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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
acaf905b | 3 | @c Copyright (C) 1990-1995, 1998-1999, 2001-2012 |
d24880de | 4 | @c Free Software Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 6 | @setfilename ../../info/files |
b8d4c8d0 GM |
7 | @node Files, Backups and Auto-Saving, Documentation, Top |
8 | @comment node-name, next, previous, up | |
9 | @chapter Files | |
10 | ||
11 | In Emacs, you can find, create, view, save, and otherwise work with | |
12 | files and file directories. This chapter describes most of the | |
13 | file-related functions of Emacs Lisp, but a few others are described in | |
14 | @ref{Buffers}, and those related to backups and auto-saving are | |
15 | described in @ref{Backups and Auto-Saving}. | |
16 | ||
17 | Many of the file functions take one or more arguments that are file | |
18 | names. A file name is actually a string. Most of these functions | |
19 | expand file name arguments by calling @code{expand-file-name}, so that | |
20 | @file{~} is handled correctly, as are relative file names (including | |
21 | @samp{../}). These functions don't recognize environment variable | |
22 | substitutions such as @samp{$HOME}. @xref{File Name Expansion}. | |
23 | ||
24 | When file I/O functions signal Lisp errors, they usually use the | |
25 | condition @code{file-error} (@pxref{Handling Errors}). The error | |
26 | message is in most cases obtained from the operating system, according | |
27 | to locale @code{system-message-locale}, and decoded using coding system | |
28 | @code{locale-coding-system} (@pxref{Locales}). | |
29 | ||
30 | @menu | |
31 | * Visiting Files:: Reading files into Emacs buffers for editing. | |
32 | * Saving Buffers:: Writing changed buffers back into files. | |
33 | * Reading from Files:: Reading files into buffers without visiting. | |
34 | * Writing to Files:: Writing new files from parts of buffers. | |
35 | * File Locks:: Locking and unlocking files, to prevent | |
36 | simultaneous editing by two people. | |
37 | * Information about Files:: Testing existence, accessibility, size of files. | |
38 | * Changing Files:: Renaming files, changing protection, etc. | |
39 | * File Names:: Decomposing and expanding file names. | |
40 | * Contents of Directories:: Getting a list of the files in a directory. | |
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41 | * Create/Delete Dirs:: Creating and Deleting Directories. |
42 | * Magic File Names:: Defining "magic" special handling | |
43 | for certain file names. | |
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44 | * Format Conversion:: Conversion to and from various file formats. |
45 | @end menu | |
46 | ||
47 | @node Visiting Files | |
48 | @section Visiting Files | |
49 | @cindex finding files | |
50 | @cindex visiting files | |
51 | ||
52 | Visiting a file means reading a file into a buffer. Once this is | |
53 | done, we say that the buffer is @dfn{visiting} that file, and call the | |
54 | file ``the visited file'' of the buffer. | |
55 | ||
56 | A file and a buffer are two different things. A file is information | |
57 | recorded permanently in the computer (unless you delete it). A buffer, | |
58 | on the other hand, is information inside of Emacs that will vanish at | |
59 | the end of the editing session (or when you kill the buffer). Usually, | |
60 | a buffer contains information that you have copied from a file; then we | |
61 | say the buffer is visiting that file. The copy in the buffer is what | |
62 | you modify with editing commands. Such changes to the buffer do not | |
63 | change the file; therefore, to make the changes permanent, you must | |
64 | @dfn{save} the buffer, which means copying the altered buffer contents | |
65 | back into the file. | |
66 | ||
67 | In spite of the distinction between files and buffers, people often | |
68 | refer to a file when they mean a buffer and vice-versa. Indeed, we say, | |
69 | ``I am editing a file,'' rather than, ``I am editing a buffer that I | |
70 | will soon save as a file of the same name.'' Humans do not usually need | |
71 | to make the distinction explicit. When dealing with a computer program, | |
72 | however, it is good to keep the distinction in mind. | |
73 | ||
74 | @menu | |
75 | * Visiting Functions:: The usual interface functions for visiting. | |
76 | * Subroutines of Visiting:: Lower-level subroutines that they use. | |
77 | @end menu | |
78 | ||
79 | @node Visiting Functions | |
80 | @subsection Functions for Visiting Files | |
81 | ||
82 | This section describes the functions normally used to visit files. | |
83 | For historical reasons, these functions have names starting with | |
84 | @samp{find-} rather than @samp{visit-}. @xref{Buffer File Name}, for | |
85 | functions and variables that access the visited file name of a buffer or | |
86 | that find an existing buffer by its visited file name. | |
87 | ||
88 | In a Lisp program, if you want to look at the contents of a file but | |
89 | not alter it, the fastest way is to use @code{insert-file-contents} in a | |
90 | temporary buffer. Visiting the file is not necessary and takes longer. | |
91 | @xref{Reading from Files}. | |
92 | ||
93 | @deffn Command find-file filename &optional wildcards | |
94 | This command selects a buffer visiting the file @var{filename}, | |
95 | using an existing buffer if there is one, and otherwise creating a | |
96 | new buffer and reading the file into it. It also returns that buffer. | |
97 | ||
98 | Aside from some technical details, the body of the @code{find-file} | |
99 | function is basically equivalent to: | |
100 | ||
101 | @smallexample | |
102 | (switch-to-buffer (find-file-noselect filename nil nil wildcards)) | |
103 | @end smallexample | |
104 | ||
105 | @noindent | |
0e406a72 | 106 | (See @code{switch-to-buffer} in @ref{Switching Buffers}.) |
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107 | |
108 | If @var{wildcards} is non-@code{nil}, which is always true in an | |
109 | interactive call, then @code{find-file} expands wildcard characters in | |
110 | @var{filename} and visits all the matching files. | |
111 | ||
112 | When @code{find-file} is called interactively, it prompts for | |
113 | @var{filename} in the minibuffer. | |
114 | @end deffn | |
115 | ||
e03b2fd4 EZ |
116 | @deffn Command find-file-literally filename |
117 | This command visits @var{filename}, like @code{find-file} does, but it | |
118 | does not perform any format conversions (@pxref{Format Conversion}), | |
119 | character code conversions (@pxref{Coding Systems}), or end-of-line | |
120 | conversions (@pxref{Coding System Basics, End of line conversion}). | |
121 | The buffer visiting the file is made unibyte, and its major mode is | |
122 | Fundamental mode, regardless of the file name. File local variable | |
123 | specifications in the file (@pxref{File Local Variables}) are | |
124 | ignored, and automatic decompression and adding a newline at the end | |
125 | of the file due to @code{require-final-newline} (@pxref{Saving | |
126 | Buffers, require-final-newline}) are also disabled. | |
127 | ||
128 | Note that if Emacs already has a buffer visiting the same file | |
129 | non-literally, it will not visit the same file literally, but instead | |
130 | just switch to the existing buffer. If you want to be sure of | |
131 | accessing a file's contents literally, you should create a temporary | |
132 | buffer and then read the file contents into it using | |
133 | @code{insert-file-contents-literally} (@pxref{Reading from Files}). | |
134 | @end deffn | |
135 | ||
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136 | @defun find-file-noselect filename &optional nowarn rawfile wildcards |
137 | This function is the guts of all the file-visiting functions. It | |
138 | returns a buffer visiting the file @var{filename}. You may make the | |
139 | buffer current or display it in a window if you wish, but this | |
140 | function does not do so. | |
141 | ||
142 | The function returns an existing buffer if there is one; otherwise it | |
143 | creates a new buffer and reads the file into it. When | |
144 | @code{find-file-noselect} uses an existing buffer, it first verifies | |
145 | that the file has not changed since it was last visited or saved in | |
146 | that buffer. If the file has changed, this function asks the user | |
147 | whether to reread the changed file. If the user says @samp{yes}, any | |
148 | edits previously made in the buffer are lost. | |
149 | ||
150 | Reading the file involves decoding the file's contents (@pxref{Coding | |
151 | Systems}), including end-of-line conversion, and format conversion | |
152 | (@pxref{Format Conversion}). If @var{wildcards} is non-@code{nil}, | |
153 | then @code{find-file-noselect} expands wildcard characters in | |
154 | @var{filename} and visits all the matching files. | |
155 | ||
156 | This function displays warning or advisory messages in various peculiar | |
157 | cases, unless the optional argument @var{nowarn} is non-@code{nil}. For | |
158 | example, if it needs to create a buffer, and there is no file named | |
159 | @var{filename}, it displays the message @samp{(New file)} in the echo | |
160 | area, and leaves the buffer empty. | |
161 | ||
162 | The @code{find-file-noselect} function normally calls | |
163 | @code{after-find-file} after reading the file (@pxref{Subroutines of | |
164 | Visiting}). That function sets the buffer major mode, parses local | |
165 | variables, warns the user if there exists an auto-save file more recent | |
166 | than the file just visited, and finishes by running the functions in | |
167 | @code{find-file-hook}. | |
168 | ||
169 | If the optional argument @var{rawfile} is non-@code{nil}, then | |
170 | @code{after-find-file} is not called, and the | |
171 | @code{find-file-not-found-functions} are not run in case of failure. | |
172 | What's more, a non-@code{nil} @var{rawfile} value suppresses coding | |
173 | system conversion and format conversion. | |
174 | ||
175 | The @code{find-file-noselect} function usually returns the buffer that | |
176 | is visiting the file @var{filename}. But, if wildcards are actually | |
177 | used and expanded, it returns a list of buffers that are visiting the | |
178 | various files. | |
179 | ||
180 | @example | |
181 | @group | |
182 | (find-file-noselect "/etc/fstab") | |
183 | @result{} #<buffer fstab> | |
184 | @end group | |
185 | @end example | |
186 | @end defun | |
187 | ||
188 | @deffn Command find-file-other-window filename &optional wildcards | |
189 | This command selects a buffer visiting the file @var{filename}, but | |
0e406a72 CY |
190 | does so in a window other than the selected window. It may use |
191 | another existing window or split a window; see @ref{Switching | |
192 | Buffers}. | |
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193 | |
194 | When this command is called interactively, it prompts for | |
195 | @var{filename}. | |
196 | @end deffn | |
197 | ||
198 | @deffn Command find-file-read-only filename &optional wildcards | |
199 | This command selects a buffer visiting the file @var{filename}, like | |
200 | @code{find-file}, but it marks the buffer as read-only. @xref{Read Only | |
201 | Buffers}, for related functions and variables. | |
202 | ||
203 | When this command is called interactively, it prompts for | |
204 | @var{filename}. | |
205 | @end deffn | |
206 | ||
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207 | @defopt find-file-wildcards |
208 | If this variable is non-@code{nil}, then the various @code{find-file} | |
209 | commands check for wildcard characters and visit all the files that | |
210 | match them (when invoked interactively or when their @var{wildcards} | |
211 | argument is non-@code{nil}). If this option is @code{nil}, then | |
212 | the @code{find-file} commands ignore their @var{wildcards} argument | |
213 | and never treat wildcard characters specially. | |
214 | @end defopt | |
215 | ||
01f17ae2 | 216 | @defopt find-file-hook |
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217 | The value of this variable is a list of functions to be called after a |
218 | file is visited. The file's local-variables specification (if any) will | |
219 | have been processed before the hooks are run. The buffer visiting the | |
220 | file is current when the hook functions are run. | |
221 | ||
222 | This variable is a normal hook. @xref{Hooks}. | |
01f17ae2 | 223 | @end defopt |
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224 | |
225 | @defvar find-file-not-found-functions | |
226 | The value of this variable is a list of functions to be called when | |
227 | @code{find-file} or @code{find-file-noselect} is passed a nonexistent | |
228 | file name. @code{find-file-noselect} calls these functions as soon as | |
229 | it detects a nonexistent file. It calls them in the order of the list, | |
230 | until one of them returns non-@code{nil}. @code{buffer-file-name} is | |
231 | already set up. | |
232 | ||
233 | This is not a normal hook because the values of the functions are | |
234 | used, and in many cases only some of the functions are called. | |
235 | @end defvar | |
236 | ||
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237 | @defvar find-file-literally |
238 | This buffer-local variable, if set to a non-@code{nil} value, makes | |
239 | @code{save-buffer} behave as if the buffer were visiting its file | |
240 | literally, i.e. without conversions of any kind. The command | |
241 | @code{find-file-literally} sets this variable's local value, but other | |
242 | equivalent functions and commands can do that as well, e.g.@: to avoid | |
243 | automatic addition of a newline at the end of the file. This variable | |
3ee240fa | 244 | is permanent local, so it is unaffected by changes of major modes. |
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245 | @end defvar |
246 | ||
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247 | @node Subroutines of Visiting |
248 | @comment node-name, next, previous, up | |
249 | @subsection Subroutines of Visiting | |
250 | ||
251 | The @code{find-file-noselect} function uses two important subroutines | |
252 | which are sometimes useful in user Lisp code: @code{create-file-buffer} | |
253 | and @code{after-find-file}. This section explains how to use them. | |
254 | ||
255 | @defun create-file-buffer filename | |
256 | This function creates a suitably named buffer for visiting | |
257 | @var{filename}, and returns it. It uses @var{filename} (sans directory) | |
258 | as the name if that name is free; otherwise, it appends a string such as | |
259 | @samp{<2>} to get an unused name. See also @ref{Creating Buffers}. | |
260 | ||
261 | @strong{Please note:} @code{create-file-buffer} does @emph{not} | |
262 | associate the new buffer with a file and does not select the buffer. | |
263 | It also does not use the default major mode. | |
264 | ||
265 | @example | |
266 | @group | |
267 | (create-file-buffer "foo") | |
268 | @result{} #<buffer foo> | |
269 | @end group | |
270 | @group | |
271 | (create-file-buffer "foo") | |
272 | @result{} #<buffer foo<2>> | |
273 | @end group | |
274 | @group | |
275 | (create-file-buffer "foo") | |
276 | @result{} #<buffer foo<3>> | |
277 | @end group | |
278 | @end example | |
279 | ||
280 | This function is used by @code{find-file-noselect}. | |
281 | It uses @code{generate-new-buffer} (@pxref{Creating Buffers}). | |
282 | @end defun | |
283 | ||
284 | @defun after-find-file &optional error warn noauto after-find-file-from-revert-buffer nomodes | |
285 | This function sets the buffer major mode, and parses local variables | |
286 | (@pxref{Auto Major Mode}). It is called by @code{find-file-noselect} | |
287 | and by the default revert function (@pxref{Reverting}). | |
288 | ||
289 | @cindex new file message | |
290 | @cindex file open error | |
291 | If reading the file got an error because the file does not exist, but | |
292 | its directory does exist, the caller should pass a non-@code{nil} value | |
293 | for @var{error}. In that case, @code{after-find-file} issues a warning: | |
294 | @samp{(New file)}. For more serious errors, the caller should usually not | |
295 | call @code{after-find-file}. | |
296 | ||
297 | If @var{warn} is non-@code{nil}, then this function issues a warning | |
298 | if an auto-save file exists and is more recent than the visited file. | |
299 | ||
300 | If @var{noauto} is non-@code{nil}, that says not to enable or disable | |
301 | Auto-Save mode. The mode remains enabled if it was enabled before. | |
302 | ||
303 | If @var{after-find-file-from-revert-buffer} is non-@code{nil}, that | |
304 | means this call was from @code{revert-buffer}. This has no direct | |
305 | effect, but some mode functions and hook functions check the value | |
306 | of this variable. | |
307 | ||
308 | If @var{nomodes} is non-@code{nil}, that means don't alter the buffer's | |
309 | major mode, don't process local variables specifications in the file, | |
310 | and don't run @code{find-file-hook}. This feature is used by | |
311 | @code{revert-buffer} in some cases. | |
312 | ||
313 | The last thing @code{after-find-file} does is call all the functions | |
314 | in the list @code{find-file-hook}. | |
315 | @end defun | |
316 | ||
317 | @node Saving Buffers | |
318 | @section Saving Buffers | |
319 | @cindex saving buffers | |
320 | ||
321 | When you edit a file in Emacs, you are actually working on a buffer | |
322 | that is visiting that file---that is, the contents of the file are | |
323 | copied into the buffer and the copy is what you edit. Changes to the | |
324 | buffer do not change the file until you @dfn{save} the buffer, which | |
325 | means copying the contents of the buffer into the file. | |
326 | ||
327 | @deffn Command save-buffer &optional backup-option | |
328 | This function saves the contents of the current buffer in its visited | |
329 | file if the buffer has been modified since it was last visited or saved. | |
330 | Otherwise it does nothing. | |
331 | ||
332 | @code{save-buffer} is responsible for making backup files. Normally, | |
333 | @var{backup-option} is @code{nil}, and @code{save-buffer} makes a backup | |
334 | file only if this is the first save since visiting the file. Other | |
335 | values for @var{backup-option} request the making of backup files in | |
336 | other circumstances: | |
337 | ||
338 | @itemize @bullet | |
339 | @item | |
340 | With an argument of 4 or 64, reflecting 1 or 3 @kbd{C-u}'s, the | |
341 | @code{save-buffer} function marks this version of the file to be | |
342 | backed up when the buffer is next saved. | |
343 | ||
344 | @item | |
345 | With an argument of 16 or 64, reflecting 2 or 3 @kbd{C-u}'s, the | |
346 | @code{save-buffer} function unconditionally backs up the previous | |
347 | version of the file before saving it. | |
348 | ||
349 | @item | |
350 | With an argument of 0, unconditionally do @emph{not} make any backup file. | |
351 | @end itemize | |
352 | @end deffn | |
353 | ||
354 | @deffn Command save-some-buffers &optional save-silently-p pred | |
355 | @anchor{Definition of save-some-buffers} | |
356 | This command saves some modified file-visiting buffers. Normally it | |
357 | asks the user about each buffer. But if @var{save-silently-p} is | |
358 | non-@code{nil}, it saves all the file-visiting buffers without querying | |
359 | the user. | |
360 | ||
361 | The optional @var{pred} argument controls which buffers to ask about | |
362 | (or to save silently if @var{save-silently-p} is non-@code{nil}). | |
363 | If it is @code{nil}, that means to ask only about file-visiting buffers. | |
364 | If it is @code{t}, that means also offer to save certain other non-file | |
365 | buffers---those that have a non-@code{nil} buffer-local value of | |
366 | @code{buffer-offer-save} (@pxref{Killing Buffers}). A user who says | |
367 | @samp{yes} to saving a non-file buffer is asked to specify the file | |
368 | name to use. The @code{save-buffers-kill-emacs} function passes the | |
369 | value @code{t} for @var{pred}. | |
370 | ||
371 | If @var{pred} is neither @code{t} nor @code{nil}, then it should be | |
372 | a function of no arguments. It will be called in each buffer to decide | |
373 | whether to offer to save that buffer. If it returns a non-@code{nil} | |
374 | value in a certain buffer, that means do offer to save that buffer. | |
375 | @end deffn | |
376 | ||
377 | @deffn Command write-file filename &optional confirm | |
378 | @anchor{Definition of write-file} | |
379 | This function writes the current buffer into file @var{filename}, makes | |
380 | the buffer visit that file, and marks it not modified. Then it renames | |
381 | the buffer based on @var{filename}, appending a string like @samp{<2>} | |
382 | if necessary to make a unique buffer name. It does most of this work by | |
383 | calling @code{set-visited-file-name} (@pxref{Buffer File Name}) and | |
384 | @code{save-buffer}. | |
385 | ||
386 | If @var{confirm} is non-@code{nil}, that means to ask for confirmation | |
387 | before overwriting an existing file. Interactively, confirmation is | |
388 | required, unless the user supplies a prefix argument. | |
389 | ||
390 | If @var{filename} is an existing directory, or a symbolic link to one, | |
391 | @code{write-file} uses the name of the visited file, in directory | |
392 | @var{filename}. If the buffer is not visiting a file, it uses the | |
393 | buffer name instead. | |
394 | @end deffn | |
395 | ||
396 | Saving a buffer runs several hooks. It also performs format | |
397 | conversion (@pxref{Format Conversion}). | |
398 | ||
399 | @defvar write-file-functions | |
400 | The value of this variable is a list of functions to be called before | |
401 | writing out a buffer to its visited file. If one of them returns | |
402 | non-@code{nil}, the file is considered already written and the rest of | |
403 | the functions are not called, nor is the usual code for writing the file | |
404 | executed. | |
405 | ||
406 | If a function in @code{write-file-functions} returns non-@code{nil}, it | |
407 | is responsible for making a backup file (if that is appropriate). | |
408 | To do so, execute the following code: | |
409 | ||
410 | @example | |
411 | (or buffer-backed-up (backup-buffer)) | |
412 | @end example | |
413 | ||
414 | You might wish to save the file modes value returned by | |
415 | @code{backup-buffer} and use that (if non-@code{nil}) to set the mode | |
416 | bits of the file that you write. This is what @code{save-buffer} | |
417 | normally does. @xref{Making Backups,, Making Backup Files}. | |
418 | ||
419 | The hook functions in @code{write-file-functions} are also responsible | |
420 | for encoding the data (if desired): they must choose a suitable coding | |
421 | system and end-of-line conversion (@pxref{Lisp and Coding Systems}), | |
422 | perform the encoding (@pxref{Explicit Encoding}), and set | |
423 | @code{last-coding-system-used} to the coding system that was used | |
424 | (@pxref{Encoding and I/O}). | |
425 | ||
426 | If you set this hook locally in a buffer, it is assumed to be | |
427 | associated with the file or the way the contents of the buffer were | |
428 | obtained. Thus the variable is marked as a permanent local, so that | |
429 | changing the major mode does not alter a buffer-local value. On the | |
430 | other hand, calling @code{set-visited-file-name} will reset it. | |
431 | If this is not what you want, you might like to use | |
432 | @code{write-contents-functions} instead. | |
433 | ||
434 | Even though this is not a normal hook, you can use @code{add-hook} and | |
435 | @code{remove-hook} to manipulate the list. @xref{Hooks}. | |
436 | @end defvar | |
437 | ||
438 | @c Emacs 19 feature | |
439 | @defvar write-contents-functions | |
440 | This works just like @code{write-file-functions}, but it is intended | |
441 | for hooks that pertain to the buffer's contents, not to the particular | |
442 | visited file or its location. Such hooks are usually set up by major | |
443 | modes, as buffer-local bindings for this variable. This variable | |
444 | automatically becomes buffer-local whenever it is set; switching to a | |
445 | new major mode always resets this variable, but calling | |
446 | @code{set-visited-file-name} does not. | |
447 | ||
448 | If any of the functions in this hook returns non-@code{nil}, the file | |
449 | is considered already written and the rest are not called and neither | |
450 | are the functions in @code{write-file-functions}. | |
451 | @end defvar | |
452 | ||
453 | @defopt before-save-hook | |
454 | This normal hook runs before a buffer is saved in its visited file, | |
455 | regardless of whether that is done normally or by one of the hooks | |
456 | described above. For instance, the @file{copyright.el} program uses | |
457 | this hook to make sure the file you are saving has the current year in | |
458 | its copyright notice. | |
459 | @end defopt | |
460 | ||
461 | @c Emacs 19 feature | |
462 | @defopt after-save-hook | |
463 | This normal hook runs after a buffer has been saved in its visited file. | |
464 | One use of this hook is in Fast Lock mode; it uses this hook to save the | |
465 | highlighting information in a cache file. | |
466 | @end defopt | |
467 | ||
468 | @defopt file-precious-flag | |
469 | If this variable is non-@code{nil}, then @code{save-buffer} protects | |
470 | against I/O errors while saving by writing the new file to a temporary | |
471 | name instead of the name it is supposed to have, and then renaming it to | |
472 | the intended name after it is clear there are no errors. This procedure | |
473 | prevents problems such as a lack of disk space from resulting in an | |
474 | invalid file. | |
475 | ||
476 | As a side effect, backups are necessarily made by copying. @xref{Rename | |
477 | or Copy}. Yet, at the same time, saving a precious file always breaks | |
478 | all hard links between the file you save and other file names. | |
479 | ||
480 | Some modes give this variable a non-@code{nil} buffer-local value | |
481 | in particular buffers. | |
482 | @end defopt | |
483 | ||
484 | @defopt require-final-newline | |
485 | This variable determines whether files may be written out that do | |
486 | @emph{not} end with a newline. If the value of the variable is | |
487 | @code{t}, then @code{save-buffer} silently adds a newline at the end of | |
488 | the file whenever the buffer being saved does not already end in one. | |
489 | If the value of the variable is non-@code{nil}, but not @code{t}, then | |
490 | @code{save-buffer} asks the user whether to add a newline each time the | |
491 | case arises. | |
492 | ||
493 | If the value of the variable is @code{nil}, then @code{save-buffer} | |
494 | doesn't add newlines at all. @code{nil} is the default value, but a few | |
495 | major modes set it to @code{t} in particular buffers. | |
496 | @end defopt | |
497 | ||
498 | See also the function @code{set-visited-file-name} (@pxref{Buffer File | |
499 | Name}). | |
500 | ||
501 | @node Reading from Files | |
502 | @comment node-name, next, previous, up | |
503 | @section Reading from Files | |
504 | @cindex reading from files | |
505 | ||
506 | You can copy a file from the disk and insert it into a buffer | |
507 | using the @code{insert-file-contents} function. Don't use the user-level | |
508 | command @code{insert-file} in a Lisp program, as that sets the mark. | |
509 | ||
510 | @defun insert-file-contents filename &optional visit beg end replace | |
511 | This function inserts the contents of file @var{filename} into the | |
512 | current buffer after point. It returns a list of the absolute file name | |
513 | and the length of the data inserted. An error is signaled if | |
514 | @var{filename} is not the name of a file that can be read. | |
515 | ||
516 | The function @code{insert-file-contents} checks the file contents | |
517 | against the defined file formats, and converts the file contents if | |
518 | appropriate and also calls the functions in | |
519 | the list @code{after-insert-file-functions}. @xref{Format Conversion}. | |
520 | Normally, one of the functions in the | |
521 | @code{after-insert-file-functions} list determines the coding system | |
522 | (@pxref{Coding Systems}) used for decoding the file's contents, | |
7951ad77 EZ |
523 | including end-of-line conversion. However, if the file contains null |
524 | bytes, it is by default visited without any code conversions; see | |
525 | @ref{Lisp and Coding Systems, inhibit-null-byte-detection}, for how to | |
526 | control this behavior. | |
b8d4c8d0 GM |
527 | |
528 | If @var{visit} is non-@code{nil}, this function additionally marks the | |
529 | buffer as unmodified and sets up various fields in the buffer so that it | |
530 | is visiting the file @var{filename}: these include the buffer's visited | |
531 | file name and its last save file modtime. This feature is used by | |
532 | @code{find-file-noselect} and you probably should not use it yourself. | |
533 | ||
534 | If @var{beg} and @var{end} are non-@code{nil}, they should be integers | |
535 | specifying the portion of the file to insert. In this case, @var{visit} | |
536 | must be @code{nil}. For example, | |
537 | ||
538 | @example | |
539 | (insert-file-contents filename nil 0 500) | |
540 | @end example | |
541 | ||
542 | @noindent | |
543 | inserts the first 500 characters of a file. | |
544 | ||
545 | If the argument @var{replace} is non-@code{nil}, it means to replace the | |
546 | contents of the buffer (actually, just the accessible portion) with the | |
547 | contents of the file. This is better than simply deleting the buffer | |
548 | contents and inserting the whole file, because (1) it preserves some | |
549 | marker positions and (2) it puts less data in the undo list. | |
550 | ||
551 | It is possible to read a special file (such as a FIFO or an I/O device) | |
552 | with @code{insert-file-contents}, as long as @var{replace} and | |
553 | @var{visit} are @code{nil}. | |
554 | @end defun | |
555 | ||
556 | @defun insert-file-contents-literally filename &optional visit beg end replace | |
557 | This function works like @code{insert-file-contents} except that it does | |
558 | not do format decoding (@pxref{Format Conversion}), does not do | |
559 | character code conversion (@pxref{Coding Systems}), does not run | |
560 | @code{find-file-hook}, does not perform automatic uncompression, and so | |
561 | on. | |
562 | @end defun | |
563 | ||
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}. | |
567 | ||
568 | @node Writing to Files | |
569 | @comment node-name, next, previous, up | |
570 | @section Writing to Files | |
571 | @cindex writing to files | |
572 | ||
573 | You can write the contents of a buffer, or part of a buffer, directly | |
574 | to a file on disk using the @code{append-to-file} and | |
575 | @code{write-region} functions. Don't use these functions to write to | |
576 | files that are being visited; that could cause confusion in the | |
577 | mechanisms for visiting. | |
578 | ||
579 | @deffn Command append-to-file start end filename | |
580 | This function appends the contents of the region delimited by | |
581 | @var{start} and @var{end} in the current buffer to the end of file | |
582 | @var{filename}. If that file does not exist, it is created. This | |
583 | function returns @code{nil}. | |
584 | ||
585 | An error is signaled if @var{filename} specifies a nonwritable file, | |
586 | or a nonexistent file in a directory where files cannot be created. | |
587 | ||
588 | When called from Lisp, this function is completely equivalent to: | |
589 | ||
590 | @example | |
591 | (write-region start end filename t) | |
592 | @end example | |
593 | @end deffn | |
594 | ||
595 | @deffn Command write-region start end filename &optional append visit lockname mustbenew | |
596 | This function writes the region delimited by @var{start} and @var{end} | |
597 | in the current buffer into the file specified by @var{filename}. | |
598 | ||
599 | If @var{start} is @code{nil}, then the command writes the entire buffer | |
600 | contents (@emph{not} just the accessible portion) to the file and | |
601 | ignores @var{end}. | |
602 | ||
603 | @c Emacs 19 feature | |
604 | If @var{start} is a string, then @code{write-region} writes or appends | |
605 | that string, rather than text from the buffer. @var{end} is ignored in | |
606 | this case. | |
607 | ||
608 | If @var{append} is non-@code{nil}, then the specified text is appended | |
609 | to the existing file contents (if any). If @var{append} is an | |
610 | integer, @code{write-region} seeks to that byte offset from the start | |
611 | of the file and writes the data from there. | |
612 | ||
613 | If @var{mustbenew} is non-@code{nil}, then @code{write-region} asks | |
614 | for confirmation if @var{filename} names an existing file. If | |
615 | @var{mustbenew} is the symbol @code{excl}, then @code{write-region} | |
616 | does not ask for confirmation, but instead it signals an error | |
617 | @code{file-already-exists} if the file already exists. | |
618 | ||
619 | The test for an existing file, when @var{mustbenew} is @code{excl}, uses | |
620 | a special system feature. At least for files on a local disk, there is | |
621 | no chance that some other program could create a file of the same name | |
622 | before Emacs does, without Emacs's noticing. | |
623 | ||
624 | If @var{visit} is @code{t}, then Emacs establishes an association | |
625 | between the buffer and the file: the buffer is then visiting that file. | |
626 | It also sets the last file modification time for the current buffer to | |
627 | @var{filename}'s modtime, and marks the buffer as not modified. This | |
628 | feature is used by @code{save-buffer}, but you probably should not use | |
629 | it yourself. | |
630 | ||
631 | @c Emacs 19 feature | |
632 | If @var{visit} is a string, it specifies the file name to visit. This | |
633 | way, you can write the data to one file (@var{filename}) while recording | |
634 | the buffer as visiting another file (@var{visit}). The argument | |
635 | @var{visit} is used in the echo area message and also for file locking; | |
636 | @var{visit} is stored in @code{buffer-file-name}. This feature is used | |
637 | to implement @code{file-precious-flag}; don't use it yourself unless you | |
638 | really know what you're doing. | |
639 | ||
640 | The optional argument @var{lockname}, if non-@code{nil}, specifies the | |
641 | file name to use for purposes of locking and unlocking, overriding | |
642 | @var{filename} and @var{visit} for that purpose. | |
643 | ||
644 | The function @code{write-region} converts the data which it writes to | |
645 | the appropriate file formats specified by @code{buffer-file-format} | |
646 | and also calls the functions in the list | |
647 | @code{write-region-annotate-functions}. | |
648 | @xref{Format Conversion}. | |
649 | ||
650 | Normally, @code{write-region} displays the message @samp{Wrote | |
651 | @var{filename}} in the echo area. If @var{visit} is neither @code{t} | |
652 | nor @code{nil} nor a string, then this message is inhibited. This | |
653 | feature is useful for programs that use files for internal purposes, | |
654 | files that the user does not need to know about. | |
655 | @end deffn | |
656 | ||
657 | @defmac with-temp-file file body@dots{} | |
658 | @anchor{Definition of with-temp-file} | |
659 | The @code{with-temp-file} macro evaluates the @var{body} forms with a | |
660 | temporary buffer as the current buffer; then, at the end, it writes the | |
661 | buffer contents into file @var{file}. It kills the temporary buffer | |
662 | when finished, restoring the buffer that was current before the | |
663 | @code{with-temp-file} form. Then it returns the value of the last form | |
664 | in @var{body}. | |
665 | ||
666 | The current buffer is restored even in case of an abnormal exit via | |
667 | @code{throw} or error (@pxref{Nonlocal Exits}). | |
668 | ||
669 | See also @code{with-temp-buffer} in @ref{Definition of | |
670 | with-temp-buffer,, The Current Buffer}. | |
671 | @end defmac | |
672 | ||
673 | @node File Locks | |
674 | @section File Locks | |
675 | @cindex file locks | |
676 | @cindex lock file | |
677 | ||
678 | When two users edit the same file at the same time, they are likely | |
679 | to interfere with each other. Emacs tries to prevent this situation | |
680 | from arising by recording a @dfn{file lock} when a file is being | |
681 | modified. (File locks are not implemented on Microsoft systems.) | |
682 | Emacs can then detect the first attempt to modify a buffer visiting a | |
683 | file that is locked by another Emacs job, and ask the user what to do. | |
684 | The file lock is really a file, a symbolic link with a special name, | |
685 | stored in the same directory as the file you are editing. | |
686 | ||
687 | When you access files using NFS, there may be a small probability that | |
688 | you and another user will both lock the same file ``simultaneously.'' | |
689 | If this happens, it is possible for the two users to make changes | |
690 | simultaneously, but Emacs will still warn the user who saves second. | |
691 | Also, the detection of modification of a buffer visiting a file changed | |
692 | on disk catches some cases of simultaneous editing; see | |
693 | @ref{Modification Time}. | |
694 | ||
695 | @defun file-locked-p filename | |
696 | This function returns @code{nil} if the file @var{filename} is not | |
697 | locked. It returns @code{t} if it is locked by this Emacs process, and | |
698 | it returns the name of the user who has locked it if it is locked by | |
699 | some other job. | |
700 | ||
701 | @example | |
702 | @group | |
703 | (file-locked-p "foo") | |
704 | @result{} nil | |
705 | @end group | |
706 | @end example | |
707 | @end defun | |
708 | ||
709 | @defun lock-buffer &optional filename | |
710 | This function locks the file @var{filename}, if the current buffer is | |
711 | modified. The argument @var{filename} defaults to the current buffer's | |
712 | visited file. Nothing is done if the current buffer is not visiting a | |
713 | file, or is not modified, or if the system does not support locking. | |
714 | @end defun | |
715 | ||
716 | @defun unlock-buffer | |
717 | This function unlocks the file being visited in the current buffer, | |
718 | if the buffer is modified. If the buffer is not modified, then | |
719 | the file should not be locked, so this function does nothing. It also | |
720 | does nothing if the current buffer is not visiting a file, or if the | |
721 | system does not support locking. | |
722 | @end defun | |
723 | ||
724 | File locking is not supported on some systems. On systems that do not | |
725 | support it, the functions @code{lock-buffer}, @code{unlock-buffer} and | |
726 | @code{file-locked-p} do nothing and return @code{nil}. | |
727 | ||
728 | @defun ask-user-about-lock file other-user | |
729 | This function is called when the user tries to modify @var{file}, but it | |
730 | is locked by another user named @var{other-user}. The default | |
731 | definition of this function asks the user to say what to do. The value | |
732 | this function returns determines what Emacs does next: | |
733 | ||
734 | @itemize @bullet | |
735 | @item | |
736 | A value of @code{t} says to grab the lock on the file. Then | |
737 | this user may edit the file and @var{other-user} loses the lock. | |
738 | ||
739 | @item | |
740 | A value of @code{nil} says to ignore the lock and let this | |
741 | user edit the file anyway. | |
742 | ||
743 | @item | |
744 | @kindex file-locked | |
745 | This function may instead signal a @code{file-locked} error, in which | |
746 | case the change that the user was about to make does not take place. | |
747 | ||
748 | The error message for this error looks like this: | |
749 | ||
750 | @example | |
751 | @error{} File is locked: @var{file} @var{other-user} | |
752 | @end example | |
753 | ||
754 | @noindent | |
755 | where @code{file} is the name of the file and @var{other-user} is the | |
756 | name of the user who has locked the file. | |
757 | @end itemize | |
758 | ||
759 | If you wish, you can replace the @code{ask-user-about-lock} function | |
760 | with your own version that makes the decision in another way. The code | |
761 | for its usual definition is in @file{userlock.el}. | |
762 | @end defun | |
763 | ||
764 | @node Information about Files | |
765 | @section Information about Files | |
766 | @cindex file, information about | |
767 | ||
768 | The functions described in this section all operate on strings that | |
769 | designate file names. With a few exceptions, all the functions have | |
770 | names that begin with the word @samp{file}. These functions all | |
771 | return information about actual files or directories, so their | |
772 | arguments must all exist as actual files or directories unless | |
773 | otherwise noted. | |
774 | ||
775 | @menu | |
776 | * Testing Accessibility:: Is a given file readable? Writable? | |
777 | * Kinds of Files:: Is it a directory? A symbolic link? | |
d24880de | 778 | * Truenames:: Eliminating symbolic links from a file name. |
b8d4c8d0 GM |
779 | * File Attributes:: How large is it? Any other names? Etc. |
780 | * Locating Files:: How to find a file in standard places. | |
781 | @end menu | |
782 | ||
783 | @node Testing Accessibility | |
784 | @comment node-name, next, previous, up | |
785 | @subsection Testing Accessibility | |
786 | @cindex accessibility of a file | |
787 | @cindex file accessibility | |
788 | ||
789 | These functions test for permission to access a file in specific | |
790 | ways. Unless explicitly stated otherwise, they recursively follow | |
791 | symbolic links for their file name arguments, at all levels (at the | |
792 | level of the file itself and at all levels of parent directories). | |
793 | ||
794 | @defun file-exists-p filename | |
795 | This function returns @code{t} if a file named @var{filename} appears | |
796 | to exist. This does not mean you can necessarily read the file, only | |
797 | that you can find out its attributes. (On Unix and GNU/Linux, this is | |
798 | true if the file exists and you have execute permission on the | |
799 | containing directories, regardless of the protection of the file | |
800 | itself.) | |
801 | ||
802 | If the file does not exist, or if fascist access control policies | |
803 | prevent you from finding the attributes of the file, this function | |
804 | returns @code{nil}. | |
805 | ||
806 | Directories are files, so @code{file-exists-p} returns @code{t} when | |
807 | given a directory name. However, symbolic links are treated | |
808 | specially; @code{file-exists-p} returns @code{t} for a symbolic link | |
809 | name only if the target file exists. | |
810 | @end defun | |
811 | ||
812 | @defun file-readable-p filename | |
813 | This function returns @code{t} if a file named @var{filename} exists | |
814 | and you can read it. It returns @code{nil} otherwise. | |
815 | ||
816 | @example | |
817 | @group | |
818 | (file-readable-p "files.texi") | |
819 | @result{} t | |
820 | @end group | |
821 | @group | |
822 | (file-exists-p "/usr/spool/mqueue") | |
823 | @result{} t | |
824 | @end group | |
825 | @group | |
826 | (file-readable-p "/usr/spool/mqueue") | |
827 | @result{} nil | |
828 | @end group | |
829 | @end example | |
830 | @end defun | |
831 | ||
832 | @c Emacs 19 feature | |
833 | @defun file-executable-p filename | |
834 | This function returns @code{t} if a file named @var{filename} exists and | |
835 | you can execute it. It returns @code{nil} otherwise. On Unix and | |
836 | GNU/Linux, if the file is a directory, execute permission means you can | |
837 | check the existence and attributes of files inside the directory, and | |
838 | open those files if their modes permit. | |
839 | @end defun | |
840 | ||
841 | @defun file-writable-p filename | |
842 | This function returns @code{t} if the file @var{filename} can be written | |
843 | or created by you, and @code{nil} otherwise. A file is writable if the | |
844 | file exists and you can write it. It is creatable if it does not exist, | |
845 | but the specified directory does exist and you can write in that | |
846 | directory. | |
847 | ||
848 | In the third example below, @file{foo} is not writable because the | |
849 | parent directory does not exist, even though the user could create such | |
850 | a directory. | |
851 | ||
852 | @example | |
853 | @group | |
854 | (file-writable-p "~/foo") | |
855 | @result{} t | |
856 | @end group | |
857 | @group | |
858 | (file-writable-p "/foo") | |
859 | @result{} nil | |
860 | @end group | |
861 | @group | |
862 | (file-writable-p "~/no-such-dir/foo") | |
863 | @result{} nil | |
864 | @end group | |
865 | @end example | |
866 | @end defun | |
867 | ||
868 | @c Emacs 19 feature | |
869 | @defun file-accessible-directory-p dirname | |
870 | This function returns @code{t} if you have permission to open existing | |
871 | files in the directory whose name as a file is @var{dirname}; | |
872 | otherwise (or if there is no such directory), it returns @code{nil}. | |
873 | The value of @var{dirname} may be either a directory name (such as | |
874 | @file{/foo/}) or the file name of a file which is a directory | |
875 | (such as @file{/foo}, without the final slash). | |
876 | ||
877 | Example: after the following, | |
878 | ||
879 | @example | |
880 | (file-accessible-directory-p "/foo") | |
881 | @result{} nil | |
882 | @end example | |
883 | ||
884 | @noindent | |
885 | we can deduce that any attempt to read a file in @file{/foo/} will | |
886 | give an error. | |
887 | @end defun | |
888 | ||
889 | @defun access-file filename string | |
890 | This function opens file @var{filename} for reading, then closes it and | |
891 | returns @code{nil}. However, if the open fails, it signals an error | |
892 | using @var{string} as the error message text. | |
893 | @end defun | |
894 | ||
895 | @defun file-ownership-preserved-p filename | |
896 | This function returns @code{t} if deleting the file @var{filename} and | |
897 | then creating it anew would keep the file's owner unchanged. It also | |
898 | returns @code{t} for nonexistent files. | |
899 | ||
900 | If @var{filename} is a symbolic link, then, unlike the other functions | |
901 | discussed here, @code{file-ownership-preserved-p} does @emph{not} | |
902 | replace @var{filename} with its target. However, it does recursively | |
903 | follow symbolic links at all levels of parent directories. | |
904 | @end defun | |
905 | ||
906 | @defun file-newer-than-file-p filename1 filename2 | |
907 | @cindex file age | |
908 | @cindex file modification time | |
909 | This function returns @code{t} if the file @var{filename1} is | |
910 | newer than file @var{filename2}. If @var{filename1} does not | |
911 | exist, it returns @code{nil}. If @var{filename1} does exist, but | |
912 | @var{filename2} does not, it returns @code{t}. | |
913 | ||
914 | In the following example, assume that the file @file{aug-19} was written | |
915 | on the 19th, @file{aug-20} was written on the 20th, and the file | |
916 | @file{no-file} doesn't exist at all. | |
917 | ||
918 | @example | |
919 | @group | |
920 | (file-newer-than-file-p "aug-19" "aug-20") | |
921 | @result{} nil | |
922 | @end group | |
923 | @group | |
924 | (file-newer-than-file-p "aug-20" "aug-19") | |
925 | @result{} t | |
926 | @end group | |
927 | @group | |
928 | (file-newer-than-file-p "aug-19" "no-file") | |
929 | @result{} t | |
930 | @end group | |
931 | @group | |
932 | (file-newer-than-file-p "no-file" "aug-19") | |
933 | @result{} nil | |
934 | @end group | |
935 | @end example | |
936 | ||
937 | You can use @code{file-attributes} to get a file's last modification | |
938 | time as a list of two numbers. @xref{File Attributes}. | |
939 | @end defun | |
940 | ||
941 | @node Kinds of Files | |
942 | @comment node-name, next, previous, up | |
943 | @subsection Distinguishing Kinds of Files | |
944 | ||
945 | This section describes how to distinguish various kinds of files, such | |
946 | as directories, symbolic links, and ordinary files. | |
947 | ||
948 | @defun file-symlink-p filename | |
949 | @cindex file symbolic links | |
950 | If the file @var{filename} is a symbolic link, the | |
951 | @code{file-symlink-p} function returns the (non-recursive) link target | |
952 | as a string. (Determining the file name that the link points to from | |
953 | the target is nontrivial.) First, this function recursively follows | |
954 | symbolic links at all levels of parent directories. | |
955 | ||
956 | If the file @var{filename} is not a symbolic link (or there is no such file), | |
957 | @code{file-symlink-p} returns @code{nil}. | |
958 | ||
959 | @example | |
960 | @group | |
961 | (file-symlink-p "foo") | |
962 | @result{} nil | |
963 | @end group | |
964 | @group | |
965 | (file-symlink-p "sym-link") | |
966 | @result{} "foo" | |
967 | @end group | |
968 | @group | |
969 | (file-symlink-p "sym-link2") | |
970 | @result{} "sym-link" | |
971 | @end group | |
972 | @group | |
973 | (file-symlink-p "/bin") | |
974 | @result{} "/pub/bin" | |
975 | @end group | |
976 | @end example | |
977 | ||
978 | @c !!! file-symlink-p: should show output of ls -l for comparison | |
979 | @end defun | |
980 | ||
981 | The next two functions recursively follow symbolic links at | |
982 | all levels for @var{filename}. | |
983 | ||
984 | @defun file-directory-p filename | |
985 | This function returns @code{t} if @var{filename} is the name of an | |
986 | existing directory, @code{nil} otherwise. | |
987 | ||
988 | @example | |
989 | @group | |
990 | (file-directory-p "~rms") | |
991 | @result{} t | |
992 | @end group | |
993 | @group | |
994 | (file-directory-p "~rms/lewis/files.texi") | |
995 | @result{} nil | |
996 | @end group | |
997 | @group | |
998 | (file-directory-p "~rms/lewis/no-such-file") | |
999 | @result{} nil | |
1000 | @end group | |
1001 | @group | |
1002 | (file-directory-p "$HOME") | |
1003 | @result{} nil | |
1004 | @end group | |
1005 | @group | |
1006 | (file-directory-p | |
1007 | (substitute-in-file-name "$HOME")) | |
1008 | @result{} t | |
1009 | @end group | |
1010 | @end example | |
1011 | @end defun | |
1012 | ||
1013 | @defun file-regular-p filename | |
1014 | This function returns @code{t} if the file @var{filename} exists and is | |
1015 | a regular file (not a directory, named pipe, terminal, or | |
1016 | other I/O device). | |
1017 | @end defun | |
1018 | ||
1019 | @node Truenames | |
1020 | @subsection Truenames | |
1021 | @cindex truename (of file) | |
1022 | ||
1023 | @c Emacs 19 features | |
1024 | The @dfn{truename} of a file is the name that you get by following | |
1025 | symbolic links at all levels until none remain, then simplifying away | |
1026 | @samp{.}@: and @samp{..}@: appearing as name components. This results | |
1027 | in a sort of canonical name for the file. A file does not always have a | |
1028 | unique truename; the number of distinct truenames a file has is equal to | |
1029 | the number of hard links to the file. However, truenames are useful | |
1030 | because they eliminate symbolic links as a cause of name variation. | |
1031 | ||
1032 | @defun file-truename filename | |
1033 | The function @code{file-truename} returns the truename of the file | |
06083aa1 GM |
1034 | @var{filename}. If the argument is not an absolute file name, |
1035 | this function first expands it against @code{default-directory}. | |
b8d4c8d0 GM |
1036 | |
1037 | This function does not expand environment variables. Only | |
1038 | @code{substitute-in-file-name} does that. @xref{Definition of | |
1039 | substitute-in-file-name}. | |
1040 | ||
1041 | If you may need to follow symbolic links preceding @samp{..}@: | |
1042 | appearing as a name component, you should make sure to call | |
1043 | @code{file-truename} without prior direct or indirect calls to | |
1044 | @code{expand-file-name}, as otherwise the file name component | |
1045 | immediately preceding @samp{..} will be ``simplified away'' before | |
1046 | @code{file-truename} is called. To eliminate the need for a call to | |
1047 | @code{expand-file-name}, @code{file-truename} handles @samp{~} in the | |
1048 | same way that @code{expand-file-name} does. @xref{File Name | |
1049 | Expansion,, Functions that Expand Filenames}. | |
1050 | @end defun | |
1051 | ||
1052 | @defun file-chase-links filename &optional limit | |
1053 | This function follows symbolic links, starting with @var{filename}, | |
1054 | until it finds a file name which is not the name of a symbolic link. | |
1055 | Then it returns that file name. This function does @emph{not} follow | |
1056 | symbolic links at the level of parent directories. | |
1057 | ||
1058 | If you specify a number for @var{limit}, then after chasing through | |
1059 | that many links, the function just returns what it has even if that is | |
1060 | still a symbolic link. | |
1061 | @end defun | |
1062 | ||
1063 | To illustrate the difference between @code{file-chase-links} and | |
1064 | @code{file-truename}, suppose that @file{/usr/foo} is a symbolic link to | |
1065 | the directory @file{/home/foo}, and @file{/home/foo/hello} is an | |
1066 | ordinary file (or at least, not a symbolic link) or nonexistent. Then | |
1067 | we would have: | |
1068 | ||
1069 | @example | |
1070 | (file-chase-links "/usr/foo/hello") | |
1071 | ;; @r{This does not follow the links in the parent directories.} | |
1072 | @result{} "/usr/foo/hello" | |
1073 | (file-truename "/usr/foo/hello") | |
1074 | ;; @r{Assuming that @file{/home} is not a symbolic link.} | |
1075 | @result{} "/home/foo/hello" | |
1076 | @end example | |
1077 | ||
1078 | @xref{Buffer File Name}, for related information. | |
1079 | ||
1080 | @node File Attributes | |
1081 | @comment node-name, next, previous, up | |
1082 | @subsection Other Information about Files | |
1083 | ||
1084 | This section describes the functions for getting detailed information | |
1085 | about a file, other than its contents. This information includes the | |
1086 | mode bits that control access permission, the owner and group numbers, | |
1087 | the number of names, the inode number, the size, and the times of access | |
1088 | and modification. | |
1089 | ||
1090 | @defun file-modes filename | |
1091 | @cindex permission | |
1092 | @cindex file attributes | |
1093 | This function returns the mode bits of @var{filename}, as an integer. | |
1094 | The mode bits are also called the file permissions, and they specify | |
1095 | access control in the usual Unix fashion. If the low-order bit is 1, | |
1096 | then the file is executable by all users, if the second-lowest-order bit | |
1097 | is 1, then the file is writable by all users, etc. | |
1098 | ||
1099 | The highest value returnable is 4095 (7777 octal), meaning that | |
1100 | everyone has read, write, and execute permission, that the @acronym{SUID} bit | |
1101 | is set for both others and group, and that the sticky bit is set. | |
1102 | ||
1103 | If @var{filename} does not exist, @code{file-modes} returns @code{nil}. | |
1104 | ||
1105 | This function recursively follows symbolic links at all levels. | |
1106 | ||
1107 | @example | |
1108 | @group | |
1109 | (file-modes "~/junk/diffs") | |
1110 | @result{} 492 ; @r{Decimal integer.} | |
1111 | @end group | |
1112 | @group | |
1113 | (format "%o" 492) | |
1114 | @result{} "754" ; @r{Convert to octal.} | |
1115 | @end group | |
1116 | ||
1117 | @group | |
8d80ef01 | 1118 | (set-file-modes "~/junk/diffs" #o666) |
b8d4c8d0 GM |
1119 | @result{} nil |
1120 | @end group | |
1121 | ||
b8d4c8d0 GM |
1122 | @group |
1123 | % ls -l diffs | |
1124 | -rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs | |
1125 | @end group | |
1126 | @end example | |
1127 | @end defun | |
1128 | ||
1129 | If the @var{filename} argument to the next two functions is a symbolic | |
1130 | link, then these function do @emph{not} replace it with its target. | |
1131 | However, they both recursively follow symbolic links at all levels of | |
1132 | parent directories. | |
1133 | ||
1134 | @defun file-nlinks filename | |
1135 | This functions returns the number of names (i.e., hard links) that | |
1136 | file @var{filename} has. If the file does not exist, then this function | |
1137 | returns @code{nil}. Note that symbolic links have no effect on this | |
1138 | function, because they are not considered to be names of the files they | |
1139 | link to. | |
1140 | ||
1141 | @example | |
1142 | @group | |
1143 | % ls -l foo* | |
1144 | -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo | |
1145 | -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo1 | |
1146 | @end group | |
1147 | ||
1148 | @group | |
1149 | (file-nlinks "foo") | |
1150 | @result{} 2 | |
1151 | @end group | |
1152 | @group | |
1153 | (file-nlinks "doesnt-exist") | |
1154 | @result{} nil | |
1155 | @end group | |
1156 | @end example | |
1157 | @end defun | |
1158 | ||
1159 | @defun file-attributes filename &optional id-format | |
1160 | @anchor{Definition of file-attributes} | |
1161 | This function returns a list of attributes of file @var{filename}. If | |
1162 | the specified file cannot be opened, it returns @code{nil}. | |
1163 | The optional parameter @var{id-format} specifies the preferred format | |
1164 | of attributes @acronym{UID} and @acronym{GID} (see below)---the | |
1165 | valid values are @code{'string} and @code{'integer}. The latter is | |
1166 | the default, but we plan to change that, so you should specify a | |
1167 | non-@code{nil} value for @var{id-format} if you use the returned | |
1168 | @acronym{UID} or @acronym{GID}. | |
1169 | ||
1170 | The elements of the list, in order, are: | |
1171 | ||
1172 | @enumerate 0 | |
1173 | @item | |
1174 | @code{t} for a directory, a string for a symbolic link (the name | |
1175 | linked to), or @code{nil} for a text file. | |
1176 | ||
1177 | @c Wordy so as to prevent an overfull hbox. --rjc 15mar92 | |
1178 | @item | |
1179 | The number of names the file has. Alternate names, also known as hard | |
1180 | links, can be created by using the @code{add-name-to-file} function | |
1181 | (@pxref{Changing Files}). | |
1182 | ||
1183 | @item | |
1184 | The file's @acronym{UID}, normally as a string. However, if it does | |
1185 | not correspond to a named user, the value is an integer or a floating | |
1186 | point number. | |
1187 | ||
1188 | @item | |
1189 | The file's @acronym{GID}, likewise. | |
1190 | ||
1191 | @item | |
1192 | The time of last access, as a list of two integers. | |
1193 | The first integer has the high-order 16 bits of time, | |
1194 | the second has the low 16 bits. (This is similar to the | |
804543b5 EZ |
1195 | value of @code{current-time}; see @ref{Time of Day}.) Note that on |
1196 | some FAT-based filesystems, only the date of last access is recorded, | |
1197 | so this time will always hold the midnight of the day of last access. | |
b8d4c8d0 | 1198 | |
804543b5 | 1199 | @cindex modification time of file |
b8d4c8d0 GM |
1200 | @item |
1201 | The time of last modification as a list of two integers (as above). | |
804543b5 | 1202 | This is the last time when the file's contents were modified. |
b8d4c8d0 GM |
1203 | |
1204 | @item | |
1205 | The time of last status change as a list of two integers (as above). | |
804543b5 EZ |
1206 | This is the time of the last change to the file's access mode bits, |
1207 | its owner and group, and other information recorded in the filesystem | |
1208 | for the file, beyond the file's contents. | |
b8d4c8d0 GM |
1209 | |
1210 | @item | |
1211 | The size of the file in bytes. If the size is too large to fit in a | |
1212 | Lisp integer, this is a floating point number. | |
1213 | ||
1214 | @item | |
1215 | The file's modes, as a string of ten letters or dashes, | |
1216 | as in @samp{ls -l}. | |
1217 | ||
1218 | @item | |
1219 | @code{t} if the file's @acronym{GID} would change if file were | |
1220 | deleted and recreated; @code{nil} otherwise. | |
1221 | ||
1222 | @item | |
804543b5 EZ |
1223 | The file's inode number. If possible, this is an integer. If the |
1224 | inode number is too large to be represented as an integer in Emacs | |
001903b5 PE |
1225 | Lisp but dividing it by @math{2^16} yields a representable integer, |
1226 | then the value has the | |
804543b5 | 1227 | form @code{(@var{high} . @var{low})}, where @var{low} holds the low 16 |
001903b5 | 1228 | bits. If the inode number is too wide for even that, the value is of the form |
804543b5 | 1229 | @code{(@var{high} @var{middle} . @var{low})}, where @code{high} holds |
001903b5 | 1230 | the high bits, @var{middle} the middle 24 bits, and @var{low} the low |
804543b5 | 1231 | 16 bits. |
b8d4c8d0 GM |
1232 | |
1233 | @item | |
804543b5 EZ |
1234 | The filesystem number of the device that the file is on. Depending on |
1235 | the magnitude of the value, this can be either an integer or a cons | |
1236 | cell, in the same manner as the inode number. This element and the | |
1237 | file's inode number together give enough information to distinguish | |
1238 | any two files on the system---no two files can have the same values | |
1239 | for both of these numbers. | |
b8d4c8d0 GM |
1240 | @end enumerate |
1241 | ||
1242 | For example, here are the file attributes for @file{files.texi}: | |
1243 | ||
1244 | @example | |
1245 | @group | |
1246 | (file-attributes "files.texi" 'string) | |
1247 | @result{} (nil 1 "lh" "users" | |
804543b5 EZ |
1248 | (19145 42977) |
1249 | (19141 59576) | |
1250 | (18340 17300) | |
1251 | 122295 "-rw-rw-rw-" | |
1252 | nil (5888 2 . 43978) | |
1253 | (15479 . 46724)) | |
b8d4c8d0 GM |
1254 | @end group |
1255 | @end example | |
1256 | ||
1257 | @noindent | |
1258 | and here is how the result is interpreted: | |
1259 | ||
1260 | @table @code | |
1261 | @item nil | |
1262 | is neither a directory nor a symbolic link. | |
1263 | ||
1264 | @item 1 | |
1265 | has only one name (the name @file{files.texi} in the current default | |
1266 | directory). | |
1267 | ||
1268 | @item "lh" | |
1269 | is owned by the user with name "lh". | |
1270 | ||
1271 | @item "users" | |
1272 | is in the group with name "users". | |
1273 | ||
804543b5 EZ |
1274 | @item (19145 42977) |
1275 | was last accessed on Oct 5 2009, at 10:01:37. | |
b8d4c8d0 | 1276 | |
804543b5 EZ |
1277 | @item (19141 59576) |
1278 | last had its contents modified on Oct 2 2009, at 13:49:12. | |
b8d4c8d0 | 1279 | |
804543b5 EZ |
1280 | @item (18340 17300) |
1281 | last had its status changed on Feb 2 2008, at 12:19:00. | |
b8d4c8d0 | 1282 | |
804543b5 EZ |
1283 | @item 122295 |
1284 | is 122295 bytes long. (It may not contain 122295 characters, though, | |
1285 | if some of the bytes belong to multibyte sequences, and also if the | |
1286 | end-of-line format is CR-LF.) | |
b8d4c8d0 GM |
1287 | |
1288 | @item "-rw-rw-rw-" | |
1289 | has a mode of read and write access for the owner, group, and world. | |
1290 | ||
1291 | @item nil | |
1292 | would retain the same @acronym{GID} if it were recreated. | |
1293 | ||
804543b5 EZ |
1294 | @item (5888 2 . 43978) |
1295 | has an inode number of 6473924464520138. | |
1296 | ||
1297 | @item (15479 . 46724) | |
1298 | is on the file-system device whose number is 1014478468. | |
b8d4c8d0 GM |
1299 | @end table |
1300 | @end defun | |
1301 | ||
2aa8ea6e CY |
1302 | @cindex MS-DOS and file modes |
1303 | @cindex file modes and MS-DOS | |
1304 | On MS-DOS, there is no such thing as an ``executable'' file mode bit. | |
1305 | So Emacs considers a file executable if its name ends in one of the | |
1306 | standard executable extensions, such as @file{.com}, @file{.bat}, | |
1307 | @file{.exe}, and some others. Files that begin with the Unix-standard | |
1308 | @samp{#!} signature, such as shell and Perl scripts, are also considered | |
1309 | as executable files. This is reflected in the values returned by | |
1310 | @code{file-modes} and @code{file-attributes}. Directories are also | |
1311 | reported with executable bit set, for compatibility with Unix. | |
1312 | ||
b8d4c8d0 GM |
1313 | @node Locating Files |
1314 | @subsection How to Locate Files in Standard Places | |
1315 | @cindex locate file in path | |
1316 | @cindex find file in path | |
1317 | ||
1318 | This section explains how to search for a file in a list of | |
1319 | directories (a @dfn{path}). One example is when you need to look for | |
1320 | a program's executable file, e.g., to find out whether a given program | |
1321 | is installed on the user's system. Another example is the search for | |
1322 | Lisp libraries (@pxref{Library Search}). Such searches generally need | |
1323 | to try various possible file name extensions, in addition to various | |
1324 | possible directories. Emacs provides a function for such a | |
1325 | generalized search for a file. | |
1326 | ||
1327 | @defun locate-file filename path &optional suffixes predicate | |
1328 | This function searches for a file whose name is @var{filename} in a | |
1329 | list of directories given by @var{path}, trying the suffixes in | |
1330 | @var{suffixes}. If it finds such a file, it returns the full | |
1331 | @dfn{absolute file name} of the file (@pxref{Relative File Names}); | |
1332 | otherwise it returns @code{nil}. | |
1333 | ||
1334 | The optional argument @var{suffixes} gives the list of file-name | |
1335 | suffixes to append to @var{filename} when searching. | |
1336 | @code{locate-file} tries each possible directory with each of these | |
1337 | suffixes. If @var{suffixes} is @code{nil}, or @code{("")}, then there | |
1338 | are no suffixes, and @var{filename} is used only as-is. Typical | |
1339 | values of @var{suffixes} are @code{exec-suffixes} (@pxref{Subprocess | |
1340 | Creation, exec-suffixes}), @code{load-suffixes}, | |
1341 | @code{load-file-rep-suffixes} and the return value of the function | |
1342 | @code{get-load-suffixes} (@pxref{Load Suffixes}). | |
1343 | ||
1344 | Typical values for @var{path} are @code{exec-path} (@pxref{Subprocess | |
1345 | Creation, exec-path}) when looking for executable programs or | |
1346 | @code{load-path} (@pxref{Library Search, load-path}) when looking for | |
1347 | Lisp files. If @var{filename} is absolute, @var{path} has no effect, | |
1348 | but the suffixes in @var{suffixes} are still tried. | |
1349 | ||
1350 | The optional argument @var{predicate}, if non-@code{nil}, specifies | |
1351 | the predicate function to use for testing whether a candidate file is | |
1352 | suitable. The predicate function is passed the candidate file name as | |
1353 | its single argument. If @var{predicate} is @code{nil} or unspecified, | |
1354 | @code{locate-file} uses @code{file-readable-p} as the default | |
1355 | predicate. Useful non-default predicates include | |
1356 | @code{file-executable-p}, @code{file-directory-p}, and other | |
1357 | predicates described in @ref{Kinds of Files}. | |
1358 | ||
1359 | For compatibility, @var{predicate} can also be one of the symbols | |
1360 | @code{executable}, @code{readable}, @code{writable}, @code{exists}, or | |
1361 | a list of one or more of these symbols. | |
1362 | @end defun | |
1363 | ||
1364 | @defun executable-find program | |
1365 | This function searches for the executable file of the named | |
1366 | @var{program} and returns the full absolute name of the executable, | |
1367 | including its file-name extensions, if any. It returns @code{nil} if | |
1368 | the file is not found. The functions searches in all the directories | |
1369 | in @code{exec-path} and tries all the file-name extensions in | |
1370 | @code{exec-suffixes}. | |
1371 | @end defun | |
1372 | ||
1373 | @node Changing Files | |
1374 | @section Changing File Names and Attributes | |
1375 | @c @cindex renaming files Duplicates rename-file | |
1376 | @cindex copying files | |
1377 | @cindex deleting files | |
1378 | @cindex linking files | |
1379 | @cindex setting modes of files | |
1380 | ||
1381 | The functions in this section rename, copy, delete, link, and set the | |
1382 | modes of files. | |
1383 | ||
1384 | In the functions that have an argument @var{newname}, if a file by the | |
1385 | name of @var{newname} already exists, the actions taken depend on the | |
1386 | value of the argument @var{ok-if-already-exists}: | |
1387 | ||
1388 | @itemize @bullet | |
1389 | @item | |
1390 | Signal a @code{file-already-exists} error if | |
1391 | @var{ok-if-already-exists} is @code{nil}. | |
1392 | ||
1393 | @item | |
1394 | Request confirmation if @var{ok-if-already-exists} is a number. | |
1395 | ||
1396 | @item | |
1397 | Replace the old file without confirmation if @var{ok-if-already-exists} | |
1398 | is any other value. | |
1399 | @end itemize | |
1400 | ||
1401 | The next four commands all recursively follow symbolic links at all | |
1402 | levels of parent directories for their first argument, but, if that | |
1403 | argument is itself a symbolic link, then only @code{copy-file} | |
1404 | replaces it with its (recursive) target. | |
1405 | ||
1406 | @deffn Command add-name-to-file oldname newname &optional ok-if-already-exists | |
1407 | @cindex file with multiple names | |
1408 | @cindex file hard link | |
1409 | This function gives the file named @var{oldname} the additional name | |
1410 | @var{newname}. This means that @var{newname} becomes a new ``hard | |
1411 | link'' to @var{oldname}. | |
1412 | ||
1413 | In the first part of the following example, we list two files, | |
1414 | @file{foo} and @file{foo3}. | |
1415 | ||
1416 | @example | |
1417 | @group | |
1418 | % ls -li fo* | |
1419 | 81908 -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo | |
1420 | 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3 | |
1421 | @end group | |
1422 | @end example | |
1423 | ||
1424 | Now we create a hard link, by calling @code{add-name-to-file}, then list | |
1425 | the files again. This shows two names for one file, @file{foo} and | |
1426 | @file{foo2}. | |
1427 | ||
1428 | @example | |
1429 | @group | |
1430 | (add-name-to-file "foo" "foo2") | |
1431 | @result{} nil | |
1432 | @end group | |
1433 | ||
1434 | @group | |
1435 | % ls -li fo* | |
1436 | 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo | |
1437 | 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2 | |
1438 | 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3 | |
1439 | @end group | |
1440 | @end example | |
1441 | ||
1442 | Finally, we evaluate the following: | |
1443 | ||
1444 | @example | |
1445 | (add-name-to-file "foo" "foo3" t) | |
1446 | @end example | |
1447 | ||
1448 | @noindent | |
1449 | and list the files again. Now there are three names | |
1450 | for one file: @file{foo}, @file{foo2}, and @file{foo3}. The old | |
1451 | contents of @file{foo3} are lost. | |
1452 | ||
1453 | @example | |
1454 | @group | |
1455 | (add-name-to-file "foo1" "foo3") | |
1456 | @result{} nil | |
1457 | @end group | |
1458 | ||
1459 | @group | |
1460 | % ls -li fo* | |
1461 | 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo | |
1462 | 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2 | |
1463 | 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3 | |
1464 | @end group | |
1465 | @end example | |
1466 | ||
1467 | This function is meaningless on operating systems where multiple names | |
1468 | for one file are not allowed. Some systems implement multiple names | |
1469 | by copying the file instead. | |
1470 | ||
1471 | See also @code{file-nlinks} in @ref{File Attributes}. | |
1472 | @end deffn | |
1473 | ||
1474 | @deffn Command rename-file filename newname &optional ok-if-already-exists | |
1475 | This command renames the file @var{filename} as @var{newname}. | |
1476 | ||
1477 | If @var{filename} has additional names aside from @var{filename}, it | |
1478 | continues to have those names. In fact, adding the name @var{newname} | |
1479 | with @code{add-name-to-file} and then deleting @var{filename} has the | |
1480 | same effect as renaming, aside from momentary intermediate states. | |
1481 | @end deffn | |
1482 | ||
a49ca6b9 | 1483 | @deffn Command copy-file oldname newname &optional ok-if-exists time preserve-uid-gid preserve-selinux |
b8d4c8d0 GM |
1484 | This command copies the file @var{oldname} to @var{newname}. An |
1485 | error is signaled if @var{oldname} does not exist. If @var{newname} | |
1486 | names a directory, it copies @var{oldname} into that directory, | |
1487 | preserving its final name component. | |
1488 | ||
1489 | If @var{time} is non-@code{nil}, then this function gives the new file | |
1490 | the same last-modified time that the old one has. (This works on only | |
1491 | some operating systems.) If setting the time gets an error, | |
1492 | @code{copy-file} signals a @code{file-date-error} error. In an | |
1493 | interactive call, a prefix argument specifies a non-@code{nil} value | |
1494 | for @var{time}. | |
1495 | ||
1496 | This function copies the file modes, too. | |
1497 | ||
1498 | If argument @var{preserve-uid-gid} is @code{nil}, we let the operating | |
1499 | system decide the user and group ownership of the new file (this is | |
1500 | usually set to the user running Emacs). If @var{preserve-uid-gid} is | |
1501 | non-@code{nil}, we attempt to copy the user and group ownership of the | |
1502 | file. This works only on some operating systems, and only if you have | |
1503 | the correct permissions to do so. | |
a49ca6b9 GM |
1504 | |
1505 | @cindex SELinux | |
1506 | If the optional argument @var{preserve-selinux} is non-@code{nil}, we | |
1507 | attempt to copy the SELinux@footnote{@samp{Security-Enhanced Linux} | |
1508 | is a kernel feature that allows for finer access controls to be set on | |
1509 | files, and a system security policy to define who can access what. | |
1510 | The functions @code{file-selinux-context} and @code{set-file-selinux-context} | |
1511 | get and set, respectively, the SELinux properties of a file.} | |
1512 | context of the file. For this to work, Emacs must have been built | |
1513 | with libselinux support. | |
b8d4c8d0 GM |
1514 | @end deffn |
1515 | ||
1516 | @deffn Command make-symbolic-link filename newname &optional ok-if-exists | |
1517 | @pindex ln | |
1518 | @kindex file-already-exists | |
1519 | This command makes a symbolic link to @var{filename}, named | |
1520 | @var{newname}. This is like the shell command @samp{ln -s | |
1521 | @var{filename} @var{newname}}. | |
1522 | ||
1523 | This function is not available on systems that don't support symbolic | |
1524 | links. | |
1525 | @end deffn | |
1526 | ||
04e2ce72 CY |
1527 | @cindex trash |
1528 | @vindex delete-by-moving-to-trash | |
1529 | @deffn Command delete-file filename &optional trash | |
b8d4c8d0 | 1530 | @pindex rm |
04e2ce72 CY |
1531 | This command deletes the file @var{filename}. If the file has |
1532 | multiple names, it continues to exist under the other names. If | |
1533 | @var{filename} is a symbolic link, @code{delete-file} deletes only the | |
1534 | symbolic link and not its target (though it does follow symbolic links | |
1535 | at all levels of parent directories). | |
1536 | ||
1537 | A suitable kind of @code{file-error} error is signaled if the file | |
1538 | does not exist, or is not deletable. (On Unix and GNU/Linux, a file | |
1539 | is deletable if its directory is writable.) | |
1540 | ||
1541 | If the optional argument @var{trash} is non-@code{nil} and the | |
1542 | variable @code{delete-by-moving-to-trash} is non-@code{nil}, this | |
1543 | command moves the file into the system Trash instead of deleting it. | |
1544 | @xref{Misc File Ops,,Miscellaneous File Operations, emacs, The GNU | |
1545 | Emacs Manual}. When called interactively, @var{trash} is @code{t} if | |
1546 | no prefix argument is given, and @code{nil} otherwise. | |
b8d4c8d0 GM |
1547 | |
1548 | See also @code{delete-directory} in @ref{Create/Delete Dirs}. | |
1549 | @end deffn | |
1550 | ||
018a960d | 1551 | @deffn Command set-file-modes filename mode |
b8d4c8d0 | 1552 | This function sets mode bits of @var{filename} to @var{mode} (which |
018a960d EZ |
1553 | must be an integer when the function is called non-interactively). |
1554 | Only the low 12 bits of @var{mode} are used. | |
1555 | ||
1556 | Interactively, @var{mode} is read from the minibuffer using | |
1557 | @code{read-file-modes}, which accepts mode bits either as a number or | |
1558 | as a character string representing the mode bits symbolically. See | |
1559 | the description of @code{read-file-modes} below for the supported | |
1560 | forms of symbolic notation for mode bits. | |
1561 | ||
b8d4c8d0 GM |
1562 | This function recursively follows symbolic links at all levels for |
1563 | @var{filename}. | |
018a960d | 1564 | @end deffn |
b8d4c8d0 GM |
1565 | |
1566 | @c Emacs 19 feature | |
1567 | @defun set-default-file-modes mode | |
1568 | @cindex umask | |
1569 | This function sets the default file protection for new files created by | |
1570 | Emacs and its subprocesses. Every file created with Emacs initially has | |
1571 | this protection, or a subset of it (@code{write-region} will not give a | |
1572 | file execute permission even if the default file protection allows | |
1573 | execute permission). On Unix and GNU/Linux, the default protection is | |
1574 | the bitwise complement of the ``umask'' value. | |
1575 | ||
1576 | The argument @var{mode} must be an integer. On most systems, only the | |
1577 | low 9 bits of @var{mode} are meaningful. You can use the Lisp construct | |
8d80ef01 | 1578 | for octal numbers to enter @var{mode}; for example, |
b8d4c8d0 GM |
1579 | |
1580 | @example | |
8d80ef01 | 1581 | (set-default-file-modes #o644) |
b8d4c8d0 GM |
1582 | @end example |
1583 | ||
1584 | Saving a modified version of an existing file does not count as creating | |
1585 | the file; it preserves the existing file's mode, whatever that is. So | |
1586 | the default file protection has no effect. | |
1587 | @end defun | |
1588 | ||
1589 | @defun default-file-modes | |
1590 | This function returns the current default protection value. | |
1591 | @end defun | |
1592 | ||
018a960d EZ |
1593 | @defun read-file-modes &optional prompt base-file |
1594 | This function reads file mode bits from the minibuffer. The optional | |
1595 | argument @var{prompt} specifies a non-default prompt. Second optional | |
1596 | argument @var{base-file} is the name of a file on whose permissions to | |
1597 | base the mode bits that this function returns, if what the user types | |
1598 | specifies mode bits relative to permissions of an existing file. | |
1599 | ||
1600 | If user input represents an octal number, this function returns that | |
1601 | number. If it is a complete symbolic specification of mode bits, as | |
1602 | in @code{"u=rwx"}, the function converts it to the equivalent numeric | |
1603 | value using @code{file-modes-symbolic-to-number} and returns the | |
1604 | result. If the specification is relative, as in @code{"o+g"}, then | |
1586be92 | 1605 | the permissions on which the specification is based are taken from the |
018a960d EZ |
1606 | mode bits of @var{base-file}. If @var{base-file} is omitted or |
1607 | @code{nil}, the function uses @code{0} as the base mode bits. The | |
1608 | complete and relative specifications can be combined, as in | |
1609 | @code{"u+r,g+rx,o+r,g-w"}. @xref{File Permissions,,, coreutils, The | |
1610 | @sc{gnu} @code{Coreutils} Manual}, for detailed description of | |
1611 | symbolic mode bits specifications. | |
1612 | @end defun | |
1613 | ||
61331bf3 | 1614 | @defun file-modes-symbolic-to-number modes &optional base-modes |
018a960d EZ |
1615 | This subroutine converts a symbolic specification of file mode bits in |
1616 | @var{modes} into the equivalent numeric value. If the symbolic | |
1617 | specification is based on an existing file, that file's mode bits are | |
1618 | taken from the optional argument @var{base-modes}; if that argument is | |
4990219b CY |
1619 | omitted or @code{nil}, it defaults to zero, i.e.@: no access rights at |
1620 | all. | |
61331bf3 | 1621 | @end defun |
018a960d | 1622 | |
b8d4c8d0 GM |
1623 | @defun set-file-times filename &optional time |
1624 | This function sets the access and modification times of @var{filename} | |
1625 | to @var{time}. The return value is @code{t} if the times are successfully | |
1626 | set, otherwise it is @code{nil}. @var{time} defaults to the current | |
1627 | time and must be in the format returned by @code{current-time} | |
1628 | (@pxref{Time of Day}). | |
1629 | @end defun | |
1630 | ||
b8d4c8d0 GM |
1631 | @node File Names |
1632 | @section File Names | |
1633 | @cindex file names | |
1634 | ||
1635 | Files are generally referred to by their names, in Emacs as elsewhere. | |
1636 | File names in Emacs are represented as strings. The functions that | |
1637 | operate on a file all expect a file name argument. | |
1638 | ||
1639 | In addition to operating on files themselves, Emacs Lisp programs | |
1640 | often need to operate on file names; i.e., to take them apart and to use | |
1641 | part of a name to construct related file names. This section describes | |
1642 | how to manipulate file names. | |
1643 | ||
1644 | The functions in this section do not actually access files, so they | |
1645 | can operate on file names that do not refer to an existing file or | |
1646 | directory. | |
1647 | ||
1648 | On MS-DOS and MS-Windows, these functions (like the function that | |
1649 | actually operate on files) accept MS-DOS or MS-Windows file-name syntax, | |
1650 | where backslashes separate the components, as well as Unix syntax; but | |
7c2fb837 DN |
1651 | they always return Unix syntax. This enables Lisp programs to specify |
1652 | file names in Unix syntax and work properly on all systems without | |
1653 | change. | |
b8d4c8d0 GM |
1654 | |
1655 | @menu | |
1656 | * File Name Components:: The directory part of a file name, and the rest. | |
1657 | * Relative File Names:: Some file names are relative to a current directory. | |
1658 | * Directory Names:: A directory's name as a directory | |
1659 | is different from its name as a file. | |
1660 | * File Name Expansion:: Converting relative file names to absolute ones. | |
1661 | * Unique File Names:: Generating names for temporary files. | |
1662 | * File Name Completion:: Finding the completions for a given file name. | |
1663 | * Standard File Names:: If your package uses a fixed file name, | |
1664 | how to handle various operating systems simply. | |
1665 | @end menu | |
1666 | ||
1667 | @node File Name Components | |
1668 | @subsection File Name Components | |
1669 | @cindex directory part (of file name) | |
1670 | @cindex nondirectory part (of file name) | |
1671 | @cindex version number (in file name) | |
1672 | ||
1673 | The operating system groups files into directories. To specify a | |
1674 | file, you must specify the directory and the file's name within that | |
1675 | directory. Therefore, Emacs considers a file name as having two main | |
1676 | parts: the @dfn{directory name} part, and the @dfn{nondirectory} part | |
1677 | (or @dfn{file name within the directory}). Either part may be empty. | |
1678 | Concatenating these two parts reproduces the original file name. | |
1679 | ||
1680 | On most systems, the directory part is everything up to and including | |
1681 | the last slash (backslash is also allowed in input on MS-DOS or | |
7c2fb837 | 1682 | MS-Windows); the nondirectory part is the rest. |
b8d4c8d0 GM |
1683 | |
1684 | For some purposes, the nondirectory part is further subdivided into | |
1685 | the name proper and the @dfn{version number}. On most systems, only | |
7c2fb837 | 1686 | backup files have version numbers in their names. |
b8d4c8d0 GM |
1687 | |
1688 | @defun file-name-directory filename | |
1689 | This function returns the directory part of @var{filename}, as a | |
1690 | directory name (@pxref{Directory Names}), or @code{nil} if | |
1691 | @var{filename} does not include a directory part. | |
1692 | ||
1693 | On GNU and Unix systems, a string returned by this function always | |
7c2fb837 | 1694 | ends in a slash. On MS-DOS it can also end in a colon. |
b8d4c8d0 GM |
1695 | |
1696 | @example | |
1697 | @group | |
1698 | (file-name-directory "lewis/foo") ; @r{Unix example} | |
1699 | @result{} "lewis/" | |
1700 | @end group | |
1701 | @group | |
1702 | (file-name-directory "foo") ; @r{Unix example} | |
1703 | @result{} nil | |
1704 | @end group | |
b8d4c8d0 GM |
1705 | @end example |
1706 | @end defun | |
1707 | ||
1708 | @defun file-name-nondirectory filename | |
1709 | This function returns the nondirectory part of @var{filename}. | |
1710 | ||
1711 | @example | |
1712 | @group | |
1713 | (file-name-nondirectory "lewis/foo") | |
1714 | @result{} "foo" | |
1715 | @end group | |
1716 | @group | |
1717 | (file-name-nondirectory "foo") | |
1718 | @result{} "foo" | |
1719 | @end group | |
1720 | @group | |
1721 | (file-name-nondirectory "lewis/") | |
1722 | @result{} "" | |
1723 | @end group | |
b8d4c8d0 GM |
1724 | @end example |
1725 | @end defun | |
1726 | ||
1727 | @defun file-name-sans-versions filename &optional keep-backup-version | |
1728 | This function returns @var{filename} with any file version numbers, | |
1729 | backup version numbers, or trailing tildes discarded. | |
1730 | ||
1731 | If @var{keep-backup-version} is non-@code{nil}, then true file version | |
1732 | numbers understood as such by the file system are discarded from the | |
1733 | return value, but backup version numbers are kept. | |
1734 | ||
1735 | @example | |
1736 | @group | |
1737 | (file-name-sans-versions "~rms/foo.~1~") | |
1738 | @result{} "~rms/foo" | |
1739 | @end group | |
1740 | @group | |
1741 | (file-name-sans-versions "~rms/foo~") | |
1742 | @result{} "~rms/foo" | |
1743 | @end group | |
1744 | @group | |
1745 | (file-name-sans-versions "~rms/foo") | |
1746 | @result{} "~rms/foo" | |
1747 | @end group | |
b8d4c8d0 GM |
1748 | @end example |
1749 | @end defun | |
1750 | ||
1751 | @defun file-name-extension filename &optional period | |
1752 | This function returns @var{filename}'s final ``extension,'' if any, | |
1753 | after applying @code{file-name-sans-versions} to remove any | |
1754 | version/backup part. The extension, in a file name, is the part that | |
4c565c5c LK |
1755 | follows the last @samp{.} in the last name component (minus any |
1756 | version/backup part). | |
b8d4c8d0 GM |
1757 | |
1758 | This function returns @code{nil} for extensionless file names such as | |
1759 | @file{foo}. It returns @code{""} for null extensions, as in | |
1760 | @file{foo.}. If the last component of a file name begins with a | |
1761 | @samp{.}, that @samp{.} doesn't count as the beginning of an | |
1762 | extension. Thus, @file{.emacs}'s ``extension'' is @code{nil}, not | |
1763 | @samp{.emacs}. | |
1764 | ||
1765 | If @var{period} is non-@code{nil}, then the returned value includes | |
1766 | the period that delimits the extension, and if @var{filename} has no | |
1767 | extension, the value is @code{""}. | |
1768 | @end defun | |
1769 | ||
1770 | @defun file-name-sans-extension filename | |
1771 | This function returns @var{filename} minus its extension, if any. The | |
1772 | version/backup part, if present, is only removed if the file has an | |
1773 | extension. For example, | |
1774 | ||
1775 | @example | |
1776 | (file-name-sans-extension "foo.lose.c") | |
1777 | @result{} "foo.lose" | |
1778 | (file-name-sans-extension "big.hack/foo") | |
1779 | @result{} "big.hack/foo" | |
1780 | (file-name-sans-extension "/my/home/.emacs") | |
1781 | @result{} "/my/home/.emacs" | |
1782 | (file-name-sans-extension "/my/home/.emacs.el") | |
1783 | @result{} "/my/home/.emacs" | |
1784 | (file-name-sans-extension "~/foo.el.~3~") | |
1785 | @result{} "~/foo" | |
1786 | (file-name-sans-extension "~/foo.~3~") | |
1787 | @result{} "~/foo.~3~" | |
1788 | @end example | |
1789 | ||
1790 | Note that the @samp{.~3~} in the two last examples is the backup part, | |
1791 | not an extension. | |
1792 | @end defun | |
1793 | ||
b8d4c8d0 GM |
1794 | |
1795 | @node Relative File Names | |
1796 | @subsection Absolute and Relative File Names | |
1797 | @cindex absolute file name | |
1798 | @cindex relative file name | |
1799 | ||
1800 | All the directories in the file system form a tree starting at the | |
1801 | root directory. A file name can specify all the directory names | |
1802 | starting from the root of the tree; then it is called an @dfn{absolute} | |
1803 | file name. Or it can specify the position of the file in the tree | |
1804 | relative to a default directory; then it is called a @dfn{relative} file | |
1805 | name. On Unix and GNU/Linux, an absolute file name starts with a slash | |
1806 | or a tilde (@samp{~}), and a relative one does not. On MS-DOS and | |
1807 | MS-Windows, an absolute file name starts with a slash or a backslash, or | |
1808 | with a drive specification @samp{@var{x}:/}, where @var{x} is the | |
7c2fb837 | 1809 | @dfn{drive letter}. |
b8d4c8d0 GM |
1810 | |
1811 | @defun file-name-absolute-p filename | |
1812 | This function returns @code{t} if file @var{filename} is an absolute | |
7c2fb837 | 1813 | file name, @code{nil} otherwise. |
b8d4c8d0 GM |
1814 | |
1815 | @example | |
1816 | @group | |
1817 | (file-name-absolute-p "~rms/foo") | |
1818 | @result{} t | |
1819 | @end group | |
1820 | @group | |
1821 | (file-name-absolute-p "rms/foo") | |
1822 | @result{} nil | |
1823 | @end group | |
1824 | @group | |
1825 | (file-name-absolute-p "/user/rms/foo") | |
1826 | @result{} t | |
1827 | @end group | |
1828 | @end example | |
1829 | @end defun | |
1830 | ||
1831 | Given a possibly relative file name, you can convert it to an | |
1832 | absolute name using @code{expand-file-name} (@pxref{File Name | |
1833 | Expansion}). This function converts absolute file names to relative | |
1834 | names: | |
1835 | ||
1836 | @defun file-relative-name filename &optional directory | |
1837 | This function tries to return a relative name that is equivalent to | |
1838 | @var{filename}, assuming the result will be interpreted relative to | |
1839 | @var{directory} (an absolute directory name or directory file name). | |
1840 | If @var{directory} is omitted or @code{nil}, it defaults to the | |
1841 | current buffer's default directory. | |
1842 | ||
1843 | On some operating systems, an absolute file name begins with a device | |
1844 | name. On such systems, @var{filename} has no relative equivalent based | |
1845 | on @var{directory} if they start with two different device names. In | |
1846 | this case, @code{file-relative-name} returns @var{filename} in absolute | |
1847 | form. | |
1848 | ||
1849 | @example | |
1850 | (file-relative-name "/foo/bar" "/foo/") | |
1851 | @result{} "bar" | |
1852 | (file-relative-name "/foo/bar" "/hack/") | |
1853 | @result{} "../foo/bar" | |
1854 | @end example | |
1855 | @end defun | |
1856 | ||
1857 | @node Directory Names | |
1858 | @comment node-name, next, previous, up | |
1859 | @subsection Directory Names | |
1860 | @cindex directory name | |
1861 | @cindex file name of directory | |
1862 | ||
1863 | A @dfn{directory name} is the name of a directory. A directory is | |
1864 | actually a kind of file, so it has a file name, which is related to | |
1865 | the directory name but not identical to it. (This is not quite the | |
1866 | same as the usual Unix terminology.) These two different names for | |
1867 | the same entity are related by a syntactic transformation. On GNU and | |
1868 | Unix systems, this is simple: a directory name ends in a slash, | |
7c2fb837 DN |
1869 | whereas the directory's name as a file lacks that slash. On MS-DOS |
1870 | the relationship is more complicated. | |
b8d4c8d0 GM |
1871 | |
1872 | The difference between a directory name and its name as a file is | |
1873 | subtle but crucial. When an Emacs variable or function argument is | |
1874 | described as being a directory name, a file name of a directory is not | |
1875 | acceptable. When @code{file-name-directory} returns a string, that is | |
1876 | always a directory name. | |
1877 | ||
1878 | The following two functions convert between directory names and file | |
1879 | names. They do nothing special with environment variable substitutions | |
1880 | such as @samp{$HOME}, and the constructs @samp{~}, @samp{.} and @samp{..}. | |
1881 | ||
1882 | @defun file-name-as-directory filename | |
1883 | This function returns a string representing @var{filename} in a form | |
1884 | that the operating system will interpret as the name of a directory. On | |
1885 | most systems, this means appending a slash to the string (if it does not | |
7c2fb837 | 1886 | already end in one). |
b8d4c8d0 GM |
1887 | |
1888 | @example | |
1889 | @group | |
1890 | (file-name-as-directory "~rms/lewis") | |
1891 | @result{} "~rms/lewis/" | |
1892 | @end group | |
1893 | @end example | |
1894 | @end defun | |
1895 | ||
1896 | @defun directory-file-name dirname | |
1897 | This function returns a string representing @var{dirname} in a form that | |
1898 | the operating system will interpret as the name of a file. On most | |
1899 | systems, this means removing the final slash (or backslash) from the | |
7c2fb837 | 1900 | string. |
b8d4c8d0 GM |
1901 | |
1902 | @example | |
1903 | @group | |
1904 | (directory-file-name "~lewis/") | |
1905 | @result{} "~lewis" | |
1906 | @end group | |
1907 | @end example | |
1908 | @end defun | |
1909 | ||
1910 | Given a directory name, you can combine it with a relative file name | |
1911 | using @code{concat}: | |
1912 | ||
1913 | @example | |
1914 | (concat @var{dirname} @var{relfile}) | |
1915 | @end example | |
1916 | ||
1917 | @noindent | |
1918 | Be sure to verify that the file name is relative before doing that. | |
1919 | If you use an absolute file name, the results could be syntactically | |
1920 | invalid or refer to the wrong file. | |
1921 | ||
1922 | If you want to use a directory file name in making such a | |
1923 | combination, you must first convert it to a directory name using | |
1924 | @code{file-name-as-directory}: | |
1925 | ||
1926 | @example | |
1927 | (concat (file-name-as-directory @var{dirfile}) @var{relfile}) | |
1928 | @end example | |
1929 | ||
1930 | @noindent | |
1931 | Don't try concatenating a slash by hand, as in | |
1932 | ||
1933 | @example | |
1934 | ;;; @r{Wrong!} | |
1935 | (concat @var{dirfile} "/" @var{relfile}) | |
1936 | @end example | |
1937 | ||
1938 | @noindent | |
1939 | because this is not portable. Always use | |
1940 | @code{file-name-as-directory}. | |
1941 | ||
b8d4c8d0 GM |
1942 | To convert a directory name to its abbreviation, use this |
1943 | function: | |
1944 | ||
1945 | @defun abbreviate-file-name filename | |
1946 | @anchor{Definition of abbreviate-file-name} | |
362b9d48 GM |
1947 | This function returns an abbreviated form of @var{filename}. It |
1948 | applies the abbreviations specified in @code{directory-abbrev-alist} | |
1949 | (@pxref{File Aliases,,File Aliases, emacs, The GNU Emacs Manual}), | |
1950 | then substitutes @samp{~} for the user's home directory if the | |
1951 | argument names a file in the home directory or one of its | |
1952 | subdirectories. If the home directory is a root directory, it is not | |
1953 | replaced with @samp{~}, because this does not make the result shorter | |
1954 | on many systems. | |
1955 | ||
1956 | You can use this function for directory names and for file names, | |
1957 | because it recognizes abbreviations even as part of the name. | |
b8d4c8d0 GM |
1958 | @end defun |
1959 | ||
1960 | @node File Name Expansion | |
1961 | @subsection Functions that Expand Filenames | |
1962 | @cindex expansion of file names | |
1963 | ||
1964 | @dfn{Expansion} of a file name means converting a relative file name | |
1965 | to an absolute one. Since this is done relative to a default directory, | |
1966 | you must specify the default directory name as well as the file name to | |
1967 | be expanded. Expansion also simplifies file names by eliminating | |
1968 | redundancies such as @file{./} and @file{@var{name}/../}. | |
1969 | ||
1970 | @defun expand-file-name filename &optional directory | |
1971 | This function converts @var{filename} to an absolute file name. If | |
1972 | @var{directory} is supplied, it is the default directory to start with | |
1973 | if @var{filename} is relative. (The value of @var{directory} should | |
1974 | itself be an absolute directory name or directory file name; it may | |
1975 | start with @samp{~}.) Otherwise, the current buffer's value of | |
1976 | @code{default-directory} is used. For example: | |
1977 | ||
1978 | @example | |
1979 | @group | |
1980 | (expand-file-name "foo") | |
1981 | @result{} "/xcssun/users/rms/lewis/foo" | |
1982 | @end group | |
1983 | @group | |
1984 | (expand-file-name "../foo") | |
1985 | @result{} "/xcssun/users/rms/foo" | |
1986 | @end group | |
1987 | @group | |
1988 | (expand-file-name "foo" "/usr/spool/") | |
1989 | @result{} "/usr/spool/foo" | |
1990 | @end group | |
1991 | @group | |
1992 | (expand-file-name "$HOME/foo") | |
1993 | @result{} "/xcssun/users/rms/lewis/$HOME/foo" | |
1994 | @end group | |
1995 | @end example | |
1996 | ||
1997 | If the part of the combined file name before the first slash is | |
1998 | @samp{~}, it expands to the value of the @env{HOME} environment | |
1999 | variable (usually your home directory). If the part before the first | |
2000 | slash is @samp{~@var{user}} and if @var{user} is a valid login name, | |
2001 | it expands to @var{user}'s home directory. | |
2002 | ||
2003 | Filenames containing @samp{.} or @samp{..} are simplified to their | |
2004 | canonical form: | |
2005 | ||
2006 | @example | |
2007 | @group | |
2008 | (expand-file-name "bar/../foo") | |
2009 | @result{} "/xcssun/users/rms/lewis/foo" | |
2010 | @end group | |
2011 | @end example | |
2012 | ||
2013 | In some cases, a leading @samp{..} component can remain in the output: | |
2014 | ||
2015 | @example | |
2016 | @group | |
2017 | (expand-file-name "../home" "/") | |
2018 | @result{} "/../home" | |
2019 | @end group | |
2020 | @end example | |
2021 | ||
2022 | @noindent | |
2023 | This is for the sake of filesystems that have the concept of a | |
2024 | ``superroot'' above the root directory @file{/}. On other filesystems, | |
2025 | @file{/../} is interpreted exactly the same as @file{/}. | |
2026 | ||
2027 | Note that @code{expand-file-name} does @emph{not} expand environment | |
2028 | variables; only @code{substitute-in-file-name} does that. | |
2029 | ||
2030 | Note also that @code{expand-file-name} does not follow symbolic links | |
2031 | at any level. This results in a difference between the way | |
2032 | @code{file-truename} and @code{expand-file-name} treat @samp{..}. | |
2033 | Assuming that @samp{/tmp/bar} is a symbolic link to the directory | |
2034 | @samp{/tmp/foo/bar} we get: | |
2035 | ||
2036 | @example | |
2037 | @group | |
2038 | (file-truename "/tmp/bar/../myfile") | |
2039 | @result{} "/tmp/foo/myfile" | |
2040 | @end group | |
2041 | @group | |
2042 | (expand-file-name "/tmp/bar/../myfile") | |
2043 | @result{} "/tmp/myfile" | |
2044 | @end group | |
2045 | @end example | |
2046 | ||
2047 | If you may need to follow symbolic links preceding @samp{..}, you | |
2048 | should make sure to call @code{file-truename} without prior direct or | |
2049 | indirect calls to @code{expand-file-name}. @xref{Truenames}. | |
2050 | @end defun | |
2051 | ||
2052 | @defvar default-directory | |
2053 | The value of this buffer-local variable is the default directory for the | |
2054 | current buffer. It should be an absolute directory name; it may start | |
2055 | with @samp{~}. This variable is buffer-local in every buffer. | |
2056 | ||
2057 | @code{expand-file-name} uses the default directory when its second | |
2058 | argument is @code{nil}. | |
2059 | ||
7c2fb837 | 2060 | The value is always a string ending with a slash. |
b8d4c8d0 GM |
2061 | |
2062 | @example | |
2063 | @group | |
2064 | default-directory | |
2065 | @result{} "/user/lewis/manual/" | |
2066 | @end group | |
2067 | @end example | |
2068 | @end defvar | |
2069 | ||
2070 | @defun substitute-in-file-name filename | |
2071 | @anchor{Definition of substitute-in-file-name} | |
2072 | This function replaces environment variable references in | |
2073 | @var{filename} with the environment variable values. Following | |
2074 | standard Unix shell syntax, @samp{$} is the prefix to substitute an | |
2075 | environment variable value. If the input contains @samp{$$}, that is | |
2076 | converted to @samp{$}; this gives the user a way to ``quote'' a | |
2077 | @samp{$}. | |
2078 | ||
2079 | The environment variable name is the series of alphanumeric characters | |
2080 | (including underscores) that follow the @samp{$}. If the character following | |
2081 | the @samp{$} is a @samp{@{}, then the variable name is everything up to the | |
2082 | matching @samp{@}}. | |
2083 | ||
2084 | Calling @code{substitute-in-file-name} on output produced by | |
2085 | @code{substitute-in-file-name} tends to give incorrect results. For | |
2086 | instance, use of @samp{$$} to quote a single @samp{$} won't work | |
2087 | properly, and @samp{$} in an environment variable's value could lead | |
2088 | to repeated substitution. Therefore, programs that call this function | |
2089 | and put the output where it will be passed to this function need to | |
2090 | double all @samp{$} characters to prevent subsequent incorrect | |
2091 | results. | |
2092 | ||
2093 | @c Wordy to avoid overfull hbox. --rjc 15mar92 | |
2094 | Here we assume that the environment variable @code{HOME}, which holds | |
2095 | the user's home directory name, has value @samp{/xcssun/users/rms}. | |
2096 | ||
2097 | @example | |
2098 | @group | |
2099 | (substitute-in-file-name "$HOME/foo") | |
2100 | @result{} "/xcssun/users/rms/foo" | |
2101 | @end group | |
2102 | @end example | |
2103 | ||
2104 | After substitution, if a @samp{~} or a @samp{/} appears immediately | |
2105 | after another @samp{/}, the function discards everything before it (up | |
2106 | through the immediately preceding @samp{/}). | |
2107 | ||
2108 | @example | |
2109 | @group | |
2110 | (substitute-in-file-name "bar/~/foo") | |
2111 | @result{} "~/foo" | |
2112 | @end group | |
2113 | @group | |
2114 | (substitute-in-file-name "/usr/local/$HOME/foo") | |
2115 | @result{} "/xcssun/users/rms/foo" | |
2116 | ;; @r{@file{/usr/local/} has been discarded.} | |
2117 | @end group | |
2118 | @end example | |
2119 | ||
b8d4c8d0 GM |
2120 | @end defun |
2121 | ||
2122 | @node Unique File Names | |
2123 | @subsection Generating Unique File Names | |
2124 | ||
2125 | Some programs need to write temporary files. Here is the usual way to | |
2126 | construct a name for such a file: | |
2127 | ||
2128 | @example | |
2129 | (make-temp-file @var{name-of-application}) | |
2130 | @end example | |
2131 | ||
2132 | @noindent | |
2133 | The job of @code{make-temp-file} is to prevent two different users or | |
2134 | two different jobs from trying to use the exact same file name. | |
2135 | ||
2136 | @defun make-temp-file prefix &optional dir-flag suffix | |
2137 | This function creates a temporary file and returns its name. Emacs | |
2138 | creates the temporary file's name by adding to @var{prefix} some | |
2139 | random characters that are different in each Emacs job. The result is | |
2140 | guaranteed to be a newly created empty file. On MS-DOS, this function | |
2141 | can truncate the @var{string} prefix to fit into the 8+3 file-name | |
2142 | limits. If @var{prefix} is a relative file name, it is expanded | |
2143 | against @code{temporary-file-directory}. | |
2144 | ||
2145 | @example | |
2146 | @group | |
2147 | (make-temp-file "foo") | |
2148 | @result{} "/tmp/foo232J6v" | |
2149 | @end group | |
2150 | @end example | |
2151 | ||
2152 | When @code{make-temp-file} returns, the file has been created and is | |
2153 | empty. At that point, you should write the intended contents into the | |
2154 | file. | |
2155 | ||
2156 | If @var{dir-flag} is non-@code{nil}, @code{make-temp-file} creates an | |
2157 | empty directory instead of an empty file. It returns the file name, | |
2158 | not the directory name, of that directory. @xref{Directory Names}. | |
2159 | ||
2160 | If @var{suffix} is non-@code{nil}, @code{make-temp-file} adds it at | |
2161 | the end of the file name. | |
2162 | ||
2163 | To prevent conflicts among different libraries running in the same | |
2164 | Emacs, each Lisp program that uses @code{make-temp-file} should have its | |
2165 | own @var{prefix}. The number added to the end of @var{prefix} | |
2166 | distinguishes between the same application running in different Emacs | |
2167 | jobs. Additional added characters permit a large number of distinct | |
2168 | names even in one Emacs job. | |
2169 | @end defun | |
2170 | ||
2171 | The default directory for temporary files is controlled by the | |
2172 | variable @code{temporary-file-directory}. This variable gives the user | |
2173 | a uniform way to specify the directory for all temporary files. Some | |
2174 | programs use @code{small-temporary-file-directory} instead, if that is | |
2175 | non-@code{nil}. To use it, you should expand the prefix against | |
2176 | the proper directory before calling @code{make-temp-file}. | |
2177 | ||
2178 | In older Emacs versions where @code{make-temp-file} does not exist, | |
2179 | you should use @code{make-temp-name} instead: | |
2180 | ||
2181 | @example | |
2182 | (make-temp-name | |
2183 | (expand-file-name @var{name-of-application} | |
2184 | temporary-file-directory)) | |
2185 | @end example | |
2186 | ||
2187 | @defun make-temp-name string | |
2188 | This function generates a string that can be used as a unique file | |
2189 | name. The name starts with @var{string}, and has several random | |
2190 | characters appended to it, which are different in each Emacs job. It | |
2191 | is like @code{make-temp-file} except that it just constructs a name, | |
2192 | and does not create a file. Another difference is that @var{string} | |
2193 | should be an absolute file name. On MS-DOS, this function can | |
2194 | truncate the @var{string} prefix to fit into the 8+3 file-name limits. | |
2195 | @end defun | |
2196 | ||
01f17ae2 | 2197 | @defopt temporary-file-directory |
b8d4c8d0 GM |
2198 | @cindex @code{TMPDIR} environment variable |
2199 | @cindex @code{TMP} environment variable | |
2200 | @cindex @code{TEMP} environment variable | |
2201 | This variable specifies the directory name for creating temporary files. | |
2202 | Its value should be a directory name (@pxref{Directory Names}), but it | |
2203 | is good for Lisp programs to cope if the value is a directory's file | |
2204 | name instead. Using the value as the second argument to | |
2205 | @code{expand-file-name} is a good way to achieve that. | |
2206 | ||
2207 | The default value is determined in a reasonable way for your operating | |
2208 | system; it is based on the @code{TMPDIR}, @code{TMP} and @code{TEMP} | |
2209 | environment variables, with a fall-back to a system-dependent name if | |
2210 | none of these variables is defined. | |
2211 | ||
2212 | Even if you do not use @code{make-temp-file} to create the temporary | |
2213 | file, you should still use this variable to decide which directory to | |
2214 | put the file in. However, if you expect the file to be small, you | |
2215 | should use @code{small-temporary-file-directory} first if that is | |
2216 | non-@code{nil}. | |
01f17ae2 | 2217 | @end defopt |
b8d4c8d0 | 2218 | |
01f17ae2 | 2219 | @defopt small-temporary-file-directory |
b8d4c8d0 GM |
2220 | This variable specifies the directory name for |
2221 | creating certain temporary files, which are likely to be small. | |
2222 | ||
2223 | If you want to write a temporary file which is likely to be small, you | |
2224 | should compute the directory like this: | |
2225 | ||
2226 | @example | |
2227 | (make-temp-file | |
2228 | (expand-file-name @var{prefix} | |
2229 | (or small-temporary-file-directory | |
2230 | temporary-file-directory))) | |
2231 | @end example | |
01f17ae2 | 2232 | @end defopt |
b8d4c8d0 GM |
2233 | |
2234 | @node File Name Completion | |
2235 | @subsection File Name Completion | |
2236 | @cindex file name completion subroutines | |
2237 | @cindex completion, file name | |
2238 | ||
2239 | This section describes low-level subroutines for completing a file | |
2240 | name. For higher level functions, see @ref{Reading File Names}. | |
2241 | ||
2242 | @defun file-name-all-completions partial-filename directory | |
2243 | This function returns a list of all possible completions for a file | |
2244 | whose name starts with @var{partial-filename} in directory | |
2245 | @var{directory}. The order of the completions is the order of the files | |
2246 | in the directory, which is unpredictable and conveys no useful | |
2247 | information. | |
2248 | ||
2249 | The argument @var{partial-filename} must be a file name containing no | |
2250 | directory part and no slash (or backslash on some systems). The current | |
2251 | buffer's default directory is prepended to @var{directory}, if | |
2252 | @var{directory} is not absolute. | |
2253 | ||
2254 | In the following example, suppose that @file{~rms/lewis} is the current | |
2255 | default directory, and has five files whose names begin with @samp{f}: | |
2256 | @file{foo}, @file{file~}, @file{file.c}, @file{file.c.~1~}, and | |
2257 | @file{file.c.~2~}.@refill | |
2258 | ||
2259 | @example | |
2260 | @group | |
2261 | (file-name-all-completions "f" "") | |
2262 | @result{} ("foo" "file~" "file.c.~2~" | |
2263 | "file.c.~1~" "file.c") | |
2264 | @end group | |
2265 | ||
2266 | @group | |
2267 | (file-name-all-completions "fo" "") | |
2268 | @result{} ("foo") | |
2269 | @end group | |
2270 | @end example | |
2271 | @end defun | |
2272 | ||
2273 | @defun file-name-completion filename directory &optional predicate | |
2274 | This function completes the file name @var{filename} in directory | |
2275 | @var{directory}. It returns the longest prefix common to all file names | |
2276 | in directory @var{directory} that start with @var{filename}. If | |
2277 | @var{predicate} is non-@code{nil} then it ignores possible completions | |
2278 | that don't satisfy @var{predicate}, after calling that function | |
2279 | with one argument, the expanded absolute file name. | |
2280 | ||
2281 | If only one match exists and @var{filename} matches it exactly, the | |
2282 | function returns @code{t}. The function returns @code{nil} if directory | |
2283 | @var{directory} contains no name starting with @var{filename}. | |
2284 | ||
2285 | In the following example, suppose that the current default directory | |
2286 | has five files whose names begin with @samp{f}: @file{foo}, | |
2287 | @file{file~}, @file{file.c}, @file{file.c.~1~}, and | |
2288 | @file{file.c.~2~}.@refill | |
2289 | ||
2290 | @example | |
2291 | @group | |
2292 | (file-name-completion "fi" "") | |
2293 | @result{} "file" | |
2294 | @end group | |
2295 | ||
2296 | @group | |
2297 | (file-name-completion "file.c.~1" "") | |
2298 | @result{} "file.c.~1~" | |
2299 | @end group | |
2300 | ||
2301 | @group | |
2302 | (file-name-completion "file.c.~1~" "") | |
2303 | @result{} t | |
2304 | @end group | |
2305 | ||
2306 | @group | |
2307 | (file-name-completion "file.c.~3" "") | |
2308 | @result{} nil | |
2309 | @end group | |
2310 | @end example | |
2311 | @end defun | |
2312 | ||
2313 | @defopt completion-ignored-extensions | |
2314 | @code{file-name-completion} usually ignores file names that end in any | |
2315 | string in this list. It does not ignore them when all the possible | |
2316 | completions end in one of these suffixes. This variable has no effect | |
2317 | on @code{file-name-all-completions}.@refill | |
2318 | ||
2319 | A typical value might look like this: | |
2320 | ||
2321 | @example | |
2322 | @group | |
2323 | completion-ignored-extensions | |
2324 | @result{} (".o" ".elc" "~" ".dvi") | |
2325 | @end group | |
2326 | @end example | |
2327 | ||
2328 | If an element of @code{completion-ignored-extensions} ends in a slash | |
2329 | @samp{/}, it signals a directory. The elements which do @emph{not} end | |
2330 | in a slash will never match a directory; thus, the above value will not | |
2331 | filter out a directory named @file{foo.elc}. | |
2332 | @end defopt | |
2333 | ||
2334 | @node Standard File Names | |
2335 | @subsection Standard File Names | |
2336 | ||
2337 | Most of the file names used in Lisp programs are entered by the user. | |
2338 | But occasionally a Lisp program needs to specify a standard file name | |
2339 | for a particular use---typically, to hold customization information | |
2340 | about each user. For example, abbrev definitions are stored (by | |
2341 | default) in the file @file{~/.abbrev_defs}; the @code{completion} | |
2342 | package stores completions in the file @file{~/.completions}. These are | |
2343 | two of the many standard file names used by parts of Emacs for certain | |
2344 | purposes. | |
2345 | ||
2346 | Various operating systems have their own conventions for valid file | |
2347 | names and for which file names to use for user profile data. A Lisp | |
2348 | program which reads a file using a standard file name ought to use, on | |
2349 | each type of system, a file name suitable for that system. The function | |
2350 | @code{convert-standard-filename} makes this easy to do. | |
2351 | ||
2352 | @defun convert-standard-filename filename | |
2353 | This function alters the file name @var{filename} to fit the conventions | |
2354 | of the operating system in use, and returns the result as a new string. | |
2355 | @end defun | |
2356 | ||
2357 | The recommended way to specify a standard file name in a Lisp program | |
2358 | is to choose a name which fits the conventions of GNU and Unix systems, | |
2359 | usually with a nondirectory part that starts with a period, and pass it | |
2360 | to @code{convert-standard-filename} instead of using it directly. Here | |
2361 | is an example from the @code{completion} package: | |
2362 | ||
2363 | @example | |
2364 | (defvar save-completions-file-name | |
2365 | (convert-standard-filename "~/.completions") | |
2366 | "*The file name to save completions to.") | |
2367 | @end example | |
2368 | ||
2369 | On GNU and Unix systems, and on some other systems as well, | |
2370 | @code{convert-standard-filename} returns its argument unchanged. On | |
2371 | some other systems, it alters the name to fit the system's conventions. | |
2372 | ||
2373 | For example, on MS-DOS the alterations made by this function include | |
2374 | converting a leading @samp{.} to @samp{_}, converting a @samp{_} in the | |
2375 | middle of the name to @samp{.} if there is no other @samp{.}, inserting | |
2376 | a @samp{.} after eight characters if there is none, and truncating to | |
2377 | three characters after the @samp{.}. (It makes other changes as well.) | |
2378 | Thus, @file{.abbrev_defs} becomes @file{_abbrev.def}, and | |
2379 | @file{.completions} becomes @file{_complet.ion}. | |
2380 | ||
2381 | @node Contents of Directories | |
2382 | @section Contents of Directories | |
2383 | @cindex directory-oriented functions | |
2384 | @cindex file names in directory | |
2385 | ||
2386 | A directory is a kind of file that contains other files entered under | |
2387 | various names. Directories are a feature of the file system. | |
2388 | ||
2389 | Emacs can list the names of the files in a directory as a Lisp list, | |
2390 | or display the names in a buffer using the @code{ls} shell command. In | |
2391 | the latter case, it can optionally display information about each file, | |
2392 | depending on the options passed to the @code{ls} command. | |
2393 | ||
2394 | @defun directory-files directory &optional full-name match-regexp nosort | |
2395 | This function returns a list of the names of the files in the directory | |
2396 | @var{directory}. By default, the list is in alphabetical order. | |
2397 | ||
2398 | If @var{full-name} is non-@code{nil}, the function returns the files' | |
2399 | absolute file names. Otherwise, it returns the names relative to | |
2400 | the specified directory. | |
2401 | ||
2402 | If @var{match-regexp} is non-@code{nil}, this function returns only | |
2403 | those file names that contain a match for that regular expression---the | |
2404 | other file names are excluded from the list. On case-insensitive | |
2405 | filesystems, the regular expression matching is case-insensitive. | |
2406 | ||
2407 | @c Emacs 19 feature | |
2408 | If @var{nosort} is non-@code{nil}, @code{directory-files} does not sort | |
2409 | the list, so you get the file names in no particular order. Use this if | |
2410 | you want the utmost possible speed and don't care what order the files | |
2411 | are processed in. If the order of processing is visible to the user, | |
2412 | then the user will probably be happier if you do sort the names. | |
2413 | ||
2414 | @example | |
2415 | @group | |
2416 | (directory-files "~lewis") | |
2417 | @result{} ("#foo#" "#foo.el#" "." ".." | |
2418 | "dired-mods.el" "files.texi" | |
2419 | "files.texi.~1~") | |
2420 | @end group | |
2421 | @end example | |
2422 | ||
2423 | An error is signaled if @var{directory} is not the name of a directory | |
2424 | that can be read. | |
2425 | @end defun | |
2426 | ||
2427 | @defun directory-files-and-attributes directory &optional full-name match-regexp nosort id-format | |
2428 | This is similar to @code{directory-files} in deciding which files | |
2429 | to report on and how to report their names. However, instead | |
2430 | of returning a list of file names, it returns for each file a | |
2431 | list @code{(@var{filename} . @var{attributes})}, where @var{attributes} | |
2432 | is what @code{file-attributes} would return for that file. | |
2433 | The optional argument @var{id-format} has the same meaning as the | |
2434 | corresponding argument to @code{file-attributes} (@pxref{Definition | |
2435 | of file-attributes}). | |
2436 | @end defun | |
2437 | ||
b8d4c8d0 GM |
2438 | @defun file-expand-wildcards pattern &optional full |
2439 | This function expands the wildcard pattern @var{pattern}, returning | |
2440 | a list of file names that match it. | |
2441 | ||
2442 | If @var{pattern} is written as an absolute file name, | |
2443 | the values are absolute also. | |
2444 | ||
2445 | If @var{pattern} is written as a relative file name, it is interpreted | |
2446 | relative to the current default directory. The file names returned are | |
2447 | normally also relative to the current default directory. However, if | |
2448 | @var{full} is non-@code{nil}, they are absolute. | |
2449 | @end defun | |
2450 | ||
2451 | @defun insert-directory file switches &optional wildcard full-directory-p | |
2452 | This function inserts (in the current buffer) a directory listing for | |
2453 | directory @var{file}, formatted with @code{ls} according to | |
2454 | @var{switches}. It leaves point after the inserted text. | |
2455 | @var{switches} may be a string of options, or a list of strings | |
2456 | representing individual options. | |
2457 | ||
2458 | The argument @var{file} may be either a directory name or a file | |
2459 | specification including wildcard characters. If @var{wildcard} is | |
2460 | non-@code{nil}, that means treat @var{file} as a file specification with | |
2461 | wildcards. | |
2462 | ||
2463 | If @var{full-directory-p} is non-@code{nil}, that means the directory | |
2464 | listing is expected to show the full contents of a directory. You | |
2465 | should specify @code{t} when @var{file} is a directory and switches do | |
2466 | not contain @samp{-d}. (The @samp{-d} option to @code{ls} says to | |
2467 | describe a directory itself as a file, rather than showing its | |
2468 | contents.) | |
2469 | ||
2470 | On most systems, this function works by running a directory listing | |
2471 | program whose name is in the variable @code{insert-directory-program}. | |
2472 | If @var{wildcard} is non-@code{nil}, it also runs the shell specified by | |
2473 | @code{shell-file-name}, to expand the wildcards. | |
2474 | ||
2475 | MS-DOS and MS-Windows systems usually lack the standard Unix program | |
2476 | @code{ls}, so this function emulates the standard Unix program @code{ls} | |
2477 | with Lisp code. | |
2478 | ||
2479 | As a technical detail, when @var{switches} contains the long | |
2480 | @samp{--dired} option, @code{insert-directory} treats it specially, | |
2481 | for the sake of dired. However, the normally equivalent short | |
2482 | @samp{-D} option is just passed on to @code{insert-directory-program}, | |
2483 | as any other option. | |
2484 | @end defun | |
2485 | ||
2486 | @defvar insert-directory-program | |
2487 | This variable's value is the program to run to generate a directory listing | |
2488 | for the function @code{insert-directory}. It is ignored on systems | |
2489 | which generate the listing with Lisp code. | |
2490 | @end defvar | |
2491 | ||
2492 | @node Create/Delete Dirs | |
461bf92b | 2493 | @section Creating, Copying and Deleting Directories |
804543b5 | 2494 | @cindex creating, copying and deleting directories |
b8d4c8d0 GM |
2495 | @c Emacs 19 features |
2496 | ||
2497 | Most Emacs Lisp file-manipulation functions get errors when used on | |
2498 | files that are directories. For example, you cannot delete a directory | |
2499 | with @code{delete-file}. These special functions exist to create and | |
2500 | delete directories. | |
2501 | ||
2aa8ea6e | 2502 | @findex mkdir |
106e6894 CY |
2503 | @deffn Command make-directory dirname &optional parents |
2504 | This command creates a directory named @var{dirname}. If | |
2505 | @var{parents} is non-@code{nil}, as is always the case in an | |
b8d4c8d0 GM |
2506 | interactive call, that means to create the parent directories first, |
2507 | if they don't already exist. | |
2aa8ea6e | 2508 | |
106e6894 CY |
2509 | @code{mkdir} is an alias for this. |
2510 | @end deffn | |
b8d4c8d0 | 2511 | |
a6326082 | 2512 | @deffn Command copy-directory dirname newname &optional keep-time parents copy-contents |
461bf92b MA |
2513 | This command copies the directory named @var{dirname} to |
2514 | @var{newname}. If @var{newname} names an existing directory, | |
2515 | @var{dirname} will be copied to a subdirectory there. | |
2516 | ||
2517 | It always sets the file modes of the copied files to match the | |
2518 | corresponding original file. | |
2519 | ||
a6326082 | 2520 | The third argument @var{keep-time} non-@code{nil} means to preserve the |
461bf92b MA |
2521 | modification time of the copied files. A prefix arg makes |
2522 | @var{keep-time} non-@code{nil}. | |
2523 | ||
a6326082 | 2524 | The fourth argument @var{parents} says whether to |
461bf92b MA |
2525 | create parent directories if they don't exist. Interactively, |
2526 | this happens by default. | |
a6326082 CY |
2527 | |
2528 | The fifth argument @var{copy-contents}, if non-@code{nil}, means to | |
2529 | copy the contents of @var{dirname} directly into @var{newname} if the | |
2530 | latter is an existing directory, instead of copying @var{dirname} into | |
2531 | it as a subdirectory. | |
461bf92b MA |
2532 | @end deffn |
2533 | ||
04e2ce72 CY |
2534 | @cindex trash |
2535 | @vindex delete-by-moving-to-trash | |
2536 | @deffn Command delete-directory dirname &optional recursive trash | |
106e6894 | 2537 | This command deletes the directory named @var{dirname}. The function |
b8d4c8d0 | 2538 | @code{delete-file} does not work for files that are directories; you |
d3080264 MA |
2539 | must use @code{delete-directory} for them. If @var{recursive} is |
2540 | @code{nil}, and the directory contains any files, | |
2541 | @code{delete-directory} signals an error. | |
b8d4c8d0 | 2542 | |
106e6894 CY |
2543 | @code{delete-directory} only follows symbolic links at the level of |
2544 | parent directories. | |
04e2ce72 CY |
2545 | |
2546 | If the optional argument @var{trash} is non-@code{nil} and the | |
2547 | variable @code{delete-by-moving-to-trash} is non-@code{nil}, this | |
2548 | command moves the file into the system Trash instead of deleting it. | |
2549 | @xref{Misc File Ops,,Miscellaneous File Operations, emacs, The GNU | |
2550 | Emacs Manual}. When called interactively, @var{trash} is @code{t} if | |
2551 | no prefix argument is given, and @code{nil} otherwise. | |
106e6894 | 2552 | @end deffn |
b8d4c8d0 GM |
2553 | |
2554 | @node Magic File Names | |
2555 | @section Making Certain File Names ``Magic'' | |
2556 | @cindex magic file names | |
2557 | ||
2558 | @c Emacs 19 feature | |
2559 | You can implement special handling for certain file names. This is | |
2560 | called making those names @dfn{magic}. The principal use for this | |
2561 | feature is in implementing remote file names (@pxref{Remote Files,, | |
2562 | Remote Files, emacs, The GNU Emacs Manual}). | |
2563 | ||
2564 | To define a kind of magic file name, you must supply a regular | |
2565 | expression to define the class of names (all those that match the | |
2566 | regular expression), plus a handler that implements all the primitive | |
2567 | Emacs file operations for file names that do match. | |
2568 | ||
ebe479ec | 2569 | @vindex file-name-handler-alist |
b8d4c8d0 GM |
2570 | The variable @code{file-name-handler-alist} holds a list of handlers, |
2571 | together with regular expressions that determine when to apply each | |
2572 | handler. Each element has this form: | |
2573 | ||
2574 | @example | |
2575 | (@var{regexp} . @var{handler}) | |
2576 | @end example | |
2577 | ||
2578 | @noindent | |
2579 | All the Emacs primitives for file access and file name transformation | |
2580 | check the given file name against @code{file-name-handler-alist}. If | |
2581 | the file name matches @var{regexp}, the primitives handle that file by | |
2582 | calling @var{handler}. | |
2583 | ||
2584 | The first argument given to @var{handler} is the name of the | |
2585 | primitive, as a symbol; the remaining arguments are the arguments that | |
2586 | were passed to that primitive. (The first of these arguments is most | |
2587 | often the file name itself.) For example, if you do this: | |
2588 | ||
2589 | @example | |
2590 | (file-exists-p @var{filename}) | |
2591 | @end example | |
2592 | ||
2593 | @noindent | |
2594 | and @var{filename} has handler @var{handler}, then @var{handler} is | |
2595 | called like this: | |
2596 | ||
2597 | @example | |
2598 | (funcall @var{handler} 'file-exists-p @var{filename}) | |
2599 | @end example | |
2600 | ||
2601 | When a function takes two or more arguments that must be file names, | |
2602 | it checks each of those names for a handler. For example, if you do | |
2603 | this: | |
2604 | ||
2605 | @example | |
2606 | (expand-file-name @var{filename} @var{dirname}) | |
2607 | @end example | |
2608 | ||
2609 | @noindent | |
2610 | then it checks for a handler for @var{filename} and then for a handler | |
2611 | for @var{dirname}. In either case, the @var{handler} is called like | |
2612 | this: | |
2613 | ||
2614 | @example | |
2615 | (funcall @var{handler} 'expand-file-name @var{filename} @var{dirname}) | |
2616 | @end example | |
2617 | ||
2618 | @noindent | |
2619 | The @var{handler} then needs to figure out whether to handle | |
2620 | @var{filename} or @var{dirname}. | |
2621 | ||
2622 | If the specified file name matches more than one handler, the one | |
2623 | whose match starts last in the file name gets precedence. This rule | |
2624 | is chosen so that handlers for jobs such as uncompression are handled | |
2625 | first, before handlers for jobs such as remote file access. | |
2626 | ||
2627 | Here are the operations that a magic file name handler gets to handle: | |
2628 | ||
2629 | @ifnottex | |
2630 | @noindent | |
2631 | @code{access-file}, @code{add-name-to-file}, | |
2632 | @code{byte-compiler-base-file-name},@* | |
2a3f19ef MA |
2633 | @code{copy-directory}, @code{copy-file}, |
2634 | @code{delete-directory}, @code{delete-file}, | |
b8d4c8d0 GM |
2635 | @code{diff-latest-backup-file}, |
2636 | @code{directory-file-name}, | |
2637 | @code{directory-files}, | |
2638 | @code{directory-files-and-attributes}, | |
2639 | @code{dired-compress-file}, @code{dired-uncache},@* | |
2640 | @code{expand-file-name}, | |
2641 | @code{file-accessible-directory-p}, | |
2642 | @code{file-attributes}, | |
2643 | @code{file-directory-p}, | |
2644 | @code{file-executable-p}, @code{file-exists-p}, | |
2645 | @code{file-local-copy}, @code{file-remote-p}, | |
2646 | @code{file-modes}, @code{file-name-all-completions}, | |
2647 | @code{file-name-as-directory}, | |
2648 | @code{file-name-completion}, | |
2649 | @code{file-name-directory}, | |
2650 | @code{file-name-nondirectory}, | |
2651 | @code{file-name-sans-versions}, @code{file-newer-than-file-p}, | |
2652 | @code{file-ownership-preserved-p}, | |
2653 | @code{file-readable-p}, @code{file-regular-p}, @code{file-symlink-p}, | |
2654 | @code{file-truename}, @code{file-writable-p}, | |
2655 | @code{find-backup-file-name}, | |
4e47bf1f | 2656 | @c Not sure why it was here: @code{find-file-noselect},@* |
b8d4c8d0 GM |
2657 | @code{get-file-buffer}, |
2658 | @code{insert-directory}, | |
2659 | @code{insert-file-contents},@* | |
2660 | @code{load}, | |
2661 | @code{make-auto-save-file-name}, | |
2662 | @code{make-directory}, | |
2663 | @code{make-directory-internal}, | |
2664 | @code{make-symbolic-link},@* | |
2665 | @code{process-file}, | |
2666 | @code{rename-file}, @code{set-file-modes}, @code{set-file-times}, | |
2667 | @code{set-visited-file-modtime}, @code{shell-command}, | |
2668 | @code{start-file-process}, | |
2669 | @code{substitute-in-file-name},@* | |
2670 | @code{unhandled-file-name-directory}, | |
2671 | @code{vc-registered}, | |
2672 | @code{verify-visited-file-modtime},@* | |
2673 | @code{write-region}. | |
2674 | @end ifnottex | |
2675 | @iftex | |
2676 | @noindent | |
2677 | @flushleft | |
2678 | @code{access-file}, @code{add-name-to-file}, | |
2679 | @code{byte-com@discretionary{}{}{}piler-base-file-name}, | |
2a3f19ef MA |
2680 | @code{copy-directory}, @code{copy-file}, |
2681 | @code{delete-directory}, @code{delete-file}, | |
b8d4c8d0 GM |
2682 | @code{diff-latest-backup-file}, |
2683 | @code{directory-file-name}, | |
2684 | @code{directory-files}, | |
2685 | @code{directory-files-and-at@discretionary{}{}{}tributes}, | |
2686 | @code{dired-compress-file}, @code{dired-uncache}, | |
2687 | @code{expand-file-name}, | |
2688 | @code{file-accessible-direc@discretionary{}{}{}tory-p}, | |
2689 | @code{file-attributes}, | |
2690 | @code{file-direct@discretionary{}{}{}ory-p}, | |
2691 | @code{file-executable-p}, @code{file-exists-p}, | |
2692 | @code{file-local-copy}, @code{file-remote-p}, | |
2693 | @code{file-modes}, @code{file-name-all-completions}, | |
2694 | @code{file-name-as-directory}, | |
2695 | @code{file-name-completion}, | |
2696 | @code{file-name-directory}, | |
2697 | @code{file-name-nondirec@discretionary{}{}{}tory}, | |
2698 | @code{file-name-sans-versions}, @code{file-newer-than-file-p}, | |
2699 | @code{file-ownership-pre@discretionary{}{}{}served-p}, | |
2700 | @code{file-readable-p}, @code{file-regular-p}, @code{file-symlink-p}, | |
2701 | @code{file-truename}, @code{file-writable-p}, | |
2702 | @code{find-backup-file-name}, | |
4e47bf1f | 2703 | @c Not sure why it was here: @code{find-file-noselect}, |
b8d4c8d0 GM |
2704 | @code{get-file-buffer}, |
2705 | @code{insert-directory}, | |
2706 | @code{insert-file-contents}, | |
2707 | @code{load}, @code{make-direc@discretionary{}{}{}tory}, | |
2708 | @code{make-direc@discretionary{}{}{}tory-internal}, | |
2709 | @code{make-symbolic-link}, | |
2710 | @code{process-file}, | |
2711 | @code{rename-file}, @code{set-file-modes}, | |
2712 | @code{set-visited-file-modtime}, @code{shell-command}, | |
2713 | @code{start-file-process}, | |
2714 | @code{substitute-in-file-name}, | |
2715 | @code{unhandled-file-name-directory}, | |
2716 | @code{vc-regis@discretionary{}{}{}tered}, | |
2717 | @code{verify-visited-file-modtime}, | |
2718 | @code{write-region}. | |
2719 | @end flushleft | |
2720 | @end iftex | |
2721 | ||
2722 | Handlers for @code{insert-file-contents} typically need to clear the | |
2723 | buffer's modified flag, with @code{(set-buffer-modified-p nil)}, if the | |
2724 | @var{visit} argument is non-@code{nil}. This also has the effect of | |
2725 | unlocking the buffer if it is locked. | |
2726 | ||
2727 | The handler function must handle all of the above operations, and | |
2728 | possibly others to be added in the future. It need not implement all | |
2729 | these operations itself---when it has nothing special to do for a | |
2730 | certain operation, it can reinvoke the primitive, to handle the | |
2731 | operation ``in the usual way.'' It should always reinvoke the primitive | |
2732 | for an operation it does not recognize. Here's one way to do this: | |
2733 | ||
2734 | @smallexample | |
2735 | (defun my-file-handler (operation &rest args) | |
2736 | ;; @r{First check for the specific operations} | |
2737 | ;; @r{that we have special handling for.} | |
2738 | (cond ((eq operation 'insert-file-contents) @dots{}) | |
2739 | ((eq operation 'write-region) @dots{}) | |
2740 | @dots{} | |
2741 | ;; @r{Handle any operation we don't know about.} | |
2742 | (t (let ((inhibit-file-name-handlers | |
2743 | (cons 'my-file-handler | |
2744 | (and (eq inhibit-file-name-operation operation) | |
2745 | inhibit-file-name-handlers))) | |
2746 | (inhibit-file-name-operation operation)) | |
2747 | (apply operation args))))) | |
2748 | @end smallexample | |
2749 | ||
2750 | When a handler function decides to call the ordinary Emacs primitive for | |
2751 | the operation at hand, it needs to prevent the primitive from calling | |
2752 | the same handler once again, thus leading to an infinite recursion. The | |
2753 | example above shows how to do this, with the variables | |
2754 | @code{inhibit-file-name-handlers} and | |
2755 | @code{inhibit-file-name-operation}. Be careful to use them exactly as | |
2756 | shown above; the details are crucial for proper behavior in the case of | |
2757 | multiple handlers, and for operations that have two file names that may | |
2758 | each have handlers. | |
2759 | ||
2760 | @kindex safe-magic (@r{property}) | |
2761 | Handlers that don't really do anything special for actual access to the | |
2762 | file---such as the ones that implement completion of host names for | |
2763 | remote file names---should have a non-@code{nil} @code{safe-magic} | |
2764 | property. For instance, Emacs normally ``protects'' directory names | |
2765 | it finds in @code{PATH} from becoming magic, if they look like magic | |
2766 | file names, by prefixing them with @samp{/:}. But if the handler that | |
2767 | would be used for them has a non-@code{nil} @code{safe-magic} | |
2768 | property, the @samp{/:} is not added. | |
2769 | ||
2770 | @kindex operations (@r{property}) | |
2771 | A file name handler can have an @code{operations} property to | |
2772 | declare which operations it handles in a nontrivial way. If this | |
2773 | property has a non-@code{nil} value, it should be a list of | |
2774 | operations; then only those operations will call the handler. This | |
2775 | avoids inefficiency, but its main purpose is for autoloaded handler | |
2776 | functions, so that they won't be loaded except when they have real | |
2777 | work to do. | |
2778 | ||
2779 | Simply deferring all operations to the usual primitives does not | |
2780 | work. For instance, if the file name handler applies to | |
2781 | @code{file-exists-p}, then it must handle @code{load} itself, because | |
2782 | the usual @code{load} code won't work properly in that case. However, | |
2783 | if the handler uses the @code{operations} property to say it doesn't | |
2784 | handle @code{file-exists-p}, then it need not handle @code{load} | |
2785 | nontrivially. | |
2786 | ||
2787 | @defvar inhibit-file-name-handlers | |
2788 | This variable holds a list of handlers whose use is presently inhibited | |
2789 | for a certain operation. | |
2790 | @end defvar | |
2791 | ||
2792 | @defvar inhibit-file-name-operation | |
2793 | The operation for which certain handlers are presently inhibited. | |
2794 | @end defvar | |
2795 | ||
2796 | @defun find-file-name-handler file operation | |
2797 | This function returns the handler function for file name @var{file}, | |
2798 | or @code{nil} if there is none. The argument @var{operation} should | |
2799 | be the operation to be performed on the file---the value you will pass | |
2800 | to the handler as its first argument when you call it. If | |
2801 | @var{operation} equals @code{inhibit-file-name-operation}, or if it is | |
2802 | not found in the @code{operations} property of the handler, this | |
2803 | function returns @code{nil}. | |
2804 | @end defun | |
2805 | ||
2806 | @defun file-local-copy filename | |
2807 | This function copies file @var{filename} to an ordinary non-magic file | |
2808 | on the local machine, if it isn't on the local machine already. Magic | |
2809 | file names should handle the @code{file-local-copy} operation if they | |
2810 | refer to files on other machines. A magic file name that is used for | |
2811 | other purposes than remote file access should not handle | |
2812 | @code{file-local-copy}; then this function will treat the file as | |
2813 | local. | |
2814 | ||
2815 | If @var{filename} is local, whether magic or not, this function does | |
2816 | nothing and returns @code{nil}. Otherwise it returns the file name | |
2817 | of the local copy file. | |
2818 | @end defun | |
2819 | ||
2820 | @defun file-remote-p filename &optional identification connected | |
2821 | This function tests whether @var{filename} is a remote file. If | |
2822 | @var{filename} is local (not remote), the return value is @code{nil}. | |
2823 | If @var{filename} is indeed remote, the return value is a string that | |
2824 | identifies the remote system. | |
2825 | ||
2826 | This identifier string can include a host name and a user name, as | |
2827 | well as characters designating the method used to access the remote | |
2828 | system. For example, the remote identifier string for the filename | |
2829 | @code{/sudo::/some/file} is @code{/sudo:root@@localhost:}. | |
2830 | ||
2831 | If @code{file-remote-p} returns the same identifier for two different | |
2832 | filenames, that means they are stored on the same file system and can | |
2833 | be accessed locally with respect to each other. This means, for | |
2834 | example, that it is possible to start a remote process accessing both | |
f6b1b0a8 | 2835 | files at the same time. Implementers of file handlers need to ensure |
b8d4c8d0 GM |
2836 | this principle is valid. |
2837 | ||
2838 | @var{identification} specifies which part of the identifier shall be | |
2839 | returned as string. @var{identification} can be the symbol | |
2840 | @code{method}, @code{user} or @code{host}; any other value is handled | |
2841 | like @code{nil} and means to return the complete identifier string. | |
2842 | In the example above, the remote @code{user} identifier string would | |
2843 | be @code{root}. | |
2844 | ||
2845 | If @var{connected} is non-@code{nil}, this function returns @code{nil} | |
2846 | even if @var{filename} is remote, if Emacs has no network connection | |
2847 | to its host. This is useful when you want to avoid the delay of | |
2848 | making connections when they don't exist. | |
2849 | @end defun | |
2850 | ||
2851 | @defun unhandled-file-name-directory filename | |
4990219b CY |
2852 | This function returns the name of a directory that is not magic. It |
2853 | uses the directory part of @var{filename} if that is not magic. For a | |
2854 | magic file name, it invokes the file name handler, which therefore | |
2855 | decides what value to return. If @var{filename} is not accessible | |
2856 | from a local process, then the file name handler should indicate it by | |
2857 | returning @code{nil}. | |
b8d4c8d0 GM |
2858 | |
2859 | This is useful for running a subprocess; every subprocess must have a | |
2860 | non-magic directory to serve as its current directory, and this function | |
2861 | is a good way to come up with one. | |
2862 | @end defun | |
2863 | ||
178fdd41 MA |
2864 | @defopt remote-file-name-inhibit-cache |
2865 | Whether to use the remote file-name cache for read access. | |
2866 | ||
2867 | File attributes of remote files are cached for better performance. If | |
2868 | they are changed out of Emacs' control, the cached values become | |
2869 | invalid, and must be reread. | |
2870 | ||
2871 | When set to @code{nil}, cached values are always used. This shall be | |
2872 | set with care. When set to @code{t}, cached values are never used. | |
2873 | ALthough this is the safest value, it could result in performance | |
2874 | degradation. | |
2875 | ||
2876 | A compromise is to set it to a positive number. This means that | |
2877 | cached values are used for that amount of seconds since they were | |
2878 | cached. | |
2879 | ||
2880 | In case a remote file is checked regularly, it might be reasonable to | |
2881 | let-bind this variable to a value less then the time period between | |
2882 | two checks. Example: | |
2883 | ||
2884 | @example | |
2885 | (defun display-time-file-nonempty-p (file) | |
2886 | (let ((remote-file-name-inhibit-cache (- display-time-interval 5))) | |
2887 | (and (file-exists-p file) | |
2888 | (< 0 (nth 7 (file-attributes (file-chase-links file))))))) | |
2889 | @end example | |
2890 | @end defopt | |
2891 | ||
b8d4c8d0 GM |
2892 | @node Format Conversion |
2893 | @section File Format Conversion | |
2894 | ||
2895 | @cindex file format conversion | |
2896 | @cindex encoding file formats | |
2897 | @cindex decoding file formats | |
2898 | @cindex text properties in files | |
2899 | @cindex saving text properties | |
2900 | Emacs performs several steps to convert the data in a buffer (text, | |
2901 | text properties, and possibly other information) to and from a | |
2902 | representation suitable for storing into a file. This section describes | |
2903 | the fundamental functions that perform this @dfn{format conversion}, | |
2904 | namely @code{insert-file-contents} for reading a file into a buffer, | |
2905 | and @code{write-region} for writing a buffer into a file. | |
2906 | ||
2907 | @menu | |
76f444dc | 2908 | * Overview: Format Conversion Overview. @code{insert-file-contents} and @code{write-region}. |
b8d4c8d0 GM |
2909 | * Round-Trip: Format Conversion Round-Trip. Using @code{format-alist}. |
2910 | * Piecemeal: Format Conversion Piecemeal. Specifying non-paired conversion. | |
2911 | @end menu | |
2912 | ||
2913 | @node Format Conversion Overview | |
2914 | @subsection Overview | |
2915 | @noindent | |
2916 | The function @code{insert-file-contents}: | |
2917 | ||
2918 | @itemize | |
2919 | @item initially, inserts bytes from the file into the buffer; | |
2920 | @item decodes bytes to characters as appropriate; | |
2921 | @item processes formats as defined by entries in @code{format-alist}; and | |
2922 | @item calls functions in @code{after-insert-file-functions}. | |
2923 | @end itemize | |
2924 | ||
2925 | @noindent | |
2926 | The function @code{write-region}: | |
2927 | ||
2928 | @itemize | |
2929 | @item initially, calls functions in @code{write-region-annotate-functions}; | |
2930 | @item processes formats as defined by entries in @code{format-alist}; | |
2931 | @item encodes characters to bytes as appropriate; and | |
2932 | @item modifies the file with the bytes. | |
2933 | @end itemize | |
2934 | ||
2935 | This shows the symmetry of the lowest-level operations; reading and | |
2936 | writing handle things in opposite order. The rest of this section | |
2937 | describes the two facilities surrounding the three variables named | |
2938 | above, as well as some related functions. @ref{Coding Systems}, for | |
2939 | details on character encoding and decoding. | |
2940 | ||
2941 | @node Format Conversion Round-Trip | |
2942 | @subsection Round-Trip Specification | |
2943 | ||
2944 | The most general of the two facilities is controlled by the variable | |
2945 | @code{format-alist}, a list of @dfn{file format} specifications, which | |
2946 | describe textual representations used in files for the data in an Emacs | |
2947 | buffer. The descriptions for reading and writing are paired, which is | |
2948 | why we call this ``round-trip'' specification | |
2949 | (@pxref{Format Conversion Piecemeal}, for non-paired specification). | |
2950 | ||
2951 | @defvar format-alist | |
2952 | This list contains one format definition for each defined file format. | |
2953 | Each format definition is a list of this form: | |
2954 | ||
2955 | @example | |
c249fa9c | 2956 | (@var{name} @var{doc-string} @var{regexp} @var{from-fn} @var{to-fn} @var{modify} @var{mode-fn} @var{preserve}) |
b8d4c8d0 GM |
2957 | @end example |
2958 | @end defvar | |
2959 | ||
2960 | @cindex format definition | |
2961 | @noindent | |
2962 | Here is what the elements in a format definition mean: | |
2963 | ||
2964 | @table @var | |
2965 | @item name | |
2966 | The name of this format. | |
2967 | ||
2968 | @item doc-string | |
2969 | A documentation string for the format. | |
2970 | ||
2971 | @item regexp | |
2972 | A regular expression which is used to recognize files represented in | |
0706c025 | 2973 | this format. If @code{nil}, the format is never applied automatically. |
b8d4c8d0 GM |
2974 | |
2975 | @item from-fn | |
2976 | A shell command or function to decode data in this format (to convert | |
2977 | file data into the usual Emacs data representation). | |
2978 | ||
2979 | A shell command is represented as a string; Emacs runs the command as a | |
2980 | filter to perform the conversion. | |
2981 | ||
2982 | If @var{from-fn} is a function, it is called with two arguments, @var{begin} | |
2983 | and @var{end}, which specify the part of the buffer it should convert. | |
2984 | It should convert the text by editing it in place. Since this can | |
2985 | change the length of the text, @var{from-fn} should return the modified | |
2986 | end position. | |
2987 | ||
2988 | One responsibility of @var{from-fn} is to make sure that the beginning | |
2989 | of the file no longer matches @var{regexp}. Otherwise it is likely to | |
2990 | get called again. | |
2991 | ||
2992 | @item to-fn | |
2993 | A shell command or function to encode data in this format---that is, to | |
2994 | convert the usual Emacs data representation into this format. | |
2995 | ||
2996 | If @var{to-fn} is a string, it is a shell command; Emacs runs the | |
2997 | command as a filter to perform the conversion. | |
2998 | ||
2999 | If @var{to-fn} is a function, it is called with three arguments: | |
3000 | @var{begin} and @var{end}, which specify the part of the buffer it | |
3001 | should convert, and @var{buffer}, which specifies which buffer. There | |
3002 | are two ways it can do the conversion: | |
3003 | ||
3004 | @itemize @bullet | |
3005 | @item | |
3006 | By editing the buffer in place. In this case, @var{to-fn} should | |
3007 | return the end-position of the range of text, as modified. | |
3008 | ||
3009 | @item | |
3010 | By returning a list of annotations. This is a list of elements of the | |
3011 | form @code{(@var{position} . @var{string})}, where @var{position} is an | |
3012 | integer specifying the relative position in the text to be written, and | |
3013 | @var{string} is the annotation to add there. The list must be sorted in | |
3014 | order of position when @var{to-fn} returns it. | |
3015 | ||
3016 | When @code{write-region} actually writes the text from the buffer to the | |
3017 | file, it intermixes the specified annotations at the corresponding | |
3018 | positions. All this takes place without modifying the buffer. | |
3019 | @end itemize | |
3020 | ||
3021 | @item modify | |
3022 | A flag, @code{t} if the encoding function modifies the buffer, and | |
3023 | @code{nil} if it works by returning a list of annotations. | |
3024 | ||
3025 | @item mode-fn | |
3026 | A minor-mode function to call after visiting a file converted from this | |
3027 | format. The function is called with one argument, the integer 1; | |
3028 | that tells a minor-mode function to enable the mode. | |
c249fa9c GM |
3029 | |
3030 | @item preserve | |
3031 | A flag, @code{t} if @code{format-write-file} should not remove this format | |
3032 | from @code{buffer-file-format}. | |
b8d4c8d0 GM |
3033 | @end table |
3034 | ||
3035 | The function @code{insert-file-contents} automatically recognizes file | |
3036 | formats when it reads the specified file. It checks the text of the | |
3037 | beginning of the file against the regular expressions of the format | |
3038 | definitions, and if it finds a match, it calls the decoding function for | |
3039 | that format. Then it checks all the known formats over again. | |
3040 | It keeps checking them until none of them is applicable. | |
3041 | ||
3042 | Visiting a file, with @code{find-file-noselect} or the commands that use | |
3043 | it, performs conversion likewise (because it calls | |
3044 | @code{insert-file-contents}); it also calls the mode function for each | |
3045 | format that it decodes. It stores a list of the format names in the | |
3046 | buffer-local variable @code{buffer-file-format}. | |
3047 | ||
3048 | @defvar buffer-file-format | |
3049 | This variable states the format of the visited file. More precisely, | |
3050 | this is a list of the file format names that were decoded in the course | |
3051 | of visiting the current buffer's file. It is always buffer-local in all | |
3052 | buffers. | |
3053 | @end defvar | |
3054 | ||
3055 | When @code{write-region} writes data into a file, it first calls the | |
3056 | encoding functions for the formats listed in @code{buffer-file-format}, | |
3057 | in the order of appearance in the list. | |
3058 | ||
3059 | @deffn Command format-write-file file format &optional confirm | |
fa047ae7 GM |
3060 | This command writes the current buffer contents into the file @var{file} |
3061 | in a format based on @var{format}, which is a list of format names. It | |
3062 | constructs the actual format starting from @var{format}, then appending | |
3063 | any elements from the value of @code{buffer-file-format} with a non-nil | |
3064 | @var{preserve} flag (see above), if they are not already present in | |
3065 | @var{format}. It then updates @code{buffer-file-format} with this | |
3066 | format, making it the default for future saves. Except for the | |
3067 | @var{format} argument, this command is similar to @code{write-file}. In | |
3068 | particular, @var{confirm} has the same meaning and interactive treatment | |
3069 | as the corresponding argument to @code{write-file}. @xref{Definition of | |
3070 | write-file}. | |
b8d4c8d0 GM |
3071 | @end deffn |
3072 | ||
3073 | @deffn Command format-find-file file format | |
3074 | This command finds the file @var{file}, converting it according to | |
3075 | format @var{format}. It also makes @var{format} the default if the | |
3076 | buffer is saved later. | |
3077 | ||
3078 | The argument @var{format} is a list of format names. If @var{format} is | |
3079 | @code{nil}, no conversion takes place. Interactively, typing just | |
3080 | @key{RET} for @var{format} specifies @code{nil}. | |
3081 | @end deffn | |
3082 | ||
3083 | @deffn Command format-insert-file file format &optional beg end | |
3084 | This command inserts the contents of file @var{file}, converting it | |
3085 | according to format @var{format}. If @var{beg} and @var{end} are | |
3086 | non-@code{nil}, they specify which part of the file to read, as in | |
3087 | @code{insert-file-contents} (@pxref{Reading from Files}). | |
3088 | ||
3089 | The return value is like what @code{insert-file-contents} returns: a | |
3090 | list of the absolute file name and the length of the data inserted | |
3091 | (after conversion). | |
3092 | ||
3093 | The argument @var{format} is a list of format names. If @var{format} is | |
3094 | @code{nil}, no conversion takes place. Interactively, typing just | |
3095 | @key{RET} for @var{format} specifies @code{nil}. | |
3096 | @end deffn | |
3097 | ||
3098 | @defvar buffer-auto-save-file-format | |
3099 | This variable specifies the format to use for auto-saving. Its value is | |
3100 | a list of format names, just like the value of | |
3101 | @code{buffer-file-format}; however, it is used instead of | |
3102 | @code{buffer-file-format} for writing auto-save files. If the value | |
3103 | is @code{t}, the default, auto-saving uses the same format as a | |
3104 | regular save in the same buffer. This variable is always buffer-local | |
3105 | in all buffers. | |
3106 | @end defvar | |
3107 | ||
3108 | @node Format Conversion Piecemeal | |
3109 | @subsection Piecemeal Specification | |
3110 | ||
3111 | In contrast to the round-trip specification described in the previous | |
3112 | subsection (@pxref{Format Conversion Round-Trip}), you can use the variables | |
3113 | @code{after-insert-file-functions} and @code{write-region-annotate-functions} | |
3114 | to separately control the respective reading and writing conversions. | |
3115 | ||
3116 | Conversion starts with one representation and produces another | |
3117 | representation. When there is only one conversion to do, there is no | |
3118 | conflict about what to start with. However, when there are multiple | |
3119 | conversions involved, conflict may arise when two conversions need to | |
3120 | start with the same data. | |
3121 | ||
3122 | This situation is best understood in the context of converting text | |
3123 | properties during @code{write-region}. For example, the character at | |
3124 | position 42 in a buffer is @samp{X} with a text property @code{foo}. If | |
3125 | the conversion for @code{foo} is done by inserting into the buffer, say, | |
3126 | @samp{FOO:}, then that changes the character at position 42 from | |
3127 | @samp{X} to @samp{F}. The next conversion will start with the wrong | |
3128 | data straight away. | |
3129 | ||
3130 | To avoid conflict, cooperative conversions do not modify the buffer, | |
3131 | but instead specify @dfn{annotations}, a list of elements of the form | |
3132 | @code{(@var{position} . @var{string})}, sorted in order of increasing | |
3133 | @var{position}. | |
3134 | ||
3135 | If there is more than one conversion, @code{write-region} merges their | |
3136 | annotations destructively into one sorted list. Later, when the text | |
3137 | from the buffer is actually written to the file, it intermixes the | |
3138 | specified annotations at the corresponding positions. All this takes | |
3139 | place without modifying the buffer. | |
3140 | ||
3141 | @c ??? What about ``overriding'' conversions like those allowed | |
3142 | @c ??? for `write-region-annotate-functions', below? --ttn | |
3143 | ||
3144 | In contrast, when reading, the annotations intermixed with the text | |
ae12425c CY |
3145 | are handled immediately. @code{insert-file-contents} sets point to |
3146 | the beginning of some text to be converted, then calls the conversion | |
b8d4c8d0 | 3147 | functions with the length of that text. These functions should always |
ae12425c CY |
3148 | return with point at the beginning of the inserted text. This |
3149 | approach makes sense for reading because annotations removed by the | |
3150 | first converter can't be mistakenly processed by a later converter. | |
3151 | Each conversion function should scan for the annotations it | |
3152 | recognizes, remove the annotation, modify the buffer text (to set a | |
3153 | text property, for example), and return the updated length of the | |
3154 | text, as it stands after those changes. The value returned by one | |
3155 | function becomes the argument to the next function. | |
b8d4c8d0 GM |
3156 | |
3157 | @defvar write-region-annotate-functions | |
3158 | A list of functions for @code{write-region} to call. Each function in | |
3159 | the list is called with two arguments: the start and end of the region | |
3160 | to be written. These functions should not alter the contents of the | |
3161 | buffer. Instead, they should return annotations. | |
3162 | ||
ae12425c CY |
3163 | As a special case, a function may return with a different buffer |
3164 | current. Emacs takes this to mean that the current buffer contains | |
3165 | altered text to be output. It therefore changes the @var{start} and | |
3166 | @var{end} arguments of the @code{write-region} call, giving them the | |
3167 | values of @code{point-min} and @code{point-max} in the new buffer, | |
3168 | respectively. It also discards all previous annotations, because they | |
3169 | should have been dealt with by this function. | |
3170 | @end defvar | |
3171 | ||
3172 | @defvar write-region-post-annotation-function | |
3173 | The value of this variable, if non-@code{nil}, should be a function. | |
3174 | This function is called, with no arguments, after @code{write-region} | |
3175 | has completed. | |
3176 | ||
3177 | If any function in @code{write-region-annotate-functions} returns with | |
3178 | a different buffer current, Emacs calls | |
3179 | @code{write-region-post-annotation-function} more than once. Emacs | |
3180 | calls it with the last buffer that was current, and again with the | |
3181 | buffer before that, and so on back to the original buffer. | |
3182 | ||
3183 | Thus, a function in @code{write-region-annotate-functions} can create | |
3184 | a buffer, give this variable the local value of @code{kill-buffer} in | |
3185 | that buffer, set up the buffer with altered text, and make the buffer | |
3186 | current. The buffer will be killed after @code{write-region} is done. | |
b8d4c8d0 GM |
3187 | @end defvar |
3188 | ||
3189 | @defvar after-insert-file-functions | |
3190 | Each function in this list is called by @code{insert-file-contents} | |
3191 | with one argument, the number of characters inserted, and with point | |
3192 | at the beginning of the inserted text. Each function should leave | |
3193 | point unchanged, and return the new character count describing the | |
3194 | inserted text as modified by the function. | |
3195 | @c ??? The docstring mentions a handler from `file-name-handler-alist' | |
3196 | @c "intercepting" `insert-file-contents'. Hmmm. --ttn | |
3197 | @end defvar | |
3198 | ||
3199 | We invite users to write Lisp programs to store and retrieve text | |
3200 | properties in files, using these hooks, and thus to experiment with | |
3201 | various data formats and find good ones. Eventually we hope users | |
3202 | will produce good, general extensions we can install in Emacs. | |
3203 | ||
3204 | We suggest not trying to handle arbitrary Lisp objects as text property | |
3205 | names or values---because a program that general is probably difficult | |
3206 | to write, and slow. Instead, choose a set of possible data types that | |
3207 | are reasonably flexible, and not too hard to encode. |