of that directory. @xref{Directory Names}.
2126 If @var{suffix} is non-@code{nil}, @code{make-temp-file} adds it at
2127 the end of the file name.
2129 To prevent conflicts among different libraries running in the same
2130 Emacs, each Lisp program that uses @code{make-temp-file} should have its
2131 own @var{prefix}. The number added to the end of @var{prefix}
2132 distinguishes between the same application running in different Emacs
2133 jobs. Additional added characters permit a large number of distinct
2134 names even in one Emacs job.
2137 The default directory for temporary files is controlled by the
2138 variable @code{temporary-file-directory}. This variable gives the user
2139 a uniform way to specify the directory for all temporary files. Some
2140 programs use @code{small-temporary-file-directory} instead, if that is
2141 non-@code{nil}. To use it, you should expand the prefix against
2142 the proper directory before calling @code{make-temp-file}.
2144 In older Emacs versions where @code{make-temp-file} does not exist,
2145 you should use @code{make-temp-name} instead:
2149 (expand-file-name @var{name-of-application}
2150 temporary-file-directory))
2153 @defun make-temp-name string
2154 This function generates a string that can be used as a unique file
2155 name. The name starts with @var{string}, and has several random
2156 characters appended to it, which are different in each Emacs job. It
2157 is like @code{make-temp-file} except that it just constructs a name,
2158 and does not create a file. Another difference is that @var{string}
2159 should be an absolute file name. On MS-DOS, this function can
2160 truncate the @var{string} prefix to fit into the 8+3 file-name limits.
2163 @defopt temporary-file-directory
2164 @cindex @code{TMPDIR} environment variable
2165 @cindex @code{TMP} environment variable
2166 @cindex @code{TEMP} environment variable
2167 This variable specifies the directory name for creating temporary files.
2168 Its value should be a directory name (@pxref{Directory Names}), but it
2169 is good for Lisp programs to cope if the value is a directory's file
2170 name instead. Using the value as the second argument to
2171 @code{expand-file-name} is a good way to achieve that.
2173 The default value is determined in a reasonable way for your operating
2174 system; it is based on the @code{TMPDIR}, @code{TMP} and @code{TEMP}
2175 environment variables, with a fall-back to a system-dependent name if
2176 none of these variables is defined.
2178 Even if you do not use @code{make-temp-file} to create the temporary
2179 file, you should still use this variable to decide which directory to
2180 put the file in. However, if you expect the file to be small, you
2181 should use @code{small-temporary-file-directory} first if that is
2185 @defopt small-temporary-file-directory
2186 This variable specifies the directory name for
2187 creating certain temporary files, which are likely to be small.
2189 If you want to write a temporary file which is likely to be small, you
2190 should compute the directory like this:
2194 (expand-file-name @var{prefix}
2195 (or small-temporary-file-directory
2196 temporary-file-directory)))
2200 @node File Name Completion
2201 @subsection File Name Completion
2202 @cindex file name completion subroutines
2203 @cindex completion, file name
2205 This section describes low-level subroutines for completing a file
2206 name. For higher level functions, see @ref{Reading File Names}.
2208 @defun file-name-all-completions partial-filename directory
2209 This function returns a list of all possible completions for a file
2210 whose name starts with @var{partial-filename} in directory
2211 @var{directory}. The order of the completions is the order of the files
2212 in the directory, which is unpredictable and conveys no useful
2215 The argument @var{partial-filename} must be a file name containing no
2216 directory part and no slash (or backslash on some systems). The current
2217 buffer's default directory is prepended to @var{directory}, if
2218 @var{directory} is not absolute.
2220 In the following example, suppose that @file{~rms/lewis} is the current
2221 default directory, and has five files whose names begin with @samp{f}:
2222 @file{foo}, @file{file~}, @file{file.c}, @file{file.c.~1~}, and
2223 @file{file.c.~2~}.@refill
2227 (file-name-all-completions "f" "")
2228 @result{} ("foo" "file~" "file.c.~2~"
2229 "file.c.~1~" "file.c")
2233 (file-name-all-completions "fo" "")
2239 @defun file-name-completion filename directory &optional predicate
2240 This function completes the file name @var{filename} in directory
2241 @var{directory}. It returns the longest prefix common to all file names
2242 in directory @var{directory} that start with @var{filename}. If
2243 @var{predicate} is non-@code{nil} then it ignores possible completions
2244 that don't satisfy @var{predicate}, after calling that function
2245 with one argument, the expanded absolute file name.
2247 If only one match exists and @var{filename} matches it exactly, the
2248 function returns @code{t}. The function returns @code{nil} if directory
2249 @var{directory} contains no name starting with @var{filename}.
2251 In the following example, suppose that the current default directory
2252 has five files whose names begin with @samp{f}: @file{foo},
2253 @file{file~}, @file{file.c}, @file{file.c.~1~}, and
2254 @file{file.c.~2~}.@refill
2258 (file-name-completion "fi" "")
2263 (file-name-completion "file.c.~1" "")
2264 @result{} "file.c.~1~"
2268 (file-name-completion "file.c.~1~" "")
2273 (file-name-completion "file.c.~3" "")
2279 @defopt completion-ignored-extensions
2280 @code{file-name-completion} usually ignores file names that end in any
2281 string in this list. It does not ignore them when all the possible
2282 completions end in one of these suffixes. This variable has no effect
2283 on @code{file-name-all-completions}.@refill
2285 A typical value might look like this:
2289 completion-ignored-extensions
2290 @result{} (".o" ".elc" "~" ".dvi")
2294 If an element of @code{completion-ignored-extensions} ends in a slash
2295 @samp{/}, it signals a directory. The elements which do @emph{not} end
2296 in a slash will never match a directory; thus, the above value will not
2297 filter out a directory named @file{foo.elc}.
2300 @node Standard File Names
2301 @subsection Standard File Names
2303 Most of the file names used in Lisp programs are entered by the user.
2304 But occasionally a Lisp program needs to specify a standard file name
2305 for a particular use---typically, to hold customization information
2306 about each user. For example, abbrev definitions are stored (by
2307 default) in the file @file{~/.abbrev_defs}; the @code{completion}
2308 package stores completions in the file @file{~/.completions}. These are
2309 two of the many standard file names used by parts of Emacs for certain
2312 Various operating systems have their own conventions for valid file
2313 names and for which file names to use for user profile data. A Lisp
2314 program which reads a file using a standard file name ought to use, on
2315 each type of system, a file name suitable for that system. The function
2316 @code{convert-standard-filename} makes this easy to do.
2318 @defun convert-standard-filename filename
2319 This function alters the file name @var{filename} to fit the conventions
2320 of the operating system in use, and returns the result as a new string.
2323 The recommended way to specify a standard file name in a Lisp program
2324 is to choose a name which fits the conventions of GNU and Unix systems,
2325 usually with a nondirectory part that starts with a period, and pass it
2326 to @code{convert-standard-filename} instead of using it directly. Here
2327 is an example from the @code{completion} package:
2330 (defvar save-completions-file-name
2331 (convert-standard-filename "~/.completions")
2332 "*The file name to save completions to.")
2335 On GNU and Unix systems, and on some other systems as well,
2336 @code{convert-standard-filename} returns its argument unchanged. On
2337 some other systems, it alters the name to fit the system's conventions.
2339 For example, on MS-DOS the alterations made by this function include
2340 converting a leading @samp{.} to @samp{_}, converting a @samp{_} in the
2341 middle of the name to @samp{.} if there is no other @samp{.}, inserting
2342 a @samp{.} after eight characters if there is none, and truncating to
2343 three characters after the @samp{.}. (It makes other changes as well.)
2344 Thus, @file{.abbrev_defs} becomes @file{_abbrev.def}, and
2345 @file{.completions} becomes @file{_complet.ion}.
2347 @node Contents of Directories
2348 @section Contents of Directories
2349 @cindex directory-oriented functions
2350 @cindex file names in directory
2352 A directory is a kind of file that contains other files entered under
2353 various names. Directories are a feature of the file system.
2355 Emacs can list the names of the files in a directory as a Lisp list,
2356 or display the names in a buffer using the @code{ls} shell command. In
2357 the latter case, it can optionally display information about each file,
2358 depending on the options passed to the @code{ls} command.
2360 @defun directory-files directory &optional full-name match-regexp nosort
2361 This function returns a list of the names of the files in the directory
2362 @var{directory}. By default, the list is in alphabetical order.
2364 If @var{full-name} is non-@code{nil}, the function returns the files'
2365 absolute file names. Otherwise, it returns the names relative to
2366 the specified directory.
2368 If @var{match-regexp} is non-@code{nil}, this function returns only
2369 those file names that contain a match for that regular expression---the
2370 other file names are excluded from the list. On case-insensitive
2371 filesystems, the regular expression matching is case-insensitive.
2374 If @var{nosort} is non-@code{nil}, @code{directory-files} does not sort
2375 the list, so you get the file names in no particular order. Use this if
2376 you want the utmost possible speed and don't care what order the files
2377 are processed in. If the order of processing is visible to the user,
2378 then the user will probably be happier if you do sort the names.
2382 (directory-files "~lewis")
2383 @result{} ("#foo#" "#foo.el#" "." ".."
2384 "dired-mods.el" "files.texi"
2389 An error is signaled if @var{directory} is not the name of a directory
2393 @defun directory-files-and-attributes directory &optional full-name match-regexp nosort id-format
2394 This is similar to @code{directory-files} in deciding which files
2395 to report on and how to report their names. However, instead
2396 of returning a list of file names, it returns for each file a
2397 list @code{(@var{filename} . @var{attributes})}, where @var{attributes}
2398 is what @code{file-attributes} would return for that file.
2399 The optional argument @var{id-format} has the same meaning as the
2400 corresponding argument to @code{file-attributes} (@pxref{Definition
2401 of file-attributes}).
2404 @defun file-expand-wildcards pattern &optional full
2405 This function expands the wildcard pattern @var{pattern}, returning
2406 a list of file names that match it.
2408 If @var{pattern} is written as an absolute file name,
2409 the values are absolute also.
2411 If @var{pattern} is written as a relative file name, it is interpreted
2412 relative to the current default directory. The file names returned are
2413 normally also relative to the current default directory. However, if
2414 @var{full} is non-@code{nil}, they are absolute.
2417 @defun insert-directory file switches &optional wildcard full-directory-p
2418 This function inserts (in the current buffer) a directory listing for
2419 directory @var{file}, formatted with @code{ls} according to
2420 @var{switches}. It leaves point after the inserted text.
2421 @var{switches} may be a string of options, or a list of strings
2422 representing individual options.
2424 The argument @var{file} may be either a directory name or a file
2425 specification including wildcard characters. If @var{wildcard} is
2426 non-@code{nil}, that means treat @var{file} as a file specification with
2429 If @var{full-directory-p} is non-@code{nil}, that means the directory
2430 listing is expected to show the full contents of a directory. You
2431 should specify @code{t} when @var{file} is a directory and switches do
2432 not contain @samp{-d}. (The @samp{-d} option to @code{ls} says to
2433 describe a directory itself as a file, rather than showing its
2436 On most systems, this function works by running a directory listing
2437 program whose name is in the variable @code{insert-directory-program}.
2438 If @var{wildcard} is non-@code{nil}, it also runs the shell specified by
2439 @code{shell-file-name}, to expand the wildcards.
2441 MS-DOS and MS-Windows systems usually lack the standard Unix program
2442 @code{ls}, so this function emulates the standard Unix program @code{ls}
2445 As a technical detail, when @var{switches} contains the long
2446 @samp{--dired} option, @code{insert-directory} treats it specially,
2447 for the sake of dired. However, the normally equivalent short
2448 @samp{-D} option is just passed on to @code{insert-directory-program},
2449 as any other option.
2452 @defvar insert-directory-program
2453 This variable's value is the program to run to generate a directory listing
2454 for the function @code{insert-directory}. It is ignored on systems
2455 which generate the listing with Lisp code.
2458 @node Create/Delete Dirs
2459 @section Creating, Copying and Deleting Directories
2460 @cindex creating, copying and deleting directories
2461 @c Emacs 19 features
2463 Most Emacs Lisp file-manipulation functions get errors when used on
2464 files that are directories. For example, you cannot delete a directory
2465 with @code{delete-file}. These special functions exist to create and
2469 @deffn Command make-directory dirname &optional parents
2470 This command creates a directory named @var{dirname}. If
2471 @var{parents} is non-@code{nil}, as is always the case in an
2472 interactive call, that means to create the parent directories first,
2473 if they don't already exist.
2475 @code{mkdir} is an alias for this.
2478 @deffn Command copy-directory dirname newname &optional keep-time parents
2479 This command copies the directory named @var{dirname} to
2480 @var{newname}. If @var{newname} names an existing directory,
2481 @var{dirname} will be copied to a subdirectory there.
2483 It always sets the file modes of the copied files to match the
2484 corresponding original file.
2486 The third arg @var{keep-time} non-@code{nil} means to preserve the
2487 modification time of the copied files. A prefix arg makes
2488 @var{keep-time} non-@code{nil}.
2490 Noninteractively, the last argument @var{parents} says whether to
2491 create parent directories if they don't exist. Interactively,
2492 this happens by default.
2495 @deffn Command delete-directory dirname &optional recursive
2496 This command deletes the directory named @var{dirname}. The function
2497 @code{delete-file} does not work for files that are directories; you
2498 must use @code{delete-directory} for them. If @var{recursive} is
2499 @code{nil}, and the directory contains any files,
2500 @code{delete-directory} signals an error.
2502 @code{delete-directory} only follows symbolic links at the level of
2506 @node Magic File Names
2507 @section Making Certain File Names ``Magic''
2508 @cindex magic file names
2511 You can implement special handling for certain file names. This is
2512 called making those names @dfn{magic}. The principal use for this
2513 feature is in implementing remote file names (@pxref{Remote Files,,
2514 Remote Files, emacs, The GNU Emacs Manual}).
2516 To define a kind of magic file name, you must supply a regular
2517 expression to define the class of names (all those that match the
2518 regular expression), plus a handler that implements all the primitive
2519 Emacs file operations for file names that do match.
2521 @vindex file-name-handler-alist
2522 The variable @code{file-name-handler-alist} holds a list of handlers,
2523 together with regular expressions that determine when to apply each
2524 handler. Each element has this form:
2527 (@var{regexp} . @var{handler})
2531 All the Emacs primitives for file access and file name transformation
2532 check the given file name against @code{file-name-handler-alist}. If
2533 the file name matches @var{regexp}, the primitives handle that file by
2534 calling @var{handler}.
2536 The first argument given to @var{handler} is the name of the
2537 primitive, as a symbol; the remaining arguments are the arguments that
2538 were passed to that primitive. (The first of these arguments is most
2539 often the file name itself.) For example, if you do this:
2542 (file-exists-p @var{filename})
2546 and @var{filename} has handler @var{handler}, then @var{handler} is
2550 (funcall @var{handler} 'file-exists-p @var{filename})
2553 When a function takes two or more arguments that must be file names,
2554 it checks each of those names for a handler. For example, if you do
2558 (expand-file-name @var{filename} @var{dirname})
2562 then it checks for a handler for @var{filename} and then for a handler
2563 for @var{dirname}. In either case, the @var{handler} is called like
2567 (funcall @var{handler} 'expand-file-name @var{filename} @var{dirname})
2571 The @var{handler} then needs to figure out whether to handle
2572 @var{filename} or @var{dirname}.
2574 If the specified file name matches more than one handler, the one
2575 whose match starts last in the file name gets precedence. This rule
2576 is chosen so that handlers for jobs such as uncompression are handled
2577 first, before handlers for jobs such as remote file access.
2579 Here are the operations that a magic file name handler gets to handle:
2583 @code{access-file}, @code{add-name-to-file},
2584 @code{byte-compiler-base-file-name},@*
2585 @code{copy-directory}, @code{copy-file},
2586 @code{delete-directory}, @code{delete-file},
2587 @code{diff-latest-backup-file},
2588 @code{directory-file-name},
2589 @code{directory-files},
2590 @code{directory-files-and-attributes},
2591 @code{dired-compress-file}, @code{dired-uncache},@*
2592 @code{expand-file-name},
2593 @code{file-accessible-directory-p},
2594 @code{file-attributes},
2595 @code{file-directory-p},
2596 @code{file-executable-p}, @code{file-exists-p},
2597 @code{file-local-copy}, @code{file-remote-p},
2598 @code{file-modes}, @code{file-name-all-completions},
2599 @code{file-name-as-directory},
2600 @code{file-name-completion},
2601 @code{file-name-directory},
2602 @code{file-name-nondirectory},
2603 @code{file-name-sans-versions}, @code{file-newer-than-file-p},
2604 @code{file-ownership-preserved-p},
2605 @code{file-readable-p}, @code{file-regular-p}, @code{file-symlink-p},
2606 @code{file-truename}, @code{file-writable-p},
2607 @code{find-backup-file-name},
2608 @c Not sure why it was here: @code{find-file-noselect},@*
2609 @code{get-file-buffer},
2610 @code{insert-directory},
2611 @code{insert-file-contents},@*
2613 @code{make-auto-save-file-name},
2614 @code{make-directory},
2615 @code{make-directory-internal},
2616 @code{make-symbolic-link},@*
2617 @code{process-file},
2618 @code{rename-file}, @code{set-file-modes}, @code{set-file-times},
2619 @code{set-visited-file-modtime}, @code{shell-command},
2620 @code{start-file-process},
2621 @code{substitute-in-file-name},@*
2622 @code{unhandled-file-name-directory},
2623 @code{vc-registered},
2624 @code{verify-visited-file-modtime},@*
2625 @code{write-region}.
2630 @code{access-file}, @code{add-name-to-file},
2631 @code{byte-com@discretionary{}{}{}piler-base-file-name},
2632 @code{copy-directory}, @code{copy-file},
2633 @code{delete-directory}, @code{delete-file},
2634 @code{diff-latest-backup-file},
2635 @code{directory-file-name},
2636 @code{directory-files},
2637 @code{directory-files-and-at@discretionary{}{}{}tributes},
2638 @code{dired-compress-file}, @code{dired-uncache},
2639 @code{expand-file-name},
2640 @code{file-accessible-direc@discretionary{}{}{}tory-p},
2641 @code{file-attributes},
2642 @code{file-direct@discretionary{}{}{}ory-p},
2643 @code{file-executable-p}, @code{file-exists-p},
2644 @code{file-local-copy}, @code{file-remote-p},
2645 @code{file-modes}, @code{file-name-all-completions},
2646 @code{file-name-as-directory},
2647 @code{file-name-completion},
2648 @code{file-name-directory},
2649 @code{file-name-nondirec@discretionary{}{}{}tory},
2650 @code{file-name-sans-versions}, @code{file-newer-than-file-p},
2651 @code{file-ownership-pre@discretionary{}{}{}served-p},
2652 @code{file-readable-p}, @code{file-regular-p}, @code{file-symlink-p},
2653 @code{file-truename}, @code{file-writable-p},
2654 @code{find-backup-file-name},
2655 @c Not sure why it was here: @code{find-file-noselect},
2656 @code{get-file-buffer},
2657 @code{insert-directory},
2658 @code{insert-file-contents},
2659 @code{load}, @code{make-direc@discretionary{}{}{}tory},
2660 @code{make-direc@discretionary{}{}{}tory-internal},
2661 @code{make-symbolic-link},
2662 @code{process-file},
2663 @code{rename-file}, @code{set-file-modes},
2664 @code{set-visited-file-modtime}, @code{shell-command},
2665 @code{start-file-process},
2666 @code{substitute-in-file-name},
2667 @code{unhandled-file-name-directory},
2668 @code{vc-regis@discretionary{}{}{}tered},
2669 @code{verify-visited-file-modtime},
2670 @code{write-region}.
2674 Handlers for @code{insert-file-contents} typically need to clear the
2675 buffer's modified flag, with @code{(set-buffer-modified-p nil)}, if the
2676 @var{visit} argument is non-@code{nil}. This also has the effect of
2677 unlocking the buffer if it is locked.
2679 The handler function must handle all of the above operations, and
2680 possibly others to be added in the future. It need not implement all
2681 these operations itself---when it has nothing special to do for a
2682 certain operation, it can reinvoke the primitive, to handle the
2683 operation ``in the usual way.'' It should always reinvoke the primitive
2684 for an operation it does not recognize. Here's one way to do this:
2687 (defun my-file-handler (operation &rest args)
2688 ;; @r{First check for the specific operations}
2689 ;; @r{that we have special handling for.}
2690 (cond ((eq operation 'insert-file-contents) @dots{})
2691 ((eq operation 'write-region) @dots{})
2693 ;; @r{Handle any operation we don't know about.}
2694 (t (let ((inhibit-file-name-handlers
2695 (cons 'my-file-handler
2696 (and (eq inhibit-file-name-operation operation)
2697 inhibit-file-name-handlers)))
2698 (inhibit-file-name-operation operation))
2699 (apply operation args)))))
2702 When a handler function decides to call the ordinary Emacs primitive for
2703 the operation at hand, it needs to prevent the primitive from calling
2704 the same handler once again, thus leading to an infinite recursion. The
2705 example above shows how to do this, with the variables
2706 @code{inhibit-file-name-handlers} and
2707 @code{inhibit-file-name-operation}. Be careful to use them exactly as
2708 shown above; the details are crucial for proper behavior in the case of
2709 multiple handlers, and for operations that have two file names that may
2712 @kindex safe-magic (@r{property})
2713 Handlers that don't really do anything special for actual access to the
2714 file---such as the ones that implement completion of host names for
2715 remote file names---should have a non-@code{nil} @code{safe-magic}
2716 property. For instance, Emacs normally ``protects'' directory names
2717 it finds in @code{PATH} from becoming magic, if they look like magic
2718 file names, by prefixing them with @samp{/:}. But if the handler that
2719 would be used for them has a non-@code{nil} @code{safe-magic}
2720 property, the @samp{/:} is not added.
2722 @kindex operations (@r{property})
2723 A file name handler can have an @code{operations} property to
2724 declare which operations it handles in a nontrivial way. If this
2725 property has a non-@code{nil} value, it should be a list of
2726 operations; then only those operations will call the handler. This
2727 avoids inefficiency, but its main purpose is for autoloaded handler
2728 functions, so that they won't be loaded except when they have real
2731 Simply deferring all operations to the usual primitives does not
2732 work. For instance, if the file name handler applies to
2733 @code{file-exists-p}, then it must handle @code{load} itself, because
2734 the usual @code{load} code won't work properly in that case. However,
2735 if the handler uses the @code{operations} property to say it doesn't
2736 handle @code{file-exists-p}, then it need not handle @code{load}
2739 @defvar inhibit-file-name-handlers
2740 This variable holds a list of handlers whose use is presently inhibited
2741 for a certain operation.
2744 @defvar inhibit-file-name-operation
2745 The operation for which certain handlers are presently inhibited.
2748 @defun find-file-name-handler file operation
2749 This function returns the handler function for file name @var{file},
2750 or @code{nil} if there is none. The argument @var{operation} should
2751 be the operation to be performed on the file---the value you will pass
2752 to the handler as its first argument when you call it. If
2753 @var{operation} equals @code{inhibit-file-name-operation}, or if it is
2754 not found in the @code{operations} property of the handler, this
2755 function returns @code{nil}.
2758 @defun file-local-copy filename
2759 This function copies file @var{filename} to an ordinary non-magic file
2760 on the local machine, if it isn't on the local machine already. Magic
2761 file names should handle the @code{file-local-copy} operation if they
2762 refer to files on other machines. A magic file name that is used for
2763 other purposes than remote file access should not handle
2764 @code{file-local-copy}; then this function will treat the file as
2767 If @var{filename} is local, whether magic or not, this function does
2768 nothing and returns @code{nil}. Otherwise it returns the file name
2769 of the local copy file.
2772 @defun file-remote-p filename &optional identification connected
2773 This function tests whether @var{filename} is a remote file. If
2774 @var{filename} is local (not remote), the return value is @code{nil}.
2775 If @var{filename} is indeed remote, the return value is a string that
2776 identifies the remote system.
2778 This identifier string can include a host name and a user name, as
2779 well as characters designating the method used to access the remote
2780 system. For example, the remote identifier string for the filename
2781 @code{/sudo::/some/file} is @code{/sudo:root@@localhost:}.
2783 If @code{file-remote-p} returns the same identifier for two different
2784 filenames, that means they are stored on the same file system and can
2785 be accessed locally with respect to each other. This means, for
2786 example, that it is possible to start a remote process accessing both
2787 files at the same time. Implementors of file handlers need to ensure
2788 this principle is valid.
2790 @var{identification} specifies which part of the identifier shall be
2791 returned as string. @var{identification} can be the symbol
2792 @code{method}, @code{user} or @code{host}; any other value is handled
2793 like @code{nil} and means to return the complete identifier string.
2794 In the example above, the remote @code{user} identifier string would
2797 If @var{connected} is non-@code{nil}, this function returns @code{nil}
2798 even if @var{filename} is remote, if Emacs has no network connection
2799 to its host. This is useful when you want to avoid the delay of
2800 making connections when they don't exist.
2803 @defun unhandled-file-name-directory filename
2804 This function returns the name of a directory that is not magic. It
2805 uses the directory part of @var{filename} if that is not magic. For a
2806 magic file name, it invokes the file name handler, which therefore
2807 decides what value to return. If @var{filename} is not accessible
2808 from a local process, then the file name handler should indicate it by
2809 returning @code{nil}.
2811 This is useful for running a subprocess; every subprocess must have a
2812 non-magic directory to serve as its current directory, and this function
2813 is a good way to come up with one.
2816 @defopt remote-file-name-inhibit-cache
2817 Whether to use the remote file-name cache for read access.
2819 File attributes of remote files are cached for better performance. If
2820 they are changed out of Emacs' control, the cached values become
2821 invalid, and must be reread.
2823 When set to @code{nil}, cached values are always used. This shall be
2824 set with care. When set to @code{t}, cached values are never used.
2825 ALthough this is the safest value, it could result in performance
2828 A compromise is to set it to a positive number. This means that
2829 cached values are used for that amount of seconds since they were
2832 In case a remote file is checked regularly, it might be reasonable to
2833 let-bind this variable to a value less then the time period between
2834 two checks. Example:
2837 (defun display-time-file-nonempty-p (file)
2838 (let ((remote-file-name-inhibit-cache (- display-time-interval 5)))
2839 (and (file-exists-p file)
2840 (< 0 (nth 7 (file-attributes (file-chase-links file)))))))
2844 @node Format Conversion
2845 @section File Format Conversion
2847 @cindex file format conversion
2848 @cindex encoding file formats
2849 @cindex decoding file formats
2850 @cindex text properties in files
2851 @cindex saving text properties
2852 Emacs performs several steps to convert the data in a buffer (text,
2853 text properties, and possibly other information) to and from a
2854 representation suitable for storing into a file. This section describes
2855 the fundamental functions that perform this @dfn{format conversion},
2856 namely @code{insert-file-contents} for reading a file into a buffer,
2857 and @code{write-region} for writing a buffer into a file.
2860 * Overview: Format Conversion Overview. @code{insert-file-contents} and @code{write-region}.
2861 * Round-Trip: Format Conversion Round-Trip. Using @code{format-alist}.
2862 * Piecemeal: Format Conversion Piecemeal. Specifying non-paired conversion.
2865 @node Format Conversion Overview
2866 @subsection Overview
2868 The function @code{insert-file-contents}:
2871 @item initially, inserts bytes from the file into the buffer;
2872 @item decodes bytes to characters as appropriate;
2873 @item processes formats as defined by entries in @code{format-alist}; and
2874 @item calls functions in @code{after-insert-file-functions}.
2878 The function @code{write-region}:
2881 @item initially, calls functions in @code{write-region-annotate-functions};
2882 @item processes formats as defined by entries in @code{format-alist};
2883 @item encodes characters to bytes as appropriate; and
2884 @item modifies the file with the bytes.
2887 This shows the symmetry of the lowest-level operations; reading and
2888 writing handle things in opposite order. The rest of this section
2889 describes the two facilities surrounding the three variables named
2890 above, as well as some related functions. @ref{Coding Systems}, for
2891 details on character encoding and decoding.
2893 @node Format Conversion Round-Trip
2894 @subsection Round-Trip Specification
2896 The most general of the two facilities is controlled by the variable
2897 @code{format-alist}, a list of @dfn{file format} specifications, which
2898 describe textual representations used in files for the data in an Emacs
2899 buffer. The descriptions for reading and writing are paired, which is
2900 why we call this ``round-trip'' specification
2901 (@pxref{Format Conversion Piecemeal}, for non-paired specification).
2903 @defvar format-alist
2904 This list contains one format definition for each defined file format.
2905 Each format definition is a list of this form:
2908 (@var{name} @var{doc-string} @var{regexp} @var{from-fn} @var{to-fn} @var{modify} @var{mode-fn} @var{preserve})
2912 @cindex format definition
2914 Here is what the elements in a format definition mean:
2918 The name of this format.
2921 A documentation string for the format.
2924 A regular expression which is used to recognize files represented in
2925 this format. If @code{nil}, the format is never applied automatically.
2928 A shell command or function to decode data in this format (to convert
2929 file data into the usual Emacs data representation).
2931 A shell command is represented as a string; Emacs runs the command as a
2932 filter to perform the conversion.
2934 If @var{from-fn} is a function, it is called with two arguments, @var{begin}
2935 and @var{end}, which specify the part of the buffer it should convert.
2936 It should convert the text by editing it in place. Since this can
2937 change the length of the text, @var{from-fn} should return the modified
2940 One responsibility of @var{from-fn} is to make sure that the beginning
2941 of the file no longer matches @var{regexp}. Otherwise it is likely to
2945 A shell command or function to encode data in this format---that is, to
2946 convert the usual Emacs data representation into this format.
2948 If @var{to-fn} is a string, it is a shell command; Emacs runs the
2949 command as a filter to perform the conversion.
2951 If @var{to-fn} is a function, it is called with three arguments:
2952 @var{begin} and @var{end}, which specify the part of the buffer it
2953 should convert, and @var{buffer}, which specifies which buffer. There
2954 are two ways it can do the conversion:
2958 By editing the buffer in place. In this case, @var{to-fn} should
2959 return the end-position of the range of text, as modified.
2962 By returning a list of annotations. This is a list of elements of the
2963 form @code{(@var{position} . @var{string})}, where @var{position} is an
2964 integer specifying the relative position in the text to be written, and
2965 @var{string} is the annotation to add there. The list must be sorted in
2966 order of position when @var{to-fn} returns it.
2968 When @code{write-region} actually writes the text from the buffer to the
2969 file, it intermixes the specified annotations at the corresponding
2970 positions. All this takes place without modifying the buffer.
2974 A flag, @code{t} if the encoding function modifies the buffer, and
2975 @code{nil} if it works by returning a list of annotations.
2978 A minor-mode function to call after visiting a file converted from this
2979 format. The function is called with one argument, the integer 1;
2980 that tells a minor-mode function to enable the mode.
2983 A flag, @code{t} if @code{format-write-file} should not remove this format
2984 from @code{buffer-file-format}.
2987 The function @code{insert-file-contents} automatically recognizes file
2988 formats when it reads the specified file. It checks the text of the
2989 beginning of the file against the regular expressions of the format
2990 definitions, and if it finds a match, it calls the decoding function for
2991 that format. Then it checks all the known formats over again.
2992 It keeps checking them until none of them is applicable.
2994 Visiting a file, with @code{find-file-noselect} or the commands that use
2995 it, performs conversion likewise (because it calls
2996 @code{insert-file-contents}); it also calls the mode function for each
2997 format that it decodes. It stores a list of the format names in the
2998 buffer-local variable @code{buffer-file-format}.
3000 @defvar buffer-file-format
3001 This variable states the format of the visited file. More precisely,
3002 this is a list of the file format names that were decoded in the course
3003 of visiting the current buffer's file. It is always buffer-local in all
3007 When @code{write-region} writes data into a file, it first calls the
3008 encoding functions for the formats listed in @code{buffer-file-format},
3009 in the order of appearance in the list.
3011 @deffn Command format-write-file file format &optional confirm
3012 This command writes the current buffer contents into the file @var{file}
3013 in a format based on @var{format}, which is a list of format names. It
3014 constructs the actual format starting from @var{format}, then appending
3015 any elements from the value of @code{buffer-file-format} with a non-nil
3016 @var{preserve} flag (see above), if they are not already present in
3017 @var{format}. It then updates @code{buffer-file-format} with this
3018 format, making it the default for future saves. Except for the
3019 @var{format} argument, this command is similar to @code{write-file}. In
3020 particular, @var{confirm} has the same meaning and interactive treatment
3021 as the corresponding argument to @code{write-file}. @xref{Definition of
3025 @deffn Command format-find-file file format
3026 This command finds the file @var{file}, converting it according to
3027 format @var{format}. It also makes @var{format} the default if the
3028 buffer is saved later.
3030 The argument @var{format} is a list of format names. If @var{format} is
3031 @code{nil}, no conversion takes place. Interactively, typing just
3032 @key{RET} for @var{format} specifies @code{nil}.
3035 @deffn Command format-insert-file file format &optional beg end
3036 This command inserts the contents of file @var{file}, converting it
3037 according to format @var{format}. If @var{beg} and @var{end} are
3038 non-@code{nil}, they specify which part of the file to read, as in
3039 @code{insert-file-contents} (@pxref{Reading from Files}).
3041 The return value is like what @code{insert-file-contents} returns: a
3042 list of the absolute file name and the length of the data inserted
3045 The argument @var{format} is a list of format names. If @var{format} is
3046 @code{nil}, no conversion takes place. Interactively, typing just
3047 @key{RET} for @var{format} specifies @code{nil}.
3050 @defvar buffer-auto-save-file-format
3051 This variable specifies the format to use for auto-saving. Its value is
3052 a list of format names, just like the value of
3053 @code{buffer-file-format}; however, it is used instead of
3054 @code{buffer-file-format} for writing auto-save files. If the value
3055 is @code{t}, the default, auto-saving uses the same format as a
3056 regular save in the same buffer. This variable is always buffer-local
3060 @node Format Conversion Piecemeal
3061 @subsection Piecemeal Specification
3063 In contrast to the round-trip specification described in the previous
3064 subsection (@pxref{Format Conversion Round-Trip}), you can use the variables
3065 @code{after-insert-file-functions} and @code{write-region-annotate-functions}
3066 to separately control the respective reading and writing conversions.
3068 Conversion starts with one representation and produces another
3069 representation. When there is only one conversion to do, there is no
3070 conflict about what to start with. However, when there are multiple
3071 conversions involved, conflict may arise when two conversions need to
3072 start with the same data.
3074 This situation is best understood in the context of converting text
3075 properties during @code{write-region}. For example, the character at
3076 position 42 in a buffer is @samp{X} with a text property @code{foo}. If
3077 the conversion for @code{foo} is done by inserting into the buffer, say,
3078 @samp{FOO:}, then that changes the character at position 42 from
3079 @samp{X} to @samp{F}. The next conversion will start with the wrong
3082 To avoid conflict, cooperative conversions do not modify the buffer,
3083 but instead specify @dfn{annotations}, a list of elements of the form
3084 @code{(@var{position} . @var{string})}, sorted in order of increasing
3087 If there is more than one conversion, @code{write-region} merges their
3088 annotations destructively into one sorted list. Later, when the text
3089 from the buffer is actually written to the file, it intermixes the
3090 specified annotations at the corresponding positions. All this takes
3091 place without modifying the buffer.
3093 @c ??? What about ``overriding'' conversions like those allowed
3094 @c ??? for `write-region-annotate-functions', below? --ttn
3096 In contrast, when reading, the annotations intermixed with the text
3097 are handled immediately. @code{insert-file-contents} sets point to
3098 the beginning of some text to be converted, then calls the conversion
3099 functions with the length of that text. These functions should always
3100 return with point at the beginning of the inserted text. This
3101 approach makes sense for reading because annotations removed by the
3102 first converter can't be mistakenly processed by a later converter.
3103 Each conversion function should scan for the annotations it
3104 recognizes, remove the annotation, modify the buffer text (to set a
3105 text property, for example), and return the updated length of the
3106 text, as it stands after those changes. The value returned by one
3107 function becomes the argument to the next function.
3109 @defvar write-region-annotate-functions
3110 A list of functions for @code{write-region} to call. Each function in
3111 the list is called with two arguments: the start and end of the region
3112 to be written. These functions should not alter the contents of the
3113 buffer. Instead, they should return annotations.
3115 As a special case, a function may return with a different buffer
3116 current. Emacs takes this to mean that the current buffer contains
3117 altered text to be output. It therefore changes the @var{start} and
3118 @var{end} arguments of the @code{write-region} call, giving them the
3119 values of @code{point-min} and @code{point-max} in the new buffer,
3120 respectively. It also discards all previous annotations, because they
3121 should have been dealt with by this function.
3124 @defvar write-region-post-annotation-function
3125 The value of this variable, if non-@code{nil}, should be a function.
3126 This function is called, with no arguments, after @code{write-region}
3129 If any function in @code{write-region-annotate-functions} returns with
3130 a different buffer current, Emacs calls
3131 @code{write-region-post-annotation-function} more than once. Emacs
3132 calls it with the last buffer that was current, and again with the
3133 buffer before that, and so on back to the original buffer.
3135 Thus, a function in @code{write-region-annotate-functions} can create
3136 a buffer, give this variable the local value of @code{kill-buffer} in
3137 that buffer, set up the buffer with altered text, and make the buffer
3138 current. The buffer will be killed after @code{write-region} is done.
3141 @defvar after-insert-file-functions
3142 Each function in this list is called by @code{insert-file-contents}
3143 with one argument, the number of characters inserted, and with point
3144 at the beginning of the inserted text. Each function should leave
3145 point unchanged, and return the new character count describing the
3146 inserted text as modified by the function.
3147 @c ??? The docstring mentions a handler from `file-name-handler-alist'
3148 @c "intercepting" `insert-file-contents'. Hmmm. --ttn
3151 We invite users to write Lisp programs to store and retrieve text
3152 properties in files, using these hooks, and thus to experiment with
3153 various data formats and find good ones. Eventually we hope users
3154 will produce good, general extensions we can install in Emacs.
3156 We suggest not trying to handle arbitrary Lisp objects as text property
3157 names or values---because a program that general is probably difficult
3158 to write, and slow. Instead, choose a set of possible data types that
3159 are reasonably flexible, and not too hard to encode.