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
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
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.
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
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.
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}.
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
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.
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}.
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.
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}.
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}.
104 @cindex environment variables in file names
105 @cindex expansion of environment variables
106 @cindex @code{$} in file names
107 @anchor{File Names with $}
108 @samp{$} in a file name is used to substitute environment variables.
109 For example, if you have used the shell command @command{export
110 FOO=rms/hacks} to set up an environment variable named @env{FOO}, then
111 you can use @file{/u/$FOO/test.c} or @file{/u/$@{FOO@}/test.c} as an
112 abbreviation for @file{/u/rms/hacks/test.c}. The environment variable
113 name consists of all the alphanumeric characters after the @samp{$};
114 alternatively, it may be enclosed in braces after the @samp{$}. Note
115 that shell commands to set environment variables affect Emacs only if
116 done before Emacs is started.
118 @cindex home directory shorthand
119 You can use the @file{~/} in a file name to mean your home directory,
120 or @file{~@var{user-id}/} to mean the home directory of a user whose
121 login name is @code{user-id}. (On DOS and Windows systems, where a user
122 doesn't have a home directory, Emacs substitutes @file{~/} with the
123 value of the environment variable @code{HOME}; see @ref{General
126 To access a file with @samp{$} in its name, type @samp{$$}. This pair
127 is converted to a single @samp{$} at the same time as variable
128 substitution is performed for a single @samp{$}. Alternatively, quote the
129 whole file name with @samp{/:} (@pxref{Quoted File Names}). File names
130 which begin with a literal @samp{~} should also be quoted with @samp{/:}.
132 @findex substitute-in-file-name
133 The Lisp function that performs the substitution is called
134 @code{substitute-in-file-name}. The substitution is performed only on
135 file names read as such using the minibuffer.
137 You can include non-ASCII characters in file names if you set the
138 variable @code{file-name-coding-system} to a non-@code{nil} value.
139 @xref{Specify Coding}.
142 @section Visiting Files
143 @cindex visiting files
147 Visit a file (@code{find-file}).
149 Visit a file for viewing, without allowing changes to it
150 (@code{find-file-read-only}).
152 Visit a different file instead of the one visited last
153 (@code{find-alternate-file}).
155 Visit a file, in another window (@code{find-file-other-window}). Don't
156 alter what is displayed in the selected window.
158 Visit a file, in a new frame (@code{find-file-other-frame}). Don't
159 alter what is displayed in the selected frame.
160 @item M-x find-file-literally
161 Visit a file with no conversion of the contents.
164 @cindex files, visiting and saving
166 @dfn{Visiting} a file means copying its contents into an Emacs
167 buffer so you can edit them. Emacs makes a new buffer for each file
168 that you visit. We often say that this buffer ``is visiting'' that
169 file, or that the buffer's ``visited file'' is that file. Emacs
170 constructs the buffer name from the file name by throwing away the
171 directory, keeping just the name proper. For example, a file named
172 @file{/usr/rms/emacs.tex} would get a buffer named @samp{emacs.tex}.
173 If there is already a buffer with that name, Emacs constructs a unique
174 name---the normal method is to append @samp{<2>}, @samp{<3>}, and so
175 on, but you can select other methods (@pxref{Uniquify}).
177 Each window's mode line shows the name of the buffer that is being displayed
178 in that window, so you can always tell what buffer you are editing.
180 The changes you make with editing commands are made in the Emacs
181 buffer. They do not take effect in the file that you visited, or any
182 place permanent, until you @dfn{save} the buffer. Saving the buffer
183 means that Emacs writes the current contents of the buffer into its
184 visited file. @xref{Saving}.
186 @cindex modified (buffer)
187 If a buffer contains changes that have not been saved, we say the
188 buffer is @dfn{modified}. This is important because it implies that
189 some changes will be lost if the buffer is not saved. The mode line
190 displays two stars near the left margin to indicate that the buffer is
195 To visit a file, use the command @kbd{C-x C-f} (@code{find-file}). Follow
196 the command with the name of the file you wish to visit, terminated by a
199 The file name is read using the minibuffer (@pxref{Minibuffer}), with
200 defaulting and completion in the standard manner (@pxref{File Names}).
201 While in the minibuffer, you can abort @kbd{C-x C-f} by typing
202 @kbd{C-g}. File-name completion ignores certain filenames; for more
203 about this, see @ref{Completion Options}.
205 @cindex file selection dialog
206 When Emacs is built with a suitable GUI toolkit, it pops up the
207 standard File Selection dialog of that toolkit instead of prompting for
208 the file name in the minibuffer. On Unix and GNU/Linux platforms, Emacs
209 does that when built with LessTif and Motif toolkits; on MS-Windows, the
210 GUI version does that by default.
212 Your confirmation that @kbd{C-x C-f} has completed successfully is the
213 appearance of new text on the screen and a new buffer name in the mode
214 line. If the specified file does not exist and could not be created, or
215 cannot be read, then you get an error, with an error message displayed
218 If you visit a file that is already in Emacs, @kbd{C-x C-f} does not make
219 another copy. It selects the existing buffer containing that file.
220 However, before doing so, it checks that the file itself has not changed
221 since you visited or saved it last. If the file has changed, a warning
222 message is shown. @xref{Interlocking,,Simultaneous Editing}.
224 @cindex maximum buffer size exceeded, error message
225 Since Emacs reads the visited file in its entirety, files whose size
226 is larger than the maximum Emacs buffer size (@pxref{Buffers}) cannot be
227 visited; if you try, Emacs will display an error message saying that the
228 maximum buffer size has been exceeded.
230 @cindex creating files
231 What if you want to create a new file? Just visit it. Emacs displays
232 @samp{(New file)} in the echo area, but in other respects behaves as if
233 you had visited an existing empty file. If you make any changes and
234 save them, the file is created.
236 Emacs recognizes from the contents of a file which convention it uses
237 to separate lines---newline (used on GNU/Linux and on Unix),
238 carriage-return linefeed (used on Microsoft systems), or just
239 carriage-return (used on the Macintosh)---and automatically converts the
240 contents to the normal Emacs convention, which is that the newline
241 character separates lines. This is a part of the general feature of
242 coding system conversion (@pxref{Coding Systems}), and makes it possible
243 to edit files imported from different operating systems with
244 equal convenience. If you change the text and save the file, Emacs
245 performs the inverse conversion, changing newlines back into
246 carriage-return linefeed or just carriage-return if appropriate.
248 @vindex find-file-run-dired
249 If the file you specify is actually a directory, @kbd{C-x C-f} invokes
250 Dired, the Emacs directory browser, so that you can ``edit'' the contents
251 of the directory (@pxref{Dired}). Dired is a convenient way to delete,
252 look at, or operate on the files in the directory. However, if the
253 variable @code{find-file-run-dired} is @code{nil}, then it is an error
254 to try to visit a directory.
256 Files which are actually collections of other files, or @dfn{file
257 archives}, are visited in special modes which invoke a Dired-like
258 environment to allow operations on archive members. @xref{File
259 Archives}, for more about these features.
261 @cindex wildcard characters in file names
262 @vindex find-file-wildcards
263 If the file name you specify contains shell-style wildcard characters,
264 Emacs visits all the files that match it. Wildcards include @samp{?},
265 @samp{*}, and @samp{[@dots{}]} sequences. @xref{Quoted File Names}, for
266 information on how to visit a file whose name actually contains wildcard
267 characters. You can disable the wildcard feature by customizing
268 @code{find-file-wildcards}.
270 If you visit a file that the operating system won't let you modify,
271 Emacs makes the buffer read-only, so that you won't go ahead and make
272 changes that you'll have trouble saving afterward. You can make the
273 buffer writable with @kbd{C-x C-q} (@code{vc-toggle-read-only}).
277 @findex find-file-read-only
278 Occasionally you might want to visit a file as read-only in order to
279 protect yourself from entering changes accidentally; do so by visiting
280 the file with the command @kbd{C-x C-r} (@code{find-file-read-only}).
283 @findex find-alternate-file
284 If you visit a nonexistent file unintentionally (because you typed the
285 wrong file name), use the @kbd{C-x C-v} command
286 (@code{find-alternate-file}) to visit the file you really wanted.
287 @kbd{C-x C-v} is similar to @kbd{C-x C-f}, but it kills the current
288 buffer (after first offering to save it if it is modified). When
289 @kbd{C-x C-v} reads the file name to visit, it inserts the entire
290 default file name in the buffer, with point just after the directory
291 part; this is convenient if you made a slight error in typing the name.
293 If you find a file which exists but cannot be read, @kbd{C-x C-f}
297 @findex find-file-other-window
298 @kbd{C-x 4 f} (@code{find-file-other-window}) is like @kbd{C-x C-f}
299 except that the buffer containing the specified file is selected in another
300 window. The window that was selected before @kbd{C-x 4 f} continues to
301 show the same buffer it was already showing. If this command is used when
302 only one window is being displayed, that window is split in two, with one
303 window showing the same buffer as before, and the other one showing the
304 newly requested file. @xref{Windows}.
307 @findex find-file-other-frame
308 @kbd{C-x 5 f} (@code{find-file-other-frame}) is similar, but opens a
309 new frame, or makes visible any existing frame showing the file you
310 seek. This feature is available only when you are using a window
311 system. @xref{Frames}.
313 @findex find-file-literally
314 If you wish to edit a file as a sequence of ASCII characters with no special
315 encoding or conversion, use the @kbd{M-x find-file-literally} command.
316 It visits a file, like @kbd{C-x C-f}, but does not do format conversion
317 (@pxref{Formatted Text}), character code conversion (@pxref{Coding
318 Systems}), or automatic uncompression (@pxref{Compressed Files}), and
319 does not add a final newline because of @code{require-final-newline}.
320 If you already have visited the same file in the usual (non-literal)
321 manner, this command asks you whether to visit it literally instead.
323 @vindex find-file-hook
324 @vindex find-file-not-found-functions
325 Two special hook variables allow extensions to modify the operation of
326 visiting files. Visiting a file that does not exist runs the functions
327 in the list @code{find-file-not-found-functions}; this variable holds a list
328 of functions, and the functions are called one by one (with no
329 arguments) until one of them returns non-@code{nil}. This is not a
330 normal hook, and the name ends in @samp{-functions} rather than @samp{-hook}
331 to indicate that fact.
333 Successful visiting of any file, whether existing or not, calls the
334 functions in the list @code{find-file-hook}, with no arguments.
335 This variable is a normal hook. In the case of a nonexistent file, the
336 @code{find-file-not-found-functions} are run first. @xref{Hooks}.
338 There are several ways to specify automatically the major mode for
339 editing the file (@pxref{Choosing Modes}), and to specify local
340 variables defined for that file (@pxref{File Variables}).
343 @section Saving Files
345 @dfn{Saving} a buffer in Emacs means writing its contents back into the file
346 that was visited in the buffer.
350 Save the current buffer in its visited file on disk (@code{save-buffer}).
352 Save any or all buffers in their visited files (@code{save-some-buffers}).
354 Forget that the current buffer has been changed (@code{not-modified}).
355 With prefix argument (@kbd{C-u}), mark the current buffer as changed.
357 Save the current buffer as a specified file name (@code{write-file}).
358 @item M-x set-visited-file-name
359 Change the file name under which the current buffer will be saved.
364 When you wish to save the file and make your changes permanent, type
365 @kbd{C-x C-s} (@code{save-buffer}). After saving is finished, @kbd{C-x C-s}
366 displays a message like this:
369 Wrote /u/rms/gnu/gnu.tasks
373 If the selected buffer is not modified (no changes have been made in it
374 since the buffer was created or last saved), saving is not really done,
375 because it would have no effect. Instead, @kbd{C-x C-s} displays a message
376 like this in the echo area:
379 (No changes need to be saved)
383 @findex save-some-buffers
384 The command @kbd{C-x s} (@code{save-some-buffers}) offers to save any
385 or all modified buffers. It asks you what to do with each buffer. The
386 possible responses are analogous to those of @code{query-replace}:
390 Save this buffer and ask about the rest of the buffers.
392 Don't save this buffer, but ask about the rest of the buffers.
394 Save this buffer and all the rest with no more questions.
395 @c following generates acceptable underfull hbox
397 Terminate @code{save-some-buffers} without any more saving.
399 Save this buffer, then exit @code{save-some-buffers} without even asking
402 View the buffer that you are currently being asked about. When you exit
403 View mode, you get back to @code{save-some-buffers}, which asks the
406 Display a help message about these options.
409 @kbd{C-x C-c}, the key sequence to exit Emacs, invokes
410 @code{save-some-buffers} and therefore asks the same questions.
414 If you have changed a buffer but you do not want to save the changes,
415 you should take some action to prevent it. Otherwise, each time you use
416 @kbd{C-x s} or @kbd{C-x C-c}, you are liable to save this buffer by
417 mistake. One thing you can do is type @kbd{M-~} (@code{not-modified}),
418 which clears out the indication that the buffer is modified. If you do
419 this, none of the save commands will believe that the buffer needs to be
420 saved. (@samp{~} is often used as a mathematical symbol for `not'; thus
421 @kbd{M-~} is `not', metafied.) You could also use
422 @code{set-visited-file-name} (see below) to mark the buffer as visiting
423 a different file name, one which is not in use for anything important.
424 Alternatively, you can cancel all the changes made since the file was
425 visited or saved, by reading the text from the file again. This is
426 called @dfn{reverting}. @xref{Reverting}. You could also undo all the
427 changes by repeating the undo command @kbd{C-x u} until you have undone
428 all the changes; but reverting is easier.
430 @findex set-visited-file-name
431 @kbd{M-x set-visited-file-name} alters the name of the file that the
432 current buffer is visiting. It reads the new file name using the
433 minibuffer. Then it marks the buffer as visiting that file name, and
434 changes the buffer name correspondingly. @code{set-visited-file-name}
435 does not save the buffer in the newly visited file; it just alters the
436 records inside Emacs in case you do save later. It also marks the
437 buffer as ``modified'' so that @kbd{C-x C-s} in that buffer
442 If you wish to mark the buffer as visiting a different file and save it
443 right away, use @kbd{C-x C-w} (@code{write-file}). It is precisely
444 equivalent to @code{set-visited-file-name} followed by @kbd{C-x C-s}.
445 @kbd{C-x C-s} used on a buffer that is not visiting a file has the
446 same effect as @kbd{C-x C-w}; that is, it reads a file name, marks the
447 buffer as visiting that file, and saves it there. The default file name in
448 a buffer that is not visiting a file is made by combining the buffer name
449 with the buffer's default directory (@pxref{File Names}).
451 If the new file name implies a major mode, then @kbd{C-x C-w} switches
452 to that major mode, in most cases. The command
453 @code{set-visited-file-name} also does this. @xref{Choosing Modes}.
455 If Emacs is about to save a file and sees that the date of the latest
456 version on disk does not match what Emacs last read or wrote, Emacs
457 notifies you of this fact, because it probably indicates a problem caused
458 by simultaneous editing and requires your immediate attention.
459 @xref{Interlocking,, Simultaneous Editing}.
461 @vindex require-final-newline
462 If the value of the variable @code{require-final-newline} is @code{t},
463 Emacs silently puts a newline at the end of any file that doesn't
464 already end in one, every time a file is saved or written. If the value
465 is @code{nil}, Emacs leaves the end of the file unchanged; if it's
466 neither @code{nil} nor @code{t}, Emacs asks you whether to add a
467 newline. The default is @code{nil}.
470 * Backup:: How Emacs saves the old version of your file.
471 * Interlocking:: How Emacs protects against simultaneous editing
472 of one file by two users.
473 * Shadowing: File Shadowing.
474 Copying files to "shadows" automatically.
475 * Time Stamps:: Emacs can update time stamps on saved files.
479 @subsection Backup Files
481 @vindex make-backup-files
482 @vindex vc-make-backup-files
484 On most operating systems, rewriting a file automatically destroys all
485 record of what the file used to contain. Thus, saving a file from Emacs
486 throws away the old contents of the file---or it would, except that
487 Emacs carefully copies the old contents to another file, called the
488 @dfn{backup} file, before actually saving.
490 For most files, the variable @code{make-backup-files} determines
491 whether to make backup files. On most operating systems, its default
492 value is @code{t}, so that Emacs does write backup files.
494 For files managed by a version control system (@pxref{Version
495 Control}), the variable @code{vc-make-backup-files} determines whether
496 to make backup files. By default it is @code{nil}, since backup files
497 are redundant when you store all the previous versions in a version
498 control system. @xref{General VC Options}.
500 @vindex backup-enable-predicate
501 @vindex temporary-file-directory
502 @vindex small-temporary-file-directory
503 The default value of the @code{backup-enable-predicate} variable
504 prevents backup files being written for files in the directories used
505 for temporary files, specified by @code{temporary-file-directory} or
506 @code{small-temporary-file-directory}.
508 At your option, Emacs can keep either a single backup file or a series of
509 numbered backup files for each file that you edit.
511 Emacs makes a backup for a file only the first time the file is saved
512 from one buffer. No matter how many times you save a file, its backup file
513 continues to contain the contents from before the file was visited.
514 Normally this means that the backup file contains the contents from before
515 the current editing session; however, if you kill the buffer and then visit
516 the file again, a new backup file will be made by the next save.
518 You can also explicitly request making another backup file from a
519 buffer even though it has already been saved at least once. If you save
520 the buffer with @kbd{C-u C-x C-s}, the version thus saved will be made
521 into a backup file if you save the buffer again. @kbd{C-u C-u C-x C-s}
522 saves the buffer, but first makes the previous file contents into a new
523 backup file. @kbd{C-u C-u C-u C-x C-s} does both things: it makes a
524 backup from the previous contents, and arranges to make another from the
525 newly saved contents if you save again.
528 * Names: Backup Names. How backup files are named;
529 choosing single or numbered backup files.
530 * Deletion: Backup Deletion. Emacs deletes excess numbered backups.
531 * Copying: Backup Copying. Backups can be made by copying or renaming.
535 @subsubsection Single or Numbered Backups
537 If you choose to have a single backup file (this is the default),
538 the backup file's name is normally constructed by appending @samp{~} to the
539 file name being edited; thus, the backup file for @file{eval.c} would
542 @vindex make-backup-file-name-function
543 @vindex backup-directory-alist
544 You can change this behavior by defining the variable
545 @code{make-backup-file-name-function} to a suitable function.
546 Alternatively you can customize the variable
547 @code{backup-directory-alist} to specify that files matching certain
548 patterns should be backed up in specific directories.
550 A typical use is to add an element @code{("." . @var{dir})} to make
551 all backups in the directory with absolute name @var{dir}; Emacs
552 modifies the backup file names to avoid clashes between files with the
553 same names originating in different directories. Alternatively,
554 adding, say, @code{("." . ".~")} would make backups in the invisible
555 subdirectory @file{.~} of the original file's directory. Emacs
556 creates the directory, if necessary, to make the backup.
558 If access control stops Emacs from writing backup files under the usual
559 names, it writes the backup file as @file{%backup%~} in your home
560 directory. Only one such file can exist, so only the most recently
561 made such backup is available.
563 If you choose to have a series of numbered backup files, backup file
564 names contain @samp{.~}, the number, and another @samp{~} after the
565 original file name. Thus, the backup files of @file{eval.c} would be
566 called @file{eval.c.~1~}, @file{eval.c.~2~}, and so on, all the way
567 through names like @file{eval.c.~259~} and beyond. The variable
568 @code{backup-directory-alist} applies to numbered backups just as
571 @vindex version-control
572 The choice of single backup or numbered backups is controlled by the
573 variable @code{version-control}. Its possible values are
577 Make numbered backups.
579 Make numbered backups for files that have numbered backups already.
580 Otherwise, make single backups.
582 Never make numbered backups; always make single backups.
586 You can set @code{version-control} locally in an individual buffer to
587 control the making of backups for that buffer's file. For example,
588 Rmail mode locally sets @code{version-control} to @code{never} to make sure
589 that there is only one backup for an Rmail file. @xref{Locals}.
591 @cindex @env{VERSION_CONTROL} environment variable
592 If you set the environment variable @env{VERSION_CONTROL}, to tell
593 various GNU utilities what to do with backup files, Emacs also obeys the
594 environment variable by setting the Lisp variable @code{version-control}
595 accordingly at startup. If the environment variable's value is @samp{t}
596 or @samp{numbered}, then @code{version-control} becomes @code{t}; if the
597 value is @samp{nil} or @samp{existing}, then @code{version-control}
598 becomes @code{nil}; if it is @samp{never} or @samp{simple}, then
599 @code{version-control} becomes @code{never}.
601 @node Backup Deletion
602 @subsubsection Automatic Deletion of Backups
604 To prevent excessive consumption of disk space, Emacs can delete numbered
605 backup versions automatically. Generally Emacs keeps the first few backups
606 and the latest few backups, deleting any in between. This happens every
607 time a new backup is made.
609 @vindex kept-old-versions
610 @vindex kept-new-versions
611 The two variables @code{kept-old-versions} and
612 @code{kept-new-versions} control this deletion. Their values are,
613 respectively, the number of oldest (lowest-numbered) backups to keep
614 and the number of newest (highest-numbered) ones to keep, each time a
615 new backup is made. The backups in the middle (excluding those oldest
616 and newest) are the excess middle versions---those backups are
617 deleted. These variables' values are used when it is time to delete
618 excess versions, just after a new backup version is made; the newly
619 made backup is included in the count in @code{kept-new-versions}. By
620 default, both variables are 2.
622 @vindex delete-old-versions
623 If @code{delete-old-versions} is non-@code{nil}, Emacs deletes the
624 excess backup files silently. If it is @code{nil}, the default, Emacs
625 asks you whether it should delete the excess backup versions.
627 Dired's @kbd{.} (Period) command can also be used to delete old versions.
628 @xref{Dired Deletion}.
631 @subsubsection Copying vs.@: Renaming
633 Backup files can be made by copying the old file or by renaming it.
634 This makes a difference when the old file has multiple names (hard
635 links). If the old file is renamed into the backup file, then the
636 alternate names become names for the backup file. If the old file is
637 copied instead, then the alternate names remain names for the file
638 that you are editing, and the contents accessed by those names will be
641 The method of making a backup file may also affect the file's owner
642 and group. If copying is used, these do not change. If renaming is used,
643 you become the file's owner, and the file's group becomes the default
644 (different operating systems have different defaults for the group).
646 Having the owner change is usually a good idea, because then the owner
647 always shows who last edited the file. Also, the owners of the backups
648 show who produced those versions. Occasionally there is a file whose
649 owner should not change; it is a good idea for such files to contain
650 local variable lists to set @code{backup-by-copying-when-mismatch}
651 locally (@pxref{File Variables}).
653 @vindex backup-by-copying
654 @vindex backup-by-copying-when-linked
655 @vindex backup-by-copying-when-mismatch
656 @vindex backup-by-copying-when-privileged-mismatch
657 @cindex file ownership, and backup
658 @cindex backup, and user-id
659 The choice of renaming or copying is controlled by four variables.
660 Renaming is the default choice. If the variable
661 @code{backup-by-copying} is non-@code{nil}, copying is used. Otherwise,
662 if the variable @code{backup-by-copying-when-linked} is non-@code{nil},
663 then copying is used for files that have multiple names, but renaming
664 may still be used when the file being edited has only one name. If the
665 variable @code{backup-by-copying-when-mismatch} is non-@code{nil}, then
666 copying is used if renaming would cause the file's owner or group to
667 change. @code{backup-by-copying-when-mismatch} is @code{t} by default
668 if you start Emacs as the superuser. The fourth variable,
669 @code{backup-by-copying-when-privileged-mismatch}, gives the highest
670 numeric user-id for which @code{backup-by-copying-when-mismatch} will be
671 forced on. This is useful when low-numbered user-ids are assigned to
672 special system users, such as @code{root}, @code{bin}, @code{daemon},
673 etc., which must maintain ownership of files.
675 When a file is managed with a version control system (@pxref{Version
676 Control}), Emacs does not normally make backups in the usual way for
677 that file. But check-in and check-out are similar in some ways to
678 making backups. One unfortunate similarity is that these operations
679 typically break hard links, disconnecting the file name you visited from
680 any alternate names for the same file. This has nothing to do with
681 Emacs---the version control system does it.
684 @subsection Protection against Simultaneous Editing
687 @cindex simultaneous editing
688 Simultaneous editing occurs when two users visit the same file, both
689 make changes, and then both save them. If nobody were informed that
690 this was happening, whichever user saved first would later find that his
693 On some systems, Emacs notices immediately when the second user starts
694 to change the file, and issues an immediate warning. On all systems,
695 Emacs checks when you save the file, and warns if you are about to
696 overwrite another user's changes. You can prevent loss of the other
697 user's work by taking the proper corrective action instead of saving the
700 @findex ask-user-about-lock
701 @cindex locking files
702 When you make the first modification in an Emacs buffer that is
703 visiting a file, Emacs records that the file is @dfn{locked} by you.
704 (It does this by creating a symbolic link in the same directory with a
705 different name.) Emacs removes the lock when you save the changes. The
706 idea is that the file is locked whenever an Emacs buffer visiting it has
710 If you begin to modify the buffer while the visited file is locked by
711 someone else, this constitutes a @dfn{collision}. When Emacs detects a
712 collision, it asks you what to do, by calling the Lisp function
713 @code{ask-user-about-lock}. You can redefine this function for the sake
714 of customization. The standard definition of this function asks you a
715 question and accepts three possible answers:
719 Steal the lock. Whoever was already changing the file loses the lock,
720 and you gain the lock.
722 Proceed. Go ahead and edit the file despite its being locked by someone else.
724 Quit. This causes an error (@code{file-locked}), and the buffer
725 contents remain unchanged---the modification you were trying to make
726 does not actually take place.
729 Note that locking works on the basis of a file name; if a file has
730 multiple names, Emacs does not realize that the two names are the same file
731 and cannot prevent two users from editing it simultaneously under different
732 names. However, basing locking on names means that Emacs can interlock the
733 editing of new files that will not really exist until they are saved.
735 Some systems are not configured to allow Emacs to make locks, and
736 there are cases where lock files cannot be written. In these cases,
737 Emacs cannot detect trouble in advance, but it still can detect the
738 collision when you try to save a file and overwrite someone else's
741 If Emacs or the operating system crashes, this may leave behind lock
742 files which are stale, so you may occasionally get warnings about
743 spurious collisions. When you determine that the collision is spurious,
744 just use @kbd{p} to tell Emacs to go ahead anyway.
746 Every time Emacs saves a buffer, it first checks the last-modification
747 date of the existing file on disk to verify that it has not changed since the
748 file was last visited or saved. If the date does not match, it implies
749 that changes were made in the file in some other way, and these changes are
750 about to be lost if Emacs actually does save. To prevent this, Emacs
751 displays a warning message and asks for confirmation before saving.
752 Occasionally you will know why the file was changed and know that it does
753 not matter; then you can answer @kbd{yes} and proceed. Otherwise, you should
754 cancel the save with @kbd{C-g} and investigate the situation.
756 The first thing you should do when notified that simultaneous editing
757 has already taken place is to list the directory with @kbd{C-u C-x C-d}
758 (@pxref{Directories}). This shows the file's current author. You
759 should attempt to contact him to warn him not to continue editing.
760 Often the next step is to save the contents of your Emacs buffer under a
761 different name, and use @code{diff} to compare the two files.@refill
764 @subsection Shadowing Files
769 @item M-x shadow-initialize
770 Set up file shadowing.
771 @item M-x shadow-define-literal-group
772 Declare a single file to be shared between sites.
773 @item M-x shadow-define-regexp-group
774 Make all files that match each of a group of files be shared between hosts.
775 @item M-x shadow-define-cluster @key{RET} @var{name} @key{RET}
776 Define a shadow file cluster @var{name}.
777 @item M-x shadow-copy-files
778 Copy all pending shadow files.
779 @item M-x shadow-cancel
780 Cancel the instruction to shadow some files.
783 You can arrange to keep identical @dfn{shadow} copies of certain files
784 in more than one place---possibly on different machines. To do this,
785 first you must set up a @dfn{shadow file group}, which is a set of
786 identically-named files shared between a list of sites. The file
787 group is permanent and applies to further Emacs sessions as well as
788 the current one. Once the group is set up, every time you exit Emacs,
789 it will copy the file you edited to the other files in its group. You
790 can also do the copying without exiting Emacs, by typing @kbd{M-x
793 To set up a shadow file group, use @kbd{M-x
794 shadow-define-literal-group} or @kbd{M-x shadow-define-regexp-group}.
795 See their documentation strings for further information.
797 Before copying a file to its shadows, Emacs asks for confirmation.
798 You can answer ``no'' to bypass copying of this file, this time. If
799 you want to cancel the shadowing permanently for a certain file, use
800 @kbd{M-x shadow-cancel} to eliminate or change the shadow file group.
802 A @dfn{shadow cluster} is a group of hosts that share directories, so
803 that copying to or from one of them is sufficient to update the file
804 on all of them. Each shadow cluster has a name, and specifies the
805 network address of a primary host (the one we copy files to), and a
806 regular expression that matches the host names of all the other hosts
807 in the cluster. You can define a shadow cluster with @kbd{M-x
808 shadow-define-cluster}.
811 @subsection Updating Time Stamps Automatically
814 @cindex modification dates
815 @cindex locale, date format
817 You can arrange to put a time stamp in a file, so that it will be updated
818 automatically each time you edit and save the file. The time stamp
819 has to be in the first eight lines of the file, and you should
833 Then add the hook function @code{time-stamp} to the hook
834 @code{write-file-functions}; that hook function will automatically update
835 the time stamp, inserting the current date and time when you save the
836 file. You can also use the command @kbd{M-x time-stamp} to update the
837 time stamp manually. For other customizations, see the Custom group
838 @code{time-stamp}. Note that non-numeric fields in the time stamp are
839 formatted according to your locale setting (@pxref{Environment}).
842 @section Reverting a Buffer
843 @findex revert-buffer
844 @cindex drastic changes
845 @cindex reread a file
847 If you have made extensive changes to a file and then change your mind
848 about them, you can get rid of them by reading in the previous version
849 of the file. To do this, use @kbd{M-x revert-buffer}, which operates on
850 the current buffer. Since reverting a buffer unintentionally could lose
851 a lot of work, you must confirm this command with @kbd{yes}.
853 @code{revert-buffer} keeps point at the same distance (measured in
854 characters) from the beginning of the file. If the file was edited only
855 slightly, you will be at approximately the same piece of text after
856 reverting as before. If you have made drastic changes, the same value of
857 point in the old file may address a totally different piece of text.
859 Reverting marks the buffer as ``not modified'' until another change is
862 Some kinds of buffers whose contents reflect data bases other than files,
863 such as Dired buffers, can also be reverted. For them, reverting means
864 recalculating their contents from the appropriate data base. Buffers
865 created explicitly with @kbd{C-x b} cannot be reverted; @code{revert-buffer}
866 reports an error when asked to do so.
868 @vindex revert-without-query
869 When you edit a file that changes automatically and frequently---for
870 example, a log of output from a process that continues to run---it may be
871 useful for Emacs to revert the file without querying you, whenever you
872 visit the file again with @kbd{C-x C-f}.
874 To request this behavior, set the variable @code{revert-without-query}
875 to a list of regular expressions. When a file name matches one of these
876 regular expressions, @code{find-file} and @code{revert-buffer} will
877 revert it automatically if it has changed---provided the buffer itself
878 is not modified. (If you have edited the text, it would be wrong to
879 discard your changes.)
881 @cindex Global Auto-Revert mode
882 @cindex mode, Global Auto-Revert
883 @cindex Auto-Revert mode
884 @cindex mode, Auto-Revert
885 @findex global-auto-revert-mode
886 @findex auto-revert-mode
887 @vindex auto-revert-interval
888 You may find it useful to have Emacs revert files automatically when
889 they change. Two minor modes are available to do this. In Global
890 Auto-Revert mode, Emacs periodically checks all file buffers and
891 reverts any when the corresponding file has changed. The local
892 variant, Auto-Revert mode, applies only to buffers in which it was
893 activated. Checking the files is done at intervals determined by the
894 variable @code{auto-revert-interval}.
897 @section Auto-Saving: Protection Against Disasters
898 @cindex Auto Save mode
899 @cindex mode, Auto Save
902 Emacs saves all the visited files from time to time (based on counting
903 your keystrokes) without being asked. This is called @dfn{auto-saving}.
904 It prevents you from losing more than a limited amount of work if the
907 When Emacs determines that it is time for auto-saving, each buffer is
908 considered, and is auto-saved if auto-saving is turned on for it and it
909 has been changed since the last time it was auto-saved. The message
910 @samp{Auto-saving...} is displayed in the echo area during auto-saving,
911 if any files are actually auto-saved. Errors occurring during
912 auto-saving are caught so that they do not interfere with the execution
913 of commands you have been typing.
916 * Files: Auto Save Files. The file where auto-saved changes are
917 actually made until you save the file.
918 * Control: Auto Save Control. Controlling when and how often to auto-save.
919 * Recover:: Recovering text from auto-save files.
922 @node Auto Save Files
923 @subsection Auto-Save Files
925 Auto-saving does not normally save in the files that you visited, because
926 it can be very undesirable to save a program that is in an inconsistent
927 state when you have made half of a planned change. Instead, auto-saving
928 is done in a different file called the @dfn{auto-save file}, and the
929 visited file is changed only when you request saving explicitly (such as
932 Normally, the auto-save file name is made by appending @samp{#} to the
933 front and rear of the visited file name. Thus, a buffer visiting file
934 @file{foo.c} is auto-saved in a file @file{#foo.c#}. Most buffers that
935 are not visiting files are auto-saved only if you request it explicitly;
936 when they are auto-saved, the auto-save file name is made by appending
937 @samp{#} to the front and rear of buffer name, then
938 adding digits and letters at the end for uniqueness. For
939 example, the @samp{*mail*} buffer in which you compose messages to be
940 sent might auto-saved in a file named @file{#*mail*#704juu}. Auto-save file
941 names are made this way unless you reprogram parts of Emacs to do
942 something different (the functions @code{make-auto-save-file-name} and
943 @code{auto-save-file-name-p}). The file name to be used for auto-saving
944 in a buffer is calculated when auto-saving is turned on in that buffer.
946 @cindex auto-save for remote files
947 @vindex auto-save-file-name-transforms
948 The variable @code{auto-save-file-name-transforms} allows a
949 degree of control over the auto-save file name. The default value is
950 set up to put the auto-save files for remote files
951 (@pxref{Remote Files}) into the temporary file directory on the local
954 When you delete a substantial part of the text in a large buffer, auto
955 save turns off temporarily in that buffer. This is because if you
956 deleted the text unintentionally, you might find the auto-save file more
957 useful if it contains the deleted text. To reenable auto-saving after
958 this happens, save the buffer with @kbd{C-x C-s}, or use @kbd{C-u 1 M-x
961 @vindex auto-save-visited-file-name
962 If you want auto-saving to be done in the visited file rather than
963 in a separate auto-save file, set the variable
964 @code{auto-save-visited-file-name} to a non-@code{nil} value. In this
965 mode, there is no real difference between auto-saving and explicit
968 @vindex delete-auto-save-files
969 A buffer's auto-save file is deleted when you save the buffer in its
970 visited file. To inhibit this, set the variable @code{delete-auto-save-files}
971 to @code{nil}. Changing the visited file name with @kbd{C-x C-w} or
972 @code{set-visited-file-name} renames any auto-save file to go with
973 the new visited name.
975 @node Auto Save Control
976 @subsection Controlling Auto-Saving
978 @vindex auto-save-default
979 @findex auto-save-mode
980 Each time you visit a file, auto-saving is turned on for that file's
981 buffer if the variable @code{auto-save-default} is non-@code{nil} (but not
982 in batch mode; @pxref{Entering Emacs}). The default for this variable is
983 @code{t}, so auto-saving is the usual practice for file-visiting buffers.
984 Auto-saving can be turned on or off for any existing buffer with the
985 command @kbd{M-x auto-save-mode}. Like other minor mode commands, @kbd{M-x
986 auto-save-mode} turns auto-saving on with a positive argument, off with a
987 zero or negative argument; with no argument, it toggles.
989 @vindex auto-save-interval
990 Emacs does auto-saving periodically based on counting how many characters
991 you have typed since the last time auto-saving was done. The variable
992 @code{auto-save-interval} specifies how many characters there are between
993 auto-saves. By default, it is 300. Emacs doesn't accept values that are
994 too small: if you customize @code{auto-save-interval} to a value less
995 than 20, Emacs will behave as if the value is 20.
997 @vindex auto-save-timeout
998 Auto-saving also takes place when you stop typing for a while. The
999 variable @code{auto-save-timeout} says how many seconds Emacs should
1000 wait before it does an auto save (and perhaps also a garbage
1001 collection). (The actual time period is longer if the current buffer is
1002 long; this is a heuristic which aims to keep out of your way when you
1003 are editing long buffers, in which auto-save takes an appreciable amount
1004 of time.) Auto-saving during idle periods accomplishes two things:
1005 first, it makes sure all your work is saved if you go away from the
1006 terminal for a while; second, it may avoid some auto-saving while you
1007 are actually typing.
1009 Emacs also does auto-saving whenever it gets a fatal error. This
1010 includes killing the Emacs job with a shell command such as @samp{kill
1011 %emacs}, or disconnecting a phone line or network connection.
1013 @findex do-auto-save
1014 You can request an auto-save explicitly with the command @kbd{M-x
1018 @subsection Recovering Data from Auto-Saves
1020 @findex recover-file
1021 You can use the contents of an auto-save file to recover from a loss
1022 of data with the command @kbd{M-x recover-file @key{RET} @var{file}
1023 @key{RET}}. This visits @var{file} and then (after your confirmation)
1024 restores the contents from its auto-save file @file{#@var{file}#}.
1025 You can then save with @kbd{C-x C-s} to put the recovered text into
1026 @var{file} itself. For example, to recover file @file{foo.c} from its
1027 auto-save file @file{#foo.c#}, do:@refill
1030 M-x recover-file @key{RET} foo.c @key{RET}
1035 Before asking for confirmation, @kbd{M-x recover-file} displays a
1036 directory listing describing the specified file and the auto-save file,
1037 so you can compare their sizes and dates. If the auto-save file
1038 is older, @kbd{M-x recover-file} does not offer to read it.
1040 @findex recover-session
1041 If Emacs or the computer crashes, you can recover all the files you
1042 were editing from their auto save files with the command @kbd{M-x
1043 recover-session}. This first shows you a list of recorded interrupted
1044 sessions. Move point to the one you choose, and type @kbd{C-c C-c}.
1046 Then @code{recover-session} asks about each of the files that were
1047 being edited during that session, asking whether to recover that file.
1048 If you answer @kbd{y}, it calls @code{recover-file}, which works in its
1049 normal fashion. It shows the dates of the original file and its
1050 auto-save file, and asks once again whether to recover that file.
1052 When @code{recover-session} is done, the files you've chosen to
1053 recover are present in Emacs buffers. You should then save them. Only
1054 this---saving them---updates the files themselves.
1056 @vindex auto-save-list-file-prefix
1057 Emacs records interrupted sessions for later recovery in files named
1058 @file{~/.emacs.d/auto-save-list/.saves-@var{pid}-@var{hostname}}. All
1059 of this name except @file{@var{pid}-@var{hostname}} comes from the
1060 value of @code{auto-save-list-file-prefix}. You can record sessions
1061 in a different place by customizing that variable. If you set
1062 @code{auto-save-list-file-prefix} to @code{nil} in your @file{.emacs}
1063 file, sessions are not recorded for recovery.
1066 @section File Name Aliases
1068 Symbolic links and hard links both make it possible for several file
1069 names to refer to the same file. Hard links are alternate names that
1070 refer directly to the file; all the names are equally valid, and no one
1071 of them is preferred. By contrast, a symbolic link is a kind of defined
1072 alias: when @file{foo} is a symbolic link to @file{bar}, you can use
1073 either name to refer to the file, but @file{bar} is the real name, while
1074 @file{foo} is just an alias. More complex cases occur when symbolic
1075 links point to directories.
1077 If you visit two names for the same file, normally Emacs makes
1078 two different buffers, but it warns you about the situation.
1080 @vindex find-file-existing-other-name
1081 @vindex find-file-suppress-same-file-warnings
1082 Normally, if you visit a file which Emacs is already visiting under
1083 a different name, Emacs displays a message in the echo area and uses
1084 the existing buffer visiting that file. This can happen on systems
1085 that support symbolic links, or if you use a long file name on a
1086 system that truncates long file names. You can suppress the message by
1087 setting the variable @code{find-file-suppress-same-file-warnings} to a
1088 non-@code{nil} value. You can disable this feature entirely by setting
1089 the variable @code{find-file-existing-other-name} to @code{nil}: then
1090 if you visit the same file under two different names, you get a separate
1091 buffer for each file name.
1093 @vindex find-file-visit-truename
1094 @cindex truenames of files
1095 @cindex file truenames
1096 If the variable @code{find-file-visit-truename} is non-@code{nil},
1097 then the file name recorded for a buffer is the file's @dfn{truename}
1098 (made by replacing all symbolic links with their target names), rather
1099 than the name you specify. Setting @code{find-file-visit-truename} also
1100 implies the effect of @code{find-file-existing-other-name}.
1102 @node Version Control
1103 @section Version Control
1104 @cindex version control
1106 @dfn{Version control systems} are packages that can record multiple
1107 versions of a source file, usually storing the unchanged parts of the
1108 file just once. Version control systems also record history information
1109 such as the creation time of each version, who created it, and a
1110 description of what was changed in that version.
1112 The Emacs version control interface is called VC. Its commands work
1113 with three version control systems---RCS, CVS, and SCCS. The GNU
1114 project recommends RCS and CVS, which are free software and available
1115 from the Free Software Foundation. We also have free software to
1116 replace SCCS, known as CSSC; if you are using SCCS and don't want to
1117 make the incompatible change to RCS or CVS, you can switch to CSSC.
1120 * Introduction to VC:: How version control works in general.
1121 * VC Mode Line:: How the mode line shows version control status.
1122 * Basic VC Editing:: How to edit a file under version control.
1123 * Old Versions:: Examining and comparing old versions.
1124 * Secondary VC Commands:: The commands used a little less frequently.
1125 * Branches:: Multiple lines of development.
1126 * Remote Repositories:: Efficient access to remote CVS servers.
1127 * Snapshots:: Sets of file versions treated as a unit.
1128 * Miscellaneous VC:: Various other commands and features of VC.
1129 * Customizing VC:: Variables that change VC's behavior.
1132 @node Introduction to VC
1133 @subsection Introduction to Version Control
1135 VC allows you to use a version control system from within Emacs,
1136 integrating the version control operations smoothly with editing. VC
1137 provides a uniform interface to version control, so that regardless of
1138 which version control system is in use, you can use it the same way.
1140 This section provides a general overview of version control, and
1141 describes the version control systems that VC supports. You can skip
1142 this section if you are already familiar with the version control system
1146 * Version Systems:: Supported version control back-end systems.
1147 * VC Concepts:: Words and concepts related to version control.
1148 * Types of Log File:: The per-file VC log in contrast to the ChangeLog.
1151 @node Version Systems
1152 @subsubsection Supported Version Control Systems
1155 @cindex back end (version control)
1156 VC currently works with three different version control systems or
1157 ``back ends'': RCS, CVS, and SCCS.
1159 RCS is a free version control system that is available from the Free
1160 Software Foundation. It is perhaps the most mature of the supported
1161 back ends, and the VC commands are conceptually closest to RCS. Almost
1162 everything you can do with RCS can be done through VC.
1165 CVS is built on top of RCS, and extends the features of RCS, allowing
1166 for more sophisticated release management, and concurrent multi-user
1167 development. VC supports basic editing operations under CVS, but for
1168 some less common tasks you still need to call CVS from the command line.
1169 Note also that before using CVS you must set up a repository, which is a
1170 subject too complex to treat here.
1173 SCCS is a proprietary but widely used version control system. In
1174 terms of capabilities, it is the weakest of the three that VC
1175 supports. VC compensates for certain features missing in SCCS
1176 (snapshots, for example) by implementing them itself, but some other VC
1177 features, such as multiple branches, are not available with SCCS. You
1178 should use SCCS only if for some reason you cannot use RCS.
1181 @subsubsection Concepts of Version Control
1184 @cindex registered file
1185 When a file is under version control, we also say that it is
1186 @dfn{registered} in the version control system. Each registered file
1187 has a corresponding @dfn{master file} which represents the file's
1188 present state plus its change history---enough to reconstruct the
1189 current version or any earlier version. Usually the master file also
1190 records a @dfn{log entry} for each version, describing in words what was
1191 changed in that version.
1194 @cindex checking out files
1195 The file that is maintained under version control is sometimes called
1196 the @dfn{work file} corresponding to its master file. You edit the work
1197 file and make changes in it, as you would with an ordinary file. (With
1198 SCCS and RCS, you must @dfn{lock} the file before you start to edit it.)
1199 After you are done with a set of changes, you @dfn{check the file in},
1200 which records the changes in the master file, along with a log entry for
1203 With CVS, there are usually multiple work files corresponding to a
1204 single master file---often each user has his own copy. It is also
1205 possible to use RCS in this way, but this is not the usual way to use
1208 @cindex locking and version control
1209 A version control system typically has some mechanism to coordinate
1210 between users who want to change the same file. One method is
1211 @dfn{locking} (analogous to the locking that Emacs uses to detect
1212 simultaneous editing of a file, but distinct from it). The other method
1213 is to merge your changes with other people's changes when you check them
1216 With version control locking, work files are normally read-only so
1217 that you cannot change them. You ask the version control system to make
1218 a work file writable for you by locking it; only one user can do
1219 this at any given time. When you check in your changes, that unlocks
1220 the file, making the work file read-only again. This allows other users
1221 to lock the file to make further changes. SCCS always uses locking, and
1224 The other alternative for RCS is to let each user modify the work file
1225 at any time. In this mode, locking is not required, but it is
1226 permitted; check-in is still the way to record a new version.
1228 CVS normally allows each user to modify his own copy of the work file
1229 at any time, but requires merging with changes from other users at
1230 check-in time. However, CVS can also be set up to require locking.
1231 (@pxref{CVS Options}).
1233 @node Types of Log File
1234 @subsubsection Types of Log File
1235 @cindex types of log file
1236 @cindex log File, types of
1237 @cindex version control log
1239 GNU projects under a revision control system generally possess
1240 @emph{two} types of log for changes. One is the per-file log
1241 maintained by the revision control system: each time you check in a
1242 change, you must fill out a @dfn{log entry} for the change (@pxref{Log
1243 Buffer}). This kind of log is called the @dfn{version control log},
1244 also the @dfn{revision control log}, @dfn{RCS log}, or @dfn{CVS log}.
1246 The other kind of log is the change log file, typically a file called
1247 @file{ChangeLog}. It provides a chronological record of all changes
1248 to a large portion of a program---one directory and its
1249 subdirectories. A small program would use one @file{ChangeLog} file;
1250 a large program may well merit a @file{ChangeLog} file in each major
1251 directory. @xref{Change Log}.
1253 When you use version control, you can use just the per-file log if you
1254 wish, or you can use both kinds of logs. When you use both, you
1255 typically want to write just one entry for each change. You can write
1256 the entry in @file{ChangeLog}, then copy it to the log buffer when you
1257 check in the change. Or you can write the entry in the log buffer
1258 while checking in the change, and later use the @kbd{C-x v a} command
1259 to copy it to @file{ChangeLog} (@pxref{Change Logs and VC}).
1262 @subsection Version Control and the Mode Line
1264 When you visit a file that is under version control, Emacs indicates
1265 this on the mode line. For example, @samp{RCS-1.3} says that RCS is
1266 used for that file, and the current version is 1.3.
1268 The character between the back-end name and the version number
1269 indicates the version control status of the file. @samp{-} means that
1270 the work file is not locked (if locking is in use), or not modified (if
1271 locking is not in use). @samp{:} indicates that the file is locked, or
1272 that it is modified. If the file is locked by some other user (for
1273 instance, @samp{jim}), that is displayed as @samp{RCS:jim:1.3}.
1275 @node Basic VC Editing
1276 @subsection Basic Editing under Version Control
1278 The principal VC command is an all-purpose command that performs
1279 either locking or check-in, depending on the situation.
1284 Perform the next logical version control operation on this file.
1287 @findex vc-next-action
1288 @findex vc-toggle-read-only
1290 @kindex C-x C-q @r{(Version Control)}
1291 Strictly speaking, the command for this job is @code{vc-next-action},
1292 bound to @kbd{C-x v v}. However, the normal meaning of @kbd{C-x C-q} is
1293 to make a read-only buffer writable, or vice versa; we have extended it
1294 to do the same job properly for files managed by version control, by
1295 performing the appropriate version control operations. When you type
1296 @kbd{C-x C-q} on a registered file, it acts like @kbd{C-x v v}.
1298 The precise action of this command depends on the state of the file,
1299 and whether the version control system uses locking or not. SCCS and
1300 RCS normally use locking; CVS normally does not use locking.
1303 * VC with Locking:: RCS in its default mode, SCCS, and optionally CVS.
1304 * Without Locking:: Without locking: default mode for CVS.
1305 * Advanced C-x C-q:: Advanced features available with a prefix argument.
1306 * Log Buffer:: Features available in log entry buffers.
1309 @node VC with Locking
1310 @subsubsection Basic Version Control with Locking
1312 If locking is used for the file (as with SCCS, and RCS in its default
1313 mode), @kbd{C-x C-q} can either lock a file or check it in:
1317 If the file is not locked, @kbd{C-x C-q} locks it, and
1318 makes it writable so that you can change it.
1321 If the file is locked by you, and contains changes, @kbd{C-x C-q} checks
1322 in the changes. In order to do this, it first reads the log entry
1323 for the new version. @xref{Log Buffer}.
1326 If the file is locked by you, but you have not changed it since you
1327 locked it, @kbd{C-x C-q} releases the lock and makes the file read-only
1331 If the file is locked by some other user, @kbd{C-x C-q} asks you whether
1332 you want to ``steal the lock'' from that user. If you say yes, the file
1333 becomes locked by you, but a message is sent to the person who had
1334 formerly locked the file, to inform him of what has happened.
1337 These rules also apply when you use CVS in locking mode, except
1338 that there is no such thing as stealing a lock.
1340 @node Without Locking
1341 @subsubsection Basic Version Control without Locking
1343 When there is no locking---the default for CVS---work files are always
1344 writable; you do not need to do anything before you begin to edit a
1345 file. The status indicator on the mode line is @samp{-} if the file is
1346 unmodified; it flips to @samp{:} as soon as you save any changes in the
1349 Here is what @kbd{C-x C-q} does when using CVS:
1353 If some other user has checked in changes into the master file, Emacs
1354 asks you whether you want to merge those changes into your own work
1355 file. You must do this before you can check in your own changes. (To
1356 pick up any recent changes from the master file @emph{without} trying
1357 to commit your own changes, type @kbd{C-x v m @key{RET}}.)
1361 If there are no new changes in the master file, but you have made
1362 modifications in your work file, @kbd{C-x C-q} checks in your changes.
1363 In order to do this, it first reads the log entry for the new version.
1367 If the file is not modified, the @kbd{C-x C-q} does nothing.
1370 These rules also apply when you use RCS in the mode that does not
1371 require locking, except that automatic merging of changes from the
1372 master file is not implemented. Unfortunately, this means that nothing
1373 informs you if another user has checked in changes in the same file
1374 since you began editing it, and when this happens, his changes will be
1375 effectively removed when you check in your version (though they will
1376 remain in the master file, so they will not be entirely lost). You must
1377 therefore verify the current version is unchanged, before you check in your
1378 changes. We hope to eliminate this risk and provide automatic merging
1379 with RCS in a future Emacs version.
1381 In addition, locking is possible with RCS even in this mode, although
1382 it is not required; @kbd{C-x C-q} with an unmodified file locks the
1383 file, just as it does with RCS in its normal (locking) mode.
1385 @node Advanced C-x C-q
1386 @subsubsection Advanced Control in @kbd{C-x C-q}
1388 @cindex version number to check in/out
1389 When you give a prefix argument to @code{vc-next-action} (@kbd{C-u
1390 C-x C-q}), it still performs the next logical version control
1391 operation, but accepts additional arguments to specify precisely how
1392 to do the operation.
1396 If the file is modified (or locked), you can specify the version
1397 number to use for the new version that you check in. This is one way
1398 to create a new branch (@pxref{Branches}).
1401 If the file is not modified (and unlocked), you can specify the
1402 version to select; this lets you start working from an older version,
1403 or on another branch. If you do not enter any version, that takes you
1404 to the highest version on the current branch; therefore @kbd{C-u C-x
1405 C-q @key{RET}} is a convenient way to get the latest version of a file from
1409 @cindex specific version control system
1410 Instead of the version number, you can also specify the name of a
1411 version control system. This is useful when one file is being managed
1412 with two version control systems at the same time (@pxref{Local
1417 @subsubsection Features of the Log Entry Buffer
1419 When you check in changes, @kbd{C-x C-q} first reads a log entry. It
1420 pops up a buffer called @samp{*VC-Log*} for you to enter the log entry.
1421 When you are finished, type @kbd{C-c C-c} in the @samp{*VC-Log*} buffer.
1422 That is when check-in really happens.
1424 To abort check-in, just @strong{don't} type @kbd{C-c C-c} in that
1425 buffer. You can switch buffers and do other editing. As long as you
1426 don't try to check in another file, the entry you were editing remains
1427 in the @samp{*VC-Log*} buffer, and you can go back to that buffer at any
1428 time to complete the check-in.
1430 If you change several source files for the same reason, it is often
1431 convenient to specify the same log entry for many of the files. To do
1432 this, use the history of previous log entries. The commands @kbd{M-n},
1433 @kbd{M-p}, @kbd{M-s} and @kbd{M-r} for doing this work just like the
1434 minibuffer history commands (except that these versions are used outside
1437 @vindex vc-log-mode-hook
1438 Each time you check in a file, the log entry buffer is put into VC Log
1439 mode, which involves running two hooks: @code{text-mode-hook} and
1440 @code{vc-log-mode-hook}. @xref{Hooks}.
1443 @subsection Examining And Comparing Old Versions
1445 One of the convenient features of version control is the ability
1446 to examine any version of a file, or compare two versions.
1449 @item C-x v ~ @var{version} @key{RET}
1450 Examine version @var{version} of the visited file, in a buffer of its
1454 Compare the current buffer contents with the latest checked-in version
1457 @item C-u C-x v = @var{file} @key{RET} @var{oldvers} @key{RET} @var{newvers} @key{RET}
1458 Compare the specified two versions of @var{file}.
1461 Display the result of the CVS annotate command using colors.
1464 @findex vc-version-other-window
1466 To examine an old version in its entirety, visit the file and then type
1467 @kbd{C-x v ~ @var{version} @key{RET}} (@code{vc-version-other-window}).
1468 This puts the text of version @var{version} in a file named
1469 @file{@var{filename}.~@var{version}~}, and visits it in its own buffer
1470 in a separate window. (In RCS, you can also select an old version
1471 and create a branch from it. @xref{Branches}.)
1475 It is usually more convenient to compare two versions of the file,
1476 with the command @kbd{C-x v =} (@code{vc-diff}). Plain @kbd{C-x v =}
1477 compares the current buffer contents (saving them in the file if
1478 necessary) with the last checked-in version of the file. @kbd{C-u C-x
1479 v =}, with a numeric argument, reads a file name and two version
1480 numbers, then compares those versions of the specified file. Both
1481 forms display the output in a special buffer in another window.
1483 You can specify a checked-in version by its number; an empty input
1484 specifies the current contents of the work file (which may be different
1485 from all the checked-in versions). You can also specify a snapshot name
1486 (@pxref{Snapshots}) instead of one or both version numbers.
1488 If you supply a directory name instead of the name of a registered
1489 file, this command compares the two specified versions of all registered
1490 files in that directory and its subdirectories.
1492 @vindex vc-diff-switches
1493 @vindex vc-rcs-diff-switches
1494 @kbd{C-x v =} works by running a variant of the @code{diff} utility
1495 designed to work with the version control system in use. When you
1496 invoke @code{diff} this way, in addition to the options specified by
1497 @code{diff-switches} (@pxref{Comparing Files}), it receives those
1498 specified by @code{vc-diff-switches}, plus those specified for the
1499 specific back end by @code{vc-@var{backend}-diff-switches}. For
1500 instance, when the version control back end is RCS, @code{diff} uses
1501 the options in @code{vc-rcs-diff-switches}. The
1502 @samp{vc@dots{}diff-switches} variables are @code{nil} by default.
1504 Unlike the @kbd{M-x diff} command, @kbd{C-x v =} does not try to
1505 locate the changes in the old and new versions. This is because
1506 normally one or both versions do not exist as files when you compare
1507 them; they exist only in the records of the master file.
1508 @xref{Comparing Files}, for more information about @kbd{M-x diff}.
1512 For CVS-controlled files, you can display the result of the CVS
1513 annotate command, using colors to enhance the visual appearance. Use
1514 the command @kbd{M-x vc-annotate} to do this. It creates a new buffer
1515 to display file's text, colored to show how old each part is. Text
1516 colored red is new, blue means old, and intermediate colors indicate
1517 intermediate ages. By default, the time scale is 360 days, so that
1518 everything more than one year old is shown in blue.
1520 When you give a prefix argument to this command, it uses the
1521 minibuffer to read two arguments: which version number to display and
1522 annotate (instead of the current file contents), and a stretch factor
1523 for the time scale. A stretch factor of 0.1 means that the color
1524 range from red to blue spans the past 36 days instead of 360 days. A
1525 stretch factor greater than 1 means the color range spans more than a
1528 @node Secondary VC Commands
1529 @subsection The Secondary Commands of VC
1531 This section explains the secondary commands of VC; those that you might
1535 * Registering:: Putting a file under version control.
1536 * VC Status:: Viewing the VC status of files.
1537 * VC Undo:: Cancelling changes before or after check-in.
1538 * VC Dired Mode:: Listing files managed by version control.
1539 * VC Dired Commands:: Commands to use in a VC Dired buffer.
1543 @subsubsection Registering a File for Version Control
1547 You can put any file under version control by simply visiting it, and
1548 then typing @w{@kbd{C-x v i}} (@code{vc-register}).
1552 Register the visited file for version control.
1555 To register the file, Emacs must choose which version control system
1556 to use for it. If the file's directory already contains files
1557 registered in a version control system, Emacs uses that system. If
1558 there is more than one system in use for a directory, Emacs uses the one
1559 that appears first in @code{vc-handled-backends} (@pxref{Customizing VC}).
1560 On the other hand, if there are no files already registered,
1561 Emacs uses the first system from @code{vc-handled-backends} that could
1562 register the file---for example, you cannot register a file under CVS if
1563 its directory is not already part of a CVS tree.
1565 With the default value of @code{vc-handled-backends}, this means
1566 that Emacs uses RCS if there are any files under RCS control, CVS if
1567 there are any files under CVS, SCCS if any files are under SCCS, or
1568 RCS as the ultimate default.
1570 If locking is in use, @kbd{C-x v i} leaves the file unlocked and
1571 read-only. Type @kbd{C-x C-q} if you wish to start editing it. After
1572 registering a file with CVS, you must subsequently commit the initial
1573 version by typing @kbd{C-x C-q}.
1575 @vindex vc-default-init-version
1576 @cindex initial version number to register
1577 The initial version number for a newly registered file is 1.1, by
1578 default. You can specify a different default by setting the variable
1579 @code{vc-default-init-version}, or you can give @kbd{C-x v i} a numeric
1580 argument; then it reads the initial version number for this particular
1581 file using the minibuffer.
1583 @vindex vc-initial-comment
1584 If @code{vc-initial-comment} is non-@code{nil}, @kbd{C-x v i} reads an
1585 initial comment to describe the purpose of this source file. Reading
1586 the initial comment works like reading a log entry (@pxref{Log Buffer}).
1589 @subsubsection VC Status Commands
1593 Display version control state and change history.
1597 @findex vc-print-log
1598 To view the detailed version control status and history of a file,
1599 type @kbd{C-x v l} (@code{vc-print-log}). It displays the history of
1600 changes to the current file, including the text of the log entries. The
1601 output appears in a separate window.
1604 @subsubsection Undoing Version Control Actions
1608 Revert the buffer and the file to the last checked-in version.
1611 Remove the last-entered change from the master for the visited file.
1612 This undoes your last check-in.
1616 @findex vc-revert-buffer
1617 If you want to discard your current set of changes and revert to the
1618 last version checked in, use @kbd{C-x v u} (@code{vc-revert-buffer}).
1619 This leaves the file unlocked; if locking is in use, you must first lock
1620 the file again before you change it again. @kbd{C-x v u} requires
1621 confirmation, unless it sees that you haven't made any changes since the
1622 last checked-in version.
1624 @kbd{C-x v u} is also the command to unlock a file if you lock it and
1625 then decide not to change it.
1628 @findex vc-cancel-version
1629 To cancel a change that you already checked in, use @kbd{C-x v c}
1630 (@code{vc-cancel-version}). This command discards all record of the
1631 most recent checked-in version. @kbd{C-x v c} also offers to revert
1632 your work file and buffer to the previous version (the one that precedes
1633 the version that is deleted).
1635 If you answer @kbd{no}, VC keeps your changes in the buffer, and locks
1636 the file. The no-revert option is useful when you have checked in a
1637 change and then discover a trivial error in it; you can cancel the
1638 erroneous check-in, fix the error, and check the file in again.
1640 When @kbd{C-x v c} does not revert the buffer, it unexpands all
1641 version control headers in the buffer instead (@pxref{Version Headers}).
1642 This is because the buffer no longer corresponds to any existing
1643 version. If you check it in again, the check-in process will expand the
1644 headers properly for the new version number.
1646 However, it is impossible to unexpand the RCS @samp{@w{$}Log$} header
1647 automatically. If you use that header feature, you have to unexpand it
1648 by hand---by deleting the entry for the version that you just canceled.
1650 Be careful when invoking @kbd{C-x v c}, as it is easy to lose a lot of
1651 work with it. To help you be careful, this command always requires
1652 confirmation with @kbd{yes}. Note also that this command is disabled
1653 under CVS, because canceling versions is very dangerous and discouraged
1657 @subsubsection Dired under VC
1661 @cindex CVS Dired Mode
1662 The VC Dired Mode described here works with all the version control
1663 systems that VC supports. Another more powerful facility, designed
1664 specifically for CVS, is called PCL-CVS. @xref{Top, , About PCL-CVS,
1665 pcl-cvs, PCL-CVS --- The Emacs Front-End to CVS}.
1668 @findex vc-directory
1669 When you are working on a large program, it is often useful to find
1670 out which files have changed within an entire directory tree, or to view
1671 the status of all files under version control at once, and to perform
1672 version control operations on collections of files. You can use the
1673 command @kbd{C-x v d} (@code{vc-directory}) to make a directory listing
1674 that includes only files relevant for version control.
1676 @vindex vc-dired-terse-display
1677 @kbd{C-x v d} creates a buffer which uses VC Dired Mode. This looks
1678 much like an ordinary Dired buffer (@pxref{Dired}); however, normally it
1679 shows only the noteworthy files (those locked or not up-to-date). This
1680 is called @dfn{terse display}. If you set the variable
1681 @code{vc-dired-terse-display} to @code{nil}, then VC Dired shows all
1682 relevant files---those managed under version control, plus all
1683 subdirectories (@dfn{full display}). The command @kbd{v t} in a VC
1684 Dired buffer toggles between terse display and full display (@pxref{VC
1687 @vindex vc-dired-recurse
1688 By default, VC Dired produces a recursive listing of noteworthy or
1689 relevant files at or below the given directory. You can change this by
1690 setting the variable @code{vc-dired-recurse} to @code{nil}; then VC
1691 Dired shows only the files in the given directory.
1693 The line for an individual file shows the version control state in the
1694 place of the hard link count, owner, group, and size of the file. If
1695 the file is unmodified, in sync with the master file, the version
1696 control state shown is blank. Otherwise it consists of text in
1697 parentheses. Under RCS and SCCS, the name of the user locking the file
1698 is shown; under CVS, an abbreviated version of the @samp{cvs status}
1699 output is used. Here is an example using RCS:
1705 -rw-r--r-- (jim) Apr 2 23:39 file1
1706 -r--r--r-- Apr 5 20:21 file2
1711 The files @samp{file1} and @samp{file2} are under version control,
1712 @samp{file1} is locked by user jim, and @samp{file2} is unlocked.
1714 Here is an example using CVS:
1720 -rw-r--r-- (modified) Aug 2 1997 file1.c
1721 -rw-r--r-- Apr 4 20:09 file2.c
1722 -rw-r--r-- (merge) Sep 13 1996 file3.c
1726 Here @samp{file1.c} is modified with respect to the repository, and
1727 @samp{file2.c} is not. @samp{file3.c} is modified, but other changes
1728 have also been checked in to the repository---you need to merge them
1729 with the work file before you can check it in.
1731 @vindex vc-directory-exclusion-list
1732 When VC Dired displays subdirectories (in the ``full'' display mode),
1733 it omits some that should never contain any files under version control.
1734 By default, this includes Version Control subdirectories such as
1735 @samp{RCS} and @samp{CVS}; you can customize this by setting the
1736 variable @code{vc-directory-exclusion-list}.
1738 You can fine-tune VC Dired's format by typing @kbd{C-u C-x v d}---as in
1739 ordinary Dired, that allows you to specify additional switches for the
1742 @node VC Dired Commands
1743 @subsubsection VC Dired Commands
1745 All the usual Dired commands work normally in VC Dired mode, except
1746 for @kbd{v}, which is redefined as the version control prefix. You can
1747 invoke VC commands such as @code{vc-diff} and @code{vc-print-log} by
1748 typing @kbd{v =}, or @kbd{v l}, and so on. Most of these commands apply
1749 to the file name on the current line.
1751 The command @kbd{v v} (@code{vc-next-action}) operates on all the
1752 marked files, so that you can lock or check in several files at once.
1753 If it operates on more than one file, it handles each file according to
1754 its current state; thus, it might lock one file, but check in another
1755 file. This could be confusing; it is up to you to avoid confusing
1756 behavior by marking a set of files that are in a similar state.
1758 If any files call for check-in, @kbd{v v} reads a single log entry,
1759 then uses it for all the files being checked in. This is convenient for
1760 registering or checking in several files at once, as part of the same
1763 @findex vc-dired-toggle-terse-mode
1764 @findex vc-dired-mark-locked
1765 You can toggle between terse display (only locked files, or files not
1766 up-to-date) and full display at any time by typing @kbd{v t}
1767 (@code{vc-dired-toggle-terse-mode}). There is also a special command
1768 @kbd{* l} (@code{vc-dired-mark-locked}), which marks all files currently
1769 locked (or, with CVS, all files not up-to-date). Thus, typing @kbd{* l
1770 t k} is another way to delete from the buffer all files except those
1774 @subsection Multiple Branches of a File
1775 @cindex branch (version control)
1776 @cindex trunk (version control)
1778 One use of version control is to maintain multiple ``current''
1779 versions of a file. For example, you might have different versions of a
1780 program in which you are gradually adding various unfinished new
1781 features. Each such independent line of development is called a
1782 @dfn{branch}. VC allows you to create branches, switch between
1783 different branches, and merge changes from one branch to another.
1784 Please note, however, that branches are only supported for RCS at the
1787 A file's main line of development is usually called the @dfn{trunk}.
1788 The versions on the trunk are normally numbered 1.1, 1.2, 1.3, etc. At
1789 any such version, you can start an independent branch. A branch
1790 starting at version 1.2 would have version number 1.2.1.1, and consecutive
1791 versions on this branch would have numbers 1.2.1.2, 1.2.1.3, 1.2.1.4,
1792 and so on. If there is a second branch also starting at version 1.2, it
1793 would consist of versions 1.2.2.1, 1.2.2.2, 1.2.2.3, etc.
1795 @cindex head version
1796 If you omit the final component of a version number, that is called a
1797 @dfn{branch number}. It refers to the highest existing version on that
1798 branch---the @dfn{head version} of that branch. The branches in the
1799 example above have branch numbers 1.2.1 and 1.2.2.
1802 * Switching Branches:: How to get to another existing branch.
1803 * Creating Branches:: How to start a new branch.
1804 * Merging:: Transferring changes between branches.
1805 * Multi-User Branching:: Multiple users working at multiple branches
1809 @node Switching Branches
1810 @subsubsection Switching between Branches
1812 To switch between branches, type @kbd{C-u C-x C-q} and specify the
1813 version number you want to select. This version is then visited
1814 @emph{unlocked} (write-protected), so you can examine it before locking
1815 it. Switching branches in this way is allowed only when the file is not
1818 You can omit the minor version number, thus giving only the branch
1819 number; this takes you to the head version on the chosen branch. If you
1820 only type @key{RET}, Emacs goes to the highest version on the trunk.
1822 After you have switched to any branch (including the main branch), you
1823 stay on it for subsequent VC commands, until you explicitly select some
1826 @node Creating Branches
1827 @subsubsection Creating New Branches
1829 To create a new branch from a head version (one that is the latest in
1830 the branch that contains it), first select that version if necessary,
1831 lock it with @kbd{C-x C-q}, and make whatever changes you want. Then,
1832 when you check in the changes, use @kbd{C-u C-x C-q}. This lets you
1833 specify the version number for the new version. You should specify a
1834 suitable branch number for a branch starting at the current version.
1835 For example, if the current version is 2.5, the branch number should be
1836 2.5.1, 2.5.2, and so on, depending on the number of existing branches at
1839 To create a new branch at an older version (one that is no longer the
1840 head of a branch), first select that version (@pxref{Switching
1841 Branches}), then lock it with @kbd{C-x C-q}. You'll be asked to
1842 confirm, when you lock the old version, that you really mean to create a
1843 new branch---if you say no, you'll be offered a chance to lock the
1844 latest version instead.
1846 Then make your changes and type @kbd{C-x C-q} again to check in a new
1847 version. This automatically creates a new branch starting from the
1848 selected version. You need not specially request a new branch, because
1849 that's the only way to add a new version at a point that is not the head
1852 After the branch is created, you ``stay'' on it. That means that
1853 subsequent check-ins create new versions on that branch. To leave the
1854 branch, you must explicitly select a different version with @kbd{C-u C-x
1855 C-q}. To transfer changes from one branch to another, use the merge
1856 command, described in the next section.
1859 @subsubsection Merging Branches
1861 @cindex merging changes
1862 When you have finished the changes on a certain branch, you will
1863 often want to incorporate them into the file's main line of development
1864 (the trunk). This is not a trivial operation, because development might
1865 also have proceeded on the trunk, so that you must @dfn{merge} the
1866 changes into a file that has already been changed otherwise. VC allows
1867 you to do this (and other things) with the @code{vc-merge} command.
1870 @item C-x v m (vc-merge)
1871 Merge changes into the work file.
1876 @kbd{C-x v m} (@code{vc-merge}) takes a set of changes and merges it
1877 into the current version of the work file. It firsts asks you in the
1878 minibuffer where the changes should come from. If you just type
1879 @key{RET}, Emacs merges any changes that were made on the same branch
1880 since you checked the file out (we call this @dfn{merging the news}).
1881 This is the common way to pick up recent changes from the repository,
1882 regardless of whether you have already changed the file yourself.
1884 You can also enter a branch number or a pair of version numbers in
1885 the minibuffer. Then @kbd{C-x v m} finds the changes from that
1886 branch, or the differences between the two versions you specified, and
1887 merges them into the current version of the current file.
1889 As an example, suppose that you have finished a certain feature on
1890 branch 1.3.1. In the meantime, development on the trunk has proceeded
1891 to version 1.5. To merge the changes from the branch to the trunk,
1892 first go to the head version of the trunk, by typing @kbd{C-u C-x C-q
1893 @key{RET}}. Version 1.5 is now current. If locking is used for the file,
1894 type @kbd{C-x C-q} to lock version 1.5 so that you can change it. Next,
1895 type @kbd{C-x v m 1.3.1 @key{RET}}. This takes the entire set of changes on
1896 branch 1.3.1 (relative to version 1.3, where the branch started, up to
1897 the last version on the branch) and merges it into the current version
1898 of the work file. You can now check in the changed file, thus creating
1899 version 1.6 containing the changes from the branch.
1901 It is possible to do further editing after merging the branch, before
1902 the next check-in. But it is usually wiser to check in the merged
1903 version, then lock it and make the further changes. This will keep
1904 a better record of the history of changes.
1907 @cindex resolving conflicts
1908 When you merge changes into a file that has itself been modified, the
1909 changes might overlap. We call this situation a @dfn{conflict}, and
1910 reconciling the conflicting changes is called @dfn{resolving a
1913 Whenever conflicts occur during merging, VC detects them, tells you
1914 about them in the echo area, and asks whether you want help in merging.
1915 If you say yes, it starts an Ediff session (@pxref{Top,
1916 Ediff, Ediff, ediff, The Ediff Manual}).
1918 If you say no, the conflicting changes are both inserted into the
1919 file, surrounded by @dfn{conflict markers}. The example below shows how
1920 a conflict region looks; the file is called @samp{name} and the current
1921 master file version with user B's changes in it is 1.11.
1923 @c @w here is so CVS won't think this is a conflict.
1927 @var{User A's version}
1929 @var{User B's version}
1934 @cindex vc-resolve-conflicts
1935 Then you can resolve the conflicts by editing the file manually. Or
1936 you can type @code{M-x vc-resolve-conflicts} after visiting the file.
1937 This starts an Ediff session, as described above. Don't forget to
1938 check in the merged version afterwards.
1940 @node Multi-User Branching
1941 @subsubsection Multi-User Branching
1943 It is often useful for multiple developers to work simultaneously on
1944 different branches of a file. CVS allows this by default; for RCS, it
1945 is possible if you create multiple source directories. Each source
1946 directory should have a link named @file{RCS} which points to a common
1947 directory of RCS master files. Then each source directory can have its
1948 own choice of selected versions, but all share the same common RCS
1951 This technique works reliably and automatically, provided that the
1952 source files contain RCS version headers (@pxref{Version Headers}). The
1953 headers enable Emacs to be sure, at all times, which version number is
1954 present in the work file.
1956 If the files do not have version headers, you must instead tell Emacs
1957 explicitly in each session which branch you are working on. To do this,
1958 first find the file, then type @kbd{C-u C-x C-q} and specify the correct
1959 branch number. This ensures that Emacs knows which branch it is using
1960 during this particular editing session.
1962 @node Remote Repositories
1963 @subsection Remote Repositories
1964 @cindex remote repositories (CVS)
1966 A common way of using CVS is to set up a central CVS repository on
1967 some Internet host, then have each developer check out a personal
1968 working copy of the files on his local machine. Committing changes to
1969 the repository, and picking up changes from other users into one's own
1970 working area, then works by direct interactions with the CVS server.
1972 One difficulty is that access to the CVS server is often slow, and
1973 that developers might need to work off-line as well. VC is designed
1974 to reduce the amount of network interaction necessary.
1977 * Version Backups:: Keeping local copies of repository versions.
1978 * Local Version Control:: Using another version system for local editing.
1981 @node Version Backups
1982 @subsubsection Version Backups
1983 @cindex version backups
1985 @cindex automatic version backups
1986 When VC sees that the CVS repository for a file is on a remote
1987 machine, it automatically makes local backups of unmodified versions
1988 of the file---@dfn{automatic version backups}. This means that you
1989 can compare the file to the repository version (@kbd{C-x v =}), or
1990 revert to that version (@kbd{C-x v u}), without any network
1993 The local copy of the unmodified file is called a @dfn{version
1994 backup} to indicate that it corresponds exactly to a version that is
1995 stored in the repository. Note that version backups are not the same
1996 as ordinary Emacs backup files (@pxref{Backup}). But they follow a
1997 similar naming convention.
1999 For a file that comes from a remote CVS repository, VC makes a
2000 version backup whenever you save the first changes to the file, and
2001 removes it after you have committed your modified version to the
2002 repository. You can disable the making of automatic version backups by
2003 setting @code{vc-cvs-stay-local} to @code{nil} (@pxref{CVS Options}).
2005 @cindex manual version backups
2006 The name of the automatic version backup for version @var{version}
2007 of file @var{file} is @code{@var{file}.~@var{version}.~}. This is
2008 almost the same as the name used by @kbd{C-x v ~} (@pxref{Old
2009 Versions}), the only difference being the additional dot (@samp{.})
2010 after the version number. This similarity is intentional, because
2011 both kinds of files store the same kind of information. The file made
2012 by @kbd{C-x v ~} acts as a @dfn{manual version backup}.
2014 All the VC commands that operate on old versions of a file can use
2015 both kinds of version backups. For instance, @kbd{C-x v ~} uses
2016 either an automatic or a manual version backup, if possible, to get
2017 the contents of the version you request. Likewise, @kbd{C-x v =} and
2018 @kbd{C-x v u} use either an automatic or a manual version backup, if
2019 one of them exists, to get the contents of a version to compare or
2020 revert to. If you changed a file outside of Emacs, so that no
2021 automatic version backup was created for the previous text, you can
2022 create a manual backup of that version using @kbd{C-x v ~}, and thus
2023 obtain the benefit of the local copy for Emacs commands.
2025 The only difference in Emacs's handling of manual and automatic
2026 version backups, once they exist, is that Emacs deletes automatic
2027 version backups when you commit to the repository. By contrast,
2028 manual version backups remain until you delete them.
2030 @node Local Version Control
2031 @subsubsection Local Version Control
2032 @cindex local version control
2033 @cindex local back end (version control)
2035 When you make many changes to a file that comes from a remote
2036 repository, it can be convenient to have version control on your local
2037 machine as well. You can then record intermediate versions, revert to
2038 a previous state, etc., before you actually commit your changes to the
2041 VC lets you do this by putting a file under a second, local version
2042 control system, so that the file is effectively registered in two
2043 systems at the same time. For the description here, we will assume
2044 that the remote system is CVS, and you use RCS locally, although the
2045 mechanism works with any combination of version control systems
2048 To make it work with other back ends, you must make sure that the
2049 ``more local'' back end comes before the ``more remote'' back end in
2050 the setting of @code{vc-handled-backends} (@pxref{Customizing VC}). By
2051 default, this variable is set up so that you can use remote CVS and
2052 local RCS as described here.
2054 To start using local RCS for a file that comes from a remote CVS
2055 server, you must @emph{register the file in RCS}, by typing @kbd{C-u
2056 C-x v v rcs @key{RET}}. (In other words, use @code{vc-next-action} with a
2057 prefix argument, and specify RCS as the back end.)
2059 You can do this at any time; it does not matter whether you have
2060 already modified the file with respect to the version in the CVS
2061 repository. If possible, VC tries to make the RCS master start with
2062 the unmodified repository version, then checks in any local changes
2063 as a new version. This works if you have not made any changes yet, or
2064 if the unmodified repository version exists locally as a version
2065 backup (@pxref{Version Backups}). If the unmodified version is not
2066 available locally, the RCS master starts with the modified version;
2067 the only drawback to this is that you cannot compare your changes
2068 locally to what is stored in the repository.
2070 The version number of the RCS master is derived from the current CVS
2071 version, starting a branch from it. For example, if the current CVS
2072 version is 1.23, the local RCS branch will be 1.23.1. Version 1.23 in
2073 the RCS master will be identical to version 1.23 under CVS; your first
2074 changes are checked in as 1.23.1.1. (If the unmodified file is not
2075 available locally, VC will check in the modified file twice, both as
2076 1.23 and 1.23.1.1, to make the revision numbers consistent.)
2078 If you do not use locking under CVS (the default), locking is also
2079 disabled for RCS, so that editing under RCS works exactly as under
2082 When you are done with local editing, you can commit the final version
2083 back to the CVS repository by typing @kbd{C-u C-x v v cvs @key{RET}}.
2084 This initializes the log entry buffer (@pxref{Log Buffer}) to contain
2085 all the log entries you have recorded in the RCS master; you can edit
2086 them as you wish, and then commit in CVS by typing @kbd{C-c C-c}. If
2087 the commit is successful, VC removes the RCS master, so that the file
2088 is once again registered under CVS only. (The RCS master is not
2089 actually deleted, just renamed by appending @samp{~} to the name, so
2090 that you can refer to it later if you wish.)
2092 While using local RCS, you can pick up recent changes from the CVS
2093 repository into your local file, or commit some of your changes back
2094 to CVS, without terminating local RCS version control. To do this,
2095 switch to the CVS back end temporarily, with the @kbd{C-x v b} command:
2099 Switch to another back end that the current file is registered
2100 under (@code{vc-switch-backend}).
2102 @item C-u C-x v b @var{backend} @key{RET}
2103 Switch to @var{backend} for the current file.
2107 @findex vc-switch-backend
2108 @kbd{C-x v b} does not change the buffer contents, or any files; it
2109 only changes VC's perspective on how to handle the file. Any
2110 subsequent VC commands for that file will operate on the back end that
2111 is currently selected.
2113 If the current file is registered in more than one back end, typing
2114 @kbd{C-x v b} ``cycles'' through all of these back ends. With a
2115 prefix argument, it asks for the back end to use in the minibuffer.
2117 Thus, if you are using local RCS, and you want to pick up some recent
2118 changes in the file from remote CVS, first visit the file, then type
2119 @kbd{C-x v b} to switch to CVS, and finally use @kbd{C-x v m
2120 @key{RET}} to merge the news (@pxref{Merging}). You can then switch
2121 back to RCS by typing @kbd{C-x v b} again, and continue to edit
2124 But if you do this, the revision numbers in the RCS master no longer
2125 correspond to those of CVS. Technically, this is not a problem, but
2126 it can become difficult to keep track of what is in the CVS repository
2127 and what is not. So we suggest that you return from time to time to
2128 CVS-only operation, using @kbd{C-u C-x v v cvs @key{RET}}.
2131 @subsection Snapshots
2132 @cindex snapshots and version control
2134 A @dfn{snapshot} is a named set of file versions (one for each
2135 registered file) that you can treat as a unit. One important kind of
2136 snapshot is a @dfn{release}, a (theoretically) stable version of the
2137 system that is ready for distribution to users.
2140 * Making Snapshots:: The snapshot facilities.
2141 * Snapshot Caveats:: Things to be careful of when using snapshots.
2144 @node Making Snapshots
2145 @subsubsection Making and Using Snapshots
2147 There are two basic commands for snapshots; one makes a
2148 snapshot with a given name, the other retrieves a named snapshot.
2152 @findex vc-create-snapshot
2153 @item C-x v s @var{name} @key{RET}
2154 Define the last saved versions of every registered file in or under the
2155 current directory as a snapshot named @var{name}
2156 (@code{vc-create-snapshot}).
2159 @findex vc-retrieve-snapshot
2160 @item C-x v r @var{name} @key{RET}
2161 For all registered files at or below the current directory level, select
2162 whatever versions correspond to the snapshot @var{name}
2163 (@code{vc-retrieve-snapshot}).
2165 This command reports an error if any files are locked at or below the
2166 current directory, without changing anything; this is to avoid
2167 overwriting work in progress.
2170 A snapshot uses a very small amount of resources---just enough to record
2171 the list of file names and which version belongs to the snapshot. Thus,
2172 you need not hesitate to create snapshots whenever they are useful.
2174 You can give a snapshot name as an argument to @kbd{C-x v =} or
2175 @kbd{C-x v ~} (@pxref{Old Versions}). Thus, you can use it to compare a
2176 snapshot against the current files, or two snapshots against each other,
2177 or a snapshot against a named version.
2179 @node Snapshot Caveats
2180 @subsubsection Snapshot Caveats
2182 @cindex named configurations (RCS)
2183 VC's snapshot facilities are modeled on RCS's named-configuration
2184 support. They use RCS's native facilities for this, so under VC
2185 snapshots made using RCS are visible even when you bypass VC.
2187 @c worded verbosely to avoid overfull hbox.
2188 For SCCS, VC implements snapshots itself. The files it uses contain
2189 name/file/version-number triples. These snapshots are visible only
2192 A snapshot is a set of checked-in versions. So make sure that all the
2193 files are checked in and not locked when you make a snapshot.
2195 File renaming and deletion can create some difficulties with snapshots.
2196 This is not a VC-specific problem, but a general design issue in version
2197 control systems that no one has solved very well yet.
2199 If you rename a registered file, you need to rename its master along
2200 with it (the command @code{vc-rename-file} does this automatically). If
2201 you are using SCCS, you must also update the records of the snapshot, to
2202 mention the file by its new name (@code{vc-rename-file} does this,
2203 too). An old snapshot that refers to a master file that no longer
2204 exists under the recorded name is invalid; VC can no longer retrieve
2205 it. It would be beyond the scope of this manual to explain enough about
2206 RCS and SCCS to explain how to update the snapshots by hand.
2208 Using @code{vc-rename-file} makes the snapshot remain valid for
2209 retrieval, but it does not solve all problems. For example, some of the
2210 files in your program probably refer to others by name. At the very
2211 least, the makefile probably mentions the file that you renamed. If you
2212 retrieve an old snapshot, the renamed file is retrieved under its new
2213 name, which is not the name that the makefile expects. So the program
2214 won't really work as retrieved.
2216 @node Miscellaneous VC
2217 @subsection Miscellaneous Commands and Features of VC
2219 This section explains the less-frequently-used features of VC.
2222 * Change Logs and VC:: Generating a change log file from log entries.
2223 * Renaming and VC:: A command to rename both the source and master
2225 * Version Headers:: Inserting version control headers into working files.
2228 @node Change Logs and VC
2229 @subsubsection Change Logs and VC
2231 If you use RCS or CVS for a program and also maintain a change log
2232 file for it (@pxref{Change Log}), you can generate change log entries
2233 automatically from the version control log entries:
2238 @findex vc-update-change-log
2239 Visit the current directory's change log file and, for registered files
2240 in that directory, create new entries for versions checked in since the
2241 most recent entry in the change log file.
2242 (@code{vc-update-change-log}).
2244 This command works with RCS or CVS only, not with SCCS.
2247 As above, but only find entries for the current buffer's file.
2250 As above, but find entries for all the currently visited files that are
2251 maintained with version control. This works only with RCS, and it puts
2252 all entries in the log for the default directory, which may not be
2256 For example, suppose the first line of @file{ChangeLog} is dated
2257 1999-04-10, and that the only check-in since then was by Nathaniel
2258 Bowditch to @file{rcs2log} on 1999-05-22 with log text @samp{Ignore log
2259 messages that start with `#'.}. Then @kbd{C-x v a} visits
2260 @file{ChangeLog} and inserts text like this:
2267 1999-05-22 Nathaniel Bowditch <nat@@apn.org>
2269 * rcs2log: Ignore log messages that start with `#'.
2277 You can then edit the new change log entry further as you wish.
2279 Some of the new change log entries may duplicate what's already in
2280 ChangeLog. You will have to remove these duplicates by hand.
2282 Normally, the log entry for file @file{foo} is displayed as @samp{*
2283 foo: @var{text of log entry}}. The @samp{:} after @file{foo} is omitted
2284 if the text of the log entry starts with @w{@samp{(@var{functionname}):
2285 }}. For example, if the log entry for @file{vc.el} is
2286 @samp{(vc-do-command): Check call-process status.}, then the text in
2287 @file{ChangeLog} looks like this:
2294 1999-05-06 Nathaniel Bowditch <nat@@apn.org>
2296 * vc.el (vc-do-command): Check call-process status.
2303 When @kbd{C-x v a} adds several change log entries at once, it groups
2304 related log entries together if they all are checked in by the same
2305 author at nearly the same time. If the log entries for several such
2306 files all have the same text, it coalesces them into a single entry.
2307 For example, suppose the most recent check-ins have the following log
2311 @bullet{} For @file{vc.texinfo}: @samp{Fix expansion typos.}
2312 @bullet{} For @file{vc.el}: @samp{Don't call expand-file-name.}
2313 @bullet{} For @file{vc-hooks.el}: @samp{Don't call expand-file-name.}
2317 They appear like this in @file{ChangeLog}:
2324 1999-04-01 Nathaniel Bowditch <nat@@apn.org>
2326 * vc.texinfo: Fix expansion typos.
2328 * vc.el, vc-hooks.el: Don't call expand-file-name.
2335 Normally, @kbd{C-x v a} separates log entries by a blank line, but you
2336 can mark several related log entries to be clumped together (without an
2337 intervening blank line) by starting the text of each related log entry
2338 with a label of the form @w{@samp{@{@var{clumpname}@} }}. The label
2339 itself is not copied to @file{ChangeLog}. For example, suppose the log
2343 @bullet{} For @file{vc.texinfo}: @samp{@{expand@} Fix expansion typos.}
2344 @bullet{} For @file{vc.el}: @samp{@{expand@} Don't call expand-file-name.}
2345 @bullet{} For @file{vc-hooks.el}: @samp{@{expand@} Don't call expand-file-name.}
2349 Then the text in @file{ChangeLog} looks like this:
2356 1999-04-01 Nathaniel Bowditch <nat@@apn.org>
2358 * vc.texinfo: Fix expansion typos.
2359 * vc.el, vc-hooks.el: Don't call expand-file-name.
2366 A log entry whose text begins with @samp{#} is not copied to
2367 @file{ChangeLog}. For example, if you merely fix some misspellings in
2368 comments, you can log the change with an entry beginning with @samp{#}
2369 to avoid putting such trivia into @file{ChangeLog}.
2371 @node Renaming and VC
2372 @subsubsection Renaming VC Work Files and Master Files
2374 @findex vc-rename-file
2375 When you rename a registered file, you must also rename its master
2376 file correspondingly to get proper results. Use @code{vc-rename-file}
2377 to rename the source file as you specify, and rename its master file
2378 accordingly. It also updates any snapshots (@pxref{Snapshots}) that
2379 mention the file, so that they use the new name; despite this, the
2380 snapshot thus modified may not completely work (@pxref{Snapshot
2383 You cannot use @code{vc-rename-file} on a file that is locked by
2386 @node Version Headers
2387 @subsubsection Inserting Version Control Headers
2389 Sometimes it is convenient to put version identification strings
2390 directly into working files. Certain special strings called
2391 @dfn{version headers} are replaced in each successive version by the
2392 number of that version.
2394 If you are using RCS, and version headers are present in your working
2395 files, Emacs can use them to determine the current version and the
2396 locking state of the files. This is more reliable than referring to the
2397 master files, which is done when there are no version headers. Note
2398 that in a multi-branch environment, version headers are necessary to
2399 make VC behave correctly (@pxref{Multi-User Branching}).
2401 Searching for version headers is controlled by the variable
2402 @code{vc-consult-headers}. If it is non-@code{nil} (the default),
2403 Emacs searches for headers to determine the version number you are
2404 editing. Setting it to @code{nil} disables this feature.
2407 @findex vc-insert-headers
2408 You can use the @kbd{C-x v h} command (@code{vc-insert-headers}) to
2409 insert a suitable header string.
2413 Insert headers in a file for use with your version-control system.
2416 @vindex vc-header-alist
2417 The default header string is @samp{@w{$}Id$} for RCS and
2418 @samp{@w{%}W%} for SCCS. You can specify other headers to insert by
2419 setting the variable @code{vc-header-alist}. Its value is a list of
2420 elements of the form @code{(@var{program} . @var{string})} where
2421 @var{program} is @code{RCS} or @code{SCCS} and @var{string} is the
2424 Instead of a single string, you can specify a list of strings; then
2425 each string in the list is inserted as a separate header on a line of
2428 It is often necessary to use ``superfluous'' backslashes when
2429 writing the strings that you put in this variable. For instance, you
2430 might write @code{"$Id\$"} rather than @code{"$Id@w{$}"}. The extra
2431 backslash prevents the string constant from being interpreted as a
2432 header, if the Emacs Lisp file containing it is maintained with
2435 @vindex vc-comment-alist
2436 Each header is inserted surrounded by tabs, inside comment delimiters,
2437 on a new line at point. Normally the ordinary comment
2438 start and comment end strings of the current mode are used, but for
2439 certain modes, there are special comment delimiters for this purpose;
2440 the variable @code{vc-comment-alist} specifies them. Each element of
2441 this list has the form @code{(@var{mode} @var{starter} @var{ender})}.
2443 @vindex vc-static-header-alist
2444 The variable @code{vc-static-header-alist} specifies further strings
2445 to add based on the name of the buffer. Its value should be a list of
2446 elements of the form @code{(@var{regexp} . @var{format})}. Whenever
2447 @var{regexp} matches the buffer name, @var{format} is inserted as part
2448 of the header. A header line is inserted for each element that matches
2449 the buffer name, and for each string specified by
2450 @code{vc-header-alist}. The header line is made by processing the
2451 string from @code{vc-header-alist} with the format taken from the
2452 element. The default value for @code{vc-static-header-alist} is as follows:
2457 "\n#ifndef lint\nstatic char vcid[] = \"\%s\";\n\
2458 #endif /* lint */\n"))
2463 It specifies insertion of text of this form:
2469 static char vcid[] = "@var{string}";
2475 Note that the text above starts with a blank line.
2477 If you use more than one version header in a file, put them close
2478 together in the file. The mechanism in @code{revert-buffer} that
2479 preserves markers may not handle markers positioned between two version
2482 @node Customizing VC
2483 @subsection Customizing VC
2485 @vindex vc-handled-backends
2486 The variable @code{vc-handled-backends} determines which version
2487 control systems VC should handle. The default value is @code{(RCS CVS
2488 SCCS)}, so it contains all three version systems that are currently
2489 supported. If you want VC to ignore one or more of these systems,
2490 exclude its name from the list.
2492 The order of systems in the list is significant: when you visit a file
2493 registered in more than one system (@pxref{Local Version Control}),
2494 VC uses the system that comes first in @code{vc-handled-backends} by
2495 default. The order is also significant when you register a file for
2496 the first time, @pxref{Registering} for details.
2499 * General VC Options:: Options that apply to multiple back ends.
2500 * RCS and SCCS:: Options for RCS and SCCS.
2501 * CVS Options:: Options for CVS.
2504 @node General VC Options
2505 @subsubsection General Options
2507 @vindex vc-make-backup-files
2508 Emacs normally does not save backup files for source files that are
2509 maintained with version control. If you want to make backup files even
2510 for files that use version control, set the variable
2511 @code{vc-make-backup-files} to a non-@code{nil} value.
2513 @vindex vc-keep-workfiles
2514 Normally the work file exists all the time, whether it is locked or
2515 not. If you set @code{vc-keep-workfiles} to @code{nil}, then checking
2516 in a new version with @kbd{C-x C-q} deletes the work file; but any
2517 attempt to visit the file with Emacs creates it again. (With CVS, work
2518 files are always kept.)
2520 @vindex vc-follow-symlinks
2521 Editing a version-controlled file through a symbolic link can be
2522 dangerous. It bypasses the version control system---you can edit the
2523 file without locking it, and fail to check your changes in. Also,
2524 your changes might overwrite those of another user. To protect against
2525 this, VC checks each symbolic link that you visit, to see if it points
2526 to a file under version control.
2528 The variable @code{vc-follow-symlinks} controls what to do when a
2529 symbolic link points to a version-controlled file. If it is @code{nil},
2530 VC only displays a warning message. If it is @code{t}, VC automatically
2531 follows the link, and visits the real file instead, telling you about
2532 this in the echo area. If the value is @code{ask} (the default), VC
2533 asks you each time whether to follow the link.
2535 @vindex vc-suppress-confirm
2536 If @code{vc-suppress-confirm} is non-@code{nil}, then @kbd{C-x C-q}
2537 and @kbd{C-x v i} can save the current buffer without asking, and
2538 @kbd{C-x v u} also operates without asking for confirmation. (This
2539 variable does not affect @kbd{C-x v c}; that operation is so drastic
2540 that it should always ask for confirmation.)
2542 @vindex vc-command-messages
2543 VC mode does much of its work by running the shell commands for RCS,
2544 CVS and SCCS. If @code{vc-command-messages} is non-@code{nil}, VC
2545 displays messages to indicate which shell commands it runs, and
2546 additional messages when the commands finish.
2549 You can specify additional directories to search for version control
2550 programs by setting the variable @code{vc-path}. These directories
2551 are searched before the usual search path. It is rarely necessary to
2552 set this variable, because VC normally finds the proper files
2556 @subsubsection Options for RCS and SCCS
2558 @cindex non-strict locking (RCS)
2559 @cindex locking, non-strict (RCS)
2560 By default, RCS uses locking to coordinate the activities of several
2561 users, but there is a mode called @dfn{non-strict locking} in which
2562 you can check-in changes without locking the file first. Use
2563 @samp{rcs -U} to switch to non-strict locking for a particular file,
2564 see the @code{rcs} manual page for details.
2566 When deducing the version control state of an RCS file, VC first
2567 looks for an RCS version header string in the file (@pxref{Version
2568 Headers}). If there is no header string, VC normally looks at the
2569 file permissions of the work file; this is fast. But there might be
2570 situations when the file permissions cannot be trusted. In this case
2571 the master file has to be consulted, which is rather expensive. Also
2572 the master file can only tell you @emph{if} there's any lock on the
2573 file, but not whether your work file really contains that locked
2576 @vindex vc-consult-headers
2577 You can tell VC not to use version headers to determine the file
2578 status by setting @code{vc-consult-headers} to @code{nil}. VC then
2579 always uses the file permissions (if it is supposed to trust them), or
2580 else checks the master file.
2582 @vindex vc-mistrust-permissions
2583 You can specify the criterion for whether to trust the file
2584 permissions by setting the variable @code{vc-mistrust-permissions}.
2585 Its value can be @code{t} (always mistrust the file permissions and
2586 check the master file), @code{nil} (always trust the file
2587 permissions), or a function of one argument which makes the decision.
2588 The argument is the directory name of the @file{RCS} subdirectory. A
2589 non-@code{nil} value from the function says to mistrust the file
2590 permissions. If you find that the file permissions of work files are
2591 changed erroneously, set @code{vc-mistrust-permissions} to @code{t}.
2592 Then VC always checks the master file to determine the file's status.
2594 VC determines the version control state of files under SCCS much as
2595 with RCS. It does not consider SCCS version headers, though. Thus,
2596 the variable @code{vc-mistrust-permissions} affects SCCS use, but
2597 @code{vc-consult-headers} does not.
2600 @subsubsection Options specific for CVS
2602 @cindex locking (CVS)
2603 By default, CVS does not use locking to coordinate the activities of
2604 several users; anyone can change a work file at any time. However,
2605 there are ways to restrict this, resulting in behavior that resembles
2608 @cindex CVSREAD environment variable (CVS)
2609 For one thing, you can set the @env{CVSREAD} environment variable
2610 (the value you use makes no difference). If this variable is defined,
2611 CVS makes your work files read-only by default. In Emacs, you must
2612 type @kbd{C-x C-q} to make the file writable, so that editing works
2613 in fact similar as if locking was used. Note however, that no actual
2614 locking is performed, so several users can make their files writable
2615 at the same time. When setting @env{CVSREAD} for the first time, make
2616 sure to check out all your modules anew, so that the file protections
2619 @cindex cvs watch feature
2620 @cindex watching files (CVS)
2621 Another way to achieve something similar to locking is to use the
2622 @dfn{watch} feature of CVS. If a file is being watched, CVS makes it
2623 read-only by default, and you must also use @kbd{C-x C-q} in Emacs to
2624 make it writable. VC calls @code{cvs edit} to make the file writable,
2625 and CVS takes care to notify other developers of the fact that you
2626 intend to change the file. See the CVS documentation for details on
2627 using the watch feature.
2629 @vindex vc-cvs-stay-local
2630 @cindex remote repositories (CVS)
2631 When a file's repository is on a remote machine, VC tries to keep
2632 network interactions to a minimum. This is controlled by the variable
2633 @code{vc-cvs-stay-local}. If it is @code{t} (the default), then VC uses
2634 only the entry in the local CVS subdirectory to determine the file's
2635 state (and possibly information returned by previous CVS commands). One
2636 consequence of this is that when you have modified a file, and somebody
2637 else has already checked in other changes to the file, you are not
2638 notified of it until you actually try to commit. (But you can try to
2639 pick up any recent changes from the repository first, using @kbd{C-x v m
2640 @key{RET}}, @pxref{Merging}).
2642 When @code{vc-cvs-stay-local} is @code{t}, VC also makes local
2643 version backups, so that simple diff and revert operations are
2644 completely local (@pxref{Version Backups}).
2646 On the other hand, if you set @code{vc-cvs-stay-local} to @code{nil},
2647 then VC queries the remote repository @emph{before} it decides what to
2648 do in @code{vc-next-action} (@kbd{C-x v v}), just as it does for local
2649 repositories. It also does not make any version backups.
2651 You can also set @code{vc-cvs-stay-local} to a regular expression
2652 that is matched against the repository host name; VC then stays local
2653 only for repositories from hosts that match the pattern.
2656 @section File Directories
2658 @cindex file directory
2659 @cindex directory listing
2660 The file system groups files into @dfn{directories}. A @dfn{directory
2661 listing} is a list of all the files in a directory. Emacs provides
2662 commands to create and delete directories, and to make directory
2663 listings in brief format (file names only) and verbose format (sizes,
2664 dates, and authors included). There is also a directory browser called
2665 Dired; see @ref{Dired}.
2668 @item C-x C-d @var{dir-or-pattern} @key{RET}
2669 Display a brief directory listing (@code{list-directory}).
2670 @item C-u C-x C-d @var{dir-or-pattern} @key{RET}
2671 Display a verbose directory listing.
2672 @item M-x make-directory @key{RET} @var{dirname} @key{RET}
2673 Create a new directory named @var{dirname}.
2674 @item M-x delete-directory @key{RET} @var{dirname} @key{RET}
2675 Delete the directory named @var{dirname}. It must be empty,
2676 or you get an error.
2679 @findex list-directory
2681 The command to display a directory listing is @kbd{C-x C-d}
2682 (@code{list-directory}). It reads using the minibuffer a file name
2683 which is either a directory to be listed or a wildcard-containing
2684 pattern for the files to be listed. For example,
2687 C-x C-d /u2/emacs/etc @key{RET}
2691 lists all the files in directory @file{/u2/emacs/etc}. Here is an
2692 example of specifying a file name pattern:
2695 C-x C-d /u2/emacs/src/*.c @key{RET}
2698 Normally, @kbd{C-x C-d} displays a brief directory listing containing
2699 just file names. A numeric argument (regardless of value) tells it to
2700 make a verbose listing including sizes, dates, and owners (like
2703 @vindex list-directory-brief-switches
2704 @vindex list-directory-verbose-switches
2705 The text of a directory listing is obtained by running @code{ls} in an
2706 inferior process. Two Emacs variables control the switches passed to
2707 @code{ls}: @code{list-directory-brief-switches} is a string giving the
2708 switches to use in brief listings (@code{"-CF"} by default), and
2709 @code{list-directory-verbose-switches} is a string giving the switches to
2710 use in a verbose listing (@code{"-l"} by default).
2712 @node Comparing Files
2713 @section Comparing Files
2714 @cindex comparing files
2717 @vindex diff-switches
2718 The command @kbd{M-x diff} compares two files, displaying the
2719 differences in an Emacs buffer named @samp{*diff*}. It works by
2720 running the @code{diff} program, using options taken from the variable
2721 @code{diff-switches}. The value of @code{diff-switches} should be a
2722 string; the default is @code{"-c"} to specify a context diff.
2724 The buffer @samp{*diff*} has Compilation mode as its major mode, so
2725 you can use @kbd{C-x `} to visit successive changed locations in the two
2726 source files. You can also move to a particular hunk of changes and
2727 type @key{RET} or @kbd{C-c C-c}, or click @kbd{Mouse-2} on it, to move
2728 to the corresponding source location. You can also use the other
2729 special commands of Compilation mode: @key{SPC} and @key{DEL} for
2730 scrolling, and @kbd{M-p} and @kbd{M-n} for cursor motion.
2734 The command @kbd{M-x diff-backup} compares a specified file with its most
2735 recent backup. If you specify the name of a backup file,
2736 @code{diff-backup} compares it with the source file that it is a backup
2739 @findex compare-windows
2740 The command @kbd{M-x compare-windows} compares the text in the current
2741 window with that in the next window. Comparison starts at point in each
2742 window, and each starting position is pushed on the mark ring in its
2743 respective buffer. Then point moves forward in each window, a character
2744 at a time, until a mismatch between the two windows is reached. Then
2745 the command is finished. For more information about windows in Emacs,
2748 @vindex compare-ignore-case
2749 With a numeric argument, @code{compare-windows} ignores changes in
2750 whitespace. If the variable @code{compare-ignore-case} is
2751 non-@code{nil}, it ignores differences in case as well.
2757 Differences between versions of files are often distributed as
2758 @dfn{patches}, which are the output from @command{diff} or a version
2759 control system that uses @command{diff}. @kbd{M-x diff-mode} turns on
2760 Diff mode, a major mode for viewing and editing patches, either as
2761 ``unified diffs'' or ``context diffs.''
2765 @cindex failed merges
2766 @cindex merges, failed
2767 @cindex comparing 3 files (@code{diff3})
2768 You can use @kbd{M-x smerge-mode} to turn on Smerge mode, a minor
2769 mode for editing output from the @command{diff3} program. This is
2770 typically the result of a failed merge from a version control system
2771 ``update'' outside VC, due to conflicting changes to a file. Smerge
2772 mode provides commands to resolve conflicts by selecting specific
2775 See also @ref{Emerge}, and @ref{Top,,, ediff, The Ediff Manual}, for
2776 convenient facilities for merging two similar files.
2779 @section Miscellaneous File Operations
2781 Emacs has commands for performing many other operations on files.
2782 All operate on one file; they do not accept wildcard file names.
2788 @kbd{M-x view-file} allows you to scan or read a file by sequential
2789 screenfuls. It reads a file name argument using the minibuffer. After
2790 reading the file into an Emacs buffer, @code{view-file} displays the
2791 beginning. You can then type @key{SPC} to scroll forward one windowful,
2792 or @key{DEL} to scroll backward. Various other commands are provided
2793 for moving around in the file, but none for changing it; type @kbd{?}
2794 while viewing for a list of them. They are mostly the same as normal
2795 Emacs cursor motion commands. To exit from viewing, type @kbd{q}.
2796 The commands for viewing are defined by a special major mode called View
2799 A related command, @kbd{M-x view-buffer}, views a buffer already present
2800 in Emacs. @xref{Misc Buffer}.
2804 @kbd{M-x insert-file} (also @kbd{C-x i}) inserts a copy of the
2805 contents of the specified file into the current buffer at point,
2806 leaving point unchanged before the contents and the mark after them.
2808 @findex write-region
2809 @kbd{M-x write-region} is the inverse of @kbd{M-x insert-file}; it
2810 copies the contents of the region into the specified file. @kbd{M-x
2811 append-to-file} adds the text of the region to the end of the specified
2812 file. @xref{Accumulating Text}.
2815 @cindex deletion (of files)
2816 @kbd{M-x delete-file} deletes the specified file, like the @code{rm}
2817 command in the shell. If you are deleting many files in one directory, it
2818 may be more convenient to use Dired (@pxref{Dired}).
2821 @kbd{M-x rename-file} reads two file names @var{old} and @var{new} using
2822 the minibuffer, then renames file @var{old} as @var{new}. If the file name
2823 @var{new} already exists, you must confirm with @kbd{yes} or renaming is not
2824 done; this is because renaming causes the old meaning of the name @var{new}
2825 to be lost. If @var{old} and @var{new} are on different file systems, the
2826 file @var{old} is copied and deleted.
2828 @findex add-name-to-file
2829 @cindex hard links (creation)
2830 The similar command @kbd{M-x add-name-to-file} is used to add an
2831 additional name to an existing file without removing its old name.
2832 The new name is created as a ``hard link'' to the existing file.
2833 The new name must belong on the same file system that the file is on.
2834 On Windows, this command works only if the file resides in an NTFS
2835 file system. On MS-DOS, it works by copying the file.
2838 @cindex copying files
2839 @kbd{M-x copy-file} reads the file @var{old} and writes a new file named
2840 @var{new} with the same contents. Confirmation is required if a file named
2841 @var{new} already exists, because copying has the consequence of overwriting
2842 the old contents of the file @var{new}.
2844 @findex make-symbolic-link
2845 @kbd{M-x make-symbolic-link} reads two file names @var{target} and
2846 @var{linkname}, then creates a symbolic link named @var{linkname}, which
2847 points at @var{target}. The effect is that future attempts to open file
2848 @var{linkname} will refer to whatever file is named @var{target} at the
2849 time the opening is done, or will get an error if the name @var{target} is
2850 not in use at that time. This command does not expand the argument
2851 @var{target}, so that it allows you to specify a relative name
2852 as the target of the link.
2854 Confirmation is required when creating the link if @var{linkname} is
2855 in use. Note that not all systems support symbolic links; on systems
2856 that don't support them, this command is not defined.
2858 @node Compressed Files
2859 @section Accessing Compressed Files
2861 @cindex uncompression
2862 @cindex Auto Compression mode
2863 @cindex mode, Auto Compression
2866 @findex auto-compression-mode
2867 @vindex auto-compression-mode
2868 Emacs comes with a library that can automatically uncompress
2869 compressed files when you visit them, and automatically recompress them
2870 if you alter them and save them. To enable this feature, type the
2871 command @kbd{M-x auto-compression-mode}. You can enable it permanently
2872 by customizing the option @code{auto-compression-mode}.
2874 When automatic compression (which implies automatic uncompression as
2875 well) is enabled, Emacs recognizes compressed files by their file names.
2876 File names ending in @samp{.gz} indicate a file compressed with
2877 @code{gzip}. Other endings indicate other compression programs.
2879 Automatic uncompression and compression apply to all the operations in
2880 which Emacs uses the contents of a file. This includes visiting it,
2881 saving it, inserting its contents into a buffer, loading it, and byte
2885 @section File Archives
2888 @cindex file archives
2890 A file whose name ends in @samp{.tar} is normally an @dfn{archive}
2891 made by the @code{tar} program. Emacs views these files in a special
2892 mode called Tar mode which provides a Dired-like list of the contents
2893 (@pxref{Dired}). You can move around through the list just as you
2894 would in Dired, and visit the subfiles contained in the archive.
2895 However, not all Dired commands are available in Tar mode.
2897 If you enable Auto Compression mode (@pxref{Compressed Files}), then
2898 Tar mode is used also for compressed archives---files with extensions
2899 @samp{.tgz}, @code{.tar.Z} and @code{.tar.gz}.
2901 The keys @kbd{e}, @kbd{f} and @key{RET} all extract a component file
2902 into its own buffer. You can edit it there and when you save the buffer
2903 the edited version will replace the version in the Tar buffer. @kbd{v}
2904 extracts a file into a buffer in View mode. @kbd{o} extracts the file
2905 and displays it in another window, so you could edit the file and
2906 operate on the archive simultaneously. @kbd{d} marks a file for
2907 deletion when you later use @kbd{x}, and @kbd{u} unmarks a file, as in
2908 Dired. @kbd{C} copies a file from the archive to disk and @kbd{R}
2909 renames a file. @kbd{g} reverts the buffer from the archive on disk.
2911 The keys @kbd{M}, @kbd{G}, and @kbd{O} change the file's permission
2912 bits, group, and owner, respectively.
2914 If your display supports colors and the mouse, moving the mouse
2915 pointer across a file name highlights that file name, indicating that
2916 you can click on it. Clicking @kbd{Mouse-2} on the highlighted file
2917 name extracts the file into a buffer and displays that buffer.
2919 Saving the Tar buffer writes a new version of the archive to disk with
2920 the changes you made to the components.
2922 You don't need the @code{tar} program to use Tar mode---Emacs reads
2923 the archives directly. However, accessing compressed archives
2924 requires the appropriate uncompression program.
2926 @cindex Archive mode
2927 @cindex mode, archive
2938 @cindex Java class archives
2939 @cindex unzip archives
2940 A separate but similar Archive mode is used for archives produced by
2941 the programs @code{arc}, @code{jar}, @code{lzh}, @code{zip}, and
2942 @code{zoo}, which have extensions corresponding to the program names.
2944 The key bindings of Archive mode are similar to those in Tar mode,
2945 with the addition of the @kbd{m} key which marks a file for subsequent
2946 operations, and @kbd{M-@key{DEL}} which unmarks all the marked files.
2947 Also, the @kbd{a} key toggles the display of detailed file
2948 information, for those archive types where it won't fit in a single
2949 line. Operations such as renaming a subfile, or changing its mode or
2950 owner, are supported only for some of the archive formats.
2952 Unlike Tar mode, Archive mode runs the archiving program to unpack
2953 and repack archives. Details of the program names and their options
2954 can be set in the @samp{Archive} Customize group. However, you don't
2955 need these programs to look at the archive table of contents, only to
2956 extract or manipulate the subfiles in the archive.
2959 @section Remote Files
2962 In the following, file access via FTP will be discussed. In
2963 addition to that facility, it is also possible to access remote files
2964 through a shell connection. @xref{Top, The Tramp Manual,, tramp, The
2968 @cindex remote file access
2969 You can refer to files on other machines using a special file name syntax:
2973 /@var{host}:@var{filename}
2974 /@var{user}@@@var{host}:@var{filename}
2975 /@var{user}@@@var{host}#@var{port}:@var{filename}
2980 When you do this, Emacs uses the FTP program to read and write files on
2981 the specified host. It logs in through FTP using your user name or the
2982 name @var{user}. It may ask you for a password from time to time; this
2983 is used for logging in on @var{host}. The form using @var{port} allows
2984 you to access servers running on a non-default TCP port.
2986 For using Tramp, the file name syntax looks like this:
2990 /[@var{host}]@var{filename}
2991 /[@var{user}@@@var{host}]@var{filename}
2992 /[@var{method}/@var{user}@@@var{host}]@var{filename}
2997 Note that the square brackets are part of the file names.
2999 @cindex backups for remote files
3000 @vindex ange-ftp-make-backup-files
3001 If you want to disable backups for remote files, set the variable
3002 @code{ange-ftp-make-backup-files} to @code{nil}.
3004 By default, the auto-save files (@pxref{Auto Save Files}) for remote
3005 files are made in the temporary file directory on the local machine.
3006 This is achieved using the variable @code{auto-save-file-name-transforms}.
3009 @vindex ange-ftp-default-user
3010 @cindex user name for remote file access
3011 Normally, if you do not specify a user name in a remote file name,
3012 that means to use your own user name. But if you set the variable
3013 @code{ange-ftp-default-user} to a string, that string is used instead.
3014 (The Emacs package that implements FTP file access is called
3017 @cindex anonymous FTP
3018 @vindex ange-ftp-generate-anonymous-password
3019 To visit files accessible by anonymous FTP, you use special user
3020 names @samp{anonymous} or @samp{ftp}. Passwords for these user names
3021 are handled specially. The variable
3022 @code{ange-ftp-generate-anonymous-password} controls what happens: if
3023 the value of this variable is a string, then that string is used as
3024 the password; if non-@code{nil} (the default), then the value of
3025 @code{user-mail-address} is used; if @code{nil}, the user is prompted
3026 for a password as normal.
3028 @cindex firewall, and accessing remote files
3029 @cindex gateway, and remote file access with @code{ange-ftp}
3030 @vindex ange-ftp-smart-gateway
3031 @vindex ange-ftp-gateway-host
3032 Sometimes you may be unable to access files on a remote machine
3033 because a @dfn{firewall} in between blocks the connection for security
3034 reasons. If you can log in on a @dfn{gateway} machine from which the
3035 target files @emph{are} accessible, and whose FTP server supports
3036 gatewaying features, you can still use remote file names; all you have
3037 to do is specify the name of the gateway machine by setting the
3038 variable @code{ange-ftp-gateway-host}, and set
3039 @code{ange-ftp-smart-gateway} to @code{t}. Otherwise you may be able
3040 to make remote file names work, but the procedure is complex. You can
3041 read the instructions by typing @kbd{M-x finder-commentary @key{RET}
3042 ange-ftp @key{RET}}.
3044 @vindex file-name-handler-alist
3045 @cindex disabling remote files
3046 You can entirely turn off the FTP file name feature by removing the
3047 entries @code{ange-ftp-completion-hook-function} and
3048 @code{ange-ftp-hook-function} from the variable
3049 @code{file-name-handler-alist}. You can turn off the feature in
3050 individual cases by quoting the file name with @samp{/:} (@pxref{Quoted
3053 @node Quoted File Names
3054 @section Quoted File Names
3056 @cindex quoting file names
3057 You can @dfn{quote} an absolute file name to prevent special
3058 characters and syntax in it from having their special effects.
3059 The way to do this is to add @samp{/:} at the beginning.
3061 For example, you can quote a local file name which appears remote, to
3062 prevent it from being treated as a remote file name. Thus, if you have
3063 a directory named @file{/foo:} and a file named @file{bar} in it, you
3064 can refer to that file in Emacs as @samp{/:/foo:/bar}.
3066 @samp{/:} can also prevent @samp{~} from being treated as a special
3067 character for a user's home directory. For example, @file{/:/tmp/~hack}
3068 refers to a file whose name is @file{~hack} in directory @file{/tmp}.
3070 Quoting with @samp{/:} is also a way to enter in the minibuffer a
3071 file name that contains @samp{$}. In order for this to work, the
3072 @samp{/:} must be at the beginning of the minibuffer contents. (You
3073 can also double each @samp{$}; see @ref{File Names with $}.)
3075 You can also quote wildcard characters with @samp{/:}, for visiting.
3076 For example, @file{/:/tmp/foo*bar} visits the file
3077 @file{/tmp/foo*bar}.
3079 Another method of getting the same result is to enter
3080 @file{/tmp/foo[*]bar}, which is a wildcard specification that matches
3081 only @file{/tmp/foo*bar}. However, in many cases there is no need to
3082 quote the wildcard characters because even unquoted they give the
3083 right result. For example, if the only file name in @file{/tmp} that
3084 starts with @samp{foo} and ends with @samp{bar} is @file{foo*bar},
3085 then specifying @file{/tmp/foo*bar} will visit only
3086 @file{/tmp/foo*bar}.
3088 @node File Name Cache
3089 @section File Name Cache
3091 @cindex file name caching
3092 @cindex cache of file names
3095 @findex file-cache-minibuffer-complete
3096 You can use the @dfn{file name cache} to make it easy to locate a
3097 file by name, without having to remember exactly where it is located.
3098 When typing a file name in the minibuffer, @kbd{C-@key{tab}}
3099 (@code{file-cache-minibuffer-complete}) completes it using the file
3100 name cache. If you repeat @kbd{C-@key{tab}}, that cycles through the
3101 possible completions of what you had originally typed. Note that the
3102 @kbd{C-@key{tab}} character cannot be typed on most text-only
3105 The file name cache does not fill up automatically. Instead, you
3106 load file names into the cache using these commands:
3108 @findex file-cache-add-directory
3110 @item M-x file-cache-add-directory @key{RET} @var{directory} @key{RET}
3111 Add each file name in @var{directory} to the file name cache.
3112 @item M-x file-cache-add-directory-using-find @key{RET} @var{directory} @key{RET}
3113 Add each file name in @var{directory} and all of its nested
3114 subdirectories to the file name cache.
3115 @item M-x file-cache-add-directory-using-locate @key{RET} @var{directory} @key{RET}
3116 Add each file name in @var{directory} and all of its nested
3117 subdirectories to the file name cache, using @command{locate} to find
3119 @item M-x file-cache-add-directory-list @key{RET} @var{variable} @key{RET}
3120 Add each file name in each directory listed in @var{variable}
3121 to the file name cache. @var{variable} should be a Lisp variable
3122 such as @code{load-path} or @code{exec-path}, whose value is a list
3124 @item M-x file-cache-clear-cache @key{RET}
3125 Clear the cache; that is, remove all file names from it.
3128 @node File Conveniences
3129 @section Convenience Features for Finding Files
3131 @findex recentf-mode
3132 @vindex recentf-mode
3133 @findex recentf-save-list
3134 @findex recentf-edit-list
3135 If you enable Recentf mode, with @kbd{M-x recentf-mode}, the
3136 @samp{File} menu includes a submenu containing a list of recently
3137 opened files. @kbd{M-x recentf-save-list} saves the current
3138 @code{recent-file-list} to a file, and @kbd{M-x recentf-edit-list}
3141 @findex auto-image-file-mode
3142 @findex mode, auto-image-file
3143 @cindex images, visiting
3144 @cindex visiting image files
3145 @vindex image-file-name-regexps
3146 @vindex image-file-name-extensions
3147 When Auto-image-file minor mode is enabled, visiting an image file
3148 displays it as an image, not as text. Likewise, inserting an image
3149 file into a buffer inserts it as an image. This works only when Emacs
3150 can display the relevant image type. The variables
3151 @code{image-file-name-extensions} or @code{image-file-name-regexps}
3152 control which file names are recognized as containing images.
3154 The @kbd{M-x ffap} command generalizes @code{find-file} with more
3155 powerful heuristic defaults (@pxref{FFAP}), often based on the text at
3156 point. Partial Completion mode offers other features extending
3157 @code{find-file}, which can be used with @code{ffap}.
3158 @xref{Completion Options}.