2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2017 Free Software
5 @c See the file elisp.texi for copying conditions.
9 This chapter describes the Emacs Lisp functions and variables to
10 find, create, view, save, and otherwise work with files and
11 directories. A few other file-related functions are described in
12 @ref{Buffers}, and those related to backups and auto-saving are
13 described in @ref{Backups and Auto-Saving}.
15 Many of the file functions take one or more arguments that are file
16 names. A file name is a string. Most of these functions expand file
17 name arguments using the function @code{expand-file-name}, so that
18 @file{~} is handled correctly, as are relative file names (including
19 @file{../}). @xref{File Name Expansion}.
21 In addition, certain @dfn{magic} file names are handled specially.
22 For example, when a remote file name is specified, Emacs accesses the
23 file over the network via an appropriate protocol. @xref{Remote
24 Files,, Remote Files, emacs, The GNU Emacs Manual}. This handling is
25 done at a very low level, so you may assume that all the functions
26 described in this chapter accept magic file names as file name
27 arguments, except where noted. @xref{Magic File Names}, for details.
29 When file I/O functions signal Lisp errors, they usually use the
30 condition @code{file-error} (@pxref{Handling Errors}). The error
31 message is in most cases obtained from the operating system, according
32 to locale @code{system-messages-locale}, and decoded using coding system
33 @code{locale-coding-system} (@pxref{Locales}).
36 * Visiting Files:: Reading files into Emacs buffers for editing.
37 * Saving Buffers:: Writing changed buffers back into files.
38 * Reading from Files:: Reading files into buffers without visiting.
39 * Writing to Files:: Writing new files from parts of buffers.
40 * File Locks:: Locking and unlocking files, to prevent
41 simultaneous editing by two people.
42 * Information about Files:: Testing existence, accessibility, size of files.
43 * Changing Files:: Renaming files, changing permissions, etc.
44 * Files and Storage:: Surviving power and media failures
45 * File Names:: Decomposing and expanding file names.
46 * Contents of Directories:: Getting a list of the files in a directory.
47 * Create/Delete Dirs:: Creating and Deleting Directories.
48 * Magic File Names:: Special handling for certain file names.
49 * Format Conversion:: Conversion to and from various file formats.
53 @section Visiting Files
55 @cindex visiting files
57 Visiting a file means reading a file into a buffer. Once this is
58 done, we say that the buffer is @dfn{visiting} that file, and call the
59 file @dfn{the visited file} of the buffer.
61 A file and a buffer are two different things. A file is information
62 recorded permanently in the computer (unless you delete it). A
63 buffer, on the other hand, is information inside of Emacs that will
64 vanish at the end of the editing session (or when you kill the
65 buffer). When a buffer is visiting a file, it contains information
66 copied from the file. The copy in the buffer is what you modify with
67 editing commands. Changes to the buffer do not change the file; to
68 make the changes permanent, you must @dfn{save} the buffer, which
69 means copying the altered buffer contents back into the file.
71 Despite the distinction between files and buffers, people often
72 refer to a file when they mean a buffer and vice-versa. Indeed, we
73 say, ``I am editing a file'', rather than, ``I am editing a buffer
74 that I will soon save as a file of the same name''. Humans do not
75 usually need to make the distinction explicit. When dealing with a
76 computer program, however, it is good to keep the distinction in mind.
79 * Visiting Functions:: The usual interface functions for visiting.
80 * Subroutines of Visiting:: Lower-level subroutines that they use.
83 @node Visiting Functions
84 @subsection Functions for Visiting Files
85 @cindex visiting files, functions for
86 @cindex how to visit files
88 This section describes the functions normally used to visit files.
89 For historical reasons, these functions have names starting with
90 @samp{find-} rather than @samp{visit-}. @xref{Buffer File Name}, for
91 functions and variables that access the visited file name of a buffer or
92 that find an existing buffer by its visited file name.
94 In a Lisp program, if you want to look at the contents of a file but
95 not alter it, the fastest way is to use @code{insert-file-contents} in a
96 temporary buffer. Visiting the file is not necessary and takes longer.
97 @xref{Reading from Files}.
99 @deffn Command find-file filename &optional wildcards
100 This command selects a buffer visiting the file @var{filename},
101 using an existing buffer if there is one, and otherwise creating a
102 new buffer and reading the file into it. It also returns that buffer.
104 Aside from some technical details, the body of the @code{find-file}
105 function is basically equivalent to:
108 (switch-to-buffer (find-file-noselect filename nil nil wildcards))
112 (See @code{switch-to-buffer} in @ref{Switching Buffers}.)
114 If @var{wildcards} is non-@code{nil}, which is always true in an
115 interactive call, then @code{find-file} expands wildcard characters in
116 @var{filename} and visits all the matching files.
118 When @code{find-file} is called interactively, it prompts for
119 @var{filename} in the minibuffer.
122 @deffn Command find-file-literally filename
123 This command visits @var{filename}, like @code{find-file} does, but it
124 does not perform any format conversions (@pxref{Format Conversion}),
125 character code conversions (@pxref{Coding Systems}), or end-of-line
126 conversions (@pxref{Coding System Basics, End of line conversion}).
127 The buffer visiting the file is made unibyte, and its major mode is
128 Fundamental mode, regardless of the file name. File local variable
129 specifications in the file (@pxref{File Local Variables}) are
130 ignored, and automatic decompression and adding a newline at the end
131 of the file due to @code{require-final-newline} (@pxref{Saving
132 Buffers, require-final-newline}) are also disabled.
134 Note that if Emacs already has a buffer visiting the same file
135 non-literally, it will not visit the same file literally, but instead
136 just switch to the existing buffer. If you want to be sure of
137 accessing a file's contents literally, you should create a temporary
138 buffer and then read the file contents into it using
139 @code{insert-file-contents-literally} (@pxref{Reading from Files}).
142 @defun find-file-noselect filename &optional nowarn rawfile wildcards
143 This function is the guts of all the file-visiting functions. It
144 returns a buffer visiting the file @var{filename}. You may make the
145 buffer current or display it in a window if you wish, but this
146 function does not do so.
148 The function returns an existing buffer if there is one; otherwise it
149 creates a new buffer and reads the file into it. When
150 @code{find-file-noselect} uses an existing buffer, it first verifies
151 that the file has not changed since it was last visited or saved in
152 that buffer. If the file has changed, this function asks the user
153 whether to reread the changed file. If the user says @samp{yes}, any
154 edits previously made in the buffer are lost.
156 Reading the file involves decoding the file's contents (@pxref{Coding
157 Systems}), including end-of-line conversion, and format conversion
158 (@pxref{Format Conversion}). If @var{wildcards} is non-@code{nil},
159 then @code{find-file-noselect} expands wildcard characters in
160 @var{filename} and visits all the matching files.
162 This function displays warning or advisory messages in various peculiar
163 cases, unless the optional argument @var{nowarn} is non-@code{nil}. For
164 example, if it needs to create a buffer, and there is no file named
165 @var{filename}, it displays the message @samp{(New file)} in the echo
166 area, and leaves the buffer empty.
168 The @code{find-file-noselect} function normally calls
169 @code{after-find-file} after reading the file (@pxref{Subroutines of
170 Visiting}). That function sets the buffer major mode, parses local
171 variables, warns the user if there exists an auto-save file more recent
172 than the file just visited, and finishes by running the functions in
173 @code{find-file-hook}.
175 If the optional argument @var{rawfile} is non-@code{nil}, then
176 @code{after-find-file} is not called, and the
177 @code{find-file-not-found-functions} are not run in case of failure.
178 What's more, a non-@code{nil} @var{rawfile} value suppresses coding
179 system conversion and format conversion.
181 The @code{find-file-noselect} function usually returns the buffer that
182 is visiting the file @var{filename}. But, if wildcards are actually
183 used and expanded, it returns a list of buffers that are visiting the
188 (find-file-noselect "/etc/fstab")
189 @result{} #<buffer fstab>
194 @deffn Command find-file-other-window filename &optional wildcards
195 This command selects a buffer visiting the file @var{filename}, but
196 does so in a window other than the selected window. It may use
197 another existing window or split a window; see @ref{Switching
200 When this command is called interactively, it prompts for
204 @deffn Command find-file-read-only filename &optional wildcards
205 This command selects a buffer visiting the file @var{filename}, like
206 @code{find-file}, but it marks the buffer as read-only. @xref{Read Only
207 Buffers}, for related functions and variables.
209 When this command is called interactively, it prompts for
213 @defopt find-file-wildcards
214 If this variable is non-@code{nil}, then the various @code{find-file}
215 commands check for wildcard characters and visit all the files that
216 match them (when invoked interactively or when their @var{wildcards}
217 argument is non-@code{nil}). If this option is @code{nil}, then
218 the @code{find-file} commands ignore their @var{wildcards} argument
219 and never treat wildcard characters specially.
222 @defopt find-file-hook
223 The value of this variable is a list of functions to be called after a
224 file is visited. The file's local-variables specification (if any) will
225 have been processed before the hooks are run. The buffer visiting the
226 file is current when the hook functions are run.
228 This variable is a normal hook. @xref{Hooks}.
231 @defvar find-file-not-found-functions
232 The value of this variable is a list of functions to be called when
233 @code{find-file} or @code{find-file-noselect} is passed a nonexistent
234 file name. @code{find-file-noselect} calls these functions as soon as
235 it detects a nonexistent file. It calls them in the order of the list,
236 until one of them returns non-@code{nil}. @code{buffer-file-name} is
239 This is not a normal hook because the values of the functions are
240 used, and in many cases only some of the functions are called.
243 @defvar find-file-literally
244 This buffer-local variable, if set to a non-@code{nil} value, makes
245 @code{save-buffer} behave as if the buffer were visiting its file
246 literally, i.e., without conversions of any kind. The command
247 @code{find-file-literally} sets this variable's local value, but other
248 equivalent functions and commands can do that as well, e.g., to avoid
249 automatic addition of a newline at the end of the file. This variable
250 is permanent local, so it is unaffected by changes of major modes.
253 @node Subroutines of Visiting
254 @subsection Subroutines of Visiting
256 The @code{find-file-noselect} function uses two important subroutines
257 which are sometimes useful in user Lisp code: @code{create-file-buffer}
258 and @code{after-find-file}. This section explains how to use them.
260 @c FIXME This does not describe the default behavior, because
261 @c uniquify is enabled by default and advises this function.
262 @c This is confusing. uniquify should be folded into the function proper.
263 @defun create-file-buffer filename
264 This function creates a suitably named buffer for visiting
265 @var{filename}, and returns it. It uses @var{filename} (sans directory)
266 as the name if that name is free; otherwise, it appends a string such as
267 @samp{<2>} to get an unused name. See also @ref{Creating Buffers}.
268 Note that the @file{uniquify} library affects the result of this
269 function. @xref{Uniquify,,, emacs, The GNU Emacs Manual}.
271 @strong{Please note:} @code{create-file-buffer} does @emph{not}
272 associate the new buffer with a file and does not select the buffer.
273 It also does not use the default major mode.
277 (create-file-buffer "foo")
278 @result{} #<buffer foo>
281 (create-file-buffer "foo")
282 @result{} #<buffer foo<2>>
285 (create-file-buffer "foo")
286 @result{} #<buffer foo<3>>
290 This function is used by @code{find-file-noselect}.
291 It uses @code{generate-new-buffer} (@pxref{Creating Buffers}).
294 @defun after-find-file &optional error warn noauto after-find-file-from-revert-buffer nomodes
295 This function sets the buffer major mode, and parses local variables
296 (@pxref{Auto Major Mode}). It is called by @code{find-file-noselect}
297 and by the default revert function (@pxref{Reverting}).
299 @cindex new file message
300 @cindex file open error
301 If reading the file got an error because the file does not exist, but
302 its directory does exist, the caller should pass a non-@code{nil} value
303 for @var{error}. In that case, @code{after-find-file} issues a warning:
304 @samp{(New file)}. For more serious errors, the caller should usually not
305 call @code{after-find-file}.
307 If @var{warn} is non-@code{nil}, then this function issues a warning
308 if an auto-save file exists and is more recent than the visited file.
310 If @var{noauto} is non-@code{nil}, that says not to enable or disable
311 Auto-Save mode. The mode remains enabled if it was enabled before.
313 If @var{after-find-file-from-revert-buffer} is non-@code{nil}, that
314 means this call was from @code{revert-buffer}. This has no direct
315 effect, but some mode functions and hook functions check the value
318 If @var{nomodes} is non-@code{nil}, that means don't alter the buffer's
319 major mode, don't process local variables specifications in the file,
320 and don't run @code{find-file-hook}. This feature is used by
321 @code{revert-buffer} in some cases.
323 The last thing @code{after-find-file} does is call all the functions
324 in the list @code{find-file-hook}.
328 @section Saving Buffers
329 @cindex saving buffers
331 When you edit a file in Emacs, you are actually working on a buffer
332 that is visiting that file---that is, the contents of the file are
333 copied into the buffer and the copy is what you edit. Changes to the
334 buffer do not change the file until you @dfn{save} the buffer, which
335 means copying the contents of the buffer into the file.
337 @deffn Command save-buffer &optional backup-option
338 This function saves the contents of the current buffer in its visited
339 file if the buffer has been modified since it was last visited or saved.
340 Otherwise it does nothing.
342 @code{save-buffer} is responsible for making backup files. Normally,
343 @var{backup-option} is @code{nil}, and @code{save-buffer} makes a backup
344 file only if this is the first save since visiting the file. Other
345 values for @var{backup-option} request the making of backup files in
350 With an argument of 4 or 64, reflecting 1 or 3 @kbd{C-u}'s, the
351 @code{save-buffer} function marks this version of the file to be
352 backed up when the buffer is next saved.
355 With an argument of 16 or 64, reflecting 2 or 3 @kbd{C-u}'s, the
356 @code{save-buffer} function unconditionally backs up the previous
357 version of the file before saving it.
360 With an argument of 0, unconditionally do @emph{not} make any backup file.
364 @deffn Command save-some-buffers &optional save-silently-p pred
365 @anchor{Definition of save-some-buffers}
366 This command saves some modified file-visiting buffers. Normally it
367 asks the user about each buffer. But if @var{save-silently-p} is
368 non-@code{nil}, it saves all the file-visiting buffers without querying
371 @vindex save-some-buffers-default-predicate
372 The optional @var{pred} argument provides a predicate that controls
373 which buffers to ask about (or to save silently if
374 @var{save-silently-p} is non-@code{nil}). If @var{pred} is
375 @code{nil}, that means to use the value of
376 @code{save-some-buffers-default-predicate} instead of @var{pred}. If
377 the result is @code{nil}, it means ask only about file-visiting
378 buffers. If it is @code{t}, that means also offer to save certain
379 other non-file buffers---those that have a non-@code{nil} buffer-local
380 value of @code{buffer-offer-save} (@pxref{Killing Buffers}). A user
381 who says @samp{yes} to saving a non-file buffer is asked to specify
382 the file name to use. The @code{save-buffers-kill-emacs} function
383 passes the value @code{t} for @var{pred}.
385 If the predicate is neither @code{t} nor @code{nil}, then it should be
386 a function of no arguments. It will be called in each buffer to decide
387 whether to offer to save that buffer. If it returns a non-@code{nil}
388 value in a certain buffer, that means do offer to save that buffer.
391 @deffn Command write-file filename &optional confirm
392 @anchor{Definition of write-file}
393 This function writes the current buffer into file @var{filename}, makes
394 the buffer visit that file, and marks it not modified. Then it renames
395 the buffer based on @var{filename}, appending a string like @samp{<2>}
396 if necessary to make a unique buffer name. It does most of this work by
397 calling @code{set-visited-file-name} (@pxref{Buffer File Name}) and
400 If @var{confirm} is non-@code{nil}, that means to ask for confirmation
401 before overwriting an existing file. Interactively, confirmation is
402 required, unless the user supplies a prefix argument.
404 If @var{filename} is an existing directory, or a symbolic link to one,
405 @code{write-file} uses the name of the visited file, in directory
406 @var{filename}. If the buffer is not visiting a file, it uses the
410 Saving a buffer runs several hooks. It also performs format
411 conversion (@pxref{Format Conversion}). Note that these hooks,
412 described below, are only run by @code{save-buffer}, they are not run
413 by other primitives and functions that write buffer text to files, and
414 in particular auto-saving (@pxref{Auto-Saving}) doesn't run these
417 @defvar write-file-functions
418 The value of this variable is a list of functions to be called before
419 writing out a buffer to its visited file. If one of them returns
420 non-@code{nil}, the file is considered already written and the rest of
421 the functions are not called, nor is the usual code for writing the file
424 If a function in @code{write-file-functions} returns non-@code{nil}, it
425 is responsible for making a backup file (if that is appropriate).
426 To do so, execute the following code:
429 (or buffer-backed-up (backup-buffer))
432 You might wish to save the file modes value returned by
433 @code{backup-buffer} and use that (if non-@code{nil}) to set the mode
434 bits of the file that you write. This is what @code{save-buffer}
435 normally does. @xref{Making Backups,, Making Backup Files}.
437 The hook functions in @code{write-file-functions} are also responsible
438 for encoding the data (if desired): they must choose a suitable coding
439 system and end-of-line conversion (@pxref{Lisp and Coding Systems}),
440 perform the encoding (@pxref{Explicit Encoding}), and set
441 @code{last-coding-system-used} to the coding system that was used
442 (@pxref{Encoding and I/O}).
444 If you set this hook locally in a buffer, it is assumed to be
445 associated with the file or the way the contents of the buffer were
446 obtained. Thus the variable is marked as a permanent local, so that
447 changing the major mode does not alter a buffer-local value. On the
448 other hand, calling @code{set-visited-file-name} will reset it.
449 If this is not what you want, you might like to use
450 @code{write-contents-functions} instead.
452 Even though this is not a normal hook, you can use @code{add-hook} and
453 @code{remove-hook} to manipulate the list. @xref{Hooks}.
457 @defvar write-contents-functions
458 This works just like @code{write-file-functions}, but it is intended
459 for hooks that pertain to the buffer's contents, not to the particular
460 visited file or its location. Such hooks are usually set up by major
461 modes, as buffer-local bindings for this variable. This variable
462 automatically becomes buffer-local whenever it is set; switching to a
463 new major mode always resets this variable, but calling
464 @code{set-visited-file-name} does not.
466 If any of the functions in this hook returns non-@code{nil}, the file
467 is considered already written and the rest are not called and neither
468 are the functions in @code{write-file-functions}.
471 @defopt before-save-hook
472 This normal hook runs before a buffer is saved in its visited file,
473 regardless of whether that is done normally or by one of the hooks
474 described above. For instance, the @file{copyright.el} program uses
475 this hook to make sure the file you are saving has the current year in
476 its copyright notice.
480 @defopt after-save-hook
481 This normal hook runs after a buffer has been saved in its visited file.
482 One use of this hook is in Fast Lock mode; it uses this hook to save the
483 highlighting information in a cache file.
486 @defopt file-precious-flag
487 If this variable is non-@code{nil}, then @code{save-buffer} protects
488 against I/O errors while saving by writing the new file to a temporary
489 name instead of the name it is supposed to have, and then renaming it to
490 the intended name after it is clear there are no errors. This procedure
491 prevents problems such as a lack of disk space from resulting in an
494 As a side effect, backups are necessarily made by copying. @xref{Rename
495 or Copy}. Yet, at the same time, saving a precious file always breaks
496 all hard links between the file you save and other file names.
498 Some modes give this variable a non-@code{nil} buffer-local value
499 in particular buffers.
502 @defopt require-final-newline
503 This variable determines whether files may be written out that do
504 @emph{not} end with a newline. If the value of the variable is
505 @code{t}, then @code{save-buffer} silently adds a newline at the end
506 of the buffer whenever it does not already end in one. If the value
507 is @code{visit}, Emacs adds a missing newline just after it visits the
508 file. If the value is @code{visit-save}, Emacs adds a missing newline
509 both on visiting and on saving. For any other non-@code{nil} value,
510 @code{save-buffer} asks the user whether to add a newline each time
513 If the value of the variable is @code{nil}, then @code{save-buffer}
514 doesn't add newlines at all. @code{nil} is the default value, but a few
515 major modes set it to @code{t} in particular buffers.
518 See also the function @code{set-visited-file-name} (@pxref{Buffer File
521 @node Reading from Files
522 @section Reading from Files
523 @cindex reading from files
525 To copy the contents of a file into a buffer, use the function
526 @code{insert-file-contents}. (Don't use the command
527 @code{insert-file} in a Lisp program, as that sets the mark.)
529 @defun insert-file-contents filename &optional visit beg end replace
530 This function inserts the contents of file @var{filename} into the
531 current buffer after point. It returns a list of the absolute file name
532 and the length of the data inserted. An error is signaled if
533 @var{filename} is not the name of a file that can be read.
535 This function checks the file contents against the defined file
536 formats, and converts the file contents if appropriate and also calls
537 the functions in the list @code{after-insert-file-functions}.
538 @xref{Format Conversion}. Normally, one of the functions in the
539 @code{after-insert-file-functions} list determines the coding system
540 (@pxref{Coding Systems}) used for decoding the file's contents,
541 including end-of-line conversion. However, if the file contains null
542 bytes, it is by default visited without any code conversions.
543 @xref{Lisp and Coding Systems, inhibit-null-byte-detection}.
545 If @var{visit} is non-@code{nil}, this function additionally marks the
546 buffer as unmodified and sets up various fields in the buffer so that it
547 is visiting the file @var{filename}: these include the buffer's visited
548 file name and its last save file modtime. This feature is used by
549 @code{find-file-noselect} and you probably should not use it yourself.
551 If @var{beg} and @var{end} are non-@code{nil}, they should be numbers
552 that are byte offsets specifying the portion of the file to insert.
553 In this case, @var{visit} must be @code{nil}. For example,
556 (insert-file-contents filename nil 0 500)
560 inserts the first 500 characters of a file.
562 If the argument @var{replace} is non-@code{nil}, it means to replace the
563 contents of the buffer (actually, just the accessible portion) with the
564 contents of the file. This is better than simply deleting the buffer
565 contents and inserting the whole file, because (1) it preserves some
566 marker positions and (2) it puts less data in the undo list.
568 It is possible to read a special file (such as a FIFO or an I/O device)
569 with @code{insert-file-contents}, as long as @var{replace} and
570 @var{visit} are @code{nil}.
573 @defun insert-file-contents-literally filename &optional visit beg end replace
574 This function works like @code{insert-file-contents} except that it
575 does not run @code{find-file-hook}, and does not do format decoding,
576 character code conversion, automatic uncompression, and so on.
579 If you want to pass a file name to another process so that another
580 program can read the file, use the function @code{file-local-copy}; see
581 @ref{Magic File Names}.
583 @node Writing to Files
584 @section Writing to Files
585 @cindex writing to files
587 You can write the contents of a buffer, or part of a buffer, directly
588 to a file on disk using the @code{append-to-file} and
589 @code{write-region} functions. Don't use these functions to write to
590 files that are being visited; that could cause confusion in the
591 mechanisms for visiting.
593 @deffn Command append-to-file start end filename
594 This function appends the contents of the region delimited by
595 @var{start} and @var{end} in the current buffer to the end of file
596 @var{filename}. If that file does not exist, it is created. This
597 function returns @code{nil}.
599 An error is signaled if @var{filename} specifies a nonwritable file,
600 or a nonexistent file in a directory where files cannot be created.
602 When called from Lisp, this function is completely equivalent to:
605 (write-region start end filename t)
609 @deffn Command write-region start end filename &optional append visit lockname mustbenew
610 This function writes the region delimited by @var{start} and @var{end}
611 in the current buffer into the file specified by @var{filename}.
613 If @var{start} is @code{nil}, then the command writes the entire buffer
614 contents (@emph{not} just the accessible portion) to the file and
618 If @var{start} is a string, then @code{write-region} writes or appends
619 that string, rather than text from the buffer. @var{end} is ignored in
622 If @var{append} is non-@code{nil}, then the specified text is appended
623 to the existing file contents (if any). If @var{append} is a
624 number, @code{write-region} seeks to that byte offset from the start
625 of the file and writes the data from there.
627 If @var{mustbenew} is non-@code{nil}, then @code{write-region} asks
628 for confirmation if @var{filename} names an existing file. If
629 @var{mustbenew} is the symbol @code{excl}, then @code{write-region}
630 does not ask for confirmation, but instead it signals an error
631 @code{file-already-exists} if the file already exists.
633 The test for an existing file, when @var{mustbenew} is @code{excl}, uses
634 a special system feature. At least for files on a local disk, there is
635 no chance that some other program could create a file of the same name
636 before Emacs does, without Emacs's noticing.
638 If @var{visit} is @code{t}, then Emacs establishes an association
639 between the buffer and the file: the buffer is then visiting that file.
640 It also sets the last file modification time for the current buffer to
641 @var{filename}'s modtime, and marks the buffer as not modified. This
642 feature is used by @code{save-buffer}, but you probably should not use
646 If @var{visit} is a string, it specifies the file name to visit. This
647 way, you can write the data to one file (@var{filename}) while recording
648 the buffer as visiting another file (@var{visit}). The argument
649 @var{visit} is used in the echo area message and also for file locking;
650 @var{visit} is stored in @code{buffer-file-name}. This feature is used
651 to implement @code{file-precious-flag}; don't use it yourself unless you
652 really know what you're doing.
654 The optional argument @var{lockname}, if non-@code{nil}, specifies the
655 file name to use for purposes of locking and unlocking, overriding
656 @var{filename} and @var{visit} for that purpose.
658 The function @code{write-region} converts the data which it writes to
659 the appropriate file formats specified by @code{buffer-file-format}
660 and also calls the functions in the list
661 @code{write-region-annotate-functions}.
662 @xref{Format Conversion}.
664 Normally, @code{write-region} displays the message @samp{Wrote
665 @var{filename}} in the echo area. This message is inhibited if
666 @var{visit} is neither @code{t} nor @code{nil} nor a string, or if
667 Emacs is operating in batch mode (@pxref{Batch Mode}). This
668 feature is useful for programs that use files for internal purposes,
669 files that the user does not need to know about.
672 @defvar write-region-inhibit-fsync
673 If this variable's value is @code{nil}, @code{write-region} uses the
674 @code{fsync} system call after writing a file. Although this slows
675 Emacs down, it lessens the risk of data loss after power failure. If
676 the value is @code{t}, Emacs does not use @code{fsync}. The default
677 value is @code{nil} when Emacs is interactive, and @code{t} when Emacs
678 runs in batch mode. @xref{Files and Storage}.
681 @defmac with-temp-file file body@dots{}
682 @anchor{Definition of with-temp-file}
683 The @code{with-temp-file} macro evaluates the @var{body} forms with a
684 temporary buffer as the current buffer; then, at the end, it writes the
685 buffer contents into file @var{file}. It kills the temporary buffer
686 when finished, restoring the buffer that was current before the
687 @code{with-temp-file} form. Then it returns the value of the last form
690 The current buffer is restored even in case of an abnormal exit via
691 @code{throw} or error (@pxref{Nonlocal Exits}).
693 See also @code{with-temp-buffer} in @ref{Definition of
694 with-temp-buffer,, The Current Buffer}.
702 When two users edit the same file at the same time, they are likely
703 to interfere with each other. Emacs tries to prevent this situation
704 from arising by recording a @dfn{file lock} when a file is being
706 Emacs can then detect the first attempt to modify a buffer visiting a
707 file that is locked by another Emacs job, and ask the user what to do.
708 The file lock is really a file, a symbolic link with a special name,
709 stored in the same directory as the file you are editing. (On file
710 systems that do not support symbolic links, a regular file is used.)
712 When you access files using NFS, there may be a small probability that
713 you and another user will both lock the same file simultaneously.
714 If this happens, it is possible for the two users to make changes
715 simultaneously, but Emacs will still warn the user who saves second.
716 Also, the detection of modification of a buffer visiting a file changed
717 on disk catches some cases of simultaneous editing; see
718 @ref{Modification Time}.
720 @defun file-locked-p filename
721 This function returns @code{nil} if the file @var{filename} is not
722 locked. It returns @code{t} if it is locked by this Emacs process, and
723 it returns the name of the user who has locked it if it is locked by
728 (file-locked-p "foo")
734 @defun lock-buffer &optional filename
735 This function locks the file @var{filename}, if the current buffer is
736 modified. The argument @var{filename} defaults to the current buffer's
737 visited file. Nothing is done if the current buffer is not visiting a
738 file, or is not modified, or if the option @code{create-lockfiles} is
743 This function unlocks the file being visited in the current buffer,
744 if the buffer is modified. If the buffer is not modified, then
745 the file should not be locked, so this function does nothing. It also
746 does nothing if the current buffer is not visiting a file, or is not locked.
749 @defopt create-lockfiles
750 If this variable is @code{nil}, Emacs does not lock files.
753 @defun ask-user-about-lock file other-user
754 This function is called when the user tries to modify @var{file}, but it
755 is locked by another user named @var{other-user}. The default
756 definition of this function asks the user to say what to do. The value
757 this function returns determines what Emacs does next:
761 A value of @code{t} says to grab the lock on the file. Then
762 this user may edit the file and @var{other-user} loses the lock.
765 A value of @code{nil} says to ignore the lock and let this
766 user edit the file anyway.
770 This function may instead signal a @code{file-locked} error, in which
771 case the change that the user was about to make does not take place.
773 The error message for this error looks like this:
776 @error{} File is locked: @var{file} @var{other-user}
780 where @code{file} is the name of the file and @var{other-user} is the
781 name of the user who has locked the file.
784 If you wish, you can replace the @code{ask-user-about-lock} function
785 with your own version that makes the decision in another way.
788 @node Information about Files
789 @section Information about Files
790 @cindex file, information about
792 This section describes the functions for retrieving various types of
793 information about files (or directories or symbolic links), such as
794 whether a file is readable or writable, and its size. These functions
795 all take arguments which are file names. Except where noted, these
796 arguments need to specify existing files, or an error is signaled.
798 @cindex file names, trailing whitespace
799 @cindex trailing blanks in file names
800 Be careful with file names that end in spaces. On some filesystems
801 (notably, MS-Windows), trailing whitespace characters in file names
802 are silently and automatically ignored.
805 * Testing Accessibility:: Is a given file readable? Writable?
806 * Kinds of Files:: Is it a directory? A symbolic link?
807 * Truenames:: Eliminating symbolic links from a file name.
808 * File Attributes:: File sizes, modification times, etc.
809 * Extended Attributes:: Extended file attributes for access control.
810 * Locating Files:: How to find a file in standard places.
813 @node Testing Accessibility
814 @subsection Testing Accessibility
815 @cindex accessibility of a file
816 @cindex file accessibility
818 These functions test for permission to access a file for reading,
819 writing, or execution. Unless explicitly stated otherwise, they
820 recursively follow symbolic links for their file name arguments, at
821 all levels (at the level of the file itself and at all levels of
824 On some operating systems, more complex sets of access permissions
825 can be specified, via mechanisms such as Access Control Lists (ACLs).
826 @xref{Extended Attributes}, for how to query and set those
829 @defun file-exists-p filename
830 This function returns @code{t} if a file named @var{filename} appears
831 to exist. This does not mean you can necessarily read the file, only
832 that you can find out its attributes. (On Unix and GNU/Linux, this is
833 true if the file exists and you have execute permission on the
834 containing directories, regardless of the permissions of the file
837 If the file does not exist, or if access control policies prevent you
838 from finding its attributes, this function returns @code{nil}.
840 Directories are files, so @code{file-exists-p} returns @code{t} when
841 given a directory name. However, symbolic links are treated
842 specially; @code{file-exists-p} returns @code{t} for a symbolic link
843 name only if the target file exists.
846 @defun file-readable-p filename
847 This function returns @code{t} if a file named @var{filename} exists
848 and you can read it. It returns @code{nil} otherwise.
851 @defun file-executable-p filename
852 This function returns @code{t} if a file named @var{filename} exists and
853 you can execute it. It returns @code{nil} otherwise. On Unix and
854 GNU/Linux, if the file is a directory, execute permission means you can
855 check the existence and attributes of files inside the directory, and
856 open those files if their modes permit.
859 @defun file-writable-p filename
860 This function returns @code{t} if the file @var{filename} can be written
861 or created by you, and @code{nil} otherwise. A file is writable if the
862 file exists and you can write it. It is creatable if it does not exist,
863 but the specified directory does exist and you can write in that
866 In the example below, @file{foo} is not writable because the parent
867 directory does not exist, even though the user could create such a
872 (file-writable-p "~/no-such-dir/foo")
878 @defun file-accessible-directory-p dirname
879 This function returns @code{t} if you have permission to open existing
880 files in the directory whose name as a file is @var{dirname};
881 otherwise (or if there is no such directory), it returns @code{nil}.
882 The value of @var{dirname} may be either a directory name (such as
883 @file{/foo/}) or the file name of a file which is a directory
884 (such as @file{/foo}, without the final slash).
886 For example, from the following we deduce that any attempt to read a
887 file in @file{/foo/} will give an error:
890 (file-accessible-directory-p "/foo")
895 @defun access-file filename string
896 This function opens file @var{filename} for reading, then closes it and
897 returns @code{nil}. However, if the open fails, it signals an error
898 using @var{string} as the error message text.
901 @defun file-ownership-preserved-p filename &optional group
902 This function returns @code{t} if deleting the file @var{filename} and
903 then creating it anew would keep the file's owner unchanged. It also
904 returns @code{t} for nonexistent files.
906 If the optional argument @var{group} is non-@code{nil}, this function
907 also checks that the file's group would be unchanged.
909 If @var{filename} is a symbolic link, then, unlike the other functions
910 discussed here, @code{file-ownership-preserved-p} does @emph{not}
911 replace @var{filename} with its target. However, it does recursively
912 follow symbolic links at all levels of parent directories.
915 @defun file-modes filename
917 @cindex file permissions
918 @cindex permissions, file
920 This function returns the @dfn{mode bits} of @var{filename}---an
921 integer summarizing its read, write, and execution permissions.
922 Symbolic links in @var{filename} are recursively followed at all
923 levels. If the file does not exist, the return value is @code{nil}.
925 @xref{File permissions,,, coreutils, The @sc{gnu} @code{Coreutils}
926 Manual}, for a description of mode bits. For example, if the
927 low-order bit is 1, the file is executable by all users; if the
928 second-lowest-order bit is 1, the file is writable by all users; etc.
929 The highest possible value is 4095 (7777 octal), meaning that everyone
930 has read, write, and execute permission, the @acronym{SUID} bit is set
931 for both others and group, and the sticky bit is set.
933 @xref{Changing Files}, for the @code{set-file-modes} function, which
934 can be used to set these permissions.
938 (file-modes "~/junk/diffs")
939 @result{} 492 ; @r{Decimal integer.}
943 @result{} "754" ; @r{Convert to octal.}
947 (set-file-modes "~/junk/diffs" #o666)
953 -rw-rw-rw- 1 lewis lewis 3063 Oct 30 16:00 diffs
957 @cindex MS-DOS and file modes
958 @cindex file modes and MS-DOS
959 @strong{MS-DOS note:} On MS-DOS, there is no such thing as an
960 executable file mode bit. So @code{file-modes} considers a file
961 executable if its name ends in one of the standard executable
962 extensions, such as @file{.com}, @file{.bat}, @file{.exe}, and some
963 others. Files that begin with the Unix-standard @samp{#!} signature,
964 such as shell and Perl scripts, are also considered executable.
965 Directories are also reported as executable, for compatibility with
966 Unix. These conventions are also followed by @code{file-attributes}
967 (@pxref{File Attributes}).
971 @subsection Distinguishing Kinds of Files
972 @cindex file classification
973 @cindex classification of file types
975 This section describes how to distinguish various kinds of files, such
976 as directories, symbolic links, and ordinary files.
978 @defun file-symlink-p filename
979 @cindex file symbolic links
980 If the file @var{filename} is a symbolic link, the
981 @code{file-symlink-p} function returns its (non-recursive) link target
982 as a string. (The link target string is not necessarily the full
983 absolute file name of the target; determining the full file name that
984 the link points to is nontrivial, see below.) If the leading
985 directories of @var{filename} include symbolic links, this function
986 recursively follows them.
988 If the file @var{filename} is not a symbolic link, or does not exist,
989 @code{file-symlink-p} returns @code{nil}.
991 Here are a few examples of using this function:
995 (file-symlink-p "not-a-symlink")
999 (file-symlink-p "sym-link")
1000 @result{} "not-a-symlink"
1003 (file-symlink-p "sym-link2")
1004 @result{} "sym-link"
1007 (file-symlink-p "/bin")
1008 @result{} "/pub/bin"
1012 Note that in the third example, the function returned @file{sym-link},
1013 but did not proceed to resolve it, although that file is itself a
1014 symbolic link. This is what we meant by ``non-recursive'' above---the
1015 process of following the symbolic links does not recurse if the link
1016 target is itself a link.
1018 The string that this function returns is what is recorded in the
1019 symbolic link; it may or may not include any leading directories.
1020 This function does @emph{not} expand the link target to produce a
1021 fully-qualified file name, and in particular does not use the leading
1022 directories, if any, of the @var{filename} argument if the link target
1023 is not an absolute file name. Here's an example:
1027 (file-symlink-p "/foo/bar/baz")
1028 @result{} "some-file"
1033 Here, although @file{/foo/bar/baz} was given as a fully-qualified file
1034 name, the result is not, and in fact does not have any leading
1035 directories at all. And since @file{some-file} might itself be a
1036 symbolic link, you cannot simply prepend leading directories to it,
1037 nor even naively use @code{expand-file-name} (@pxref{File Name
1038 Expansion}) to produce its absolute file name.
1040 For this reason, this function is seldom useful if you need to
1041 determine more than just the fact that a file is or isn't a symbolic
1042 link. If you actually need the file name of the link target, use
1043 @code{file-chase-links} or @code{file-truename}, described in
1047 The next two functions recursively follow symbolic links at
1048 all levels for @var{filename}.
1050 @defun file-directory-p filename
1051 This function returns @code{t} if @var{filename} is the name of an
1052 existing directory, @code{nil} otherwise.
1056 (file-directory-p "~rms")
1060 (file-directory-p "~rms/lewis/files.texi")
1064 (file-directory-p "~rms/lewis/no-such-file")
1068 (file-directory-p "$HOME")
1073 (substitute-in-file-name "$HOME"))
1079 @defun file-regular-p filename
1080 This function returns @code{t} if the file @var{filename} exists and is
1081 a regular file (not a directory, named pipe, terminal, or
1086 @subsection Truenames
1087 @cindex truename (of file)
1089 The @dfn{truename} of a file is the name that you get by following
1090 symbolic links at all levels until none remain, then simplifying away
1091 @samp{.}@: and @samp{..}@: appearing as name components. This results
1092 in a sort of canonical name for the file. A file does not always have a
1093 unique truename; the number of distinct truenames a file has is equal to
1094 the number of hard links to the file. However, truenames are useful
1095 because they eliminate symbolic links as a cause of name variation.
1097 @defun file-truename filename
1098 This function returns the truename of the file @var{filename}. If the
1099 argument is not an absolute file name, this function first expands it
1100 against @code{default-directory}.
1102 This function does not expand environment variables. Only
1103 @code{substitute-in-file-name} does that. @xref{Definition of
1104 substitute-in-file-name}.
1106 If you may need to follow symbolic links preceding @samp{..}@:
1107 appearing as a name component, call @code{file-truename} without prior
1108 direct or indirect calls to @code{expand-file-name}. Otherwise, the
1109 file name component immediately preceding @samp{..} will be
1110 simplified away before @code{file-truename} is called. To
1111 eliminate the need for a call to @code{expand-file-name},
1112 @code{file-truename} handles @samp{~} in the same way that
1113 @code{expand-file-name} does. @xref{File Name Expansion,, Functions
1114 that Expand Filenames}.
1117 @defun file-chase-links filename &optional limit
1118 This function follows symbolic links, starting with @var{filename},
1119 until it finds a file name which is not the name of a symbolic link.
1120 Then it returns that file name. This function does @emph{not} follow
1121 symbolic links at the level of parent directories.
1123 If you specify a number for @var{limit}, then after chasing through
1124 that many links, the function just returns what it has even if that is
1125 still a symbolic link.
1128 To illustrate the difference between @code{file-chase-links} and
1129 @code{file-truename}, suppose that @file{/usr/foo} is a symbolic link to
1130 the directory @file{/home/foo}, and @file{/home/foo/hello} is an
1131 ordinary file (or at least, not a symbolic link) or nonexistent. Then
1135 (file-chase-links "/usr/foo/hello")
1136 ;; @r{This does not follow the links in the parent directories.}
1137 @result{} "/usr/foo/hello"
1138 (file-truename "/usr/foo/hello")
1139 ;; @r{Assuming that @file{/home} is not a symbolic link.}
1140 @result{} "/home/foo/hello"
1143 @defun file-equal-p file1 file2
1144 This function returns @code{t} if the files @var{file1} and
1145 @var{file2} name the same file. This is similar to comparing their
1146 truenames, except that remote file names are also handled in an
1147 appropriate manner. If @var{file1} or @var{file2} does not exist, the
1148 return value is unspecified.
1151 @defun file-name-case-insensitive-p filename
1152 Sometimes file names or their parts need to be compared as strings, in
1153 which case it's important to know whether the underlying filesystem is
1154 case-insensitive. This function returns @code{t} if file
1155 @var{filename} is on a case-insensitive filesystem. It always returns
1156 @code{t} on MS-DOS and MS-Windows. On Cygwin and Mac OS X,
1157 filesystems may or may not be case-insensitive, and the function tries
1158 to determine case-sensitivity by a runtime test. If the test is
1159 inconclusive, the function returns @code{t} on Cygwin and @code{nil}
1162 Currently this function always returns @code{nil} on platforms other
1163 than MS-DOS, MS-Windows, Cygwin, and Mac OS X. It does not detect
1164 case-insensitivity of mounted filesystems, such as Samba shares or
1165 NFS-mounted Windows volumes. On remote hosts, it assumes @code{t} for
1166 the @samp{smb} method. For all other connection methods, runtime
1167 tests are performed.
1170 @defun file-in-directory-p file dir
1171 This function returns @code{t} if @var{file} is a file in directory
1172 @var{dir}, or in a subdirectory of @var{dir}. It also returns
1173 @code{t} if @var{file} and @var{dir} are the same directory. It
1174 compares the truenames of the two directories. If @var{dir} does not
1175 name an existing directory, the return value is @code{nil}.
1178 @defun vc-responsible-backend file
1179 This function determines the responsible VC backend of the given
1180 @var{file}. For example, if @file{emacs.c} is a file tracked by Git,
1181 @w{@code{(vc-responsible-backend "emacs.c")}} returns @samp{Git}.
1182 Note that if @var{file} is a symbolic link,
1183 @code{vc-responsible-backend} will not resolve it---the backend of the
1184 symbolic link file itself is reported. To get the backend VC of the
1185 file to which @var{file} refers, wrap @var{file} with a symbolic link
1186 resolving function such as @code{file-chase-links}:
1189 (vc-responsible-backend (file-chase-links "emacs.c"))
1193 @node File Attributes
1194 @subsection File Attributes
1195 @cindex file attributes
1197 This section describes the functions for getting detailed
1198 information about a file, including the owner and group numbers, the
1199 number of names, the inode number, the size, and the times of access
1202 @defun file-newer-than-file-p filename1 filename2
1204 @cindex file modification time
1205 This function returns @code{t} if the file @var{filename1} is
1206 newer than file @var{filename2}. If @var{filename1} does not
1207 exist, it returns @code{nil}. If @var{filename1} does exist, but
1208 @var{filename2} does not, it returns @code{t}.
1210 In the following example, assume that the file @file{aug-19} was written
1211 on the 19th, @file{aug-20} was written on the 20th, and the file
1212 @file{no-file} doesn't exist at all.
1216 (file-newer-than-file-p "aug-19" "aug-20")
1220 (file-newer-than-file-p "aug-20" "aug-19")
1224 (file-newer-than-file-p "aug-19" "no-file")
1228 (file-newer-than-file-p "no-file" "aug-19")
1234 If the @var{filename} argument to the next two functions is a
1235 symbolic link, then these function do @emph{not} replace it with its
1236 target. However, they both recursively follow symbolic links at all
1237 levels of parent directories.
1239 @defun file-attributes filename &optional id-format
1240 @anchor{Definition of file-attributes}
1241 This function returns a list of attributes of file @var{filename}. If
1242 the specified file cannot be opened, it returns @code{nil}.
1243 The optional parameter @var{id-format} specifies the preferred format
1244 of attributes @acronym{UID} and @acronym{GID} (see below)---the
1245 valid values are @code{'string} and @code{'integer}. The latter is
1246 the default, but we plan to change that, so you should specify a
1247 non-@code{nil} value for @var{id-format} if you use the returned
1248 @acronym{UID} or @acronym{GID}.
1250 Accessor functions are provided to access the elements in this list.
1251 The accessors are mentioned along with the descriptions of the
1254 The elements of the list, in order, are:
1258 @code{t} for a directory, a string for a symbolic link (the name
1259 linked to), or @code{nil} for a text file
1260 (@code{file-attribute-type}).
1262 @c Wordy so as to prevent an overfull hbox. --rjc 15mar92
1264 The number of names the file has (@code{file-attribute-link-number}).
1265 Alternate names, also known as hard links, can be created by using the
1266 @code{add-name-to-file} function (@pxref{Changing Files}).
1269 The file's @acronym{UID}, normally as a string
1270 (@code{file-attribute-user-id}). However, if it does not correspond
1271 to a named user, the value is a number.
1274 The file's @acronym{GID}, likewise (@code{file-attribute-group-id}).
1277 The time of last access, as a list of four integers
1278 @code{(@var{sec-high} @var{sec-low} @var{microsec} @var{picosec})}
1279 (@code{file-attribute-access-time}). (This is similar to the value of
1280 @code{current-time}; see @ref{Time of Day}.) Note that on some
1281 FAT-based filesystems, only the date of last access is recorded, so
1282 this time will always hold the midnight of the day of last access.
1284 @cindex modification time of file
1286 The time of last modification as a list of four integers (as above)
1287 (@code{file-attribute-modification-time}). This is the last time when
1288 the file's contents were modified.
1291 The time of last status change as a list of four integers (as above)
1292 (@code{file-attribute-status-change-time}). This is the time of the
1293 last change to the file's access mode bits, its owner and group, and
1294 other information recorded in the filesystem for the file, beyond the
1298 The size of the file in bytes (@code{file-attribute-size}). This is
1299 floating point if the size is too large to fit in a Lisp integer.
1302 The file's modes, as a string of ten letters or dashes, as in
1303 @samp{ls -l} (@code{file-attribute-modes}).
1306 An unspecified value, present for backward compatibility.
1309 The file's inode number (@code{file-attribute-inode-number}). If
1310 possible, this is an integer. If the inode number is too large to be
1311 represented as an integer in Emacs Lisp but dividing it by
1312 @math{2^{16}} yields a representable integer, then the value has the
1313 form @code{(@var{high} . @var{low})}, where @var{low} holds the low 16
1314 bits. If the inode number is too wide for even that, the value is of
1315 the form @code{(@var{high} @var{middle} . @var{low})}, where
1316 @code{high} holds the high bits, @var{middle} the middle 24 bits, and
1317 @var{low} the low 16 bits.
1320 The filesystem number of the device that the file is on
1321 @code{file-attribute-device-number}). Depending on the magnitude of
1322 the value, this can be either an integer or a cons cell, in the same
1323 manner as the inode number. This element and the file's inode number
1324 together give enough information to distinguish any two files on the
1325 system---no two files can have the same values for both of these
1329 For example, here are the file attributes for @file{files.texi}:
1333 (file-attributes "files.texi" 'string)
1334 @result{} (nil 1 "lh" "users"
1335 (20614 64019 50040 152000)
1337 (20614 64555 902289 872000)
1345 and here is how the result is interpreted:
1349 is neither a directory nor a symbolic link.
1352 has only one name (the name @file{files.texi} in the current default
1356 is owned by the user with name @samp{lh}.
1359 is in the group with name @samp{users}.
1361 @item (20614 64019 50040 152000)
1362 was last accessed on October 23, 2012, at 20:12:03.050040152 UTC.
1364 @item (20000 23 0 0)
1365 was last modified on July 15, 2001, at 08:53:43 UTC.
1367 @item (20614 64555 902289 872000)
1368 last had its status changed on October 23, 2012, at 20:20:59.902289872 UTC.
1371 is 122295 bytes long. (It may not contain 122295 characters, though,
1372 if some of the bytes belong to multibyte sequences, and also if the
1373 end-of-line format is CR-LF.)
1376 has a mode of read and write access for the owner, group, and world.
1379 is merely a placeholder; it carries no information.
1381 @item (5888 2 . 43978)
1382 has an inode number of 6473924464520138.
1384 @item (15479 . 46724)
1385 is on the file-system device whose number is 1014478468.
1389 @defun file-nlinks filename
1390 This function returns the number of names (i.e., hard links) that
1391 file @var{filename} has. If the file does not exist, this function
1392 returns @code{nil}. Note that symbolic links have no effect on this
1393 function, because they are not considered to be names of the files
1399 -rw-rw-rw- 2 rms rms 4 Aug 19 01:27 foo
1400 -rw-rw-rw- 2 rms rms 4 Aug 19 01:27 foo1
1408 (file-nlinks "doesnt-exist")
1414 @node Extended Attributes
1415 @subsection Extended File Attributes
1416 @cindex extended file attributes
1418 On some operating systems, each file can be associated with arbitrary
1419 @dfn{extended file attributes}. At present, Emacs supports querying
1420 and setting two specific sets of extended file attributes: Access
1421 Control Lists (ACLs) and SELinux contexts. These extended file
1422 attributes are used, on some systems, to impose more sophisticated
1423 file access controls than the basic Unix-style permissions
1424 discussed in the previous sections.
1426 @cindex access control list
1428 @cindex SELinux context
1429 A detailed explanation of ACLs and SELinux is beyond the scope of
1430 this manual. For our purposes, each file can be associated with an
1431 @dfn{ACL}, which specifies its properties under an ACL-based file
1432 control system, and/or an @dfn{SELinux context}, which specifies its
1433 properties under the SELinux system.
1435 @defun file-acl filename
1436 This function returns the ACL for the file @var{filename}. The exact
1437 Lisp representation of the ACL is unspecified (and may change in
1438 future Emacs versions), but it is the same as what @code{set-file-acl}
1439 takes for its @var{acl} argument (@pxref{Changing Files}).
1441 The underlying ACL implementation is platform-specific; on GNU/Linux
1442 and BSD, Emacs uses the POSIX ACL interface, while on MS-Windows Emacs
1443 emulates the POSIX ACL interface with native file security APIs.
1445 If Emacs was not compiled with ACL support, or the file does not exist
1446 or is inaccessible, or Emacs was unable to determine the ACL entries
1447 for any other reason, then the return value is @code{nil}.
1450 @defun file-selinux-context filename
1451 This function returns the SELinux context of the file @var{filename},
1452 as a list of the form @code{(@var{user} @var{role} @var{type}
1453 @var{range})}. The list elements are the context's user, role, type,
1454 and range respectively, as Lisp strings; see the SELinux documentation
1455 for details about what these actually mean. The return value has the
1456 same form as what @code{set-file-selinux-context} takes for its
1457 @var{context} argument (@pxref{Changing Files}).
1459 If Emacs was not compiled with SELinux support, or the file does not
1460 exist or is inaccessible, or if the system does not support SELinux,
1461 then the return value is @code{(nil nil nil nil)}.
1464 @defun file-extended-attributes filename
1465 This function returns an alist of the Emacs-recognized extended
1466 attributes of file @var{filename}. Currently, it serves as a
1467 convenient way to retrieve both the ACL and SELinux context; you can
1468 then call the function @code{set-file-extended-attributes}, with the
1469 returned alist as its second argument, to apply the same file access
1470 attributes to another file (@pxref{Changing Files}).
1472 One of the elements is @code{(acl . @var{acl})}, where @var{acl} has
1473 the same form returned by @code{file-acl}.
1475 Another element is @code{(selinux-context . @var{context})}, where
1476 @var{context} is the SELinux context, in the same form returned by
1477 @code{file-selinux-context}.
1480 @node Locating Files
1481 @subsection Locating Files in Standard Places
1482 @cindex locate file in path
1483 @cindex find file in path
1485 This section explains how to search for a file in a list of
1486 directories (a @dfn{path}), or for an executable file in the standard
1487 list of executable file directories.
1489 To search for a user-specific configuration file, @xref{Standard
1490 File Names}, for the @code{locate-user-emacs-file} function.
1492 @defun locate-file filename path &optional suffixes predicate
1493 This function searches for a file whose name is @var{filename} in a
1494 list of directories given by @var{path}, trying the suffixes in
1495 @var{suffixes}. If it finds such a file, it returns the file's
1496 absolute file name (@pxref{Relative File Names}); otherwise it returns
1499 The optional argument @var{suffixes} gives the list of file-name
1500 suffixes to append to @var{filename} when searching.
1501 @code{locate-file} tries each possible directory with each of these
1502 suffixes. If @var{suffixes} is @code{nil}, or @code{("")}, then there
1503 are no suffixes, and @var{filename} is used only as-is. Typical
1504 values of @var{suffixes} are @code{exec-suffixes} (@pxref{Subprocess
1505 Creation}), @code{load-suffixes}, @code{load-file-rep-suffixes} and
1506 the return value of the function @code{get-load-suffixes} (@pxref{Load
1509 Typical values for @var{path} are @code{exec-path} (@pxref{Subprocess
1510 Creation}) when looking for executable programs, or @code{load-path}
1511 (@pxref{Library Search}) when looking for Lisp files. If
1512 @var{filename} is absolute, @var{path} has no effect, but the suffixes
1513 in @var{suffixes} are still tried.
1515 The optional argument @var{predicate}, if non-@code{nil}, specifies a
1516 predicate function for testing whether a candidate file is suitable.
1517 The predicate is passed the candidate file name as its single
1518 argument. If @var{predicate} is @code{nil} or omitted,
1519 @code{locate-file} uses @code{file-readable-p} as the predicate.
1520 @xref{Kinds of Files}, for other useful predicates, e.g.,
1521 @code{file-executable-p} and @code{file-directory-p}.
1523 For compatibility, @var{predicate} can also be one of the symbols
1524 @code{executable}, @code{readable}, @code{writable}, @code{exists}, or
1525 a list of one or more of these symbols.
1528 @defun executable-find program
1529 This function searches for the executable file of the named
1530 @var{program} and returns the absolute file name of the executable,
1531 including its file-name extensions, if any. It returns @code{nil} if
1532 the file is not found. The functions searches in all the directories
1533 in @code{exec-path}, and tries all the file-name extensions in
1534 @code{exec-suffixes} (@pxref{Subprocess Creation}).
1537 @node Changing Files
1538 @section Changing File Names and Attributes
1539 @c @cindex renaming files Duplicates rename-file
1540 @cindex copying files
1541 @cindex deleting files
1542 @cindex linking files
1543 @cindex setting modes of files
1545 The functions in this section rename, copy, delete, link, and set
1546 the modes (permissions) of files. Typically, they signal a
1547 @code{file-error} error if they fail to perform their function,
1548 reporting the system-dependent error message that describes the reason
1549 for the failure. If they fail because a file is missing, they signal
1550 a @code{file-missing} error instead.
1552 For performance, the operating system may cache or alias changes
1553 made by these functions instead of writing them immediately to
1554 secondary storage. @xref{Files and Storage}.
1556 In the functions that have an argument @var{newname}, if a file by the
1557 name of @var{newname} already exists, the actions taken depend on the
1558 value of the argument @var{ok-if-already-exists}:
1562 Signal a @code{file-already-exists} error if
1563 @var{ok-if-already-exists} is @code{nil}.
1566 Request confirmation if @var{ok-if-already-exists} is a number.
1569 Replace the old file without confirmation if @var{ok-if-already-exists}
1573 The next four commands all recursively follow symbolic links at all
1574 levels of parent directories for their first argument, but, if that
1575 argument is itself a symbolic link, then only @code{copy-file}
1576 replaces it with its (recursive) target.
1578 @deffn Command add-name-to-file oldname newname &optional ok-if-already-exists
1579 @cindex file with multiple names
1580 @cindex file hard link
1581 This function gives the file named @var{oldname} the additional name
1582 @var{newname}. This means that @var{newname} becomes a new hard
1583 link to @var{oldname}.
1585 In the first part of the following example, we list two files,
1586 @file{foo} and @file{foo3}.
1591 81908 -rw-rw-rw- 1 rms rms 29 Aug 18 20:32 foo
1592 84302 -rw-rw-rw- 1 rms rms 24 Aug 18 20:31 foo3
1596 Now we create a hard link, by calling @code{add-name-to-file}, then list
1597 the files again. This shows two names for one file, @file{foo} and
1602 (add-name-to-file "foo" "foo2")
1608 81908 -rw-rw-rw- 2 rms rms 29 Aug 18 20:32 foo
1609 81908 -rw-rw-rw- 2 rms rms 29 Aug 18 20:32 foo2
1610 84302 -rw-rw-rw- 1 rms rms 24 Aug 18 20:31 foo3
1614 Finally, we evaluate the following:
1617 (add-name-to-file "foo" "foo3" t)
1621 and list the files again. Now there are three names
1622 for one file: @file{foo}, @file{foo2}, and @file{foo3}. The old
1623 contents of @file{foo3} are lost.
1627 (add-name-to-file "foo1" "foo3")
1633 81908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo
1634 81908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo2
1635 81908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo3
1639 This function is meaningless on operating systems where multiple names
1640 for one file are not allowed. Some systems implement multiple names
1641 by copying the file instead.
1643 See also @code{file-nlinks} in @ref{File Attributes}.
1646 @deffn Command rename-file filename newname &optional ok-if-already-exists
1647 This command renames the file @var{filename} as @var{newname}.
1649 If @var{filename} has additional names aside from @var{filename}, it
1650 continues to have those names. In fact, adding the name @var{newname}
1651 with @code{add-name-to-file} and then deleting @var{filename} has the
1652 same effect as renaming, aside from momentary intermediate states.
1655 @deffn Command copy-file oldname newname &optional ok-if-already-exists time preserve-uid-gid preserve-extended-attributes
1656 This command copies the file @var{oldname} to @var{newname}. An
1657 error is signaled if @var{oldname} does not exist. If @var{newname}
1658 names a directory, it copies @var{oldname} into that directory,
1659 preserving its final name component.
1661 If @var{time} is non-@code{nil}, then this function gives the new file
1662 the same last-modified time that the old one has. (This works on only
1663 some operating systems.) If setting the time gets an error,
1664 @code{copy-file} signals a @code{file-date-error} error. In an
1665 interactive call, a prefix argument specifies a non-@code{nil} value
1668 If argument @var{preserve-uid-gid} is @code{nil}, we let the operating
1669 system decide the user and group ownership of the new file (this is
1670 usually set to the user running Emacs). If @var{preserve-uid-gid} is
1671 non-@code{nil}, we attempt to copy the user and group ownership of the
1672 file. This works only on some operating systems, and only if you have
1673 the correct permissions to do so.
1675 If the optional argument @var{preserve-permissions} is non-@code{nil},
1676 this function copies the file modes (or ``permissions'') of
1677 @var{oldname} to @var{newname}, as well as the Access Control List and
1678 SELinux context (if any). @xref{Information about Files}.
1680 Otherwise, the file modes of @var{newname} are left unchanged if it is
1681 an existing file, and set to those of @var{oldname}, masked by the
1682 default file permissions (see @code{set-default-file-modes} below), if
1683 @var{newname} is to be newly created. The Access Control List or
1684 SELinux context are not copied over in either case.
1687 @deffn Command make-symbolic-link filename newname &optional ok-if-already-exists
1689 @kindex file-already-exists
1690 This command makes a symbolic link to @var{filename}, named
1691 @var{newname}. This is like the shell command @samp{ln -s
1692 @var{filename} @var{newname}}.
1694 This function is not available on systems that don't support symbolic
1699 @vindex delete-by-moving-to-trash
1700 @deffn Command delete-file filename &optional trash
1702 This command deletes the file @var{filename}. If the file has
1703 multiple names, it continues to exist under the other names. If
1704 @var{filename} is a symbolic link, @code{delete-file} deletes only the
1705 symbolic link and not its target (though it does follow symbolic links
1706 at all levels of parent directories).
1708 A suitable kind of @code{file-error} error is signaled if the file
1709 does not exist, or is not deletable. (On Unix and GNU/Linux, a file
1710 is deletable if its directory is writable.)
1712 If the optional argument @var{trash} is non-@code{nil} and the
1713 variable @code{delete-by-moving-to-trash} is non-@code{nil}, this
1714 command moves the file into the system Trash instead of deleting it.
1715 @xref{Misc File Ops,,Miscellaneous File Operations, emacs, The GNU
1716 Emacs Manual}. When called interactively, @var{trash} is @code{t} if
1717 no prefix argument is given, and @code{nil} otherwise.
1719 See also @code{delete-directory} in @ref{Create/Delete Dirs}.
1722 @cindex file permissions, setting
1723 @cindex permissions, file
1724 @cindex file modes, setting
1725 @deffn Command set-file-modes filename mode
1726 This function sets the @dfn{file mode} (or @dfn{permissions}) of
1727 @var{filename} to @var{mode}. It recursively follows symbolic links
1728 at all levels for @var{filename}.
1730 If called non-interactively, @var{mode} must be an integer. Only the
1731 lowest 12 bits of the integer are used; on most systems, only the
1732 lowest 9 bits are meaningful. You can use the Lisp construct for
1733 octal numbers to enter @var{mode}. For example,
1736 (set-file-modes #o644)
1740 specifies that the file should be readable and writable for its owner,
1741 readable for group members, and readable for all other users.
1742 @xref{File permissions,,, coreutils, The @sc{gnu} @code{Coreutils}
1743 Manual}, for a description of mode bit specifications.
1745 Interactively, @var{mode} is read from the minibuffer using
1746 @code{read-file-modes} (see below), which lets the user type in either
1747 an integer or a string representing the permissions symbolically.
1749 @xref{File Attributes}, for the function @code{file-modes}, which
1750 returns the permissions of a file.
1753 @defun set-default-file-modes mode
1755 This function sets the default permissions for new files created by
1756 Emacs and its subprocesses. Every file created with Emacs initially
1757 has these permissions, or a subset of them (@code{write-region} will
1758 not grant execute permissions even if the default file permissions
1759 allow execution). On Unix and GNU/Linux, the default permissions are
1760 given by the bitwise complement of the @samp{umask} value.
1762 The argument @var{mode} should be an integer which specifies the
1763 permissions, similar to @code{set-file-modes} above. Only the lowest
1764 9 bits are meaningful.
1766 The default file permissions have no effect when you save a modified
1767 version of an existing file; saving a file preserves its existing
1771 @defmac with-file-modes mode body@dots{}
1772 This macro evaluates the @var{body} forms with the default
1773 permissions for new files temporarily set to @var{modes} (whose value
1774 is as for @code{set-file-modes} above). When finished, it restores
1775 the original default file permissions, and returns the value of the
1776 last form in @var{body}.
1778 This is useful for creating private files, for example.
1781 @defun default-file-modes
1782 This function returns the default file permissions, as an integer.
1785 @defun read-file-modes &optional prompt base-file
1786 This function reads a set of file mode bits from the minibuffer. The
1787 first optional argument @var{prompt} specifies a non-default prompt.
1788 Second second optional argument @var{base-file} is the name of a file
1789 on whose permissions to base the mode bits that this function returns,
1790 if what the user types specifies mode bits relative to permissions of
1793 If user input represents an octal number, this function returns that
1794 number. If it is a complete symbolic specification of mode bits, as
1795 in @code{"u=rwx"}, the function converts it to the equivalent numeric
1796 value using @code{file-modes-symbolic-to-number} and returns the
1797 result. If the specification is relative, as in @code{"o+g"}, then
1798 the permissions on which the specification is based are taken from the
1799 mode bits of @var{base-file}. If @var{base-file} is omitted or
1800 @code{nil}, the function uses @code{0} as the base mode bits. The
1801 complete and relative specifications can be combined, as in
1802 @code{"u+r,g+rx,o+r,g-w"}. @xref{File permissions,,, coreutils, The
1803 @sc{gnu} @code{Coreutils} Manual}, for a description of file mode
1807 @defun file-modes-symbolic-to-number modes &optional base-modes
1808 This function converts a symbolic file mode specification in
1809 @var{modes} into the equivalent integer. If the symbolic
1810 specification is based on an existing file, that file's mode bits are
1811 taken from the optional argument @var{base-modes}; if that argument is
1812 omitted or @code{nil}, it defaults to 0, i.e., no access rights at
1816 @defun set-file-times filename &optional time
1817 This function sets the access and modification times of @var{filename}
1818 to @var{time}. The return value is @code{t} if the times are successfully
1819 set, otherwise it is @code{nil}. @var{time} defaults to the current
1820 time and must be in the format returned by @code{current-time}
1821 (@pxref{Time of Day}).
1824 @defun set-file-extended-attributes filename attribute-alist
1825 This function sets the Emacs-recognized extended file attributes for
1826 @code{filename}. The second argument @var{attribute-alist} should be
1827 an alist of the same form returned by @code{file-extended-attributes}.
1828 The return value is @code{t} if the attributes are successfully set,
1829 otherwise it is @code{nil}.
1830 @xref{Extended Attributes}.
1833 @defun set-file-selinux-context filename context
1834 This function sets the SELinux security context for @var{filename} to
1835 @var{context}. The @var{context} argument should be a list
1836 @code{(@var{user} @var{role} @var{type} @var{range})}, where each
1837 element is a string. @xref{Extended Attributes}.
1839 The function returns @code{t} if it succeeds in setting the SELinux
1840 context of @var{filename}. It returns @code{nil} if the context was
1841 not set (e.g., if SELinux is disabled, or if Emacs was compiled
1842 without SELinux support).
1845 @defun set-file-acl filename acl
1846 This function sets the Access Control List for @var{filename} to
1847 @var{acl}. The @var{acl} argument should have the same form returned
1848 by the function @code{file-acl}. @xref{Extended Attributes}.
1850 The function returns @code{t} if it successfully sets the ACL of
1851 @var{filename}, @code{nil} otherwise.
1854 @node Files and Storage
1855 @section Files and Secondary Storage
1856 @cindex secondary storage
1858 After Emacs changes a file, there are two reasons the changes might
1859 not survive later failures of power or media, both having to do with
1860 efficiency. First, the operating system might alias written data with
1861 data already stored elsewhere on secondary storage until one file or
1862 the other is later modified; this will lose both files if the only
1863 copy on secondary storage is lost due to media failure. Second, the
1864 operating system might not write data to secondary storage
1865 immediately, which will lose the data if power is lost.
1867 @findex write-region
1868 Although both sorts of failures can largely be avoided by a suitably
1869 configured file system, such systems are typically more expensive or
1870 less efficient. In more-typical systems, to survive media failure you
1871 can copy the file to a different device, and to survive a power
1872 failure you can use the @code{write-region} function with the
1873 @code{write-region-inhibit-fsync} variable set to @code{nil}.
1874 @xref{Writing to Files}.
1880 Files are generally referred to by their names, in Emacs as elsewhere.
1881 File names in Emacs are represented as strings. The functions that
1882 operate on a file all expect a file name argument.
1884 In addition to operating on files themselves, Emacs Lisp programs
1885 often need to operate on file names; i.e., to take them apart and to use
1886 part of a name to construct related file names. This section describes
1887 how to manipulate file names.
1889 The functions in this section do not actually access files, so they
1890 can operate on file names that do not refer to an existing file or
1893 @findex cygwin-convert-file-name-from-windows
1894 @findex cygwin-convert-file-name-to-windows
1895 @cindex MS-Windows file-name syntax
1896 @cindex converting file names from/to MS-Windows syntax
1897 On MS-DOS and MS-Windows, these functions (like the function that
1898 actually operate on files) accept MS-DOS or MS-Windows file-name syntax,
1899 where backslashes separate the components, as well as Unix syntax; but
1900 they always return Unix syntax. This enables Lisp programs to specify
1901 file names in Unix syntax and work properly on all systems without
1902 change.@footnote{In MS-Windows versions of Emacs compiled for the Cygwin
1903 environment, you can use the functions
1904 @code{cygwin-convert-file-name-to-windows} and
1905 @code{cygwin-convert-file-name-from-windows} to convert between the
1906 two file-name syntaxes.}
1909 * File Name Components:: The directory part of a file name, and the rest.
1910 * Relative File Names:: Some file names are relative to a current directory.
1911 * Directory Names:: A directory's name as a directory
1912 is different from its name as a file.
1913 * File Name Expansion:: Converting relative file names to absolute ones.
1914 * Unique File Names:: Generating names for temporary files.
1915 * File Name Completion:: Finding the completions for a given file name.
1916 * Standard File Names:: If your package uses a fixed file name,
1917 how to handle various operating systems simply.
1920 @node File Name Components
1921 @subsection File Name Components
1922 @cindex directory part (of file name)
1923 @cindex nondirectory part (of file name)
1924 @cindex version number (in file name)
1926 The operating system groups files into directories. To specify a
1927 file, you must specify the directory and the file's name within that
1928 directory. Therefore, Emacs considers a file name as having two main
1929 parts: the @dfn{directory name} part, and the @dfn{nondirectory} part
1930 (or @dfn{file name within the directory}). Either part may be empty.
1931 Concatenating these two parts reproduces the original file name.
1933 On most systems, the directory part is everything up to and including
1934 the last slash (backslash is also allowed in input on MS-DOS or
1935 MS-Windows); the nondirectory part is the rest.
1937 For some purposes, the nondirectory part is further subdivided into
1938 the name proper and the @dfn{version number}. On most systems, only
1939 backup files have version numbers in their names.
1941 @defun file-name-directory filename
1942 This function returns the directory part of @var{filename}, as a
1943 directory name (@pxref{Directory Names}), or @code{nil} if
1944 @var{filename} does not include a directory part.
1946 On GNU and Unix systems, a string returned by this function always
1947 ends in a slash. On MS-DOS it can also end in a colon.
1951 (file-name-directory "lewis/foo") ; @r{Unix example}
1955 (file-name-directory "foo") ; @r{Unix example}
1961 @defun file-name-nondirectory filename
1962 This function returns the nondirectory part of @var{filename}.
1966 (file-name-nondirectory "lewis/foo")
1970 (file-name-nondirectory "foo")
1974 (file-name-nondirectory "lewis/")
1980 @defun file-name-sans-versions filename &optional keep-backup-version
1981 This function returns @var{filename} with any file version numbers,
1982 backup version numbers, or trailing tildes discarded.
1984 If @var{keep-backup-version} is non-@code{nil}, then true file version
1985 numbers understood as such by the file system are discarded from the
1986 return value, but backup version numbers are kept.
1990 (file-name-sans-versions "~rms/foo.~1~")
1991 @result{} "~rms/foo"
1994 (file-name-sans-versions "~rms/foo~")
1995 @result{} "~rms/foo"
1998 (file-name-sans-versions "~rms/foo")
1999 @result{} "~rms/foo"
2004 @defun file-name-extension filename &optional period
2005 This function returns @var{filename}'s final extension, if any,
2006 after applying @code{file-name-sans-versions} to remove any
2007 version/backup part. The extension, in a file name, is the part that
2008 follows the last @samp{.} in the last name component (minus any
2009 version/backup part).
2011 This function returns @code{nil} for extensionless file names such as
2012 @file{foo}. It returns @code{""} for null extensions, as in
2013 @file{foo.}. If the last component of a file name begins with a
2014 @samp{.}, that @samp{.} doesn't count as the beginning of an
2015 extension. Thus, @file{.emacs}'s extension is @code{nil}, not
2018 If @var{period} is non-@code{nil}, then the returned value includes
2019 the period that delimits the extension, and if @var{filename} has no
2020 extension, the value is @code{""}.
2023 @defun file-name-sans-extension filename
2024 This function returns @var{filename} minus its extension, if any. The
2025 version/backup part, if present, is only removed if the file has an
2026 extension. For example,
2029 (file-name-sans-extension "foo.lose.c")
2030 @result{} "foo.lose"
2031 (file-name-sans-extension "big.hack/foo")
2032 @result{} "big.hack/foo"
2033 (file-name-sans-extension "/my/home/.emacs")
2034 @result{} "/my/home/.emacs"
2035 (file-name-sans-extension "/my/home/.emacs.el")
2036 @result{} "/my/home/.emacs"
2037 (file-name-sans-extension "~/foo.el.~3~")
2039 (file-name-sans-extension "~/foo.~3~")
2040 @result{} "~/foo.~3~"
2043 Note that the @samp{.~3~} in the two last examples is the backup part,
2047 @defun file-name-base &optional filename
2048 This function is the composition of @code{file-name-sans-extension}
2049 and @code{file-name-nondirectory}. For example,
2052 (file-name-base "/my/home/foo.c")
2056 The @var{filename} argument defaults to @code{buffer-file-name}.
2059 @node Relative File Names
2060 @subsection Absolute and Relative File Names
2061 @cindex absolute file name
2062 @cindex relative file name
2064 All the directories in the file system form a tree starting at the
2065 root directory. A file name can specify all the directory names
2066 starting from the root of the tree; then it is called an
2067 @dfn{absolute} file name. Or it can specify the position of the file
2068 in the tree relative to a default directory; then it is called a
2069 @dfn{relative} file name. On Unix and GNU/Linux, an absolute file
2070 name starts with a @samp{/} or a @samp{~}
2071 (@pxref{abbreviate-file-name}), and a relative one does not. On
2072 MS-DOS and MS-Windows, an absolute file name starts with a slash or a
2073 backslash, or with a drive specification @samp{@var{x}:/}, where
2074 @var{x} is the @dfn{drive letter}.
2076 @defun file-name-absolute-p filename
2077 This function returns @code{t} if file @var{filename} is an absolute
2078 file name, @code{nil} otherwise.
2082 (file-name-absolute-p "~rms/foo")
2086 (file-name-absolute-p "rms/foo")
2090 (file-name-absolute-p "/user/rms/foo")
2096 Given a possibly relative file name, you can convert it to an
2097 absolute name using @code{expand-file-name} (@pxref{File Name
2098 Expansion}). This function converts absolute file names to relative
2101 @defun file-relative-name filename &optional directory
2102 This function tries to return a relative name that is equivalent to
2103 @var{filename}, assuming the result will be interpreted relative to
2104 @var{directory} (an absolute directory name or directory file name).
2105 If @var{directory} is omitted or @code{nil}, it defaults to the
2106 current buffer's default directory.
2108 On some operating systems, an absolute file name begins with a device
2109 name. On such systems, @var{filename} has no relative equivalent based
2110 on @var{directory} if they start with two different device names. In
2111 this case, @code{file-relative-name} returns @var{filename} in absolute
2115 (file-relative-name "/foo/bar" "/foo/")
2117 (file-relative-name "/foo/bar" "/hack/")
2118 @result{} "../foo/bar"
2122 @node Directory Names
2123 @subsection Directory Names
2124 @cindex directory name
2125 @cindex directory file name
2126 @cindex file name of directory
2128 A @dfn{directory name} is the name of a directory. A directory is
2129 actually a kind of file, so it has a file name (called the
2130 @dfn{directory file name}, which is related to the directory name but
2131 not identical to it. (This is not quite the same as the usual Unix
2132 terminology.) These two different names for the same entity are
2133 related by a syntactic transformation. On GNU and Unix systems, this
2134 is simple: a directory name ends in a slash, whereas the directory
2135 file name lacks that slash. On MS-DOS the relationship is more
2138 The difference between directory name and directory file name is
2139 subtle but crucial. When an Emacs variable or function argument is
2140 described as being a directory name, a directory file name is not
2141 acceptable. When @code{file-name-directory} returns a string, that is
2142 always a directory name.
2144 The following two functions convert between directory names and
2145 directory file names. They do nothing special with environment
2146 variable substitutions such as @samp{$HOME}, and the constructs
2147 @samp{~}, @samp{.} and @samp{..}.
2149 @defun file-name-as-directory filename
2150 This function returns a string representing @var{filename} in a form
2151 that the operating system will interpret as the name of a directory (a
2152 directory name). On most systems, this means appending a slash to the
2153 string (if it does not already end in one).
2157 (file-name-as-directory "~rms/lewis")
2158 @result{} "~rms/lewis/"
2163 @defun directory-name-p filename
2164 This function returns non-@code{nil} if @var{filename} ends with a
2165 directory separator character. This is the forward slash @samp{/} on
2166 Unix and GNU systems; MS-Windows and MS-DOS recognize both the forward
2167 slash and the backslash @samp{\} as directory separators.
2170 @defun directory-file-name dirname
2171 This function returns a string representing @var{dirname} in a form
2172 that the operating system will interpret as the name of a file (a
2173 directory file name). On most systems, this means removing the final
2174 slash (or backslash) from the string.
2178 (directory-file-name "~lewis/")
2184 Given a directory name, you can combine it with a relative file name
2185 using @code{concat}:
2188 (concat @var{dirname} @var{relfile})
2192 Be sure to verify that the file name is relative before doing that.
2193 If you use an absolute file name, the results could be syntactically
2194 invalid or refer to the wrong file.
2196 If you want to use a directory file name in making such a
2197 combination, you must first convert it to a directory name using
2198 @code{file-name-as-directory}:
2201 (concat (file-name-as-directory @var{dirfile}) @var{relfile})
2205 Don't try concatenating a slash by hand, as in
2209 (concat @var{dirfile} "/" @var{relfile})
2213 because this is not portable. Always use
2214 @code{file-name-as-directory}.
2216 To avoid the issues mentioned above, or if the @var{dirname} value
2217 might be nil (for example, from an element of @code{load-path}), use:
2220 (expand-file-name @var{relfile} @var{dirname})
2223 To convert a directory name to its abbreviation, use this
2226 @cindex file name abbreviations
2227 @cindex abbreviated file names
2228 @vindex directory-abbrev-alist
2229 @defun abbreviate-file-name filename
2230 @anchor{abbreviate-file-name}
2231 This function returns an abbreviated form of @var{filename}. It
2232 applies the abbreviations specified in @code{directory-abbrev-alist}
2233 (@pxref{File Aliases,,File Aliases, emacs, The GNU Emacs Manual}),
2234 then substitutes @samp{~} for the user's home directory if the
2235 argument names a file in the home directory or one of its
2236 subdirectories. If the home directory is a root directory, it is not
2237 replaced with @samp{~}, because this does not make the result shorter
2240 You can use this function for directory names and for file names,
2241 because it recognizes abbreviations even as part of the name.
2244 @node File Name Expansion
2245 @subsection Functions that Expand Filenames
2246 @cindex expansion of file names
2248 @dfn{Expanding} a file name means converting a relative file name to
2249 an absolute one. Since this is done relative to a default directory,
2250 you must specify the default directory name as well as the file name
2251 to be expanded. It also involves expanding abbreviations like
2254 (@pxref{abbreviate-file-name}),
2256 and eliminating redundancies like @file{./} and @file{@var{name}/../}.
2258 @defun expand-file-name filename &optional directory
2259 This function converts @var{filename} to an absolute file name. If
2260 @var{directory} is supplied, it is the default directory to start with
2261 if @var{filename} is relative. (The value of @var{directory} should
2262 itself be an absolute directory name or directory file name; it may
2263 start with @samp{~}.) Otherwise, the current buffer's value of
2264 @code{default-directory} is used. For example:
2268 (expand-file-name "foo")
2269 @result{} "/xcssun/users/rms/lewis/foo"
2272 (expand-file-name "../foo")
2273 @result{} "/xcssun/users/rms/foo"
2276 (expand-file-name "foo" "/usr/spool/")
2277 @result{} "/usr/spool/foo"
2281 If the part of the combined file name before the first slash is
2282 @samp{~}, it expands to the value of the @env{HOME} environment
2283 variable (usually your home directory). If the part before the first
2284 slash is @samp{~@var{user}} and if @var{user} is a valid login name,
2285 it expands to @var{user}'s home directory.
2287 Filenames containing @samp{.} or @samp{..} are simplified to their
2292 (expand-file-name "bar/../foo")
2293 @result{} "/xcssun/users/rms/lewis/foo"
2297 In some cases, a leading @samp{..} component can remain in the output:
2301 (expand-file-name "../home" "/")
2302 @result{} "/../home"
2307 This is for the sake of filesystems that have the concept of a
2308 superroot above the root directory @file{/}. On other filesystems,
2309 @file{/../} is interpreted exactly the same as @file{/}.
2311 Note that @code{expand-file-name} does @emph{not} expand environment
2312 variables; only @code{substitute-in-file-name} does that:
2316 (expand-file-name "$HOME/foo")
2317 @result{} "/xcssun/users/rms/lewis/$HOME/foo"
2321 Note also that @code{expand-file-name} does not follow symbolic links
2322 at any level. This results in a difference between the way
2323 @code{file-truename} and @code{expand-file-name} treat @samp{..}.
2324 Assuming that @samp{/tmp/bar} is a symbolic link to the directory
2325 @samp{/tmp/foo/bar} we get:
2329 (file-truename "/tmp/bar/../myfile")
2330 @result{} "/tmp/foo/myfile"
2333 (expand-file-name "/tmp/bar/../myfile")
2334 @result{} "/tmp/myfile"
2338 If you may need to follow symbolic links preceding @samp{..}, you
2339 should make sure to call @code{file-truename} without prior direct or
2340 indirect calls to @code{expand-file-name}. @xref{Truenames}.
2343 @defvar default-directory
2344 The value of this buffer-local variable is the default directory for the
2345 current buffer. It should be an absolute directory name; it may start
2346 with @samp{~}. This variable is buffer-local in every buffer.
2348 @code{expand-file-name} uses the default directory when its second
2349 argument is @code{nil}.
2351 The value is always a string ending with a slash.
2356 @result{} "/user/lewis/manual/"
2361 @defun substitute-in-file-name filename
2362 @anchor{Definition of substitute-in-file-name}
2363 This function replaces environment variable references in
2364 @var{filename} with the environment variable values. Following
2365 standard Unix shell syntax, @samp{$} is the prefix to substitute an
2366 environment variable value. If the input contains @samp{$$}, that is
2367 converted to @samp{$}; this gives the user a way to quote a
2370 The environment variable name is the series of alphanumeric characters
2371 (including underscores) that follow the @samp{$}. If the character following
2372 the @samp{$} is a @samp{@{}, then the variable name is everything up to the
2375 Calling @code{substitute-in-file-name} on output produced by
2376 @code{substitute-in-file-name} tends to give incorrect results. For
2377 instance, use of @samp{$$} to quote a single @samp{$} won't work
2378 properly, and @samp{$} in an environment variable's value could lead
2379 to repeated substitution. Therefore, programs that call this function
2380 and put the output where it will be passed to this function need to
2381 double all @samp{$} characters to prevent subsequent incorrect
2384 @c Wordy to avoid overfull hbox. --rjc 15mar92
2385 Here we assume that the environment variable @env{HOME}, which holds
2386 the user's home directory name, has value @samp{/xcssun/users/rms}.
2390 (substitute-in-file-name "$HOME/foo")
2391 @result{} "/xcssun/users/rms/foo"
2395 After substitution, if a @samp{~} or a @samp{/} appears immediately
2396 after another @samp{/}, the function discards everything before it (up
2397 through the immediately preceding @samp{/}).
2401 (substitute-in-file-name "bar/~/foo")
2405 (substitute-in-file-name "/usr/local/$HOME/foo")
2406 @result{} "/xcssun/users/rms/foo"
2407 ;; @r{@file{/usr/local/} has been discarded.}
2413 Sometimes, it is not desired to expand file names. In such cases,
2414 the file name can be quoted to suppress the expansion, and to handle
2415 the file name literally. Quoting happens by prefixing the file name
2418 @defmac file-name-quote name
2419 This macro adds the quotation prefix @samp{/:} to the file @var{name}.
2420 For a local file @var{name}, it prefixes @var{name} with @samp{/:}.
2421 If @var{name} is a remote file name, the local part of @var{name} is
2422 quoted. If @var{name} is already a quoted file name, @var{name} is
2427 (substitute-in-file-name (file-name-quote "bar/~/foo"))
2428 @result{} "/:bar/~/foo"
2432 (substitute-in-file-name (file-name-quote "/ssh:host:bar/~/foo"))
2433 @result{} "/ssh:host:/:bar/~/foo"
2437 The macro cannot be used to suppress file name handlers from magic
2438 file names (@pxref{Magic File Names}).
2441 @defmac file-name-unquote name
2442 This macro removes the quotation prefix @samp{/:} from the file
2443 @var{name}, if any. If @var{name} is a remote file name, the local
2444 part of @var{name} is unquoted.
2447 @defmac file-name-quoted-p name
2448 This macro returns non-@code{nil}, when @var{name} is quoted with the
2449 prefix @samp{/:}. If @var{name} is a remote file name, the local part
2450 of @var{name} is checked.
2454 @node Unique File Names
2455 @subsection Generating Unique File Names
2456 @cindex unique file names
2457 @cindex temporary files
2459 Some programs need to write temporary files. Here is the usual way to
2460 construct a name for such a file:
2463 (make-temp-file @var{name-of-application})
2467 The job of @code{make-temp-file} is to prevent two different users or
2468 two different jobs from trying to use the exact same file name.
2470 @defun make-temp-file prefix &optional dir-flag suffix
2471 This function creates a temporary file and returns its name. Emacs
2472 creates the temporary file's name by adding to @var{prefix} some
2473 random characters that are different in each Emacs job. The result is
2474 guaranteed to be a newly created empty file. On MS-DOS, this function
2475 can truncate the @var{string} prefix to fit into the 8+3 file-name
2476 limits. If @var{prefix} is a relative file name, it is expanded
2477 against @code{temporary-file-directory}.
2481 (make-temp-file "foo")
2482 @result{} "/tmp/foo232J6v"
2486 When @code{make-temp-file} returns, the file has been created and is
2487 empty. At that point, you should write the intended contents into the
2490 If @var{dir-flag} is non-@code{nil}, @code{make-temp-file} creates an
2491 empty directory instead of an empty file. It returns the file name,
2492 not the directory name, of that directory. @xref{Directory Names}.
2494 If @var{suffix} is non-@code{nil}, @code{make-temp-file} adds it at
2495 the end of the file name.
2497 To prevent conflicts among different libraries running in the same
2498 Emacs, each Lisp program that uses @code{make-temp-file} should have its
2499 own @var{prefix}. The number added to the end of @var{prefix}
2500 distinguishes between the same application running in different Emacs
2501 jobs. Additional added characters permit a large number of distinct
2502 names even in one Emacs job.
2505 The default directory for temporary files is controlled by the
2506 variable @code{temporary-file-directory}. This variable gives the user
2507 a uniform way to specify the directory for all temporary files. Some
2508 programs use @code{small-temporary-file-directory} instead, if that is
2509 non-@code{nil}. To use it, you should expand the prefix against
2510 the proper directory before calling @code{make-temp-file}.
2512 @defopt temporary-file-directory
2513 @cindex @env{TMPDIR} environment variable
2514 @cindex @env{TMP} environment variable
2515 @cindex @env{TEMP} environment variable
2516 This variable specifies the directory name for creating temporary files.
2517 Its value should be a directory name (@pxref{Directory Names}), but it
2518 is good for Lisp programs to cope if the value is a directory's file
2519 name instead. Using the value as the second argument to
2520 @code{expand-file-name} is a good way to achieve that.
2522 The default value is determined in a reasonable way for your operating
2523 system; it is based on the @env{TMPDIR}, @env{TMP} and @env{TEMP}
2524 environment variables, with a fall-back to a system-dependent name if
2525 none of these variables is defined.
2527 Even if you do not use @code{make-temp-file} to create the temporary
2528 file, you should still use this variable to decide which directory to
2529 put the file in. However, if you expect the file to be small, you
2530 should use @code{small-temporary-file-directory} first if that is
2534 @defopt small-temporary-file-directory
2535 This variable specifies the directory name for
2536 creating certain temporary files, which are likely to be small.
2538 If you want to write a temporary file which is likely to be small, you
2539 should compute the directory like this:
2543 (expand-file-name @var{prefix}
2544 (or small-temporary-file-directory
2545 temporary-file-directory)))
2549 @defun make-temp-name base-name
2550 This function generates a string that might be a unique file
2551 name. The name starts with @var{base-name}, and has several random
2552 characters appended to it, which are different in each Emacs job. It
2553 is like @code{make-temp-file} except that (i) it just constructs a
2554 name and does not create a file, (ii) @var{base-name} should be an
2555 absolute file name that is not magic, and (iii) if the returned file
2556 name is magic, it might name an existing file. @xref{Magic File
2559 @strong{Warning:} In most cases, you should not use this function; use
2560 @code{make-temp-file} instead! This function is susceptible to a race
2561 condition, between the @code{make-temp-name} call and the creation of
2562 the file, which in some cases may cause a security hole.
2565 Sometimes, it is necessary to create a temporary file on a remote host
2566 or a mounted directory. The following two functions support this.
2568 @defun make-nearby-temp-file prefix &optional dir-flag suffix
2569 This function is similar to @code{make-temp-file}, but it creates a
2570 temporary file as close as possible to @code{default-directory}. If
2571 @var{prefix} is a relative file name, and @code{default-directory} is
2572 a remote file name or located on a mounted file systems, the temporary
2573 file is created in the directory returned by the function
2574 @code{temporary-file-directory}. Otherwise, the function
2575 @code{make-temp-file} is used. @var{prefix}, @var{dir-flag} and
2576 @var{suffix} have the same meaning as in @code{make-temp-file}.
2580 (let ((default-directory "/ssh:remotehost:"))
2581 (make-nearby-temp-file "foo"))
2582 @result{} "/ssh:remotehost:/tmp/foo232J6v"
2587 @defun temporary-file-directory
2588 The directory for writing temporary files via
2589 @code{make-nearby-temp-file}. In case of a remote
2590 @code{default-directory}, this is a directory for temporary files on
2591 that remote host. If such a directory does not exist, or
2592 @code{default-directory} ought to be located on a mounted file system
2593 (see @code{mounted-file-systems}), the function returns
2594 @code{default-directory}. For a non-remote and non-mounted
2595 @code{default-directory}, the value of the variable
2596 @code{temporary-file-directory} is returned.
2599 In order to extract the local part of the path name from a temporary
2600 file, @code{file-local-name} could be used.
2602 @node File Name Completion
2603 @subsection File Name Completion
2604 @cindex file name completion subroutines
2605 @cindex completion, file name
2607 This section describes low-level subroutines for completing a file
2608 name. For higher level functions, see @ref{Reading File Names}.
2610 @defun file-name-all-completions partial-filename directory
2611 This function returns a list of all possible completions for a file
2612 whose name starts with @var{partial-filename} in directory
2613 @var{directory}. The order of the completions is the order of the files
2614 in the directory, which is unpredictable and conveys no useful
2617 The argument @var{partial-filename} must be a file name containing no
2618 directory part and no slash (or backslash on some systems). The current
2619 buffer's default directory is prepended to @var{directory}, if
2620 @var{directory} is not absolute.
2622 In the following example, suppose that @file{~rms/lewis} is the current
2623 default directory, and has five files whose names begin with @samp{f}:
2624 @file{foo}, @file{file~}, @file{file.c}, @file{file.c.~1~}, and
2629 (file-name-all-completions "f" "")
2630 @result{} ("foo" "file~" "file.c.~2~"
2631 "file.c.~1~" "file.c")
2635 (file-name-all-completions "fo" "")
2641 @defun file-name-completion filename directory &optional predicate
2642 This function completes the file name @var{filename} in directory
2643 @var{directory}. It returns the longest prefix common to all file names
2644 in directory @var{directory} that start with @var{filename}. If
2645 @var{predicate} is non-@code{nil} then it ignores possible completions
2646 that don't satisfy @var{predicate}, after calling that function
2647 with one argument, the expanded absolute file name.
2649 If only one match exists and @var{filename} matches it exactly, the
2650 function returns @code{t}. The function returns @code{nil} if directory
2651 @var{directory} contains no name starting with @var{filename}.
2653 In the following example, suppose that the current default directory
2654 has five files whose names begin with @samp{f}: @file{foo},
2655 @file{file~}, @file{file.c}, @file{file.c.~1~}, and
2660 (file-name-completion "fi" "")
2665 (file-name-completion "file.c.~1" "")
2666 @result{} "file.c.~1~"
2670 (file-name-completion "file.c.~1~" "")
2675 (file-name-completion "file.c.~3" "")
2681 @defopt completion-ignored-extensions
2682 @code{file-name-completion} usually ignores file names that end in any
2683 string in this list. It does not ignore them when all the possible
2684 completions end in one of these suffixes. This variable has no effect
2685 on @code{file-name-all-completions}.
2687 A typical value might look like this:
2691 completion-ignored-extensions
2692 @result{} (".o" ".elc" "~" ".dvi")
2696 If an element of @code{completion-ignored-extensions} ends in a slash
2697 @samp{/}, it signals a directory. The elements which do @emph{not} end
2698 in a slash will never match a directory; thus, the above value will not
2699 filter out a directory named @file{foo.elc}.
2702 @node Standard File Names
2703 @subsection Standard File Names
2705 Sometimes, an Emacs Lisp program needs to specify a standard file
2706 name for a particular use---typically, to hold configuration data
2707 specified by the current user. Usually, such files should be located
2708 in the directory specified by @code{user-emacs-directory}, which is
2709 @file{~/.emacs.d} by default (@pxref{Init File}). For example, abbrev
2710 definitions are stored by default in @file{~/.emacs.d/abbrev_defs}.
2711 The easiest way to specify such a file name is to use the function
2712 @code{locate-user-emacs-file}.
2714 @defun locate-user-emacs-file base-name &optional old-name
2715 This function returns an absolute file name for an Emacs-specific
2716 configuration or data file. The argument @file{base-name} should be a
2717 relative file name. The return value is the absolute name of a file
2718 in the directory specified by @code{user-emacs-directory}; if that
2719 directory does not exist, this function creates it.
2721 If the optional argument @var{old-name} is non-@code{nil}, it
2722 specifies a file in the user's home directory,
2723 @file{~/@var{old-name}}. If such a file exists, the return value is
2724 the absolute name of that file, instead of the file specified by
2725 @var{base-name}. This argument is intended to be used by Emacs
2726 packages to provide backward compatibility. For instance, prior to
2727 the introduction of @code{user-emacs-directory}, the abbrev file was
2728 located in @file{~/.abbrev_defs}. Here is the definition of
2729 @code{abbrev-file-name}:
2732 (defcustom abbrev-file-name
2733 (locate-user-emacs-file "abbrev_defs" ".abbrev_defs")
2734 "Default name of file from which to read abbrevs."
2740 A lower-level function for standardizing file names, which
2741 @code{locate-user-emacs-file} uses as a subroutine, is
2742 @code{convert-standard-filename}.
2744 @defun convert-standard-filename filename
2745 This function returns a file name based on @var{filename}, which fits
2746 the conventions of the current operating system.
2748 On GNU and Unix systems, this simply returns @var{filename}. On other
2749 operating systems, it may enforce system-specific file name
2750 conventions; for example, on MS-DOS this function performs a variety
2751 of changes to enforce MS-DOS file name limitations, including
2752 converting any leading @samp{.} to @samp{_} and truncating to three
2753 characters after the @samp{.}.
2755 The recommended way to use this function is to specify a name which
2756 fits the conventions of GNU and Unix systems, and pass it to
2757 @code{convert-standard-filename}.
2760 @node Contents of Directories
2761 @section Contents of Directories
2762 @cindex directory-oriented functions
2763 @cindex file names in directory
2765 A directory is a kind of file that contains other files entered under
2766 various names. Directories are a feature of the file system.
2768 Emacs can list the names of the files in a directory as a Lisp list,
2769 or display the names in a buffer using the @code{ls} shell command. In
2770 the latter case, it can optionally display information about each file,
2771 depending on the options passed to the @code{ls} command.
2773 @defun directory-files directory &optional full-name match-regexp nosort
2774 This function returns a list of the names of the files in the directory
2775 @var{directory}. By default, the list is in alphabetical order.
2777 If @var{full-name} is non-@code{nil}, the function returns the files'
2778 absolute file names. Otherwise, it returns the names relative to
2779 the specified directory.
2781 If @var{match-regexp} is non-@code{nil}, this function returns only
2782 those file names that contain a match for that regular expression---the
2783 other file names are excluded from the list. On case-insensitive
2784 filesystems, the regular expression matching is case-insensitive.
2787 If @var{nosort} is non-@code{nil}, @code{directory-files} does not sort
2788 the list, so you get the file names in no particular order. Use this if
2789 you want the utmost possible speed and don't care what order the files
2790 are processed in. If the order of processing is visible to the user,
2791 then the user will probably be happier if you do sort the names.
2795 (directory-files "~lewis")
2796 @result{} ("#foo#" "#foo.el#" "." ".."
2797 "dired-mods.el" "files.texi"
2802 An error is signaled if @var{directory} is not the name of a directory
2806 @defun directory-files-recursively directory regexp &optional include-directories
2807 Return all files under @var{directory} whose names match @var{regexp}.
2808 This function searches the specified @var{directory} and its
2809 sub-directories, recursively, for files whose basenames (i.e., without
2810 the leading directories) match the specified @var{regexp}, and returns
2811 a list of the absolute file names of the matching files
2812 (@pxref{Relative File Names, absolute file names}). The file names
2813 are returned in depth-first order, meaning that files in some
2814 sub-directory are returned before the files in its parent directory.
2815 In addition, matching files found in each subdirectory are sorted
2816 alphabetically by their basenames. By default, directories whose
2817 names match @var{regexp} are omitted from the list, but if the
2818 optional argument @var{include-directories} is non-@code{nil}, they
2822 @defun directory-files-and-attributes directory &optional full-name match-regexp nosort id-format
2823 This is similar to @code{directory-files} in deciding which files
2824 to report on and how to report their names. However, instead
2825 of returning a list of file names, it returns for each file a
2826 list @code{(@var{filename} . @var{attributes})}, where @var{attributes}
2827 is what @code{file-attributes} would return for that file.
2828 The optional argument @var{id-format} has the same meaning as the
2829 corresponding argument to @code{file-attributes} (@pxref{Definition
2830 of file-attributes}).
2833 @defun file-expand-wildcards pattern &optional full
2834 This function expands the wildcard pattern @var{pattern}, returning
2835 a list of file names that match it.
2837 If @var{pattern} is written as an absolute file name,
2838 the values are absolute also.
2840 If @var{pattern} is written as a relative file name, it is interpreted
2841 relative to the current default directory. The file names returned are
2842 normally also relative to the current default directory. However, if
2843 @var{full} is non-@code{nil}, they are absolute.
2846 @defun insert-directory file switches &optional wildcard full-directory-p
2847 This function inserts (in the current buffer) a directory listing for
2848 directory @var{file}, formatted with @code{ls} according to
2849 @var{switches}. It leaves point after the inserted text.
2850 @var{switches} may be a string of options, or a list of strings
2851 representing individual options.
2853 The argument @var{file} may be either a directory name or a file
2854 specification including wildcard characters. If @var{wildcard} is
2855 non-@code{nil}, that means treat @var{file} as a file specification with
2858 If @var{full-directory-p} is non-@code{nil}, that means the directory
2859 listing is expected to show the full contents of a directory. You
2860 should specify @code{t} when @var{file} is a directory and switches do
2861 not contain @samp{-d}. (The @samp{-d} option to @code{ls} says to
2862 describe a directory itself as a file, rather than showing its
2865 On most systems, this function works by running a directory listing
2866 program whose name is in the variable @code{insert-directory-program}.
2867 If @var{wildcard} is non-@code{nil}, it also runs the shell specified by
2868 @code{shell-file-name}, to expand the wildcards.
2870 MS-DOS and MS-Windows systems usually lack the standard Unix program
2871 @code{ls}, so this function emulates the standard Unix program @code{ls}
2874 As a technical detail, when @var{switches} contains the long
2875 @samp{--dired} option, @code{insert-directory} treats it specially,
2876 for the sake of dired. However, the normally equivalent short
2877 @samp{-D} option is just passed on to @code{insert-directory-program},
2878 as any other option.
2881 @defvar insert-directory-program
2882 This variable's value is the program to run to generate a directory listing
2883 for the function @code{insert-directory}. It is ignored on systems
2884 which generate the listing with Lisp code.
2887 @node Create/Delete Dirs
2888 @section Creating, Copying and Deleting Directories
2889 @cindex creating, copying and deleting directories
2890 @c Emacs 19 features
2892 Most Emacs Lisp file-manipulation functions get errors when used on
2893 files that are directories. For example, you cannot delete a directory
2894 with @code{delete-file}. These special functions exist to create and
2898 @deffn Command make-directory dirname &optional parents
2899 This command creates a directory named @var{dirname}. If
2900 @var{parents} is non-@code{nil}, as is always the case in an
2901 interactive call, that means to create the parent directories first,
2902 if they don't already exist.
2904 @code{mkdir} is an alias for this.
2907 @deffn Command copy-directory dirname newname &optional keep-time parents copy-contents
2908 This command copies the directory named @var{dirname} to
2909 @var{newname}. If @var{newname} names an existing directory,
2910 @var{dirname} will be copied to a subdirectory there.
2912 It always sets the file modes of the copied files to match the
2913 corresponding original file.
2915 The third argument @var{keep-time} non-@code{nil} means to preserve the
2916 modification time of the copied files. A prefix arg makes
2917 @var{keep-time} non-@code{nil}.
2919 The fourth argument @var{parents} says whether to
2920 create parent directories if they don't exist. Interactively,
2921 this happens by default.
2923 The fifth argument @var{copy-contents}, if non-@code{nil}, means to
2924 copy the contents of @var{dirname} directly into @var{newname} if the
2925 latter is an existing directory, instead of copying @var{dirname} into
2926 it as a subdirectory.
2930 @vindex delete-by-moving-to-trash
2931 @deffn Command delete-directory dirname &optional recursive trash
2932 This command deletes the directory named @var{dirname}. The function
2933 @code{delete-file} does not work for files that are directories; you
2934 must use @code{delete-directory} for them. If @var{recursive} is
2935 @code{nil}, and the directory contains any files,
2936 @code{delete-directory} signals an error.
2937 If recursive is non-@code{nil}, there is no error merely because the
2938 directory or its files are deleted by some other process before
2939 @code{delete-directory} gets to them.
2941 @code{delete-directory} only follows symbolic links at the level of
2944 If the optional argument @var{trash} is non-@code{nil} and the
2945 variable @code{delete-by-moving-to-trash} is non-@code{nil}, this
2946 command moves the file into the system Trash instead of deleting it.
2947 @xref{Misc File Ops,,Miscellaneous File Operations, emacs, The GNU
2948 Emacs Manual}. When called interactively, @var{trash} is @code{t} if
2949 no prefix argument is given, and @code{nil} otherwise.
2952 @node Magic File Names
2953 @section Making Certain File Names ``Magic''
2954 @cindex magic file names
2956 You can implement special handling for certain file names. This is
2957 called making those names @dfn{magic}. The principal use for this
2958 feature is in implementing access to remote files (@pxref{Remote Files,,
2959 Remote Files, emacs, The GNU Emacs Manual}).
2961 To define a kind of magic file name, you must supply a regular
2962 expression to define the class of names (all those that match the
2963 regular expression), plus a handler that implements all the primitive
2964 Emacs file operations for file names that match.
2966 @cindex file handler
2967 @vindex file-name-handler-alist
2968 The variable @code{file-name-handler-alist} holds a list of handlers,
2969 together with regular expressions that determine when to apply each
2970 handler. Each element has this form:
2973 (@var{regexp} . @var{handler})
2977 All the Emacs primitives for file access and file name transformation
2978 check the given file name against @code{file-name-handler-alist}. If
2979 the file name matches @var{regexp}, the primitives handle that file by
2980 calling @var{handler}.
2982 The first argument given to @var{handler} is the name of the
2983 primitive, as a symbol; the remaining arguments are the arguments that
2984 were passed to that primitive. (The first of these arguments is most
2985 often the file name itself.) For example, if you do this:
2988 (file-exists-p @var{filename})
2992 and @var{filename} has handler @var{handler}, then @var{handler} is
2996 (funcall @var{handler} 'file-exists-p @var{filename})
2999 When a function takes two or more arguments that must be file names,
3000 it checks each of those names for a handler. For example, if you do
3004 (expand-file-name @var{filename} @var{dirname})
3008 then it checks for a handler for @var{filename} and then for a handler
3009 for @var{dirname}. In either case, the @var{handler} is called like
3013 (funcall @var{handler} 'expand-file-name @var{filename} @var{dirname})
3017 The @var{handler} then needs to figure out whether to handle
3018 @var{filename} or @var{dirname}.
3020 If the specified file name matches more than one handler, the one
3021 whose match starts last in the file name gets precedence. This rule
3022 is chosen so that handlers for jobs such as uncompression are handled
3023 first, before handlers for jobs such as remote file access.
3025 Here are the operations that a magic file name handler gets to handle:
3029 @code{access-file}, @code{add-name-to-file},
3030 @code{byte-compiler-base-file-name},@*
3031 @code{copy-directory}, @code{copy-file},
3032 @code{delete-directory}, @code{delete-file},
3033 @code{diff-latest-backup-file},
3034 @code{directory-file-name},
3035 @code{directory-files},
3036 @code{directory-files-and-attributes},
3037 @code{dired-compress-file}, @code{dired-uncache},@*
3038 @code{expand-file-name},
3039 @code{file-accessible-directory-p},
3041 @code{file-attributes},
3042 @code{file-directory-p},
3043 @code{file-equal-p},
3044 @code{file-executable-p}, @code{file-exists-p},
3045 @code{file-in-directory-p},
3046 @code{file-local-copy},
3047 @code{file-modes}, @code{file-name-all-completions},
3048 @code{file-name-as-directory},
3049 @code{file-name-case-insensitive-p},
3050 @code{file-name-completion},
3051 @code{file-name-directory},
3052 @code{file-name-nondirectory},
3053 @code{file-name-sans-versions}, @code{file-newer-than-file-p},
3054 @code{file-notify-add-watch}, @code{file-notify-rm-watch},
3055 @code{file-notify-valid-p},
3056 @code{file-ownership-preserved-p},
3057 @code{file-readable-p}, @code{file-regular-p},
3058 @code{file-remote-p}, @code{file-selinux-context},
3059 @code{file-symlink-p}, @code{file-truename}, @code{file-writable-p},
3060 @code{find-backup-file-name},@*
3061 @code{get-file-buffer},
3062 @code{insert-directory},
3063 @code{insert-file-contents},@*
3065 @code{make-auto-save-file-name},
3066 @code{make-directory},
3067 @code{make-directory-internal},
3068 @code{make-nearby-temp-file},
3069 @code{make-symbolic-link},@*
3070 @code{process-file},
3071 @code{rename-file}, @code{set-file-acl}, @code{set-file-modes},
3072 @code{set-file-selinux-context}, @code{set-file-times},
3073 @code{set-visited-file-modtime}, @code{shell-command},
3074 @code{start-file-process},
3075 @code{substitute-in-file-name},@*
3076 @code{temporary-file-directory},
3077 @code{unhandled-file-name-directory},
3078 @code{vc-registered},
3079 @code{verify-visited-file-modtime},@*
3080 @code{write-region}.
3085 @code{access-file}, @code{add-name-to-file},
3086 @code{byte-com@discretionary{}{}{}piler-base-file-name},
3087 @code{copy-directory}, @code{copy-file},
3088 @code{delete-directory}, @code{delete-file},
3089 @code{diff-latest-backup-file},
3090 @code{directory-file-name},
3091 @code{directory-files},
3092 @code{directory-files-and-at@discretionary{}{}{}tributes},
3093 @code{dired-compress-file}, @code{dired-uncache},
3094 @code{expand-file-name},
3095 @code{file-accessible-direc@discretionary{}{}{}tory-p},
3097 @code{file-attributes},
3098 @code{file-direc@discretionary{}{}{}tory-p},
3099 @code{file-equal-p},
3100 @code{file-executable-p}, @code{file-exists-p},
3101 @code{file-in-directory-p},
3102 @code{file-local-copy},
3103 @code{file-modes}, @code{file-name-all-completions},
3104 @code{file-name-as-directory},
3105 @code{file-name-case-insensitive-p},
3106 @code{file-name-completion},
3107 @code{file-name-directory},
3108 @code{file-name-nondirec@discretionary{}{}{}tory},
3109 @code{file-name-sans-versions}, @code{file-newer-than-file-p},
3110 @code{file-notify-add-watch}, @code{file-notify-rm-watch},
3111 @code{file-notify-valid-p},
3112 @code{file-ownership-pre@discretionary{}{}{}served-p},
3113 @code{file-readable-p}, @code{file-regular-p},
3114 @code{file-remote-p}, @code{file-selinux-context},
3115 @code{file-symlink-p}, @code{file-truename}, @code{file-writable-p},
3116 @code{find-backup-file-name},
3117 @code{get-file-buffer},
3118 @code{insert-directory},
3119 @code{insert-file-contents},
3121 @code{make-auto-save-file-name},
3122 @code{make-direc@discretionary{}{}{}tory},
3123 @code{make-direc@discretionary{}{}{}tory-internal},
3124 @code{make-symbolic-link},
3125 @code{process-file},
3126 @code{rename-file}, @code{set-file-acl}, @code{set-file-modes},
3127 @code{set-file-selinux-context}, @code{set-file-times},
3128 @code{set-visited-file-modtime}, @code{shell-command},
3129 @code{start-file-process},
3130 @code{substitute-in-file-name},
3131 @code{unhandled-file-name-directory},
3132 @code{vc-regis@discretionary{}{}{}tered},
3133 @code{verify-visited-file-modtime},
3134 @code{write-region}.
3138 Handlers for @code{insert-file-contents} typically need to clear the
3139 buffer's modified flag, with @code{(set-buffer-modified-p nil)}, if the
3140 @var{visit} argument is non-@code{nil}. This also has the effect of
3141 unlocking the buffer if it is locked.
3143 The handler function must handle all of the above operations, and
3144 possibly others to be added in the future. It need not implement all
3145 these operations itself---when it has nothing special to do for a
3146 certain operation, it can reinvoke the primitive, to handle the
3147 operation in the usual way. It should always reinvoke the primitive
3148 for an operation it does not recognize. Here's one way to do this:
3151 (defun my-file-handler (operation &rest args)
3152 ;; @r{First check for the specific operations}
3153 ;; @r{that we have special handling for.}
3154 (cond ((eq operation 'insert-file-contents) @dots{})
3155 ((eq operation 'write-region) @dots{})
3157 ;; @r{Handle any operation we don't know about.}
3158 (t (let ((inhibit-file-name-handlers
3159 (cons 'my-file-handler
3160 (and (eq inhibit-file-name-operation operation)
3161 inhibit-file-name-handlers)))
3162 (inhibit-file-name-operation operation))
3163 (apply operation args)))))
3166 When a handler function decides to call the ordinary Emacs primitive for
3167 the operation at hand, it needs to prevent the primitive from calling
3168 the same handler once again, thus leading to an infinite recursion. The
3169 example above shows how to do this, with the variables
3170 @code{inhibit-file-name-handlers} and
3171 @code{inhibit-file-name-operation}. Be careful to use them exactly as
3172 shown above; the details are crucial for proper behavior in the case of
3173 multiple handlers, and for operations that have two file names that may
3176 @kindex safe-magic (@r{property})
3177 Handlers that don't really do anything special for actual access to the
3178 file---such as the ones that implement completion of host names for
3179 remote file names---should have a non-@code{nil} @code{safe-magic}
3180 property. For instance, Emacs normally protects directory names
3181 it finds in @code{PATH} from becoming magic, if they look like magic
3182 file names, by prefixing them with @samp{/:}. But if the handler that
3183 would be used for them has a non-@code{nil} @code{safe-magic}
3184 property, the @samp{/:} is not added.
3186 @kindex operations (@r{property})
3187 A file name handler can have an @code{operations} property to
3188 declare which operations it handles in a nontrivial way. If this
3189 property has a non-@code{nil} value, it should be a list of
3190 operations; then only those operations will call the handler. This
3191 avoids inefficiency, but its main purpose is for autoloaded handler
3192 functions, so that they won't be loaded except when they have real
3195 Simply deferring all operations to the usual primitives does not
3196 work. For instance, if the file name handler applies to
3197 @code{file-exists-p}, then it must handle @code{load} itself, because
3198 the usual @code{load} code won't work properly in that case. However,
3199 if the handler uses the @code{operations} property to say it doesn't
3200 handle @code{file-exists-p}, then it need not handle @code{load}
3203 @defvar inhibit-file-name-handlers
3204 This variable holds a list of handlers whose use is presently inhibited
3205 for a certain operation.
3208 @defvar inhibit-file-name-operation
3209 The operation for which certain handlers are presently inhibited.
3212 @defun find-file-name-handler file operation
3213 This function returns the handler function for file name @var{file},
3214 or @code{nil} if there is none. The argument @var{operation} should
3215 be the operation to be performed on the file---the value you will pass
3216 to the handler as its first argument when you call it. If
3217 @var{operation} equals @code{inhibit-file-name-operation}, or if it is
3218 not found in the @code{operations} property of the handler, this
3219 function returns @code{nil}.
3222 @defun file-local-copy filename
3223 This function copies file @var{filename} to an ordinary non-magic file
3224 on the local machine, if it isn't on the local machine already. Magic
3225 file names should handle the @code{file-local-copy} operation if they
3226 refer to files on other machines. A magic file name that is used for
3227 other purposes than remote file access should not handle
3228 @code{file-local-copy}; then this function will treat the file as
3231 If @var{filename} is local, whether magic or not, this function does
3232 nothing and returns @code{nil}. Otherwise it returns the file name
3233 of the local copy file.
3236 @defun file-remote-p filename &optional identification connected
3237 This function tests whether @var{filename} is a remote file. If
3238 @var{filename} is local (not remote), the return value is @code{nil}.
3239 If @var{filename} is indeed remote, the return value is a string that
3240 identifies the remote system.
3242 This identifier string can include a host name and a user name, as
3243 well as characters designating the method used to access the remote
3244 system. For example, the remote identifier string for the filename
3245 @code{/sudo::/some/file} is @code{/sudo:root@@localhost:}.
3247 If @code{file-remote-p} returns the same identifier for two different
3248 filenames, that means they are stored on the same file system and can
3249 be accessed locally with respect to each other. This means, for
3250 example, that it is possible to start a remote process accessing both
3251 files at the same time. Implementers of file handlers need to ensure
3252 this principle is valid.
3254 @var{identification} specifies which part of the identifier shall be
3255 returned as string. @var{identification} can be the symbol
3256 @code{method}, @code{user} or @code{host}; any other value is handled
3257 like @code{nil} and means to return the complete identifier string.
3258 In the example above, the remote @code{user} identifier string would
3261 If @var{connected} is non-@code{nil}, this function returns @code{nil}
3262 even if @var{filename} is remote, if Emacs has no network connection
3263 to its host. This is useful when you want to avoid the delay of
3264 making connections when they don't exist.
3267 @defun unhandled-file-name-directory filename
3268 This function returns the name of a directory that is not magic. For
3269 a non-magic @var{filename} it returns the corresponding directory name
3270 (@pxref{Directory Names}). For a magic @var{filename}, it invokes the
3271 file name handler, which therefore decides what value to return. If
3272 @var{filename} is not accessible from a local process, then the file
3273 name handler should indicate that by returning @code{nil}.
3275 This is useful for running a subprocess; every subprocess must have a
3276 non-magic directory to serve as its current directory, and this function
3277 is a good way to come up with one.
3280 @defun file-local-name filename
3281 This function returns the local part of file @var{filename}. For a
3282 remote @var{filename}, it returns a file name which could be used
3283 directly as argument of a remote process. If @var{filename} is local,
3284 this function returns the file name.
3287 @defopt remote-file-name-inhibit-cache
3288 The attributes of remote files can be cached for better performance. If
3289 they are changed outside of Emacs's control, the cached values become
3290 invalid, and must be reread.
3292 When this variable is set to @code{nil}, cached values are never
3293 expired. Use this setting with caution, only if you are sure nothing
3294 other than Emacs ever changes the remote files. If it is set to
3295 @code{t}, cached values are never used. This is the safest value, but
3296 could result in performance degradation.
3298 A compromise is to set it to a positive number. This means that
3299 cached values are used for that amount of seconds since they were
3300 cached. If a remote file is checked regularly, it might be a good
3301 idea to let-bind this variable to a value less than the time period
3302 between consecutive checks. For example:
3305 (defun display-time-file-nonempty-p (file)
3306 (let ((remote-file-name-inhibit-cache
3307 (- display-time-interval 5)))
3308 (and (file-exists-p file)
3309 (< 0 (nth 7 (file-attributes
3310 (file-chase-links file)))))))
3314 @node Format Conversion
3315 @section File Format Conversion
3317 @cindex file format conversion
3318 @cindex encoding file formats
3319 @cindex decoding file formats
3320 @cindex text properties in files
3321 @cindex saving text properties
3322 Emacs performs several steps to convert the data in a buffer (text,
3323 text properties, and possibly other information) to and from a
3324 representation suitable for storing into a file. This section describes
3325 the fundamental functions that perform this @dfn{format conversion},
3326 namely @code{insert-file-contents} for reading a file into a buffer,
3327 and @code{write-region} for writing a buffer into a file.
3330 * Overview: Format Conversion Overview. @code{insert-file-contents} and @code{write-region}.
3331 * Round-Trip: Format Conversion Round-Trip. Using @code{format-alist}.
3332 * Piecemeal: Format Conversion Piecemeal. Specifying non-paired conversion.
3335 @node Format Conversion Overview
3336 @subsection Overview
3338 The function @code{insert-file-contents}:
3341 @item initially, inserts bytes from the file into the buffer;
3342 @item decodes bytes to characters as appropriate;
3343 @item processes formats as defined by entries in @code{format-alist}; and
3344 @item calls functions in @code{after-insert-file-functions}.
3348 The function @code{write-region}:
3351 @item initially, calls functions in @code{write-region-annotate-functions};
3352 @item processes formats as defined by entries in @code{format-alist};
3353 @item encodes characters to bytes as appropriate; and
3354 @item modifies the file with the bytes.
3357 This shows the symmetry of the lowest-level operations; reading and
3358 writing handle things in opposite order. The rest of this section
3359 describes the two facilities surrounding the three variables named
3360 above, as well as some related functions. @ref{Coding Systems}, for
3361 details on character encoding and decoding.
3363 @node Format Conversion Round-Trip
3364 @subsection Round-Trip Specification
3366 The most general of the two facilities is controlled by the variable
3367 @code{format-alist}, a list of @dfn{file format} specifications, which
3368 describe textual representations used in files for the data in an Emacs
3369 buffer. The descriptions for reading and writing are paired, which is
3370 why we call this ``round-trip'' specification
3371 (@pxref{Format Conversion Piecemeal}, for non-paired specification).
3373 @defvar format-alist
3374 This list contains one format definition for each defined file format.
3375 Each format definition is a list of this form:
3378 (@var{name} @var{doc-string} @var{regexp} @var{from-fn} @var{to-fn} @var{modify} @var{mode-fn} @var{preserve})
3382 @cindex format definition
3384 Here is what the elements in a format definition mean:
3388 The name of this format.
3391 A documentation string for the format.
3394 A regular expression which is used to recognize files represented in
3395 this format. If @code{nil}, the format is never applied automatically.
3398 A shell command or function to decode data in this format (to convert
3399 file data into the usual Emacs data representation).
3401 A shell command is represented as a string; Emacs runs the command as a
3402 filter to perform the conversion.
3404 If @var{from-fn} is a function, it is called with two arguments, @var{begin}
3405 and @var{end}, which specify the part of the buffer it should convert.
3406 It should convert the text by editing it in place. Since this can
3407 change the length of the text, @var{from-fn} should return the modified
3410 One responsibility of @var{from-fn} is to make sure that the beginning
3411 of the file no longer matches @var{regexp}. Otherwise it is likely to
3412 get called again. Also, @var{from-fn} must not involve buffers or
3413 files other than the one being decoded, otherwise the internal buffer
3414 used for formatting might be overwritten.
3417 A shell command or function to encode data in this format---that is, to
3418 convert the usual Emacs data representation into this format.
3420 If @var{to-fn} is a string, it is a shell command; Emacs runs the
3421 command as a filter to perform the conversion.
3423 If @var{to-fn} is a function, it is called with three arguments:
3424 @var{begin} and @var{end}, which specify the part of the buffer it
3425 should convert, and @var{buffer}, which specifies which buffer. There
3426 are two ways it can do the conversion:
3430 By editing the buffer in place. In this case, @var{to-fn} should
3431 return the end-position of the range of text, as modified.
3434 By returning a list of annotations. This is a list of elements of the
3435 form @code{(@var{position} . @var{string})}, where @var{position} is an
3436 integer specifying the relative position in the text to be written, and
3437 @var{string} is the annotation to add there. The list must be sorted in
3438 order of position when @var{to-fn} returns it.
3440 When @code{write-region} actually writes the text from the buffer to the
3441 file, it intermixes the specified annotations at the corresponding
3442 positions. All this takes place without modifying the buffer.
3445 @var{to-fn} must not involve buffers or files other than the one being
3446 encoded, otherwise the internal buffer used for formatting might be
3450 A flag, @code{t} if the encoding function modifies the buffer, and
3451 @code{nil} if it works by returning a list of annotations.
3454 A minor-mode function to call after visiting a file converted from this
3455 format. The function is called with one argument, the integer 1;
3456 that tells a minor-mode function to enable the mode.
3459 A flag, @code{t} if @code{format-write-file} should not remove this format
3460 from @code{buffer-file-format}.
3463 The function @code{insert-file-contents} automatically recognizes file
3464 formats when it reads the specified file. It checks the text of the
3465 beginning of the file against the regular expressions of the format
3466 definitions, and if it finds a match, it calls the decoding function for
3467 that format. Then it checks all the known formats over again.
3468 It keeps checking them until none of them is applicable.
3470 Visiting a file, with @code{find-file-noselect} or the commands that use
3471 it, performs conversion likewise (because it calls
3472 @code{insert-file-contents}); it also calls the mode function for each
3473 format that it decodes. It stores a list of the format names in the
3474 buffer-local variable @code{buffer-file-format}.
3476 @defvar buffer-file-format
3477 This variable states the format of the visited file. More precisely,
3478 this is a list of the file format names that were decoded in the course
3479 of visiting the current buffer's file. It is always buffer-local in all
3483 When @code{write-region} writes data into a file, it first calls the
3484 encoding functions for the formats listed in @code{buffer-file-format},
3485 in the order of appearance in the list.
3487 @deffn Command format-write-file file format &optional confirm
3488 This command writes the current buffer contents into the file @var{file}
3489 in a format based on @var{format}, which is a list of format names. It
3490 constructs the actual format starting from @var{format}, then appending
3491 any elements from the value of @code{buffer-file-format} with a
3492 non-@code{nil} @var{preserve} flag (see above), if they are not already
3493 present in @var{format}. It then updates @code{buffer-file-format} with
3494 this format, making it the default for future saves. Except for the
3495 @var{format} argument, this command is similar to @code{write-file}. In
3496 particular, @var{confirm} has the same meaning and interactive treatment
3497 as the corresponding argument to @code{write-file}. @xref{Definition of
3501 @deffn Command format-find-file file format
3502 This command finds the file @var{file}, converting it according to
3503 format @var{format}. It also makes @var{format} the default if the
3504 buffer is saved later.
3506 The argument @var{format} is a list of format names. If @var{format} is
3507 @code{nil}, no conversion takes place. Interactively, typing just
3508 @key{RET} for @var{format} specifies @code{nil}.
3511 @deffn Command format-insert-file file format &optional beg end
3512 This command inserts the contents of file @var{file}, converting it
3513 according to format @var{format}. If @var{beg} and @var{end} are
3514 non-@code{nil}, they specify which part of the file to read, as in
3515 @code{insert-file-contents} (@pxref{Reading from Files}).
3517 The return value is like what @code{insert-file-contents} returns: a
3518 list of the absolute file name and the length of the data inserted
3521 The argument @var{format} is a list of format names. If @var{format} is
3522 @code{nil}, no conversion takes place. Interactively, typing just
3523 @key{RET} for @var{format} specifies @code{nil}.
3526 @defvar buffer-auto-save-file-format
3527 This variable specifies the format to use for auto-saving. Its value is
3528 a list of format names, just like the value of
3529 @code{buffer-file-format}; however, it is used instead of
3530 @code{buffer-file-format} for writing auto-save files. If the value
3531 is @code{t}, the default, auto-saving uses the same format as a
3532 regular save in the same buffer. This variable is always buffer-local
3536 @node Format Conversion Piecemeal
3537 @subsection Piecemeal Specification
3539 In contrast to the round-trip specification described in the previous
3540 subsection (@pxref{Format Conversion Round-Trip}), you can use the variables
3541 @code{after-insert-file-functions} and @code{write-region-annotate-functions}
3542 to separately control the respective reading and writing conversions.
3544 Conversion starts with one representation and produces another
3545 representation. When there is only one conversion to do, there is no
3546 conflict about what to start with. However, when there are multiple
3547 conversions involved, conflict may arise when two conversions need to
3548 start with the same data.
3550 This situation is best understood in the context of converting text
3551 properties during @code{write-region}. For example, the character at
3552 position 42 in a buffer is @samp{X} with a text property @code{foo}. If
3553 the conversion for @code{foo} is done by inserting into the buffer, say,
3554 @samp{FOO:}, then that changes the character at position 42 from
3555 @samp{X} to @samp{F}. The next conversion will start with the wrong
3558 To avoid conflict, cooperative conversions do not modify the buffer,
3559 but instead specify @dfn{annotations}, a list of elements of the form
3560 @code{(@var{position} . @var{string})}, sorted in order of increasing
3563 If there is more than one conversion, @code{write-region} merges their
3564 annotations destructively into one sorted list. Later, when the text
3565 from the buffer is actually written to the file, it intermixes the
3566 specified annotations at the corresponding positions. All this takes
3567 place without modifying the buffer.
3569 @c ??? What about "overriding" conversions like those allowed
3570 @c ??? for 'write-region-annotate-functions', below? --ttn
3572 In contrast, when reading, the annotations intermixed with the text
3573 are handled immediately. @code{insert-file-contents} sets point to
3574 the beginning of some text to be converted, then calls the conversion
3575 functions with the length of that text. These functions should always
3576 return with point at the beginning of the inserted text. This
3577 approach makes sense for reading because annotations removed by the
3578 first converter can't be mistakenly processed by a later converter.
3579 Each conversion function should scan for the annotations it
3580 recognizes, remove the annotation, modify the buffer text (to set a
3581 text property, for example), and return the updated length of the
3582 text, as it stands after those changes. The value returned by one
3583 function becomes the argument to the next function.
3585 @defvar write-region-annotate-functions
3586 A list of functions for @code{write-region} to call. Each function in
3587 the list is called with two arguments: the start and end of the region
3588 to be written. These functions should not alter the contents of the
3589 buffer. Instead, they should return annotations.
3591 As a special case, a function may return with a different buffer
3592 current. Emacs takes this to mean that the current buffer contains
3593 altered text to be output. It therefore changes the @var{start} and
3594 @var{end} arguments of the @code{write-region} call, giving them the
3595 values of @code{point-min} and @code{point-max} in the new buffer,
3596 respectively. It also discards all previous annotations, because they
3597 should have been dealt with by this function.
3600 @defvar write-region-post-annotation-function
3601 The value of this variable, if non-@code{nil}, should be a function.
3602 This function is called, with no arguments, after @code{write-region}
3605 If any function in @code{write-region-annotate-functions} returns with
3606 a different buffer current, Emacs calls
3607 @code{write-region-post-annotation-function} more than once. Emacs
3608 calls it with the last buffer that was current, and again with the
3609 buffer before that, and so on back to the original buffer.
3611 Thus, a function in @code{write-region-annotate-functions} can create
3612 a buffer, give this variable the local value of @code{kill-buffer} in
3613 that buffer, set up the buffer with altered text, and make the buffer
3614 current. The buffer will be killed after @code{write-region} is done.
3617 @defvar after-insert-file-functions
3618 Each function in this list is called by @code{insert-file-contents}
3619 with one argument, the number of characters inserted, and with point
3620 at the beginning of the inserted text. Each function should leave
3621 point unchanged, and return the new character count describing the
3622 inserted text as modified by the function.
3623 @c ??? The docstring mentions a handler from 'file-name-handler-alist'
3624 @c "intercepting" 'insert-file-contents'. Hmmm. --ttn
3627 We invite users to write Lisp programs to store and retrieve text
3628 properties in files, using these hooks, and thus to experiment with
3629 various data formats and find good ones. Eventually we hope users
3630 will produce good, general extensions we can install in Emacs.
3632 We suggest not trying to handle arbitrary Lisp objects as text property
3633 names or values---because a program that general is probably difficult
3634 to write, and slow. Instead, choose a set of possible data types that
3635 are reasonably flexible, and not too hard to encode.