2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2018 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. Buffers which
336 are not visiting a file can still be ``saved'', in a sense, using
337 functions in the buffer-local @code{write-contents-functions} hook.
339 @deffn Command save-buffer &optional backup-option
340 This function saves the contents of the current buffer in its visited
341 file if the buffer has been modified since it was last visited or saved.
342 Otherwise it does nothing.
344 @code{save-buffer} is responsible for making backup files. Normally,
345 @var{backup-option} is @code{nil}, and @code{save-buffer} makes a backup
346 file only if this is the first save since visiting the file. Other
347 values for @var{backup-option} request the making of backup files in
352 With an argument of 4 or 64, reflecting 1 or 3 @kbd{C-u}'s, the
353 @code{save-buffer} function marks this version of the file to be
354 backed up when the buffer is next saved.
357 With an argument of 16 or 64, reflecting 2 or 3 @kbd{C-u}'s, the
358 @code{save-buffer} function unconditionally backs up the previous
359 version of the file before saving it.
362 With an argument of 0, unconditionally do @emph{not} make any backup file.
366 @deffn Command save-some-buffers &optional save-silently-p pred
367 @anchor{Definition of save-some-buffers}
368 This command saves some modified file-visiting buffers. Normally it
369 asks the user about each buffer. But if @var{save-silently-p} is
370 non-@code{nil}, it saves all the file-visiting buffers without
373 @vindex save-some-buffers-default-predicate
374 The optional @var{pred} argument provides a predicate that controls
375 which buffers to ask about (or to save silently if
376 @var{save-silently-p} is non-@code{nil}). If @var{pred} is
377 @code{nil}, that means to use the value of
378 @code{save-some-buffers-default-predicate} instead of @var{pred}. If
379 the result is @code{nil}, it means ask only about file-visiting
380 buffers. If it is @code{t}, that means also offer to save certain
381 other non-file buffers---those that have a non-@code{nil} buffer-local
382 value of @code{buffer-offer-save} (@pxref{Killing Buffers}). A user
383 who says @samp{yes} to saving a non-file buffer is asked to specify
384 the file name to use. The @code{save-buffers-kill-emacs} function
385 passes the value @code{t} for @var{pred}.
387 If the predicate is neither @code{t} nor @code{nil}, then it should be
388 a function of no arguments. It will be called in each buffer to decide
389 whether to offer to save that buffer. If it returns a non-@code{nil}
390 value in a certain buffer, that means do offer to save that buffer.
393 @deffn Command write-file filename &optional confirm
394 @anchor{Definition of write-file}
395 This function writes the current buffer into file @var{filename}, makes
396 the buffer visit that file, and marks it not modified. Then it renames
397 the buffer based on @var{filename}, appending a string like @samp{<2>}
398 if necessary to make a unique buffer name. It does most of this work by
399 calling @code{set-visited-file-name} (@pxref{Buffer File Name}) and
402 If @var{confirm} is non-@code{nil}, that means to ask for confirmation
403 before overwriting an existing file. Interactively, confirmation is
404 required, unless the user supplies a prefix argument.
406 If @var{filename} is a directory name (@pxref{Directory Names}),
407 @code{write-file} uses the name of the visited file, in directory
408 @var{filename}. If the buffer is not visiting a file, it uses the
412 Saving a buffer runs several hooks. It also performs format
413 conversion (@pxref{Format Conversion}). Note that these hooks,
414 described below, are only run by @code{save-buffer}, they are not run
415 by other primitives and functions that write buffer text to files, and
416 in particular auto-saving (@pxref{Auto-Saving}) doesn't run these
419 @defvar write-file-functions
420 The value of this variable is a list of functions to be called before
421 writing out a buffer to its visited file. If one of them returns
422 non-@code{nil}, the file is considered already written and the rest of
423 the functions are not called, nor is the usual code for writing the file
426 If a function in @code{write-file-functions} returns non-@code{nil}, it
427 is responsible for making a backup file (if that is appropriate).
428 To do so, execute the following code:
431 (or buffer-backed-up (backup-buffer))
434 You might wish to save the file modes value returned by
435 @code{backup-buffer} and use that (if non-@code{nil}) to set the mode
436 bits of the file that you write. This is what @code{save-buffer}
437 normally does. @xref{Making Backups,, Making Backup Files}.
439 The hook functions in @code{write-file-functions} are also responsible
440 for encoding the data (if desired): they must choose a suitable coding
441 system and end-of-line conversion (@pxref{Lisp and Coding Systems}),
442 perform the encoding (@pxref{Explicit Encoding}), and set
443 @code{last-coding-system-used} to the coding system that was used
444 (@pxref{Encoding and I/O}).
446 If you set this hook locally in a buffer, it is assumed to be
447 associated with the file or the way the contents of the buffer were
448 obtained. Thus the variable is marked as a permanent local, so that
449 changing the major mode does not alter a buffer-local value. On the
450 other hand, calling @code{set-visited-file-name} will reset it.
451 If this is not what you want, you might like to use
452 @code{write-contents-functions} instead.
454 Even though this is not a normal hook, you can use @code{add-hook} and
455 @code{remove-hook} to manipulate the list. @xref{Hooks}.
459 @defvar write-contents-functions
460 This works just like @code{write-file-functions}, but it is intended
461 for hooks that pertain to the buffer's contents, not to the particular
462 visited file or its location, and can be used to create arbitrary save
463 processes for buffers that aren't visiting files at all. Such hooks
464 are usually set up by major modes, as buffer-local bindings for this
465 variable. This variable automatically becomes buffer-local whenever
466 it is set; switching to a new major mode always resets this variable,
467 but calling @code{set-visited-file-name} does not.
469 If any of the functions in this hook returns non-@code{nil}, the file
470 is considered already written and the rest are not called and neither
471 are the functions in @code{write-file-functions}.
473 When using this hook to save buffers that are not visiting files (for
474 instance, special-mode buffers), keep in mind that, if the function
475 fails to save correctly and returns a @code{nil} value,
476 @code{save-buffer} will go on to prompt the user for a file to save
477 the buffer in. If this is undesirable, consider having the function
478 fail by raising an error.
481 @defopt before-save-hook
482 This normal hook runs before a buffer is saved in its visited file,
483 regardless of whether that is done normally or by one of the hooks
484 described above. For instance, the @file{copyright.el} program uses
485 this hook to make sure the file you are saving has the current year in
486 its copyright notice.
490 @defopt after-save-hook
491 This normal hook runs after a buffer has been saved in its visited file.
492 One use of this hook is in Fast Lock mode; it uses this hook to save the
493 highlighting information in a cache file.
496 @defopt file-precious-flag
497 If this variable is non-@code{nil}, then @code{save-buffer} protects
498 against I/O errors while saving by writing the new file to a temporary
499 name instead of the name it is supposed to have, and then renaming it to
500 the intended name after it is clear there are no errors. This procedure
501 prevents problems such as a lack of disk space from resulting in an
504 As a side effect, backups are necessarily made by copying. @xref{Rename
505 or Copy}. Yet, at the same time, saving a precious file always breaks
506 all hard links between the file you save and other file names.
508 Some modes give this variable a non-@code{nil} buffer-local value
509 in particular buffers.
512 @defopt require-final-newline
513 This variable determines whether files may be written out that do
514 @emph{not} end with a newline. If the value of the variable is
515 @code{t}, then @code{save-buffer} silently adds a newline at the end
516 of the buffer whenever it does not already end in one. If the value
517 is @code{visit}, Emacs adds a missing newline just after it visits the
518 file. If the value is @code{visit-save}, Emacs adds a missing newline
519 both on visiting and on saving. For any other non-@code{nil} value,
520 @code{save-buffer} asks the user whether to add a newline each time
523 If the value of the variable is @code{nil}, then @code{save-buffer}
524 doesn't add newlines at all. @code{nil} is the default value, but a few
525 major modes set it to @code{t} in particular buffers.
528 See also the function @code{set-visited-file-name} (@pxref{Buffer File
531 @node Reading from Files
532 @section Reading from Files
533 @cindex reading from files
535 To copy the contents of a file into a buffer, use the function
536 @code{insert-file-contents}. (Don't use the command
537 @code{insert-file} in a Lisp program, as that sets the mark.)
539 @defun insert-file-contents filename &optional visit beg end replace
540 This function inserts the contents of file @var{filename} into the
541 current buffer after point. It returns a list of the absolute file name
542 and the length of the data inserted. An error is signaled if
543 @var{filename} is not the name of a file that can be read.
545 This function checks the file contents against the defined file
546 formats, and converts the file contents if appropriate and also calls
547 the functions in the list @code{after-insert-file-functions}.
548 @xref{Format Conversion}. Normally, one of the functions in the
549 @code{after-insert-file-functions} list determines the coding system
550 (@pxref{Coding Systems}) used for decoding the file's contents,
551 including end-of-line conversion. However, if the file contains null
552 bytes, it is by default visited without any code conversions.
553 @xref{Lisp and Coding Systems, inhibit-null-byte-detection}.
555 If @var{visit} is non-@code{nil}, this function additionally marks the
556 buffer as unmodified and sets up various fields in the buffer so that it
557 is visiting the file @var{filename}: these include the buffer's visited
558 file name and its last save file modtime. This feature is used by
559 @code{find-file-noselect} and you probably should not use it yourself.
561 If @var{beg} and @var{end} are non-@code{nil}, they should be numbers
562 that are byte offsets specifying the portion of the file to insert.
563 In this case, @var{visit} must be @code{nil}. For example,
566 (insert-file-contents filename nil 0 500)
570 inserts the first 500 characters of a file.
572 If the argument @var{replace} is non-@code{nil}, it means to replace the
573 contents of the buffer (actually, just the accessible portion) with the
574 contents of the file. This is better than simply deleting the buffer
575 contents and inserting the whole file, because (1) it preserves some
576 marker positions and (2) it puts less data in the undo list.
578 It is possible to read a special file (such as a FIFO or an I/O device)
579 with @code{insert-file-contents}, as long as @var{replace} and
580 @var{visit} are @code{nil}.
583 @defun insert-file-contents-literally filename &optional visit beg end replace
584 This function works like @code{insert-file-contents} except that it
585 does not run @code{after-insert-file-functions}, and does not do
586 format decoding, character code conversion, automatic uncompression,
590 If you want to pass a file name to another process so that another
591 program can read the file, use the function @code{file-local-copy}; see
592 @ref{Magic File Names}.
594 @node Writing to Files
595 @section Writing to Files
596 @cindex writing to files
598 You can write the contents of a buffer, or part of a buffer, directly
599 to a file on disk using the @code{append-to-file} and
600 @code{write-region} functions. Don't use these functions to write to
601 files that are being visited; that could cause confusion in the
602 mechanisms for visiting.
604 @deffn Command append-to-file start end filename
605 This function appends the contents of the region delimited by
606 @var{start} and @var{end} in the current buffer to the end of file
607 @var{filename}. If that file does not exist, it is created. This
608 function returns @code{nil}.
610 An error is signaled if @var{filename} specifies a nonwritable file,
611 or a nonexistent file in a directory where files cannot be created.
613 When called from Lisp, this function is completely equivalent to:
616 (write-region start end filename t)
620 @deffn Command write-region start end filename &optional append visit lockname mustbenew
621 This function writes the region delimited by @var{start} and @var{end}
622 in the current buffer into the file specified by @var{filename}.
624 If @var{start} is @code{nil}, then the command writes the entire buffer
625 contents (@emph{not} just the accessible portion) to the file and
629 If @var{start} is a string, then @code{write-region} writes or appends
630 that string, rather than text from the buffer. @var{end} is ignored in
633 If @var{append} is non-@code{nil}, then the specified text is appended
634 to the existing file contents (if any). If @var{append} is a
635 number, @code{write-region} seeks to that byte offset from the start
636 of the file and writes the data from there.
638 If @var{mustbenew} is non-@code{nil}, then @code{write-region} asks
639 for confirmation if @var{filename} names an existing file. If
640 @var{mustbenew} is the symbol @code{excl}, then @code{write-region}
641 does not ask for confirmation, but instead it signals an error
642 @code{file-already-exists} if the file already exists. Although
643 @code{write-region} normally follows a symbolic link and creates the
644 pointed-to file if the symbolic link is dangling, it does not follow
645 symbolic links if @var{mustbenew} is @code{excl}.
647 The test for an existing file, when @var{mustbenew} is @code{excl}, uses
648 a special system feature. At least for files on a local disk, there is
649 no chance that some other program could create a file of the same name
650 before Emacs does, without Emacs's noticing.
652 If @var{visit} is @code{t}, then Emacs establishes an association
653 between the buffer and the file: the buffer is then visiting that file.
654 It also sets the last file modification time for the current buffer to
655 @var{filename}'s modtime, and marks the buffer as not modified. This
656 feature is used by @code{save-buffer}, but you probably should not use
660 If @var{visit} is a string, it specifies the file name to visit. This
661 way, you can write the data to one file (@var{filename}) while recording
662 the buffer as visiting another file (@var{visit}). The argument
663 @var{visit} is used in the echo area message and also for file locking;
664 @var{visit} is stored in @code{buffer-file-name}. This feature is used
665 to implement @code{file-precious-flag}; don't use it yourself unless you
666 really know what you're doing.
668 The optional argument @var{lockname}, if non-@code{nil}, specifies the
669 file name to use for purposes of locking and unlocking, overriding
670 @var{filename} and @var{visit} for that purpose.
672 The function @code{write-region} converts the data which it writes to
673 the appropriate file formats specified by @code{buffer-file-format}
674 and also calls the functions in the list
675 @code{write-region-annotate-functions}.
676 @xref{Format Conversion}.
678 Normally, @code{write-region} displays the message @samp{Wrote
679 @var{filename}} in the echo area. This message is inhibited if
680 @var{visit} is neither @code{t} nor @code{nil} nor a string, or if
681 Emacs is operating in batch mode (@pxref{Batch Mode}). This
682 feature is useful for programs that use files for internal purposes,
683 files that the user does not need to know about.
686 @defvar write-region-inhibit-fsync
687 If this variable's value is @code{nil}, @code{write-region} uses the
688 @code{fsync} system call after writing a file. Although this slows
689 Emacs down, it lessens the risk of data loss after power failure. If
690 the value is @code{t}, Emacs does not use @code{fsync}. The default
691 value is @code{nil} when Emacs is interactive, and @code{t} when Emacs
692 runs in batch mode. @xref{Files and Storage}.
695 @defmac with-temp-file file body@dots{}
696 @anchor{Definition of with-temp-file}
697 The @code{with-temp-file} macro evaluates the @var{body} forms with a
698 temporary buffer as the current buffer; then, at the end, it writes the
699 buffer contents into file @var{file}. It kills the temporary buffer
700 when finished, restoring the buffer that was current before the
701 @code{with-temp-file} form. Then it returns the value of the last form
704 The current buffer is restored even in case of an abnormal exit via
705 @code{throw} or error (@pxref{Nonlocal Exits}).
707 See also @code{with-temp-buffer} in @ref{Definition of
708 with-temp-buffer,, The Current Buffer}.
716 When two users edit the same file at the same time, they are likely
717 to interfere with each other. Emacs tries to prevent this situation
718 from arising by recording a @dfn{file lock} when a file is being
720 Emacs can then detect the first attempt to modify a buffer visiting a
721 file that is locked by another Emacs job, and ask the user what to do.
722 The file lock is really a file, a symbolic link with a special name,
723 stored in the same directory as the file you are editing. (On file
724 systems that do not support symbolic links, a regular file is used.)
726 When you access files using NFS, there may be a small probability that
727 you and another user will both lock the same file simultaneously.
728 If this happens, it is possible for the two users to make changes
729 simultaneously, but Emacs will still warn the user who saves second.
730 Also, the detection of modification of a buffer visiting a file changed
731 on disk catches some cases of simultaneous editing; see
732 @ref{Modification Time}.
734 @defun file-locked-p filename
735 This function returns @code{nil} if the file @var{filename} is not
736 locked. It returns @code{t} if it is locked by this Emacs process, and
737 it returns the name of the user who has locked it if it is locked by
742 (file-locked-p "foo")
748 @defun lock-buffer &optional filename
749 This function locks the file @var{filename}, if the current buffer is
750 modified. The argument @var{filename} defaults to the current buffer's
751 visited file. Nothing is done if the current buffer is not visiting a
752 file, or is not modified, or if the option @code{create-lockfiles} is
757 This function unlocks the file being visited in the current buffer,
758 if the buffer is modified. If the buffer is not modified, then
759 the file should not be locked, so this function does nothing. It also
760 does nothing if the current buffer is not visiting a file, or is not locked.
763 @defopt create-lockfiles
764 If this variable is @code{nil}, Emacs does not lock files.
767 @defun ask-user-about-lock file other-user
768 This function is called when the user tries to modify @var{file}, but it
769 is locked by another user named @var{other-user}. The default
770 definition of this function asks the user to say what to do. The value
771 this function returns determines what Emacs does next:
775 A value of @code{t} says to grab the lock on the file. Then
776 this user may edit the file and @var{other-user} loses the lock.
779 A value of @code{nil} says to ignore the lock and let this
780 user edit the file anyway.
784 This function may instead signal a @code{file-locked} error, in which
785 case the change that the user was about to make does not take place.
787 The error message for this error looks like this:
790 @error{} File is locked: @var{file} @var{other-user}
794 where @code{file} is the name of the file and @var{other-user} is the
795 name of the user who has locked the file.
798 If you wish, you can replace the @code{ask-user-about-lock} function
799 with your own version that makes the decision in another way.
802 @node Information about Files
803 @section Information about Files
804 @cindex file, information about
806 This section describes the functions for retrieving various types of
807 information about files (or directories or symbolic links), such as
808 whether a file is readable or writable, and its size. These functions
809 all take arguments which are file names. Except where noted, these
810 arguments need to specify existing files, or an error is signaled.
812 @cindex file names, trailing whitespace
813 @cindex trailing blanks in file names
814 Be careful with file names that end in spaces. On some filesystems
815 (notably, MS-Windows), trailing whitespace characters in file names
816 are silently and automatically ignored.
819 * Testing Accessibility:: Is a given file readable? Writable?
820 * Kinds of Files:: Is it a directory? A symbolic link?
821 * Truenames:: Eliminating symbolic links from a file name.
822 * File Attributes:: File sizes, modification times, etc.
823 * Extended Attributes:: Extended file attributes for access control.
824 * Locating Files:: How to find a file in standard places.
827 @node Testing Accessibility
828 @subsection Testing Accessibility
829 @cindex accessibility of a file
830 @cindex file accessibility
832 These functions test for permission to access a file for reading,
833 writing, or execution. Unless explicitly stated otherwise, they
834 follow symbolic links. @xref{Kinds of Files}.
836 On some operating systems, more complex sets of access permissions
837 can be specified, via mechanisms such as Access Control Lists (ACLs).
838 @xref{Extended Attributes}, for how to query and set those
841 @defun file-exists-p filename
842 This function returns @code{t} if a file named @var{filename} appears
843 to exist. This does not mean you can necessarily read the file, only
844 that you can find out its attributes. (On GNU and other POSIX-like
845 systems, this is true if the file exists and you have execute
846 permission on the containing directories, regardless of the
847 permissions of the file itself.)
849 If the file does not exist, or if access control policies prevent you
850 from finding its attributes, this function returns @code{nil}.
852 Directories are files, so @code{file-exists-p} can return @code{t} when
853 given a directory. However, because @code{file-exists-p} follows
854 symbolic links, it returns @code{t} for a symbolic link
855 name only if the target file exists.
858 @defun file-readable-p filename
859 This function returns @code{t} if a file named @var{filename} exists
860 and you can read it. It returns @code{nil} otherwise.
863 @defun file-executable-p filename
864 This function returns @code{t} if a file named @var{filename} exists
865 and you can execute it. It returns @code{nil} otherwise. On GNU and
866 other POSIX-like systems, if the file is a directory, execute
867 permission means you can check the existence and attributes of files
868 inside the directory, and open those files if their modes permit.
871 @defun file-writable-p filename
872 This function returns @code{t} if the file @var{filename} can be written
873 or created by you, and @code{nil} otherwise. A file is writable if the
874 file exists and you can write it. It is creatable if it does not exist,
875 but the specified directory does exist and you can write in that
878 In the example below, @file{foo} is not writable because the parent
879 directory does not exist, even though the user could create such a
884 (file-writable-p "~/no-such-dir/foo")
890 @defun file-accessible-directory-p dirname
891 This function returns @code{t} if you have permission to open existing
892 files in the directory whose name as a file is @var{dirname};
893 otherwise (or if there is no such directory), it returns @code{nil}.
894 The value of @var{dirname} may be either a directory name (such as
895 @file{/foo/}) or the file name of a file which is a directory
896 (such as @file{/foo}, without the final slash).
898 For example, from the following we deduce that any attempt to read a
899 file in @file{/foo/} will give an error:
902 (file-accessible-directory-p "/foo")
907 @defun access-file filename string
908 This function opens file @var{filename} for reading, then closes it and
909 returns @code{nil}. However, if the open fails, it signals an error
910 using @var{string} as the error message text.
913 @defun file-ownership-preserved-p filename &optional group
914 This function returns @code{t} if deleting the file @var{filename} and
915 then creating it anew would keep the file's owner unchanged. It also
916 returns @code{t} for nonexistent files.
918 If the optional argument @var{group} is non-@code{nil}, this function
919 also checks that the file's group would be unchanged.
921 This function does not follow symbolic links.
924 @defun file-modes filename
926 @cindex file permissions
927 @cindex permissions, file
929 This function returns the @dfn{mode bits} of @var{filename}---an
930 integer summarizing its read, write, and execution permissions.
931 This function follows symbolic links. If the file does not exist, the
932 return value is @code{nil}.
934 @xref{File permissions,,, coreutils, The @sc{gnu} @code{Coreutils}
935 Manual}, for a description of mode bits. For example, if the
936 low-order bit is 1, the file is executable by all users; if the
937 second-lowest-order bit is 1, the file is writable by all users; etc.
938 The highest possible value is 4095 (7777 octal), meaning that everyone
939 has read, write, and execute permission, the @acronym{SUID} bit is set
940 for both others and group, and the sticky bit is set.
942 @xref{Changing Files}, for the @code{set-file-modes} function, which
943 can be used to set these permissions.
947 (file-modes "~/junk/diffs")
948 @result{} 492 ; @r{Decimal integer.}
952 @result{} "754" ; @r{Convert to octal.}
956 (set-file-modes "~/junk/diffs" #o666)
962 -rw-rw-rw- 1 lewis lewis 3063 Oct 30 16:00 diffs
966 @cindex MS-DOS and file modes
967 @cindex file modes and MS-DOS
968 @strong{MS-DOS note:} On MS-DOS, there is no such thing as an
969 executable file mode bit. So @code{file-modes} considers a file
970 executable if its name ends in one of the standard executable
971 extensions, such as @file{.com}, @file{.bat}, @file{.exe}, and some
972 others. Files that begin with the POSIX-standard @samp{#!} signature,
973 such as shell and Perl scripts, are also considered executable.
974 Directories are also reported as executable, for compatibility with
975 POSIX@. These conventions are also followed by @code{file-attributes}
976 (@pxref{File Attributes}).
980 @subsection Distinguishing Kinds of Files
981 @cindex file classification
982 @cindex classification of file types
983 @cindex symbolic links
985 This section describes how to distinguish various kinds of files, such
986 as directories, symbolic links, and ordinary files.
988 Symbolic links are ordinarily followed wherever they appear. For
989 example, to interpret the file name @file{a/b/c}, any of @file{a},
990 @file{a/b}, and @file{a/b/c} can be symbolic links that are followed,
991 possibly recursively if the link targets are themselves symbolic
992 links. However, a few functions do not follow symbolic links at the
993 end of a file name (@file{a/b/c} in this example). Such a function
994 is said to @dfn{not follow symbolic links}.
996 @defun file-symlink-p filename
997 @cindex symbolic links
998 If the file @var{filename} is a symbolic link, this function does not
999 follow it and instead returns its link target
1000 as a string. (The link target string is not necessarily the full
1001 absolute file name of the target; determining the full file name that
1002 the link points to is nontrivial, see below.)
1004 If the file @var{filename} is not a symbolic link, or does not exist,
1005 @code{file-symlink-p} returns @code{nil}.
1007 Here are a few examples of using this function:
1011 (file-symlink-p "not-a-symlink")
1015 (file-symlink-p "sym-link")
1016 @result{} "not-a-symlink"
1019 (file-symlink-p "sym-link2")
1020 @result{} "sym-link"
1023 (file-symlink-p "/bin")
1024 @result{} "/pub/bin"
1028 Note that in the third example, the function returned @file{sym-link},
1029 but did not proceed to resolve it, although that file is itself a
1030 symbolic link. That is because this function does not follow symbolic
1031 links---the process of following the symbolic links does not apply to
1032 the last component of the file name.
1034 The string that this function returns is what is recorded in the
1035 symbolic link; it may or may not include any leading directories.
1036 This function does @emph{not} expand the link target to produce a
1037 fully-qualified file name, and in particular does not use the leading
1038 directories, if any, of the @var{filename} argument if the link target
1039 is not an absolute file name. Here's an example:
1043 (file-symlink-p "/foo/bar/baz")
1044 @result{} "some-file"
1049 Here, although @file{/foo/bar/baz} was given as a fully-qualified file
1050 name, the result is not, and in fact does not have any leading
1051 directories at all. And since @file{some-file} might itself be a
1052 symbolic link, you cannot simply prepend leading directories to it,
1053 nor even naively use @code{expand-file-name} (@pxref{File Name
1054 Expansion}) to produce its absolute file name.
1056 For this reason, this function is seldom useful if you need to
1057 determine more than just the fact that a file is or isn't a symbolic
1058 link. If you actually need the file name of the link target, use
1059 @code{file-chase-links} or @code{file-truename}, described in
1063 @defun file-directory-p filename
1064 This function returns @code{t} if @var{filename} is the name of an
1065 existing directory, @code{nil} otherwise.
1066 This function follows symbolic links.
1070 (file-directory-p "~rms")
1074 (file-directory-p "~rms/lewis/files.texi")
1078 (file-directory-p "~rms/lewis/no-such-file")
1082 (file-directory-p "$HOME")
1087 (substitute-in-file-name "$HOME"))
1093 @defun file-regular-p filename
1094 This function returns @code{t} if the file @var{filename} exists and is
1095 a regular file (not a directory, named pipe, terminal, or
1097 This function follows symbolic links.
1101 @subsection Truenames
1102 @cindex truename (of file)
1104 The @dfn{truename} of a file is the name that you get by following
1105 symbolic links at all levels until none remain, then simplifying away
1106 @samp{.}@: and @samp{..}@: appearing as name components. This results
1107 in a sort of canonical name for the file. A file does not always have a
1108 unique truename; the number of distinct truenames a file has is equal to
1109 the number of hard links to the file. However, truenames are useful
1110 because they eliminate symbolic links as a cause of name variation.
1112 @defun file-truename filename
1113 This function returns the truename of the file @var{filename}. If the
1114 argument is not an absolute file name, this function first expands it
1115 against @code{default-directory}.
1117 This function does not expand environment variables. Only
1118 @code{substitute-in-file-name} does that. @xref{Definition of
1119 substitute-in-file-name}.
1121 If you may need to follow symbolic links preceding @samp{..}@:
1122 appearing as a name component, call @code{file-truename} without prior
1123 direct or indirect calls to @code{expand-file-name}. Otherwise, the
1124 file name component immediately preceding @samp{..} will be
1125 simplified away before @code{file-truename} is called. To
1126 eliminate the need for a call to @code{expand-file-name},
1127 @code{file-truename} handles @samp{~} in the same way that
1128 @code{expand-file-name} does.
1130 If the target of a symbolic links has remote file name syntax,
1131 @code{file-truename} returns it quoted. @xref{File Name Expansion,,
1132 Functions that Expand Filenames}.
1135 @defun file-chase-links filename &optional limit
1136 This function follows symbolic links, starting with @var{filename},
1137 until it finds a file name which is not the name of a symbolic link.
1138 Then it returns that file name. This function does @emph{not} follow
1139 symbolic links at the level of parent directories.
1141 If you specify a number for @var{limit}, then after chasing through
1142 that many links, the function just returns what it has even if that is
1143 still a symbolic link.
1146 To illustrate the difference between @code{file-chase-links} and
1147 @code{file-truename}, suppose that @file{/usr/foo} is a symbolic link to
1148 the directory @file{/home/foo}, and @file{/home/foo/hello} is an
1149 ordinary file (or at least, not a symbolic link) or nonexistent. Then
1153 (file-chase-links "/usr/foo/hello")
1154 ;; @r{This does not follow the links in the parent directories.}
1155 @result{} "/usr/foo/hello"
1156 (file-truename "/usr/foo/hello")
1157 ;; @r{Assuming that @file{/home} is not a symbolic link.}
1158 @result{} "/home/foo/hello"
1161 @defun file-equal-p file1 file2
1162 This function returns @code{t} if the files @var{file1} and
1163 @var{file2} name the same file. This is similar to comparing their
1164 truenames, except that remote file names are also handled in an
1165 appropriate manner. If @var{file1} or @var{file2} does not exist, the
1166 return value is unspecified.
1169 @defun file-name-case-insensitive-p filename
1170 Sometimes file names or their parts need to be compared as strings, in
1171 which case it's important to know whether the underlying filesystem is
1172 case-insensitive. This function returns @code{t} if file
1173 @var{filename} is on a case-insensitive filesystem. It always returns
1174 @code{t} on MS-DOS and MS-Windows. On Cygwin and macOS,
1175 filesystems may or may not be case-insensitive, and the function tries
1176 to determine case-sensitivity by a runtime test. If the test is
1177 inconclusive, the function returns @code{t} on Cygwin and @code{nil}
1180 Currently this function always returns @code{nil} on platforms other
1181 than MS-DOS, MS-Windows, Cygwin, and macOS. It does not detect
1182 case-insensitivity of mounted filesystems, such as Samba shares or
1183 NFS-mounted Windows volumes. On remote hosts, it assumes @code{t} for
1184 the @samp{smb} method. For all other connection methods, runtime
1185 tests are performed.
1188 @defun file-in-directory-p file dir
1189 This function returns @code{t} if @var{file} is a file in directory
1190 @var{dir}, or in a subdirectory of @var{dir}. It also returns
1191 @code{t} if @var{file} and @var{dir} are the same directory. It
1192 compares the truenames of the two directories. If @var{dir} does not
1193 name an existing directory, the return value is @code{nil}.
1196 @defun vc-responsible-backend file
1197 This function determines the responsible VC backend of the given
1198 @var{file}. For example, if @file{emacs.c} is a file tracked by Git,
1199 @w{@code{(vc-responsible-backend "emacs.c")}} returns @samp{Git}.
1200 Note that if @var{file} is a symbolic link,
1201 @code{vc-responsible-backend} will not resolve it---the backend of the
1202 symbolic link file itself is reported. To get the backend VC of the
1203 file to which @var{file} refers, wrap @var{file} with a symbolic link
1204 resolving function such as @code{file-chase-links}:
1207 (vc-responsible-backend (file-chase-links "emacs.c"))
1211 @node File Attributes
1212 @subsection File Attributes
1213 @cindex file attributes
1215 This section describes the functions for getting detailed
1216 information about a file, including the owner and group numbers, the
1217 number of names, the inode number, the size, and the times of access
1220 @defun file-newer-than-file-p filename1 filename2
1222 @cindex file modification time
1223 This function returns @code{t} if the file @var{filename1} is
1224 newer than file @var{filename2}. If @var{filename1} does not
1225 exist, it returns @code{nil}. If @var{filename1} does exist, but
1226 @var{filename2} does not, it returns @code{t}.
1228 In the following example, assume that the file @file{aug-19} was written
1229 on the 19th, @file{aug-20} was written on the 20th, and the file
1230 @file{no-file} doesn't exist at all.
1234 (file-newer-than-file-p "aug-19" "aug-20")
1238 (file-newer-than-file-p "aug-20" "aug-19")
1242 (file-newer-than-file-p "aug-19" "no-file")
1246 (file-newer-than-file-p "no-file" "aug-19")
1252 @defun file-attributes filename &optional id-format
1253 @anchor{Definition of file-attributes}
1254 This function returns a list of attributes of file @var{filename}. If
1255 the specified file's attributes cannot be accessed, it returns @code{nil}.
1256 This function does not follow symbolic links.
1257 The optional parameter @var{id-format} specifies the preferred format
1258 of attributes @acronym{UID} and @acronym{GID} (see below)---the
1259 valid values are @code{'string} and @code{'integer}. The latter is
1260 the default, but we plan to change that, so you should specify a
1261 non-@code{nil} value for @var{id-format} if you use the returned
1262 @acronym{UID} or @acronym{GID}.
1264 On GNU platforms when operating on a local file, this function is
1265 atomic: if the filesystem is simultaneously being changed by some
1266 other process, this function returns the file's attributes either
1267 before or after the change. Otherwise this function is not atomic,
1268 and might return @code{nil} if it detects the race condition, or might
1269 return a hodgepodge of the previous and current file attributes.
1271 Accessor functions are provided to access the elements in this list.
1272 The accessors are mentioned along with the descriptions of the
1275 The elements of the list, in order, are:
1279 @code{t} for a directory, a string for a symbolic link (the name
1280 linked to), or @code{nil} for a text file
1281 (@code{file-attribute-type}).
1283 @c Wordy so as to prevent an overfull hbox. --rjc 15mar92
1285 The number of names the file has (@code{file-attribute-link-number}).
1286 Alternate names, also known as hard links, can be created by using the
1287 @code{add-name-to-file} function (@pxref{Changing Files}).
1290 The file's @acronym{UID}, normally as a string
1291 (@code{file-attribute-user-id}). However, if it does not correspond
1292 to a named user, the value is a number.
1295 The file's @acronym{GID}, likewise (@code{file-attribute-group-id}).
1298 The time of last access, as a list of four integers
1299 @code{(@var{sec-high} @var{sec-low} @var{microsec} @var{picosec})}
1300 (@code{file-attribute-access-time}). (This is similar to the value of
1301 @code{current-time}; see @ref{Time of Day}.) The value is truncated
1302 to that of the filesystem's timestamp resolution; for example, on some
1303 FAT-based filesystems, only the date of last access is recorded, so
1304 this time will always hold the midnight of the day of the last access.
1306 @cindex modification time of file
1308 The time of last modification as a list of four integers (as above)
1309 (@code{file-attribute-modification-time}). This is the last time when
1310 the file's contents were modified.
1313 The time of last status change as a list of four integers (as above)
1314 (@code{file-attribute-status-change-time}). This is the time of the
1315 last change to the file's access mode bits, its owner and group, and
1316 other information recorded in the filesystem for the file, beyond the
1320 The size of the file in bytes (@code{file-attribute-size}). This is
1321 floating point if the size is too large to fit in a Lisp integer.
1324 The file's modes, as a string of ten letters or dashes, as in
1325 @samp{ls -l} (@code{file-attribute-modes}).
1328 An unspecified value, present for backward compatibility.
1331 The file's inode number (@code{file-attribute-inode-number}). If
1332 possible, this is an integer. If the inode number is too large to be
1333 represented as an integer in Emacs Lisp but dividing it by
1334 @math{2^{16}} yields a representable integer, then the value has the
1335 form @code{(@var{high} . @var{low})}, where @var{low} holds the low 16
1336 bits. If the inode number is too wide for even that, the value is of
1337 the form @code{(@var{high} @var{middle} . @var{low})}, where
1338 @code{high} holds the high bits, @var{middle} the middle 24 bits, and
1339 @var{low} the low 16 bits.
1342 The filesystem number of the device that the file is on
1343 @code{file-attribute-device-number}). Depending on the magnitude of
1344 the value, this can be either an integer or a cons cell, in the same
1345 manner as the inode number. This element and the file's inode number
1346 together give enough information to distinguish any two files on the
1347 system---no two files can have the same values for both of these
1351 For example, here are the file attributes for @file{files.texi}:
1355 (file-attributes "files.texi" 'string)
1356 @result{} (nil 1 "lh" "users"
1357 (20614 64019 50040 152000)
1359 (20614 64555 902289 872000)
1367 and here is how the result is interpreted:
1371 is neither a directory nor a symbolic link.
1374 has only one name (the name @file{files.texi} in the current default
1378 is owned by the user with name @samp{lh}.
1381 is in the group with name @samp{users}.
1383 @item (20614 64019 50040 152000)
1384 was last accessed on October 23, 2012, at 20:12:03.050040152 UTC.
1386 @item (20000 23 0 0)
1387 was last modified on July 15, 2001, at 08:53:43 UTC.
1389 @item (20614 64555 902289 872000)
1390 last had its status changed on October 23, 2012, at 20:20:59.902289872 UTC.
1393 is 122295 bytes long. (It may not contain 122295 characters, though,
1394 if some of the bytes belong to multibyte sequences, and also if the
1395 end-of-line format is CR-LF.)
1398 has a mode of read and write access for the owner, group, and world.
1401 is merely a placeholder; it carries no information.
1403 @item (5888 2 . 43978)
1404 has an inode number of 6473924464520138.
1406 @item (15479 . 46724)
1407 is on the file-system device whose number is 1014478468.
1411 @defun file-nlinks filename
1412 This function returns the number of names (i.e., hard links) that
1413 file @var{filename} has. If the file does not exist, this function
1414 returns @code{nil}. Note that symbolic links have no effect on this
1415 function, because they are not considered to be names of the files
1416 they link to. This function does not follow symbolic links.
1421 -rw-rw-rw- 2 rms rms 4 Aug 19 01:27 foo
1422 -rw-rw-rw- 2 rms rms 4 Aug 19 01:27 foo1
1430 (file-nlinks "doesnt-exist")
1436 @node Extended Attributes
1437 @subsection Extended File Attributes
1438 @cindex extended file attributes
1440 On some operating systems, each file can be associated with arbitrary
1441 @dfn{extended file attributes}. At present, Emacs supports querying
1442 and setting two specific sets of extended file attributes: Access
1443 Control Lists (ACLs) and SELinux contexts. These extended file
1444 attributes are used, on some systems, to impose more sophisticated
1445 file access controls than the basic Unix-style permissions
1446 discussed in the previous sections.
1448 @cindex access control list
1450 @cindex SELinux context
1451 A detailed explanation of ACLs and SELinux is beyond the scope of
1452 this manual. For our purposes, each file can be associated with an
1453 @dfn{ACL}, which specifies its properties under an ACL-based file
1454 control system, and/or an @dfn{SELinux context}, which specifies its
1455 properties under the SELinux system.
1457 @defun file-acl filename
1458 This function returns the ACL for the file @var{filename}. The exact
1459 Lisp representation of the ACL is unspecified (and may change in
1460 future Emacs versions), but it is the same as what @code{set-file-acl}
1461 takes for its @var{acl} argument (@pxref{Changing Files}).
1463 The underlying ACL implementation is platform-specific; on GNU/Linux
1464 and BSD, Emacs uses the POSIX ACL interface, while on MS-Windows Emacs
1465 emulates the POSIX ACL interface with native file security APIs.
1467 If Emacs was not compiled with ACL support, or the file does not exist
1468 or is inaccessible, or Emacs was unable to determine the ACL entries
1469 for any other reason, then the return value is @code{nil}.
1472 @defun file-selinux-context filename
1473 This function returns the SELinux context of the file @var{filename},
1474 as a list of the form @code{(@var{user} @var{role} @var{type}
1475 @var{range})}. The list elements are the context's user, role, type,
1476 and range respectively, as Lisp strings; see the SELinux documentation
1477 for details about what these actually mean. The return value has the
1478 same form as what @code{set-file-selinux-context} takes for its
1479 @var{context} argument (@pxref{Changing Files}).
1481 If Emacs was not compiled with SELinux support, or the file does not
1482 exist or is inaccessible, or if the system does not support SELinux,
1483 then the return value is @code{(nil nil nil nil)}.
1486 @defun file-extended-attributes filename
1487 This function returns an alist of the Emacs-recognized extended
1488 attributes of file @var{filename}. Currently, it serves as a
1489 convenient way to retrieve both the ACL and SELinux context; you can
1490 then call the function @code{set-file-extended-attributes}, with the
1491 returned alist as its second argument, to apply the same file access
1492 attributes to another file (@pxref{Changing Files}).
1494 One of the elements is @code{(acl . @var{acl})}, where @var{acl} has
1495 the same form returned by @code{file-acl}.
1497 Another element is @code{(selinux-context . @var{context})}, where
1498 @var{context} is the SELinux context, in the same form returned by
1499 @code{file-selinux-context}.
1502 @node Locating Files
1503 @subsection Locating Files in Standard Places
1504 @cindex locate file in path
1505 @cindex find file in path
1507 This section explains how to search for a file in a list of
1508 directories (a @dfn{path}), or for an executable file in the standard
1509 list of executable file directories.
1511 To search for a user-specific configuration file, @xref{Standard
1512 File Names}, for the @code{locate-user-emacs-file} function.
1514 @defun locate-file filename path &optional suffixes predicate
1515 This function searches for a file whose name is @var{filename} in a
1516 list of directories given by @var{path}, trying the suffixes in
1517 @var{suffixes}. If it finds such a file, it returns the file's
1518 absolute file name (@pxref{Relative File Names}); otherwise it returns
1521 The optional argument @var{suffixes} gives the list of file-name
1522 suffixes to append to @var{filename} when searching.
1523 @code{locate-file} tries each possible directory with each of these
1524 suffixes. If @var{suffixes} is @code{nil}, or @code{("")}, then there
1525 are no suffixes, and @var{filename} is used only as-is. Typical
1526 values of @var{suffixes} are @code{exec-suffixes} (@pxref{Subprocess
1527 Creation}), @code{load-suffixes}, @code{load-file-rep-suffixes} and
1528 the return value of the function @code{get-load-suffixes} (@pxref{Load
1531 Typical values for @var{path} are @code{exec-path} (@pxref{Subprocess
1532 Creation}) when looking for executable programs, or @code{load-path}
1533 (@pxref{Library Search}) when looking for Lisp files. If
1534 @var{filename} is absolute, @var{path} has no effect, but the suffixes
1535 in @var{suffixes} are still tried.
1537 The optional argument @var{predicate}, if non-@code{nil}, specifies a
1538 predicate function for testing whether a candidate file is suitable.
1539 The predicate is passed the candidate file name as its single
1540 argument. If @var{predicate} is @code{nil} or omitted,
1541 @code{locate-file} uses @code{file-readable-p} as the predicate.
1542 @xref{Kinds of Files}, for other useful predicates, e.g.,
1543 @code{file-executable-p} and @code{file-directory-p}.
1545 This function will normally skip directories, so if you want it to
1546 find directories, make sure the @var{predicate} function returns
1547 @code{dir-ok} for them. For example:
1550 (locate-file "html" '("/var/www" "/srv") nil
1551 (lambda (f) (if (file-directory-p f) 'dir-ok)))
1555 For compatibility, @var{predicate} can also be one of the symbols
1556 @code{executable}, @code{readable}, @code{writable}, @code{exists}, or
1557 a list of one or more of these symbols.
1560 @defun executable-find program
1561 This function searches for the executable file of the named
1562 @var{program} and returns the absolute file name of the executable,
1563 including its file-name extensions, if any. It returns @code{nil} if
1564 the file is not found. The functions searches in all the directories
1565 in @code{exec-path}, and tries all the file-name extensions in
1566 @code{exec-suffixes} (@pxref{Subprocess Creation}).
1569 @node Changing Files
1570 @section Changing File Names and Attributes
1571 @c @cindex renaming files Duplicates rename-file
1572 @cindex copying files
1573 @cindex deleting files
1574 @cindex linking files
1575 @cindex setting modes of files
1577 The functions in this section rename, copy, delete, link, and set
1578 the modes (permissions) of files. Typically, they signal a
1579 @code{file-error} error if they fail to perform their function,
1580 reporting the system-dependent error message that describes the reason
1581 for the failure. If they fail because a file is missing, they signal
1582 a @code{file-missing} error instead.
1584 For performance, the operating system may cache or alias changes
1585 made by these functions instead of writing them immediately to
1586 secondary storage. @xref{Files and Storage}.
1588 In the functions that have an argument @var{newname}, if this
1589 argument is a directory name it is treated as if the nondirectory part
1590 of the source name were appended. Typically, a directory name is one
1591 that ends in @samp{/} (@pxref{Directory Names}). For example, if the
1592 old name is @file{a/b/c}, the @var{newname} @file{d/e/f/} is treated
1593 as if it were @file{d/e/f/c}. This special treatment does not apply
1594 if @var{newname} is not a directory name but names a file that is a
1595 directory; for example, the @var{newname} @file{d/e/f} is left as-is
1596 even if @file{d/e/f} happens to be a directory.
1598 In the functions that have an argument @var{newname}, if a file by the
1599 name of @var{newname} already exists, the actions taken depend on the
1600 value of the argument @var{ok-if-already-exists}:
1604 Signal a @code{file-already-exists} error if
1605 @var{ok-if-already-exists} is @code{nil}.
1608 Request confirmation if @var{ok-if-already-exists} is a number.
1611 Replace the old file without confirmation if @var{ok-if-already-exists}
1615 @deffn Command add-name-to-file oldname newname &optional ok-if-already-exists
1616 @cindex file with multiple names
1617 @cindex file hard link
1618 This function gives the file named @var{oldname} the additional name
1619 @var{newname}. This means that @var{newname} becomes a new hard
1620 link to @var{oldname}.
1622 If @var{newname} is a symbolic link, its directory entry is replaced,
1623 not the directory entry it points to. If @var{oldname} is a symbolic
1624 link, this function might or might not follow the link; it does not
1625 follow the link on GNU platforms. If @var{oldname} is a directory,
1626 this function typically fails, although for the superuser on a few
1627 old-fashioned non-GNU platforms it can succeed and create a filesystem
1628 that is not tree-structured.
1630 In the first part of the following example, we list two files,
1631 @file{foo} and @file{foo3}.
1636 81908 -rw-rw-rw- 1 rms rms 29 Aug 18 20:32 foo
1637 84302 -rw-rw-rw- 1 rms rms 24 Aug 18 20:31 foo3
1641 Now we create a hard link, by calling @code{add-name-to-file}, then list
1642 the files again. This shows two names for one file, @file{foo} and
1647 (add-name-to-file "foo" "foo2")
1653 81908 -rw-rw-rw- 2 rms rms 29 Aug 18 20:32 foo
1654 81908 -rw-rw-rw- 2 rms rms 29 Aug 18 20:32 foo2
1655 84302 -rw-rw-rw- 1 rms rms 24 Aug 18 20:31 foo3
1659 Finally, we evaluate the following:
1662 (add-name-to-file "foo" "foo3" t)
1666 and list the files again. Now there are three names
1667 for one file: @file{foo}, @file{foo2}, and @file{foo3}. The old
1668 contents of @file{foo3} are lost.
1672 (add-name-to-file "foo1" "foo3")
1678 81908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo
1679 81908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo2
1680 81908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo3
1684 This function is meaningless on operating systems where multiple names
1685 for one file are not allowed. Some systems implement multiple names
1686 by copying the file instead.
1688 See also @code{file-nlinks} in @ref{File Attributes}.
1691 @deffn Command rename-file filename newname &optional ok-if-already-exists
1692 This command renames the file @var{filename} as @var{newname}.
1694 If @var{filename} has additional names aside from @var{filename}, it
1695 continues to have those names. In fact, adding the name @var{newname}
1696 with @code{add-name-to-file} and then deleting @var{filename} has the
1697 same effect as renaming, aside from momentary intermediate states and
1698 treatment of errors, directories and symbolic links.
1700 This command does not follow symbolic links. If @var{filename} is a
1701 symbolic link, this command renames the symbolic link, not the file it
1702 points to. If @var{newname} is a symbolic link, its directory entry
1703 is replaced, not the directory entry it points to.
1705 This command does nothing if @var{filename} and @var{newname} are the
1706 same directory entry, i.e., if they refer to the same parent directory
1707 and give the same name within that directory. Otherwise, if
1708 @var{filename} and @var{newname} name the same file, this command does
1709 nothing on POSIX-conforming systems, and removes @var{filename} on
1710 some non-POSIX systems.
1712 If @var{newname} exists, then it must be an empty directory if
1713 @var{oldname} is a directory and a non-directory otherwise.
1716 @deffn Command copy-file oldname newname &optional ok-if-already-exists time preserve-uid-gid preserve-extended-attributes
1717 This command copies the file @var{oldname} to @var{newname}. An
1718 error is signaled if @var{oldname} is not a regular file. If @var{newname}
1719 names a directory, it copies @var{oldname} into that directory,
1720 preserving its final name component.
1721 @c FIXME: See Bug#27986 for how the previous sentence might change.
1723 This function follows symbolic links, except that it does not follow a
1724 dangling symbolic link to create @var{newname}.
1726 If @var{time} is non-@code{nil}, then this function gives the new file
1727 the same last-modified time that the old one has. (This works on only
1728 some operating systems.) If setting the time gets an error,
1729 @code{copy-file} signals a @code{file-date-error} error. In an
1730 interactive call, a prefix argument specifies a non-@code{nil} value
1733 If argument @var{preserve-uid-gid} is @code{nil}, we let the operating
1734 system decide the user and group ownership of the new file (this is
1735 usually set to the user running Emacs). If @var{preserve-uid-gid} is
1736 non-@code{nil}, we attempt to copy the user and group ownership of the
1737 file. This works only on some operating systems, and only if you have
1738 the correct permissions to do so.
1740 If the optional argument @var{preserve-permissions} is non-@code{nil},
1741 this function copies the file modes (or ``permissions'') of
1742 @var{oldname} to @var{newname}, as well as the Access Control List and
1743 SELinux context (if any). @xref{Information about Files}.
1745 Otherwise, the file modes of @var{newname} are left unchanged if it is
1746 an existing file, and set to those of @var{oldname}, masked by the
1747 default file permissions (see @code{set-default-file-modes} below), if
1748 @var{newname} is to be newly created. The Access Control List or
1749 SELinux context are not copied over in either case.
1752 @deffn Command make-symbolic-link target newname &optional ok-if-already-exists
1754 @kindex file-already-exists
1755 This command makes a symbolic link to @var{target}, named
1756 @var{newname}. This is like the shell command @samp{ln -s
1757 @var{target} @var{newname}}. The @var{target} argument
1758 is treated only as a string; it need not name an existing file.
1759 If @var{ok-if-already-exists} is an integer, indicating interactive
1760 use, then leading @samp{~} is expanded and leading @samp{/:} is
1761 stripped in the @var{target} string.
1763 If @var{target} is a relative file name, the resulting symbolic link
1764 is interpreted relative to the directory containing the symbolic link.
1765 @xref{Relative File Names}.
1767 If both @var{target} and @var{newname} have remote file name syntax,
1768 and if both remote identifications are equal, the symbolic link points
1769 to the local file name part of @var{target}.
1771 This function is not available on systems that don't support symbolic
1776 @vindex delete-by-moving-to-trash
1777 @deffn Command delete-file filename &optional trash
1779 This command deletes the file @var{filename}. If the file has
1780 multiple names, it continues to exist under the other names. If
1781 @var{filename} is a symbolic link, @code{delete-file} deletes only the
1782 symbolic link and not its target.
1784 A suitable kind of @code{file-error} error is signaled if the file
1785 does not exist, or is not deletable. (On GNU and other POSIX-like
1786 systems, a file is deletable if its directory is writable.)
1788 If the optional argument @var{trash} is non-@code{nil} and the
1789 variable @code{delete-by-moving-to-trash} is non-@code{nil}, this
1790 command moves the file into the system Trash instead of deleting it.
1791 @xref{Misc File Ops,,Miscellaneous File Operations, emacs, The GNU
1792 Emacs Manual}. When called interactively, @var{trash} is @code{t} if
1793 no prefix argument is given, and @code{nil} otherwise.
1795 See also @code{delete-directory} in @ref{Create/Delete Dirs}.
1798 @cindex file permissions, setting
1799 @cindex permissions, file
1800 @cindex file modes, setting
1801 @deffn Command set-file-modes filename mode
1802 This function sets the @dfn{file mode} (or @dfn{permissions}) of
1803 @var{filename} to @var{mode}. This function follows symbolic links.
1805 If called non-interactively, @var{mode} must be an integer. Only the
1806 lowest 12 bits of the integer are used; on most systems, only the
1807 lowest 9 bits are meaningful. You can use the Lisp construct for
1808 octal numbers to enter @var{mode}. For example,
1811 (set-file-modes #o644)
1815 specifies that the file should be readable and writable for its owner,
1816 readable for group members, and readable for all other users.
1817 @xref{File permissions,,, coreutils, The @sc{gnu} @code{Coreutils}
1818 Manual}, for a description of mode bit specifications.
1820 Interactively, @var{mode} is read from the minibuffer using
1821 @code{read-file-modes} (see below), which lets the user type in either
1822 an integer or a string representing the permissions symbolically.
1824 @xref{File Attributes}, for the function @code{file-modes}, which
1825 returns the permissions of a file.
1828 @defun set-default-file-modes mode
1830 This function sets the default permissions for new files created by
1831 Emacs and its subprocesses. Every file created with Emacs initially
1832 has these permissions, or a subset of them (@code{write-region} will
1833 not grant execute permissions even if the default file permissions
1834 allow execution). On GNU and other POSIX-like systems, the default
1835 permissions are given by the bitwise complement of the @samp{umask}
1836 value, i.e.@: each bit that is set in the argument @var{mode} will be
1837 @emph{reset} in the default permissions with which Emacs creates
1840 The argument @var{mode} should be an integer which specifies the
1841 permissions, similar to @code{set-file-modes} above. Only the lowest
1842 9 bits are meaningful.
1844 The default file permissions have no effect when you save a modified
1845 version of an existing file; saving a file preserves its existing
1849 @defmac with-file-modes mode body@dots{}
1850 This macro evaluates the @var{body} forms with the default
1851 permissions for new files temporarily set to @var{modes} (whose value
1852 is as for @code{set-file-modes} above). When finished, it restores
1853 the original default file permissions, and returns the value of the
1854 last form in @var{body}.
1856 This is useful for creating private files, for example.
1859 @defun default-file-modes
1860 This function returns the default file permissions, as an integer.
1863 @defun read-file-modes &optional prompt base-file
1864 This function reads a set of file mode bits from the minibuffer. The
1865 first optional argument @var{prompt} specifies a non-default prompt.
1866 Second second optional argument @var{base-file} is the name of a file
1867 on whose permissions to base the mode bits that this function returns,
1868 if what the user types specifies mode bits relative to permissions of
1871 If user input represents an octal number, this function returns that
1872 number. If it is a complete symbolic specification of mode bits, as
1873 in @code{"u=rwx"}, the function converts it to the equivalent numeric
1874 value using @code{file-modes-symbolic-to-number} and returns the
1875 result. If the specification is relative, as in @code{"o+g"}, then
1876 the permissions on which the specification is based are taken from the
1877 mode bits of @var{base-file}. If @var{base-file} is omitted or
1878 @code{nil}, the function uses @code{0} as the base mode bits. The
1879 complete and relative specifications can be combined, as in
1880 @code{"u+r,g+rx,o+r,g-w"}. @xref{File permissions,,, coreutils, The
1881 @sc{gnu} @code{Coreutils} Manual}, for a description of file mode
1885 @defun file-modes-symbolic-to-number modes &optional base-modes
1886 This function converts a symbolic file mode specification in
1887 @var{modes} into the equivalent integer. If the symbolic
1888 specification is based on an existing file, that file's mode bits are
1889 taken from the optional argument @var{base-modes}; if that argument is
1890 omitted or @code{nil}, it defaults to 0, i.e., no access rights at
1894 @defun set-file-times filename &optional time
1895 This function sets the access and modification times of @var{filename}
1896 to @var{time}. The return value is @code{t} if the times are successfully
1897 set, otherwise it is @code{nil}. @var{time} defaults to the current
1898 time and must be a time value (@pxref{Time of Day}).
1901 @defun set-file-extended-attributes filename attribute-alist
1902 This function sets the Emacs-recognized extended file attributes for
1903 @code{filename}. The second argument @var{attribute-alist} should be
1904 an alist of the same form returned by @code{file-extended-attributes}.
1905 The return value is @code{t} if the attributes are successfully set,
1906 otherwise it is @code{nil}.
1907 @xref{Extended Attributes}.
1910 @defun set-file-selinux-context filename context
1911 This function sets the SELinux security context for @var{filename} to
1912 @var{context}. The @var{context} argument should be a list
1913 @code{(@var{user} @var{role} @var{type} @var{range})}, where each
1914 element is a string. @xref{Extended Attributes}.
1916 The function returns @code{t} if it succeeds in setting the SELinux
1917 context of @var{filename}. It returns @code{nil} if the context was
1918 not set (e.g., if SELinux is disabled, or if Emacs was compiled
1919 without SELinux support).
1922 @defun set-file-acl filename acl
1923 This function sets the Access Control List for @var{filename} to
1924 @var{acl}. The @var{acl} argument should have the same form returned
1925 by the function @code{file-acl}. @xref{Extended Attributes}.
1927 The function returns @code{t} if it successfully sets the ACL of
1928 @var{filename}, @code{nil} otherwise.
1931 @node Files and Storage
1932 @section Files and Secondary Storage
1933 @cindex secondary storage
1935 After Emacs changes a file, there are two reasons the changes might
1936 not survive later failures of power or media, both having to do with
1937 efficiency. First, the operating system might alias written data with
1938 data already stored elsewhere on secondary storage until one file or
1939 the other is later modified; this will lose both files if the only
1940 copy on secondary storage is lost due to media failure. Second, the
1941 operating system might not write data to secondary storage
1942 immediately, which will lose the data if power is lost.
1944 @findex write-region
1945 Although both sorts of failures can largely be avoided by a suitably
1946 configured file system, such systems are typically more expensive or
1947 less efficient. In more-typical systems, to survive media failure you
1948 can copy the file to a different device, and to survive a power
1949 failure you can use the @code{write-region} function with the
1950 @code{write-region-inhibit-fsync} variable set to @code{nil}.
1951 @xref{Writing to Files}.
1957 Files are generally referred to by their names, in Emacs as elsewhere.
1958 File names in Emacs are represented as strings. The functions that
1959 operate on a file all expect a file name argument.
1961 In addition to operating on files themselves, Emacs Lisp programs
1962 often need to operate on file names; i.e., to take them apart and to use
1963 part of a name to construct related file names. This section describes
1964 how to manipulate file names.
1966 The functions in this section do not actually access files, so they
1967 can operate on file names that do not refer to an existing file or
1970 @findex cygwin-convert-file-name-from-windows
1971 @findex cygwin-convert-file-name-to-windows
1972 @cindex MS-Windows file-name syntax
1973 @cindex converting file names from/to MS-Windows syntax
1974 On MS-DOS and MS-Windows, these functions (like the function that
1975 actually operate on files) accept MS-DOS or MS-Windows file-name syntax,
1976 where backslashes separate the components, as well as POSIX syntax; but
1977 they always return POSIX syntax. This enables Lisp programs to specify
1978 file names in POSIX syntax and work properly on all systems without
1979 change.@footnote{In MS-Windows versions of Emacs compiled for the Cygwin
1980 environment, you can use the functions
1981 @code{cygwin-convert-file-name-to-windows} and
1982 @code{cygwin-convert-file-name-from-windows} to convert between the
1983 two file-name syntaxes.}
1986 * File Name Components:: The directory part of a file name, and the rest.
1987 * Relative File Names:: Some file names are relative to a current directory.
1988 * Directory Names:: A directory's name as a directory
1989 is different from its name as a file.
1990 * File Name Expansion:: Converting relative file names to absolute ones.
1991 * Unique File Names:: Generating names for temporary files.
1992 * File Name Completion:: Finding the completions for a given file name.
1993 * Standard File Names:: If your package uses a fixed file name,
1994 how to handle various operating systems simply.
1997 @node File Name Components
1998 @subsection File Name Components
1999 @cindex directory part (of file name)
2000 @cindex nondirectory part (of file name)
2001 @cindex version number (in file name)
2003 The operating system groups files into directories. To specify a
2004 file, you must specify the directory and the file's name within that
2005 directory. Therefore, Emacs considers a file name as having two main
2006 parts: the @dfn{directory name} part, and the @dfn{nondirectory} part
2007 (or @dfn{file name within the directory}). Either part may be empty.
2008 Concatenating these two parts reproduces the original file name.
2010 On most systems, the directory part is everything up to and including
2011 the last slash (backslash is also allowed in input on MS-DOS or
2012 MS-Windows); the nondirectory part is the rest.
2014 For some purposes, the nondirectory part is further subdivided into
2015 the name proper and the @dfn{version number}. On most systems, only
2016 backup files have version numbers in their names.
2018 @defun file-name-directory filename
2019 This function returns the directory part of @var{filename}, as a
2020 directory name (@pxref{Directory Names}), or @code{nil} if
2021 @var{filename} does not include a directory part.
2023 On GNU and other POSIX-like systems, a string returned by this function always
2024 ends in a slash. On MS-DOS it can also end in a colon.
2028 (file-name-directory "lewis/foo") ; @r{GNU example}
2032 (file-name-directory "foo") ; @r{GNU example}
2038 @defun file-name-nondirectory filename
2039 This function returns the nondirectory part of @var{filename}.
2043 (file-name-nondirectory "lewis/foo")
2047 (file-name-nondirectory "foo")
2051 (file-name-nondirectory "lewis/")
2057 @defun file-name-sans-versions filename &optional keep-backup-version
2058 This function returns @var{filename} with any file version numbers,
2059 backup version numbers, or trailing tildes discarded.
2061 If @var{keep-backup-version} is non-@code{nil}, then true file version
2062 numbers understood as such by the file system are discarded from the
2063 return value, but backup version numbers are kept.
2067 (file-name-sans-versions "~rms/foo.~1~")
2068 @result{} "~rms/foo"
2071 (file-name-sans-versions "~rms/foo~")
2072 @result{} "~rms/foo"
2075 (file-name-sans-versions "~rms/foo")
2076 @result{} "~rms/foo"
2081 @defun file-name-extension filename &optional period
2082 This function returns @var{filename}'s final extension, if any,
2083 after applying @code{file-name-sans-versions} to remove any
2084 version/backup part. The extension, in a file name, is the part that
2085 follows the last @samp{.} in the last name component (minus any
2086 version/backup part).
2088 This function returns @code{nil} for extensionless file names such as
2089 @file{foo}. It returns @code{""} for null extensions, as in
2090 @file{foo.}. If the last component of a file name begins with a
2091 @samp{.}, that @samp{.} doesn't count as the beginning of an
2092 extension. Thus, @file{.emacs}'s extension is @code{nil}, not
2095 If @var{period} is non-@code{nil}, then the returned value includes
2096 the period that delimits the extension, and if @var{filename} has no
2097 extension, the value is @code{""}.
2100 @defun file-name-sans-extension filename
2101 This function returns @var{filename} minus its extension, if any. The
2102 version/backup part, if present, is only removed if the file has an
2103 extension. For example,
2106 (file-name-sans-extension "foo.lose.c")
2107 @result{} "foo.lose"
2108 (file-name-sans-extension "big.hack/foo")
2109 @result{} "big.hack/foo"
2110 (file-name-sans-extension "/my/home/.emacs")
2111 @result{} "/my/home/.emacs"
2112 (file-name-sans-extension "/my/home/.emacs.el")
2113 @result{} "/my/home/.emacs"
2114 (file-name-sans-extension "~/foo.el.~3~")
2116 (file-name-sans-extension "~/foo.~3~")
2117 @result{} "~/foo.~3~"
2120 Note that the @samp{.~3~} in the two last examples is the backup part,
2124 @defun file-name-base &optional filename
2125 This function is the composition of @code{file-name-sans-extension}
2126 and @code{file-name-nondirectory}. For example,
2129 (file-name-base "/my/home/foo.c")
2133 The @var{filename} argument defaults to @code{buffer-file-name}.
2136 @node Relative File Names
2137 @subsection Absolute and Relative File Names
2138 @cindex absolute file name
2139 @cindex relative file name
2141 All the directories in the file system form a tree starting at the
2142 root directory. A file name can specify all the directory names
2143 starting from the root of the tree; then it is called an
2144 @dfn{absolute} file name. Or it can specify the position of the file
2145 in the tree relative to a default directory; then it is called a
2146 @dfn{relative} file name. On GNU and other POSIX-like systems,
2147 after any leading @samp{~} has been expanded, an absolute file name
2148 starts with a @samp{/}
2149 (@pxref{abbreviate-file-name}), and a relative one does not. On
2150 MS-DOS and MS-Windows, an absolute file name starts with a slash or a
2151 backslash, or with a drive specification @samp{@var{x}:/}, where
2152 @var{x} is the @dfn{drive letter}.
2154 @defun file-name-absolute-p filename
2155 This function returns @code{t} if file @var{filename} is an absolute
2156 file name or begins with @samp{~}, @code{nil} otherwise.
2160 (file-name-absolute-p "~rms/foo")
2164 (file-name-absolute-p "rms/foo")
2168 (file-name-absolute-p "/user/rms/foo")
2174 Given a possibly relative file name, you can expand any
2175 leading @samp{~} and convert the result to an
2176 absolute name using @code{expand-file-name} (@pxref{File Name
2177 Expansion}). This function converts absolute file names to relative
2180 @defun file-relative-name filename &optional directory
2181 This function tries to return a relative name that is equivalent to
2182 @var{filename}, assuming the result will be interpreted relative to
2183 @var{directory} (an absolute directory name or directory file name).
2184 If @var{directory} is omitted or @code{nil}, it defaults to the
2185 current buffer's default directory.
2187 On some operating systems, an absolute file name begins with a device
2188 name. On such systems, @var{filename} has no relative equivalent based
2189 on @var{directory} if they start with two different device names. In
2190 this case, @code{file-relative-name} returns @var{filename} in absolute
2194 (file-relative-name "/foo/bar" "/foo/")
2196 (file-relative-name "/foo/bar" "/hack/")
2197 @result{} "../foo/bar"
2201 @node Directory Names
2202 @subsection Directory Names
2203 @cindex directory name
2204 @cindex directory file name
2205 @cindex file name of directory
2207 A @dfn{directory name} is a string that must name a directory if it
2208 names any file at all. A directory is actually a kind of file, and it
2209 has a file name (called the @dfn{directory file name}, which is
2210 related to the directory name but is typically not identical. (This
2211 is not quite the same as the usual POSIX terminology.) These two
2212 names for the same entity are related by a syntactic transformation.
2213 On GNU and other POSIX-like systems, this is simple: to obtain a
2214 directory name, append a @samp{/} to a directory file name that does
2215 not already end in @samp{/}. On MS-DOS the relationship is more
2218 The difference between a directory name and a directory file name is
2219 subtle but crucial. When an Emacs variable or function argument is
2220 described as being a directory name, a directory file name is not
2221 acceptable. When @code{file-name-directory} returns a string, that is
2222 always a directory name.
2224 The following two functions convert between directory names and
2225 directory file names. They do nothing special with environment
2226 variable substitutions such as @samp{$HOME}, and the constructs
2227 @samp{~}, @samp{.} and @samp{..}.
2229 @defun file-name-as-directory filename
2230 This function returns a string representing @var{filename} in a form
2231 that the operating system will interpret as the name of a directory (a
2232 directory name). On most systems, this means appending a slash to the
2233 string (if it does not already end in one).
2237 (file-name-as-directory "~rms/lewis")
2238 @result{} "~rms/lewis/"
2243 @defun directory-name-p filename
2244 This function returns non-@code{nil} if @var{filename} ends with a
2245 directory separator character. This is the forward slash @samp{/} on
2246 GNU and other POSIX-like systems; MS-Windows and MS-DOS recognize both
2247 the forward slash and the backslash @samp{\} as directory separators.
2250 @defun directory-file-name dirname
2251 This function returns a string representing @var{dirname} in a form
2252 that the operating system will interpret as the name of a file (a
2253 directory file name). On most systems, this means removing the final
2254 directory separators from the string, unless the string consists
2255 entirely of directory separators.
2259 (directory-file-name "~lewis/")
2265 Given a directory name, you can combine it with a relative file name
2266 using @code{concat}:
2269 (concat @var{dirname} @var{relfile})
2273 Be sure to verify that the file name is relative before doing that.
2274 If you use an absolute file name, the results could be syntactically
2275 invalid or refer to the wrong file.
2277 If you want to use a directory file name in making such a
2278 combination, you must first convert it to a directory name using
2279 @code{file-name-as-directory}:
2282 (concat (file-name-as-directory @var{dirfile}) @var{relfile})
2286 Don't try concatenating a slash by hand, as in
2290 (concat @var{dirfile} "/" @var{relfile})
2294 because this is not portable. Always use
2295 @code{file-name-as-directory}.
2297 To avoid the issues mentioned above, or if the @var{dirname} value
2298 might be @code{nil} (for example, from an element of @code{load-path}),
2302 (expand-file-name @var{relfile} @var{dirname})
2305 However, @code{expand-file-name} expands leading @samp{~} in
2306 @var{relfile}, which may not be what you want. @xref{File Name
2309 To convert a directory name to its abbreviation, use this
2312 @cindex file name abbreviations
2313 @cindex abbreviated file names
2314 @vindex directory-abbrev-alist
2315 @defun abbreviate-file-name filename
2316 @anchor{abbreviate-file-name}
2317 This function returns an abbreviated form of @var{filename}. It
2318 applies the abbreviations specified in @code{directory-abbrev-alist}
2319 (@pxref{File Aliases,,File Aliases, emacs, The GNU Emacs Manual}),
2320 then substitutes @samp{~} for the user's home directory if the
2321 argument names a file in the home directory or one of its
2322 subdirectories. If the home directory is a root directory, it is not
2323 replaced with @samp{~}, because this does not make the result shorter
2326 You can use this function for directory names and for file names,
2327 because it recognizes abbreviations even as part of the name.
2330 @node File Name Expansion
2331 @subsection Functions that Expand Filenames
2332 @cindex expansion of file names
2334 @dfn{Expanding} a file name means converting a relative file name to
2335 an absolute one. Since this is done relative to a default directory,
2336 you must specify the default directory as well as the file name
2337 to be expanded. It also involves expanding abbreviations like
2340 (@pxref{abbreviate-file-name}),
2342 and eliminating redundancies like @file{./} and @file{@var{name}/../}.
2344 @defun expand-file-name filename &optional directory
2345 This function converts @var{filename} to an absolute file name. If
2346 @var{directory} is supplied, it is the default directory to start with
2347 if @var{filename} is relative and does not start with @samp{~}.
2348 (The value of @var{directory} should
2349 itself be an absolute directory name or directory file name; it may
2350 start with @samp{~}.) Otherwise, the current buffer's value of
2351 @code{default-directory} is used. For example:
2355 (expand-file-name "foo")
2356 @result{} "/xcssun/users/rms/lewis/foo"
2359 (expand-file-name "../foo")
2360 @result{} "/xcssun/users/rms/foo"
2363 (expand-file-name "foo" "/usr/spool/")
2364 @result{} "/usr/spool/foo"
2368 If the part of @var{filename} before the first slash is
2369 @samp{~}, it expands to the value of the @env{HOME} environment
2370 variable (usually your home directory). If the part before the first
2371 slash is @samp{~@var{user}} and if @var{user} is a valid login name,
2372 it expands to @var{user}'s home directory.
2373 If you do not want this expansion for a relative @var{filename} that
2374 might begin with a literal @samp{~}, you can use @code{(concat
2375 (file-name-as-directory directory) filename)} instead of
2376 @code{(expand-file-name filename directory)}.
2378 Filenames containing @samp{.} or @samp{..} are simplified to their
2383 (expand-file-name "bar/../foo")
2384 @result{} "/xcssun/users/rms/lewis/foo"
2388 In some cases, a leading @samp{..} component can remain in the output:
2392 (expand-file-name "../home" "/")
2393 @result{} "/../home"
2398 This is for the sake of filesystems that have the concept of a
2399 superroot above the root directory @file{/}. On other filesystems,
2400 @file{/../} is interpreted exactly the same as @file{/}.
2402 Note that @code{expand-file-name} does @emph{not} expand environment
2403 variables; only @code{substitute-in-file-name} does that:
2407 (expand-file-name "$HOME/foo")
2408 @result{} "/xcssun/users/rms/lewis/$HOME/foo"
2412 Note also that @code{expand-file-name} does not follow symbolic links
2413 at any level. This results in a difference between the way
2414 @code{file-truename} and @code{expand-file-name} treat @samp{..}.
2415 Assuming that @samp{/tmp/bar} is a symbolic link to the directory
2416 @samp{/tmp/foo/bar} we get:
2420 (file-truename "/tmp/bar/../myfile")
2421 @result{} "/tmp/foo/myfile"
2424 (expand-file-name "/tmp/bar/../myfile")
2425 @result{} "/tmp/myfile"
2429 If you may need to follow symbolic links preceding @samp{..}, you
2430 should make sure to call @code{file-truename} without prior direct or
2431 indirect calls to @code{expand-file-name}. @xref{Truenames}.
2434 @defvar default-directory
2435 The value of this buffer-local variable is the default directory for the
2436 current buffer. It should be an absolute directory name; it may start
2437 with @samp{~}. This variable is buffer-local in every buffer.
2439 @code{expand-file-name} uses the default directory when its second
2440 argument is @code{nil}.
2442 The value is always a string ending with a slash.
2447 @result{} "/user/lewis/manual/"
2452 @defun substitute-in-file-name filename
2453 @anchor{Definition of substitute-in-file-name}
2454 This function replaces environment variable references in
2455 @var{filename} with the environment variable values. Following
2456 standard Unix shell syntax, @samp{$} is the prefix to substitute an
2457 environment variable value. If the input contains @samp{$$}, that is
2458 converted to @samp{$}; this gives the user a way to quote a
2461 The environment variable name is the series of alphanumeric characters
2462 (including underscores) that follow the @samp{$}. If the character following
2463 the @samp{$} is a @samp{@{}, then the variable name is everything up to the
2466 Calling @code{substitute-in-file-name} on output produced by
2467 @code{substitute-in-file-name} tends to give incorrect results. For
2468 instance, use of @samp{$$} to quote a single @samp{$} won't work
2469 properly, and @samp{$} in an environment variable's value could lead
2470 to repeated substitution. Therefore, programs that call this function
2471 and put the output where it will be passed to this function need to
2472 double all @samp{$} characters to prevent subsequent incorrect
2475 @c Wordy to avoid overfull hbox. --rjc 15mar92
2476 Here we assume that the environment variable @env{HOME}, which holds
2477 the user's home directory, has value @samp{/xcssun/users/rms}.
2481 (substitute-in-file-name "$HOME/foo")
2482 @result{} "/xcssun/users/rms/foo"
2486 After substitution, if a @samp{~} or a @samp{/} appears immediately
2487 after another @samp{/}, the function discards everything before it (up
2488 through the immediately preceding @samp{/}).
2492 (substitute-in-file-name "bar/~/foo")
2496 (substitute-in-file-name "/usr/local/$HOME/foo")
2497 @result{} "/xcssun/users/rms/foo"
2498 ;; @r{@file{/usr/local/} has been discarded.}
2504 Sometimes, it is not desired to expand file names. In such cases,
2505 the file name can be quoted to suppress the expansion, and to handle
2506 the file name literally. Quoting happens by prefixing the file name
2509 @defmac file-name-quote name
2510 This macro adds the quotation prefix @samp{/:} to the file @var{name}.
2511 For a local file @var{name}, it prefixes @var{name} with @samp{/:}.
2512 If @var{name} is a remote file name, the local part of @var{name} is
2513 quoted. If @var{name} is already a quoted file name, @var{name} is
2518 (substitute-in-file-name (file-name-quote "bar/~/foo"))
2519 @result{} "/:bar/~/foo"
2523 (substitute-in-file-name (file-name-quote "/ssh:host:bar/~/foo"))
2524 @result{} "/ssh:host:/:bar/~/foo"
2528 The macro cannot be used to suppress file name handlers from magic
2529 file names (@pxref{Magic File Names}).
2532 @defmac file-name-unquote name
2533 This macro removes the quotation prefix @samp{/:} from the file
2534 @var{name}, if any. If @var{name} is a remote file name, the local
2535 part of @var{name} is unquoted.
2538 @defmac file-name-quoted-p name
2539 This macro returns non-@code{nil}, when @var{name} is quoted with the
2540 prefix @samp{/:}. If @var{name} is a remote file name, the local part
2541 of @var{name} is checked.
2545 @node Unique File Names
2546 @subsection Generating Unique File Names
2547 @cindex unique file names
2548 @cindex temporary files
2550 Some programs need to write temporary files. Here is the usual way to
2551 construct a name for such a file:
2554 (make-temp-file @var{name-of-application})
2558 The job of @code{make-temp-file} is to prevent two different users or
2559 two different jobs from trying to use the exact same file name.
2561 @defun make-temp-file prefix &optional dir-flag suffix text
2562 This function creates a temporary file and returns its name. Emacs
2563 creates the temporary file's name by adding to @var{prefix} some
2564 random characters that are different in each Emacs job. The result is
2565 guaranteed to be a newly created file, containing @var{text} if that's
2566 given as a string and empty otherwise. On MS-DOS, this function
2567 can truncate the @var{string} prefix to fit into the 8+3 file-name
2568 limits. If @var{prefix} is a relative file name, it is expanded
2569 against @code{temporary-file-directory}.
2573 (make-temp-file "foo")
2574 @result{} "/tmp/foo232J6v"
2578 When @code{make-temp-file} returns, the file has been created and is
2579 empty. At that point, you should write the intended contents into the
2582 If @var{dir-flag} is non-@code{nil}, @code{make-temp-file} creates an
2583 empty directory instead of an empty file. It returns the file name,
2584 not the directory name, of that directory. @xref{Directory Names}.
2586 If @var{suffix} is non-@code{nil}, @code{make-temp-file} adds it at
2587 the end of the file name.
2589 If @var{text} is a string, @code{make-temp-file} inserts it in the file.
2591 To prevent conflicts among different libraries running in the same
2592 Emacs, each Lisp program that uses @code{make-temp-file} should have its
2593 own @var{prefix}. The number added to the end of @var{prefix}
2594 distinguishes between the same application running in different Emacs
2595 jobs. Additional added characters permit a large number of distinct
2596 names even in one Emacs job.
2599 The default directory for temporary files is controlled by the
2600 variable @code{temporary-file-directory}. This variable gives the user
2601 a uniform way to specify the directory for all temporary files. Some
2602 programs use @code{small-temporary-file-directory} instead, if that is
2603 non-@code{nil}. To use it, you should expand the prefix against
2604 the proper directory before calling @code{make-temp-file}.
2606 @defopt temporary-file-directory
2607 @cindex @env{TMPDIR} environment variable
2608 @cindex @env{TMP} environment variable
2609 @cindex @env{TEMP} environment variable
2610 This variable specifies the directory name for creating temporary files.
2611 Its value should be a directory name (@pxref{Directory Names}), but it
2612 is good for Lisp programs to cope if the value is a directory's file
2613 name instead. Using the value as the second argument to
2614 @code{expand-file-name} is a good way to achieve that.
2616 The default value is determined in a reasonable way for your operating
2617 system; it is based on the @env{TMPDIR}, @env{TMP} and @env{TEMP}
2618 environment variables, with a fall-back to a system-dependent name if
2619 none of these variables is defined.
2621 Even if you do not use @code{make-temp-file} to create the temporary
2622 file, you should still use this variable to decide which directory to
2623 put the file in. However, if you expect the file to be small, you
2624 should use @code{small-temporary-file-directory} first if that is
2628 @defopt small-temporary-file-directory
2629 This variable specifies the directory name for
2630 creating certain temporary files, which are likely to be small.
2632 If you want to write a temporary file which is likely to be small, you
2633 should compute the directory like this:
2637 (expand-file-name @var{prefix}
2638 (or small-temporary-file-directory
2639 temporary-file-directory)))
2643 @defun make-temp-name base-name
2644 This function generates a string that might be a unique file
2645 name. The name starts with @var{base-name}, and has several random
2646 characters appended to it, which are different in each Emacs job. It
2647 is like @code{make-temp-file} except that (i) it just constructs a
2648 name and does not create a file, (ii) @var{base-name} should be an
2649 absolute file name that is not magic, and (iii) if the returned file
2650 name is magic, it might name an existing file. @xref{Magic File
2653 @strong{Warning:} In most cases, you should not use this function; use
2654 @code{make-temp-file} instead! This function is susceptible to a race
2655 condition, between the @code{make-temp-name} call and the creation of
2656 the file, which in some cases may cause a security hole.
2659 Sometimes, it is necessary to create a temporary file on a remote host
2660 or a mounted directory. The following two functions support this.
2662 @defun make-nearby-temp-file prefix &optional dir-flag suffix
2663 This function is similar to @code{make-temp-file}, but it creates a
2664 temporary file as close as possible to @code{default-directory}. If
2665 @var{prefix} is a relative file name, and @code{default-directory} is
2666 a remote file name or located on a mounted file systems, the temporary
2667 file is created in the directory returned by the function
2668 @code{temporary-file-directory}. Otherwise, the function
2669 @code{make-temp-file} is used. @var{prefix}, @var{dir-flag} and
2670 @var{suffix} have the same meaning as in @code{make-temp-file}.
2674 (let ((default-directory "/ssh:remotehost:"))
2675 (make-nearby-temp-file "foo"))
2676 @result{} "/ssh:remotehost:/tmp/foo232J6v"
2681 @defun temporary-file-directory
2682 The directory for writing temporary files via
2683 @code{make-nearby-temp-file}. In case of a remote
2684 @code{default-directory}, this is a directory for temporary files on
2685 that remote host. If such a directory does not exist, or
2686 @code{default-directory} ought to be located on a mounted file system
2687 (see @code{mounted-file-systems}), the function returns
2688 @code{default-directory}. For a non-remote and non-mounted
2689 @code{default-directory}, the value of the variable
2690 @code{temporary-file-directory} is returned.
2693 In order to extract the local part of the path name from a temporary
2694 file, @code{file-local-name} could be used.
2696 @node File Name Completion
2697 @subsection File Name Completion
2698 @cindex file name completion subroutines
2699 @cindex completion, file name
2701 This section describes low-level subroutines for completing a file
2702 name. For higher level functions, see @ref{Reading File Names}.
2704 @defun file-name-all-completions partial-filename directory
2705 This function returns a list of all possible completions for a file
2706 whose name starts with @var{partial-filename} in directory
2707 @var{directory}. The order of the completions is the order of the files
2708 in the directory, which is unpredictable and conveys no useful
2711 The argument @var{partial-filename} must be a file name containing no
2712 directory part and no slash (or backslash on some systems). The current
2713 buffer's default directory is prepended to @var{directory}, if
2714 @var{directory} is not absolute.
2716 In the following example, suppose that @file{~rms/lewis} is the current
2717 default directory, and has five files whose names begin with @samp{f}:
2718 @file{foo}, @file{file~}, @file{file.c}, @file{file.c.~1~}, and
2723 (file-name-all-completions "f" "")
2724 @result{} ("foo" "file~" "file.c.~2~"
2725 "file.c.~1~" "file.c")
2729 (file-name-all-completions "fo" "")
2735 @defun file-name-completion filename directory &optional predicate
2736 This function completes the file name @var{filename} in directory
2737 @var{directory}. It returns the longest prefix common to all file names
2738 in directory @var{directory} that start with @var{filename}. If
2739 @var{predicate} is non-@code{nil} then it ignores possible completions
2740 that don't satisfy @var{predicate}, after calling that function
2741 with one argument, the expanded absolute file name.
2743 If only one match exists and @var{filename} matches it exactly, the
2744 function returns @code{t}. The function returns @code{nil} if directory
2745 @var{directory} contains no name starting with @var{filename}.
2747 In the following example, suppose that the current default directory
2748 has five files whose names begin with @samp{f}: @file{foo},
2749 @file{file~}, @file{file.c}, @file{file.c.~1~}, and
2754 (file-name-completion "fi" "")
2759 (file-name-completion "file.c.~1" "")
2760 @result{} "file.c.~1~"
2764 (file-name-completion "file.c.~1~" "")
2769 (file-name-completion "file.c.~3" "")
2775 @defopt completion-ignored-extensions
2776 @code{file-name-completion} usually ignores file names that end in any
2777 string in this list. It does not ignore them when all the possible
2778 completions end in one of these suffixes. This variable has no effect
2779 on @code{file-name-all-completions}.
2781 A typical value might look like this:
2785 completion-ignored-extensions
2786 @result{} (".o" ".elc" "~" ".dvi")
2790 If an element of @code{completion-ignored-extensions} ends in a slash
2791 @samp{/}, it signals a directory. The elements which do @emph{not} end
2792 in a slash will never match a directory; thus, the above value will not
2793 filter out a directory named @file{foo.elc}.
2796 @node Standard File Names
2797 @subsection Standard File Names
2799 Sometimes, an Emacs Lisp program needs to specify a standard file
2800 name for a particular use---typically, to hold configuration data
2801 specified by the current user. Usually, such files should be located
2802 in the directory specified by @code{user-emacs-directory}, which is
2803 @file{~/.emacs.d} by default (@pxref{Init File}). For example, abbrev
2804 definitions are stored by default in @file{~/.emacs.d/abbrev_defs}.
2805 The easiest way to specify such a file name is to use the function
2806 @code{locate-user-emacs-file}.
2808 @defun locate-user-emacs-file base-name &optional old-name
2809 This function returns an absolute file name for an Emacs-specific
2810 configuration or data file. The argument @file{base-name} should be a
2811 relative file name. The return value is the absolute name of a file
2812 in the directory specified by @code{user-emacs-directory}; if that
2813 directory does not exist, this function creates it.
2815 If the optional argument @var{old-name} is non-@code{nil}, it
2816 specifies a file in the user's home directory,
2817 @file{~/@var{old-name}}. If such a file exists, the return value is
2818 the absolute name of that file, instead of the file specified by
2819 @var{base-name}. This argument is intended to be used by Emacs
2820 packages to provide backward compatibility. For instance, prior to
2821 the introduction of @code{user-emacs-directory}, the abbrev file was
2822 located in @file{~/.abbrev_defs}. Here is the definition of
2823 @code{abbrev-file-name}:
2826 (defcustom abbrev-file-name
2827 (locate-user-emacs-file "abbrev_defs" ".abbrev_defs")
2828 "Default name of file from which to read abbrevs."
2834 A lower-level function for standardizing file names, which
2835 @code{locate-user-emacs-file} uses as a subroutine, is
2836 @code{convert-standard-filename}.
2838 @defun convert-standard-filename filename
2839 This function returns a file name based on @var{filename}, which fits
2840 the conventions of the current operating system.
2842 On GNU and other POSIX-like systems, this simply returns @var{filename}.
2843 On other operating systems, it may enforce system-specific file name
2844 conventions; for example, on MS-DOS this function performs a variety
2845 of changes to enforce MS-DOS file name limitations, including
2846 converting any leading @samp{.} to @samp{_} and truncating to three
2847 characters after the @samp{.}.
2849 The recommended way to use this function is to specify a name which
2850 fits the conventions of GNU and Unix systems, and pass it to
2851 @code{convert-standard-filename}.
2854 @node Contents of Directories
2855 @section Contents of Directories
2856 @cindex directory-oriented functions
2857 @cindex file names in directory
2859 A directory is a kind of file that contains other files entered under
2860 various names. Directories are a feature of the file system.
2862 Emacs can list the names of the files in a directory as a Lisp list,
2863 or display the names in a buffer using the @code{ls} shell command. In
2864 the latter case, it can optionally display information about each file,
2865 depending on the options passed to the @code{ls} command.
2867 @defun directory-files directory &optional full-name match-regexp nosort
2868 This function returns a list of the names of the files in the directory
2869 @var{directory}. By default, the list is in alphabetical order.
2871 If @var{full-name} is non-@code{nil}, the function returns the files'
2872 absolute file names. Otherwise, it returns the names relative to
2873 the specified directory.
2875 If @var{match-regexp} is non-@code{nil}, this function returns only
2876 those file names that contain a match for that regular expression---the
2877 other file names are excluded from the list. On case-insensitive
2878 filesystems, the regular expression matching is case-insensitive.
2881 If @var{nosort} is non-@code{nil}, @code{directory-files} does not sort
2882 the list, so you get the file names in no particular order. Use this if
2883 you want the utmost possible speed and don't care what order the files
2884 are processed in. If the order of processing is visible to the user,
2885 then the user will probably be happier if you do sort the names.
2889 (directory-files "~lewis")
2890 @result{} ("#foo#" "#foo.el#" "." ".."
2891 "dired-mods.el" "files.texi"
2896 An error is signaled if @var{directory} is not the name of a directory
2900 @defun directory-files-recursively directory regexp &optional include-directories
2901 Return all files under @var{directory} whose names match @var{regexp}.
2902 This function searches the specified @var{directory} and its
2903 sub-directories, recursively, for files whose basenames (i.e., without
2904 the leading directories) match the specified @var{regexp}, and returns
2905 a list of the absolute file names of the matching files
2906 (@pxref{Relative File Names, absolute file names}). The file names
2907 are returned in depth-first order, meaning that files in some
2908 sub-directory are returned before the files in its parent directory.
2909 In addition, matching files found in each subdirectory are sorted
2910 alphabetically by their basenames. By default, directories whose
2911 names match @var{regexp} are omitted from the list, but if the
2912 optional argument @var{include-directories} is non-@code{nil}, they
2916 @defun directory-files-and-attributes directory &optional full-name match-regexp nosort id-format
2917 This is similar to @code{directory-files} in deciding which files
2918 to report on and how to report their names. However, instead
2919 of returning a list of file names, it returns for each file a
2920 list @code{(@var{filename} . @var{attributes})}, where @var{attributes}
2921 is what @code{file-attributes} would return for that file.
2922 The optional argument @var{id-format} has the same meaning as the
2923 corresponding argument to @code{file-attributes} (@pxref{Definition
2924 of file-attributes}).
2927 @defun file-expand-wildcards pattern &optional full
2928 This function expands the wildcard pattern @var{pattern}, returning
2929 a list of file names that match it.
2931 If @var{pattern} is written as an absolute file name,
2932 the values are absolute also.
2934 If @var{pattern} is written as a relative file name, it is interpreted
2935 relative to the current default directory. The file names returned are
2936 normally also relative to the current default directory. However, if
2937 @var{full} is non-@code{nil}, they are absolute.
2940 @defun insert-directory file switches &optional wildcard full-directory-p
2941 This function inserts (in the current buffer) a directory listing for
2942 directory @var{file}, formatted with @code{ls} according to
2943 @var{switches}. It leaves point after the inserted text.
2944 @var{switches} may be a string of options, or a list of strings
2945 representing individual options.
2947 The argument @var{file} may be either a directory or a file
2948 specification including wildcard characters. If @var{wildcard} is
2949 non-@code{nil}, that means treat @var{file} as a file specification with
2952 If @var{full-directory-p} is non-@code{nil}, that means the directory
2953 listing is expected to show the full contents of a directory. You
2954 should specify @code{t} when @var{file} is a directory and switches do
2955 not contain @samp{-d}. (The @samp{-d} option to @code{ls} says to
2956 describe a directory itself as a file, rather than showing its
2959 On most systems, this function works by running a directory listing
2960 program whose name is in the variable @code{insert-directory-program}.
2961 If @var{wildcard} is non-@code{nil}, it also runs the shell specified by
2962 @code{shell-file-name}, to expand the wildcards.
2964 MS-DOS and MS-Windows systems usually lack the standard Unix program
2965 @code{ls}, so this function emulates the standard Unix program @code{ls}
2968 As a technical detail, when @var{switches} contains the long
2969 @samp{--dired} option, @code{insert-directory} treats it specially,
2970 for the sake of dired. However, the normally equivalent short
2971 @samp{-D} option is just passed on to @code{insert-directory-program},
2972 as any other option.
2975 @defvar insert-directory-program
2976 This variable's value is the program to run to generate a directory listing
2977 for the function @code{insert-directory}. It is ignored on systems
2978 which generate the listing with Lisp code.
2981 @node Create/Delete Dirs
2982 @section Creating, Copying and Deleting Directories
2983 @cindex creating, copying and deleting directories
2984 @c Emacs 19 features
2986 Most Emacs Lisp file-manipulation functions get errors when used on
2987 files that are directories. For example, you cannot delete a directory
2988 with @code{delete-file}. These special functions exist to create and
2992 @deffn Command make-directory dirname &optional parents
2993 This command creates a directory named @var{dirname}. If
2994 @var{parents} is non-@code{nil}, as is always the case in an
2995 interactive call, that means to create the parent directories first,
2996 if they don't already exist.
2998 @code{mkdir} is an alias for this.
3001 @deffn Command copy-directory dirname newname &optional keep-time parents copy-contents
3002 This command copies the directory named @var{dirname} to
3003 @var{newname}. If @var{newname} is a directory name,
3004 @var{dirname} will be copied to a subdirectory there.
3005 @xref{Directory Names}.
3007 It always sets the file modes of the copied files to match the
3008 corresponding original file.
3010 The third argument @var{keep-time} non-@code{nil} means to preserve the
3011 modification time of the copied files. A prefix arg makes
3012 @var{keep-time} non-@code{nil}.
3014 The fourth argument @var{parents} says whether to
3015 create parent directories if they don't exist. Interactively,
3016 this happens by default.
3018 The fifth argument @var{copy-contents}, if non-@code{nil}, means to
3019 copy the contents of @var{dirname} directly into @var{newname} if the
3020 latter is a directory name, instead of copying @var{dirname} into
3021 it as a subdirectory.
3025 @vindex delete-by-moving-to-trash
3026 @deffn Command delete-directory dirname &optional recursive trash
3027 This command deletes the directory named @var{dirname}. The function
3028 @code{delete-file} does not work for files that are directories; you
3029 must use @code{delete-directory} for them. If @var{recursive} is
3030 @code{nil}, and the directory contains any files,
3031 @code{delete-directory} signals an error.
3032 If recursive is non-@code{nil}, there is no error merely because the
3033 directory or its files are deleted by some other process before
3034 @code{delete-directory} gets to them.
3036 @code{delete-directory} only follows symbolic links at the level of
3039 If the optional argument @var{trash} is non-@code{nil} and the
3040 variable @code{delete-by-moving-to-trash} is non-@code{nil}, this
3041 command moves the file into the system Trash instead of deleting it.
3042 @xref{Misc File Ops,,Miscellaneous File Operations, emacs, The GNU
3043 Emacs Manual}. When called interactively, @var{trash} is @code{t} if
3044 no prefix argument is given, and @code{nil} otherwise.
3047 @node Magic File Names
3048 @section Making Certain File Names ``Magic''
3049 @cindex magic file names
3051 You can implement special handling for certain file names. This is
3052 called making those names @dfn{magic}. The principal use for this
3053 feature is in implementing access to remote files (@pxref{Remote Files,,
3054 Remote Files, emacs, The GNU Emacs Manual}).
3056 To define a kind of magic file name, you must supply a regular
3057 expression to define the class of names (all those that match the
3058 regular expression), plus a handler that implements all the primitive
3059 Emacs file operations for file names that match.
3061 @cindex file handler
3062 @vindex file-name-handler-alist
3063 The variable @code{file-name-handler-alist} holds a list of handlers,
3064 together with regular expressions that determine when to apply each
3065 handler. Each element has this form:
3068 (@var{regexp} . @var{handler})
3072 All the Emacs primitives for file access and file name transformation
3073 check the given file name against @code{file-name-handler-alist}. If
3074 the file name matches @var{regexp}, the primitives handle that file by
3075 calling @var{handler}.
3077 The first argument given to @var{handler} is the name of the
3078 primitive, as a symbol; the remaining arguments are the arguments that
3079 were passed to that primitive. (The first of these arguments is most
3080 often the file name itself.) For example, if you do this:
3083 (file-exists-p @var{filename})
3087 and @var{filename} has handler @var{handler}, then @var{handler} is
3091 (funcall @var{handler} 'file-exists-p @var{filename})
3094 When a function takes two or more arguments that must be file names,
3095 it checks each of those names for a handler. For example, if you do
3099 (expand-file-name @var{filename} @var{dirname})
3103 then it checks for a handler for @var{filename} and then for a handler
3104 for @var{dirname}. In either case, the @var{handler} is called like
3108 (funcall @var{handler} 'expand-file-name @var{filename} @var{dirname})
3112 The @var{handler} then needs to figure out whether to handle
3113 @var{filename} or @var{dirname}.
3115 If the specified file name matches more than one handler, the one
3116 whose match starts last in the file name gets precedence. This rule
3117 is chosen so that handlers for jobs such as uncompression are handled
3118 first, before handlers for jobs such as remote file access.
3120 Here are the operations that a magic file name handler gets to handle:
3124 @code{access-file}, @code{add-name-to-file},
3125 @code{byte-compiler-base-file-name},@*
3126 @code{copy-directory}, @code{copy-file},
3127 @code{delete-directory}, @code{delete-file},
3128 @code{diff-latest-backup-file},
3129 @code{directory-file-name},
3130 @code{directory-files},
3131 @code{directory-files-and-attributes},
3132 @code{dired-compress-file}, @code{dired-uncache},@*
3133 @code{expand-file-name},
3134 @code{file-accessible-directory-p},
3136 @code{file-attributes},
3137 @code{file-directory-p},
3138 @code{file-equal-p},
3139 @code{file-executable-p}, @code{file-exists-p},
3140 @code{file-in-directory-p},
3141 @code{file-local-copy},
3142 @code{file-modes}, @code{file-name-all-completions},
3143 @code{file-name-as-directory},
3144 @code{file-name-case-insensitive-p},
3145 @code{file-name-completion},
3146 @code{file-name-directory},
3147 @code{file-name-nondirectory},
3148 @code{file-name-sans-versions}, @code{file-newer-than-file-p},
3149 @code{file-notify-add-watch}, @code{file-notify-rm-watch},
3150 @code{file-notify-valid-p},
3151 @code{file-ownership-preserved-p},
3152 @code{file-readable-p}, @code{file-regular-p},
3153 @code{file-remote-p}, @code{file-selinux-context},
3154 @code{file-symlink-p}, @code{file-truename}, @code{file-writable-p},
3155 @code{find-backup-file-name},@*
3156 @code{get-file-buffer},
3157 @code{insert-directory},
3158 @code{insert-file-contents},@*
3160 @code{make-auto-save-file-name},
3161 @code{make-directory},
3162 @code{make-directory-internal},
3163 @code{make-nearby-temp-file},
3164 @code{make-symbolic-link},@*
3165 @code{process-file},
3166 @code{rename-file}, @code{set-file-acl}, @code{set-file-modes},
3167 @code{set-file-selinux-context}, @code{set-file-times},
3168 @code{set-visited-file-modtime}, @code{shell-command},
3169 @code{start-file-process},
3170 @code{substitute-in-file-name},@*
3171 @code{temporary-file-directory},
3172 @code{unhandled-file-name-directory},
3173 @code{vc-registered},
3174 @code{verify-visited-file-modtime},@*
3175 @code{write-region}.
3180 @code{access-file}, @code{add-name-to-file},
3181 @code{byte-com@discretionary{}{}{}piler-base-file-name},
3182 @code{copy-directory}, @code{copy-file},
3183 @code{delete-directory}, @code{delete-file},
3184 @code{diff-latest-backup-file},
3185 @code{directory-file-name},
3186 @code{directory-files},
3187 @code{directory-files-and-at@discretionary{}{}{}tributes},
3188 @code{dired-compress-file}, @code{dired-uncache},
3189 @code{expand-file-name},
3190 @code{file-accessible-direc@discretionary{}{}{}tory-p},
3192 @code{file-attributes},
3193 @code{file-direc@discretionary{}{}{}tory-p},
3194 @code{file-equal-p},
3195 @code{file-executable-p}, @code{file-exists-p},
3196 @code{file-in-directory-p},
3197 @code{file-local-copy},
3198 @code{file-modes}, @code{file-name-all-completions},
3199 @code{file-name-as-directory},
3200 @code{file-name-case-insensitive-p},
3201 @code{file-name-completion},
3202 @code{file-name-directory},
3203 @code{file-name-nondirec@discretionary{}{}{}tory},
3204 @code{file-name-sans-versions}, @code{file-newer-than-file-p},
3205 @code{file-notify-add-watch}, @code{file-notify-rm-watch},
3206 @code{file-notify-valid-p},
3207 @code{file-ownership-pre@discretionary{}{}{}served-p},
3208 @code{file-readable-p}, @code{file-regular-p},
3209 @code{file-remote-p}, @code{file-selinux-context},
3210 @code{file-symlink-p}, @code{file-truename}, @code{file-writable-p},
3211 @code{find-backup-file-name},
3212 @code{get-file-buffer},
3213 @code{insert-directory},
3214 @code{insert-file-contents},
3216 @code{make-auto-save-file-name},
3217 @code{make-direc@discretionary{}{}{}tory},
3218 @code{make-direc@discretionary{}{}{}tory-internal},
3219 @code{make-symbolic-link},
3220 @code{process-file},
3221 @code{rename-file}, @code{set-file-acl}, @code{set-file-modes},
3222 @code{set-file-selinux-context}, @code{set-file-times},
3223 @code{set-visited-file-modtime}, @code{shell-command},
3224 @code{start-file-process},
3225 @code{substitute-in-file-name},
3226 @code{unhandled-file-name-directory},
3227 @code{vc-regis@discretionary{}{}{}tered},
3228 @code{verify-visited-file-modtime},
3229 @code{write-region}.
3233 Handlers for @code{insert-file-contents} typically need to clear the
3234 buffer's modified flag, with @code{(set-buffer-modified-p nil)}, if the
3235 @var{visit} argument is non-@code{nil}. This also has the effect of
3236 unlocking the buffer if it is locked.
3238 The handler function must handle all of the above operations, and
3239 possibly others to be added in the future. It need not implement all
3240 these operations itself---when it has nothing special to do for a
3241 certain operation, it can reinvoke the primitive, to handle the
3242 operation in the usual way. It should always reinvoke the primitive
3243 for an operation it does not recognize. Here's one way to do this:
3246 (defun my-file-handler (operation &rest args)
3247 ;; @r{First check for the specific operations}
3248 ;; @r{that we have special handling for.}
3249 (cond ((eq operation 'insert-file-contents) @dots{})
3250 ((eq operation 'write-region) @dots{})
3252 ;; @r{Handle any operation we don't know about.}
3253 (t (let ((inhibit-file-name-handlers
3254 (cons 'my-file-handler
3255 (and (eq inhibit-file-name-operation operation)
3256 inhibit-file-name-handlers)))
3257 (inhibit-file-name-operation operation))
3258 (apply operation args)))))
3261 When a handler function decides to call the ordinary Emacs primitive for
3262 the operation at hand, it needs to prevent the primitive from calling
3263 the same handler once again, thus leading to an infinite recursion. The
3264 example above shows how to do this, with the variables
3265 @code{inhibit-file-name-handlers} and
3266 @code{inhibit-file-name-operation}. Be careful to use them exactly as
3267 shown above; the details are crucial for proper behavior in the case of
3268 multiple handlers, and for operations that have two file names that may
3271 @kindex safe-magic @r{(property)}
3272 Handlers that don't really do anything special for actual access to the
3273 file---such as the ones that implement completion of host names for
3274 remote file names---should have a non-@code{nil} @code{safe-magic}
3275 property. For instance, Emacs normally protects directory names
3276 it finds in @code{PATH} from becoming magic, if they look like magic
3277 file names, by prefixing them with @samp{/:}. But if the handler that
3278 would be used for them has a non-@code{nil} @code{safe-magic}
3279 property, the @samp{/:} is not added.
3281 @kindex operations @r{(property)}
3282 A file name handler can have an @code{operations} property to
3283 declare which operations it handles in a nontrivial way. If this
3284 property has a non-@code{nil} value, it should be a list of
3285 operations; then only those operations will call the handler. This
3286 avoids inefficiency, but its main purpose is for autoloaded handler
3287 functions, so that they won't be loaded except when they have real
3290 Simply deferring all operations to the usual primitives does not
3291 work. For instance, if the file name handler applies to
3292 @code{file-exists-p}, then it must handle @code{load} itself, because
3293 the usual @code{load} code won't work properly in that case. However,
3294 if the handler uses the @code{operations} property to say it doesn't
3295 handle @code{file-exists-p}, then it need not handle @code{load}
3298 @defvar inhibit-file-name-handlers
3299 This variable holds a list of handlers whose use is presently inhibited
3300 for a certain operation.
3303 @defvar inhibit-file-name-operation
3304 The operation for which certain handlers are presently inhibited.
3307 @defun find-file-name-handler file operation
3308 This function returns the handler function for file name @var{file},
3309 or @code{nil} if there is none. The argument @var{operation} should
3310 be the operation to be performed on the file---the value you will pass
3311 to the handler as its first argument when you call it. If
3312 @var{operation} equals @code{inhibit-file-name-operation}, or if it is
3313 not found in the @code{operations} property of the handler, this
3314 function returns @code{nil}.
3317 @defun file-local-copy filename
3318 This function copies file @var{filename} to an ordinary non-magic file
3319 on the local machine, if it isn't on the local machine already. Magic
3320 file names should handle the @code{file-local-copy} operation if they
3321 refer to files on other machines. A magic file name that is used for
3322 other purposes than remote file access should not handle
3323 @code{file-local-copy}; then this function will treat the file as
3326 If @var{filename} is local, whether magic or not, this function does
3327 nothing and returns @code{nil}. Otherwise it returns the file name
3328 of the local copy file.
3331 @defun file-remote-p filename &optional identification connected
3332 This function tests whether @var{filename} is a remote file. If
3333 @var{filename} is local (not remote), the return value is @code{nil}.
3334 If @var{filename} is indeed remote, the return value is a string that
3335 identifies the remote system.
3337 This identifier string can include a host name and a user name, as
3338 well as characters designating the method used to access the remote
3339 system. For example, the remote identifier string for the filename
3340 @code{/sudo::/some/file} is @code{/sudo:root@@localhost:}.
3342 If @code{file-remote-p} returns the same identifier for two different
3343 filenames, that means they are stored on the same file system and can
3344 be accessed locally with respect to each other. This means, for
3345 example, that it is possible to start a remote process accessing both
3346 files at the same time. Implementers of file handlers need to ensure
3347 this principle is valid.
3349 @var{identification} specifies which part of the identifier shall be
3350 returned as string. @var{identification} can be the symbol
3351 @code{method}, @code{user} or @code{host}; any other value is handled
3352 like @code{nil} and means to return the complete identifier string.
3353 In the example above, the remote @code{user} identifier string would
3356 If @var{connected} is non-@code{nil}, this function returns @code{nil}
3357 even if @var{filename} is remote, if Emacs has no network connection
3358 to its host. This is useful when you want to avoid the delay of
3359 making connections when they don't exist.
3362 @defun unhandled-file-name-directory filename
3363 This function returns the name of a directory that is not magic. For
3364 a non-magic @var{filename} it returns the corresponding directory name
3365 (@pxref{Directory Names}). For a magic @var{filename}, it invokes the
3366 file name handler, which therefore decides what value to return. If
3367 @var{filename} is not accessible from a local process, then the file
3368 name handler should indicate that by returning @code{nil}.
3370 This is useful for running a subprocess; every subprocess must have a
3371 non-magic directory to serve as its current directory, and this function
3372 is a good way to come up with one.
3375 @defun file-local-name filename
3376 This function returns the local part of file @var{filename}. For a
3377 remote @var{filename}, it returns a file name which could be used
3378 directly as argument of a remote process. If @var{filename} is local,
3379 this function returns the file name.
3382 @defopt remote-file-name-inhibit-cache
3383 The attributes of remote files can be cached for better performance. If
3384 they are changed outside of Emacs's control, the cached values become
3385 invalid, and must be reread.
3387 When this variable is set to @code{nil}, cached values are never
3388 expired. Use this setting with caution, only if you are sure nothing
3389 other than Emacs ever changes the remote files. If it is set to
3390 @code{t}, cached values are never used. This is the safest value, but
3391 could result in performance degradation.
3393 A compromise is to set it to a positive number. This means that
3394 cached values are used for that amount of seconds since they were
3395 cached. If a remote file is checked regularly, it might be a good
3396 idea to let-bind this variable to a value less than the time period
3397 between consecutive checks. For example:
3400 (defun display-time-file-nonempty-p (file)
3401 (let ((remote-file-name-inhibit-cache
3402 (- display-time-interval 5)))
3403 (and (file-exists-p file)
3404 (< 0 (nth 7 (file-attributes
3405 (file-chase-links file)))))))
3409 @node Format Conversion
3410 @section File Format Conversion
3412 @cindex file format conversion
3413 @cindex encoding file formats
3414 @cindex decoding file formats
3415 @cindex text properties in files
3416 @cindex saving text properties
3417 Emacs performs several steps to convert the data in a buffer (text,
3418 text properties, and possibly other information) to and from a
3419 representation suitable for storing into a file. This section describes
3420 the fundamental functions that perform this @dfn{format conversion},
3421 namely @code{insert-file-contents} for reading a file into a buffer,
3422 and @code{write-region} for writing a buffer into a file.
3425 * Overview: Format Conversion Overview. @code{insert-file-contents} and @code{write-region}.
3426 * Round-Trip: Format Conversion Round-Trip. Using @code{format-alist}.
3427 * Piecemeal: Format Conversion Piecemeal. Specifying non-paired conversion.
3430 @node Format Conversion Overview
3431 @subsection Overview
3433 The function @code{insert-file-contents}:
3436 @item initially, inserts bytes from the file into the buffer;
3437 @item decodes bytes to characters as appropriate;
3438 @item processes formats as defined by entries in @code{format-alist}; and
3439 @item calls functions in @code{after-insert-file-functions}.
3443 The function @code{write-region}:
3446 @item initially, calls functions in @code{write-region-annotate-functions};
3447 @item processes formats as defined by entries in @code{format-alist};
3448 @item encodes characters to bytes as appropriate; and
3449 @item modifies the file with the bytes.
3452 This shows the symmetry of the lowest-level operations; reading and
3453 writing handle things in opposite order. The rest of this section
3454 describes the two facilities surrounding the three variables named
3455 above, as well as some related functions. @ref{Coding Systems}, for
3456 details on character encoding and decoding.
3458 @node Format Conversion Round-Trip
3459 @subsection Round-Trip Specification
3461 The most general of the two facilities is controlled by the variable
3462 @code{format-alist}, a list of @dfn{file format} specifications, which
3463 describe textual representations used in files for the data in an Emacs
3464 buffer. The descriptions for reading and writing are paired, which is
3465 why we call this ``round-trip'' specification
3466 (@pxref{Format Conversion Piecemeal}, for non-paired specification).
3468 @defvar format-alist
3469 This list contains one format definition for each defined file format.
3470 Each format definition is a list of this form:
3473 (@var{name} @var{doc-string} @var{regexp} @var{from-fn} @var{to-fn} @var{modify} @var{mode-fn} @var{preserve})
3477 @cindex format definition
3479 Here is what the elements in a format definition mean:
3483 The name of this format.
3486 A documentation string for the format.
3489 A regular expression which is used to recognize files represented in
3490 this format. If @code{nil}, the format is never applied automatically.
3493 A shell command or function to decode data in this format (to convert
3494 file data into the usual Emacs data representation).
3496 A shell command is represented as a string; Emacs runs the command as a
3497 filter to perform the conversion.
3499 If @var{from-fn} is a function, it is called with two arguments, @var{begin}
3500 and @var{end}, which specify the part of the buffer it should convert.
3501 It should convert the text by editing it in place. Since this can
3502 change the length of the text, @var{from-fn} should return the modified
3505 One responsibility of @var{from-fn} is to make sure that the beginning
3506 of the file no longer matches @var{regexp}. Otherwise it is likely to
3507 get called again. Also, @var{from-fn} must not involve buffers or
3508 files other than the one being decoded, otherwise the internal buffer
3509 used for formatting might be overwritten.
3512 A shell command or function to encode data in this format---that is, to
3513 convert the usual Emacs data representation into this format.
3515 If @var{to-fn} is a string, it is a shell command; Emacs runs the
3516 command as a filter to perform the conversion.
3518 If @var{to-fn} is a function, it is called with three arguments:
3519 @var{begin} and @var{end}, which specify the part of the buffer it
3520 should convert, and @var{buffer}, which specifies which buffer. There
3521 are two ways it can do the conversion:
3525 By editing the buffer in place. In this case, @var{to-fn} should
3526 return the end-position of the range of text, as modified.
3529 By returning a list of annotations. This is a list of elements of the
3530 form @code{(@var{position} . @var{string})}, where @var{position} is an
3531 integer specifying the relative position in the text to be written, and
3532 @var{string} is the annotation to add there. The list must be sorted in
3533 order of position when @var{to-fn} returns it.
3535 When @code{write-region} actually writes the text from the buffer to the
3536 file, it intermixes the specified annotations at the corresponding
3537 positions. All this takes place without modifying the buffer.
3540 @var{to-fn} must not involve buffers or files other than the one being
3541 encoded, otherwise the internal buffer used for formatting might be
3545 A flag, @code{t} if the encoding function modifies the buffer, and
3546 @code{nil} if it works by returning a list of annotations.
3549 A minor-mode function to call after visiting a file converted from this
3550 format. The function is called with one argument, the integer 1;
3551 that tells a minor-mode function to enable the mode.
3554 A flag, @code{t} if @code{format-write-file} should not remove this format
3555 from @code{buffer-file-format}.
3558 The function @code{insert-file-contents} automatically recognizes file
3559 formats when it reads the specified file. It checks the text of the
3560 beginning of the file against the regular expressions of the format
3561 definitions, and if it finds a match, it calls the decoding function for
3562 that format. Then it checks all the known formats over again.
3563 It keeps checking them until none of them is applicable.
3565 Visiting a file, with @code{find-file-noselect} or the commands that use
3566 it, performs conversion likewise (because it calls
3567 @code{insert-file-contents}); it also calls the mode function for each
3568 format that it decodes. It stores a list of the format names in the
3569 buffer-local variable @code{buffer-file-format}.
3571 @defvar buffer-file-format
3572 This variable states the format of the visited file. More precisely,
3573 this is a list of the file format names that were decoded in the course
3574 of visiting the current buffer's file. It is always buffer-local in all
3578 When @code{write-region} writes data into a file, it first calls the
3579 encoding functions for the formats listed in @code{buffer-file-format},
3580 in the order of appearance in the list.
3582 @deffn Command format-write-file file format &optional confirm
3583 This command writes the current buffer contents into the file @var{file}
3584 in a format based on @var{format}, which is a list of format names. It
3585 constructs the actual format starting from @var{format}, then appending
3586 any elements from the value of @code{buffer-file-format} with a
3587 non-@code{nil} @var{preserve} flag (see above), if they are not already
3588 present in @var{format}. It then updates @code{buffer-file-format} with
3589 this format, making it the default for future saves. Except for the
3590 @var{format} argument, this command is similar to @code{write-file}. In
3591 particular, @var{confirm} has the same meaning and interactive treatment
3592 as the corresponding argument to @code{write-file}. @xref{Definition of
3596 @deffn Command format-find-file file format
3597 This command finds the file @var{file}, converting it according to
3598 format @var{format}. It also makes @var{format} the default if the
3599 buffer is saved later.
3601 The argument @var{format} is a list of format names. If @var{format} is
3602 @code{nil}, no conversion takes place. Interactively, typing just
3603 @key{RET} for @var{format} specifies @code{nil}.
3606 @deffn Command format-insert-file file format &optional beg end
3607 This command inserts the contents of file @var{file}, converting it
3608 according to format @var{format}. If @var{beg} and @var{end} are
3609 non-@code{nil}, they specify which part of the file to read, as in
3610 @code{insert-file-contents} (@pxref{Reading from Files}).
3612 The return value is like what @code{insert-file-contents} returns: a
3613 list of the absolute file name and the length of the data inserted
3616 The argument @var{format} is a list of format names. If @var{format} is
3617 @code{nil}, no conversion takes place. Interactively, typing just
3618 @key{RET} for @var{format} specifies @code{nil}.
3621 @defvar buffer-auto-save-file-format
3622 This variable specifies the format to use for auto-saving. Its value is
3623 a list of format names, just like the value of
3624 @code{buffer-file-format}; however, it is used instead of
3625 @code{buffer-file-format} for writing auto-save files. If the value
3626 is @code{t}, the default, auto-saving uses the same format as a
3627 regular save in the same buffer. This variable is always buffer-local
3631 @node Format Conversion Piecemeal
3632 @subsection Piecemeal Specification
3634 In contrast to the round-trip specification described in the previous
3635 subsection (@pxref{Format Conversion Round-Trip}), you can use the variables
3636 @code{after-insert-file-functions} and @code{write-region-annotate-functions}
3637 to separately control the respective reading and writing conversions.
3639 Conversion starts with one representation and produces another
3640 representation. When there is only one conversion to do, there is no
3641 conflict about what to start with. However, when there are multiple
3642 conversions involved, conflict may arise when two conversions need to
3643 start with the same data.
3645 This situation is best understood in the context of converting text
3646 properties during @code{write-region}. For example, the character at
3647 position 42 in a buffer is @samp{X} with a text property @code{foo}. If
3648 the conversion for @code{foo} is done by inserting into the buffer, say,
3649 @samp{FOO:}, then that changes the character at position 42 from
3650 @samp{X} to @samp{F}. The next conversion will start with the wrong
3653 To avoid conflict, cooperative conversions do not modify the buffer,
3654 but instead specify @dfn{annotations}, a list of elements of the form
3655 @code{(@var{position} . @var{string})}, sorted in order of increasing
3658 If there is more than one conversion, @code{write-region} merges their
3659 annotations destructively into one sorted list. Later, when the text
3660 from the buffer is actually written to the file, it intermixes the
3661 specified annotations at the corresponding positions. All this takes
3662 place without modifying the buffer.
3664 @c ??? What about "overriding" conversions like those allowed
3665 @c ??? for 'write-region-annotate-functions', below? --ttn
3667 In contrast, when reading, the annotations intermixed with the text
3668 are handled immediately. @code{insert-file-contents} sets point to
3669 the beginning of some text to be converted, then calls the conversion
3670 functions with the length of that text. These functions should always
3671 return with point at the beginning of the inserted text. This
3672 approach makes sense for reading because annotations removed by the
3673 first converter can't be mistakenly processed by a later converter.
3674 Each conversion function should scan for the annotations it
3675 recognizes, remove the annotation, modify the buffer text (to set a
3676 text property, for example), and return the updated length of the
3677 text, as it stands after those changes. The value returned by one
3678 function becomes the argument to the next function.
3680 @defvar write-region-annotate-functions
3681 A list of functions for @code{write-region} to call. Each function in
3682 the list is called with two arguments: the start and end of the region
3683 to be written. These functions should not alter the contents of the
3684 buffer. Instead, they should return annotations.
3686 As a special case, a function may return with a different buffer
3687 current. Emacs takes this to mean that the current buffer contains
3688 altered text to be output. It therefore changes the @var{start} and
3689 @var{end} arguments of the @code{write-region} call, giving them the
3690 values of @code{point-min} and @code{point-max} in the new buffer,
3691 respectively. It also discards all previous annotations, because they
3692 should have been dealt with by this function.
3695 @defvar write-region-post-annotation-function
3696 The value of this variable, if non-@code{nil}, should be a function.
3697 This function is called, with no arguments, after @code{write-region}
3700 If any function in @code{write-region-annotate-functions} returns with
3701 a different buffer current, Emacs calls
3702 @code{write-region-post-annotation-function} more than once. Emacs
3703 calls it with the last buffer that was current, and again with the
3704 buffer before that, and so on back to the original buffer.
3706 Thus, a function in @code{write-region-annotate-functions} can create
3707 a buffer, give this variable the local value of @code{kill-buffer} in
3708 that buffer, set up the buffer with altered text, and make the buffer
3709 current. The buffer will be killed after @code{write-region} is done.
3712 @defvar after-insert-file-functions
3713 Each function in this list is called by @code{insert-file-contents}
3714 with one argument, the number of characters inserted, and with point
3715 at the beginning of the inserted text. Each function should leave
3716 point unchanged, and return the new character count describing the
3717 inserted text as modified by the function.
3718 @c ??? The docstring mentions a handler from 'file-name-handler-alist'
3719 @c "intercepting" 'insert-file-contents'. Hmmm. --ttn
3722 We invite users to write Lisp programs to store and retrieve text
3723 properties in files, using these hooks, and thus to experiment with
3724 various data formats and find good ones. Eventually we hope users
3725 will produce good, general extensions we can install in Emacs.
3727 We suggest not trying to handle arbitrary Lisp objects as text property
3728 names or values---because a program that general is probably difficult
3729 to write, and slow. Instead, choose a set of possible data types that
3730 are reasonably flexible, and not too hard to encode.