2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2012
4 @c Free Software Foundation, Inc.
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 file
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 actually a string. Most of these functions
17 expand file name arguments by calling @code{expand-file-name}, so that
18 @file{~} is handled correctly, as are relative file names (including
19 @samp{../}). @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 (@pxref{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-message-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 * File Names:: Decomposing and expanding file names.
45 * Contents of Directories:: Getting a list of the files in a directory.
46 * Create/Delete Dirs:: Creating and Deleting Directories.
47 * Magic File Names:: Special handling for certain file names.
48 * Format Conversion:: Conversion to and from various file formats.
52 @section Visiting Files
54 @cindex visiting files
56 Visiting a file means reading a file into a buffer. Once this is
57 done, we say that the buffer is @dfn{visiting} that file, and call the
58 file ``the visited file'' of the buffer.
60 A file and a buffer are two different things. A file is information
61 recorded permanently in the computer (unless you delete it). A buffer,
62 on the other hand, is information inside of Emacs that will vanish at
63 the end of the editing session (or when you kill the buffer). Usually,
64 a buffer contains information that you have copied from a file; then we
65 say the buffer is visiting that file. The copy in the buffer is what
66 you modify with editing commands. Such changes to the buffer do not
67 change the file; therefore, to make the changes permanent, you must
68 @dfn{save} the buffer, which means copying the altered buffer contents
71 In spite of the distinction between files and buffers, people often
72 refer to a file when they mean a buffer and vice-versa. Indeed, we say,
73 ``I am editing a file'', rather than, ``I am editing a buffer that I
74 will soon save as a file of the same name''. Humans do not usually need
75 to make the distinction explicit. When dealing with a computer program,
76 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
86 This section describes the functions normally used to visit files.
87 For historical reasons, these functions have names starting with
88 @samp{find-} rather than @samp{visit-}. @xref{Buffer File Name}, for
89 functions and variables that access the visited file name of a buffer or
90 that find an existing buffer by its visited file name.
92 In a Lisp program, if you want to look at the contents of a file but
93 not alter it, the fastest way is to use @code{insert-file-contents} in a
94 temporary buffer. Visiting the file is not necessary and takes longer.
95 @xref{Reading from Files}.
97 @deffn Command find-file filename &optional wildcards
98 This command selects a buffer visiting the file @var{filename},
99 using an existing buffer if there is one, and otherwise creating a
100 new buffer and reading the file into it. It also returns that buffer.
102 Aside from some technical details, the body of the @code{find-file}
103 function is basically equivalent to:
106 (switch-to-buffer (find-file-noselect filename nil nil wildcards))
110 (See @code{switch-to-buffer} in @ref{Switching Buffers}.)
112 If @var{wildcards} is non-@code{nil}, which is always true in an
113 interactive call, then @code{find-file} expands wildcard characters in
114 @var{filename} and visits all the matching files.
116 When @code{find-file} is called interactively, it prompts for
117 @var{filename} in the minibuffer.
120 @deffn Command find-file-literally filename
121 This command visits @var{filename}, like @code{find-file} does, but it
122 does not perform any format conversions (@pxref{Format Conversion}),
123 character code conversions (@pxref{Coding Systems}), or end-of-line
124 conversions (@pxref{Coding System Basics, End of line conversion}).
125 The buffer visiting the file is made unibyte, and its major mode is
126 Fundamental mode, regardless of the file name. File local variable
127 specifications in the file (@pxref{File Local Variables}) are
128 ignored, and automatic decompression and adding a newline at the end
129 of the file due to @code{require-final-newline} (@pxref{Saving
130 Buffers, require-final-newline}) are also disabled.
132 Note that if Emacs already has a buffer visiting the same file
133 non-literally, it will not visit the same file literally, but instead
134 just switch to the existing buffer. If you want to be sure of
135 accessing a file's contents literally, you should create a temporary
136 buffer and then read the file contents into it using
137 @code{insert-file-contents-literally} (@pxref{Reading from Files}).
140 @defun find-file-noselect filename &optional nowarn rawfile wildcards
141 This function is the guts of all the file-visiting functions. It
142 returns a buffer visiting the file @var{filename}. You may make the
143 buffer current or display it in a window if you wish, but this
144 function does not do so.
146 The function returns an existing buffer if there is one; otherwise it
147 creates a new buffer and reads the file into it. When
148 @code{find-file-noselect} uses an existing buffer, it first verifies
149 that the file has not changed since it was last visited or saved in
150 that buffer. If the file has changed, this function asks the user
151 whether to reread the changed file. If the user says @samp{yes}, any
152 edits previously made in the buffer are lost.
154 Reading the file involves decoding the file's contents (@pxref{Coding
155 Systems}), including end-of-line conversion, and format conversion
156 (@pxref{Format Conversion}). If @var{wildcards} is non-@code{nil},
157 then @code{find-file-noselect} expands wildcard characters in
158 @var{filename} and visits all the matching files.
160 This function displays warning or advisory messages in various peculiar
161 cases, unless the optional argument @var{nowarn} is non-@code{nil}. For
162 example, if it needs to create a buffer, and there is no file named
163 @var{filename}, it displays the message @samp{(New file)} in the echo
164 area, and leaves the buffer empty.
166 The @code{find-file-noselect} function normally calls
167 @code{after-find-file} after reading the file (@pxref{Subroutines of
168 Visiting}). That function sets the buffer major mode, parses local
169 variables, warns the user if there exists an auto-save file more recent
170 than the file just visited, and finishes by running the functions in
171 @code{find-file-hook}.
173 If the optional argument @var{rawfile} is non-@code{nil}, then
174 @code{after-find-file} is not called, and the
175 @code{find-file-not-found-functions} are not run in case of failure.
176 What's more, a non-@code{nil} @var{rawfile} value suppresses coding
177 system conversion and format conversion.
179 The @code{find-file-noselect} function usually returns the buffer that
180 is visiting the file @var{filename}. But, if wildcards are actually
181 used and expanded, it returns a list of buffers that are visiting the
186 (find-file-noselect "/etc/fstab")
187 @result{} #<buffer fstab>
192 @deffn Command find-file-other-window filename &optional wildcards
193 This command selects a buffer visiting the file @var{filename}, but
194 does so in a window other than the selected window. It may use
195 another existing window or split a window; see @ref{Switching
198 When this command is called interactively, it prompts for
202 @deffn Command find-file-read-only filename &optional wildcards
203 This command selects a buffer visiting the file @var{filename}, like
204 @code{find-file}, but it marks the buffer as read-only. @xref{Read Only
205 Buffers}, for related functions and variables.
207 When this command is called interactively, it prompts for
211 @defopt find-file-wildcards
212 If this variable is non-@code{nil}, then the various @code{find-file}
213 commands check for wildcard characters and visit all the files that
214 match them (when invoked interactively or when their @var{wildcards}
215 argument is non-@code{nil}). If this option is @code{nil}, then
216 the @code{find-file} commands ignore their @var{wildcards} argument
217 and never treat wildcard characters specially.
220 @defopt find-file-hook
221 The value of this variable is a list of functions to be called after a
222 file is visited. The file's local-variables specification (if any) will
223 have been processed before the hooks are run. The buffer visiting the
224 file is current when the hook functions are run.
226 This variable is a normal hook. @xref{Hooks}.
229 @defvar find-file-not-found-functions
230 The value of this variable is a list of functions to be called when
231 @code{find-file} or @code{find-file-noselect} is passed a nonexistent
232 file name. @code{find-file-noselect} calls these functions as soon as
233 it detects a nonexistent file. It calls them in the order of the list,
234 until one of them returns non-@code{nil}. @code{buffer-file-name} is
237 This is not a normal hook because the values of the functions are
238 used, and in many cases only some of the functions are called.
241 @defvar find-file-literally
242 This buffer-local variable, if set to a non-@code{nil} value, makes
243 @code{save-buffer} behave as if the buffer were visiting its file
244 literally, i.e. without conversions of any kind. The command
245 @code{find-file-literally} sets this variable's local value, but other
246 equivalent functions and commands can do that as well, e.g.@: to avoid
247 automatic addition of a newline at the end of the file. This variable
248 is permanent local, so it is unaffected by changes of major modes.
251 @node Subroutines of Visiting
252 @subsection Subroutines of Visiting
254 The @code{find-file-noselect} function uses two important subroutines
255 which are sometimes useful in user Lisp code: @code{create-file-buffer}
256 and @code{after-find-file}. This section explains how to use them.
258 @defun create-file-buffer filename
259 This function creates a suitably named buffer for visiting
260 @var{filename}, and returns it. It uses @var{filename} (sans directory)
261 as the name if that name is free; otherwise, it appends a string such as
262 @samp{<2>} to get an unused name. See also @ref{Creating Buffers}.
264 @strong{Please note:} @code{create-file-buffer} does @emph{not}
265 associate the new buffer with a file and does not select the buffer.
266 It also does not use the default major mode.
270 (create-file-buffer "foo")
271 @result{} #<buffer foo>
274 (create-file-buffer "foo")
275 @result{} #<buffer foo<2>>
278 (create-file-buffer "foo")
279 @result{} #<buffer foo<3>>
283 This function is used by @code{find-file-noselect}.
284 It uses @code{generate-new-buffer} (@pxref{Creating Buffers}).
287 @defun after-find-file &optional error warn noauto after-find-file-from-revert-buffer nomodes
288 This function sets the buffer major mode, and parses local variables
289 (@pxref{Auto Major Mode}). It is called by @code{find-file-noselect}
290 and by the default revert function (@pxref{Reverting}).
292 @cindex new file message
293 @cindex file open error
294 If reading the file got an error because the file does not exist, but
295 its directory does exist, the caller should pass a non-@code{nil} value
296 for @var{error}. In that case, @code{after-find-file} issues a warning:
297 @samp{(New file)}. For more serious errors, the caller should usually not
298 call @code{after-find-file}.
300 If @var{warn} is non-@code{nil}, then this function issues a warning
301 if an auto-save file exists and is more recent than the visited file.
303 If @var{noauto} is non-@code{nil}, that says not to enable or disable
304 Auto-Save mode. The mode remains enabled if it was enabled before.
306 If @var{after-find-file-from-revert-buffer} is non-@code{nil}, that
307 means this call was from @code{revert-buffer}. This has no direct
308 effect, but some mode functions and hook functions check the value
311 If @var{nomodes} is non-@code{nil}, that means don't alter the buffer's
312 major mode, don't process local variables specifications in the file,
313 and don't run @code{find-file-hook}. This feature is used by
314 @code{revert-buffer} in some cases.
316 The last thing @code{after-find-file} does is call all the functions
317 in the list @code{find-file-hook}.
321 @section Saving Buffers
322 @cindex saving buffers
324 When you edit a file in Emacs, you are actually working on a buffer
325 that is visiting that file---that is, the contents of the file are
326 copied into the buffer and the copy is what you edit. Changes to the
327 buffer do not change the file until you @dfn{save} the buffer, which
328 means copying the contents of the buffer into the file.
330 @deffn Command save-buffer &optional backup-option
331 This function saves the contents of the current buffer in its visited
332 file if the buffer has been modified since it was last visited or saved.
333 Otherwise it does nothing.
335 @code{save-buffer} is responsible for making backup files. Normally,
336 @var{backup-option} is @code{nil}, and @code{save-buffer} makes a backup
337 file only if this is the first save since visiting the file. Other
338 values for @var{backup-option} request the making of backup files in
343 With an argument of 4 or 64, reflecting 1 or 3 @kbd{C-u}'s, the
344 @code{save-buffer} function marks this version of the file to be
345 backed up when the buffer is next saved.
348 With an argument of 16 or 64, reflecting 2 or 3 @kbd{C-u}'s, the
349 @code{save-buffer} function unconditionally backs up the previous
350 version of the file before saving it.
353 With an argument of 0, unconditionally do @emph{not} make any backup file.
357 @deffn Command save-some-buffers &optional save-silently-p pred
358 @anchor{Definition of save-some-buffers}
359 This command saves some modified file-visiting buffers. Normally it
360 asks the user about each buffer. But if @var{save-silently-p} is
361 non-@code{nil}, it saves all the file-visiting buffers without querying
364 The optional @var{pred} argument controls which buffers to ask about
365 (or to save silently if @var{save-silently-p} is non-@code{nil}).
366 If it is @code{nil}, that means to ask only about file-visiting buffers.
367 If it is @code{t}, that means also offer to save certain other non-file
368 buffers---those that have a non-@code{nil} buffer-local value of
369 @code{buffer-offer-save} (@pxref{Killing Buffers}). A user who says
370 @samp{yes} to saving a non-file buffer is asked to specify the file
371 name to use. The @code{save-buffers-kill-emacs} function passes the
372 value @code{t} for @var{pred}.
374 If @var{pred} is neither @code{t} nor @code{nil}, then it should be
375 a function of no arguments. It will be called in each buffer to decide
376 whether to offer to save that buffer. If it returns a non-@code{nil}
377 value in a certain buffer, that means do offer to save that buffer.
380 @deffn Command write-file filename &optional confirm
381 @anchor{Definition of write-file}
382 This function writes the current buffer into file @var{filename}, makes
383 the buffer visit that file, and marks it not modified. Then it renames
384 the buffer based on @var{filename}, appending a string like @samp{<2>}
385 if necessary to make a unique buffer name. It does most of this work by
386 calling @code{set-visited-file-name} (@pxref{Buffer File Name}) and
389 If @var{confirm} is non-@code{nil}, that means to ask for confirmation
390 before overwriting an existing file. Interactively, confirmation is
391 required, unless the user supplies a prefix argument.
393 If @var{filename} is an existing directory, or a symbolic link to one,
394 @code{write-file} uses the name of the visited file, in directory
395 @var{filename}. If the buffer is not visiting a file, it uses the
399 Saving a buffer runs several hooks. It also performs format
400 conversion (@pxref{Format Conversion}).
402 @defvar write-file-functions
403 The value of this variable is a list of functions to be called before
404 writing out a buffer to its visited file. If one of them returns
405 non-@code{nil}, the file is considered already written and the rest of
406 the functions are not called, nor is the usual code for writing the file
409 If a function in @code{write-file-functions} returns non-@code{nil}, it
410 is responsible for making a backup file (if that is appropriate).
411 To do so, execute the following code:
414 (or buffer-backed-up (backup-buffer))
417 You might wish to save the file modes value returned by
418 @code{backup-buffer} and use that (if non-@code{nil}) to set the mode
419 bits of the file that you write. This is what @code{save-buffer}
420 normally does. @xref{Making Backups,, Making Backup Files}.
422 The hook functions in @code{write-file-functions} are also responsible
423 for encoding the data (if desired): they must choose a suitable coding
424 system and end-of-line conversion (@pxref{Lisp and Coding Systems}),
425 perform the encoding (@pxref{Explicit Encoding}), and set
426 @code{last-coding-system-used} to the coding system that was used
427 (@pxref{Encoding and I/O}).
429 If you set this hook locally in a buffer, it is assumed to be
430 associated with the file or the way the contents of the buffer were
431 obtained. Thus the variable is marked as a permanent local, so that
432 changing the major mode does not alter a buffer-local value. On the
433 other hand, calling @code{set-visited-file-name} will reset it.
434 If this is not what you want, you might like to use
435 @code{write-contents-functions} instead.
437 Even though this is not a normal hook, you can use @code{add-hook} and
438 @code{remove-hook} to manipulate the list. @xref{Hooks}.
442 @defvar write-contents-functions
443 This works just like @code{write-file-functions}, but it is intended
444 for hooks that pertain to the buffer's contents, not to the particular
445 visited file or its location. Such hooks are usually set up by major
446 modes, as buffer-local bindings for this variable. This variable
447 automatically becomes buffer-local whenever it is set; switching to a
448 new major mode always resets this variable, but calling
449 @code{set-visited-file-name} does not.
451 If any of the functions in this hook returns non-@code{nil}, the file
452 is considered already written and the rest are not called and neither
453 are the functions in @code{write-file-functions}.
456 @defopt before-save-hook
457 This normal hook runs before a buffer is saved in its visited file,
458 regardless of whether that is done normally or by one of the hooks
459 described above. For instance, the @file{copyright.el} program uses
460 this hook to make sure the file you are saving has the current year in
461 its copyright notice.
465 @defopt after-save-hook
466 This normal hook runs after a buffer has been saved in its visited file.
467 One use of this hook is in Fast Lock mode; it uses this hook to save the
468 highlighting information in a cache file.
471 @defopt file-precious-flag
472 If this variable is non-@code{nil}, then @code{save-buffer} protects
473 against I/O errors while saving by writing the new file to a temporary
474 name instead of the name it is supposed to have, and then renaming it to
475 the intended name after it is clear there are no errors. This procedure
476 prevents problems such as a lack of disk space from resulting in an
479 As a side effect, backups are necessarily made by copying. @xref{Rename
480 or Copy}. Yet, at the same time, saving a precious file always breaks
481 all hard links between the file you save and other file names.
483 Some modes give this variable a non-@code{nil} buffer-local value
484 in particular buffers.
487 @defopt require-final-newline
488 This variable determines whether files may be written out that do
489 @emph{not} end with a newline. If the value of the variable is
490 @code{t}, then @code{save-buffer} silently adds a newline at the end
491 of the buffer whenever it does not already end in one. If the value
492 is @code{visit}, Emacs adds a missing newline just after it visits the
493 file. If the value is @code{visit-save}, Emacs adds a missing newline
494 both on visiting and on saving. For any other non-@code{nil} value,
495 @code{save-buffer} asks the user whether to add a newline each time
498 If the value of the variable is @code{nil}, then @code{save-buffer}
499 doesn't add newlines at all. @code{nil} is the default value, but a few
500 major modes set it to @code{t} in particular buffers.
503 See also the function @code{set-visited-file-name} (@pxref{Buffer File
506 @node Reading from Files
507 @section Reading from Files
508 @cindex reading from files
510 You can copy a file from the disk and insert it into a buffer
511 using the @code{insert-file-contents} function. Don't use the user-level
512 command @code{insert-file} in a Lisp program, as that sets the mark.
514 @defun insert-file-contents filename &optional visit beg end replace
515 This function inserts the contents of file @var{filename} into the
516 current buffer after point. It returns a list of the absolute file name
517 and the length of the data inserted. An error is signaled if
518 @var{filename} is not the name of a file that can be read.
520 This function checks the file contents against the defined file
521 formats, and converts the file contents if appropriate and also calls
522 the functions in the list @code{after-insert-file-functions}.
523 @xref{Format Conversion}. Normally, one of the functions in the
524 @code{after-insert-file-functions} list determines the coding system
525 (@pxref{Coding Systems}) used for decoding the file's contents,
526 including end-of-line conversion. However, if the file contains null
527 bytes, it is by default visited without any code conversions.
528 @xref{Lisp and Coding Systems, inhibit-null-byte-detection}.
530 If @var{visit} is non-@code{nil}, this function additionally marks the
531 buffer as unmodified and sets up various fields in the buffer so that it
532 is visiting the file @var{filename}: these include the buffer's visited
533 file name and its last save file modtime. This feature is used by
534 @code{find-file-noselect} and you probably should not use it yourself.
536 If @var{beg} and @var{end} are non-@code{nil}, they should be integers
537 specifying the portion of the file to insert. In this case, @var{visit}
538 must be @code{nil}. For example,
541 (insert-file-contents filename nil 0 500)
545 inserts the first 500 characters of a file.
547 If the argument @var{replace} is non-@code{nil}, it means to replace the
548 contents of the buffer (actually, just the accessible portion) with the
549 contents of the file. This is better than simply deleting the buffer
550 contents and inserting the whole file, because (1) it preserves some
551 marker positions and (2) it puts less data in the undo list.
553 It is possible to read a special file (such as a FIFO or an I/O device)
554 with @code{insert-file-contents}, as long as @var{replace} and
555 @var{visit} are @code{nil}.
558 @defun insert-file-contents-literally filename &optional visit beg end replace
559 This function works like @code{insert-file-contents} except that it
560 does not run @code{find-file-hook}, and does not do format decoding,
561 character code conversion, automatic uncompression, and so on.
564 If you want to pass a file name to another process so that another
565 program can read the file, use the function @code{file-local-copy}; see
566 @ref{Magic File Names}.
568 @node Writing to Files
569 @section Writing to Files
570 @cindex writing to files
572 You can write the contents of a buffer, or part of a buffer, directly
573 to a file on disk using the @code{append-to-file} and
574 @code{write-region} functions. Don't use these functions to write to
575 files that are being visited; that could cause confusion in the
576 mechanisms for visiting.
578 @deffn Command append-to-file start end filename
579 This function appends the contents of the region delimited by
580 @var{start} and @var{end} in the current buffer to the end of file
581 @var{filename}. If that file does not exist, it is created. This
582 function returns @code{nil}.
584 An error is signaled if @var{filename} specifies a nonwritable file,
585 or a nonexistent file in a directory where files cannot be created.
587 When called from Lisp, this function is completely equivalent to:
590 (write-region start end filename t)
594 @deffn Command write-region start end filename &optional append visit lockname mustbenew
595 This function writes the region delimited by @var{start} and @var{end}
596 in the current buffer into the file specified by @var{filename}.
598 If @var{start} is @code{nil}, then the command writes the entire buffer
599 contents (@emph{not} just the accessible portion) to the file and
603 If @var{start} is a string, then @code{write-region} writes or appends
604 that string, rather than text from the buffer. @var{end} is ignored in
607 If @var{append} is non-@code{nil}, then the specified text is appended
608 to the existing file contents (if any). If @var{append} is an
609 integer, @code{write-region} seeks to that byte offset from the start
610 of the file and writes the data from there.
612 If @var{mustbenew} is non-@code{nil}, then @code{write-region} asks
613 for confirmation if @var{filename} names an existing file. If
614 @var{mustbenew} is the symbol @code{excl}, then @code{write-region}
615 does not ask for confirmation, but instead it signals an error
616 @code{file-already-exists} if the file already exists.
618 The test for an existing file, when @var{mustbenew} is @code{excl}, uses
619 a special system feature. At least for files on a local disk, there is
620 no chance that some other program could create a file of the same name
621 before Emacs does, without Emacs's noticing.
623 If @var{visit} is @code{t}, then Emacs establishes an association
624 between the buffer and the file: the buffer is then visiting that file.
625 It also sets the last file modification time for the current buffer to
626 @var{filename}'s modtime, and marks the buffer as not modified. This
627 feature is used by @code{save-buffer}, but you probably should not use
631 If @var{visit} is a string, it specifies the file name to visit. This
632 way, you can write the data to one file (@var{filename}) while recording
633 the buffer as visiting another file (@var{visit}). The argument
634 @var{visit} is used in the echo area message and also for file locking;
635 @var{visit} is stored in @code{buffer-file-name}. This feature is used
636 to implement @code{file-precious-flag}; don't use it yourself unless you
637 really know what you're doing.
639 The optional argument @var{lockname}, if non-@code{nil}, specifies the
640 file name to use for purposes of locking and unlocking, overriding
641 @var{filename} and @var{visit} for that purpose.
643 The function @code{write-region} converts the data which it writes to
644 the appropriate file formats specified by @code{buffer-file-format}
645 and also calls the functions in the list
646 @code{write-region-annotate-functions}.
647 @xref{Format Conversion}.
649 Normally, @code{write-region} displays the message @samp{Wrote
650 @var{filename}} in the echo area. If @var{visit} is neither @code{t}
651 nor @code{nil} nor a string, then this message is inhibited. This
652 feature is useful for programs that use files for internal purposes,
653 files that the user does not need to know about.
656 @defmac with-temp-file file body@dots{}
657 @anchor{Definition of with-temp-file}
658 The @code{with-temp-file} macro evaluates the @var{body} forms with a
659 temporary buffer as the current buffer; then, at the end, it writes the
660 buffer contents into file @var{file}. It kills the temporary buffer
661 when finished, restoring the buffer that was current before the
662 @code{with-temp-file} form. Then it returns the value of the last form
665 The current buffer is restored even in case of an abnormal exit via
666 @code{throw} or error (@pxref{Nonlocal Exits}).
668 See also @code{with-temp-buffer} in @ref{Definition of
669 with-temp-buffer,, The Current Buffer}.
677 When two users edit the same file at the same time, they are likely
678 to interfere with each other. Emacs tries to prevent this situation
679 from arising by recording a @dfn{file lock} when a file is being
680 modified. (File locks are not implemented on Microsoft systems.)
681 Emacs can then detect the first attempt to modify a buffer visiting a
682 file that is locked by another Emacs job, and ask the user what to do.
683 The file lock is really a file, a symbolic link with a special name,
684 stored in the same directory as the file you are editing.
686 When you access files using NFS, there may be a small probability that
687 you and another user will both lock the same file ``simultaneously''.
688 If this happens, it is possible for the two users to make changes
689 simultaneously, but Emacs will still warn the user who saves second.
690 Also, the detection of modification of a buffer visiting a file changed
691 on disk catches some cases of simultaneous editing; see
692 @ref{Modification Time}.
694 @defun file-locked-p filename
695 This function returns @code{nil} if the file @var{filename} is not
696 locked. It returns @code{t} if it is locked by this Emacs process, and
697 it returns the name of the user who has locked it if it is locked by
702 (file-locked-p "foo")
708 @defun lock-buffer &optional filename
709 This function locks the file @var{filename}, if the current buffer is
710 modified. The argument @var{filename} defaults to the current buffer's
711 visited file. Nothing is done if the current buffer is not visiting a
712 file, or is not modified, or if the system does not support locking.
716 This function unlocks the file being visited in the current buffer,
717 if the buffer is modified. If the buffer is not modified, then
718 the file should not be locked, so this function does nothing. It also
719 does nothing if the current buffer is not visiting a file, or if the
720 system does not support locking.
723 File locking is not supported on some systems. On systems that do not
724 support it, the functions @code{lock-buffer}, @code{unlock-buffer} and
725 @code{file-locked-p} do nothing and return @code{nil}. It is also
726 possible to disable locking, by setting the variable @code{create-lockfiles}.
728 @defopt create-lockfiles
729 If this variable is @code{nil}, Emacs does not lock files.
732 @defun ask-user-about-lock file other-user
733 This function is called when the user tries to modify @var{file}, but it
734 is locked by another user named @var{other-user}. The default
735 definition of this function asks the user to say what to do. The value
736 this function returns determines what Emacs does next:
740 A value of @code{t} says to grab the lock on the file. Then
741 this user may edit the file and @var{other-user} loses the lock.
744 A value of @code{nil} says to ignore the lock and let this
745 user edit the file anyway.
749 This function may instead signal a @code{file-locked} error, in which
750 case the change that the user was about to make does not take place.
752 The error message for this error looks like this:
755 @error{} File is locked: @var{file} @var{other-user}
759 where @code{file} is the name of the file and @var{other-user} is the
760 name of the user who has locked the file.
763 If you wish, you can replace the @code{ask-user-about-lock} function
764 with your own version that makes the decision in another way. The code
765 for its usual definition is in @file{userlock.el}.
768 @node Information about Files
769 @section Information about Files
770 @cindex file, information about
772 The functions described in this section all operate on strings that
773 designate file names. With a few exceptions, all the functions have
774 names that begin with the word @samp{file}. These functions all
775 return information about actual files or directories, so their
776 arguments must all exist as actual files or directories unless
780 * Testing Accessibility:: Is a given file readable? Writable?
781 * Kinds of Files:: Is it a directory? A symbolic link?
782 * Truenames:: Eliminating symbolic links from a file name.
783 * File Attributes:: How large is it? Any other names? Etc.
784 * Locating Files:: How to find a file in standard places.
787 @node Testing Accessibility
788 @subsection Testing Accessibility
789 @cindex accessibility of a file
790 @cindex file accessibility
792 These functions test for permission to access a file in specific
793 ways. Unless explicitly stated otherwise, they recursively follow
794 symbolic links for their file name arguments, at all levels (at the
795 level of the file itself and at all levels of parent directories).
797 @defun file-exists-p filename
798 This function returns @code{t} if a file named @var{filename} appears
799 to exist. This does not mean you can necessarily read the file, only
800 that you can find out its attributes. (On Unix and GNU/Linux, this is
801 true if the file exists and you have execute permission on the
802 containing directories, regardless of the permissions of the file
805 If the file does not exist, or if fascist access control policies
806 prevent you from finding the attributes of the file, this function
809 Directories are files, so @code{file-exists-p} returns @code{t} when
810 given a directory name. However, symbolic links are treated
811 specially; @code{file-exists-p} returns @code{t} for a symbolic link
812 name only if the target file exists.
815 @defun file-readable-p filename
816 This function returns @code{t} if a file named @var{filename} exists
817 and you can read it. It returns @code{nil} otherwise.
821 (file-readable-p "files.texi")
825 (file-exists-p "/usr/spool/mqueue")
829 (file-readable-p "/usr/spool/mqueue")
836 @defun file-executable-p filename
837 This function returns @code{t} if a file named @var{filename} exists and
838 you can execute it. It returns @code{nil} otherwise. On Unix and
839 GNU/Linux, if the file is a directory, execute permission means you can
840 check the existence and attributes of files inside the directory, and
841 open those files if their modes permit.
844 @defun file-writable-p filename
845 This function returns @code{t} if the file @var{filename} can be written
846 or created by you, and @code{nil} otherwise. A file is writable if the
847 file exists and you can write it. It is creatable if it does not exist,
848 but the specified directory does exist and you can write in that
851 In the third example below, @file{foo} is not writable because the
852 parent directory does not exist, even though the user could create such
857 (file-writable-p "~/foo")
861 (file-writable-p "/foo")
865 (file-writable-p "~/no-such-dir/foo")
872 @defun file-accessible-directory-p dirname
873 This function returns @code{t} if you have permission to open existing
874 files in the directory whose name as a file is @var{dirname};
875 otherwise (or if there is no such directory), it returns @code{nil}.
876 The value of @var{dirname} may be either a directory name (such as
877 @file{/foo/}) or the file name of a file which is a directory
878 (such as @file{/foo}, without the final slash).
880 Example: after the following,
883 (file-accessible-directory-p "/foo")
888 we can deduce that any attempt to read a file in @file{/foo/} will
892 @defun access-file filename string
893 This function opens file @var{filename} for reading, then closes it and
894 returns @code{nil}. However, if the open fails, it signals an error
895 using @var{string} as the error message text.
898 @defun file-ownership-preserved-p filename
899 This function returns @code{t} if deleting the file @var{filename} and
900 then creating it anew would keep the file's owner unchanged. It also
901 returns @code{t} for nonexistent files.
903 If @var{filename} is a symbolic link, then, unlike the other functions
904 discussed here, @code{file-ownership-preserved-p} does @emph{not}
905 replace @var{filename} with its target. However, it does recursively
906 follow symbolic links at all levels of parent directories.
909 @defun file-newer-than-file-p filename1 filename2
911 @cindex file modification time
912 This function returns @code{t} if the file @var{filename1} is
913 newer than file @var{filename2}. If @var{filename1} does not
914 exist, it returns @code{nil}. If @var{filename1} does exist, but
915 @var{filename2} does not, it returns @code{t}.
917 In the following example, assume that the file @file{aug-19} was written
918 on the 19th, @file{aug-20} was written on the 20th, and the file
919 @file{no-file} doesn't exist at all.
923 (file-newer-than-file-p "aug-19" "aug-20")
927 (file-newer-than-file-p "aug-20" "aug-19")
931 (file-newer-than-file-p "aug-19" "no-file")
935 (file-newer-than-file-p "no-file" "aug-19")
940 You can use @code{file-attributes} to get a file's last modification
941 time as a list of two numbers. @xref{File Attributes}.
945 @subsection Distinguishing Kinds of Files
947 This section describes how to distinguish various kinds of files, such
948 as directories, symbolic links, and ordinary files.
950 @defun file-symlink-p filename
951 @cindex file symbolic links
952 If the file @var{filename} is a symbolic link, the
953 @code{file-symlink-p} function returns the (non-recursive) link target
954 as a string. (Determining the file name that the link points to from
955 the target is nontrivial.) First, this function recursively follows
956 symbolic links at all levels of parent directories.
958 If the file @var{filename} is not a symbolic link (or there is no such file),
959 @code{file-symlink-p} returns @code{nil}.
963 (file-symlink-p "foo")
967 (file-symlink-p "sym-link")
971 (file-symlink-p "sym-link2")
975 (file-symlink-p "/bin")
980 @c !!! file-symlink-p: should show output of ls -l for comparison
983 The next two functions recursively follow symbolic links at
984 all levels for @var{filename}.
986 @defun file-directory-p filename
987 This function returns @code{t} if @var{filename} is the name of an
988 existing directory, @code{nil} otherwise.
992 (file-directory-p "~rms")
996 (file-directory-p "~rms/lewis/files.texi")
1000 (file-directory-p "~rms/lewis/no-such-file")
1004 (file-directory-p "$HOME")
1009 (substitute-in-file-name "$HOME"))
1015 @defun file-regular-p filename
1016 This function returns @code{t} if the file @var{filename} exists and is
1017 a regular file (not a directory, named pipe, terminal, or
1021 @defun file-equal-p file1 file2
1022 This function returns @code{t} if the files @var{file1} and
1023 @var{file2} name the same file. If @var{file1} or @var{file2} does
1024 not exist, the return value is unspecified.
1027 @defun file-in-directory-p file dir
1028 This function returns @code{t} if @var{file} is a file in directory
1029 @var{dir}, or in a subdirectory of @var{dir}. It also returns
1030 @code{t} if @var{file} and @var{dir} are the same directory. It
1031 compares the @code{file-truename} values of the two directories
1032 (@pxref{Truenames}). If @var{dir} does not name an existing
1033 directory, the return value is @code{nil}.
1037 @subsection Truenames
1038 @cindex truename (of file)
1040 The @dfn{truename} of a file is the name that you get by following
1041 symbolic links at all levels until none remain, then simplifying away
1042 @samp{.}@: and @samp{..}@: appearing as name components. This results
1043 in a sort of canonical name for the file. A file does not always have a
1044 unique truename; the number of distinct truenames a file has is equal to
1045 the number of hard links to the file. However, truenames are useful
1046 because they eliminate symbolic links as a cause of name variation.
1048 @defun file-truename filename
1049 This function returns the truename of the file @var{filename}. If the
1050 argument is not an absolute file name, this function first expands it
1051 against @code{default-directory}.
1053 This function does not expand environment variables. Only
1054 @code{substitute-in-file-name} does that. @xref{Definition of
1055 substitute-in-file-name}.
1057 If you may need to follow symbolic links preceding @samp{..}@:
1058 appearing as a name component, you should make sure to call
1059 @code{file-truename} without prior direct or indirect calls to
1060 @code{expand-file-name}, as otherwise the file name component
1061 immediately preceding @samp{..} will be ``simplified away'' before
1062 @code{file-truename} is called. To eliminate the need for a call to
1063 @code{expand-file-name}, @code{file-truename} handles @samp{~} in the
1064 same way that @code{expand-file-name} does. @xref{File Name
1065 Expansion,, Functions that Expand Filenames}.
1068 @defun file-chase-links filename &optional limit
1069 This function follows symbolic links, starting with @var{filename},
1070 until it finds a file name which is not the name of a symbolic link.
1071 Then it returns that file name. This function does @emph{not} follow
1072 symbolic links at the level of parent directories.
1074 If you specify a number for @var{limit}, then after chasing through
1075 that many links, the function just returns what it has even if that is
1076 still a symbolic link.
1079 To illustrate the difference between @code{file-chase-links} and
1080 @code{file-truename}, suppose that @file{/usr/foo} is a symbolic link to
1081 the directory @file{/home/foo}, and @file{/home/foo/hello} is an
1082 ordinary file (or at least, not a symbolic link) or nonexistent. Then
1086 (file-chase-links "/usr/foo/hello")
1087 ;; @r{This does not follow the links in the parent directories.}
1088 @result{} "/usr/foo/hello"
1089 (file-truename "/usr/foo/hello")
1090 ;; @r{Assuming that @file{/home} is not a symbolic link.}
1091 @result{} "/home/foo/hello"
1094 @xref{Buffer File Name}, for related information.
1096 @node File Attributes
1097 @subsection Other Information about Files
1099 This section describes the functions for getting detailed
1100 information about a file, other than its contents. This information
1101 includes the mode bits that control access permissions, the owner and
1102 group numbers, the number of names, the inode number, the size, and
1103 the times of access and modification.
1105 @defun file-modes filename
1106 @cindex file permissions
1107 @cindex permissions, file
1108 @cindex file attributes
1110 This function returns the @dfn{mode bits} describing the @dfn{file
1111 permissions} of @var{filename}, as an integer. It recursively follows
1112 symbolic links in @var{filename} at all levels. If @var{filename}
1113 does not exist, the return value is @code{nil}.
1115 @xref{File Permissions,,, coreutils, The @sc{gnu} @code{Coreutils}
1116 Manual}, for a description of mode bits. If the low-order bit is 1,
1117 then the file is executable by all users, if the second-lowest-order
1118 bit is 1, then the file is writable by all users, etc. The highest
1119 value returnable is 4095 (7777 octal), meaning that everyone has read,
1120 write, and execute permission, that the @acronym{SUID} bit is set for
1121 both others and group, and that the sticky bit is set.
1125 (file-modes "~/junk/diffs")
1126 @result{} 492 ; @r{Decimal integer.}
1130 @result{} "754" ; @r{Convert to octal.}
1134 (set-file-modes "~/junk/diffs" #o666)
1140 -rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs
1144 @xref{Changing Files}, for functions that change file permissions,
1145 such as @code{set-file-modes}.
1147 @cindex MS-DOS and file modes
1148 @cindex file modes and MS-DOS
1149 @strong{MS-DOS note:} On MS-DOS, there is no such thing as an
1150 ``executable'' file mode bit. So @code{file-modes} considers a file
1151 executable if its name ends in one of the standard executable
1152 extensions, such as @file{.com}, @file{.bat}, @file{.exe}, and some
1153 others. Files that begin with the Unix-standard @samp{#!} signature,
1154 such as shell and Perl scripts, are also considered executable.
1155 Directories are also reported as executable, for compatibility with
1156 Unix. These conventions are also followed by @code{file-attributes},
1160 If the @var{filename} argument to the next two functions is a
1161 symbolic link, then these function do @emph{not} replace it with its
1162 target. However, they both recursively follow symbolic links at all
1163 levels of parent directories.
1165 @defun file-nlinks filename
1166 This functions returns the number of names (i.e., hard links) that
1167 file @var{filename} has. If the file does not exist, then this function
1168 returns @code{nil}. Note that symbolic links have no effect on this
1169 function, because they are not considered to be names of the files they
1175 -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo
1176 -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo1
1184 (file-nlinks "doesnt-exist")
1190 @defun file-attributes filename &optional id-format
1191 @anchor{Definition of file-attributes}
1192 This function returns a list of attributes of file @var{filename}. If
1193 the specified file cannot be opened, it returns @code{nil}.
1194 The optional parameter @var{id-format} specifies the preferred format
1195 of attributes @acronym{UID} and @acronym{GID} (see below)---the
1196 valid values are @code{'string} and @code{'integer}. The latter is
1197 the default, but we plan to change that, so you should specify a
1198 non-@code{nil} value for @var{id-format} if you use the returned
1199 @acronym{UID} or @acronym{GID}.
1201 The elements of the list, in order, are:
1205 @code{t} for a directory, a string for a symbolic link (the name
1206 linked to), or @code{nil} for a text file.
1208 @c Wordy so as to prevent an overfull hbox. --rjc 15mar92
1210 The number of names the file has. Alternate names, also known as hard
1211 links, can be created by using the @code{add-name-to-file} function
1212 (@pxref{Changing Files}).
1215 The file's @acronym{UID}, normally as a string. However, if it does
1216 not correspond to a named user, the value is an integer or a floating
1220 The file's @acronym{GID}, likewise.
1223 The time of last access, as a list of two integers.
1224 The first integer has the high-order 16 bits of time,
1225 the second has the low 16 bits. (This is similar to the
1226 value of @code{current-time}; see @ref{Time of Day}.) Note that on
1227 some FAT-based filesystems, only the date of last access is recorded,
1228 so this time will always hold the midnight of the day of last access.
1230 @cindex modification time of file
1232 The time of last modification as a list of two integers (as above).
1233 This is the last time when the file's contents were modified.
1236 The time of last status change as a list of two integers (as above).
1237 This is the time of the last change to the file's access mode bits,
1238 its owner and group, and other information recorded in the filesystem
1239 for the file, beyond the file's contents.
1242 The size of the file in bytes. If the size is too large to fit in a
1243 Lisp integer, this is a floating point number.
1246 The file's modes, as a string of ten letters or dashes,
1250 @code{t} if the file's @acronym{GID} would change if file were
1251 deleted and recreated; @code{nil} otherwise.
1254 The file's inode number. If possible, this is an integer. If the
1255 inode number is too large to be represented as an integer in Emacs
1256 Lisp but dividing it by @math{2^16} yields a representable integer,
1257 then the value has the
1258 form @code{(@var{high} . @var{low})}, where @var{low} holds the low 16
1259 bits. If the inode number is too wide for even that, the value is of the form
1260 @code{(@var{high} @var{middle} . @var{low})}, where @code{high} holds
1261 the high bits, @var{middle} the middle 24 bits, and @var{low} the low
1265 The filesystem number of the device that the file is on. Depending on
1266 the magnitude of the value, this can be either an integer or a cons
1267 cell, in the same manner as the inode number. This element and the
1268 file's inode number together give enough information to distinguish
1269 any two files on the system---no two files can have the same values
1270 for both of these numbers.
1273 For example, here are the file attributes for @file{files.texi}:
1277 (file-attributes "files.texi" 'string)
1278 @result{} (nil 1 "lh" "users"
1283 nil (5888 2 . 43978)
1289 and here is how the result is interpreted:
1293 is neither a directory nor a symbolic link.
1296 has only one name (the name @file{files.texi} in the current default
1300 is owned by the user with name "lh".
1303 is in the group with name "users".
1306 was last accessed on Oct 5 2009, at 10:01:37.
1309 last had its contents modified on Oct 2 2009, at 13:49:12.
1312 last had its status changed on Feb 2 2008, at 12:19:00.
1315 is 122295 bytes long. (It may not contain 122295 characters, though,
1316 if some of the bytes belong to multibyte sequences, and also if the
1317 end-of-line format is CR-LF.)
1320 has a mode of read and write access for the owner, group, and world.
1323 would retain the same @acronym{GID} if it were recreated.
1325 @item (5888 2 . 43978)
1326 has an inode number of 6473924464520138.
1328 @item (15479 . 46724)
1329 is on the file-system device whose number is 1014478468.
1333 @cindex SELinux context
1334 SELinux is a Linux kernel feature which provides more sophisticated
1335 file access controls than ordinary ``Unix-style'' file permissions.
1336 If Emacs has been compiled with SELinux support on a system with
1337 SELinux enabled, you can use the function @code{file-selinux-context}
1338 to retrieve a file's SELinux security context. For the function
1339 @code{set-file-selinux-context}, see @ref{Changing Files}.
1341 @defun file-selinux-context filename
1342 This function returns the SELinux security context of the file
1343 @var{filename}. This return value is a list of the form
1344 @code{(@var{user} @var{role} @var{type} @var{range})}, whose elements
1345 are the context's user, role, type, and range respectively, as Lisp
1346 strings. See the SELinux documentation for details about what these
1349 If the file does not exist or is inaccessible, or if the system does
1350 not support SELinux, or if Emacs was not compiled with SELinux
1351 support, then the return value is @code{(nil nil nil nil)}.
1354 @node Locating Files
1355 @subsection How to Locate Files in Standard Places
1356 @cindex locate file in path
1357 @cindex find file in path
1359 This section explains how to search for a file in a list of
1360 directories (a @dfn{path}), or for an executable file in the standard
1361 list of executable file directories.
1363 To search for a user-specific configuration file, @xref{Standard
1364 File Names}, for the @code{locate-user-emacs-file} function.
1366 @defun locate-file filename path &optional suffixes predicate
1367 This function searches for a file whose name is @var{filename} in a
1368 list of directories given by @var{path}, trying the suffixes in
1369 @var{suffixes}. If it finds such a file, it returns the file's
1370 absolute file name (@pxref{Relative File Names}); otherwise it returns
1373 The optional argument @var{suffixes} gives the list of file-name
1374 suffixes to append to @var{filename} when searching.
1375 @code{locate-file} tries each possible directory with each of these
1376 suffixes. If @var{suffixes} is @code{nil}, or @code{("")}, then there
1377 are no suffixes, and @var{filename} is used only as-is. Typical
1378 values of @var{suffixes} are @code{exec-suffixes} (@pxref{Subprocess
1379 Creation}), @code{load-suffixes}, @code{load-file-rep-suffixes} and
1380 the return value of the function @code{get-load-suffixes} (@pxref{Load
1383 Typical values for @var{path} are @code{exec-path} (@pxref{Subprocess
1384 Creation}) when looking for executable programs, or @code{load-path}
1385 (@pxref{Library Search}) when looking for Lisp files. If
1386 @var{filename} is absolute, @var{path} has no effect, but the suffixes
1387 in @var{suffixes} are still tried.
1389 The optional argument @var{predicate}, if non-@code{nil}, specifies a
1390 predicate function for testing whether a candidate file is suitable.
1391 The predicate is passed the candidate file name as its single
1392 argument. If @var{predicate} is @code{nil} or omitted,
1393 @code{locate-file} uses @code{file-readable-p} as the predicate.
1394 @xref{Kinds of Files}, for other useful predicates, e.g.@:
1395 @code{file-executable-p} and @code{file-directory-p}.
1397 For compatibility, @var{predicate} can also be one of the symbols
1398 @code{executable}, @code{readable}, @code{writable}, @code{exists}, or
1399 a list of one or more of these symbols.
1402 @defun executable-find program
1403 This function searches for the executable file of the named
1404 @var{program} and returns the absolute file name of the executable,
1405 including its file-name extensions, if any. It returns @code{nil} if
1406 the file is not found. The functions searches in all the directories
1407 in @code{exec-path}, and tries all the file-name extensions in
1408 @code{exec-suffixes} (@pxref{Subprocess Creation}).
1411 @node Changing Files
1412 @section Changing File Names and Attributes
1413 @c @cindex renaming files Duplicates rename-file
1414 @cindex copying files
1415 @cindex deleting files
1416 @cindex linking files
1417 @cindex setting modes of files
1419 The functions in this section rename, copy, delete, link, and set
1420 the modes (permissions) of files.
1422 In the functions that have an argument @var{newname}, if a file by the
1423 name of @var{newname} already exists, the actions taken depend on the
1424 value of the argument @var{ok-if-already-exists}:
1428 Signal a @code{file-already-exists} error if
1429 @var{ok-if-already-exists} is @code{nil}.
1432 Request confirmation if @var{ok-if-already-exists} is a number.
1435 Replace the old file without confirmation if @var{ok-if-already-exists}
1439 The next four commands all recursively follow symbolic links at all
1440 levels of parent directories for their first argument, but, if that
1441 argument is itself a symbolic link, then only @code{copy-file}
1442 replaces it with its (recursive) target.
1444 @deffn Command add-name-to-file oldname newname &optional ok-if-already-exists
1445 @cindex file with multiple names
1446 @cindex file hard link
1447 This function gives the file named @var{oldname} the additional name
1448 @var{newname}. This means that @var{newname} becomes a new ``hard
1449 link'' to @var{oldname}.
1451 In the first part of the following example, we list two files,
1452 @file{foo} and @file{foo3}.
1457 81908 -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo
1458 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
1462 Now we create a hard link, by calling @code{add-name-to-file}, then list
1463 the files again. This shows two names for one file, @file{foo} and
1468 (add-name-to-file "foo" "foo2")
1474 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo
1475 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2
1476 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
1480 Finally, we evaluate the following:
1483 (add-name-to-file "foo" "foo3" t)
1487 and list the files again. Now there are three names
1488 for one file: @file{foo}, @file{foo2}, and @file{foo3}. The old
1489 contents of @file{foo3} are lost.
1493 (add-name-to-file "foo1" "foo3")
1499 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo
1500 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2
1501 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3
1505 This function is meaningless on operating systems where multiple names
1506 for one file are not allowed. Some systems implement multiple names
1507 by copying the file instead.
1509 See also @code{file-nlinks} in @ref{File Attributes}.
1512 @deffn Command rename-file filename newname &optional ok-if-already-exists
1513 This command renames the file @var{filename} as @var{newname}.
1515 If @var{filename} has additional names aside from @var{filename}, it
1516 continues to have those names. In fact, adding the name @var{newname}
1517 with @code{add-name-to-file} and then deleting @var{filename} has the
1518 same effect as renaming, aside from momentary intermediate states.
1521 @deffn Command copy-file oldname newname &optional ok-if-exists time preserve-uid-gid preserve-selinux
1522 This command copies the file @var{oldname} to @var{newname}. An
1523 error is signaled if @var{oldname} does not exist. If @var{newname}
1524 names a directory, it copies @var{oldname} into that directory,
1525 preserving its final name component.
1527 If @var{time} is non-@code{nil}, then this function gives the new file
1528 the same last-modified time that the old one has. (This works on only
1529 some operating systems.) If setting the time gets an error,
1530 @code{copy-file} signals a @code{file-date-error} error. In an
1531 interactive call, a prefix argument specifies a non-@code{nil} value
1534 This function copies the file modes, too.
1536 If argument @var{preserve-uid-gid} is @code{nil}, we let the operating
1537 system decide the user and group ownership of the new file (this is
1538 usually set to the user running Emacs). If @var{preserve-uid-gid} is
1539 non-@code{nil}, we attempt to copy the user and group ownership of the
1540 file. This works only on some operating systems, and only if you have
1541 the correct permissions to do so.
1543 If the optional argument @var{preserve-selinux} is non-@code{nil}, and
1544 Emacs has been compiled with SELinux support, this function attempts
1545 to copy the file's SELinux context (@pxref{File Attributes}).
1548 @deffn Command make-symbolic-link filename newname &optional ok-if-exists
1550 @kindex file-already-exists
1551 This command makes a symbolic link to @var{filename}, named
1552 @var{newname}. This is like the shell command @samp{ln -s
1553 @var{filename} @var{newname}}.
1555 This function is not available on systems that don't support symbolic
1560 @vindex delete-by-moving-to-trash
1561 @deffn Command delete-file filename &optional trash
1563 This command deletes the file @var{filename}. If the file has
1564 multiple names, it continues to exist under the other names. If
1565 @var{filename} is a symbolic link, @code{delete-file} deletes only the
1566 symbolic link and not its target (though it does follow symbolic links
1567 at all levels of parent directories).
1569 A suitable kind of @code{file-error} error is signaled if the file
1570 does not exist, or is not deletable. (On Unix and GNU/Linux, a file
1571 is deletable if its directory is writable.)
1573 If the optional argument @var{trash} is non-@code{nil} and the
1574 variable @code{delete-by-moving-to-trash} is non-@code{nil}, this
1575 command moves the file into the system Trash instead of deleting it.
1576 @xref{Misc File Ops,,Miscellaneous File Operations, emacs, The GNU
1577 Emacs Manual}. When called interactively, @var{trash} is @code{t} if
1578 no prefix argument is given, and @code{nil} otherwise.
1580 See also @code{delete-directory} in @ref{Create/Delete Dirs}.
1583 @cindex file permissions, setting
1584 @cindex permissions, file
1585 @cindex file modes, setting
1586 @deffn Command set-file-modes filename mode
1587 This function sets the @dfn{file mode} (or @dfn{file permissions}) of
1588 @var{filename} to @var{mode}. It recursively follows symbolic links
1589 at all levels for @var{filename}.
1591 If called non-interactively, @var{mode} must be an integer. Only the
1592 lowest 12 bits of the integer are used; on most systems, only the
1593 lowest 9 bits are meaningful. You can use the Lisp construct for
1594 octal numbers to enter @var{mode}. For example,
1597 (set-file-modes #o644)
1601 specifies that the file should be readable and writable for its owner,
1602 readable for group members, and readable for all other users.
1603 @xref{File Permissions,,, coreutils, The @sc{gnu} @code{Coreutils}
1604 Manual}, for a description of mode bit specifications.
1606 Interactively, @var{mode} is read from the minibuffer using
1607 @code{read-file-modes} (see below), which lets the user type in either
1608 an integer or a string representing the permissions symbolically.
1610 @xref{File Attributes}, for the function @code{file-modes}, which
1611 returns the permissions of a file.
1614 @defun set-default-file-modes mode
1616 This function sets the default file permissions for new files created
1617 by Emacs and its subprocesses. Every file created with Emacs
1618 initially has these permissions, or a subset of them
1619 (@code{write-region} will not grant execute permissions even if the
1620 default file permissions allow execution). On Unix and GNU/Linux, the
1621 default permissions are given by the bitwise complement of the
1624 The argument @var{mode} should be an integer which specifies the
1625 permissions, similar to @code{set-file-modes} above. Only the lowest
1626 9 bits are meaningful.
1628 The default file permissions have no effect when you save a modified
1629 version of an existing file; saving a file preserves its existing
1633 @defun default-file-modes
1634 This function returns the default file permissions, as an integer.
1637 @defun read-file-modes &optional prompt base-file
1638 This function reads a set of file mode bits from the minibuffer. The
1639 first optional argument @var{prompt} specifies a non-default prompt.
1640 Second second optional argument @var{base-file} is the name of a file
1641 on whose permissions to base the mode bits that this function returns,
1642 if what the user types specifies mode bits relative to permissions of
1645 If user input represents an octal number, this function returns that
1646 number. If it is a complete symbolic specification of mode bits, as
1647 in @code{"u=rwx"}, the function converts it to the equivalent numeric
1648 value using @code{file-modes-symbolic-to-number} and returns the
1649 result. If the specification is relative, as in @code{"o+g"}, then
1650 the permissions on which the specification is based are taken from the
1651 mode bits of @var{base-file}. If @var{base-file} is omitted or
1652 @code{nil}, the function uses @code{0} as the base mode bits. The
1653 complete and relative specifications can be combined, as in
1654 @code{"u+r,g+rx,o+r,g-w"}. @xref{File Permissions,,, coreutils, The
1655 @sc{gnu} @code{Coreutils} Manual}, for a description of file mode
1659 @defun file-modes-symbolic-to-number modes &optional base-modes
1660 This function converts a symbolic file mode specification in
1661 @var{modes} into the equivalent integer value. If the symbolic
1662 specification is based on an existing file, that file's mode bits are
1663 taken from the optional argument @var{base-modes}; if that argument is
1664 omitted or @code{nil}, it defaults to 0, i.e.@: no access rights at
1668 @defun set-file-times filename &optional time
1669 This function sets the access and modification times of @var{filename}
1670 to @var{time}. The return value is @code{t} if the times are successfully
1671 set, otherwise it is @code{nil}. @var{time} defaults to the current
1672 time and must be in the format returned by @code{current-time}
1673 (@pxref{Time of Day}).
1676 @defun set-file-selinux-context filename context
1677 This function sets the SELinux security context of the file
1678 @var{filename} to @var{context}. @xref{File Attributes}, for a brief
1679 description of SELinux contexts. The @var{context} argument should be
1680 a list @code{(@var{user} @var{role} @var{type} @var{range})}, like the
1681 return value of @code{file-selinux-context}. The function does
1682 nothing if SELinux is disabled, or if Emacs was compiled without
1690 Files are generally referred to by their names, in Emacs as elsewhere.
1691 File names in Emacs are represented as strings. The functions that
1692 operate on a file all expect a file name argument.
1694 In addition to operating on files themselves, Emacs Lisp programs
1695 often need to operate on file names; i.e., to take them apart and to use
1696 part of a name to construct related file names. This section describes
1697 how to manipulate file names.
1699 The functions in this section do not actually access files, so they
1700 can operate on file names that do not refer to an existing file or
1703 On MS-DOS and MS-Windows, these functions (like the function that
1704 actually operate on files) accept MS-DOS or MS-Windows file-name syntax,
1705 where backslashes separate the components, as well as Unix syntax; but
1706 they always return Unix syntax. This enables Lisp programs to specify
1707 file names in Unix syntax and work properly on all systems without
1711 * File Name Components:: The directory part of a file name, and the rest.
1712 * Relative File Names:: Some file names are relative to a current directory.
1713 * Directory Names:: A directory's name as a directory
1714 is different from its name as a file.
1715 * File Name Expansion:: Converting relative file names to absolute ones.
1716 * Unique File Names:: Generating names for temporary files.
1717 * File Name Completion:: Finding the completions for a given file name.
1718 * Standard File Names:: If your package uses a fixed file name,
1719 how to handle various operating systems simply.
1722 @node File Name Components
1723 @subsection File Name Components
1724 @cindex directory part (of file name)
1725 @cindex nondirectory part (of file name)
1726 @cindex version number (in file name)
1728 The operating system groups files into directories. To specify a
1729 file, you must specify the directory and the file's name within that
1730 directory. Therefore, Emacs considers a file name as having two main
1731 parts: the @dfn{directory name} part, and the @dfn{nondirectory} part
1732 (or @dfn{file name within the directory}). Either part may be empty.
1733 Concatenating these two parts reproduces the original file name.
1735 On most systems, the directory part is everything up to and including
1736 the last slash (backslash is also allowed in input on MS-DOS or
1737 MS-Windows); the nondirectory part is the rest.
1739 For some purposes, the nondirectory part is further subdivided into
1740 the name proper and the @dfn{version number}. On most systems, only
1741 backup files have version numbers in their names.
1743 @defun file-name-directory filename
1744 This function returns the directory part of @var{filename}, as a
1745 directory name (@pxref{Directory Names}), or @code{nil} if
1746 @var{filename} does not include a directory part.
1748 On GNU and Unix systems, a string returned by this function always
1749 ends in a slash. On MS-DOS it can also end in a colon.
1753 (file-name-directory "lewis/foo") ; @r{Unix example}
1757 (file-name-directory "foo") ; @r{Unix example}
1763 @defun file-name-nondirectory filename
1764 This function returns the nondirectory part of @var{filename}.
1768 (file-name-nondirectory "lewis/foo")
1772 (file-name-nondirectory "foo")
1776 (file-name-nondirectory "lewis/")
1782 @defun file-name-sans-versions filename &optional keep-backup-version
1783 This function returns @var{filename} with any file version numbers,
1784 backup version numbers, or trailing tildes discarded.
1786 If @var{keep-backup-version} is non-@code{nil}, then true file version
1787 numbers understood as such by the file system are discarded from the
1788 return value, but backup version numbers are kept.
1792 (file-name-sans-versions "~rms/foo.~1~")
1793 @result{} "~rms/foo"
1796 (file-name-sans-versions "~rms/foo~")
1797 @result{} "~rms/foo"
1800 (file-name-sans-versions "~rms/foo")
1801 @result{} "~rms/foo"
1806 @defun file-name-extension filename &optional period
1807 This function returns @var{filename}'s final ``extension'', if any,
1808 after applying @code{file-name-sans-versions} to remove any
1809 version/backup part. The extension, in a file name, is the part that
1810 follows the last @samp{.} in the last name component (minus any
1811 version/backup part).
1813 This function returns @code{nil} for extensionless file names such as
1814 @file{foo}. It returns @code{""} for null extensions, as in
1815 @file{foo.}. If the last component of a file name begins with a
1816 @samp{.}, that @samp{.} doesn't count as the beginning of an
1817 extension. Thus, @file{.emacs}'s ``extension'' is @code{nil}, not
1820 If @var{period} is non-@code{nil}, then the returned value includes
1821 the period that delimits the extension, and if @var{filename} has no
1822 extension, the value is @code{""}.
1825 @defun file-name-sans-extension filename
1826 This function returns @var{filename} minus its extension, if any. The
1827 version/backup part, if present, is only removed if the file has an
1828 extension. For example,
1831 (file-name-sans-extension "foo.lose.c")
1832 @result{} "foo.lose"
1833 (file-name-sans-extension "big.hack/foo")
1834 @result{} "big.hack/foo"
1835 (file-name-sans-extension "/my/home/.emacs")
1836 @result{} "/my/home/.emacs"
1837 (file-name-sans-extension "/my/home/.emacs.el")
1838 @result{} "/my/home/.emacs"
1839 (file-name-sans-extension "~/foo.el.~3~")
1841 (file-name-sans-extension "~/foo.~3~")
1842 @result{} "~/foo.~3~"
1845 Note that the @samp{.~3~} in the two last examples is the backup part,
1850 @node Relative File Names
1851 @subsection Absolute and Relative File Names
1852 @cindex absolute file name
1853 @cindex relative file name
1855 All the directories in the file system form a tree starting at the
1856 root directory. A file name can specify all the directory names
1857 starting from the root of the tree; then it is called an
1858 @dfn{absolute} file name. Or it can specify the position of the file
1859 in the tree relative to a default directory; then it is called a
1860 @dfn{relative} file name. On Unix and GNU/Linux, an absolute file
1861 name starts with a @samp{/} or a @samp{~}
1862 (@pxref{abbreviate-file-name}), and a relative one does not. On
1863 MS-DOS and MS-Windows, an absolute file name starts with a slash or a
1864 backslash, or with a drive specification @samp{@var{x}:/}, where
1865 @var{x} is the @dfn{drive letter}.
1867 @defun file-name-absolute-p filename
1868 This function returns @code{t} if file @var{filename} is an absolute
1869 file name, @code{nil} otherwise.
1873 (file-name-absolute-p "~rms/foo")
1877 (file-name-absolute-p "rms/foo")
1881 (file-name-absolute-p "/user/rms/foo")
1887 Given a possibly relative file name, you can convert it to an
1888 absolute name using @code{expand-file-name} (@pxref{File Name
1889 Expansion}). This function converts absolute file names to relative
1892 @defun file-relative-name filename &optional directory
1893 This function tries to return a relative name that is equivalent to
1894 @var{filename}, assuming the result will be interpreted relative to
1895 @var{directory} (an absolute directory name or directory file name).
1896 If @var{directory} is omitted or @code{nil}, it defaults to the
1897 current buffer's default directory.
1899 On some operating systems, an absolute file name begins with a device
1900 name. On such systems, @var{filename} has no relative equivalent based
1901 on @var{directory} if they start with two different device names. In
1902 this case, @code{file-relative-name} returns @var{filename} in absolute
1906 (file-relative-name "/foo/bar" "/foo/")
1908 (file-relative-name "/foo/bar" "/hack/")
1909 @result{} "../foo/bar"
1913 @node Directory Names
1914 @subsection Directory Names
1915 @cindex directory name
1916 @cindex file name of directory
1918 A @dfn{directory name} is the name of a directory. A directory is
1919 actually a kind of file, so it has a file name, which is related to
1920 the directory name but not identical to it. (This is not quite the
1921 same as the usual Unix terminology.) These two different names for
1922 the same entity are related by a syntactic transformation. On GNU and
1923 Unix systems, this is simple: a directory name ends in a slash,
1924 whereas the directory's name as a file lacks that slash. On MS-DOS
1925 the relationship is more complicated.
1927 The difference between a directory name and its name as a file is
1928 subtle but crucial. When an Emacs variable or function argument is
1929 described as being a directory name, a file name of a directory is not
1930 acceptable. When @code{file-name-directory} returns a string, that is
1931 always a directory name.
1933 The following two functions convert between directory names and file
1934 names. They do nothing special with environment variable substitutions
1935 such as @samp{$HOME}, and the constructs @samp{~}, @samp{.} and @samp{..}.
1937 @defun file-name-as-directory filename
1938 This function returns a string representing @var{filename} in a form
1939 that the operating system will interpret as the name of a directory. On
1940 most systems, this means appending a slash to the string (if it does not
1941 already end in one).
1945 (file-name-as-directory "~rms/lewis")
1946 @result{} "~rms/lewis/"
1951 @defun directory-file-name dirname
1952 This function returns a string representing @var{dirname} in a form that
1953 the operating system will interpret as the name of a file. On most
1954 systems, this means removing the final slash (or backslash) from the
1959 (directory-file-name "~lewis/")
1965 Given a directory name, you can combine it with a relative file name
1966 using @code{concat}:
1969 (concat @var{dirname} @var{relfile})
1973 Be sure to verify that the file name is relative before doing that.
1974 If you use an absolute file name, the results could be syntactically
1975 invalid or refer to the wrong file.
1977 If you want to use a directory file name in making such a
1978 combination, you must first convert it to a directory name using
1979 @code{file-name-as-directory}:
1982 (concat (file-name-as-directory @var{dirfile}) @var{relfile})
1986 Don't try concatenating a slash by hand, as in
1990 (concat @var{dirfile} "/" @var{relfile})
1994 because this is not portable. Always use
1995 @code{file-name-as-directory}.
1997 To convert a directory name to its abbreviation, use this
2000 @cindex file name abbreviations
2001 @cindex abbreviated file names
2002 @defun abbreviate-file-name filename
2003 @anchor{abbreviate-file-name}
2004 This function returns an abbreviated form of @var{filename}. It
2005 applies the abbreviations specified in @code{directory-abbrev-alist}
2006 (@pxref{File Aliases,,File Aliases, emacs, The GNU Emacs Manual}),
2007 then substitutes @samp{~} for the user's home directory if the
2008 argument names a file in the home directory or one of its
2009 subdirectories. If the home directory is a root directory, it is not
2010 replaced with @samp{~}, because this does not make the result shorter
2013 You can use this function for directory names and for file names,
2014 because it recognizes abbreviations even as part of the name.
2017 @node File Name Expansion
2018 @subsection Functions that Expand Filenames
2019 @cindex expansion of file names
2021 @dfn{Expanding} a file name means converting a relative file name to
2022 an absolute one. Since this is done relative to a default directory,
2023 you must specify the default directory name as well as the file name
2024 to be expanded. It also involves expanding abbreviations like
2027 (@pxref{abbreviate-file-name}),
2029 and eliminating redundancies like @file{./} and @file{@var{name}/../}.
2031 @defun expand-file-name filename &optional directory
2032 This function converts @var{filename} to an absolute file name. If
2033 @var{directory} is supplied, it is the default directory to start with
2034 if @var{filename} is relative. (The value of @var{directory} should
2035 itself be an absolute directory name or directory file name; it may
2036 start with @samp{~}.) Otherwise, the current buffer's value of
2037 @code{default-directory} is used. For example:
2041 (expand-file-name "foo")
2042 @result{} "/xcssun/users/rms/lewis/foo"
2045 (expand-file-name "../foo")
2046 @result{} "/xcssun/users/rms/foo"
2049 (expand-file-name "foo" "/usr/spool/")
2050 @result{} "/usr/spool/foo"
2053 (expand-file-name "$HOME/foo")
2054 @result{} "/xcssun/users/rms/lewis/$HOME/foo"
2058 If the part of the combined file name before the first slash is
2059 @samp{~}, it expands to the value of the @env{HOME} environment
2060 variable (usually your home directory). If the part before the first
2061 slash is @samp{~@var{user}} and if @var{user} is a valid login name,
2062 it expands to @var{user}'s home directory.
2064 Filenames containing @samp{.} or @samp{..} are simplified to their
2069 (expand-file-name "bar/../foo")
2070 @result{} "/xcssun/users/rms/lewis/foo"
2074 In some cases, a leading @samp{..} component can remain in the output:
2078 (expand-file-name "../home" "/")
2079 @result{} "/../home"
2084 This is for the sake of filesystems that have the concept of a
2085 ``superroot'' above the root directory @file{/}. On other filesystems,
2086 @file{/../} is interpreted exactly the same as @file{/}.
2088 Note that @code{expand-file-name} does @emph{not} expand environment
2089 variables; only @code{substitute-in-file-name} does that.
2091 Note also that @code{expand-file-name} does not follow symbolic links
2092 at any level. This results in a difference between the way
2093 @code{file-truename} and @code{expand-file-name} treat @samp{..}.
2094 Assuming that @samp{/tmp/bar} is a symbolic link to the directory
2095 @samp{/tmp/foo/bar} we get:
2099 (file-truename "/tmp/bar/../myfile")
2100 @result{} "/tmp/foo/myfile"
2103 (expand-file-name "/tmp/bar/../myfile")
2104 @result{} "/tmp/myfile"
2108 If you may need to follow symbolic links preceding @samp{..}, you
2109 should make sure to call @code{file-truename} without prior direct or
2110 indirect calls to @code{expand-file-name}. @xref{Truenames}.
2113 @defvar default-directory
2114 The value of this buffer-local variable is the default directory for the
2115 current buffer. It should be an absolute directory name; it may start
2116 with @samp{~}. This variable is buffer-local in every buffer.
2118 @code{expand-file-name} uses the default directory when its second
2119 argument is @code{nil}.
2121 The value is always a string ending with a slash.
2126 @result{} "/user/lewis/manual/"
2131 @defun substitute-in-file-name filename
2132 @anchor{Definition of substitute-in-file-name}
2133 This function replaces environment variable references in
2134 @var{filename} with the environment variable values. Following
2135 standard Unix shell syntax, @samp{$} is the prefix to substitute an
2136 environment variable value. If the input contains @samp{$$}, that is
2137 converted to @samp{$}; this gives the user a way to ``quote'' a
2140 The environment variable name is the series of alphanumeric characters
2141 (including underscores) that follow the @samp{$}. If the character following
2142 the @samp{$} is a @samp{@{}, then the variable name is everything up to the
2145 Calling @code{substitute-in-file-name} on output produced by
2146 @code{substitute-in-file-name} tends to give incorrect results. For
2147 instance, use of @samp{$$} to quote a single @samp{$} won't work
2148 properly, and @samp{$} in an environment variable's value could lead
2149 to repeated substitution. Therefore, programs that call this function
2150 and put the output where it will be passed to this function need to
2151 double all @samp{$} characters to prevent subsequent incorrect
2154 @c Wordy to avoid overfull hbox. --rjc 15mar92
2155 Here we assume that the environment variable @env{HOME}, which holds
2156 the user's home directory name, has value @samp{/xcssun/users/rms}.
2160 (substitute-in-file-name "$HOME/foo")
2161 @result{} "/xcssun/users/rms/foo"
2165 After substitution, if a @samp{~} or a @samp{/} appears immediately
2166 after another @samp{/}, the function discards everything before it (up
2167 through the immediately preceding @samp{/}).
2171 (substitute-in-file-name "bar/~/foo")
2175 (substitute-in-file-name "/usr/local/$HOME/foo")
2176 @result{} "/xcssun/users/rms/foo"
2177 ;; @r{@file{/usr/local/} has been discarded.}
2183 @node Unique File Names
2184 @subsection Generating Unique File Names
2186 Some programs need to write temporary files. Here is the usual way to
2187 construct a name for such a file:
2190 (make-temp-file @var{name-of-application})
2194 The job of @code{make-temp-file} is to prevent two different users or
2195 two different jobs from trying to use the exact same file name.
2197 @defun make-temp-file prefix &optional dir-flag suffix
2198 This function creates a temporary file and returns its name. Emacs
2199 creates the temporary file's name by adding to @var{prefix} some
2200 random characters that are different in each Emacs job. The result is
2201 guaranteed to be a newly created empty file. On MS-DOS, this function
2202 can truncate the @var{string} prefix to fit into the 8+3 file-name
2203 limits. If @var{prefix} is a relative file name, it is expanded
2204 against @code{temporary-file-directory}.
2208 (make-temp-file "foo")
2209 @result{} "/tmp/foo232J6v"
2213 When @code{make-temp-file} returns, the file has been created and is
2214 empty. At that point, you should write the intended contents into the
2217 If @var{dir-flag} is non-@code{nil}, @code{make-temp-file} creates an
2218 empty directory instead of an empty file. It returns the file name,
2219 not the directory name, of that directory. @xref{Directory Names}.
2221 If @var{suffix} is non-@code{nil}, @code{make-temp-file} adds it at
2222 the end of the file name.
2224 To prevent conflicts among different libraries running in the same
2225 Emacs, each Lisp program that uses @code{make-temp-file} should have its
2226 own @var{prefix}. The number added to the end of @var{prefix}
2227 distinguishes between the same application running in different Emacs
2228 jobs. Additional added characters permit a large number of distinct
2229 names even in one Emacs job.
2232 The default directory for temporary files is controlled by the
2233 variable @code{temporary-file-directory}. This variable gives the user
2234 a uniform way to specify the directory for all temporary files. Some
2235 programs use @code{small-temporary-file-directory} instead, if that is
2236 non-@code{nil}. To use it, you should expand the prefix against
2237 the proper directory before calling @code{make-temp-file}.
2239 @defopt temporary-file-directory
2240 @cindex @env{TMPDIR} environment variable
2241 @cindex @env{TMP} environment variable
2242 @cindex @env{TEMP} environment variable
2243 This variable specifies the directory name for creating temporary files.
2244 Its value should be a directory name (@pxref{Directory Names}), but it
2245 is good for Lisp programs to cope if the value is a directory's file
2246 name instead. Using the value as the second argument to
2247 @code{expand-file-name} is a good way to achieve that.
2249 The default value is determined in a reasonable way for your operating
2250 system; it is based on the @env{TMPDIR}, @env{TMP} and @env{TEMP}
2251 environment variables, with a fall-back to a system-dependent name if
2252 none of these variables is defined.
2254 Even if you do not use @code{make-temp-file} to create the temporary
2255 file, you should still use this variable to decide which directory to
2256 put the file in. However, if you expect the file to be small, you
2257 should use @code{small-temporary-file-directory} first if that is
2261 @defopt small-temporary-file-directory
2262 This variable specifies the directory name for
2263 creating certain temporary files, which are likely to be small.
2265 If you want to write a temporary file which is likely to be small, you
2266 should compute the directory like this:
2270 (expand-file-name @var{prefix}
2271 (or small-temporary-file-directory
2272 temporary-file-directory)))
2276 @defun make-temp-name base-name
2277 This function generates a string that can be used as a unique file
2278 name. The name starts with @var{base-name}, and has several random
2279 characters appended to it, which are different in each Emacs job. It
2280 is like @code{make-temp-file} except that (i) it just constructs a
2281 name, and does not create a file, and (ii) @var{base-name} should be
2282 an absolute file name (on MS-DOS, this function can truncate
2283 @var{base-name} to fit into the 8+3 file-name limits).
2285 @strong{Warning:} In most cases, you should not use this function; use
2286 @code{make-temp-file} instead! This function is susceptible to a race
2287 condition, between the @code{make-temp-name} call and the creation of
2288 the file, which in some cases may cause a security hole.
2291 @node File Name Completion
2292 @subsection File Name Completion
2293 @cindex file name completion subroutines
2294 @cindex completion, file name
2296 This section describes low-level subroutines for completing a file
2297 name. For higher level functions, see @ref{Reading File Names}.
2299 @defun file-name-all-completions partial-filename directory
2300 This function returns a list of all possible completions for a file
2301 whose name starts with @var{partial-filename} in directory
2302 @var{directory}. The order of the completions is the order of the files
2303 in the directory, which is unpredictable and conveys no useful
2306 The argument @var{partial-filename} must be a file name containing no
2307 directory part and no slash (or backslash on some systems). The current
2308 buffer's default directory is prepended to @var{directory}, if
2309 @var{directory} is not absolute.
2311 In the following example, suppose that @file{~rms/lewis} is the current
2312 default directory, and has five files whose names begin with @samp{f}:
2313 @file{foo}, @file{file~}, @file{file.c}, @file{file.c.~1~}, and
2314 @file{file.c.~2~}.@refill
2318 (file-name-all-completions "f" "")
2319 @result{} ("foo" "file~" "file.c.~2~"
2320 "file.c.~1~" "file.c")
2324 (file-name-all-completions "fo" "")
2330 @defun file-name-completion filename directory &optional predicate
2331 This function completes the file name @var{filename} in directory
2332 @var{directory}. It returns the longest prefix common to all file names
2333 in directory @var{directory} that start with @var{filename}. If
2334 @var{predicate} is non-@code{nil} then it ignores possible completions
2335 that don't satisfy @var{predicate}, after calling that function
2336 with one argument, the expanded absolute file name.
2338 If only one match exists and @var{filename} matches it exactly, the
2339 function returns @code{t}. The function returns @code{nil} if directory
2340 @var{directory} contains no name starting with @var{filename}.
2342 In the following example, suppose that the current default directory
2343 has five files whose names begin with @samp{f}: @file{foo},
2344 @file{file~}, @file{file.c}, @file{file.c.~1~}, and
2345 @file{file.c.~2~}.@refill
2349 (file-name-completion "fi" "")
2354 (file-name-completion "file.c.~1" "")
2355 @result{} "file.c.~1~"
2359 (file-name-completion "file.c.~1~" "")
2364 (file-name-completion "file.c.~3" "")
2370 @defopt completion-ignored-extensions
2371 @code{file-name-completion} usually ignores file names that end in any
2372 string in this list. It does not ignore them when all the possible
2373 completions end in one of these suffixes. This variable has no effect
2374 on @code{file-name-all-completions}.@refill
2376 A typical value might look like this:
2380 completion-ignored-extensions
2381 @result{} (".o" ".elc" "~" ".dvi")
2385 If an element of @code{completion-ignored-extensions} ends in a slash
2386 @samp{/}, it signals a directory. The elements which do @emph{not} end
2387 in a slash will never match a directory; thus, the above value will not
2388 filter out a directory named @file{foo.elc}.
2391 @node Standard File Names
2392 @subsection Standard File Names
2394 Sometimes, an Emacs Lisp program needs to specify a standard file
2395 name for a particular use---typically, to hold configuration data
2396 specified by the current user. Usually, such files should be located
2397 in the directory specified by @code{user-emacs-directory}, which is
2398 @file{~/.emacs.d} by default (@pxref{Init File}). For example, abbrev
2399 definitions are stored by default in @file{~/.emacs.d/abbrev_defs}.
2400 The easiest way to specify such a file name is to use the function
2401 @code{locate-user-emacs-file}.
2403 @defun locate-user-emacs-file base-name &optional old-name
2404 This function returns an absolute file name for an Emacs-specific
2405 configuration or data file. The argument @file{base-name} should be a
2406 relative file name. The return value is the absolute name of a file
2407 in the directory specified by @code{user-emacs-directory}; if that
2408 directory does not exist, this function creates it.
2410 If the optional argument @var{old-name} is non-@code{nil}, it
2411 specifies a file in the user's home directory,
2412 @file{~/@var{old-name}}. If such a file exists, the return value is
2413 the absolute name of that file, instead of the file specified by
2414 @var{base-name}. This argument is intended to be used by Emacs
2415 packages to provide backward compatibility. For instance, prior to
2416 the introduction of @code{user-emacs-directory}, the abbrev file was
2417 located in @file{~/.abbrev_defs}. Here is the definition of
2418 @code{abbrev-file-name}:
2421 (defcustom abbrev-file-name
2422 (locate-user-emacs-file "abbrev_defs" ".abbrev_defs")
2423 "Default name of file from which to read abbrevs."
2429 A lower-level function for standardizing file names, which
2430 @code{locate-user-emacs-file} uses as a subroutine, is
2431 @code{convert-standard-filename}.
2433 @defun convert-standard-filename filename
2434 This function returns a file name based on @var{filename}, which fits
2435 the conventions of the current operating system.
2437 On GNU and Unix systems, this simply returns @var{filename}. On other
2438 operating systems, it may enforce system-specific file name
2439 conventions; for example, on MS-DOS this function performs a variety
2440 of changes to enforce MS-DOS file name limitations, including
2441 converting any leading @samp{.} to @samp{_} and truncating to three
2442 characters after the @samp{.}.
2444 The recommended way to use this function is to specify a name which
2445 fits the conventions of GNU and Unix systems, and pass it to
2446 @code{convert-standard-filename}.
2449 @node Contents of Directories
2450 @section Contents of Directories
2451 @cindex directory-oriented functions
2452 @cindex file names in directory
2454 A directory is a kind of file that contains other files entered under
2455 various names. Directories are a feature of the file system.
2457 Emacs can list the names of the files in a directory as a Lisp list,
2458 or display the names in a buffer using the @code{ls} shell command. In
2459 the latter case, it can optionally display information about each file,
2460 depending on the options passed to the @code{ls} command.
2462 @defun directory-files directory &optional full-name match-regexp nosort
2463 This function returns a list of the names of the files in the directory
2464 @var{directory}. By default, the list is in alphabetical order.
2466 If @var{full-name} is non-@code{nil}, the function returns the files'
2467 absolute file names. Otherwise, it returns the names relative to
2468 the specified directory.
2470 If @var{match-regexp} is non-@code{nil}, this function returns only
2471 those file names that contain a match for that regular expression---the
2472 other file names are excluded from the list. On case-insensitive
2473 filesystems, the regular expression matching is case-insensitive.
2476 If @var{nosort} is non-@code{nil}, @code{directory-files} does not sort
2477 the list, so you get the file names in no particular order. Use this if
2478 you want the utmost possible speed and don't care what order the files
2479 are processed in. If the order of processing is visible to the user,
2480 then the user will probably be happier if you do sort the names.
2484 (directory-files "~lewis")
2485 @result{} ("#foo#" "#foo.el#" "." ".."
2486 "dired-mods.el" "files.texi"
2491 An error is signaled if @var{directory} is not the name of a directory
2495 @defun directory-files-and-attributes directory &optional full-name match-regexp nosort id-format
2496 This is similar to @code{directory-files} in deciding which files
2497 to report on and how to report their names. However, instead
2498 of returning a list of file names, it returns for each file a
2499 list @code{(@var{filename} . @var{attributes})}, where @var{attributes}
2500 is what @code{file-attributes} would return for that file.
2501 The optional argument @var{id-format} has the same meaning as the
2502 corresponding argument to @code{file-attributes} (@pxref{Definition
2503 of file-attributes}).
2506 @defun file-expand-wildcards pattern &optional full
2507 This function expands the wildcard pattern @var{pattern}, returning
2508 a list of file names that match it.
2510 If @var{pattern} is written as an absolute file name,
2511 the values are absolute also.
2513 If @var{pattern} is written as a relative file name, it is interpreted
2514 relative to the current default directory. The file names returned are
2515 normally also relative to the current default directory. However, if
2516 @var{full} is non-@code{nil}, they are absolute.
2519 @defun insert-directory file switches &optional wildcard full-directory-p
2520 This function inserts (in the current buffer) a directory listing for
2521 directory @var{file}, formatted with @code{ls} according to
2522 @var{switches}. It leaves point after the inserted text.
2523 @var{switches} may be a string of options, or a list of strings
2524 representing individual options.
2526 The argument @var{file} may be either a directory name or a file
2527 specification including wildcard characters. If @var{wildcard} is
2528 non-@code{nil}, that means treat @var{file} as a file specification with
2531 If @var{full-directory-p} is non-@code{nil}, that means the directory
2532 listing is expected to show the full contents of a directory. You
2533 should specify @code{t} when @var{file} is a directory and switches do
2534 not contain @samp{-d}. (The @samp{-d} option to @code{ls} says to
2535 describe a directory itself as a file, rather than showing its
2538 On most systems, this function works by running a directory listing
2539 program whose name is in the variable @code{insert-directory-program}.
2540 If @var{wildcard} is non-@code{nil}, it also runs the shell specified by
2541 @code{shell-file-name}, to expand the wildcards.
2543 MS-DOS and MS-Windows systems usually lack the standard Unix program
2544 @code{ls}, so this function emulates the standard Unix program @code{ls}
2547 As a technical detail, when @var{switches} contains the long
2548 @samp{--dired} option, @code{insert-directory} treats it specially,
2549 for the sake of dired. However, the normally equivalent short
2550 @samp{-D} option is just passed on to @code{insert-directory-program},
2551 as any other option.
2554 @defvar insert-directory-program
2555 This variable's value is the program to run to generate a directory listing
2556 for the function @code{insert-directory}. It is ignored on systems
2557 which generate the listing with Lisp code.
2560 @node Create/Delete Dirs
2561 @section Creating, Copying and Deleting Directories
2562 @cindex creating, copying and deleting directories
2563 @c Emacs 19 features
2565 Most Emacs Lisp file-manipulation functions get errors when used on
2566 files that are directories. For example, you cannot delete a directory
2567 with @code{delete-file}. These special functions exist to create and
2571 @deffn Command make-directory dirname &optional parents
2572 This command creates a directory named @var{dirname}. If
2573 @var{parents} is non-@code{nil}, as is always the case in an
2574 interactive call, that means to create the parent directories first,
2575 if they don't already exist.
2577 @code{mkdir} is an alias for this.
2580 @deffn Command copy-directory dirname newname &optional keep-time parents copy-contents
2581 This command copies the directory named @var{dirname} to
2582 @var{newname}. If @var{newname} names an existing directory,
2583 @var{dirname} will be copied to a subdirectory there.
2585 It always sets the file modes of the copied files to match the
2586 corresponding original file.
2588 The third argument @var{keep-time} non-@code{nil} means to preserve the
2589 modification time of the copied files. A prefix arg makes
2590 @var{keep-time} non-@code{nil}.
2592 The fourth argument @var{parents} says whether to
2593 create parent directories if they don't exist. Interactively,
2594 this happens by default.
2596 The fifth argument @var{copy-contents}, if non-@code{nil}, means to
2597 copy the contents of @var{dirname} directly into @var{newname} if the
2598 latter is an existing directory, instead of copying @var{dirname} into
2599 it as a subdirectory.
2603 @vindex delete-by-moving-to-trash
2604 @deffn Command delete-directory dirname &optional recursive trash
2605 This command deletes the directory named @var{dirname}. The function
2606 @code{delete-file} does not work for files that are directories; you
2607 must use @code{delete-directory} for them. If @var{recursive} is
2608 @code{nil}, and the directory contains any files,
2609 @code{delete-directory} signals an error.
2611 @code{delete-directory} only follows symbolic links at the level of
2614 If the optional argument @var{trash} is non-@code{nil} and the
2615 variable @code{delete-by-moving-to-trash} is non-@code{nil}, this
2616 command moves the file into the system Trash instead of deleting it.
2617 @xref{Misc File Ops,,Miscellaneous File Operations, emacs, The GNU
2618 Emacs Manual}. When called interactively, @var{trash} is @code{t} if
2619 no prefix argument is given, and @code{nil} otherwise.
2622 @node Magic File Names
2623 @section Making Certain File Names ``Magic''
2624 @cindex magic file names
2626 You can implement special handling for certain file names. This is
2627 called making those names @dfn{magic}. The principal use for this
2628 feature is in implementing remote file names (@pxref{Remote Files,,
2629 Remote Files, emacs, The GNU Emacs Manual}).
2631 To define a kind of magic file name, you must supply a regular
2632 expression to define the class of names (all those that match the
2633 regular expression), plus a handler that implements all the primitive
2634 Emacs file operations for file names that match.
2636 @vindex file-name-handler-alist
2637 The variable @code{file-name-handler-alist} holds a list of handlers,
2638 together with regular expressions that determine when to apply each
2639 handler. Each element has this form:
2642 (@var{regexp} . @var{handler})
2646 All the Emacs primitives for file access and file name transformation
2647 check the given file name against @code{file-name-handler-alist}. If
2648 the file name matches @var{regexp}, the primitives handle that file by
2649 calling @var{handler}.
2651 The first argument given to @var{handler} is the name of the
2652 primitive, as a symbol; the remaining arguments are the arguments that
2653 were passed to that primitive. (The first of these arguments is most
2654 often the file name itself.) For example, if you do this:
2657 (file-exists-p @var{filename})
2661 and @var{filename} has handler @var{handler}, then @var{handler} is
2665 (funcall @var{handler} 'file-exists-p @var{filename})
2668 When a function takes two or more arguments that must be file names,
2669 it checks each of those names for a handler. For example, if you do
2673 (expand-file-name @var{filename} @var{dirname})
2677 then it checks for a handler for @var{filename} and then for a handler
2678 for @var{dirname}. In either case, the @var{handler} is called like
2682 (funcall @var{handler} 'expand-file-name @var{filename} @var{dirname})
2686 The @var{handler} then needs to figure out whether to handle
2687 @var{filename} or @var{dirname}.
2689 If the specified file name matches more than one handler, the one
2690 whose match starts last in the file name gets precedence. This rule
2691 is chosen so that handlers for jobs such as uncompression are handled
2692 first, before handlers for jobs such as remote file access.
2694 Here are the operations that a magic file name handler gets to handle:
2698 @code{access-file}, @code{add-name-to-file},
2699 @code{byte-compiler-base-file-name},@*
2700 @code{copy-directory}, @code{copy-file},
2701 @code{delete-directory}, @code{delete-file},
2702 @code{diff-latest-backup-file},
2703 @code{directory-file-name},
2704 @code{directory-files},
2705 @code{directory-files-and-attributes},
2706 @code{dired-compress-file}, @code{dired-uncache},@*
2707 @code{expand-file-name},
2708 @code{file-accessible-directory-p},
2709 @code{file-attributes},
2710 @code{file-directory-p},
2711 @code{file-executable-p}, @code{file-exists-p},
2712 @code{file-local-copy}, @code{file-remote-p},
2713 @code{file-modes}, @code{file-name-all-completions},
2714 @code{file-name-as-directory},
2715 @code{file-name-completion},
2716 @code{file-name-directory},
2717 @code{file-name-nondirectory},
2718 @code{file-name-sans-versions}, @code{file-newer-than-file-p},
2719 @code{file-ownership-preserved-p},
2720 @code{file-readable-p}, @code{file-regular-p}, @code{file-in-directory-p},
2721 @code{file-symlink-p}, @code{file-truename}, @code{file-writable-p},
2722 @code{file-equal-p}, @code{find-backup-file-name},
2723 @c Not sure why it was here: @code{find-file-noselect},@*
2724 @code{get-file-buffer},
2725 @code{insert-directory},
2726 @code{insert-file-contents},@*
2728 @code{make-auto-save-file-name},
2729 @code{make-directory},
2730 @code{make-directory-internal},
2731 @code{make-symbolic-link},@*
2732 @code{process-file},
2733 @code{rename-file}, @code{set-file-modes}, @code{set-file-times},
2734 @code{set-visited-file-modtime}, @code{shell-command},
2735 @code{start-file-process},
2736 @code{substitute-in-file-name},@*
2737 @code{unhandled-file-name-directory},
2738 @code{vc-registered},
2739 @code{verify-visited-file-modtime},@*
2740 @code{write-region}.
2745 @code{access-file}, @code{add-name-to-file},
2746 @code{byte-com@discretionary{}{}{}piler-base-file-name},
2747 @code{copy-directory}, @code{copy-file},
2748 @code{delete-directory}, @code{delete-file},
2749 @code{diff-latest-backup-file},
2750 @code{directory-file-name},
2751 @code{directory-files},
2752 @code{directory-files-and-at@discretionary{}{}{}tributes},
2753 @code{dired-compress-file}, @code{dired-uncache},
2754 @code{expand-file-name},
2755 @code{file-accessible-direc@discretionary{}{}{}tory-p},
2756 @code{file-attributes},
2757 @code{file-direct@discretionary{}{}{}ory-p},
2758 @code{file-executable-p}, @code{file-exists-p},
2759 @code{file-local-copy}, @code{file-remote-p},
2760 @code{file-modes}, @code{file-name-all-completions},
2761 @code{file-name-as-directory},
2762 @code{file-name-completion},
2763 @code{file-name-directory},
2764 @code{file-name-nondirec@discretionary{}{}{}tory},
2765 @code{file-name-sans-versions}, @code{file-newer-than-file-p},
2766 @code{file-ownership-pre@discretionary{}{}{}served-p},
2767 @code{file-readable-p}, @code{file-regular-p}, @code{file-symlink-p},
2768 @code{file-truename}, @code{file-writable-p},
2769 @code{find-backup-file-name},
2770 @c Not sure why it was here: @code{find-file-noselect},
2771 @code{get-file-buffer},
2772 @code{insert-directory},
2773 @code{insert-file-contents},
2774 @code{load}, @code{make-direc@discretionary{}{}{}tory},
2775 @code{make-direc@discretionary{}{}{}tory-internal},
2776 @code{make-symbolic-link},
2777 @code{process-file},
2778 @code{rename-file}, @code{set-file-modes},
2779 @code{set-visited-file-modtime}, @code{shell-command},
2780 @code{start-file-process},
2781 @code{substitute-in-file-name},
2782 @code{unhandled-file-name-directory},
2783 @code{vc-regis@discretionary{}{}{}tered},
2784 @code{verify-visited-file-modtime},
2785 @code{write-region}.
2789 Handlers for @code{insert-file-contents} typically need to clear the
2790 buffer's modified flag, with @code{(set-buffer-modified-p nil)}, if the
2791 @var{visit} argument is non-@code{nil}. This also has the effect of
2792 unlocking the buffer if it is locked.
2794 The handler function must handle all of the above operations, and
2795 possibly others to be added in the future. It need not implement all
2796 these operations itself---when it has nothing special to do for a
2797 certain operation, it can reinvoke the primitive, to handle the
2798 operation ``in the usual way''. It should always reinvoke the primitive
2799 for an operation it does not recognize. Here's one way to do this:
2802 (defun my-file-handler (operation &rest args)
2803 ;; @r{First check for the specific operations}
2804 ;; @r{that we have special handling for.}
2805 (cond ((eq operation 'insert-file-contents) @dots{})
2806 ((eq operation 'write-region) @dots{})
2808 ;; @r{Handle any operation we don't know about.}
2809 (t (let ((inhibit-file-name-handlers
2810 (cons 'my-file-handler
2811 (and (eq inhibit-file-name-operation operation)
2812 inhibit-file-name-handlers)))
2813 (inhibit-file-name-operation operation))
2814 (apply operation args)))))
2817 When a handler function decides to call the ordinary Emacs primitive for
2818 the operation at hand, it needs to prevent the primitive from calling
2819 the same handler once again, thus leading to an infinite recursion. The
2820 example above shows how to do this, with the variables
2821 @code{inhibit-file-name-handlers} and
2822 @code{inhibit-file-name-operation}. Be careful to use them exactly as
2823 shown above; the details are crucial for proper behavior in the case of
2824 multiple handlers, and for operations that have two file names that may
2827 @kindex safe-magic (@r{property})
2828 Handlers that don't really do anything special for actual access to the
2829 file---such as the ones that implement completion of host names for
2830 remote file names---should have a non-@code{nil} @code{safe-magic}
2831 property. For instance, Emacs normally ``protects'' directory names
2832 it finds in @code{PATH} from becoming magic, if they look like magic
2833 file names, by prefixing them with @samp{/:}. But if the handler that
2834 would be used for them has a non-@code{nil} @code{safe-magic}
2835 property, the @samp{/:} is not added.
2837 @kindex operations (@r{property})
2838 A file name handler can have an @code{operations} property to
2839 declare which operations it handles in a nontrivial way. If this
2840 property has a non-@code{nil} value, it should be a list of
2841 operations; then only those operations will call the handler. This
2842 avoids inefficiency, but its main purpose is for autoloaded handler
2843 functions, so that they won't be loaded except when they have real
2846 Simply deferring all operations to the usual primitives does not
2847 work. For instance, if the file name handler applies to
2848 @code{file-exists-p}, then it must handle @code{load} itself, because
2849 the usual @code{load} code won't work properly in that case. However,
2850 if the handler uses the @code{operations} property to say it doesn't
2851 handle @code{file-exists-p}, then it need not handle @code{load}
2854 @defvar inhibit-file-name-handlers
2855 This variable holds a list of handlers whose use is presently inhibited
2856 for a certain operation.
2859 @defvar inhibit-file-name-operation
2860 The operation for which certain handlers are presently inhibited.
2863 @defun find-file-name-handler file operation
2864 This function returns the handler function for file name @var{file},
2865 or @code{nil} if there is none. The argument @var{operation} should
2866 be the operation to be performed on the file---the value you will pass
2867 to the handler as its first argument when you call it. If
2868 @var{operation} equals @code{inhibit-file-name-operation}, or if it is
2869 not found in the @code{operations} property of the handler, this
2870 function returns @code{nil}.
2873 @defun file-local-copy filename
2874 This function copies file @var{filename} to an ordinary non-magic file
2875 on the local machine, if it isn't on the local machine already. Magic
2876 file names should handle the @code{file-local-copy} operation if they
2877 refer to files on other machines. A magic file name that is used for
2878 other purposes than remote file access should not handle
2879 @code{file-local-copy}; then this function will treat the file as
2882 If @var{filename} is local, whether magic or not, this function does
2883 nothing and returns @code{nil}. Otherwise it returns the file name
2884 of the local copy file.
2887 @defun file-remote-p filename &optional identification connected
2888 This function tests whether @var{filename} is a remote file. If
2889 @var{filename} is local (not remote), the return value is @code{nil}.
2890 If @var{filename} is indeed remote, the return value is a string that
2891 identifies the remote system.
2893 This identifier string can include a host name and a user name, as
2894 well as characters designating the method used to access the remote
2895 system. For example, the remote identifier string for the filename
2896 @code{/sudo::/some/file} is @code{/sudo:root@@localhost:}.
2898 If @code{file-remote-p} returns the same identifier for two different
2899 filenames, that means they are stored on the same file system and can
2900 be accessed locally with respect to each other. This means, for
2901 example, that it is possible to start a remote process accessing both
2902 files at the same time. Implementers of file handlers need to ensure
2903 this principle is valid.
2905 @var{identification} specifies which part of the identifier shall be
2906 returned as string. @var{identification} can be the symbol
2907 @code{method}, @code{user} or @code{host}; any other value is handled
2908 like @code{nil} and means to return the complete identifier string.
2909 In the example above, the remote @code{user} identifier string would
2912 If @var{connected} is non-@code{nil}, this function returns @code{nil}
2913 even if @var{filename} is remote, if Emacs has no network connection
2914 to its host. This is useful when you want to avoid the delay of
2915 making connections when they don't exist.
2918 @defun unhandled-file-name-directory filename
2919 This function returns the name of a directory that is not magic. It
2920 uses the directory part of @var{filename} if that is not magic. For a
2921 magic file name, it invokes the file name handler, which therefore
2922 decides what value to return. If @var{filename} is not accessible
2923 from a local process, then the file name handler should indicate it by
2924 returning @code{nil}.
2926 This is useful for running a subprocess; every subprocess must have a
2927 non-magic directory to serve as its current directory, and this function
2928 is a good way to come up with one.
2931 @defopt remote-file-name-inhibit-cache
2932 The attributes of remote files can be cached for better performance. If
2933 they are changed outside of Emacs's control, the cached values become
2934 invalid, and must be reread.
2936 When this variable is set to @code{nil}, cached values are never
2937 expired. Use this setting with caution, only if you are sure nothing
2938 other than Emacs ever changes the remote files. If it is set to
2939 @code{t}, cached values are never used. This is the safest value, but
2940 could result in performance degradation.
2942 A compromise is to set it to a positive number. This means that
2943 cached values are used for that amount of seconds since they were
2944 cached. If a remote file is checked regularly, it might be a good
2945 idea to let-bind this variable to a value less than the time period
2946 between consecutive checks. For example:
2949 (defun display-time-file-nonempty-p (file)
2950 (let ((remote-file-name-inhibit-cache
2951 (- display-time-interval 5)))
2952 (and (file-exists-p file)
2953 (< 0 (nth 7 (file-attributes
2954 (file-chase-links file)))))))
2958 @node Format Conversion
2959 @section File Format Conversion
2961 @cindex file format conversion
2962 @cindex encoding file formats
2963 @cindex decoding file formats
2964 @cindex text properties in files
2965 @cindex saving text properties
2966 Emacs performs several steps to convert the data in a buffer (text,
2967 text properties, and possibly other information) to and from a
2968 representation suitable for storing into a file. This section describes
2969 the fundamental functions that perform this @dfn{format conversion},
2970 namely @code{insert-file-contents} for reading a file into a buffer,
2971 and @code{write-region} for writing a buffer into a file.
2974 * Overview: Format Conversion Overview. @code{insert-file-contents} and @code{write-region}.
2975 * Round-Trip: Format Conversion Round-Trip. Using @code{format-alist}.
2976 * Piecemeal: Format Conversion Piecemeal. Specifying non-paired conversion.
2979 @node Format Conversion Overview
2980 @subsection Overview
2982 The function @code{insert-file-contents}:
2985 @item initially, inserts bytes from the file into the buffer;
2986 @item decodes bytes to characters as appropriate;
2987 @item processes formats as defined by entries in @code{format-alist}; and
2988 @item calls functions in @code{after-insert-file-functions}.
2992 The function @code{write-region}:
2995 @item initially, calls functions in @code{write-region-annotate-functions};
2996 @item processes formats as defined by entries in @code{format-alist};
2997 @item encodes characters to bytes as appropriate; and
2998 @item modifies the file with the bytes.
3001 This shows the symmetry of the lowest-level operations; reading and
3002 writing handle things in opposite order. The rest of this section
3003 describes the two facilities surrounding the three variables named
3004 above, as well as some related functions. @ref{Coding Systems}, for
3005 details on character encoding and decoding.
3007 @node Format Conversion Round-Trip
3008 @subsection Round-Trip Specification
3010 The most general of the two facilities is controlled by the variable
3011 @code{format-alist}, a list of @dfn{file format} specifications, which
3012 describe textual representations used in files for the data in an Emacs
3013 buffer. The descriptions for reading and writing are paired, which is
3014 why we call this ``round-trip'' specification
3015 (@pxref{Format Conversion Piecemeal}, for non-paired specification).
3017 @defvar format-alist
3018 This list contains one format definition for each defined file format.
3019 Each format definition is a list of this form:
3022 (@var{name} @var{doc-string} @var{regexp} @var{from-fn} @var{to-fn} @var{modify} @var{mode-fn} @var{preserve})
3026 @cindex format definition
3028 Here is what the elements in a format definition mean:
3032 The name of this format.
3035 A documentation string for the format.
3038 A regular expression which is used to recognize files represented in
3039 this format. If @code{nil}, the format is never applied automatically.
3042 A shell command or function to decode data in this format (to convert
3043 file data into the usual Emacs data representation).
3045 A shell command is represented as a string; Emacs runs the command as a
3046 filter to perform the conversion.
3048 If @var{from-fn} is a function, it is called with two arguments, @var{begin}
3049 and @var{end}, which specify the part of the buffer it should convert.
3050 It should convert the text by editing it in place. Since this can
3051 change the length of the text, @var{from-fn} should return the modified
3054 One responsibility of @var{from-fn} is to make sure that the beginning
3055 of the file no longer matches @var{regexp}. Otherwise it is likely to
3059 A shell command or function to encode data in this format---that is, to
3060 convert the usual Emacs data representation into this format.
3062 If @var{to-fn} is a string, it is a shell command; Emacs runs the
3063 command as a filter to perform the conversion.
3065 If @var{to-fn} is a function, it is called with three arguments:
3066 @var{begin} and @var{end}, which specify the part of the buffer it
3067 should convert, and @var{buffer}, which specifies which buffer. There
3068 are two ways it can do the conversion:
3072 By editing the buffer in place. In this case, @var{to-fn} should
3073 return the end-position of the range of text, as modified.
3076 By returning a list of annotations. This is a list of elements of the
3077 form @code{(@var{position} . @var{string})}, where @var{position} is an
3078 integer specifying the relative position in the text to be written, and
3079 @var{string} is the annotation to add there. The list must be sorted in
3080 order of position when @var{to-fn} returns it.
3082 When @code{write-region} actually writes the text from the buffer to the
3083 file, it intermixes the specified annotations at the corresponding
3084 positions. All this takes place without modifying the buffer.
3088 A flag, @code{t} if the encoding function modifies the buffer, and
3089 @code{nil} if it works by returning a list of annotations.
3092 A minor-mode function to call after visiting a file converted from this
3093 format. The function is called with one argument, the integer 1;
3094 that tells a minor-mode function to enable the mode.
3097 A flag, @code{t} if @code{format-write-file} should not remove this format
3098 from @code{buffer-file-format}.
3101 The function @code{insert-file-contents} automatically recognizes file
3102 formats when it reads the specified file. It checks the text of the
3103 beginning of the file against the regular expressions of the format
3104 definitions, and if it finds a match, it calls the decoding function for
3105 that format. Then it checks all the known formats over again.
3106 It keeps checking them until none of them is applicable.
3108 Visiting a file, with @code{find-file-noselect} or the commands that use
3109 it, performs conversion likewise (because it calls
3110 @code{insert-file-contents}); it also calls the mode function for each
3111 format that it decodes. It stores a list of the format names in the
3112 buffer-local variable @code{buffer-file-format}.
3114 @defvar buffer-file-format
3115 This variable states the format of the visited file. More precisely,
3116 this is a list of the file format names that were decoded in the course
3117 of visiting the current buffer's file. It is always buffer-local in all
3121 When @code{write-region} writes data into a file, it first calls the
3122 encoding functions for the formats listed in @code{buffer-file-format},
3123 in the order of appearance in the list.
3125 @deffn Command format-write-file file format &optional confirm
3126 This command writes the current buffer contents into the file @var{file}
3127 in a format based on @var{format}, which is a list of format names. It
3128 constructs the actual format starting from @var{format}, then appending
3129 any elements from the value of @code{buffer-file-format} with a
3130 non-@code{nil} @var{preserve} flag (see above), if they are not already
3131 present in @var{format}. It then updates @code{buffer-file-format} with
3132 this format, making it the default for future saves. Except for the
3133 @var{format} argument, this command is similar to @code{write-file}. In
3134 particular, @var{confirm} has the same meaning and interactive treatment
3135 as the corresponding argument to @code{write-file}. @xref{Definition of
3139 @deffn Command format-find-file file format
3140 This command finds the file @var{file}, converting it according to
3141 format @var{format}. It also makes @var{format} the default if the
3142 buffer is saved later.
3144 The argument @var{format} is a list of format names. If @var{format} is
3145 @code{nil}, no conversion takes place. Interactively, typing just
3146 @key{RET} for @var{format} specifies @code{nil}.
3149 @deffn Command format-insert-file file format &optional beg end
3150 This command inserts the contents of file @var{file}, converting it
3151 according to format @var{format}. If @var{beg} and @var{end} are
3152 non-@code{nil}, they specify which part of the file to read, as in
3153 @code{insert-file-contents} (@pxref{Reading from Files}).
3155 The return value is like what @code{insert-file-contents} returns: a
3156 list of the absolute file name and the length of the data inserted
3159 The argument @var{format} is a list of format names. If @var{format} is
3160 @code{nil}, no conversion takes place. Interactively, typing just
3161 @key{RET} for @var{format} specifies @code{nil}.
3164 @defvar buffer-auto-save-file-format
3165 This variable specifies the format to use for auto-saving. Its value is
3166 a list of format names, just like the value of
3167 @code{buffer-file-format}; however, it is used instead of
3168 @code{buffer-file-format} for writing auto-save files. If the value
3169 is @code{t}, the default, auto-saving uses the same format as a
3170 regular save in the same buffer. This variable is always buffer-local
3174 @node Format Conversion Piecemeal
3175 @subsection Piecemeal Specification
3177 In contrast to the round-trip specification described in the previous
3178 subsection (@pxref{Format Conversion Round-Trip}), you can use the variables
3179 @code{after-insert-file-functions} and @code{write-region-annotate-functions}
3180 to separately control the respective reading and writing conversions.
3182 Conversion starts with one representation and produces another
3183 representation. When there is only one conversion to do, there is no
3184 conflict about what to start with. However, when there are multiple
3185 conversions involved, conflict may arise when two conversions need to
3186 start with the same data.
3188 This situation is best understood in the context of converting text
3189 properties during @code{write-region}. For example, the character at
3190 position 42 in a buffer is @samp{X} with a text property @code{foo}. If
3191 the conversion for @code{foo} is done by inserting into the buffer, say,
3192 @samp{FOO:}, then that changes the character at position 42 from
3193 @samp{X} to @samp{F}. The next conversion will start with the wrong
3196 To avoid conflict, cooperative conversions do not modify the buffer,
3197 but instead specify @dfn{annotations}, a list of elements of the form
3198 @code{(@var{position} . @var{string})}, sorted in order of increasing
3201 If there is more than one conversion, @code{write-region} merges their
3202 annotations destructively into one sorted list. Later, when the text
3203 from the buffer is actually written to the file, it intermixes the
3204 specified annotations at the corresponding positions. All this takes
3205 place without modifying the buffer.
3207 @c ??? What about ``overriding'' conversions like those allowed
3208 @c ??? for `write-region-annotate-functions', below? --ttn
3210 In contrast, when reading, the annotations intermixed with the text
3211 are handled immediately. @code{insert-file-contents} sets point to
3212 the beginning of some text to be converted, then calls the conversion
3213 functions with the length of that text. These functions should always
3214 return with point at the beginning of the inserted text. This
3215 approach makes sense for reading because annotations removed by the
3216 first converter can't be mistakenly processed by a later converter.
3217 Each conversion function should scan for the annotations it
3218 recognizes, remove the annotation, modify the buffer text (to set a
3219 text property, for example), and return the updated length of the
3220 text, as it stands after those changes. The value returned by one
3221 function becomes the argument to the next function.
3223 @defvar write-region-annotate-functions
3224 A list of functions for @code{write-region} to call. Each function in
3225 the list is called with two arguments: the start and end of the region
3226 to be written. These functions should not alter the contents of the
3227 buffer. Instead, they should return annotations.
3229 As a special case, a function may return with a different buffer
3230 current. Emacs takes this to mean that the current buffer contains
3231 altered text to be output. It therefore changes the @var{start} and
3232 @var{end} arguments of the @code{write-region} call, giving them the
3233 values of @code{point-min} and @code{point-max} in the new buffer,
3234 respectively. It also discards all previous annotations, because they
3235 should have been dealt with by this function.
3238 @defvar write-region-post-annotation-function
3239 The value of this variable, if non-@code{nil}, should be a function.
3240 This function is called, with no arguments, after @code{write-region}
3243 If any function in @code{write-region-annotate-functions} returns with
3244 a different buffer current, Emacs calls
3245 @code{write-region-post-annotation-function} more than once. Emacs
3246 calls it with the last buffer that was current, and again with the
3247 buffer before that, and so on back to the original buffer.
3249 Thus, a function in @code{write-region-annotate-functions} can create
3250 a buffer, give this variable the local value of @code{kill-buffer} in
3251 that buffer, set up the buffer with altered text, and make the buffer
3252 current. The buffer will be killed after @code{write-region} is done.
3255 @defvar after-insert-file-functions
3256 Each function in this list is called by @code{insert-file-contents}
3257 with one argument, the number of characters inserted, and with point
3258 at the beginning of the inserted text. Each function should leave
3259 point unchanged, and return the new character count describing the
3260 inserted text as modified by the function.
3261 @c ??? The docstring mentions a handler from `file-name-handler-alist'
3262 @c "intercepting" `insert-file-contents'. Hmmm. --ttn
3265 We invite users to write Lisp programs to store and retrieve text
3266 properties in files, using these hooks, and thus to experiment with
3267 various data formats and find good ones. Eventually we hope users
3268 will produce good, general extensions we can install in Emacs.
3270 We suggest not trying to handle arbitrary Lisp objects as text property
3271 names or values---because a program that general is probably difficult
3272 to write, and slow. Instead, choose a set of possible data types that
3273 are reasonably flexible, and not too hard to encode.