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1 @c This is part of the Emacs manual.
2 @c Copyright (C) 1985,86,87,93,94,95,97,99, 2000, 2001
3 @c Free Software Foundation, Inc.
4 @c See file emacs.texi for copying conditions.
5 @node Files, Buffers, Fixit, Top
6 @chapter File Handling
7 @cindex files
8
9 The operating system stores data permanently in named @dfn{files}, so
10 most of the text you edit with Emacs comes from a file and is ultimately
11 stored in a file.
12
13 To edit a file, you must tell Emacs to read the file and prepare a
14 buffer containing a copy of the file's text. This is called
15 @dfn{visiting} the file. Editing commands apply directly to text in the
16 buffer; that is, to the copy inside Emacs. Your changes appear in the
17 file itself only when you @dfn{save} the buffer back into the file.
18
19 In addition to visiting and saving files, Emacs can delete, copy,
20 rename, and append to files, keep multiple versions of them, and operate
21 on file directories.
22
23 @menu
24 * File Names:: How to type and edit file-name arguments.
25 * Visiting:: Visiting a file prepares Emacs to edit the file.
26 * Saving:: Saving makes your changes permanent.
27 * Reverting:: Reverting cancels all the changes not saved.
28 * Auto Save:: Auto Save periodically protects against loss of data.
29 * File Aliases:: Handling multiple names for one file.
30 * Version Control:: Version control systems (RCS, CVS and SCCS).
31 * Directories:: Creating, deleting, and listing file directories.
32 * Comparing Files:: Finding where two files differ.
33 * Misc File Ops:: Other things you can do on files.
34 * Compressed Files:: Accessing compressed files.
35 * File Archives:: Operating on tar, zip, jar etc. archive files.
36 * Remote Files:: Accessing files on other sites.
37 * Quoted File Names:: Quoting special characters in file names.
38 * File Name Cache:: Completion against a list of files you often use.
39 * File Conveniences:: Convenience Features for Finding Files.
40 @end menu
41
42 @node File Names
43 @section File Names
44 @cindex file names
45
46 Most Emacs commands that operate on a file require you to specify the
47 file name. (Saving and reverting are exceptions; the buffer knows which
48 file name to use for them.) You enter the file name using the
49 minibuffer (@pxref{Minibuffer}). @dfn{Completion} is available
50 (@pxref{Completion}) to make it easier to specify long file names. When
51 completing file names, Emacs ignores those whose file-name extensions
52 appear in the variable @code{completion-ignored-extensions}; see
53 @ref{Completion Options}.
54
55 For most operations, there is a @dfn{default file name} which is used
56 if you type just @key{RET} to enter an empty argument. Normally the
57 default file name is the name of the file visited in the current buffer;
58 this makes it easy to operate on that file with any of the Emacs file
59 commands.
60
61 @vindex default-directory
62 Each buffer has a default directory which is normally the same as the
63 directory of the file visited in that buffer. When you enter a file
64 name without a directory, the default directory is used. If you specify
65 a directory in a relative fashion, with a name that does not start with
66 a slash, it is interpreted with respect to the default directory. The
67 default directory is kept in the variable @code{default-directory},
68 which has a separate value in every buffer.
69
70 For example, if the default file name is @file{/u/rms/gnu/gnu.tasks} then
71 the default directory is @file{/u/rms/gnu/}. If you type just @samp{foo},
72 which does not specify a directory, it is short for @file{/u/rms/gnu/foo}.
73 @samp{../.login} would stand for @file{/u/rms/.login}. @samp{new/foo}
74 would stand for the file name @file{/u/rms/gnu/new/foo}.
75
76 @findex cd
77 @findex pwd
78 The command @kbd{M-x pwd} displays the current buffer's default
79 directory, and the command @kbd{M-x cd} sets it (to a value read using
80 the minibuffer). A buffer's default directory changes only when the
81 @code{cd} command is used. A file-visiting buffer's default directory
82 is initialized to the directory of the file that is visited in that buffer. If
83 you create a buffer with @kbd{C-x b}, its default directory is copied
84 from that of the buffer that was current at the time.
85
86 @vindex insert-default-directory
87 The default directory actually appears in the minibuffer when the
88 minibuffer becomes active to read a file name. This serves two
89 purposes: it @emph{shows} you what the default is, so that you can type
90 a relative file name and know with certainty what it will mean, and it
91 allows you to @emph{edit} the default to specify a different directory.
92 This insertion of the default directory is inhibited if the variable
93 @code{insert-default-directory} is set to @code{nil}.
94
95 Note that it is legitimate to type an absolute file name after you
96 enter the minibuffer, ignoring the presence of the default directory
97 name as part of the text. The final minibuffer contents may look
98 invalid, but that is not so. For example, if the minibuffer starts out
99 with @samp{/usr/tmp/} and you add @samp{/x1/rms/foo}, you get
100 @samp{/usr/tmp//x1/rms/foo}; but Emacs ignores everything through the
101 first slash in the double slash; the result is @samp{/x1/rms/foo}.
102 @xref{Minibuffer File}.
103
104 @cindex environment variables in file names
105 @cindex expansion of environment variables
106 @samp{$} in a file name is used to substitute environment variables.
107 For example, if you have used the shell command @command{export
108 FOO=rms/hacks} to set up an environment variable named @env{FOO}, then
109 you can use @file{/u/$FOO/test.c} or @file{/u/$@{FOO@}/test.c} as an
110 abbreviation for @file{/u/rms/hacks/test.c}. The environment variable
111 name consists of all the alphanumeric characters after the @samp{$};
112 alternatively, it may be enclosed in braces after the @samp{$}. Note
113 that shell commands to set environment variables affect Emacs only if
114 done before Emacs is started.
115
116 @cindex home directory shorthand
117 You can use the @file{~/} in a file name to mean your home directory,
118 or @file{~@var{user-id}/} to mean the home directory of a user whose
119 login name is @code{user-id}. (On DOS and Windows systems, where a user
120 doesn't have a home directory, Emacs substitutes @file{~/} with the
121 value of the environment variable @code{HOME}; see @ref{General
122 Variables}.)
123
124 To access a file with @samp{$} in its name, type @samp{$$}. This pair
125 is converted to a single @samp{$} at the same time as variable
126 substitution is performed for a single @samp{$}. Alternatively, quote the
127 whole file name with @samp{/:} (@pxref{Quoted File Names}). File names
128 which begin with a literal @samp{~} should also be quoted with @samp{/:}.
129
130 @findex substitute-in-file-name
131 The Lisp function that performs the substitution is called
132 @code{substitute-in-file-name}. The substitution is performed only on
133 file names read as such using the minibuffer.
134
135 You can include non-ASCII characters in file names if you set the
136 variable @code{file-name-coding-system} to a non-@code{nil} value.
137 @xref{Specify Coding}.
138
139 @node Visiting
140 @section Visiting Files
141 @cindex visiting files
142
143 @table @kbd
144 @item C-x C-f
145 Visit a file (@code{find-file}).
146 @item C-x C-r
147 Visit a file for viewing, without allowing changes to it
148 (@code{find-file-read-only}).
149 @item C-x C-v
150 Visit a different file instead of the one visited last
151 (@code{find-alternate-file}).
152 @item C-x 4 f
153 Visit a file, in another window (@code{find-file-other-window}). Don't
154 alter what is displayed in the selected window.
155 @item C-x 5 f
156 Visit a file, in a new frame (@code{find-file-other-frame}). Don't
157 alter what is displayed in the selected frame.
158 @item M-x find-file-literally
159 Visit a file with no conversion of the contents.
160 @end table
161
162 @cindex files, visiting and saving
163 @cindex saving files
164 @dfn{Visiting} a file means copying its contents into an Emacs
165 buffer so you can edit them. Emacs makes a new buffer for each file
166 that you visit. We often say that this buffer ``is visiting'' that
167 file, or that the buffer's ``visited file'' is that file. Emacs
168 constructs the buffer name from the file name by throwing away the
169 directory, keeping just the name proper. For example, a file named
170 @file{/usr/rms/emacs.tex} would get a buffer named @samp{emacs.tex}.
171 If there is already a buffer with that name, Emacs constructs a unique
172 name---the normal method is to append @samp{<2>}, @samp{<3>}, and so
173 on, but you can select other methods (@pxref{Uniquify}).
174
175 Each window's mode line shows the name of the buffer that is being displayed
176 in that window, so you can always tell what buffer you are editing.
177
178 The changes you make with editing commands are made in the Emacs
179 buffer. They do not take effect in the file that you visited, or any
180 place permanent, until you @dfn{save} the buffer. Saving the buffer
181 means that Emacs writes the current contents of the buffer into its
182 visited file. @xref{Saving}.
183
184 @cindex modified (buffer)
185 If a buffer contains changes that have not been saved, we say the
186 buffer is @dfn{modified}. This is important because it implies that
187 some changes will be lost if the buffer is not saved. The mode line
188 displays two stars near the left margin to indicate that the buffer is
189 modified.
190
191 @kindex C-x C-f
192 @findex find-file
193 To visit a file, use the command @kbd{C-x C-f} (@code{find-file}). Follow
194 the command with the name of the file you wish to visit, terminated by a
195 @key{RET}.
196
197 The file name is read using the minibuffer (@pxref{Minibuffer}), with
198 defaulting and completion in the standard manner (@pxref{File Names}).
199 While in the minibuffer, you can abort @kbd{C-x C-f} by typing
200 @kbd{C-g}. File-name completion ignores certain filenames; for more
201 about this, see @ref{Completion Options}.
202
203 @cindex file selection dialog
204 When Emacs is built with a suitable GUI toolkit, it pops up the
205 standard File Selection dialog of that toolkit instead of prompting for
206 the file name in the minibuffer. On Unix and GNU/Linux platforms, Emacs
207 does that when built with LessTif and Motif toolkits; on MS-Windows, the
208 GUI version does that by default.
209
210 Your confirmation that @kbd{C-x C-f} has completed successfully is the
211 appearance of new text on the screen and a new buffer name in the mode
212 line. If the specified file does not exist and could not be created, or
213 cannot be read, then you get an error, with an error message displayed
214 in the echo area.
215
216 If you visit a file that is already in Emacs, @kbd{C-x C-f} does not make
217 another copy. It selects the existing buffer containing that file.
218 However, before doing so, it checks that the file itself has not changed
219 since you visited or saved it last. If the file has changed, a warning
220 message is shown. @xref{Interlocking,,Simultaneous Editing}.
221
222 @cindex maximum buffer size exceeded, error message
223 Since Emacs reads the visited file in its entirety, files whose size
224 is larger than the maximum Emacs buffer size (@pxref{Buffers}) cannot be
225 visited; if you try, Emacs will display an error message saying that the
226 maximum buffer size has been exceeded.
227
228 @cindex creating files
229 What if you want to create a new file? Just visit it. Emacs displays
230 @samp{(New file)} in the echo area, but in other respects behaves as if
231 you had visited an existing empty file. If you make any changes and
232 save them, the file is created.
233
234 Emacs recognizes from the contents of a file which convention it uses
235 to separate lines---newline (used on GNU/Linux and on Unix),
236 carriage-return linefeed (used on Microsoft systems), or just
237 carriage-return (used on the Macintosh)---and automatically converts the
238 contents to the normal Emacs convention, which is that the newline
239 character separates lines. This is a part of the general feature of
240 coding system conversion (@pxref{Coding Systems}), and makes it possible
241 to edit files imported from different operating systems with
242 equal convenience. If you change the text and save the file, Emacs
243 performs the inverse conversion, changing newlines back into
244 carriage-return linefeed or just carriage-return if appropriate.
245
246 @vindex find-file-run-dired
247 If the file you specify is actually a directory, @kbd{C-x C-f} invokes
248 Dired, the Emacs directory browser, so that you can ``edit'' the contents
249 of the directory (@pxref{Dired}). Dired is a convenient way to delete,
250 look at, or operate on the files in the directory. However, if the
251 variable @code{find-file-run-dired} is @code{nil}, then it is an error
252 to try to visit a directory.
253
254 Files which are actually collections of other files, or @dfn{file
255 archives}, are visited in special modes which invoke a Dired-like
256 environment to allow operations on archive members. @xref{File
257 Archives}, for more about these features.
258
259 @cindex wildcard characters in file names
260 @vindex find-file-wildcards
261 If the file name you specify contains shell-style wildcard characters,
262 Emacs visits all the files that match it. Wildcards include @samp{?},
263 @samp{*}, and @samp{[@dots{}]} sequences. @xref{Quoted File Names}, for
264 information on how to visit a file whose name actually contains wildcard
265 characters. You can disable the wildcard feature by customizing
266 @code{find-file-wildcards}.
267
268 If you visit a file that the operating system won't let you modify,
269 Emacs makes the buffer read-only, so that you won't go ahead and make
270 changes that you'll have trouble saving afterward. You can make the
271 buffer writable with @kbd{C-x C-q} (@code{vc-toggle-read-only}).
272 @xref{Misc Buffer}.
273
274 @kindex C-x C-r
275 @findex find-file-read-only
276 Occasionally you might want to visit a file as read-only in order to
277 protect yourself from entering changes accidentally; do so by visiting
278 the file with the command @kbd{C-x C-r} (@code{find-file-read-only}).
279
280 @kindex C-x C-v
281 @findex find-alternate-file
282 If you visit a nonexistent file unintentionally (because you typed the
283 wrong file name), use the @kbd{C-x C-v} command
284 (@code{find-alternate-file}) to visit the file you really wanted.
285 @kbd{C-x C-v} is similar to @kbd{C-x C-f}, but it kills the current
286 buffer (after first offering to save it if it is modified). When
287 @kbd{C-x C-v} reads the file name to visit, it inserts the entire
288 default file name in the buffer, with point just after the directory
289 part; this is convenient if you made a slight error in typing the name.
290
291 If you find a file which exists but cannot be read, @kbd{C-x C-f}
292 signals an error.
293
294 @kindex C-x 4 f
295 @findex find-file-other-window
296 @kbd{C-x 4 f} (@code{find-file-other-window}) is like @kbd{C-x C-f}
297 except that the buffer containing the specified file is selected in another
298 window. The window that was selected before @kbd{C-x 4 f} continues to
299 show the same buffer it was already showing. If this command is used when
300 only one window is being displayed, that window is split in two, with one
301 window showing the same buffer as before, and the other one showing the
302 newly requested file. @xref{Windows}.
303
304 @kindex C-x 5 f
305 @findex find-file-other-frame
306 @kbd{C-x 5 f} (@code{find-file-other-frame}) is similar, but opens a
307 new frame, or makes visible any existing frame showing the file you
308 seek. This feature is available only when you are using a window
309 system. @xref{Frames}.
310
311 @findex find-file-literally
312 If you wish to edit a file as a sequence of ASCII characters with no special
313 encoding or conversion, use the @kbd{M-x find-file-literally} command.
314 It visits a file, like @kbd{C-x C-f}, but does not do format conversion
315 (@pxref{Formatted Text}), character code conversion (@pxref{Coding
316 Systems}), or automatic uncompression (@pxref{Compressed Files}), and
317 does not add a final newline because of @code{require-final-newline}.
318 If you already have visited the same file in the usual (non-literal)
319 manner, this command asks you whether to visit it literally instead.
320
321 @vindex find-file-hooks
322 @vindex find-file-not-found-hooks
323 Two special hook variables allow extensions to modify the operation of
324 visiting files. Visiting a file that does not exist runs the functions
325 in the list @code{find-file-not-found-hooks}; this variable holds a list
326 of functions, and the functions are called one by one (with no
327 arguments) until one of them returns non-@code{nil}. This is not a
328 normal hook, and the name ends in @samp{-hooks} rather than @samp{-hook}
329 to indicate that fact.
330
331 Successful visiting of any file, whether existing or not, calls the
332 functions in the list @code{find-file-hooks}, with no arguments.
333 This variable is really a normal hook, but it has an abnormal name for
334 historical compatibility. In the case of a nonexistent file, the
335 @code{find-file-not-found-hooks} are run first. @xref{Hooks}.
336
337 There are several ways to specify automatically the major mode for
338 editing the file (@pxref{Choosing Modes}), and to specify local
339 variables defined for that file (@pxref{File Variables}).
340
341 @node Saving
342 @section Saving Files
343
344 @dfn{Saving} a buffer in Emacs means writing its contents back into the file
345 that was visited in the buffer.
346
347 @table @kbd
348 @item C-x C-s
349 Save the current buffer in its visited file on disk (@code{save-buffer}).
350 @item C-x s
351 Save any or all buffers in their visited files (@code{save-some-buffers}).
352 @item M-~
353 Forget that the current buffer has been changed (@code{not-modified}).
354 With prefix argument (@kbd{C-u}), mark the current buffer as changed.
355 @item C-x C-w
356 Save the current buffer as a specified file name (@code{write-file}).
357 @item M-x set-visited-file-name
358 Change the file name under which the current buffer will be saved.
359 @end table
360
361 @kindex C-x C-s
362 @findex save-buffer
363 When you wish to save the file and make your changes permanent, type
364 @kbd{C-x C-s} (@code{save-buffer}). After saving is finished, @kbd{C-x C-s}
365 displays a message like this:
366
367 @example
368 Wrote /u/rms/gnu/gnu.tasks
369 @end example
370
371 @noindent
372 If the selected buffer is not modified (no changes have been made in it
373 since the buffer was created or last saved), saving is not really done,
374 because it would have no effect. Instead, @kbd{C-x C-s} displays a message
375 like this in the echo area:
376
377 @example
378 (No changes need to be saved)
379 @end example
380
381 @kindex C-x s
382 @findex save-some-buffers
383 The command @kbd{C-x s} (@code{save-some-buffers}) offers to save any
384 or all modified buffers. It asks you what to do with each buffer. The
385 possible responses are analogous to those of @code{query-replace}:
386
387 @table @kbd
388 @item y
389 Save this buffer and ask about the rest of the buffers.
390 @item n
391 Don't save this buffer, but ask about the rest of the buffers.
392 @item !
393 Save this buffer and all the rest with no more questions.
394 @c following generates acceptable underfull hbox
395 @item @key{RET}
396 Terminate @code{save-some-buffers} without any more saving.
397 @item .
398 Save this buffer, then exit @code{save-some-buffers} without even asking
399 about other buffers.
400 @item C-r
401 View the buffer that you are currently being asked about. When you exit
402 View mode, you get back to @code{save-some-buffers}, which asks the
403 question again.
404 @item C-h
405 Display a help message about these options.
406 @end table
407
408 @kbd{C-x C-c}, the key sequence to exit Emacs, invokes
409 @code{save-some-buffers} and therefore asks the same questions.
410
411 @kindex M-~
412 @findex not-modified
413 If you have changed a buffer but you do not want to save the changes,
414 you should take some action to prevent it. Otherwise, each time you use
415 @kbd{C-x s} or @kbd{C-x C-c}, you are liable to save this buffer by
416 mistake. One thing you can do is type @kbd{M-~} (@code{not-modified}),
417 which clears out the indication that the buffer is modified. If you do
418 this, none of the save commands will believe that the buffer needs to be
419 saved. (@samp{~} is often used as a mathematical symbol for `not'; thus
420 @kbd{M-~} is `not', metafied.) You could also use
421 @code{set-visited-file-name} (see below) to mark the buffer as visiting
422 a different file name, one which is not in use for anything important.
423 Alternatively, you can cancel all the changes made since the file was
424 visited or saved, by reading the text from the file again. This is
425 called @dfn{reverting}. @xref{Reverting}. You could also undo all the
426 changes by repeating the undo command @kbd{C-x u} until you have undone
427 all the changes; but reverting is easier.
428
429 @findex set-visited-file-name
430 @kbd{M-x set-visited-file-name} alters the name of the file that the
431 current buffer is visiting. It reads the new file name using the
432 minibuffer. Then it marks the buffer as visiting that file name, and
433 changes the buffer name correspondingly. @code{set-visited-file-name}
434 does not save the buffer in the newly visited file; it just alters the
435 records inside Emacs in case you do save later. It also marks the
436 buffer as ``modified'' so that @kbd{C-x C-s} in that buffer
437 @emph{will} save.
438
439 @kindex C-x C-w
440 @findex write-file
441 If you wish to mark the buffer as visiting a different file and save it
442 right away, use @kbd{C-x C-w} (@code{write-file}). It is precisely
443 equivalent to @code{set-visited-file-name} followed by @kbd{C-x C-s}.
444 @kbd{C-x C-s} used on a buffer that is not visiting a file has the
445 same effect as @kbd{C-x C-w}; that is, it reads a file name, marks the
446 buffer as visiting that file, and saves it there. The default file name in
447 a buffer that is not visiting a file is made by combining the buffer name
448 with the buffer's default directory (@pxref{File Names}).
449
450 If the new file name implies a major mode, then @kbd{C-x C-w} switches
451 to that major mode, in most cases. The command
452 @code{set-visited-file-name} also does this. @xref{Choosing Modes}.
453
454 If Emacs is about to save a file and sees that the date of the latest
455 version on disk does not match what Emacs last read or wrote, Emacs
456 notifies you of this fact, because it probably indicates a problem caused
457 by simultaneous editing and requires your immediate attention.
458 @xref{Interlocking,, Simultaneous Editing}.
459
460 @vindex require-final-newline
461 If the value of the variable @code{require-final-newline} is @code{t},
462 Emacs silently puts a newline at the end of any file that doesn't
463 already end in one, every time a file is saved or written. If the value
464 is @code{nil}, Emacs leaves the end of the file unchanged; if it's
465 neither @code{nil} nor @code{t}, Emacs asks you whether to add a
466 newline. The default is @code{nil}.
467
468 @menu
469 * Backup:: How Emacs saves the old version of your file.
470 * Interlocking:: How Emacs protects against simultaneous editing
471 of one file by two users.
472 * Shadowing: File Shadowing.
473 Copying files to "shadows" automatically.
474 * Time Stamps:: Emacs can update time stamps on saved files.
475 @end menu
476
477 @node Backup
478 @subsection Backup Files
479 @cindex backup file
480 @vindex make-backup-files
481 @vindex vc-make-backup-files
482
483 On most operating systems, rewriting a file automatically destroys all
484 record of what the file used to contain. Thus, saving a file from Emacs
485 throws away the old contents of the file---or it would, except that
486 Emacs carefully copies the old contents to another file, called the
487 @dfn{backup} file, before actually saving.
488
489 For most files, the variable @code{make-backup-files} determines
490 whether to make backup files. On most operating systems, its default
491 value is @code{t}, so that Emacs does write backup files.
492
493 For files managed by a version control system (@pxref{Version
494 Control}), the variable @code{vc-make-backup-files} determines whether
495 to make backup files. By default it is @code{nil}, since backup files
496 are redundant when you store all the previous versions in a version
497 control system. @xref{General VC Options}.
498
499 @vindex backup-enable-predicate
500 @vindex temporary-file-directory
501 @vindex small-temporary-file-directory
502 The default value of the @code{backup-enable-predicate} variable
503 prevents backup files being written for files in the directories used
504 for temporary files, specified by @code{temporary-file-directory} or
505 @code{small-temporary-file-directory}.
506
507 At your option, Emacs can keep either a single backup file or a series of
508 numbered backup files for each file that you edit.
509
510 Emacs makes a backup for a file only the first time the file is saved
511 from one buffer. No matter how many times you save a file, its backup file
512 continues to contain the contents from before the file was visited.
513 Normally this means that the backup file contains the contents from before
514 the current editing session; however, if you kill the buffer and then visit
515 the file again, a new backup file will be made by the next save.
516
517 You can also explicitly request making another backup file from a
518 buffer even though it has already been saved at least once. If you save
519 the buffer with @kbd{C-u C-x C-s}, the version thus saved will be made
520 into a backup file if you save the buffer again. @kbd{C-u C-u C-x C-s}
521 saves the buffer, but first makes the previous file contents into a new
522 backup file. @kbd{C-u C-u C-u C-x C-s} does both things: it makes a
523 backup from the previous contents, and arranges to make another from the
524 newly saved contents if you save again.
525
526 @menu
527 * Names: Backup Names. How backup files are named;
528 choosing single or numbered backup files.
529 * Deletion: Backup Deletion. Emacs deletes excess numbered backups.
530 * Copying: Backup Copying. Backups can be made by copying or renaming.
531 @end menu
532
533 @node Backup Names
534 @subsubsection Single or Numbered Backups
535
536 If you choose to have a single backup file (this is the default),
537 the backup file's name is normally constructed by appending @samp{~} to the
538 file name being edited; thus, the backup file for @file{eval.c} would
539 be @file{eval.c~}.
540
541 @vindex make-backup-file-name-function
542 @vindex backup-directory-alist
543 You can change this behavior by defining the variable
544 @code{make-backup-file-name-function} to a suitable function.
545 Alternatively you can customize the variable
546 @code{backup-directory-alist} to specify that files matching certain
547 patterns should be backed up in specific directories.
548
549 A typical use is to add an element @code{("." . @var{dir})} to make
550 all backups in the directory with absolute name @var{dir}; Emacs
551 modifies the backup file names to avoid clashes between files with the
552 same names originating in different directories. Alternatively,
553 adding, say, @code{("." . ".~")} would make backups in the invisible
554 subdirectory @file{.~} of the original file's directory. Emacs
555 creates the directory, if necessary, to make the backup.
556
557 If access control stops Emacs from writing backup files under the usual
558 names, it writes the backup file as @file{%backup%~} in your home
559 directory. Only one such file can exist, so only the most recently
560 made such backup is available.
561
562 If you choose to have a series of numbered backup files, backup file
563 names contain @samp{.~}, the number, and another @samp{~} after the
564 original file name. Thus, the backup files of @file{eval.c} would be
565 called @file{eval.c.~1~}, @file{eval.c.~2~}, and so on, all the way
566 through names like @file{eval.c.~259~} and beyond. The variable
567 @code{backup-directory-alist} applies to numbered backups just as
568 usual.
569
570 @vindex version-control
571 The choice of single backup or numbered backups is controlled by the
572 variable @code{version-control}. Its possible values are
573
574 @table @code
575 @item t
576 Make numbered backups.
577 @item nil
578 Make numbered backups for files that have numbered backups already.
579 Otherwise, make single backups.
580 @item never
581 Never make numbered backups; always make single backups.
582 @end table
583
584 @noindent
585 You can set @code{version-control} locally in an individual buffer to
586 control the making of backups for that buffer's file. For example,
587 Rmail mode locally sets @code{version-control} to @code{never} to make sure
588 that there is only one backup for an Rmail file. @xref{Locals}.
589
590 @cindex @env{VERSION_CONTROL} environment variable
591 If you set the environment variable @env{VERSION_CONTROL}, to tell
592 various GNU utilities what to do with backup files, Emacs also obeys the
593 environment variable by setting the Lisp variable @code{version-control}
594 accordingly at startup. If the environment variable's value is @samp{t}
595 or @samp{numbered}, then @code{version-control} becomes @code{t}; if the
596 value is @samp{nil} or @samp{existing}, then @code{version-control}
597 becomes @code{nil}; if it is @samp{never} or @samp{simple}, then
598 @code{version-control} becomes @code{never}.
599
600 @node Backup Deletion
601 @subsubsection Automatic Deletion of Backups
602
603 To prevent excessive consumption of disk space, Emacs can delete numbered
604 backup versions automatically. Generally Emacs keeps the first few backups
605 and the latest few backups, deleting any in between. This happens every
606 time a new backup is made.
607
608 @vindex kept-old-versions
609 @vindex kept-new-versions
610 The two variables @code{kept-old-versions} and
611 @code{kept-new-versions} control this deletion. Their values are,
612 respectively, the number of oldest (lowest-numbered) backups to keep
613 and the number of newest (highest-numbered) ones to keep, each time a
614 new backup is made. The backups in the middle (excluding those oldest
615 and newest) are the excess middle versions---those backups are
616 deleted. These variables' values are used when it is time to delete
617 excess versions, just after a new backup version is made; the newly
618 made backup is included in the count in @code{kept-new-versions}. By
619 default, both variables are 2.
620
621 @vindex delete-old-versions
622 If @code{delete-old-versions} is non-@code{nil}, Emacs deletes the
623 excess backup files silently. If it is @code{nil}, the default, Emacs
624 asks you whether it should delete the excess backup versions.
625
626 Dired's @kbd{.} (Period) command can also be used to delete old versions.
627 @xref{Dired Deletion}.
628
629 @node Backup Copying
630 @subsubsection Copying vs.@: Renaming
631
632 Backup files can be made by copying the old file or by renaming it.
633 This makes a difference when the old file has multiple names (hard
634 links). If the old file is renamed into the backup file, then the
635 alternate names become names for the backup file. If the old file is
636 copied instead, then the alternate names remain names for the file
637 that you are editing, and the contents accessed by those names will be
638 the new contents.
639
640 The method of making a backup file may also affect the file's owner
641 and group. If copying is used, these do not change. If renaming is used,
642 you become the file's owner, and the file's group becomes the default
643 (different operating systems have different defaults for the group).
644
645 Having the owner change is usually a good idea, because then the owner
646 always shows who last edited the file. Also, the owners of the backups
647 show who produced those versions. Occasionally there is a file whose
648 owner should not change; it is a good idea for such files to contain
649 local variable lists to set @code{backup-by-copying-when-mismatch}
650 locally (@pxref{File Variables}).
651
652 @vindex backup-by-copying
653 @vindex backup-by-copying-when-linked
654 @vindex backup-by-copying-when-mismatch
655 @vindex backup-by-copying-when-privileged-mismatch
656 @cindex file ownership, and backup
657 @cindex backup, and user-id
658 The choice of renaming or copying is controlled by four variables.
659 Renaming is the default choice. If the variable
660 @code{backup-by-copying} is non-@code{nil}, copying is used. Otherwise,
661 if the variable @code{backup-by-copying-when-linked} is non-@code{nil},
662 then copying is used for files that have multiple names, but renaming
663 may still be used when the file being edited has only one name. If the
664 variable @code{backup-by-copying-when-mismatch} is non-@code{nil}, then
665 copying is used if renaming would cause the file's owner or group to
666 change. @code{backup-by-copying-when-mismatch} is @code{t} by default
667 if you start Emacs as the superuser. The fourth variable,
668 @code{backup-by-copying-when-privileged-mismatch}, gives the highest
669 numeric user-id for which @code{backup-by-copying-when-mismatch} will be
670 forced on. This is useful when low-numbered user-ids are assigned to
671 special system users, such as @code{root}, @code{bin}, @code{daemon},
672 etc., which must maintain ownership of files.
673
674 When a file is managed with a version control system (@pxref{Version
675 Control}), Emacs does not normally make backups in the usual way for
676 that file. But check-in and check-out are similar in some ways to
677 making backups. One unfortunate similarity is that these operations
678 typically break hard links, disconnecting the file name you visited from
679 any alternate names for the same file. This has nothing to do with
680 Emacs---the version control system does it.
681
682 @node Interlocking
683 @subsection Protection against Simultaneous Editing
684
685 @cindex file dates
686 @cindex simultaneous editing
687 Simultaneous editing occurs when two users visit the same file, both
688 make changes, and then both save them. If nobody were informed that
689 this was happening, whichever user saved first would later find that his
690 changes were lost.
691
692 On some systems, Emacs notices immediately when the second user starts
693 to change the file, and issues an immediate warning. On all systems,
694 Emacs checks when you save the file, and warns if you are about to
695 overwrite another user's changes. You can prevent loss of the other
696 user's work by taking the proper corrective action instead of saving the
697 file.
698
699 @findex ask-user-about-lock
700 @cindex locking files
701 When you make the first modification in an Emacs buffer that is
702 visiting a file, Emacs records that the file is @dfn{locked} by you.
703 (It does this by creating a symbolic link in the same directory with a
704 different name.) Emacs removes the lock when you save the changes. The
705 idea is that the file is locked whenever an Emacs buffer visiting it has
706 unsaved changes.
707
708 @cindex collision
709 If you begin to modify the buffer while the visited file is locked by
710 someone else, this constitutes a @dfn{collision}. When Emacs detects a
711 collision, it asks you what to do, by calling the Lisp function
712 @code{ask-user-about-lock}. You can redefine this function for the sake
713 of customization. The standard definition of this function asks you a
714 question and accepts three possible answers:
715
716 @table @kbd
717 @item s
718 Steal the lock. Whoever was already changing the file loses the lock,
719 and you gain the lock.
720 @item p
721 Proceed. Go ahead and edit the file despite its being locked by someone else.
722 @item q
723 Quit. This causes an error (@code{file-locked}), and the buffer
724 contents remain unchanged---the modification you were trying to make
725 does not actually take place.
726 @end table
727
728 Note that locking works on the basis of a file name; if a file has
729 multiple names, Emacs does not realize that the two names are the same file
730 and cannot prevent two users from editing it simultaneously under different
731 names. However, basing locking on names means that Emacs can interlock the
732 editing of new files that will not really exist until they are saved.
733
734 Some systems are not configured to allow Emacs to make locks, and
735 there are cases where lock files cannot be written. In these cases,
736 Emacs cannot detect trouble in advance, but it still can detect the
737 collision when you try to save a file and overwrite someone else's
738 changes.
739
740 If Emacs or the operating system crashes, this may leave behind lock
741 files which are stale, so you may occasionally get warnings about
742 spurious collisions. When you determine that the collision is spurious,
743 just use @kbd{p} to tell Emacs to go ahead anyway.
744
745 Every time Emacs saves a buffer, it first checks the last-modification
746 date of the existing file on disk to verify that it has not changed since the
747 file was last visited or saved. If the date does not match, it implies
748 that changes were made in the file in some other way, and these changes are
749 about to be lost if Emacs actually does save. To prevent this, Emacs
750 displays a warning message and asks for confirmation before saving.
751 Occasionally you will know why the file was changed and know that it does
752 not matter; then you can answer @kbd{yes} and proceed. Otherwise, you should
753 cancel the save with @kbd{C-g} and investigate the situation.
754
755 The first thing you should do when notified that simultaneous editing
756 has already taken place is to list the directory with @kbd{C-u C-x C-d}
757 (@pxref{Directories}). This shows the file's current author. You
758 should attempt to contact him to warn him not to continue editing.
759 Often the next step is to save the contents of your Emacs buffer under a
760 different name, and use @code{diff} to compare the two files.@refill
761
762 @node File Shadowing
763 @subsection Shadowing Files
764 @cindex shadow files
765 @cindex file shadows
766
767 @table @kbd
768 @item M-x shadow-initialize
769 Set up file shadowing.
770 @item M-x shadow-define-literal-group
771 Declare a single file to be shared between sites.
772 @item M-x shadow-define-regexp-group
773 Make all files that match each of a group of files be shared between hosts.
774 @item M-x shadow-define-cluster @key{RET} @var{name} @key{RET}
775 Define a shadow file cluster @var{name}.
776 @item M-x shadow-copy-files
777 Copy all pending shadow files.
778 @item M-x shadow-cancel
779 Cancel the instruction to shadow some files.
780 @end table
781
782 You can arrange to keep identical @dfn{shadow} copies of certain files
783 in more than one place---possibly on different machines. To do this,
784 first you must set up a @dfn{shadow file group}, which is a set of
785 identically-named files shared between a list of sites. The file
786 group is permanent and applies to further Emacs sessions as well as
787 the current one. Once the group is set up, every time you exit Emacs,
788 it will copy the file you edited to the other files in its group. You
789 can also do the copying without exiting Emacs, by typing @kbd{M-x
790 shadow-copy-files}.
791
792 To set up a shadow file group, use @kbd{M-x
793 shadow-define-literal-group} or @kbd{M-x shadow-define-regexp-group}.
794 See their documentation strings for further information.
795
796 Before copying a file to its shadows, Emacs asks for confirmation.
797 You can answer ``no'' to bypass copying of this file, this time. If
798 you want to cancel the shadowing permanently for a certain file, use
799 @kbd{M-x shadow-cancel} to eliminate or change the shadow file group.
800
801 A @dfn{shadow cluster} is a group of hosts that share directories, so
802 that copying to or from one of them is sufficient to update the file
803 on all of them. Each shadow cluster has a name, and specifies the
804 network address of a primary host (the one we copy files to), and a
805 regular expression that matches the host names of all the other hosts
806 in the cluster. You can define a shadow cluster with @kbd{M-x
807 shadow-define-cluster}.
808
809 @node Time Stamps
810 @subsection Updating Time Stamps Automatically
811 @findex time-stamp
812 @cindex time stamps
813 @cindex modification dates
814 @cindex locale, date format
815
816 You can arrange to put a time stamp in a file, so that it will be updated
817 automatically each time you edit and save the file. The time stamp
818 has to be in the first eight lines of the file, and you should
819 insert it like this:
820
821 @example
822 Time-stamp: <>
823 @end example
824
825 @noindent
826 or like this:
827
828 @example
829 Time-stamp: ""
830 @end example
831
832 Then add the hook function @code{time-stamp} to the hook
833 @code{write-file-hooks}; that hook function will automatically update
834 the time stamp, inserting the current date and time when you save the
835 file. You can also use the command @kbd{M-x time-stamp} to update the
836 time stamp manually. For other customizations, see the Custom group
837 @code{time-stamp}. Note that non-numeric fields in the time stamp are
838 formatted according to your locale setting (@pxref{Environment}).
839
840 @node Reverting
841 @section Reverting a Buffer
842 @findex revert-buffer
843 @cindex drastic changes
844 @cindex reread a file
845
846 If you have made extensive changes to a file and then change your mind
847 about them, you can get rid of them by reading in the previous version
848 of the file. To do this, use @kbd{M-x revert-buffer}, which operates on
849 the current buffer. Since reverting a buffer unintentionally could lose
850 a lot of work, you must confirm this command with @kbd{yes}.
851
852 @code{revert-buffer} keeps point at the same distance (measured in
853 characters) from the beginning of the file. If the file was edited only
854 slightly, you will be at approximately the same piece of text after
855 reverting as before. If you have made drastic changes, the same value of
856 point in the old file may address a totally different piece of text.
857
858 Reverting marks the buffer as ``not modified'' until another change is
859 made.
860
861 Some kinds of buffers whose contents reflect data bases other than files,
862 such as Dired buffers, can also be reverted. For them, reverting means
863 recalculating their contents from the appropriate data base. Buffers
864 created explicitly with @kbd{C-x b} cannot be reverted; @code{revert-buffer}
865 reports an error when asked to do so.
866
867 @vindex revert-without-query
868 When you edit a file that changes automatically and frequently---for
869 example, a log of output from a process that continues to run---it may be
870 useful for Emacs to revert the file without querying you, whenever you
871 visit the file again with @kbd{C-x C-f}.
872
873 To request this behavior, set the variable @code{revert-without-query}
874 to a list of regular expressions. When a file name matches one of these
875 regular expressions, @code{find-file} and @code{revert-buffer} will
876 revert it automatically if it has changed---provided the buffer itself
877 is not modified. (If you have edited the text, it would be wrong to
878 discard your changes.)
879
880 @cindex Global Auto-Revert mode
881 @cindex mode, Global Auto-Revert
882 @cindex Auto-Revert mode
883 @cindex mode, Auto-Revert
884 @findex global-auto-revert-mode
885 @findex auto-revert-mode
886 @vindex auto-revert-interval
887 You may find it useful to have Emacs revert files automatically when
888 they change. Two minor modes are available to do this. In Global
889 Auto-Revert mode, Emacs periodically checks all file buffers and
890 reverts any when the corresponding file has changed. The local
891 variant, Auto-Revert mode, applies only to buffers in which it was
892 activated. Checking the files is done at intervals determined by the
893 variable @code{auto-revert-interval}.
894
895 @node Auto Save
896 @section Auto-Saving: Protection Against Disasters
897 @cindex Auto Save mode
898 @cindex mode, Auto Save
899 @cindex crashes
900
901 Emacs saves all the visited files from time to time (based on counting
902 your keystrokes) without being asked. This is called @dfn{auto-saving}.
903 It prevents you from losing more than a limited amount of work if the
904 system crashes.
905
906 When Emacs determines that it is time for auto-saving, each buffer is
907 considered, and is auto-saved if auto-saving is turned on for it and it
908 has been changed since the last time it was auto-saved. The message
909 @samp{Auto-saving...} is displayed in the echo area during auto-saving,
910 if any files are actually auto-saved. Errors occurring during
911 auto-saving are caught so that they do not interfere with the execution
912 of commands you have been typing.
913
914 @menu
915 * Files: Auto Save Files. The file where auto-saved changes are
916 actually made until you save the file.
917 * Control: Auto Save Control. Controlling when and how often to auto-save.
918 * Recover:: Recovering text from auto-save files.
919 @end menu
920
921 @node Auto Save Files
922 @subsection Auto-Save Files
923
924 Auto-saving does not normally save in the files that you visited, because
925 it can be very undesirable to save a program that is in an inconsistent
926 state when you have made half of a planned change. Instead, auto-saving
927 is done in a different file called the @dfn{auto-save file}, and the
928 visited file is changed only when you request saving explicitly (such as
929 with @kbd{C-x C-s}).
930
931 Normally, the auto-save file name is made by appending @samp{#} to the
932 front and rear of the visited file name. Thus, a buffer visiting file
933 @file{foo.c} is auto-saved in a file @file{#foo.c#}. Most buffers that
934 are not visiting files are auto-saved only if you request it explicitly;
935 when they are auto-saved, the auto-save file name is made by appending
936 @samp{#%} to the front and @samp{#} to the rear of buffer name. For
937 example, the @samp{*mail*} buffer in which you compose messages to be
938 sent is auto-saved in a file named @file{#%*mail*#}. Auto-save file
939 names are made this way unless you reprogram parts of Emacs to do
940 something different (the functions @code{make-auto-save-file-name} and
941 @code{auto-save-file-name-p}). The file name to be used for auto-saving
942 in a buffer is calculated when auto-saving is turned on in that buffer.
943
944 When you delete a substantial part of the text in a large buffer, auto
945 save turns off temporarily in that buffer. This is because if you
946 deleted the text unintentionally, you might find the auto-save file more
947 useful if it contains the deleted text. To reenable auto-saving after
948 this happens, save the buffer with @kbd{C-x C-s}, or use @kbd{C-u 1 M-x
949 auto-save}.
950
951 @vindex auto-save-visited-file-name
952 If you want auto-saving to be done in the visited file rather than
953 in a separate auto-save file, set the variable
954 @code{auto-save-visited-file-name} to a non-@code{nil} value. In this
955 mode, there is no real difference between auto-saving and explicit
956 saving.
957
958 @vindex delete-auto-save-files
959 A buffer's auto-save file is deleted when you save the buffer in its
960 visited file. To inhibit this, set the variable @code{delete-auto-save-files}
961 to @code{nil}. Changing the visited file name with @kbd{C-x C-w} or
962 @code{set-visited-file-name} renames any auto-save file to go with
963 the new visited name.
964
965 @node Auto Save Control
966 @subsection Controlling Auto-Saving
967
968 @vindex auto-save-default
969 @findex auto-save-mode
970 Each time you visit a file, auto-saving is turned on for that file's
971 buffer if the variable @code{auto-save-default} is non-@code{nil} (but not
972 in batch mode; @pxref{Entering Emacs}). The default for this variable is
973 @code{t}, so auto-saving is the usual practice for file-visiting buffers.
974 Auto-saving can be turned on or off for any existing buffer with the
975 command @kbd{M-x auto-save-mode}. Like other minor mode commands, @kbd{M-x
976 auto-save-mode} turns auto-saving on with a positive argument, off with a
977 zero or negative argument; with no argument, it toggles.
978
979 @vindex auto-save-interval
980 Emacs does auto-saving periodically based on counting how many characters
981 you have typed since the last time auto-saving was done. The variable
982 @code{auto-save-interval} specifies how many characters there are between
983 auto-saves. By default, it is 300. Emacs doesn't accept values that are
984 too small: if you customize @code{auto-save-interval} to a value less
985 than 20, Emacs will behave as if the value is 20.
986
987 @vindex auto-save-timeout
988 Auto-saving also takes place when you stop typing for a while. The
989 variable @code{auto-save-timeout} says how many seconds Emacs should
990 wait before it does an auto save (and perhaps also a garbage
991 collection). (The actual time period is longer if the current buffer is
992 long; this is a heuristic which aims to keep out of your way when you
993 are editing long buffers, in which auto-save takes an appreciable amount
994 of time.) Auto-saving during idle periods accomplishes two things:
995 first, it makes sure all your work is saved if you go away from the
996 terminal for a while; second, it may avoid some auto-saving while you
997 are actually typing.
998
999 Emacs also does auto-saving whenever it gets a fatal error. This
1000 includes killing the Emacs job with a shell command such as @samp{kill
1001 %emacs}, or disconnecting a phone line or network connection.
1002
1003 @findex do-auto-save
1004 You can request an auto-save explicitly with the command @kbd{M-x
1005 do-auto-save}.
1006
1007 @node Recover
1008 @subsection Recovering Data from Auto-Saves
1009
1010 @findex recover-file
1011 You can use the contents of an auto-save file to recover from a loss
1012 of data with the command @kbd{M-x recover-file @key{RET} @var{file}
1013 @key{RET}}. This visits @var{file} and then (after your confirmation)
1014 restores the contents from its auto-save file @file{#@var{file}#}.
1015 You can then save with @kbd{C-x C-s} to put the recovered text into
1016 @var{file} itself. For example, to recover file @file{foo.c} from its
1017 auto-save file @file{#foo.c#}, do:@refill
1018
1019 @example
1020 M-x recover-file @key{RET} foo.c @key{RET}
1021 yes @key{RET}
1022 C-x C-s
1023 @end example
1024
1025 Before asking for confirmation, @kbd{M-x recover-file} displays a
1026 directory listing describing the specified file and the auto-save file,
1027 so you can compare their sizes and dates. If the auto-save file
1028 is older, @kbd{M-x recover-file} does not offer to read it.
1029
1030 @findex recover-session
1031 If Emacs or the computer crashes, you can recover all the files you
1032 were editing from their auto save files with the command @kbd{M-x
1033 recover-session}. This first shows you a list of recorded interrupted
1034 sessions. Move point to the one you choose, and type @kbd{C-c C-c}.
1035
1036 Then @code{recover-session} asks about each of the files that were
1037 being edited during that session, asking whether to recover that file.
1038 If you answer @kbd{y}, it calls @code{recover-file}, which works in its
1039 normal fashion. It shows the dates of the original file and its
1040 auto-save file, and asks once again whether to recover that file.
1041
1042 When @code{recover-session} is done, the files you've chosen to
1043 recover are present in Emacs buffers. You should then save them. Only
1044 this---saving them---updates the files themselves.
1045
1046 @vindex auto-save-list-file-prefix
1047 Emacs records interrupted sessions for later recovery in files named
1048 @file{~/.emacs.d/auto-save-list/.saves-@var{pid}-@var{hostname}}. The
1049 @samp{~/.emacs.d/auto-save-list/.saves-} portion of these names comes
1050 from the value of @code{auto-save-list-file-prefix}. You can record
1051 sessions in a different place by customizing that variable. If you
1052 set @code{auto-save-list-file-prefix} to @code{nil} in your
1053 @file{.emacs} file, sessions are not recorded for recovery.
1054
1055 @node File Aliases
1056 @section File Name Aliases
1057
1058 Symbolic links and hard links both make it possible for several file
1059 names to refer to the same file. Hard links are alternate names that
1060 refer directly to the file; all the names are equally valid, and no one
1061 of them is preferred. By contrast, a symbolic link is a kind of defined
1062 alias: when @file{foo} is a symbolic link to @file{bar}, you can use
1063 either name to refer to the file, but @file{bar} is the real name, while
1064 @file{foo} is just an alias. More complex cases occur when symbolic
1065 links point to directories.
1066
1067 If you visit two names for the same file, normally Emacs makes
1068 two different buffers, but it warns you about the situation.
1069
1070 @vindex find-file-existing-other-name
1071 @vindex find-file-suppress-same-file-warnings
1072 Normally, if you visit a file which Emacs is already visiting under
1073 a different name, Emacs displays a message in the echo area and uses
1074 the existing buffer visiting that file. This can happen on systems
1075 that support symbolic links, or if you use a long file name on a
1076 system that truncates long file names. You can suppress the message by
1077 setting the variable @code{find-file-suppress-same-file-warnings} to a
1078 non-@code{nil} value. You can disable this feature entirely by setting
1079 the variable @code{find-file-existing-other-name} to @code{nil}: then
1080 if you visit the same file under two different names, you get a separate
1081 buffer for each file name.
1082
1083 @vindex find-file-visit-truename
1084 @cindex truenames of files
1085 @cindex file truenames
1086 If the variable @code{find-file-visit-truename} is non-@code{nil},
1087 then the file name recorded for a buffer is the file's @dfn{truename}
1088 (made by replacing all symbolic links with their target names), rather
1089 than the name you specify. Setting @code{find-file-visit-truename} also
1090 implies the effect of @code{find-file-existing-other-name}.
1091
1092 @node Version Control
1093 @section Version Control
1094 @cindex version control
1095
1096 @dfn{Version control systems} are packages that can record multiple
1097 versions of a source file, usually storing the unchanged parts of the
1098 file just once. Version control systems also record history information
1099 such as the creation time of each version, who created it, and a
1100 description of what was changed in that version.
1101
1102 The Emacs version control interface is called VC. Its commands work
1103 with three version control systems---RCS, CVS, and SCCS. The GNU
1104 project recommends RCS and CVS, which are free software and available
1105 from the Free Software Foundation. We also have free software to
1106 replace SCCS, known as CSSC; if you are using SCCS and don't want to
1107 make the incompatible change to RCS or CVS, you can switch to CSSC.
1108
1109 @menu
1110 * Introduction to VC:: How version control works in general.
1111 * VC Mode Line:: How the mode line shows version control status.
1112 * Basic VC Editing:: How to edit a file under version control.
1113 * Old Versions:: Examining and comparing old versions.
1114 * Secondary VC Commands:: The commands used a little less frequently.
1115 * Branches:: Multiple lines of development.
1116 * Remote Repositories:: Efficient access to remote CVS servers.
1117 * Snapshots:: Sets of file versions treated as a unit.
1118 * Miscellaneous VC:: Various other commands and features of VC.
1119 * Customizing VC:: Variables that change VC's behavior.
1120 @end menu
1121
1122 @node Introduction to VC
1123 @subsection Introduction to Version Control
1124
1125 VC allows you to use a version control system from within Emacs,
1126 integrating the version control operations smoothly with editing. VC
1127 provides a uniform interface to version control, so that regardless of
1128 which version control system is in use, you can use it the same way.
1129
1130 This section provides a general overview of version control, and
1131 describes the version control systems that VC supports. You can skip
1132 this section if you are already familiar with the version control system
1133 you want to use.
1134
1135 @menu
1136 * Version Systems:: Supported version control back-end systems.
1137 * VC Concepts:: Words and concepts related to version control.
1138 @end menu
1139
1140 @node Version Systems
1141 @subsubsection Supported Version Control Systems
1142
1143 @cindex RCS
1144 @cindex back end (version control)
1145 VC currently works with three different version control systems or
1146 ``back ends'': RCS, CVS, and SCCS.
1147
1148 RCS is a free version control system that is available from the Free
1149 Software Foundation. It is perhaps the most mature of the supported
1150 back ends, and the VC commands are conceptually closest to RCS. Almost
1151 everything you can do with RCS can be done through VC.
1152
1153 @cindex CVS
1154 CVS is built on top of RCS, and extends the features of RCS, allowing
1155 for more sophisticated release management, and concurrent multi-user
1156 development. VC supports basic editing operations under CVS, but for
1157 some less common tasks you still need to call CVS from the command line.
1158 Note also that before using CVS you must set up a repository, which is a
1159 subject too complex to treat here.
1160
1161 @cindex SCCS
1162 SCCS is a proprietary but widely used version control system. In
1163 terms of capabilities, it is the weakest of the three that VC
1164 supports. VC compensates for certain features missing in SCCS
1165 (snapshots, for example) by implementing them itself, but some other VC
1166 features, such as multiple branches, are not available with SCCS. You
1167 should use SCCS only if for some reason you cannot use RCS.
1168
1169 @node VC Concepts
1170 @subsubsection Concepts of Version Control
1171
1172 @cindex master file
1173 @cindex registered file
1174 When a file is under version control, we also say that it is
1175 @dfn{registered} in the version control system. Each registered file
1176 has a corresponding @dfn{master file} which represents the file's
1177 present state plus its change history---enough to reconstruct the
1178 current version or any earlier version. Usually the master file also
1179 records a @dfn{log entry} for each version, describing in words what was
1180 changed in that version.
1181
1182 @cindex work file
1183 @cindex checking out files
1184 The file that is maintained under version control is sometimes called
1185 the @dfn{work file} corresponding to its master file. You edit the work
1186 file and make changes in it, as you would with an ordinary file. (With
1187 SCCS and RCS, you must @dfn{lock} the file before you start to edit it.)
1188 After you are done with a set of changes, you @dfn{check the file in},
1189 which records the changes in the master file, along with a log entry for
1190 them.
1191
1192 With CVS, there are usually multiple work files corresponding to a
1193 single master file---often each user has his own copy. It is also
1194 possible to use RCS in this way, but this is not the usual way to use
1195 RCS.
1196
1197 @cindex locking and version control
1198 A version control system typically has some mechanism to coordinate
1199 between users who want to change the same file. One method is
1200 @dfn{locking} (analogous to the locking that Emacs uses to detect
1201 simultaneous editing of a file, but distinct from it). The other method
1202 is to merge your changes with other people's changes when you check them
1203 in.
1204
1205 With version control locking, work files are normally read-only so
1206 that you cannot change them. You ask the version control system to make
1207 a work file writable for you by locking it; only one user can do
1208 this at any given time. When you check in your changes, that unlocks
1209 the file, making the work file read-only again. This allows other users
1210 to lock the file to make further changes. SCCS always uses locking, and
1211 RCS normally does.
1212
1213 The other alternative for RCS is to let each user modify the work file
1214 at any time. In this mode, locking is not required, but it is
1215 permitted; check-in is still the way to record a new version.
1216
1217 CVS normally allows each user to modify his own copy of the work file
1218 at any time, but requires merging with changes from other users at
1219 check-in time. However, CVS can also be set up to require locking.
1220 (@pxref{CVS Options}).
1221
1222 @node VC Mode Line
1223 @subsection Version Control and the Mode Line
1224
1225 When you visit a file that is under version control, Emacs indicates
1226 this on the mode line. For example, @samp{RCS-1.3} says that RCS is
1227 used for that file, and the current version is 1.3.
1228
1229 The character between the back-end name and the version number
1230 indicates the version control status of the file. @samp{-} means that
1231 the work file is not locked (if locking is in use), or not modified (if
1232 locking is not in use). @samp{:} indicates that the file is locked, or
1233 that it is modified. If the file is locked by some other user (for
1234 instance, @samp{jim}), that is displayed as @samp{RCS:jim:1.3}.
1235
1236 @node Basic VC Editing
1237 @subsection Basic Editing under Version Control
1238
1239 The principal VC command is an all-purpose command that performs
1240 either locking or check-in, depending on the situation.
1241
1242 @table @kbd
1243 @item C-x C-q
1244 @itemx C-x v v
1245 Perform the next logical version control operation on this file.
1246 @end table
1247
1248 @findex vc-next-action
1249 @findex vc-toggle-read-only
1250 @kindex C-x v v
1251 @kindex C-x C-q @r{(Version Control)}
1252 Strictly speaking, the command for this job is @code{vc-next-action},
1253 bound to @kbd{C-x v v}. However, the normal meaning of @kbd{C-x C-q} is
1254 to make a read-only buffer writable, or vice versa; we have extended it
1255 to do the same job properly for files managed by version control, by
1256 performing the appropriate version control operations. When you type
1257 @kbd{C-x C-q} on a registered file, it acts like @kbd{C-x v v}.
1258
1259 The precise action of this command depends on the state of the file,
1260 and whether the version control system uses locking or not. SCCS and
1261 RCS normally use locking; CVS normally does not use locking.
1262
1263 @menu
1264 * VC with Locking:: RCS in its default mode, SCCS, and optionally CVS.
1265 * Without Locking:: Without locking: default mode for CVS.
1266 * Advanced C-x C-q:: Advanced features available with a prefix argument.
1267 * Log Buffer:: Features available in log entry buffers.
1268 @end menu
1269
1270 @node VC with Locking
1271 @subsubsection Basic Version Control with Locking
1272
1273 If locking is used for the file (as with SCCS, and RCS in its default
1274 mode), @kbd{C-x C-q} can either lock a file or check it in:
1275
1276 @itemize @bullet
1277 @item
1278 If the file is not locked, @kbd{C-x C-q} locks it, and
1279 makes it writable so that you can change it.
1280
1281 @item
1282 If the file is locked by you, and contains changes, @kbd{C-x C-q} checks
1283 in the changes. In order to do this, it first reads the log entry
1284 for the new version. @xref{Log Buffer}.
1285
1286 @item
1287 If the file is locked by you, but you have not changed it since you
1288 locked it, @kbd{C-x C-q} releases the lock and makes the file read-only
1289 again.
1290
1291 @item
1292 If the file is locked by some other user, @kbd{C-x C-q} asks you whether
1293 you want to ``steal the lock'' from that user. If you say yes, the file
1294 becomes locked by you, but a message is sent to the person who had
1295 formerly locked the file, to inform him of what has happened.
1296 @end itemize
1297
1298 These rules also apply when you use CVS in locking mode, except
1299 that there is no such thing as stealing a lock.
1300
1301 @node Without Locking
1302 @subsubsection Basic Version Control without Locking
1303
1304 When there is no locking---the default for CVS---work files are always
1305 writable; you do not need to do anything before you begin to edit a
1306 file. The status indicator on the mode line is @samp{-} if the file is
1307 unmodified; it flips to @samp{:} as soon as you save any changes in the
1308 work file.
1309
1310 Here is what @kbd{C-x C-q} does when using CVS:
1311
1312 @itemize @bullet
1313 @item
1314 If some other user has checked in changes into the master file, Emacs
1315 asks you whether you want to merge those changes into your own work
1316 file. You must do this before you can check in your own changes. (To
1317 pick up any recent changes from the master file @emph{without} trying
1318 to commit your own changes, type @kbd{C-x v m @key{RET}}.)
1319 @xref{Merging}.
1320
1321 @item
1322 If there are no new changes in the master file, but you have made
1323 modifications in your work file, @kbd{C-x C-q} checks in your changes.
1324 In order to do this, it first reads the log entry for the new version.
1325 @xref{Log Buffer}.
1326
1327 @item
1328 If the file is not modified, the @kbd{C-x C-q} does nothing.
1329 @end itemize
1330
1331 These rules also apply when you use RCS in the mode that does not
1332 require locking, except that automatic merging of changes from the
1333 master file is not implemented. Unfortunately, this means that nothing
1334 informs you if another user has checked in changes in the same file
1335 since you began editing it, and when this happens, his changes will be
1336 effectively removed when you check in your version (though they will
1337 remain in the master file, so they will not be entirely lost). You must
1338 therefore verify the current version is unchanged, before you check in your
1339 changes. We hope to eliminate this risk and provide automatic merging
1340 with RCS in a future Emacs version.
1341
1342 In addition, locking is possible with RCS even in this mode, although
1343 it is not required; @kbd{C-x C-q} with an unmodified file locks the
1344 file, just as it does with RCS in its normal (locking) mode.
1345
1346 @node Advanced C-x C-q
1347 @subsubsection Advanced Control in @kbd{C-x C-q}
1348
1349 When you give a prefix argument to @code{vc-next-action} (@kbd{C-u
1350 C-x C-q}), it still performs the next logical version control
1351 operation, but accepts additional arguments to specify precisely how
1352 to do the operation.
1353
1354 @itemize @bullet
1355 @item
1356 If the file is modified (or locked), you can specify the version
1357 number to use for the new version that you check in. This is one way
1358 to create a new branch (@pxref{Branches}).
1359
1360 @item
1361 If the file is not modified (and unlocked), you can specify the
1362 version to select; this lets you start working from an older version,
1363 or on another branch. If you do not enter any version, that takes you
1364 to the highest version on the current branch; therefore @kbd{C-u C-x
1365 C-q @key{RET}} is a convenient way to get the latest version of a file from
1366 the repository.
1367
1368 @item
1369 Instead of the version number, you can also specify the name of a
1370 version control system. This is useful when one file is being managed
1371 with two version control systems at the same time (@pxref{Local
1372 Version Control}).
1373 @end itemize
1374
1375 @node Log Buffer
1376 @subsubsection Features of the Log Entry Buffer
1377
1378 When you check in changes, @kbd{C-x C-q} first reads a log entry. It
1379 pops up a buffer called @samp{*VC-Log*} for you to enter the log entry.
1380 When you are finished, type @kbd{C-c C-c} in the @samp{*VC-Log*} buffer.
1381 That is when check-in really happens.
1382
1383 To abort check-in, just @strong{don't} type @kbd{C-c C-c} in that
1384 buffer. You can switch buffers and do other editing. As long as you
1385 don't try to check in another file, the entry you were editing remains
1386 in the @samp{*VC-Log*} buffer, and you can go back to that buffer at any
1387 time to complete the check-in.
1388
1389 If you change several source files for the same reason, it is often
1390 convenient to specify the same log entry for many of the files. To do
1391 this, use the history of previous log entries. The commands @kbd{M-n},
1392 @kbd{M-p}, @kbd{M-s} and @kbd{M-r} for doing this work just like the
1393 minibuffer history commands (except that these versions are used outside
1394 the minibuffer).
1395
1396 @vindex vc-log-mode-hook
1397 Each time you check in a file, the log entry buffer is put into VC Log
1398 mode, which involves running two hooks: @code{text-mode-hook} and
1399 @code{vc-log-mode-hook}. @xref{Hooks}.
1400
1401 @node Old Versions
1402 @subsection Examining And Comparing Old Versions
1403
1404 One of the convenient features of version control is the ability
1405 to examine any version of a file, or compare two versions.
1406
1407 @table @kbd
1408 @item C-x v ~ @var{version} @key{RET}
1409 Examine version @var{version} of the visited file, in a buffer of its
1410 own.
1411
1412 @item C-x v =
1413 Compare the current buffer contents with the latest checked-in version
1414 of the file.
1415
1416 @item C-u C-x v = @var{file} @key{RET} @var{oldvers} @key{RET} @var{newvers} @key{RET}
1417 Compare the specified two versions of @var{file}.
1418
1419 @item C-x v g
1420 Display the result of the CVS annotate command using colors.
1421 @end table
1422
1423 @findex vc-version-other-window
1424 @kindex C-x v ~
1425 To examine an old version in its entirety, visit the file and then type
1426 @kbd{C-x v ~ @var{version} @key{RET}} (@code{vc-version-other-window}).
1427 This puts the text of version @var{version} in a file named
1428 @file{@var{filename}.~@var{version}~}, and visits it in its own buffer
1429 in a separate window. (In RCS, you can also select an old version
1430 and create a branch from it. @xref{Branches}.)
1431
1432 @findex vc-diff
1433 @kindex C-x v =
1434 It is usually more convenient to compare two versions of the file,
1435 with the command @kbd{C-x v =} (@code{vc-diff}). Plain @kbd{C-x v =}
1436 compares the current buffer contents (saving them in the file if
1437 necessary) with the last checked-in version of the file. @kbd{C-u C-x
1438 v =}, with a numeric argument, reads a file name and two version
1439 numbers, then compares those versions of the specified file. Both
1440 forms display the output in a special buffer in another window.
1441
1442 You can specify a checked-in version by its number; an empty input
1443 specifies the current contents of the work file (which may be different
1444 from all the checked-in versions). You can also specify a snapshot name
1445 (@pxref{Snapshots}) instead of one or both version numbers.
1446
1447 If you supply a directory name instead of the name of a registered
1448 file, this command compares the two specified versions of all registered
1449 files in that directory and its subdirectories.
1450
1451 @vindex vc-diff-switches
1452 @vindex vc-rcs-diff-switches
1453 @kbd{C-x v =} works by running a variant of the @code{diff} utility
1454 designed to work with the version control system in use. When you
1455 invoke @code{diff} this way, in addition to the options specified by
1456 @code{diff-switches} (@pxref{Comparing Files}), it receives those
1457 specified by @code{vc-diff-switches}, plus those specified for the
1458 specific back end by @code{vc-@var{backend}-diff-switches}. For
1459 instance, when the version control back end is RCS, @code{diff} uses
1460 the options in @code{vc-rcs-diff-switches}. The
1461 @samp{vc@dots{}diff-switches} variables are @code{nil} by default.
1462
1463 Unlike the @kbd{M-x diff} command, @kbd{C-x v =} does not try to
1464 locate the changes in the old and new versions. This is because
1465 normally one or both versions do not exist as files when you compare
1466 them; they exist only in the records of the master file.
1467 @xref{Comparing Files}, for more information about @kbd{M-x diff}.
1468
1469 @findex vc-annotate
1470 @kindex C-x v g
1471 For CVS-controlled files, you can display the result of the CVS
1472 annotate command, using colors to enhance the visual appearance. Use
1473 the command @kbd{M-x vc-annotate} to do this. It creates a new buffer
1474 to display file's text, colored to show how old each part is. Text
1475 colored red is new, blue means old, and intermediate colors indicate
1476 intermediate ages. By default, the time scale is 360 days, so that
1477 everything more than one year old is shown in blue.
1478
1479 When you give a prefix argument to this command, it uses the
1480 minibuffer to read two arguments: which version number to display and
1481 annotate (instead of the current file contents), and a stretch factor
1482 for the time scale. A stretch factor of 0.1 means that the color
1483 range from red to blue spans the past 36 days instead of 360 days. A
1484 stretch factor greater than 1 means the color range spans more than a
1485 year.
1486
1487 @node Secondary VC Commands
1488 @subsection The Secondary Commands of VC
1489
1490 This section explains the secondary commands of VC; those that you might
1491 use once a day.
1492
1493 @menu
1494 * Registering:: Putting a file under version control.
1495 * VC Status:: Viewing the VC status of files.
1496 * VC Undo:: Cancelling changes before or after check-in.
1497 * VC Dired Mode:: Listing files managed by version control.
1498 * VC Dired Commands:: Commands to use in a VC Dired buffer.
1499 @end menu
1500
1501 @node Registering
1502 @subsubsection Registering a File for Version Control
1503
1504 @kindex C-x v i
1505 @findex vc-register
1506 You can put any file under version control by simply visiting it, and
1507 then typing @w{@kbd{C-x v i}} (@code{vc-register}).
1508
1509 @table @kbd
1510 @item C-x v i
1511 Register the visited file for version control.
1512 @end table
1513
1514 To register the file, Emacs must choose which version control system
1515 to use for it. If the file's directory already contains files
1516 registered in a version control system, Emacs uses that system. If
1517 there is more than one system in use for a directory, Emacs uses the one
1518 that appears first in @code{vc-handled-backends} (@pxref{Customizing VC}).
1519 On the other hand, if there are no files already registered,
1520 Emacs uses the first system from @code{vc-handled-backends} that could
1521 register the file---for example, you cannot register a file under CVS if
1522 its directory is not already part of a CVS tree.
1523
1524 With the default value of @code{vc-handled-backends}, this means
1525 that Emacs uses RCS if there are any files under RCS control, CVS if
1526 there are any files under CVS, SCCS if any files are under SCCS, or
1527 RCS as the ultimate default.
1528
1529 If locking is in use, @kbd{C-x v i} leaves the file unlocked and
1530 read-only. Type @kbd{C-x C-q} if you wish to start editing it. After
1531 registering a file with CVS, you must subsequently commit the initial
1532 version by typing @kbd{C-x C-q}.
1533
1534 @vindex vc-default-init-version
1535 The initial version number for a newly registered file is 1.1, by
1536 default. You can specify a different default by setting the variable
1537 @code{vc-default-init-version}, or you can give @kbd{C-x v i} a numeric
1538 argument; then it reads the initial version number for this particular
1539 file using the minibuffer.
1540
1541 @vindex vc-initial-comment
1542 If @code{vc-initial-comment} is non-@code{nil}, @kbd{C-x v i} reads an
1543 initial comment to describe the purpose of this source file. Reading
1544 the initial comment works like reading a log entry (@pxref{Log Buffer}).
1545
1546 @node VC Status
1547 @subsubsection VC Status Commands
1548
1549 @table @kbd
1550 @item C-x v l
1551 Display version control state and change history.
1552 @end table
1553
1554 @kindex C-x v l
1555 @findex vc-print-log
1556 To view the detailed version control status and history of a file,
1557 type @kbd{C-x v l} (@code{vc-print-log}). It displays the history of
1558 changes to the current file, including the text of the log entries. The
1559 output appears in a separate window.
1560
1561 @node VC Undo
1562 @subsubsection Undoing Version Control Actions
1563
1564 @table @kbd
1565 @item C-x v u
1566 Revert the buffer and the file to the last checked-in version.
1567
1568 @item C-x v c
1569 Remove the last-entered change from the master for the visited file.
1570 This undoes your last check-in.
1571 @end table
1572
1573 @kindex C-x v u
1574 @findex vc-revert-buffer
1575 If you want to discard your current set of changes and revert to the
1576 last version checked in, use @kbd{C-x v u} (@code{vc-revert-buffer}).
1577 This leaves the file unlocked; if locking is in use, you must first lock
1578 the file again before you change it again. @kbd{C-x v u} requires
1579 confirmation, unless it sees that you haven't made any changes since the
1580 last checked-in version.
1581
1582 @kbd{C-x v u} is also the command to unlock a file if you lock it and
1583 then decide not to change it.
1584
1585 @kindex C-x v c
1586 @findex vc-cancel-version
1587 To cancel a change that you already checked in, use @kbd{C-x v c}
1588 (@code{vc-cancel-version}). This command discards all record of the
1589 most recent checked-in version. @kbd{C-x v c} also offers to revert
1590 your work file and buffer to the previous version (the one that precedes
1591 the version that is deleted).
1592
1593 If you answer @kbd{no}, VC keeps your changes in the buffer, and locks
1594 the file. The no-revert option is useful when you have checked in a
1595 change and then discover a trivial error in it; you can cancel the
1596 erroneous check-in, fix the error, and check the file in again.
1597
1598 When @kbd{C-x v c} does not revert the buffer, it unexpands all
1599 version control headers in the buffer instead (@pxref{Version Headers}).
1600 This is because the buffer no longer corresponds to any existing
1601 version. If you check it in again, the check-in process will expand the
1602 headers properly for the new version number.
1603
1604 However, it is impossible to unexpand the RCS @samp{@w{$}Log$} header
1605 automatically. If you use that header feature, you have to unexpand it
1606 by hand---by deleting the entry for the version that you just canceled.
1607
1608 Be careful when invoking @kbd{C-x v c}, as it is easy to lose a lot of
1609 work with it. To help you be careful, this command always requires
1610 confirmation with @kbd{yes}. Note also that this command is disabled
1611 under CVS, because canceling versions is very dangerous and discouraged
1612 with CVS.
1613
1614 @node VC Dired Mode
1615 @subsubsection Dired under VC
1616
1617 @cindex PCL-CVS
1618 @pindex cvs
1619 @cindex CVS Dired Mode
1620 The VC Dired Mode described here works with all the version control
1621 systems that VC supports. Another more powerful facility, designed
1622 specifically for CVS, is called PCL-CVS. @xref{Top, , About PCL-CVS,
1623 pcl-cvs, PCL-CVS --- The Emacs Front-End to CVS}.
1624
1625 @kindex C-x v d
1626 @findex vc-directory
1627 When you are working on a large program, it is often useful to find
1628 out which files have changed within an entire directory tree, or to view
1629 the status of all files under version control at once, and to perform
1630 version control operations on collections of files. You can use the
1631 command @kbd{C-x v d} (@code{vc-directory}) to make a directory listing
1632 that includes only files relevant for version control.
1633
1634 @vindex vc-dired-terse-display
1635 @kbd{C-x v d} creates a buffer which uses VC Dired Mode. This looks
1636 much like an ordinary Dired buffer (@pxref{Dired}); however, normally it
1637 shows only the noteworthy files (those locked or not up-to-date). This
1638 is called @dfn{terse display}. If you set the variable
1639 @code{vc-dired-terse-display} to @code{nil}, then VC Dired shows all
1640 relevant files---those managed under version control, plus all
1641 subdirectories (@dfn{full display}). The command @kbd{v t} in a VC
1642 Dired buffer toggles between terse display and full display (@pxref{VC
1643 Dired Commands}).
1644
1645 @vindex vc-dired-recurse
1646 By default, VC Dired produces a recursive listing of noteworthy or
1647 relevant files at or below the given directory. You can change this by
1648 setting the variable @code{vc-dired-recurse} to @code{nil}; then VC
1649 Dired shows only the files in the given directory.
1650
1651 The line for an individual file shows the version control state in the
1652 place of the hard link count, owner, group, and size of the file. If
1653 the file is unmodified, in sync with the master file, the version
1654 control state shown is blank. Otherwise it consists of text in
1655 parentheses. Under RCS and SCCS, the name of the user locking the file
1656 is shown; under CVS, an abbreviated version of the @samp{cvs status}
1657 output is used. Here is an example using RCS:
1658
1659 @smallexample
1660 @group
1661 /home/jim/project:
1662
1663 -rw-r--r-- (jim) Apr 2 23:39 file1
1664 -r--r--r-- Apr 5 20:21 file2
1665 @end group
1666 @end smallexample
1667
1668 @noindent
1669 The files @samp{file1} and @samp{file2} are under version control,
1670 @samp{file1} is locked by user jim, and @samp{file2} is unlocked.
1671
1672 Here is an example using CVS:
1673
1674 @smallexample
1675 @group
1676 /home/joe/develop:
1677
1678 -rw-r--r-- (modified) Aug 2 1997 file1.c
1679 -rw-r--r-- Apr 4 20:09 file2.c
1680 -rw-r--r-- (merge) Sep 13 1996 file3.c
1681 @end group
1682 @end smallexample
1683
1684 Here @samp{file1.c} is modified with respect to the repository, and
1685 @samp{file2.c} is not. @samp{file3.c} is modified, but other changes
1686 have also been checked in to the repository---you need to merge them
1687 with the work file before you can check it in.
1688
1689 @vindex vc-directory-exclusion-list
1690 When VC Dired displays subdirectories (in the ``full'' display mode),
1691 it omits some that should never contain any files under version control.
1692 By default, this includes Version Control subdirectories such as
1693 @samp{RCS} and @samp{CVS}; you can customize this by setting the
1694 variable @code{vc-directory-exclusion-list}.
1695
1696 You can fine-tune VC Dired's format by typing @kbd{C-u C-x v d}---as in
1697 ordinary Dired, that allows you to specify additional switches for the
1698 @samp{ls} command.
1699
1700 @node VC Dired Commands
1701 @subsubsection VC Dired Commands
1702
1703 All the usual Dired commands work normally in VC Dired mode, except
1704 for @kbd{v}, which is redefined as the version control prefix. You can
1705 invoke VC commands such as @code{vc-diff} and @code{vc-print-log} by
1706 typing @kbd{v =}, or @kbd{v l}, and so on. Most of these commands apply
1707 to the file name on the current line.
1708
1709 The command @kbd{v v} (@code{vc-next-action}) operates on all the
1710 marked files, so that you can lock or check in several files at once.
1711 If it operates on more than one file, it handles each file according to
1712 its current state; thus, it might lock one file, but check in another
1713 file. This could be confusing; it is up to you to avoid confusing
1714 behavior by marking a set of files that are in a similar state.
1715
1716 If any files call for check-in, @kbd{v v} reads a single log entry,
1717 then uses it for all the files being checked in. This is convenient for
1718 registering or checking in several files at once, as part of the same
1719 change.
1720
1721 @findex vc-dired-toggle-terse-mode
1722 @findex vc-dired-mark-locked
1723 You can toggle between terse display (only locked files, or files not
1724 up-to-date) and full display at any time by typing @kbd{v t}
1725 (@code{vc-dired-toggle-terse-mode}). There is also a special command
1726 @kbd{* l} (@code{vc-dired-mark-locked}), which marks all files currently
1727 locked (or, with CVS, all files not up-to-date). Thus, typing @kbd{* l
1728 t k} is another way to delete from the buffer all files except those
1729 currently locked.
1730
1731 @node Branches
1732 @subsection Multiple Branches of a File
1733 @cindex branch (version control)
1734 @cindex trunk (version control)
1735
1736 One use of version control is to maintain multiple ``current''
1737 versions of a file. For example, you might have different versions of a
1738 program in which you are gradually adding various unfinished new
1739 features. Each such independent line of development is called a
1740 @dfn{branch}. VC allows you to create branches, switch between
1741 different branches, and merge changes from one branch to another.
1742 Please note, however, that branches are only supported for RCS at the
1743 moment.
1744
1745 A file's main line of development is usually called the @dfn{trunk}.
1746 The versions on the trunk are normally numbered 1.1, 1.2, 1.3, etc. At
1747 any such version, you can start an independent branch. A branch
1748 starting at version 1.2 would have version number 1.2.1.1, and consecutive
1749 versions on this branch would have numbers 1.2.1.2, 1.2.1.3, 1.2.1.4,
1750 and so on. If there is a second branch also starting at version 1.2, it
1751 would consist of versions 1.2.2.1, 1.2.2.2, 1.2.2.3, etc.
1752
1753 @cindex head version
1754 If you omit the final component of a version number, that is called a
1755 @dfn{branch number}. It refers to the highest existing version on that
1756 branch---the @dfn{head version} of that branch. The branches in the
1757 example above have branch numbers 1.2.1 and 1.2.2.
1758
1759 @menu
1760 * Switching Branches:: How to get to another existing branch.
1761 * Creating Branches:: How to start a new branch.
1762 * Merging:: Transferring changes between branches.
1763 * Multi-User Branching:: Multiple users working at multiple branches
1764 in parallel.
1765 @end menu
1766
1767 @node Switching Branches
1768 @subsubsection Switching between Branches
1769
1770 To switch between branches, type @kbd{C-u C-x C-q} and specify the
1771 version number you want to select. This version is then visited
1772 @emph{unlocked} (write-protected), so you can examine it before locking
1773 it. Switching branches in this way is allowed only when the file is not
1774 locked.
1775
1776 You can omit the minor version number, thus giving only the branch
1777 number; this takes you to the head version on the chosen branch. If you
1778 only type @key{RET}, Emacs goes to the highest version on the trunk.
1779
1780 After you have switched to any branch (including the main branch), you
1781 stay on it for subsequent VC commands, until you explicitly select some
1782 other branch.
1783
1784 @node Creating Branches
1785 @subsubsection Creating New Branches
1786
1787 To create a new branch from a head version (one that is the latest in
1788 the branch that contains it), first select that version if necessary,
1789 lock it with @kbd{C-x C-q}, and make whatever changes you want. Then,
1790 when you check in the changes, use @kbd{C-u C-x C-q}. This lets you
1791 specify the version number for the new version. You should specify a
1792 suitable branch number for a branch starting at the current version.
1793 For example, if the current version is 2.5, the branch number should be
1794 2.5.1, 2.5.2, and so on, depending on the number of existing branches at
1795 that point.
1796
1797 To create a new branch at an older version (one that is no longer the
1798 head of a branch), first select that version (@pxref{Switching
1799 Branches}), then lock it with @kbd{C-x C-q}. You'll be asked to
1800 confirm, when you lock the old version, that you really mean to create a
1801 new branch---if you say no, you'll be offered a chance to lock the
1802 latest version instead.
1803
1804 Then make your changes and type @kbd{C-x C-q} again to check in a new
1805 version. This automatically creates a new branch starting from the
1806 selected version. You need not specially request a new branch, because
1807 that's the only way to add a new version at a point that is not the head
1808 of a branch.
1809
1810 After the branch is created, you ``stay'' on it. That means that
1811 subsequent check-ins create new versions on that branch. To leave the
1812 branch, you must explicitly select a different version with @kbd{C-u C-x
1813 C-q}. To transfer changes from one branch to another, use the merge
1814 command, described in the next section.
1815
1816 @node Merging
1817 @subsubsection Merging Branches
1818
1819 @cindex merging changes
1820 When you have finished the changes on a certain branch, you will
1821 often want to incorporate them into the file's main line of development
1822 (the trunk). This is not a trivial operation, because development might
1823 also have proceeded on the trunk, so that you must @dfn{merge} the
1824 changes into a file that has already been changed otherwise. VC allows
1825 you to do this (and other things) with the @code{vc-merge} command.
1826
1827 @table @kbd
1828 @item C-x v m (vc-merge)
1829 Merge changes into the work file.
1830 @end table
1831
1832 @kindex C-x v m
1833 @findex vc-merge
1834 @kbd{C-x v m} (@code{vc-merge}) takes a set of changes and merges it
1835 into the current version of the work file. It firsts asks you in the
1836 minibuffer where the changes should come from. If you just type
1837 @key{RET}, Emacs merges any changes that were made on the same branch
1838 since you checked the file out (we call this @dfn{merging the news}).
1839 This is the common way to pick up recent changes from the repository,
1840 regardless of whether you have already changed the file yourself.
1841
1842 You can also enter a branch number or a pair of version numbers in
1843 the minibuffer. Then @kbd{C-x v m} finds the changes from that
1844 branch, or the differences between the two versions you specified, and
1845 merges them into the current version of the current file.
1846
1847 As an example, suppose that you have finished a certain feature on
1848 branch 1.3.1. In the meantime, development on the trunk has proceeded
1849 to version 1.5. To merge the changes from the branch to the trunk,
1850 first go to the head version of the trunk, by typing @kbd{C-u C-x C-q
1851 @key{RET}}. Version 1.5 is now current. If locking is used for the file,
1852 type @kbd{C-x C-q} to lock version 1.5 so that you can change it. Next,
1853 type @kbd{C-x v m 1.3.1 @key{RET}}. This takes the entire set of changes on
1854 branch 1.3.1 (relative to version 1.3, where the branch started, up to
1855 the last version on the branch) and merges it into the current version
1856 of the work file. You can now check in the changed file, thus creating
1857 version 1.6 containing the changes from the branch.
1858
1859 It is possible to do further editing after merging the branch, before
1860 the next check-in. But it is usually wiser to check in the merged
1861 version, then lock it and make the further changes. This will keep
1862 a better record of the history of changes.
1863
1864 @cindex conflicts
1865 @cindex resolving conflicts
1866 When you merge changes into a file that has itself been modified, the
1867 changes might overlap. We call this situation a @dfn{conflict}, and
1868 reconciling the conflicting changes is called @dfn{resolving a
1869 conflict}.
1870
1871 Whenever conflicts occur during merging, VC detects them, tells you
1872 about them in the echo area, and asks whether you want help in merging.
1873 If you say yes, it starts an Ediff session (@pxref{Top,
1874 Ediff, Ediff, ediff, The Ediff Manual}).
1875
1876 If you say no, the conflicting changes are both inserted into the
1877 file, surrounded by @dfn{conflict markers}. The example below shows how
1878 a conflict region looks; the file is called @samp{name} and the current
1879 master file version with user B's changes in it is 1.11.
1880
1881 @c @w here is so CVS won't think this is a conflict.
1882 @smallexample
1883 @group
1884 @w{<}<<<<<< name
1885 @var{User A's version}
1886 =======
1887 @var{User B's version}
1888 @w{>}>>>>>> 1.11
1889 @end group
1890 @end smallexample
1891
1892 @cindex vc-resolve-conflicts
1893 Then you can resolve the conflicts by editing the file manually. Or
1894 you can type @code{M-x vc-resolve-conflicts} after visiting the file.
1895 This starts an Ediff session, as described above. Don't forget to
1896 check in the merged version afterwards.
1897
1898 @node Multi-User Branching
1899 @subsubsection Multi-User Branching
1900
1901 It is often useful for multiple developers to work simultaneously on
1902 different branches of a file. CVS allows this by default; for RCS, it
1903 is possible if you create multiple source directories. Each source
1904 directory should have a link named @file{RCS} which points to a common
1905 directory of RCS master files. Then each source directory can have its
1906 own choice of selected versions, but all share the same common RCS
1907 records.
1908
1909 This technique works reliably and automatically, provided that the
1910 source files contain RCS version headers (@pxref{Version Headers}). The
1911 headers enable Emacs to be sure, at all times, which version number is
1912 present in the work file.
1913
1914 If the files do not have version headers, you must instead tell Emacs
1915 explicitly in each session which branch you are working on. To do this,
1916 first find the file, then type @kbd{C-u C-x C-q} and specify the correct
1917 branch number. This ensures that Emacs knows which branch it is using
1918 during this particular editing session.
1919
1920 @node Remote Repositories
1921 @subsection Remote Repositories
1922 @cindex remote repositories (CVS)
1923
1924 A common way of using CVS is to set up a central CVS repository on
1925 some Internet host, then have each developer check out a personal
1926 working copy of the files on his local machine. Committing changes to
1927 the repository, and picking up changes from other users into one's own
1928 working area, then works by direct interactions with the CVS server.
1929
1930 One difficulty is that access to the CVS server is often slow, and
1931 that developers might need to work off-line as well. VC is designed
1932 to reduce the amount of network interaction necessary.
1933
1934 @menu
1935 * Version Backups:: Keeping local copies of repository versions.
1936 * Local Version Control:: Using another version system for local editing.
1937 @end menu
1938
1939 @node Version Backups
1940 @subsubsection Version Backups
1941 @cindex version backups
1942
1943 @cindex automatic version backups
1944 When VC sees that the CVS repository for a file is on a remote
1945 machine, it automatically makes local backups of unmodified versions
1946 of the file---@dfn{automatic version backups}. This means that you
1947 can compare the file to the repository version (@kbd{C-x v =}), or
1948 revert to that version (@kbd{C-x v u}), without any network
1949 interactions.
1950
1951 The local copy of the unmodified file is called a @dfn{version
1952 backup} to indicate that it corresponds exactly to a version that is
1953 stored in the repository. Note that version backups are not the same
1954 as ordinary Emacs backup files (@pxref{Backup}). But they follow a
1955 similar naming convention.
1956
1957 For a file that comes from a remote CVS repository, VC makes a
1958 version backup whenever you save the first changes to the file, and
1959 removes it after you have committed your modified version to the
1960 repository. You can disable the making of automatic version backups by
1961 setting @code{vc-cvs-stay-local} to @code{nil} (@pxref{CVS Options}).
1962
1963 @cindex manual version backups
1964 The name of the automatic version backup for version @var{version}
1965 of file @var{file} is @code{@var{file}.~@var{version}.~}. This is
1966 almost the same as the name used by @kbd{C-x v ~} (@pxref{Old
1967 Versions}), the only difference being the additional dot (@samp{.})
1968 after the version number. This similarity is intentional, because
1969 both kinds of files store the same kind of information. The file made
1970 by @kbd{C-x v ~} acts as a @dfn{manual version backup}.
1971
1972 All the VC commands that operate on old versions of a file can use
1973 both kinds of version backups. For instance, @kbd{C-x v ~} uses
1974 either an automatic or a manual version backup, if possible, to get
1975 the contents of the version you request. Likewise, @kbd{C-x v =} and
1976 @kbd{C-x v u} use either an automatic or a manual version backup, if
1977 one of them exists, to get the contents of a version to compare or
1978 revert to. If you changed a file outside of Emacs, so that no
1979 automatic version backup was created for the previous text, you can
1980 create a manual backup of that version using @kbd{C-x v ~}, and thus
1981 obtain the benefit of the local copy for Emacs commands.
1982
1983 The only difference in Emacs's handling of manual and automatic
1984 version backups, once they exist, is that Emacs deletes automatic
1985 version backups when you commit to the repository. By contrast,
1986 manual version backups remain until you delete them.
1987
1988 @node Local Version Control
1989 @subsubsection Local Version Control
1990 @cindex local version control
1991 @cindex local back end (version control)
1992
1993 When you make many changes to a file that comes from a remote
1994 repository, it can be convenient to have version control on your local
1995 machine as well. You can then record intermediate versions, revert to
1996 a previous state, etc., before you actually commit your changes to the
1997 remote server.
1998
1999 VC lets you do this by putting a file under a second, local version
2000 control system, so that the file is effectively registered in two
2001 systems at the same time. For the description here, we will assume
2002 that the remote system is CVS, and you use RCS locally, although the
2003 mechanism works with any combination of version control systems
2004 (@dfn{back ends}).
2005
2006 To make it work with other back ends, you must make sure that the
2007 ``more local'' back end comes before the ``more remote'' back end in
2008 the setting of @code{vc-handled-backends} (@pxref{Customizing VC}). By
2009 default, this variable is set up so that you can use remote CVS and
2010 local RCS as described here.
2011
2012 To start using local RCS for a file that comes from a remote CVS
2013 server, you must @emph{register the file in RCS}, by typing @kbd{C-u
2014 C-x v v rcs @key{RET}}. (In other words, use @code{vc-next-action} with a
2015 prefix argument, and specify RCS as the back end.)
2016
2017 You can do this at any time; it does not matter whether you have
2018 already modified the file with respect to the version in the CVS
2019 repository. If possible, VC tries to make the RCS master start with
2020 the unmodified repository version, then checks in any local changes
2021 as a new version. This works if you have not made any changes yet, or
2022 if the unmodified repository version exists locally as a version
2023 backup (@pxref{Version Backups}). If the unmodified version is not
2024 available locally, the RCS master starts with the modified version;
2025 the only drawback to this is that you cannot compare your changes
2026 locally to what is stored in the repository.
2027
2028 The version number of the RCS master is derived from the current CVS
2029 version, starting a branch from it. For example, if the current CVS
2030 version is 1.23, the local RCS branch will be 1.23.1. Version 1.23 in
2031 the RCS master will be identical to version 1.23 under CVS; your first
2032 changes are checked in as 1.23.1.1. (If the unmodified file is not
2033 available locally, VC will check in the modified file twice, both as
2034 1.23 and 1.23.1.1, to make the revision numbers consistent.)
2035
2036 If you do not use locking under CVS (the default), locking is also
2037 disabled for RCS, so that editing under RCS works exactly as under
2038 CVS.
2039
2040 When you are done with local editing, you can commit the final version
2041 back to the CVS repository by typing @kbd{C-u C-x v v cvs @key{RET}}.
2042 This initializes the log entry buffer (@pxref{Log Buffer}) to contain
2043 all the log entries you have recorded in the RCS master; you can edit
2044 them as you wish, and then commit in CVS by typing @kbd{C-c C-c}. If
2045 the commit is successful, VC removes the RCS master, so that the file
2046 is once again registered under CVS only. (The RCS master is not
2047 actually deleted, just renamed by appending @samp{~} to the name, so
2048 that you can refer to it later if you wish.)
2049
2050 While using local RCS, you can pick up recent changes from the CVS
2051 repository into your local file, or commit some of your changes back
2052 to CVS, without terminating local RCS version control. To do this,
2053 switch to the CVS back end temporarily, with the @kbd{C-x v b} command:
2054
2055 @table @kbd
2056 @item C-x v b
2057 Switch to another back end that the current file is registered
2058 under (@code{vc-switch-backend}).
2059
2060 @item C-u C-x v b @var{backend} @key{RET}
2061 Switch to @var{backend} for the current file.
2062 @end table
2063
2064 @kindex C-x v b
2065 @findex vc-switch-backend
2066 @kbd{C-x v b} does not change the buffer contents, or any files; it
2067 only changes VC's perspective on how to handle the file. Any
2068 subsequent VC commands for that file will operate on the back end that
2069 is currently selected.
2070
2071 If the current file is registered in more than one back end, typing
2072 @kbd{C-x v b} ``cycles'' through all of these back ends. With a
2073 prefix argument, it asks for the back end to use in the minibuffer.
2074
2075 Thus, if you are using local RCS, and you want to pick up some recent
2076 changes in the file from remote CVS, first visit the file, then type
2077 @kbd{C-x v b} to switch to CVS, and finally use @kbd{C-x v m
2078 @key{RET}} to merge the news (@pxref{Merging}). You can then switch
2079 back to RCS by typing @kbd{C-x v b} again, and continue to edit
2080 locally.
2081
2082 But if you do this, the revision numbers in the RCS master no longer
2083 correspond to those of CVS. Technically, this is not a problem, but
2084 it can become difficult to keep track of what is in the CVS repository
2085 and what is not. So we suggest that you return from time to time to
2086 CVS-only operation, using @kbd{C-u C-x v v cvs @key{RET}}.
2087
2088 @node Snapshots
2089 @subsection Snapshots
2090 @cindex snapshots and version control
2091
2092 A @dfn{snapshot} is a named set of file versions (one for each
2093 registered file) that you can treat as a unit. One important kind of
2094 snapshot is a @dfn{release}, a (theoretically) stable version of the
2095 system that is ready for distribution to users.
2096
2097 @menu
2098 * Making Snapshots:: The snapshot facilities.
2099 * Snapshot Caveats:: Things to be careful of when using snapshots.
2100 @end menu
2101
2102 @node Making Snapshots
2103 @subsubsection Making and Using Snapshots
2104
2105 There are two basic commands for snapshots; one makes a
2106 snapshot with a given name, the other retrieves a named snapshot.
2107
2108 @table @code
2109 @kindex C-x v s
2110 @findex vc-create-snapshot
2111 @item C-x v s @var{name} @key{RET}
2112 Define the last saved versions of every registered file in or under the
2113 current directory as a snapshot named @var{name}
2114 (@code{vc-create-snapshot}).
2115
2116 @kindex C-x v r
2117 @findex vc-retrieve-snapshot
2118 @item C-x v r @var{name} @key{RET}
2119 For all registered files at or below the current directory level, select
2120 whatever versions correspond to the snapshot @var{name}
2121 (@code{vc-retrieve-snapshot}).
2122
2123 This command reports an error if any files are locked at or below the
2124 current directory, without changing anything; this is to avoid
2125 overwriting work in progress.
2126 @end table
2127
2128 A snapshot uses a very small amount of resources---just enough to record
2129 the list of file names and which version belongs to the snapshot. Thus,
2130 you need not hesitate to create snapshots whenever they are useful.
2131
2132 You can give a snapshot name as an argument to @kbd{C-x v =} or
2133 @kbd{C-x v ~} (@pxref{Old Versions}). Thus, you can use it to compare a
2134 snapshot against the current files, or two snapshots against each other,
2135 or a snapshot against a named version.
2136
2137 @node Snapshot Caveats
2138 @subsubsection Snapshot Caveats
2139
2140 @cindex named configurations (RCS)
2141 VC's snapshot facilities are modeled on RCS's named-configuration
2142 support. They use RCS's native facilities for this, so under VC
2143 snapshots made using RCS are visible even when you bypass VC.
2144
2145 @c worded verbosely to avoid overfull hbox.
2146 For SCCS, VC implements snapshots itself. The files it uses contain
2147 name/file/version-number triples. These snapshots are visible only
2148 through VC.
2149
2150 A snapshot is a set of checked-in versions. So make sure that all the
2151 files are checked in and not locked when you make a snapshot.
2152
2153 File renaming and deletion can create some difficulties with snapshots.
2154 This is not a VC-specific problem, but a general design issue in version
2155 control systems that no one has solved very well yet.
2156
2157 If you rename a registered file, you need to rename its master along
2158 with it (the command @code{vc-rename-file} does this automatically). If
2159 you are using SCCS, you must also update the records of the snapshot, to
2160 mention the file by its new name (@code{vc-rename-file} does this,
2161 too). An old snapshot that refers to a master file that no longer
2162 exists under the recorded name is invalid; VC can no longer retrieve
2163 it. It would be beyond the scope of this manual to explain enough about
2164 RCS and SCCS to explain how to update the snapshots by hand.
2165
2166 Using @code{vc-rename-file} makes the snapshot remain valid for
2167 retrieval, but it does not solve all problems. For example, some of the
2168 files in your program probably refer to others by name. At the very
2169 least, the makefile probably mentions the file that you renamed. If you
2170 retrieve an old snapshot, the renamed file is retrieved under its new
2171 name, which is not the name that the makefile expects. So the program
2172 won't really work as retrieved.
2173
2174 @node Miscellaneous VC
2175 @subsection Miscellaneous Commands and Features of VC
2176
2177 This section explains the less-frequently-used features of VC.
2178
2179 @menu
2180 * Change Logs and VC:: Generating a change log file from log entries.
2181 * Renaming and VC:: A command to rename both the source and master
2182 file correctly.
2183 * Version Headers:: Inserting version control headers into working files.
2184 @end menu
2185
2186 @node Change Logs and VC
2187 @subsubsection Change Logs and VC
2188
2189 If you use RCS or CVS for a program and also maintain a change log
2190 file for it (@pxref{Change Log}), you can generate change log entries
2191 automatically from the version control log entries:
2192
2193 @table @kbd
2194 @item C-x v a
2195 @kindex C-x v a
2196 @findex vc-update-change-log
2197 Visit the current directory's change log file and, for registered files
2198 in that directory, create new entries for versions checked in since the
2199 most recent entry in the change log file.
2200 (@code{vc-update-change-log}).
2201
2202 This command works with RCS or CVS only, not with SCCS.
2203
2204 @item C-u C-x v a
2205 As above, but only find entries for the current buffer's file.
2206
2207 @item M-1 C-x v a
2208 As above, but find entries for all the currently visited files that are
2209 maintained with version control. This works only with RCS, and it puts
2210 all entries in the log for the default directory, which may not be
2211 appropriate.
2212 @end table
2213
2214 For example, suppose the first line of @file{ChangeLog} is dated
2215 1999-04-10, and that the only check-in since then was by Nathaniel
2216 Bowditch to @file{rcs2log} on 1999-05-22 with log text @samp{Ignore log
2217 messages that start with `#'.}. Then @kbd{C-x v a} visits
2218 @file{ChangeLog} and inserts text like this:
2219
2220 @iftex
2221 @medbreak
2222 @end iftex
2223 @smallexample
2224 @group
2225 1999-05-22 Nathaniel Bowditch <nat@@apn.org>
2226
2227 * rcs2log: Ignore log messages that start with `#'.
2228 @end group
2229 @end smallexample
2230 @iftex
2231 @medbreak
2232 @end iftex
2233
2234 @noindent
2235 You can then edit the new change log entry further as you wish.
2236
2237 Some of the new change log entries may duplicate what's already in
2238 ChangeLog. You will have to remove these duplicates by hand.
2239
2240 Normally, the log entry for file @file{foo} is displayed as @samp{*
2241 foo: @var{text of log entry}}. The @samp{:} after @file{foo} is omitted
2242 if the text of the log entry starts with @w{@samp{(@var{functionname}):
2243 }}. For example, if the log entry for @file{vc.el} is
2244 @samp{(vc-do-command): Check call-process status.}, then the text in
2245 @file{ChangeLog} looks like this:
2246
2247 @iftex
2248 @medbreak
2249 @end iftex
2250 @smallexample
2251 @group
2252 1999-05-06 Nathaniel Bowditch <nat@@apn.org>
2253
2254 * vc.el (vc-do-command): Check call-process status.
2255 @end group
2256 @end smallexample
2257 @iftex
2258 @medbreak
2259 @end iftex
2260
2261 When @kbd{C-x v a} adds several change log entries at once, it groups
2262 related log entries together if they all are checked in by the same
2263 author at nearly the same time. If the log entries for several such
2264 files all have the same text, it coalesces them into a single entry.
2265 For example, suppose the most recent check-ins have the following log
2266 entries:
2267
2268 @flushleft
2269 @bullet{} For @file{vc.texinfo}: @samp{Fix expansion typos.}
2270 @bullet{} For @file{vc.el}: @samp{Don't call expand-file-name.}
2271 @bullet{} For @file{vc-hooks.el}: @samp{Don't call expand-file-name.}
2272 @end flushleft
2273
2274 @noindent
2275 They appear like this in @file{ChangeLog}:
2276
2277 @iftex
2278 @medbreak
2279 @end iftex
2280 @smallexample
2281 @group
2282 1999-04-01 Nathaniel Bowditch <nat@@apn.org>
2283
2284 * vc.texinfo: Fix expansion typos.
2285
2286 * vc.el, vc-hooks.el: Don't call expand-file-name.
2287 @end group
2288 @end smallexample
2289 @iftex
2290 @medbreak
2291 @end iftex
2292
2293 Normally, @kbd{C-x v a} separates log entries by a blank line, but you
2294 can mark several related log entries to be clumped together (without an
2295 intervening blank line) by starting the text of each related log entry
2296 with a label of the form @w{@samp{@{@var{clumpname}@} }}. The label
2297 itself is not copied to @file{ChangeLog}. For example, suppose the log
2298 entries are:
2299
2300 @flushleft
2301 @bullet{} For @file{vc.texinfo}: @samp{@{expand@} Fix expansion typos.}
2302 @bullet{} For @file{vc.el}: @samp{@{expand@} Don't call expand-file-name.}
2303 @bullet{} For @file{vc-hooks.el}: @samp{@{expand@} Don't call expand-file-name.}
2304 @end flushleft
2305
2306 @noindent
2307 Then the text in @file{ChangeLog} looks like this:
2308
2309 @iftex
2310 @medbreak
2311 @end iftex
2312 @smallexample
2313 @group
2314 1999-04-01 Nathaniel Bowditch <nat@@apn.org>
2315
2316 * vc.texinfo: Fix expansion typos.
2317 * vc.el, vc-hooks.el: Don't call expand-file-name.
2318 @end group
2319 @end smallexample
2320 @iftex
2321 @medbreak
2322 @end iftex
2323
2324 A log entry whose text begins with @samp{#} is not copied to
2325 @file{ChangeLog}. For example, if you merely fix some misspellings in
2326 comments, you can log the change with an entry beginning with @samp{#}
2327 to avoid putting such trivia into @file{ChangeLog}.
2328
2329 @node Renaming and VC
2330 @subsubsection Renaming VC Work Files and Master Files
2331
2332 @findex vc-rename-file
2333 When you rename a registered file, you must also rename its master
2334 file correspondingly to get proper results. Use @code{vc-rename-file}
2335 to rename the source file as you specify, and rename its master file
2336 accordingly. It also updates any snapshots (@pxref{Snapshots}) that
2337 mention the file, so that they use the new name; despite this, the
2338 snapshot thus modified may not completely work (@pxref{Snapshot
2339 Caveats}).
2340
2341 You cannot use @code{vc-rename-file} on a file that is locked by
2342 someone else.
2343
2344 @node Version Headers
2345 @subsubsection Inserting Version Control Headers
2346
2347 Sometimes it is convenient to put version identification strings
2348 directly into working files. Certain special strings called
2349 @dfn{version headers} are replaced in each successive version by the
2350 number of that version.
2351
2352 If you are using RCS, and version headers are present in your working
2353 files, Emacs can use them to determine the current version and the
2354 locking state of the files. This is more reliable than referring to the
2355 master files, which is done when there are no version headers. Note
2356 that in a multi-branch environment, version headers are necessary to
2357 make VC behave correctly (@pxref{Multi-User Branching}).
2358
2359 Searching for version headers is controlled by the variable
2360 @code{vc-consult-headers}. If it is non-@code{nil} (the default),
2361 Emacs searches for headers to determine the version number you are
2362 editing. Setting it to @code{nil} disables this feature.
2363
2364 @kindex C-x v h
2365 @findex vc-insert-headers
2366 You can use the @kbd{C-x v h} command (@code{vc-insert-headers}) to
2367 insert a suitable header string.
2368
2369 @table @kbd
2370 @item C-x v h
2371 Insert headers in a file for use with your version-control system.
2372 @end table
2373
2374 @vindex vc-header-alist
2375 The default header string is @samp{@w{$}Id$} for RCS and
2376 @samp{@w{%}W%} for SCCS. You can specify other headers to insert by
2377 setting the variable @code{vc-header-alist}. Its value is a list of
2378 elements of the form @code{(@var{program} . @var{string})} where
2379 @var{program} is @code{RCS} or @code{SCCS} and @var{string} is the
2380 string to use.
2381
2382 Instead of a single string, you can specify a list of strings; then
2383 each string in the list is inserted as a separate header on a line of
2384 its own.
2385
2386 It is often necessary to use ``superfluous'' backslashes when
2387 writing the strings that you put in this variable. For instance, you
2388 might write @code{"$Id\$"} rather than @code{"$Id@w{$}"}. The extra
2389 backslash prevents the string constant from being interpreted as a
2390 header, if the Emacs Lisp file containing it is maintained with
2391 version control.
2392
2393 @vindex vc-comment-alist
2394 Each header is inserted surrounded by tabs, inside comment delimiters,
2395 on a new line at point. Normally the ordinary comment
2396 start and comment end strings of the current mode are used, but for
2397 certain modes, there are special comment delimiters for this purpose;
2398 the variable @code{vc-comment-alist} specifies them. Each element of
2399 this list has the form @code{(@var{mode} @var{starter} @var{ender})}.
2400
2401 @vindex vc-static-header-alist
2402 The variable @code{vc-static-header-alist} specifies further strings
2403 to add based on the name of the buffer. Its value should be a list of
2404 elements of the form @code{(@var{regexp} . @var{format})}. Whenever
2405 @var{regexp} matches the buffer name, @var{format} is inserted as part
2406 of the header. A header line is inserted for each element that matches
2407 the buffer name, and for each string specified by
2408 @code{vc-header-alist}. The header line is made by processing the
2409 string from @code{vc-header-alist} with the format taken from the
2410 element. The default value for @code{vc-static-header-alist} is as follows:
2411
2412 @example
2413 @group
2414 (("\\.c$" .
2415 "\n#ifndef lint\nstatic char vcid[] = \"\%s\";\n\
2416 #endif /* lint */\n"))
2417 @end group
2418 @end example
2419
2420 @noindent
2421 It specifies insertion of text of this form:
2422
2423 @example
2424 @group
2425
2426 #ifndef lint
2427 static char vcid[] = "@var{string}";
2428 #endif /* lint */
2429 @end group
2430 @end example
2431
2432 @noindent
2433 Note that the text above starts with a blank line.
2434
2435 If you use more than one version header in a file, put them close
2436 together in the file. The mechanism in @code{revert-buffer} that
2437 preserves markers may not handle markers positioned between two version
2438 headers.
2439
2440 @node Customizing VC
2441 @subsection Customizing VC
2442
2443 @vindex vc-handled-backends
2444 The variable @code{vc-handled-backends} determines which version
2445 control systems VC should handle. The default value is @code{(RCS CVS
2446 SCCS)}, so it contains all three version systems that are currently
2447 supported. If you want VC to ignore one or more of these systems,
2448 exclude its name from the list.
2449
2450 The order of systems in the list is significant: when you visit a file
2451 registered in more than one system (@pxref{Local Version Control}),
2452 VC uses the system that comes first in @code{vc-handled-backends} by
2453 default. The order is also significant when you register a file for
2454 the first time, @pxref{Registering} for details.
2455
2456 @menu
2457 * General VC Options:: Options that apply to multiple back ends.
2458 * RCS and SCCS:: Options for RCS and SCCS.
2459 * CVS Options:: Options for CVS.
2460 @end menu
2461
2462 @node General VC Options
2463 @subsubsection General Options
2464
2465 @vindex vc-make-backup-files
2466 Emacs normally does not save backup files for source files that are
2467 maintained with version control. If you want to make backup files even
2468 for files that use version control, set the variable
2469 @code{vc-make-backup-files} to a non-@code{nil} value.
2470
2471 @vindex vc-keep-workfiles
2472 Normally the work file exists all the time, whether it is locked or
2473 not. If you set @code{vc-keep-workfiles} to @code{nil}, then checking
2474 in a new version with @kbd{C-x C-q} deletes the work file; but any
2475 attempt to visit the file with Emacs creates it again. (With CVS, work
2476 files are always kept.)
2477
2478 @vindex vc-follow-symlinks
2479 Editing a version-controlled file through a symbolic link can be
2480 dangerous. It bypasses the version control system---you can edit the
2481 file without locking it, and fail to check your changes in. Also,
2482 your changes might overwrite those of another user. To protect against
2483 this, VC checks each symbolic link that you visit, to see if it points
2484 to a file under version control.
2485
2486 The variable @code{vc-follow-symlinks} controls what to do when a
2487 symbolic link points to a version-controlled file. If it is @code{nil},
2488 VC only displays a warning message. If it is @code{t}, VC automatically
2489 follows the link, and visits the real file instead, telling you about
2490 this in the echo area. If the value is @code{ask} (the default), VC
2491 asks you each time whether to follow the link.
2492
2493 @vindex vc-suppress-confirm
2494 If @code{vc-suppress-confirm} is non-@code{nil}, then @kbd{C-x C-q}
2495 and @kbd{C-x v i} can save the current buffer without asking, and
2496 @kbd{C-x v u} also operates without asking for confirmation. (This
2497 variable does not affect @kbd{C-x v c}; that operation is so drastic
2498 that it should always ask for confirmation.)
2499
2500 @vindex vc-command-messages
2501 VC mode does much of its work by running the shell commands for RCS,
2502 CVS and SCCS. If @code{vc-command-messages} is non-@code{nil}, VC
2503 displays messages to indicate which shell commands it runs, and
2504 additional messages when the commands finish.
2505
2506 @vindex vc-path
2507 You can specify additional directories to search for version control
2508 programs by setting the variable @code{vc-path}. These directories
2509 are searched before the usual search path. It is rarely necessary to
2510 set this variable, because VC normally finds the proper files
2511 automatically.
2512
2513 @node RCS and SCCS
2514 @subsubsection Options for RCS and SCCS
2515
2516 @cindex non-strict locking (RCS)
2517 @cindex locking, non-strict (RCS)
2518 By default, RCS uses locking to coordinate the activities of several
2519 users, but there is a mode called @dfn{non-strict locking} in which
2520 you can check-in changes without locking the file first. Use
2521 @samp{rcs -U} to switch to non-strict locking for a particular file,
2522 see the @code{rcs} manual page for details.
2523
2524 When deducing the version control state of an RCS file, VC first
2525 looks for an RCS version header string in the file (@pxref{Version
2526 Headers}). If there is no header string, VC normally looks at the
2527 file permissions of the work file; this is fast. But there might be
2528 situations when the file permissions cannot be trusted. In this case
2529 the master file has to be consulted, which is rather expensive. Also
2530 the master file can only tell you @emph{if} there's any lock on the
2531 file, but not whether your work file really contains that locked
2532 version.
2533
2534 @vindex vc-consult-headers
2535 You can tell VC not to use version headers to determine the file
2536 status by setting @code{vc-consult-headers} to @code{nil}. VC then
2537 always uses the file permissions (if it is supposed to trust them), or
2538 else checks the master file.
2539
2540 @vindex vc-mistrust-permissions
2541 You can specify the criterion for whether to trust the file
2542 permissions by setting the variable @code{vc-mistrust-permissions}.
2543 Its value can be @code{t} (always mistrust the file permissions and
2544 check the master file), @code{nil} (always trust the file
2545 permissions), or a function of one argument which makes the decision.
2546 The argument is the directory name of the @file{RCS} subdirectory. A
2547 non-@code{nil} value from the function says to mistrust the file
2548 permissions. If you find that the file permissions of work files are
2549 changed erroneously, set @code{vc-mistrust-permissions} to @code{t}.
2550 Then VC always checks the master file to determine the file's status.
2551
2552 VC determines the version control state of files under SCCS much as
2553 with RCS. It does not consider SCCS version headers, though. Thus,
2554 the variable @code{vc-mistrust-permissions} affects SCCS use, but
2555 @code{vc-consult-headers} does not.
2556
2557 @node CVS Options
2558 @subsubsection Options specific for CVS
2559
2560 @cindex locking (CVS)
2561 By default, CVS does not use locking to coordinate the activities of
2562 several users; anyone can change a work file at any time. However,
2563 there are ways to restrict this, resulting in behavior that resembles
2564 locking.
2565
2566 @cindex CVSREAD environment variable (CVS)
2567 For one thing, you can set the @env{CVSREAD} environment variable
2568 (the value you use makes no difference). If this variable is defined,
2569 CVS makes your work files read-only by default. In Emacs, you must
2570 type @kbd{C-x C-q} to make the file writable, so that editing works
2571 in fact similar as if locking was used. Note however, that no actual
2572 locking is performed, so several users can make their files writable
2573 at the same time. When setting @env{CVSREAD} for the first time, make
2574 sure to check out all your modules anew, so that the file protections
2575 are set correctly.
2576
2577 @cindex cvs watch feature
2578 @cindex watching files (CVS)
2579 Another way to achieve something similar to locking is to use the
2580 @dfn{watch} feature of CVS. If a file is being watched, CVS makes it
2581 read-only by default, and you must also use @kbd{C-x C-q} in Emacs to
2582 make it writable. VC calls @code{cvs edit} to make the file writable,
2583 and CVS takes care to notify other developers of the fact that you
2584 intend to change the file. See the CVS documentation for details on
2585 using the watch feature.
2586
2587 @vindex vc-cvs-stay-local
2588 @cindex remote repositories (CVS)
2589 When a file's repository is on a remote machine, VC tries to keep
2590 network interactions to a minimum. This is controlled by the variable
2591 @code{vc-cvs-stay-local}. If it is @code{t} (the default), then VC uses
2592 only the entry in the local CVS subdirectory to determine the file's
2593 state (and possibly information returned by previous CVS commands). One
2594 consequence of this is that when you have modified a file, and somebody
2595 else has already checked in other changes to the file, you are not
2596 notified of it until you actually try to commit. (But you can try to
2597 pick up any recent changes from the repository first, using @kbd{C-x v m
2598 @key{RET}}, @pxref{Merging}).
2599
2600 When @code{vc-cvs-stay-local} is @code{t}, VC also makes local
2601 version backups, so that simple diff and revert operations are
2602 completely local (@pxref{Version Backups}).
2603
2604 On the other hand, if you set @code{vc-cvs-stay-local} to @code{nil},
2605 then VC queries the remote repository @emph{before} it decides what to
2606 do in @code{vc-next-action} (@kbd{C-x v v}), just as it does for local
2607 repositories. It also does not make any version backups.
2608
2609 You can also set @code{vc-cvs-stay-local} to a regular expression
2610 that is matched against the repository host name; VC then stays local
2611 only for repositories from hosts that match the pattern.
2612
2613 @node Directories
2614 @section File Directories
2615
2616 @cindex file directory
2617 @cindex directory listing
2618 The file system groups files into @dfn{directories}. A @dfn{directory
2619 listing} is a list of all the files in a directory. Emacs provides
2620 commands to create and delete directories, and to make directory
2621 listings in brief format (file names only) and verbose format (sizes,
2622 dates, and authors included). There is also a directory browser called
2623 Dired; see @ref{Dired}.
2624
2625 @table @kbd
2626 @item C-x C-d @var{dir-or-pattern} @key{RET}
2627 Display a brief directory listing (@code{list-directory}).
2628 @item C-u C-x C-d @var{dir-or-pattern} @key{RET}
2629 Display a verbose directory listing.
2630 @item M-x make-directory @key{RET} @var{dirname} @key{RET}
2631 Create a new directory named @var{dirname}.
2632 @item M-x delete-directory @key{RET} @var{dirname} @key{RET}
2633 Delete the directory named @var{dirname}. It must be empty,
2634 or you get an error.
2635 @end table
2636
2637 @findex list-directory
2638 @kindex C-x C-d
2639 The command to display a directory listing is @kbd{C-x C-d}
2640 (@code{list-directory}). It reads using the minibuffer a file name
2641 which is either a directory to be listed or a wildcard-containing
2642 pattern for the files to be listed. For example,
2643
2644 @example
2645 C-x C-d /u2/emacs/etc @key{RET}
2646 @end example
2647
2648 @noindent
2649 lists all the files in directory @file{/u2/emacs/etc}. Here is an
2650 example of specifying a file name pattern:
2651
2652 @example
2653 C-x C-d /u2/emacs/src/*.c @key{RET}
2654 @end example
2655
2656 Normally, @kbd{C-x C-d} displays a brief directory listing containing
2657 just file names. A numeric argument (regardless of value) tells it to
2658 make a verbose listing including sizes, dates, and owners (like
2659 @samp{ls -l}).
2660
2661 @vindex list-directory-brief-switches
2662 @vindex list-directory-verbose-switches
2663 The text of a directory listing is obtained by running @code{ls} in an
2664 inferior process. Two Emacs variables control the switches passed to
2665 @code{ls}: @code{list-directory-brief-switches} is a string giving the
2666 switches to use in brief listings (@code{"-CF"} by default), and
2667 @code{list-directory-verbose-switches} is a string giving the switches to
2668 use in a verbose listing (@code{"-l"} by default).
2669
2670 @node Comparing Files
2671 @section Comparing Files
2672 @cindex comparing files
2673
2674 @findex diff
2675 @vindex diff-switches
2676 The command @kbd{M-x diff} compares two files, displaying the
2677 differences in an Emacs buffer named @samp{*diff*}. It works by
2678 running the @code{diff} program, using options taken from the variable
2679 @code{diff-switches}. The value of @code{diff-switches} should be a
2680 string; the default is @code{"-c"} to specify a context diff.
2681
2682 The buffer @samp{*diff*} has Compilation mode as its major mode, so
2683 you can use @kbd{C-x `} to visit successive changed locations in the two
2684 source files. You can also move to a particular hunk of changes and
2685 type @key{RET} or @kbd{C-c C-c}, or click @kbd{Mouse-2} on it, to move
2686 to the corresponding source location. You can also use the other
2687 special commands of Compilation mode: @key{SPC} and @key{DEL} for
2688 scrolling, and @kbd{M-p} and @kbd{M-n} for cursor motion.
2689 @xref{Compilation}.
2690
2691 @findex diff-backup
2692 The command @kbd{M-x diff-backup} compares a specified file with its most
2693 recent backup. If you specify the name of a backup file,
2694 @code{diff-backup} compares it with the source file that it is a backup
2695 of.
2696
2697 @findex compare-windows
2698 The command @kbd{M-x compare-windows} compares the text in the current
2699 window with that in the next window. Comparison starts at point in each
2700 window, and each starting position is pushed on the mark ring in its
2701 respective buffer. Then point moves forward in each window, a character
2702 at a time, until a mismatch between the two windows is reached. Then
2703 the command is finished. For more information about windows in Emacs,
2704 @ref{Windows}.
2705
2706 @vindex compare-ignore-case
2707 With a numeric argument, @code{compare-windows} ignores changes in
2708 whitespace. If the variable @code{compare-ignore-case} is
2709 non-@code{nil}, it ignores differences in case as well.
2710
2711 @findex diff-mode
2712 @cindex diffs
2713 @cindex patches
2714 @cindex Diff mode
2715 Differences between versions of files are often distributed as
2716 @dfn{patches}, which are the output from @command{diff} or a version
2717 control system that uses @command{diff}. @kbd{M-x diff-mode} turns on
2718 Diff mode, a major mode for viewing and editing patches, either as
2719 ``unified diffs'' or ``context diffs.''
2720
2721 @cindex Smerge mode
2722 @findex smerge-mode
2723 @cindex failed merges
2724 @cindex merges, failed
2725 @cindex comparing 3 files (@code{diff3})
2726 You can use @kbd{M-x smerge-mode} to turn on Smerge mode, a minor
2727 mode for editing output from the @command{diff3} program. This is
2728 typically the result of a failed merge from a version control system
2729 ``update'' outside VC, due to conflicting changes to a file. Smerge
2730 mode provides commands to resolve conflicts by selecting specific
2731 changes.
2732
2733 See also @ref{Emerge}, and @ref{Top,,, ediff, The Ediff Manual}, for
2734 convenient facilities for merging two similar files.
2735
2736 @node Misc File Ops
2737 @section Miscellaneous File Operations
2738
2739 Emacs has commands for performing many other operations on files.
2740 All operate on one file; they do not accept wildcard file names.
2741
2742 @findex view-file
2743 @cindex viewing
2744 @cindex View mode
2745 @cindex mode, View
2746 @kbd{M-x view-file} allows you to scan or read a file by sequential
2747 screenfuls. It reads a file name argument using the minibuffer. After
2748 reading the file into an Emacs buffer, @code{view-file} displays the
2749 beginning. You can then type @key{SPC} to scroll forward one windowful,
2750 or @key{DEL} to scroll backward. Various other commands are provided
2751 for moving around in the file, but none for changing it; type @kbd{?}
2752 while viewing for a list of them. They are mostly the same as normal
2753 Emacs cursor motion commands. To exit from viewing, type @kbd{q}.
2754 The commands for viewing are defined by a special major mode called View
2755 mode.
2756
2757 A related command, @kbd{M-x view-buffer}, views a buffer already present
2758 in Emacs. @xref{Misc Buffer}.
2759
2760 @kindex C-x i
2761 @findex insert-file
2762 @kbd{M-x insert-file} (also @kbd{C-x i}) inserts a copy of the
2763 contents of the specified file into the current buffer at point,
2764 leaving point unchanged before the contents and the mark after them.
2765
2766 @findex write-region
2767 @kbd{M-x write-region} is the inverse of @kbd{M-x insert-file}; it
2768 copies the contents of the region into the specified file. @kbd{M-x
2769 append-to-file} adds the text of the region to the end of the specified
2770 file. @xref{Accumulating Text}.
2771
2772 @findex delete-file
2773 @cindex deletion (of files)
2774 @kbd{M-x delete-file} deletes the specified file, like the @code{rm}
2775 command in the shell. If you are deleting many files in one directory, it
2776 may be more convenient to use Dired (@pxref{Dired}).
2777
2778 @findex rename-file
2779 @kbd{M-x rename-file} reads two file names @var{old} and @var{new} using
2780 the minibuffer, then renames file @var{old} as @var{new}. If the file name
2781 @var{new} already exists, you must confirm with @kbd{yes} or renaming is not
2782 done; this is because renaming causes the old meaning of the name @var{new}
2783 to be lost. If @var{old} and @var{new} are on different file systems, the
2784 file @var{old} is copied and deleted.
2785
2786 @findex add-name-to-file
2787 @cindex hard links (creation)
2788 The similar command @kbd{M-x add-name-to-file} is used to add an
2789 additional name to an existing file without removing its old name.
2790 The new name is created as a ``hard link'' to the existing file.
2791 The new name must belong on the same file system that the file is on.
2792 On Windows, this command works only if the file resides in an NTFS
2793 file system. On MS-DOS, it works by copying the file.
2794
2795 @findex copy-file
2796 @cindex copying files
2797 @kbd{M-x copy-file} reads the file @var{old} and writes a new file named
2798 @var{new} with the same contents. Confirmation is required if a file named
2799 @var{new} already exists, because copying has the consequence of overwriting
2800 the old contents of the file @var{new}.
2801
2802 @findex make-symbolic-link
2803 @kbd{M-x make-symbolic-link} reads two file names @var{target} and
2804 @var{linkname}, then creates a symbolic link named @var{linkname}, which
2805 points at @var{target}. The effect is that future attempts to open file
2806 @var{linkname} will refer to whatever file is named @var{target} at the
2807 time the opening is done, or will get an error if the name @var{target} is
2808 not in use at that time. This command does not expand the argument
2809 @var{target}, so that it allows you to specify a relative name
2810 as the target of the link.
2811
2812 Confirmation is required when creating the link if @var{linkname} is
2813 in use. Note that not all systems support symbolic links; on systems
2814 that don't support them, this command is not defined.
2815
2816 @node Compressed Files
2817 @section Accessing Compressed Files
2818 @cindex compression
2819 @cindex uncompression
2820 @cindex Auto Compression mode
2821 @cindex mode, Auto Compression
2822 @pindex gzip
2823
2824 @findex auto-compression-mode
2825 @vindex auto-compression-mode
2826 Emacs comes with a library that can automatically uncompress
2827 compressed files when you visit them, and automatically recompress them
2828 if you alter them and save them. To enable this feature, type the
2829 command @kbd{M-x auto-compression-mode}. You can enable it permanently
2830 by customizing the option @code{auto-compression-mode}.
2831
2832 When automatic compression (which implies automatic uncompression as
2833 well) is enabled, Emacs recognizes compressed files by their file names.
2834 File names ending in @samp{.gz} indicate a file compressed with
2835 @code{gzip}. Other endings indicate other compression programs.
2836
2837 Automatic uncompression and compression apply to all the operations in
2838 which Emacs uses the contents of a file. This includes visiting it,
2839 saving it, inserting its contents into a buffer, loading it, and byte
2840 compiling it.
2841
2842 @node File Archives
2843 @section File Archives
2844 @cindex mode, tar
2845 @cindex Tar mode
2846 @cindex file archives
2847
2848 A file whose name ends in @samp{.tar} is normally an @dfn{archive}
2849 made by the @code{tar} program. Emacs views these files in a special
2850 mode called Tar mode which provides a Dired-like list of the contents
2851 (@pxref{Dired}). You can move around through the list just as you
2852 would in Dired, and visit the subfiles contained in the archive.
2853 However, not all Dired commands are available in Tar mode.
2854
2855 If you enable Auto Compression mode (@pxref{Compressed Files}), then
2856 Tar mode is used also for compressed archives---files with extensions
2857 @samp{.tgz}, @code{.tar.Z} and @code{.tar.gz}.
2858
2859 The keys @kbd{e}, @kbd{f} and @key{RET} all extract a component file
2860 into its own buffer. You can edit it there and when you save the buffer
2861 the edited version will replace the version in the Tar buffer. @kbd{v}
2862 extracts a file into a buffer in View mode. @kbd{o} extracts the file
2863 and displays it in another window, so you could edit the file and
2864 operate on the archive simultaneously. @kbd{d} marks a file for
2865 deletion when you later use @kbd{x}, and @kbd{u} unmarks a file, as in
2866 Dired. @kbd{C} copies a file from the archive to disk and @kbd{R}
2867 renames a file. @kbd{g} reverts the buffer from the archive on disk.
2868
2869 The keys @kbd{M}, @kbd{G}, and @kbd{O} change the file's permission
2870 bits, group, and owner, respectively.
2871
2872 If your display supports colors and the mouse, moving the mouse
2873 pointer across a file name highlights that file name, indicating that
2874 you can click on it. Clicking @kbd{Mouse-2} on the highlighted file
2875 name extracts the file into a buffer and displays that buffer.
2876
2877 Saving the Tar buffer writes a new version of the archive to disk with
2878 the changes you made to the components.
2879
2880 You don't need the @code{tar} program to use Tar mode---Emacs reads
2881 the archives directly. However, accessing compressed archives
2882 requires the appropriate uncompression program.
2883
2884 @cindex Archive mode
2885 @cindex mode, archive
2886 @cindex @code{arc}
2887 @cindex @code{jar}
2888 @cindex @code{zip}
2889 @cindex @code{lzh}
2890 @cindex @code{zoo}
2891 @pindex arc
2892 @pindex jar
2893 @pindex zip
2894 @pindex lzh
2895 @pindex zoo
2896 @cindex Java class archives
2897 @cindex unzip archives
2898 A separate but similar Archive mode is used for archives produced by
2899 the programs @code{arc}, @code{jar}, @code{lzh}, @code{zip}, and
2900 @code{zoo}, which have extensions corresponding to the program names.
2901
2902 The key bindings of Archive mode are similar to those in Tar mode,
2903 with the addition of the @kbd{m} key which marks a file for subsequent
2904 operations, and @kbd{M-@key{DEL}} which unmarks all the marked files.
2905 Also, the @kbd{a} key toggles the display of detailed file
2906 information, for those archive types where it won't fit in a single
2907 line. Operations such as renaming a subfile, or changing its mode or
2908 owner, are supported only for some of the archive formats.
2909
2910 Unlike Tar mode, Archive mode runs the archiving program to unpack
2911 and repack archives. Details of the program names and their options
2912 can be set in the @samp{Archive} Customize group. However, you don't
2913 need these programs to look at the archive table of contents, only to
2914 extract or manipulate the subfiles in the archive.
2915
2916 @node Remote Files
2917 @section Remote Files
2918
2919 @cindex FTP
2920 @cindex remote file access
2921 You can refer to files on other machines using a special file name syntax:
2922
2923 @example
2924 @group
2925 /@var{host}:@var{filename}
2926 /@var{user}@@@var{host}:@var{filename}
2927 /@var{user}@@@var{host}#@var{port}:@var{filename}
2928 @end group
2929 @end example
2930
2931 @noindent
2932 When you do this, Emacs uses the FTP program to read and write files on
2933 the specified host. It logs in through FTP using your user name or the
2934 name @var{user}. It may ask you for a password from time to time; this
2935 is used for logging in on @var{host}. The form using @var{port} allows
2936 you to access servers running on a non-default TCP port.
2937
2938 @cindex backups for remote files
2939 @vindex ange-ftp-make-backup-files
2940 If you want to disable backups for remote files, set the variable
2941 @code{ange-ftp-make-backup-files} to @code{nil}.
2942
2943 @cindex ange-ftp
2944 @vindex ange-ftp-default-user
2945 @cindex user name for remote file access
2946 Normally, if you do not specify a user name in a remote file name,
2947 that means to use your own user name. But if you set the variable
2948 @code{ange-ftp-default-user} to a string, that string is used instead.
2949 (The Emacs package that implements FTP file access is called
2950 @code{ange-ftp}.)
2951
2952 @cindex anonymous FTP
2953 @vindex ange-ftp-generate-anonymous-password
2954 To visit files accessible by anonymous FTP, you use special user
2955 names @samp{anonymous} or @samp{ftp}. Passwords for these user names
2956 are handled specially. The variable
2957 @code{ange-ftp-generate-anonymous-password} controls what happens: if
2958 the value of this variable is a string, then that string is used as
2959 the password; if non-@code{nil} (the default), then the value of
2960 @code{user-mail-address} is used; if @code{nil}, the user is prompted
2961 for a password as normal.
2962
2963 @cindex firewall, and accessing remote files
2964 @cindex gateway, and remote file access with @code{ange-ftp}
2965 @vindex ange-ftp-smart-gateway
2966 @vindex ange-ftp-gateway-host
2967 Sometimes you may be unable to access files on a remote machine
2968 because a @dfn{firewall} in between blocks the connection for security
2969 reasons. If you can log in on a @dfn{gateway} machine from which the
2970 target files @emph{are} accessible, and whose FTP server supports
2971 gatewaying features, you can still use remote file names; all you have
2972 to do is specify the name of the gateway machine by setting the
2973 variable @code{ange-ftp-gateway-host}, and set
2974 @code{ange-ftp-smart-gateway} to @code{t}. Otherwise you may be able
2975 to make remote file names work, but the procedure is complex. You can
2976 read the instructions by typing @kbd{M-x finder-commentary @key{RET}
2977 ange-ftp @key{RET}}.
2978
2979 @vindex file-name-handler-alist
2980 @cindex disabling remote files
2981 You can entirely turn off the FTP file name feature by removing the
2982 entries @code{ange-ftp-completion-hook-function} and
2983 @code{ange-ftp-hook-function} from the variable
2984 @code{file-name-handler-alist}. You can turn off the feature in
2985 individual cases by quoting the file name with @samp{/:} (@pxref{Quoted
2986 File Names}).
2987
2988 @node Quoted File Names
2989 @section Quoted File Names
2990
2991 @cindex quoting file names
2992 You can @dfn{quote} an absolute file name to prevent special
2993 characters and syntax in it from having their special effects.
2994 The way to do this is to add @samp{/:} at the beginning.
2995
2996 For example, you can quote a local file name which appears remote, to
2997 prevent it from being treated as a remote file name. Thus, if you have
2998 a directory named @file{/foo:} and a file named @file{bar} in it, you
2999 can refer to that file in Emacs as @samp{/:/foo:/bar}.
3000
3001 @samp{/:} can also prevent @samp{~} from being treated as a special
3002 character for a user's home directory. For example, @file{/:/tmp/~hack}
3003 refers to a file whose name is @file{~hack} in directory @file{/tmp}.
3004
3005 Likewise, quoting with @samp{/:} is one way to enter in the minibuffer
3006 a file name that contains @samp{$}. However, the @samp{/:} must be at
3007 the beginning of the minibuffer in order to quote @samp{$}.
3008
3009 You can also quote wildcard characters with @samp{/:}, for visiting.
3010 For example, @file{/:/tmp/foo*bar} visits the file @file{/tmp/foo*bar}.
3011 However, in most cases you can simply type the wildcard characters for
3012 themselves. For example, if the only file name in @file{/tmp} that
3013 starts with @samp{foo} and ends with @samp{bar} is @file{foo*bar}, then
3014 specifying @file{/tmp/foo*bar} will visit just @file{/tmp/foo*bar}.
3015 Another way is to specify @file{/tmp/foo[*]bar}.
3016
3017 @node File Name Cache
3018 @section File Name Cache
3019
3020 @cindex file name caching
3021 @cindex cache of file names
3022 @pindex find
3023 @kindex C-@key{TAB}
3024 @findex file-cache-minibuffer-complete
3025 You can use the @dfn{file name cache} to make it easy to locate a
3026 file by name, without having to remember exactly where it is located.
3027 When typing a file name in the minibuffer, @kbd{C-@key{tab}}
3028 (@code{file-cache-minibuffer-complete}) completes it using the file
3029 name cache. If you repeat @kbd{C-@key{tab}}, that cycles through the
3030 possible completions of what you had originally typed. Note that the
3031 @kbd{C-@key{tab}} character cannot be typed on most text-only
3032 terminals.
3033
3034 The file name cache does not fill up automatically. Instead, you
3035 load file names into the cache using these commands:
3036
3037 @findex file-cache-add-directory
3038 @table @kbd
3039 @item M-x file-cache-add-directory @key{RET} @var{directory} @key{RET}
3040 Add each file name in @var{directory} to the file name cache.
3041 @item M-x file-cache-add-directory-using-find @key{RET} @var{directory} @key{RET}
3042 Add each file name in @var{directory} and all of its nested
3043 subdirectories to the file name cache.
3044 @item M-x file-cache-add-directory-using-locate @key{RET} @var{directory} @key{RET}
3045 Add each file name in @var{directory} and all of its nested
3046 subdirectories to the file name cache, using @command{locate} to find
3047 them all.
3048 @item M-x file-cache-add-directory-list @key{RET} @var{variable} @key{RET}
3049 Add each file name in each directory listed in @var{variable}
3050 to the file name cache. @var{variable} should be a Lisp variable
3051 such as @code{load-path} or @code{exec-path}, whose value is a list
3052 of directory names.
3053 @item M-x file-cache-clear-cache @key{RET}
3054 Clear the cache; that is, remove all file names from it.
3055 @end table
3056
3057 @node File Conveniences
3058 @section Convenience Features for Finding Files
3059
3060 @findex recentf-mode
3061 @vindex recentf-mode
3062 @findex recentf-save-list
3063 @findex recentf-edit-list
3064 If you enable Recentf mode, with @kbd{M-x recentf-mode}, the
3065 @samp{File} menu includes a submenu containing a list of recently
3066 opened files. @kbd{M-x recentf-save-list} saves the current
3067 @code{recent-file-list} to a file, and @kbd{M-x recentf-edit-list}
3068 edits it.
3069
3070 @findex auto-image-file-mode
3071 @findex mode, auto-image-file
3072 @cindex images, visiting
3073 @cindex visiting image files
3074 @vindex image-file-name-regexps
3075 @vindex image-file-name-extensions
3076 When Auto-image-file minor mode is enabled, visiting an image file
3077 displays it as an image, not as text. Likewise, inserting an image
3078 file into a buffer inserts it as an image. This works only when Emacs
3079 can display the relevant image type. The variables
3080 @code{image-file-name-extensions} or @code{image-file-name-regexps}
3081 control which file names are recognized as containing images.
3082
3083 The @kbd{M-x ffap} command generalizes @code{find-file} with more
3084 powerful heuristic defaults (@pxref{FFAP}), often based on the text at
3085 point. Partial Completion mode offers other features extending
3086 @code{find-file}, which can be used with @code{ffap}.
3087 @xref{Completion Options}.