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 @samp{$} in a file name is used to substitute environment variables.
107 For example, if you have used the shell command @command{export
108 FOO=rms/hacks} to set up an environment variable named @env{FOO}, then
109 you can use @file{/u/$FOO/test.c} or @file{/u/$@{FOO@}/test.c} as an
110 abbreviation for @file{/u/rms/hacks/test.c}. The environment variable
111 name consists of all the alphanumeric characters after the @samp{$};
112 alternatively, it may be enclosed in braces after the @samp{$}. Note
113 that shell commands to set environment variables affect Emacs only if
114 done before Emacs is started.
116 @cindex home directory shorthand
117 You can use the @file{~/} in a file name to mean your home directory,
118 or @file{~@var{user-id}/} to mean the home directory of a user whose
119 login name is @code{user-id}. (On DOS and Windows systems, where a user
120 doesn't have a home directory, Emacs substitutes @file{~/} with the
121 value of the environment variable @code{HOME}; see @ref{General
124 To access a file with @samp{$} in its name, type @samp{$$}. This pair
125 is converted to a single @samp{$} at the same time as variable
126 substitution is performed for a single @samp{$}. Alternatively, quote the
127 whole file name with @samp{/:} (@pxref{Quoted File Names}). File names
128 which begin with a literal @samp{~} should also be quoted with @samp{/:}.
130 @findex substitute-in-file-name
131 The Lisp function that performs the substitution is called
132 @code{substitute-in-file-name}. The substitution is performed only on
133 file names read as such using the minibuffer.
135 You can include non-ASCII characters in file names if you set the
136 variable @code{file-name-coding-system} to a non-@code{nil} value.
137 @xref{Specify Coding}.
140 @section Visiting Files
141 @cindex visiting files
145 Visit a file (@code{find-file}).
147 Visit a file for viewing, without allowing changes to it
148 (@code{find-file-read-only}).
150 Visit a different file instead of the one visited last
151 (@code{find-alternate-file}).
153 Visit a file, in another window (@code{find-file-other-window}). Don't
154 alter what is displayed in the selected window.
156 Visit a file, in a new frame (@code{find-file-other-frame}). Don't
157 alter what is displayed in the selected frame.
158 @item M-x find-file-literally
159 Visit a file with no conversion of the contents.
162 @cindex files, visiting and saving
164 @dfn{Visiting} a file means copying its contents into an Emacs
165 buffer so you can edit them. Emacs makes a new buffer for each file
166 that you visit. We often say that this buffer ``is visiting'' that
167 file, or that the buffer's ``visited file'' is that file. Emacs
168 constructs the buffer name from the file name by throwing away the
169 directory, keeping just the name proper. For example, a file named
170 @file{/usr/rms/emacs.tex} would get a buffer named @samp{emacs.tex}.
171 If there is already a buffer with that name, Emacs constructs a unique
172 name---the normal method is to append @samp{<2>}, @samp{<3>}, and so
173 on, but you can select other methods (@pxref{Uniquify}).
175 Each window's mode line shows the name of the buffer that is being displayed
176 in that window, so you can always tell what buffer you are editing.
178 The changes you make with editing commands are made in the Emacs
179 buffer. They do not take effect in the file that you visited, or any
180 place permanent, until you @dfn{save} the buffer. Saving the buffer
181 means that Emacs writes the current contents of the buffer into its
182 visited file. @xref{Saving}.
184 @cindex modified (buffer)
185 If a buffer contains changes that have not been saved, we say the
186 buffer is @dfn{modified}. This is important because it implies that
187 some changes will be lost if the buffer is not saved. The mode line
188 displays two stars near the left margin to indicate that the buffer is
193 To visit a file, use the command @kbd{C-x C-f} (@code{find-file}). Follow
194 the command with the name of the file you wish to visit, terminated by a
197 The file name is read using the minibuffer (@pxref{Minibuffer}), with
198 defaulting and completion in the standard manner (@pxref{File Names}).
199 While in the minibuffer, you can abort @kbd{C-x C-f} by typing
200 @kbd{C-g}. File-name completion ignores certain filenames; for more
201 about this, see @ref{Completion Options}.
203 @cindex file selection dialog
204 When Emacs is built with a suitable GUI toolkit, it pops up the
205 standard File Selection dialog of that toolkit instead of prompting for
206 the file name in the minibuffer. On Unix and GNU/Linux platforms, Emacs
207 does that when built with LessTif and Motif toolkits; on MS-Windows, the
208 GUI version does that by default.
210 Your confirmation that @kbd{C-x C-f} has completed successfully is the
211 appearance of new text on the screen and a new buffer name in the mode
212 line. If the specified file does not exist and could not be created, or
213 cannot be read, then you get an error, with an error message displayed
216 If you visit a file that is already in Emacs, @kbd{C-x C-f} does not make
217 another copy. It selects the existing buffer containing that file.
218 However, before doing so, it checks that the file itself has not changed
219 since you visited or saved it last. If the file has changed, a warning
220 message is shown. @xref{Interlocking,,Simultaneous Editing}.
222 @cindex maximum buffer size exceeded, error message
223 Since Emacs reads the visited file in its entirety, files whose size
224 is larger than the maximum Emacs buffer size (@pxref{Buffers}) cannot be
225 visited; if you try, Emacs will display an error message saying that the
226 maximum buffer size has been exceeded.
228 @cindex creating files
229 What if you want to create a new file? Just visit it. Emacs displays
230 @samp{(New file)} in the echo area, but in other respects behaves as if
231 you had visited an existing empty file. If you make any changes and
232 save them, the file is created.
234 Emacs recognizes from the contents of a file which convention it uses
235 to separate lines---newline (used on GNU/Linux and on Unix),
236 carriage-return linefeed (used on Microsoft systems), or just
237 carriage-return (used on the Macintosh)---and automatically converts the
238 contents to the normal Emacs convention, which is that the newline
239 character separates lines. This is a part of the general feature of
240 coding system conversion (@pxref{Coding Systems}), and makes it possible
241 to edit files imported from different operating systems with
242 equal convenience. If you change the text and save the file, Emacs
243 performs the inverse conversion, changing newlines back into
244 carriage-return linefeed or just carriage-return if appropriate.
246 @vindex find-file-run-dired
247 If the file you specify is actually a directory, @kbd{C-x C-f} invokes
248 Dired, the Emacs directory browser, so that you can ``edit'' the contents
249 of the directory (@pxref{Dired}). Dired is a convenient way to delete,
250 look at, or operate on the files in the directory. However, if the
251 variable @code{find-file-run-dired} is @code{nil}, then it is an error
252 to try to visit a directory.
254 Files which are actually collections of other files, or @dfn{file
255 archives}, are visited in special modes which invoke a Dired-like
256 environment to allow operations on archive members. @xref{File
257 Archives}, for more about these features.
259 @cindex wildcard characters in file names
260 @vindex find-file-wildcards
261 If the file name you specify contains shell-style wildcard characters,
262 Emacs visits all the files that match it. Wildcards include @samp{?},
263 @samp{*}, and @samp{[@dots{}]} sequences. @xref{Quoted File Names}, for
264 information on how to visit a file whose name actually contains wildcard
265 characters. You can disable the wildcard feature by customizing
266 @code{find-file-wildcards}.
268 If you visit a file that the operating system won't let you modify,
269 Emacs makes the buffer read-only, so that you won't go ahead and make
270 changes that you'll have trouble saving afterward. You can make the
271 buffer writable with @kbd{C-x C-q} (@code{vc-toggle-read-only}).
275 @findex find-file-read-only
276 Occasionally you might want to visit a file as read-only in order to
277 protect yourself from entering changes accidentally; do so by visiting
278 the file with the command @kbd{C-x C-r} (@code{find-file-read-only}).
281 @findex find-alternate-file
282 If you visit a nonexistent file unintentionally (because you typed the
283 wrong file name), use the @kbd{C-x C-v} command
284 (@code{find-alternate-file}) to visit the file you really wanted.
285 @kbd{C-x C-v} is similar to @kbd{C-x C-f}, but it kills the current
286 buffer (after first offering to save it if it is modified). When
287 @kbd{C-x C-v} reads the file name to visit, it inserts the entire
288 default file name in the buffer, with point just after the directory
289 part; this is convenient if you made a slight error in typing the name.
291 If you find a file which exists but cannot be read, @kbd{C-x C-f}
295 @findex find-file-other-window
296 @kbd{C-x 4 f} (@code{find-file-other-window}) is like @kbd{C-x C-f}
297 except that the buffer containing the specified file is selected in another
298 window. The window that was selected before @kbd{C-x 4 f} continues to
299 show the same buffer it was already showing. If this command is used when
300 only one window is being displayed, that window is split in two, with one
301 window showing the same buffer as before, and the other one showing the
302 newly requested file. @xref{Windows}.
305 @findex find-file-other-frame
306 @kbd{C-x 5 f} (@code{find-file-other-frame}) is similar, but opens a
307 new frame, or makes visible any existing frame showing the file you
308 seek. This feature is available only when you are using a window
309 system. @xref{Frames}.
311 @findex find-file-literally
312 If you wish to edit a file as a sequence of ASCII characters with no special
313 encoding or conversion, use the @kbd{M-x find-file-literally} command.
314 It visits a file, like @kbd{C-x C-f}, but does not do format conversion
315 (@pxref{Formatted Text}), character code conversion (@pxref{Coding
316 Systems}), or automatic uncompression (@pxref{Compressed Files}), and
317 does not add a final newline because of @code{require-final-newline}.
318 If you already have visited the same file in the usual (non-literal)
319 manner, this command asks you whether to visit it literally instead.
321 @vindex find-file-hooks
322 @vindex find-file-not-found-hooks
323 Two special hook variables allow extensions to modify the operation of
324 visiting files. Visiting a file that does not exist runs the functions
325 in the list @code{find-file-not-found-hooks}; this variable holds a list
326 of functions, and the functions are called one by one (with no
327 arguments) until one of them returns non-@code{nil}. This is not a
328 normal hook, and the name ends in @samp{-hooks} rather than @samp{-hook}
329 to indicate that fact.
331 Successful visiting of any file, whether existing or not, calls the
332 functions in the list @code{find-file-hooks}, with no arguments.
333 This variable is really a normal hook, but it has an abnormal name for
334 historical compatibility. In the case of a nonexistent file, the
335 @code{find-file-not-found-hooks} are run first. @xref{Hooks}.
337 There are several ways to specify automatically the major mode for
338 editing the file (@pxref{Choosing Modes}), and to specify local
339 variables defined for that file (@pxref{File Variables}).
342 @section Saving Files
344 @dfn{Saving} a buffer in Emacs means writing its contents back into the file
345 that was visited in the buffer.
349 Save the current buffer in its visited file on disk (@code{save-buffer}).
351 Save any or all buffers in their visited files (@code{save-some-buffers}).
353 Forget that the current buffer has been changed (@code{not-modified}).
354 With prefix argument (@kbd{C-u}), mark the current buffer as changed.
356 Save the current buffer as a specified file name (@code{write-file}).
357 @item M-x set-visited-file-name
358 Change the file name under which the current buffer will be saved.
363 When you wish to save the file and make your changes permanent, type
364 @kbd{C-x C-s} (@code{save-buffer}). After saving is finished, @kbd{C-x C-s}
365 displays a message like this:
368 Wrote /u/rms/gnu/gnu.tasks
372 If the selected buffer is not modified (no changes have been made in it
373 since the buffer was created or last saved), saving is not really done,
374 because it would have no effect. Instead, @kbd{C-x C-s} displays a message
375 like this in the echo area:
378 (No changes need to be saved)
382 @findex save-some-buffers
383 The command @kbd{C-x s} (@code{save-some-buffers}) offers to save any
384 or all modified buffers. It asks you what to do with each buffer. The
385 possible responses are analogous to those of @code{query-replace}:
389 Save this buffer and ask about the rest of the buffers.
391 Don't save this buffer, but ask about the rest of the buffers.
393 Save this buffer and all the rest with no more questions.
394 @c following generates acceptable underfull hbox
396 Terminate @code{save-some-buffers} without any more saving.
398 Save this buffer, then exit @code{save-some-buffers} without even asking
401 View the buffer that you are currently being asked about. When you exit
402 View mode, you get back to @code{save-some-buffers}, which asks the
405 Display a help message about these options.
408 @kbd{C-x C-c}, the key sequence to exit Emacs, invokes
409 @code{save-some-buffers} and therefore asks the same questions.
413 If you have changed a buffer but you do not want to save the changes,
414 you should take some action to prevent it. Otherwise, each time you use
415 @kbd{C-x s} or @kbd{C-x C-c}, you are liable to save this buffer by
416 mistake. One thing you can do is type @kbd{M-~} (@code{not-modified}),
417 which clears out the indication that the buffer is modified. If you do
418 this, none of the save commands will believe that the buffer needs to be
419 saved. (@samp{~} is often used as a mathematical symbol for `not'; thus
420 @kbd{M-~} is `not', metafied.) You could also use
421 @code{set-visited-file-name} (see below) to mark the buffer as visiting
422 a different file name, one which is not in use for anything important.
423 Alternatively, you can cancel all the changes made since the file was
424 visited or saved, by reading the text from the file again. This is
425 called @dfn{reverting}. @xref{Reverting}. You could also undo all the
426 changes by repeating the undo command @kbd{C-x u} until you have undone
427 all the changes; but reverting is easier.
429 @findex set-visited-file-name
430 @kbd{M-x set-visited-file-name} alters the name of the file that the
431 current buffer is visiting. It reads the new file name using the
432 minibuffer. Then it marks the buffer as visiting that file name, and
433 changes the buffer name correspondingly. @code{set-visited-file-name}
434 does not save the buffer in the newly visited file; it just alters the
435 records inside Emacs in case you do save later. It also marks the
436 buffer as ``modified'' so that @kbd{C-x C-s} in that buffer
441 If you wish to mark the buffer as visiting a different file and save it
442 right away, use @kbd{C-x C-w} (@code{write-file}). It is precisely
443 equivalent to @code{set-visited-file-name} followed by @kbd{C-x C-s}.
444 @kbd{C-x C-s} used on a buffer that is not visiting a file has the
445 same effect as @kbd{C-x C-w}; that is, it reads a file name, marks the
446 buffer as visiting that file, and saves it there. The default file name in
447 a buffer that is not visiting a file is made by combining the buffer name
448 with the buffer's default directory (@pxref{File Names}).
450 If the new file name implies a major mode, then @kbd{C-x C-w} switches
451 to that major mode, in most cases. The command
452 @code{set-visited-file-name} also does this. @xref{Choosing Modes}.
454 If Emacs is about to save a file and sees that the date of the latest
455 version on disk does not match what Emacs last read or wrote, Emacs
456 notifies you of this fact, because it probably indicates a problem caused
457 by simultaneous editing and requires your immediate attention.
458 @xref{Interlocking,, Simultaneous Editing}.
460 @vindex require-final-newline
461 If the value of the variable @code{require-final-newline} is @code{t},
462 Emacs silently puts a newline at the end of any file that doesn't
463 already end in one, every time a file is saved or written. If the value
464 is @code{nil}, Emacs leaves the end of the file unchanged; if it's
465 neither @code{nil} nor @code{t}, Emacs asks you whether to add a
466 newline. The default is @code{nil}.
469 * Backup:: How Emacs saves the old version of your file.
470 * Interlocking:: How Emacs protects against simultaneous editing
471 of one file by two users.
472 * Shadowing: File Shadowing.
473 Copying files to "shadows" automatically.
474 * Time Stamps:: Emacs can update time stamps on saved files.
478 @subsection Backup Files
480 @vindex make-backup-files
481 @vindex vc-make-backup-files
483 On most operating systems, rewriting a file automatically destroys all
484 record of what the file used to contain. Thus, saving a file from Emacs
485 throws away the old contents of the file---or it would, except that
486 Emacs carefully copies the old contents to another file, called the
487 @dfn{backup} file, before actually saving.
489 For most files, the variable @code{make-backup-files} determines
490 whether to make backup files. On most operating systems, its default
491 value is @code{t}, so that Emacs does write backup files.
493 For files managed by a version control system (@pxref{Version
494 Control}), the variable @code{vc-make-backup-files} determines whether
495 to make backup files. By default it is @code{nil}, since backup files
496 are redundant when you store all the previous versions in a version
497 control system. @xref{General VC Options}.
499 @vindex backup-enable-predicate
500 @vindex temporary-file-directory
501 @vindex small-temporary-file-directory
502 The default value of the @code{backup-enable-predicate} variable
503 prevents backup files being written for files in the directories used
504 for temporary files, specified by @code{temporary-file-directory} or
505 @code{small-temporary-file-directory}.
507 At your option, Emacs can keep either a single backup file or a series of
508 numbered backup files for each file that you edit.
510 Emacs makes a backup for a file only the first time the file is saved
511 from one buffer. No matter how many times you save a file, its backup file
512 continues to contain the contents from before the file was visited.
513 Normally this means that the backup file contains the contents from before
514 the current editing session; however, if you kill the buffer and then visit
515 the file again, a new backup file will be made by the next save.
517 You can also explicitly request making another backup file from a
518 buffer even though it has already been saved at least once. If you save
519 the buffer with @kbd{C-u C-x C-s}, the version thus saved will be made
520 into a backup file if you save the buffer again. @kbd{C-u C-u C-x C-s}
521 saves the buffer, but first makes the previous file contents into a new
522 backup file. @kbd{C-u C-u C-u C-x C-s} does both things: it makes a
523 backup from the previous contents, and arranges to make another from the
524 newly saved contents if you save again.
527 * Names: Backup Names. How backup files are named;
528 choosing single or numbered backup files.
529 * Deletion: Backup Deletion. Emacs deletes excess numbered backups.
530 * Copying: Backup Copying. Backups can be made by copying or renaming.
534 @subsubsection Single or Numbered Backups
536 If you choose to have a single backup file (this is the default),
537 the backup file's name is normally constructed by appending @samp{~} to the
538 file name being edited; thus, the backup file for @file{eval.c} would
541 @vindex make-backup-file-name-function
542 @vindex backup-directory-alist
543 You can change this behavior by defining the variable
544 @code{make-backup-file-name-function} to a suitable function.
545 Alternatively you can customize the variable
546 @code{backup-directory-alist} to specify that files matching certain
547 patterns should be backed up in specific directories.
549 A typical use is to add an element @code{("." . @var{dir})} to make
550 all backups in the directory with absolute name @var{dir}; Emacs
551 modifies the backup file names to avoid clashes between files with the
552 same names originating in different directories. Alternatively,
553 adding, say, @code{("." . ".~")} would make backups in the invisible
554 subdirectory @file{.~} of the original file's directory. Emacs
555 creates the directory, if necessary, to make the backup.
557 If access control stops Emacs from writing backup files under the usual
558 names, it writes the backup file as @file{%backup%~} in your home
559 directory. Only one such file can exist, so only the most recently
560 made such backup is available.
562 If you choose to have a series of numbered backup files, backup file
563 names contain @samp{.~}, the number, and another @samp{~} after the
564 original file name. Thus, the backup files of @file{eval.c} would be
565 called @file{eval.c.~1~}, @file{eval.c.~2~}, and so on, all the way
566 through names like @file{eval.c.~259~} and beyond. The variable
567 @code{backup-directory-alist} applies to numbered backups just as
570 @vindex version-control
571 The choice of single backup or numbered backups is controlled by the
572 variable @code{version-control}. Its possible values are
576 Make numbered backups.
578 Make numbered backups for files that have numbered backups already.
579 Otherwise, make single backups.
581 Never make numbered backups; always make single backups.
585 You can set @code{version-control} locally in an individual buffer to
586 control the making of backups for that buffer's file. For example,
587 Rmail mode locally sets @code{version-control} to @code{never} to make sure
588 that there is only one backup for an Rmail file. @xref{Locals}.
590 @cindex @env{VERSION_CONTROL} environment variable
591 If you set the environment variable @env{VERSION_CONTROL}, to tell
592 various GNU utilities what to do with backup files, Emacs also obeys the
593 environment variable by setting the Lisp variable @code{version-control}
594 accordingly at startup. If the environment variable's value is @samp{t}
595 or @samp{numbered}, then @code{version-control} becomes @code{t}; if the
596 value is @samp{nil} or @samp{existing}, then @code{version-control}
597 becomes @code{nil}; if it is @samp{never} or @samp{simple}, then
598 @code{version-control} becomes @code{never}.
600 @node Backup Deletion
601 @subsubsection Automatic Deletion of Backups
603 To prevent excessive consumption of disk space, Emacs can delete numbered
604 backup versions automatically. Generally Emacs keeps the first few backups
605 and the latest few backups, deleting any in between. This happens every
606 time a new backup is made.
608 @vindex kept-old-versions
609 @vindex kept-new-versions
610 The two variables @code{kept-old-versions} and
611 @code{kept-new-versions} control this deletion. Their values are,
612 respectively, the number of oldest (lowest-numbered) backups to keep
613 and the number of newest (highest-numbered) ones to keep, each time a
614 new backup is made. The backups in the middle (excluding those oldest
615 and newest) are the excess middle versions---those backups are
616 deleted. These variables' values are used when it is time to delete
617 excess versions, just after a new backup version is made; the newly
618 made backup is included in the count in @code{kept-new-versions}. By
619 default, both variables are 2.
621 @vindex delete-old-versions
622 If @code{delete-old-versions} is non-@code{nil}, Emacs deletes the
623 excess backup files silently. If it is @code{nil}, the default, Emacs
624 asks you whether it should delete the excess backup versions.
626 Dired's @kbd{.} (Period) command can also be used to delete old versions.
627 @xref{Dired Deletion}.
630 @subsubsection Copying vs.@: Renaming
632 Backup files can be made by copying the old file or by renaming it.
633 This makes a difference when the old file has multiple names (hard
634 links). If the old file is renamed into the backup file, then the
635 alternate names become names for the backup file. If the old file is
636 copied instead, then the alternate names remain names for the file
637 that you are editing, and the contents accessed by those names will be
640 The method of making a backup file may also affect the file's owner
641 and group. If copying is used, these do not change. If renaming is used,
642 you become the file's owner, and the file's group becomes the default
643 (different operating systems have different defaults for the group).
645 Having the owner change is usually a good idea, because then the owner
646 always shows who last edited the file. Also, the owners of the backups
647 show who produced those versions. Occasionally there is a file whose
648 owner should not change; it is a good idea for such files to contain
649 local variable lists to set @code{backup-by-copying-when-mismatch}
650 locally (@pxref{File Variables}).
652 @vindex backup-by-copying
653 @vindex backup-by-copying-when-linked
654 @vindex backup-by-copying-when-mismatch
655 @vindex backup-by-copying-when-privileged-mismatch
656 @cindex file ownership, and backup
657 @cindex backup, and user-id
658 The choice of renaming or copying is controlled by four variables.
659 Renaming is the default choice. If the variable
660 @code{backup-by-copying} is non-@code{nil}, copying is used. Otherwise,
661 if the variable @code{backup-by-copying-when-linked} is non-@code{nil},
662 then copying is used for files that have multiple names, but renaming
663 may still be used when the file being edited has only one name. If the
664 variable @code{backup-by-copying-when-mismatch} is non-@code{nil}, then
665 copying is used if renaming would cause the file's owner or group to
666 change. @code{backup-by-copying-when-mismatch} is @code{t} by default
667 if you start Emacs as the superuser. The fourth variable,
668 @code{backup-by-copying-when-privileged-mismatch}, gives the highest
669 numeric user-id for which @code{backup-by-copying-when-mismatch} will be
670 forced on. This is useful when low-numbered user-ids are assigned to
671 special system users, such as @code{root}, @code{bin}, @code{daemon},
672 etc., which must maintain ownership of files.
674 When a file is managed with a version control system (@pxref{Version
675 Control}), Emacs does not normally make backups in the usual way for
676 that file. But check-in and check-out are similar in some ways to
677 making backups. One unfortunate similarity is that these operations
678 typically break hard links, disconnecting the file name you visited from
679 any alternate names for the same file. This has nothing to do with
680 Emacs---the version control system does it.
683 @subsection Protection against Simultaneous Editing
686 @cindex simultaneous editing
687 Simultaneous editing occurs when two users visit the same file, both
688 make changes, and then both save them. If nobody were informed that
689 this was happening, whichever user saved first would later find that his
692 On some systems, Emacs notices immediately when the second user starts
693 to change the file, and issues an immediate warning. On all systems,
694 Emacs checks when you save the file, and warns if you are about to
695 overwrite another user's changes. You can prevent loss of the other
696 user's work by taking the proper corrective action instead of saving the
699 @findex ask-user-about-lock
700 @cindex locking files
701 When you make the first modification in an Emacs buffer that is
702 visiting a file, Emacs records that the file is @dfn{locked} by you.
703 (It does this by creating a symbolic link in the same directory with a
704 different name.) Emacs removes the lock when you save the changes. The
705 idea is that the file is locked whenever an Emacs buffer visiting it has
709 If you begin to modify the buffer while the visited file is locked by
710 someone else, this constitutes a @dfn{collision}. When Emacs detects a
711 collision, it asks you what to do, by calling the Lisp function
712 @code{ask-user-about-lock}. You can redefine this function for the sake
713 of customization. The standard definition of this function asks you a
714 question and accepts three possible answers:
718 Steal the lock. Whoever was already changing the file loses the lock,
719 and you gain the lock.
721 Proceed. Go ahead and edit the file despite its being locked by someone else.
723 Quit. This causes an error (@code{file-locked}), and the buffer
724 contents remain unchanged---the modification you were trying to make
725 does not actually take place.
728 Note that locking works on the basis of a file name; if a file has
729 multiple names, Emacs does not realize that the two names are the same file
730 and cannot prevent two users from editing it simultaneously under different
731 names. However, basing locking on names means that Emacs can interlock the
732 editing of new files that will not really exist until they are saved.
734 Some systems are not configured to allow Emacs to make locks, and
735 there are cases where lock files cannot be written. In these cases,
736 Emacs cannot detect trouble in advance, but it still can detect the
737 collision when you try to save a file and overwrite someone else's
740 If Emacs or the operating system crashes, this may leave behind lock
741 files which are stale, so you may occasionally get warnings about
742 spurious collisions. When you determine that the collision is spurious,
743 just use @kbd{p} to tell Emacs to go ahead anyway.
745 Every time Emacs saves a buffer, it first checks the last-modification
746 date of the existing file on disk to verify that it has not changed since the
747 file was last visited or saved. If the date does not match, it implies
748 that changes were made in the file in some other way, and these changes are
749 about to be lost if Emacs actually does save. To prevent this, Emacs
750 displays a warning message and asks for confirmation before saving.
751 Occasionally you will know why the file was changed and know that it does
752 not matter; then you can answer @kbd{yes} and proceed. Otherwise, you should
753 cancel the save with @kbd{C-g} and investigate the situation.
755 The first thing you should do when notified that simultaneous editing
756 has already taken place is to list the directory with @kbd{C-u C-x C-d}
757 (@pxref{Directories}). This shows the file's current author. You
758 should attempt to contact him to warn him not to continue editing.
759 Often the next step is to save the contents of your Emacs buffer under a
760 different name, and use @code{diff} to compare the two files.@refill
763 @subsection Shadowing Files
768 @item M-x shadow-initialize
769 Set up file shadowing.
770 @item M-x shadow-define-literal-group
771 Declare a single file to be shared between sites.
772 @item M-x shadow-define-regexp-group
773 Make all files that match each of a group of files be shared between hosts.
774 @item M-x shadow-define-cluster @key{RET} @var{name} @key{RET}
775 Define a shadow file cluster @var{name}.
776 @item M-x shadow-copy-files
777 Copy all pending shadow files.
778 @item M-x shadow-cancel
779 Cancel the instruction to shadow some files.
782 You can arrange to keep identical @dfn{shadow} copies of certain files
783 in more than one place---possibly on different machines. To do this,
784 first you must set up a @dfn{shadow file group}, which is a set of
785 identically-named files shared between a list of sites. The file
786 group is permanent and applies to further Emacs sessions as well as
787 the current one. Once the group is set up, every time you exit Emacs,
788 it will copy the file you edited to the other files in its group. You
789 can also do the copying without exiting Emacs, by typing @kbd{M-x
792 To set up a shadow file group, use @kbd{M-x
793 shadow-define-literal-group} or @kbd{M-x shadow-define-regexp-group}.
794 See their documentation strings for further information.
796 Before copying a file to its shadows, Emacs asks for confirmation.
797 You can answer ``no'' to bypass copying of this file, this time. If
798 you want to cancel the shadowing permanently for a certain file, use
799 @kbd{M-x shadow-cancel} to eliminate or change the shadow file group.
801 A @dfn{shadow cluster} is a group of hosts that share directories, so
802 that copying to or from one of them is sufficient to update the file
803 on all of them. Each shadow cluster has a name, and specifies the
804 network address of a primary host (the one we copy files to), and a
805 regular expression that matches the host names of all the other hosts
806 in the cluster. You can define a shadow cluster with @kbd{M-x
807 shadow-define-cluster}.
810 @subsection Updating Time Stamps Automatically
813 @cindex modification dates
814 @cindex locale, date format
816 You can arrange to put a time stamp in a file, so that it will be updated
817 automatically each time you edit and save the file. The time stamp
818 has to be in the first eight lines of the file, and you should
832 Then add the hook function @code{time-stamp} to the hook
833 @code{write-file-hooks}; that hook function will automatically update
834 the time stamp, inserting the current date and time when you save the
835 file. You can also use the command @kbd{M-x time-stamp} to update the
836 time stamp manually. For other customizations, see the Custom group
837 @code{time-stamp}. Note that non-numeric fields in the time stamp are
838 formatted according to your locale setting (@pxref{Environment}).
841 @section Reverting a Buffer
842 @findex revert-buffer
843 @cindex drastic changes
844 @cindex reread a file
846 If you have made extensive changes to a file and then change your mind
847 about them, you can get rid of them by reading in the previous version
848 of the file. To do this, use @kbd{M-x revert-buffer}, which operates on
849 the current buffer. Since reverting a buffer unintentionally could lose
850 a lot of work, you must confirm this command with @kbd{yes}.
852 @code{revert-buffer} keeps point at the same distance (measured in
853 characters) from the beginning of the file. If the file was edited only
854 slightly, you will be at approximately the same piece of text after
855 reverting as before. If you have made drastic changes, the same value of
856 point in the old file may address a totally different piece of text.
858 Reverting marks the buffer as ``not modified'' until another change is
861 Some kinds of buffers whose contents reflect data bases other than files,
862 such as Dired buffers, can also be reverted. For them, reverting means
863 recalculating their contents from the appropriate data base. Buffers
864 created explicitly with @kbd{C-x b} cannot be reverted; @code{revert-buffer}
865 reports an error when asked to do so.
867 @vindex revert-without-query
868 When you edit a file that changes automatically and frequently---for
869 example, a log of output from a process that continues to run---it may be
870 useful for Emacs to revert the file without querying you, whenever you
871 visit the file again with @kbd{C-x C-f}.
873 To request this behavior, set the variable @code{revert-without-query}
874 to a list of regular expressions. When a file name matches one of these
875 regular expressions, @code{find-file} and @code{revert-buffer} will
876 revert it automatically if it has changed---provided the buffer itself
877 is not modified. (If you have edited the text, it would be wrong to
878 discard your changes.)
880 @cindex Global Auto-Revert mode
881 @cindex mode, Global Auto-Revert
882 @cindex Auto-Revert mode
883 @cindex mode, Auto-Revert
884 @findex global-auto-revert-mode
885 @findex auto-revert-mode
886 @vindex auto-revert-interval
887 You may find it useful to have Emacs revert files automatically when
888 they change. Two minor modes are available to do this. In Global
889 Auto-Revert mode, Emacs periodically checks all file buffers and
890 reverts any when the corresponding file has changed. The local
891 variant, Auto-Revert mode, applies only to buffers in which it was
892 activated. Checking the files is done at intervals determined by the
893 variable @code{auto-revert-interval}.
896 @section Auto-Saving: Protection Against Disasters
897 @cindex Auto Save mode
898 @cindex mode, Auto Save
901 Emacs saves all the visited files from time to time (based on counting
902 your keystrokes) without being asked. This is called @dfn{auto-saving}.
903 It prevents you from losing more than a limited amount of work if the
906 When Emacs determines that it is time for auto-saving, each buffer is
907 considered, and is auto-saved if auto-saving is turned on for it and it
908 has been changed since the last time it was auto-saved. The message
909 @samp{Auto-saving...} is displayed in the echo area during auto-saving,
910 if any files are actually auto-saved. Errors occurring during
911 auto-saving are caught so that they do not interfere with the execution
912 of commands you have been typing.
915 * Files: Auto Save Files. The file where auto-saved changes are
916 actually made until you save the file.
917 * Control: Auto Save Control. Controlling when and how often to auto-save.
918 * Recover:: Recovering text from auto-save files.
921 @node Auto Save Files
922 @subsection Auto-Save Files
924 Auto-saving does not normally save in the files that you visited, because
925 it can be very undesirable to save a program that is in an inconsistent
926 state when you have made half of a planned change. Instead, auto-saving
927 is done in a different file called the @dfn{auto-save file}, and the
928 visited file is changed only when you request saving explicitly (such as
931 Normally, the auto-save file name is made by appending @samp{#} to the
932 front and rear of the visited file name. Thus, a buffer visiting file
933 @file{foo.c} is auto-saved in a file @file{#foo.c#}. Most buffers that
934 are not visiting files are auto-saved only if you request it explicitly;
935 when they are auto-saved, the auto-save file name is made by appending
936 @samp{#%} to the front and @samp{#} to the rear of buffer name. For
937 example, the @samp{*mail*} buffer in which you compose messages to be
938 sent is auto-saved in a file named @file{#%*mail*#}. Auto-save file
939 names are made this way unless you reprogram parts of Emacs to do
940 something different (the functions @code{make-auto-save-file-name} and
941 @code{auto-save-file-name-p}). The file name to be used for auto-saving
942 in a buffer is calculated when auto-saving is turned on in that buffer.
944 When you delete a substantial part of the text in a large buffer, auto
945 save turns off temporarily in that buffer. This is because if you
946 deleted the text unintentionally, you might find the auto-save file more
947 useful if it contains the deleted text. To reenable auto-saving after
948 this happens, save the buffer with @kbd{C-x C-s}, or use @kbd{C-u 1 M-x
951 @vindex auto-save-visited-file-name
952 If you want auto-saving to be done in the visited file rather than
953 in a separate auto-save file, set the variable
954 @code{auto-save-visited-file-name} to a non-@code{nil} value. In this
955 mode, there is no real difference between auto-saving and explicit
958 @vindex delete-auto-save-files
959 A buffer's auto-save file is deleted when you save the buffer in its
960 visited file. To inhibit this, set the variable @code{delete-auto-save-files}
961 to @code{nil}. Changing the visited file name with @kbd{C-x C-w} or
962 @code{set-visited-file-name} renames any auto-save file to go with
963 the new visited name.
965 @node Auto Save Control
966 @subsection Controlling Auto-Saving
968 @vindex auto-save-default
969 @findex auto-save-mode
970 Each time you visit a file, auto-saving is turned on for that file's
971 buffer if the variable @code{auto-save-default} is non-@code{nil} (but not
972 in batch mode; @pxref{Entering Emacs}). The default for this variable is
973 @code{t}, so auto-saving is the usual practice for file-visiting buffers.
974 Auto-saving can be turned on or off for any existing buffer with the
975 command @kbd{M-x auto-save-mode}. Like other minor mode commands, @kbd{M-x
976 auto-save-mode} turns auto-saving on with a positive argument, off with a
977 zero or negative argument; with no argument, it toggles.
979 @vindex auto-save-interval
980 Emacs does auto-saving periodically based on counting how many characters
981 you have typed since the last time auto-saving was done. The variable
982 @code{auto-save-interval} specifies how many characters there are between
983 auto-saves. By default, it is 300. Emacs doesn't accept values that are
984 too small: if you customize @code{auto-save-interval} to a value less
985 than 20, Emacs will behave as if the value is 20.
987 @vindex auto-save-timeout
988 Auto-saving also takes place when you stop typing for a while. The
989 variable @code{auto-save-timeout} says how many seconds Emacs should
990 wait before it does an auto save (and perhaps also a garbage
991 collection). (The actual time period is longer if the current buffer is
992 long; this is a heuristic which aims to keep out of your way when you
993 are editing long buffers, in which auto-save takes an appreciable amount
994 of time.) Auto-saving during idle periods accomplishes two things:
995 first, it makes sure all your work is saved if you go away from the
996 terminal for a while; second, it may avoid some auto-saving while you
999 Emacs also does auto-saving whenever it gets a fatal error. This
1000 includes killing the Emacs job with a shell command such as @samp{kill
1001 %emacs}, or disconnecting a phone line or network connection.
1003 @findex do-auto-save
1004 You can request an auto-save explicitly with the command @kbd{M-x
1008 @subsection Recovering Data from Auto-Saves
1010 @findex recover-file
1011 You can use the contents of an auto-save file to recover from a loss
1012 of data with the command @kbd{M-x recover-file @key{RET} @var{file}
1013 @key{RET}}. This visits @var{file} and then (after your confirmation)
1014 restores the contents from its auto-save file @file{#@var{file}#}.
1015 You can then save with @kbd{C-x C-s} to put the recovered text into
1016 @var{file} itself. For example, to recover file @file{foo.c} from its
1017 auto-save file @file{#foo.c#}, do:@refill
1020 M-x recover-file @key{RET} foo.c @key{RET}
1025 Before asking for confirmation, @kbd{M-x recover-file} displays a
1026 directory listing describing the specified file and the auto-save file,
1027 so you can compare their sizes and dates. If the auto-save file
1028 is older, @kbd{M-x recover-file} does not offer to read it.
1030 @findex recover-session
1031 If Emacs or the computer crashes, you can recover all the files you
1032 were editing from their auto save files with the command @kbd{M-x
1033 recover-session}. This first shows you a list of recorded interrupted
1034 sessions. Move point to the one you choose, and type @kbd{C-c C-c}.
1036 Then @code{recover-session} asks about each of the files that were
1037 being edited during that session, asking whether to recover that file.
1038 If you answer @kbd{y}, it calls @code{recover-file}, which works in its
1039 normal fashion. It shows the dates of the original file and its
1040 auto-save file, and asks once again whether to recover that file.
1042 When @code{recover-session} is done, the files you've chosen to
1043 recover are present in Emacs buffers. You should then save them. Only
1044 this---saving them---updates the files themselves.
1046 @vindex auto-save-list-file-prefix
1047 Emacs records interrupted sessions for later recovery in files named
1048 @file{~/.emacs.d/auto-save-list/.saves-@var{pid}-@var{hostname}}. The
1049 @samp{~/.emacs.d/auto-save-list/.saves-} portion of these names comes
1050 from the value of @code{auto-save-list-file-prefix}. You can record
1051 sessions in a different place by customizing that variable. If you
1052 set @code{auto-save-list-file-prefix} to @code{nil} in your
1053 @file{.emacs} file, sessions are not recorded for recovery.
1056 @section File Name Aliases
1058 Symbolic links and hard links both make it possible for several file
1059 names to refer to the same file. Hard links are alternate names that
1060 refer directly to the file; all the names are equally valid, and no one
1061 of them is preferred. By contrast, a symbolic link is a kind of defined
1062 alias: when @file{foo} is a symbolic link to @file{bar}, you can use
1063 either name to refer to the file, but @file{bar} is the real name, while
1064 @file{foo} is just an alias. More complex cases occur when symbolic
1065 links point to directories.
1067 If you visit two names for the same file, normally Emacs makes
1068 two different buffers, but it warns you about the situation.
1070 @vindex find-file-existing-other-name
1071 @vindex find-file-suppress-same-file-warnings
1072 Normally, if you visit a file which Emacs is already visiting under
1073 a different name, Emacs displays a message in the echo area and uses
1074 the existing buffer visiting that file. This can happen on systems
1075 that support symbolic links, or if you use a long file name on a
1076 system that truncates long file names. You can suppress the message by
1077 setting the variable @code{find-file-suppress-same-file-warnings} to a
1078 non-@code{nil} value. You can disable this feature entirely by setting
1079 the variable @code{find-file-existing-other-name} to @code{nil}: then
1080 if you visit the same file under two different names, you get a separate
1081 buffer for each file name.
1083 @vindex find-file-visit-truename
1084 @cindex truenames of files
1085 @cindex file truenames
1086 If the variable @code{find-file-visit-truename} is non-@code{nil},
1087 then the file name recorded for a buffer is the file's @dfn{truename}
1088 (made by replacing all symbolic links with their target names), rather
1089 than the name you specify. Setting @code{find-file-visit-truename} also
1090 implies the effect of @code{find-file-existing-other-name}.
1092 @node Version Control
1093 @section Version Control
1094 @cindex version control
1096 @dfn{Version control systems} are packages that can record multiple
1097 versions of a source file, usually storing the unchanged parts of the
1098 file just once. Version control systems also record history information
1099 such as the creation time of each version, who created it, and a
1100 description of what was changed in that version.
1102 The Emacs version control interface is called VC. Its commands work
1103 with three version control systems---RCS, CVS, and SCCS. The GNU
1104 project recommends RCS and CVS, which are free software and available
1105 from the Free Software Foundation. We also have free software to
1106 replace SCCS, known as CSSC; if you are using SCCS and don't want to
1107 make the incompatible change to RCS or CVS, you can switch to CSSC.
1110 * Introduction to VC:: How version control works in general.
1111 * VC Mode Line:: How the mode line shows version control status.
1112 * Basic VC Editing:: How to edit a file under version control.
1113 * Old Versions:: Examining and comparing old versions.
1114 * Secondary VC Commands:: The commands used a little less frequently.
1115 * Branches:: Multiple lines of development.
1116 * Remote Repositories:: Efficient access to remote CVS servers.
1117 * Snapshots:: Sets of file versions treated as a unit.
1118 * Miscellaneous VC:: Various other commands and features of VC.
1119 * Customizing VC:: Variables that change VC's behavior.
1122 @node Introduction to VC
1123 @subsection Introduction to Version Control
1125 VC allows you to use a version control system from within Emacs,
1126 integrating the version control operations smoothly with editing. VC
1127 provides a uniform interface to version control, so that regardless of
1128 which version control system is in use, you can use it the same way.
1130 This section provides a general overview of version control, and
1131 describes the version control systems that VC supports. You can skip
1132 this section if you are already familiar with the version control system
1136 * Version Systems:: Supported version control back-end systems.
1137 * VC Concepts:: Words and concepts related to version control.
1138 * Types of Log File:: The per-file VC log in contrast to the ChangeLog.
1141 @node Version Systems
1142 @subsubsection Supported Version Control Systems
1145 @cindex back end (version control)
1146 VC currently works with three different version control systems or
1147 ``back ends'': RCS, CVS, and SCCS.
1149 RCS is a free version control system that is available from the Free
1150 Software Foundation. It is perhaps the most mature of the supported
1151 back ends, and the VC commands are conceptually closest to RCS. Almost
1152 everything you can do with RCS can be done through VC.
1155 CVS is built on top of RCS, and extends the features of RCS, allowing
1156 for more sophisticated release management, and concurrent multi-user
1157 development. VC supports basic editing operations under CVS, but for
1158 some less common tasks you still need to call CVS from the command line.
1159 Note also that before using CVS you must set up a repository, which is a
1160 subject too complex to treat here.
1163 SCCS is a proprietary but widely used version control system. In
1164 terms of capabilities, it is the weakest of the three that VC
1165 supports. VC compensates for certain features missing in SCCS
1166 (snapshots, for example) by implementing them itself, but some other VC
1167 features, such as multiple branches, are not available with SCCS. You
1168 should use SCCS only if for some reason you cannot use RCS.
1171 @subsubsection Concepts of Version Control
1174 @cindex registered file
1175 When a file is under version control, we also say that it is
1176 @dfn{registered} in the version control system. Each registered file
1177 has a corresponding @dfn{master file} which represents the file's
1178 present state plus its change history---enough to reconstruct the
1179 current version or any earlier version. Usually the master file also
1180 records a @dfn{log entry} for each version, describing in words what was
1181 changed in that version.
1184 @cindex checking out files
1185 The file that is maintained under version control is sometimes called
1186 the @dfn{work file} corresponding to its master file. You edit the work
1187 file and make changes in it, as you would with an ordinary file. (With
1188 SCCS and RCS, you must @dfn{lock} the file before you start to edit it.)
1189 After you are done with a set of changes, you @dfn{check the file in},
1190 which records the changes in the master file, along with a log entry for
1193 With CVS, there are usually multiple work files corresponding to a
1194 single master file---often each user has his own copy. It is also
1195 possible to use RCS in this way, but this is not the usual way to use
1198 @cindex locking and version control
1199 A version control system typically has some mechanism to coordinate
1200 between users who want to change the same file. One method is
1201 @dfn{locking} (analogous to the locking that Emacs uses to detect
1202 simultaneous editing of a file, but distinct from it). The other method
1203 is to merge your changes with other people's changes when you check them
1206 With version control locking, work files are normally read-only so
1207 that you cannot change them. You ask the version control system to make
1208 a work file writable for you by locking it; only one user can do
1209 this at any given time. When you check in your changes, that unlocks
1210 the file, making the work file read-only again. This allows other users
1211 to lock the file to make further changes. SCCS always uses locking, and
1214 The other alternative for RCS is to let each user modify the work file
1215 at any time. In this mode, locking is not required, but it is
1216 permitted; check-in is still the way to record a new version.
1218 CVS normally allows each user to modify his own copy of the work file
1219 at any time, but requires merging with changes from other users at
1220 check-in time. However, CVS can also be set up to require locking.
1221 (@pxref{CVS Options}).
1223 @node Types of Log File
1224 @subsubsection Types of Log File
1225 @cindex Types of log file
1226 @cindex Log File, types of
1228 GNU projects under a revision control system generally possess
1229 @emph{two} types of log. These help you keep track of what goes on.
1231 One kind of log is the per-file log maintained by the revision control
1232 system. This kind of log is called the @dfn{version control log}, or
1233 sometimes the @dfn{revision control log}, `@samp{*rcs*} log', or
1234 `@samp{*cvs*} log'. The other kind of log is a per-directory or
1235 per-project log called the change log or @file{ChangeLog}.
1237 @cindex Version control log
1238 @cindex Revision control log
1239 @cindex Per-file log
1240 The per-file log is designed to tell you about each and every change
1241 to a file. Each time you check in a change, you fill out a version
1242 control log entry. (@xref{Log Buffer, Log Buffer, Features of the Log
1243 Entry Buffer}.) Consequently, a per-file log is very detailed, with
1244 remarks such as `fixed typo' as well as `re-wrote from scratch'.
1247 @cindex Per-directory log
1248 @cindex Per-project log
1249 On the other hand, a per-directory or per-project log is intended to
1250 provide a chronological record of when and why you and others changed
1251 a program. A @file{ChangeLog} should be moderately, but not
1252 excessively detailed.
1254 A single @file{ChangeLog} file can record changes for all
1255 the files in its directory and all its subdirectories. A small
1256 program merits one @file{ChangeLog} file; a large program may well
1257 merit several @file{ChangeLog} file, one in each major directory.
1258 (@xref{Change Log, Change Log, Change Logs}.)
1260 You can use the Emacs command @r{@kbd{C-x 4 a}}
1261 (@code{add-change-log-entry-other-window}) to add a new entry to a
1264 If you use RCS or CVS, you can generate change log entries
1265 automatically from the version control log entries using
1266 the @r{@kbd{C-x v a}} (@code{vc-update-change-log}) command.
1267 (@xref{Change Logs and VC, Change Logs and VC, Change Logs and VC}.)
1268 When you do this, you will probably want to edit and shorten the
1269 resulting @file{ChangeLog}.
1272 @subsection Version Control and the Mode Line
1274 When you visit a file that is under version control, Emacs indicates
1275 this on the mode line. For example, @samp{RCS-1.3} says that RCS is
1276 used for that file, and the current version is 1.3.
1278 The character between the back-end name and the version number
1279 indicates the version control status of the file. @samp{-} means that
1280 the work file is not locked (if locking is in use), or not modified (if
1281 locking is not in use). @samp{:} indicates that the file is locked, or
1282 that it is modified. If the file is locked by some other user (for
1283 instance, @samp{jim}), that is displayed as @samp{RCS:jim:1.3}.
1285 @node Basic VC Editing
1286 @subsection Basic Editing under Version Control
1288 The principal VC command is an all-purpose command that performs
1289 either locking or check-in, depending on the situation.
1294 Perform the next logical version control operation on this file.
1297 @findex vc-next-action
1298 @findex vc-toggle-read-only
1300 @kindex C-x C-q @r{(Version Control)}
1301 Strictly speaking, the command for this job is @code{vc-next-action},
1302 bound to @kbd{C-x v v}. However, the normal meaning of @kbd{C-x C-q} is
1303 to make a read-only buffer writable, or vice versa; we have extended it
1304 to do the same job properly for files managed by version control, by
1305 performing the appropriate version control operations. When you type
1306 @kbd{C-x C-q} on a registered file, it acts like @kbd{C-x v v}.
1308 The precise action of this command depends on the state of the file,
1309 and whether the version control system uses locking or not. SCCS and
1310 RCS normally use locking; CVS normally does not use locking.
1313 * VC with Locking:: RCS in its default mode, SCCS, and optionally CVS.
1314 * Without Locking:: Without locking: default mode for CVS.
1315 * Advanced C-x C-q:: Advanced features available with a prefix argument.
1316 * Log Buffer:: Features available in log entry buffers.
1319 @node VC with Locking
1320 @subsubsection Basic Version Control with Locking
1322 If locking is used for the file (as with SCCS, and RCS in its default
1323 mode), @kbd{C-x C-q} can either lock a file or check it in:
1327 If the file is not locked, @kbd{C-x C-q} locks it, and
1328 makes it writable so that you can change it.
1331 If the file is locked by you, and contains changes, @kbd{C-x C-q} checks
1332 in the changes. In order to do this, it first reads the log entry
1333 for the new version. @xref{Log Buffer}.
1336 If the file is locked by you, but you have not changed it since you
1337 locked it, @kbd{C-x C-q} releases the lock and makes the file read-only
1341 If the file is locked by some other user, @kbd{C-x C-q} asks you whether
1342 you want to ``steal the lock'' from that user. If you say yes, the file
1343 becomes locked by you, but a message is sent to the person who had
1344 formerly locked the file, to inform him of what has happened.
1347 These rules also apply when you use CVS in locking mode, except
1348 that there is no such thing as stealing a lock.
1350 @node Without Locking
1351 @subsubsection Basic Version Control without Locking
1353 When there is no locking---the default for CVS---work files are always
1354 writable; you do not need to do anything before you begin to edit a
1355 file. The status indicator on the mode line is @samp{-} if the file is
1356 unmodified; it flips to @samp{:} as soon as you save any changes in the
1359 Here is what @kbd{C-x C-q} does when using CVS:
1363 If some other user has checked in changes into the master file, Emacs
1364 asks you whether you want to merge those changes into your own work
1365 file. You must do this before you can check in your own changes. (To
1366 pick up any recent changes from the master file @emph{without} trying
1367 to commit your own changes, type @kbd{C-x v m @key{RET}}.)
1371 If there are no new changes in the master file, but you have made
1372 modifications in your work file, @kbd{C-x C-q} checks in your changes.
1373 In order to do this, it first reads the log entry for the new version.
1377 If the file is not modified, the @kbd{C-x C-q} does nothing.
1380 These rules also apply when you use RCS in the mode that does not
1381 require locking, except that automatic merging of changes from the
1382 master file is not implemented. Unfortunately, this means that nothing
1383 informs you if another user has checked in changes in the same file
1384 since you began editing it, and when this happens, his changes will be
1385 effectively removed when you check in your version (though they will
1386 remain in the master file, so they will not be entirely lost). You must
1387 therefore verify the current version is unchanged, before you check in your
1388 changes. We hope to eliminate this risk and provide automatic merging
1389 with RCS in a future Emacs version.
1391 In addition, locking is possible with RCS even in this mode, although
1392 it is not required; @kbd{C-x C-q} with an unmodified file locks the
1393 file, just as it does with RCS in its normal (locking) mode.
1395 @node Advanced C-x C-q
1396 @subsubsection Advanced Control in @kbd{C-x C-q}
1398 When you give a prefix argument to @code{vc-next-action} (@kbd{C-u
1399 C-x C-q}), it still performs the next logical version control
1400 operation, but accepts additional arguments to specify precisely how
1401 to do the operation.
1405 If the file is modified (or locked), you can specify the version
1406 number to use for the new version that you check in. This is one way
1407 to create a new branch (@pxref{Branches}).
1410 If the file is not modified (and unlocked), you can specify the
1411 version to select; this lets you start working from an older version,
1412 or on another branch. If you do not enter any version, that takes you
1413 to the highest version on the current branch; therefore @kbd{C-u C-x
1414 C-q @key{RET}} is a convenient way to get the latest version of a file from
1418 Instead of the version number, you can also specify the name of a
1419 version control system. This is useful when one file is being managed
1420 with two version control systems at the same time (@pxref{Local
1425 @subsubsection Features of the Log Entry Buffer
1427 When you check in changes, @kbd{C-x C-q} first reads a log entry. It
1428 pops up a buffer called @samp{*VC-Log*} for you to enter the log entry.
1429 When you are finished, type @kbd{C-c C-c} in the @samp{*VC-Log*} buffer.
1430 That is when check-in really happens.
1432 To abort check-in, just @strong{don't} type @kbd{C-c C-c} in that
1433 buffer. You can switch buffers and do other editing. As long as you
1434 don't try to check in another file, the entry you were editing remains
1435 in the @samp{*VC-Log*} buffer, and you can go back to that buffer at any
1436 time to complete the check-in.
1438 If you change several source files for the same reason, it is often
1439 convenient to specify the same log entry for many of the files. To do
1440 this, use the history of previous log entries. The commands @kbd{M-n},
1441 @kbd{M-p}, @kbd{M-s} and @kbd{M-r} for doing this work just like the
1442 minibuffer history commands (except that these versions are used outside
1445 @vindex vc-log-mode-hook
1446 Each time you check in a file, the log entry buffer is put into VC Log
1447 mode, which involves running two hooks: @code{text-mode-hook} and
1448 @code{vc-log-mode-hook}. @xref{Hooks}.
1451 @subsection Examining And Comparing Old Versions
1453 One of the convenient features of version control is the ability
1454 to examine any version of a file, or compare two versions.
1457 @item C-x v ~ @var{version} @key{RET}
1458 Examine version @var{version} of the visited file, in a buffer of its
1462 Compare the current buffer contents with the latest checked-in version
1465 @item C-u C-x v = @var{file} @key{RET} @var{oldvers} @key{RET} @var{newvers} @key{RET}
1466 Compare the specified two versions of @var{file}.
1469 Display the result of the CVS annotate command using colors.
1472 @findex vc-version-other-window
1474 To examine an old version in its entirety, visit the file and then type
1475 @kbd{C-x v ~ @var{version} @key{RET}} (@code{vc-version-other-window}).
1476 This puts the text of version @var{version} in a file named
1477 @file{@var{filename}.~@var{version}~}, and visits it in its own buffer
1478 in a separate window. (In RCS, you can also select an old version
1479 and create a branch from it. @xref{Branches}.)
1483 It is usually more convenient to compare two versions of the file,
1484 with the command @kbd{C-x v =} (@code{vc-diff}). Plain @kbd{C-x v =}
1485 compares the current buffer contents (saving them in the file if
1486 necessary) with the last checked-in version of the file. @kbd{C-u C-x
1487 v =}, with a numeric argument, reads a file name and two version
1488 numbers, then compares those versions of the specified file. Both
1489 forms display the output in a special buffer in another window.
1491 You can specify a checked-in version by its number; an empty input
1492 specifies the current contents of the work file (which may be different
1493 from all the checked-in versions). You can also specify a snapshot name
1494 (@pxref{Snapshots}) instead of one or both version numbers.
1496 If you supply a directory name instead of the name of a registered
1497 file, this command compares the two specified versions of all registered
1498 files in that directory and its subdirectories.
1500 @vindex vc-diff-switches
1501 @vindex vc-rcs-diff-switches
1502 @kbd{C-x v =} works by running a variant of the @code{diff} utility
1503 designed to work with the version control system in use. When you
1504 invoke @code{diff} this way, in addition to the options specified by
1505 @code{diff-switches} (@pxref{Comparing Files}), it receives those
1506 specified by @code{vc-diff-switches}, plus those specified for the
1507 specific back end by @code{vc-@var{backend}-diff-switches}. For
1508 instance, when the version control back end is RCS, @code{diff} uses
1509 the options in @code{vc-rcs-diff-switches}. The
1510 @samp{vc@dots{}diff-switches} variables are @code{nil} by default.
1512 Unlike the @kbd{M-x diff} command, @kbd{C-x v =} does not try to
1513 locate the changes in the old and new versions. This is because
1514 normally one or both versions do not exist as files when you compare
1515 them; they exist only in the records of the master file.
1516 @xref{Comparing Files}, for more information about @kbd{M-x diff}.
1520 For CVS-controlled files, you can display the result of the CVS
1521 annotate command, using colors to enhance the visual appearance. Use
1522 the command @kbd{M-x vc-annotate} to do this. It creates a new buffer
1523 to display file's text, colored to show how old each part is. Text
1524 colored red is new, blue means old, and intermediate colors indicate
1525 intermediate ages. By default, the time scale is 360 days, so that
1526 everything more than one year old is shown in blue.
1528 When you give a prefix argument to this command, it uses the
1529 minibuffer to read two arguments: which version number to display and
1530 annotate (instead of the current file contents), and a stretch factor
1531 for the time scale. A stretch factor of 0.1 means that the color
1532 range from red to blue spans the past 36 days instead of 360 days. A
1533 stretch factor greater than 1 means the color range spans more than a
1536 @node Secondary VC Commands
1537 @subsection The Secondary Commands of VC
1539 This section explains the secondary commands of VC; those that you might
1543 * Registering:: Putting a file under version control.
1544 * VC Status:: Viewing the VC status of files.
1545 * VC Undo:: Cancelling changes before or after check-in.
1546 * VC Dired Mode:: Listing files managed by version control.
1547 * VC Dired Commands:: Commands to use in a VC Dired buffer.
1551 @subsubsection Registering a File for Version Control
1555 You can put any file under version control by simply visiting it, and
1556 then typing @w{@kbd{C-x v i}} (@code{vc-register}).
1560 Register the visited file for version control.
1563 To register the file, Emacs must choose which version control system
1564 to use for it. If the file's directory already contains files
1565 registered in a version control system, Emacs uses that system. If
1566 there is more than one system in use for a directory, Emacs uses the one
1567 that appears first in @code{vc-handled-backends} (@pxref{Customizing VC}).
1568 On the other hand, if there are no files already registered,
1569 Emacs uses the first system from @code{vc-handled-backends} that could
1570 register the file---for example, you cannot register a file under CVS if
1571 its directory is not already part of a CVS tree.
1573 With the default value of @code{vc-handled-backends}, this means
1574 that Emacs uses RCS if there are any files under RCS control, CVS if
1575 there are any files under CVS, SCCS if any files are under SCCS, or
1576 RCS as the ultimate default.
1578 If locking is in use, @kbd{C-x v i} leaves the file unlocked and
1579 read-only. Type @kbd{C-x C-q} if you wish to start editing it. After
1580 registering a file with CVS, you must subsequently commit the initial
1581 version by typing @kbd{C-x C-q}.
1583 @vindex vc-default-init-version
1584 The initial version number for a newly registered file is 1.1, by
1585 default. You can specify a different default by setting the variable
1586 @code{vc-default-init-version}, or you can give @kbd{C-x v i} a numeric
1587 argument; then it reads the initial version number for this particular
1588 file using the minibuffer.
1590 @vindex vc-initial-comment
1591 If @code{vc-initial-comment} is non-@code{nil}, @kbd{C-x v i} reads an
1592 initial comment to describe the purpose of this source file. Reading
1593 the initial comment works like reading a log entry (@pxref{Log Buffer}).
1596 @subsubsection VC Status Commands
1600 Display version control state and change history.
1604 @findex vc-print-log
1605 To view the detailed version control status and history of a file,
1606 type @kbd{C-x v l} (@code{vc-print-log}). It displays the history of
1607 changes to the current file, including the text of the log entries. The
1608 output appears in a separate window.
1611 @subsubsection Undoing Version Control Actions
1615 Revert the buffer and the file to the last checked-in version.
1618 Remove the last-entered change from the master for the visited file.
1619 This undoes your last check-in.
1623 @findex vc-revert-buffer
1624 If you want to discard your current set of changes and revert to the
1625 last version checked in, use @kbd{C-x v u} (@code{vc-revert-buffer}).
1626 This leaves the file unlocked; if locking is in use, you must first lock
1627 the file again before you change it again. @kbd{C-x v u} requires
1628 confirmation, unless it sees that you haven't made any changes since the
1629 last checked-in version.
1631 @kbd{C-x v u} is also the command to unlock a file if you lock it and
1632 then decide not to change it.
1635 @findex vc-cancel-version
1636 To cancel a change that you already checked in, use @kbd{C-x v c}
1637 (@code{vc-cancel-version}). This command discards all record of the
1638 most recent checked-in version. @kbd{C-x v c} also offers to revert
1639 your work file and buffer to the previous version (the one that precedes
1640 the version that is deleted).
1642 If you answer @kbd{no}, VC keeps your changes in the buffer, and locks
1643 the file. The no-revert option is useful when you have checked in a
1644 change and then discover a trivial error in it; you can cancel the
1645 erroneous check-in, fix the error, and check the file in again.
1647 When @kbd{C-x v c} does not revert the buffer, it unexpands all
1648 version control headers in the buffer instead (@pxref{Version Headers}).
1649 This is because the buffer no longer corresponds to any existing
1650 version. If you check it in again, the check-in process will expand the
1651 headers properly for the new version number.
1653 However, it is impossible to unexpand the RCS @samp{@w{$}Log$} header
1654 automatically. If you use that header feature, you have to unexpand it
1655 by hand---by deleting the entry for the version that you just canceled.
1657 Be careful when invoking @kbd{C-x v c}, as it is easy to lose a lot of
1658 work with it. To help you be careful, this command always requires
1659 confirmation with @kbd{yes}. Note also that this command is disabled
1660 under CVS, because canceling versions is very dangerous and discouraged
1664 @subsubsection Dired under VC
1668 @cindex CVS Dired Mode
1669 The VC Dired Mode described here works with all the version control
1670 systems that VC supports. Another more powerful facility, designed
1671 specifically for CVS, is called PCL-CVS. @xref{Top, , About PCL-CVS,
1672 pcl-cvs, PCL-CVS --- The Emacs Front-End to CVS}.
1675 @findex vc-directory
1676 When you are working on a large program, it is often useful to find
1677 out which files have changed within an entire directory tree, or to view
1678 the status of all files under version control at once, and to perform
1679 version control operations on collections of files. You can use the
1680 command @kbd{C-x v d} (@code{vc-directory}) to make a directory listing
1681 that includes only files relevant for version control.
1683 @vindex vc-dired-terse-display
1684 @kbd{C-x v d} creates a buffer which uses VC Dired Mode. This looks
1685 much like an ordinary Dired buffer (@pxref{Dired}); however, normally it
1686 shows only the noteworthy files (those locked or not up-to-date). This
1687 is called @dfn{terse display}. If you set the variable
1688 @code{vc-dired-terse-display} to @code{nil}, then VC Dired shows all
1689 relevant files---those managed under version control, plus all
1690 subdirectories (@dfn{full display}). The command @kbd{v t} in a VC
1691 Dired buffer toggles between terse display and full display (@pxref{VC
1694 @vindex vc-dired-recurse
1695 By default, VC Dired produces a recursive listing of noteworthy or
1696 relevant files at or below the given directory. You can change this by
1697 setting the variable @code{vc-dired-recurse} to @code{nil}; then VC
1698 Dired shows only the files in the given directory.
1700 The line for an individual file shows the version control state in the
1701 place of the hard link count, owner, group, and size of the file. If
1702 the file is unmodified, in sync with the master file, the version
1703 control state shown is blank. Otherwise it consists of text in
1704 parentheses. Under RCS and SCCS, the name of the user locking the file
1705 is shown; under CVS, an abbreviated version of the @samp{cvs status}
1706 output is used. Here is an example using RCS:
1712 -rw-r--r-- (jim) Apr 2 23:39 file1
1713 -r--r--r-- Apr 5 20:21 file2
1718 The files @samp{file1} and @samp{file2} are under version control,
1719 @samp{file1} is locked by user jim, and @samp{file2} is unlocked.
1721 Here is an example using CVS:
1727 -rw-r--r-- (modified) Aug 2 1997 file1.c
1728 -rw-r--r-- Apr 4 20:09 file2.c
1729 -rw-r--r-- (merge) Sep 13 1996 file3.c
1733 Here @samp{file1.c} is modified with respect to the repository, and
1734 @samp{file2.c} is not. @samp{file3.c} is modified, but other changes
1735 have also been checked in to the repository---you need to merge them
1736 with the work file before you can check it in.
1738 @vindex vc-directory-exclusion-list
1739 When VC Dired displays subdirectories (in the ``full'' display mode),
1740 it omits some that should never contain any files under version control.
1741 By default, this includes Version Control subdirectories such as
1742 @samp{RCS} and @samp{CVS}; you can customize this by setting the
1743 variable @code{vc-directory-exclusion-list}.
1745 You can fine-tune VC Dired's format by typing @kbd{C-u C-x v d}---as in
1746 ordinary Dired, that allows you to specify additional switches for the
1749 @node VC Dired Commands
1750 @subsubsection VC Dired Commands
1752 All the usual Dired commands work normally in VC Dired mode, except
1753 for @kbd{v}, which is redefined as the version control prefix. You can
1754 invoke VC commands such as @code{vc-diff} and @code{vc-print-log} by
1755 typing @kbd{v =}, or @kbd{v l}, and so on. Most of these commands apply
1756 to the file name on the current line.
1758 The command @kbd{v v} (@code{vc-next-action}) operates on all the
1759 marked files, so that you can lock or check in several files at once.
1760 If it operates on more than one file, it handles each file according to
1761 its current state; thus, it might lock one file, but check in another
1762 file. This could be confusing; it is up to you to avoid confusing
1763 behavior by marking a set of files that are in a similar state.
1765 If any files call for check-in, @kbd{v v} reads a single log entry,
1766 then uses it for all the files being checked in. This is convenient for
1767 registering or checking in several files at once, as part of the same
1770 @findex vc-dired-toggle-terse-mode
1771 @findex vc-dired-mark-locked
1772 You can toggle between terse display (only locked files, or files not
1773 up-to-date) and full display at any time by typing @kbd{v t}
1774 (@code{vc-dired-toggle-terse-mode}). There is also a special command
1775 @kbd{* l} (@code{vc-dired-mark-locked}), which marks all files currently
1776 locked (or, with CVS, all files not up-to-date). Thus, typing @kbd{* l
1777 t k} is another way to delete from the buffer all files except those
1781 @subsection Multiple Branches of a File
1782 @cindex branch (version control)
1783 @cindex trunk (version control)
1785 One use of version control is to maintain multiple ``current''
1786 versions of a file. For example, you might have different versions of a
1787 program in which you are gradually adding various unfinished new
1788 features. Each such independent line of development is called a
1789 @dfn{branch}. VC allows you to create branches, switch between
1790 different branches, and merge changes from one branch to another.
1791 Please note, however, that branches are only supported for RCS at the
1794 A file's main line of development is usually called the @dfn{trunk}.
1795 The versions on the trunk are normally numbered 1.1, 1.2, 1.3, etc. At
1796 any such version, you can start an independent branch. A branch
1797 starting at version 1.2 would have version number 1.2.1.1, and consecutive
1798 versions on this branch would have numbers 1.2.1.2, 1.2.1.3, 1.2.1.4,
1799 and so on. If there is a second branch also starting at version 1.2, it
1800 would consist of versions 1.2.2.1, 1.2.2.2, 1.2.2.3, etc.
1802 @cindex head version
1803 If you omit the final component of a version number, that is called a
1804 @dfn{branch number}. It refers to the highest existing version on that
1805 branch---the @dfn{head version} of that branch. The branches in the
1806 example above have branch numbers 1.2.1 and 1.2.2.
1809 * Switching Branches:: How to get to another existing branch.
1810 * Creating Branches:: How to start a new branch.
1811 * Merging:: Transferring changes between branches.
1812 * Multi-User Branching:: Multiple users working at multiple branches
1816 @node Switching Branches
1817 @subsubsection Switching between Branches
1819 To switch between branches, type @kbd{C-u C-x C-q} and specify the
1820 version number you want to select. This version is then visited
1821 @emph{unlocked} (write-protected), so you can examine it before locking
1822 it. Switching branches in this way is allowed only when the file is not
1825 You can omit the minor version number, thus giving only the branch
1826 number; this takes you to the head version on the chosen branch. If you
1827 only type @key{RET}, Emacs goes to the highest version on the trunk.
1829 After you have switched to any branch (including the main branch), you
1830 stay on it for subsequent VC commands, until you explicitly select some
1833 @node Creating Branches
1834 @subsubsection Creating New Branches
1836 To create a new branch from a head version (one that is the latest in
1837 the branch that contains it), first select that version if necessary,
1838 lock it with @kbd{C-x C-q}, and make whatever changes you want. Then,
1839 when you check in the changes, use @kbd{C-u C-x C-q}. This lets you
1840 specify the version number for the new version. You should specify a
1841 suitable branch number for a branch starting at the current version.
1842 For example, if the current version is 2.5, the branch number should be
1843 2.5.1, 2.5.2, and so on, depending on the number of existing branches at
1846 To create a new branch at an older version (one that is no longer the
1847 head of a branch), first select that version (@pxref{Switching
1848 Branches}), then lock it with @kbd{C-x C-q}. You'll be asked to
1849 confirm, when you lock the old version, that you really mean to create a
1850 new branch---if you say no, you'll be offered a chance to lock the
1851 latest version instead.
1853 Then make your changes and type @kbd{C-x C-q} again to check in a new
1854 version. This automatically creates a new branch starting from the
1855 selected version. You need not specially request a new branch, because
1856 that's the only way to add a new version at a point that is not the head
1859 After the branch is created, you ``stay'' on it. That means that
1860 subsequent check-ins create new versions on that branch. To leave the
1861 branch, you must explicitly select a different version with @kbd{C-u C-x
1862 C-q}. To transfer changes from one branch to another, use the merge
1863 command, described in the next section.
1866 @subsubsection Merging Branches
1868 @cindex merging changes
1869 When you have finished the changes on a certain branch, you will
1870 often want to incorporate them into the file's main line of development
1871 (the trunk). This is not a trivial operation, because development might
1872 also have proceeded on the trunk, so that you must @dfn{merge} the
1873 changes into a file that has already been changed otherwise. VC allows
1874 you to do this (and other things) with the @code{vc-merge} command.
1877 @item C-x v m (vc-merge)
1878 Merge changes into the work file.
1883 @kbd{C-x v m} (@code{vc-merge}) takes a set of changes and merges it
1884 into the current version of the work file. It firsts asks you in the
1885 minibuffer where the changes should come from. If you just type
1886 @key{RET}, Emacs merges any changes that were made on the same branch
1887 since you checked the file out (we call this @dfn{merging the news}).
1888 This is the common way to pick up recent changes from the repository,
1889 regardless of whether you have already changed the file yourself.
1891 You can also enter a branch number or a pair of version numbers in
1892 the minibuffer. Then @kbd{C-x v m} finds the changes from that
1893 branch, or the differences between the two versions you specified, and
1894 merges them into the current version of the current file.
1896 As an example, suppose that you have finished a certain feature on
1897 branch 1.3.1. In the meantime, development on the trunk has proceeded
1898 to version 1.5. To merge the changes from the branch to the trunk,
1899 first go to the head version of the trunk, by typing @kbd{C-u C-x C-q
1900 @key{RET}}. Version 1.5 is now current. If locking is used for the file,
1901 type @kbd{C-x C-q} to lock version 1.5 so that you can change it. Next,
1902 type @kbd{C-x v m 1.3.1 @key{RET}}. This takes the entire set of changes on
1903 branch 1.3.1 (relative to version 1.3, where the branch started, up to
1904 the last version on the branch) and merges it into the current version
1905 of the work file. You can now check in the changed file, thus creating
1906 version 1.6 containing the changes from the branch.
1908 It is possible to do further editing after merging the branch, before
1909 the next check-in. But it is usually wiser to check in the merged
1910 version, then lock it and make the further changes. This will keep
1911 a better record of the history of changes.
1914 @cindex resolving conflicts
1915 When you merge changes into a file that has itself been modified, the
1916 changes might overlap. We call this situation a @dfn{conflict}, and
1917 reconciling the conflicting changes is called @dfn{resolving a
1920 Whenever conflicts occur during merging, VC detects them, tells you
1921 about them in the echo area, and asks whether you want help in merging.
1922 If you say yes, it starts an Ediff session (@pxref{Top,
1923 Ediff, Ediff, ediff, The Ediff Manual}).
1925 If you say no, the conflicting changes are both inserted into the
1926 file, surrounded by @dfn{conflict markers}. The example below shows how
1927 a conflict region looks; the file is called @samp{name} and the current
1928 master file version with user B's changes in it is 1.11.
1930 @c @w here is so CVS won't think this is a conflict.
1934 @var{User A's version}
1936 @var{User B's version}
1941 @cindex vc-resolve-conflicts
1942 Then you can resolve the conflicts by editing the file manually. Or
1943 you can type @code{M-x vc-resolve-conflicts} after visiting the file.
1944 This starts an Ediff session, as described above. Don't forget to
1945 check in the merged version afterwards.
1947 @node Multi-User Branching
1948 @subsubsection Multi-User Branching
1950 It is often useful for multiple developers to work simultaneously on
1951 different branches of a file. CVS allows this by default; for RCS, it
1952 is possible if you create multiple source directories. Each source
1953 directory should have a link named @file{RCS} which points to a common
1954 directory of RCS master files. Then each source directory can have its
1955 own choice of selected versions, but all share the same common RCS
1958 This technique works reliably and automatically, provided that the
1959 source files contain RCS version headers (@pxref{Version Headers}). The
1960 headers enable Emacs to be sure, at all times, which version number is
1961 present in the work file.
1963 If the files do not have version headers, you must instead tell Emacs
1964 explicitly in each session which branch you are working on. To do this,
1965 first find the file, then type @kbd{C-u C-x C-q} and specify the correct
1966 branch number. This ensures that Emacs knows which branch it is using
1967 during this particular editing session.
1969 @node Remote Repositories
1970 @subsection Remote Repositories
1971 @cindex remote repositories (CVS)
1973 A common way of using CVS is to set up a central CVS repository on
1974 some Internet host, then have each developer check out a personal
1975 working copy of the files on his local machine. Committing changes to
1976 the repository, and picking up changes from other users into one's own
1977 working area, then works by direct interactions with the CVS server.
1979 One difficulty is that access to the CVS server is often slow, and
1980 that developers might need to work off-line as well. VC is designed
1981 to reduce the amount of network interaction necessary.
1984 * Version Backups:: Keeping local copies of repository versions.
1985 * Local Version Control:: Using another version system for local editing.
1988 @node Version Backups
1989 @subsubsection Version Backups
1990 @cindex version backups
1992 @cindex automatic version backups
1993 When VC sees that the CVS repository for a file is on a remote
1994 machine, it automatically makes local backups of unmodified versions
1995 of the file---@dfn{automatic version backups}. This means that you
1996 can compare the file to the repository version (@kbd{C-x v =}), or
1997 revert to that version (@kbd{C-x v u}), without any network
2000 The local copy of the unmodified file is called a @dfn{version
2001 backup} to indicate that it corresponds exactly to a version that is
2002 stored in the repository. Note that version backups are not the same
2003 as ordinary Emacs backup files (@pxref{Backup}). But they follow a
2004 similar naming convention.
2006 For a file that comes from a remote CVS repository, VC makes a
2007 version backup whenever you save the first changes to the file, and
2008 removes it after you have committed your modified version to the
2009 repository. You can disable the making of automatic version backups by
2010 setting @code{vc-cvs-stay-local} to @code{nil} (@pxref{CVS Options}).
2012 @cindex manual version backups
2013 The name of the automatic version backup for version @var{version}
2014 of file @var{file} is @code{@var{file}.~@var{version}.~}. This is
2015 almost the same as the name used by @kbd{C-x v ~} (@pxref{Old
2016 Versions}), the only difference being the additional dot (@samp{.})
2017 after the version number. This similarity is intentional, because
2018 both kinds of files store the same kind of information. The file made
2019 by @kbd{C-x v ~} acts as a @dfn{manual version backup}.
2021 All the VC commands that operate on old versions of a file can use
2022 both kinds of version backups. For instance, @kbd{C-x v ~} uses
2023 either an automatic or a manual version backup, if possible, to get
2024 the contents of the version you request. Likewise, @kbd{C-x v =} and
2025 @kbd{C-x v u} use either an automatic or a manual version backup, if
2026 one of them exists, to get the contents of a version to compare or
2027 revert to. If you changed a file outside of Emacs, so that no
2028 automatic version backup was created for the previous text, you can
2029 create a manual backup of that version using @kbd{C-x v ~}, and thus
2030 obtain the benefit of the local copy for Emacs commands.
2032 The only difference in Emacs's handling of manual and automatic
2033 version backups, once they exist, is that Emacs deletes automatic
2034 version backups when you commit to the repository. By contrast,
2035 manual version backups remain until you delete them.
2037 @node Local Version Control
2038 @subsubsection Local Version Control
2039 @cindex local version control
2040 @cindex local back end (version control)
2042 When you make many changes to a file that comes from a remote
2043 repository, it can be convenient to have version control on your local
2044 machine as well. You can then record intermediate versions, revert to
2045 a previous state, etc., before you actually commit your changes to the
2048 VC lets you do this by putting a file under a second, local version
2049 control system, so that the file is effectively registered in two
2050 systems at the same time. For the description here, we will assume
2051 that the remote system is CVS, and you use RCS locally, although the
2052 mechanism works with any combination of version control systems
2055 To make it work with other back ends, you must make sure that the
2056 ``more local'' back end comes before the ``more remote'' back end in
2057 the setting of @code{vc-handled-backends} (@pxref{Customizing VC}). By
2058 default, this variable is set up so that you can use remote CVS and
2059 local RCS as described here.
2061 To start using local RCS for a file that comes from a remote CVS
2062 server, you must @emph{register the file in RCS}, by typing @kbd{C-u
2063 C-x v v rcs @key{RET}}. (In other words, use @code{vc-next-action} with a
2064 prefix argument, and specify RCS as the back end.)
2066 You can do this at any time; it does not matter whether you have
2067 already modified the file with respect to the version in the CVS
2068 repository. If possible, VC tries to make the RCS master start with
2069 the unmodified repository version, then checks in any local changes
2070 as a new version. This works if you have not made any changes yet, or
2071 if the unmodified repository version exists locally as a version
2072 backup (@pxref{Version Backups}). If the unmodified version is not
2073 available locally, the RCS master starts with the modified version;
2074 the only drawback to this is that you cannot compare your changes
2075 locally to what is stored in the repository.
2077 The version number of the RCS master is derived from the current CVS
2078 version, starting a branch from it. For example, if the current CVS
2079 version is 1.23, the local RCS branch will be 1.23.1. Version 1.23 in
2080 the RCS master will be identical to version 1.23 under CVS; your first
2081 changes are checked in as 1.23.1.1. (If the unmodified file is not
2082 available locally, VC will check in the modified file twice, both as
2083 1.23 and 1.23.1.1, to make the revision numbers consistent.)
2085 If you do not use locking under CVS (the default), locking is also
2086 disabled for RCS, so that editing under RCS works exactly as under
2089 When you are done with local editing, you can commit the final version
2090 back to the CVS repository by typing @kbd{C-u C-x v v cvs @key{RET}}.
2091 This initializes the log entry buffer (@pxref{Log Buffer}) to contain
2092 all the log entries you have recorded in the RCS master; you can edit
2093 them as you wish, and then commit in CVS by typing @kbd{C-c C-c}. If
2094 the commit is successful, VC removes the RCS master, so that the file
2095 is once again registered under CVS only. (The RCS master is not
2096 actually deleted, just renamed by appending @samp{~} to the name, so
2097 that you can refer to it later if you wish.)
2099 While using local RCS, you can pick up recent changes from the CVS
2100 repository into your local file, or commit some of your changes back
2101 to CVS, without terminating local RCS version control. To do this,
2102 switch to the CVS back end temporarily, with the @kbd{C-x v b} command:
2106 Switch to another back end that the current file is registered
2107 under (@code{vc-switch-backend}).
2109 @item C-u C-x v b @var{backend} @key{RET}
2110 Switch to @var{backend} for the current file.
2114 @findex vc-switch-backend
2115 @kbd{C-x v b} does not change the buffer contents, or any files; it
2116 only changes VC's perspective on how to handle the file. Any
2117 subsequent VC commands for that file will operate on the back end that
2118 is currently selected.
2120 If the current file is registered in more than one back end, typing
2121 @kbd{C-x v b} ``cycles'' through all of these back ends. With a
2122 prefix argument, it asks for the back end to use in the minibuffer.
2124 Thus, if you are using local RCS, and you want to pick up some recent
2125 changes in the file from remote CVS, first visit the file, then type
2126 @kbd{C-x v b} to switch to CVS, and finally use @kbd{C-x v m
2127 @key{RET}} to merge the news (@pxref{Merging}). You can then switch
2128 back to RCS by typing @kbd{C-x v b} again, and continue to edit
2131 But if you do this, the revision numbers in the RCS master no longer
2132 correspond to those of CVS. Technically, this is not a problem, but
2133 it can become difficult to keep track of what is in the CVS repository
2134 and what is not. So we suggest that you return from time to time to
2135 CVS-only operation, using @kbd{C-u C-x v v cvs @key{RET}}.
2138 @subsection Snapshots
2139 @cindex snapshots and version control
2141 A @dfn{snapshot} is a named set of file versions (one for each
2142 registered file) that you can treat as a unit. One important kind of
2143 snapshot is a @dfn{release}, a (theoretically) stable version of the
2144 system that is ready for distribution to users.
2147 * Making Snapshots:: The snapshot facilities.
2148 * Snapshot Caveats:: Things to be careful of when using snapshots.
2151 @node Making Snapshots
2152 @subsubsection Making and Using Snapshots
2154 There are two basic commands for snapshots; one makes a
2155 snapshot with a given name, the other retrieves a named snapshot.
2159 @findex vc-create-snapshot
2160 @item C-x v s @var{name} @key{RET}
2161 Define the last saved versions of every registered file in or under the
2162 current directory as a snapshot named @var{name}
2163 (@code{vc-create-snapshot}).
2166 @findex vc-retrieve-snapshot
2167 @item C-x v r @var{name} @key{RET}
2168 For all registered files at or below the current directory level, select
2169 whatever versions correspond to the snapshot @var{name}
2170 (@code{vc-retrieve-snapshot}).
2172 This command reports an error if any files are locked at or below the
2173 current directory, without changing anything; this is to avoid
2174 overwriting work in progress.
2177 A snapshot uses a very small amount of resources---just enough to record
2178 the list of file names and which version belongs to the snapshot. Thus,
2179 you need not hesitate to create snapshots whenever they are useful.
2181 You can give a snapshot name as an argument to @kbd{C-x v =} or
2182 @kbd{C-x v ~} (@pxref{Old Versions}). Thus, you can use it to compare a
2183 snapshot against the current files, or two snapshots against each other,
2184 or a snapshot against a named version.
2186 @node Snapshot Caveats
2187 @subsubsection Snapshot Caveats
2189 @cindex named configurations (RCS)
2190 VC's snapshot facilities are modeled on RCS's named-configuration
2191 support. They use RCS's native facilities for this, so under VC
2192 snapshots made using RCS are visible even when you bypass VC.
2194 @c worded verbosely to avoid overfull hbox.
2195 For SCCS, VC implements snapshots itself. The files it uses contain
2196 name/file/version-number triples. These snapshots are visible only
2199 A snapshot is a set of checked-in versions. So make sure that all the
2200 files are checked in and not locked when you make a snapshot.
2202 File renaming and deletion can create some difficulties with snapshots.
2203 This is not a VC-specific problem, but a general design issue in version
2204 control systems that no one has solved very well yet.
2206 If you rename a registered file, you need to rename its master along
2207 with it (the command @code{vc-rename-file} does this automatically). If
2208 you are using SCCS, you must also update the records of the snapshot, to
2209 mention the file by its new name (@code{vc-rename-file} does this,
2210 too). An old snapshot that refers to a master file that no longer
2211 exists under the recorded name is invalid; VC can no longer retrieve
2212 it. It would be beyond the scope of this manual to explain enough about
2213 RCS and SCCS to explain how to update the snapshots by hand.
2215 Using @code{vc-rename-file} makes the snapshot remain valid for
2216 retrieval, but it does not solve all problems. For example, some of the
2217 files in your program probably refer to others by name. At the very
2218 least, the makefile probably mentions the file that you renamed. If you
2219 retrieve an old snapshot, the renamed file is retrieved under its new
2220 name, which is not the name that the makefile expects. So the program
2221 won't really work as retrieved.
2223 @node Miscellaneous VC
2224 @subsection Miscellaneous Commands and Features of VC
2226 This section explains the less-frequently-used features of VC.
2229 * Change Logs and VC:: Generating a change log file from log entries.
2230 * Renaming and VC:: A command to rename both the source and master
2232 * Version Headers:: Inserting version control headers into working files.
2235 @node Change Logs and VC
2236 @subsubsection Change Logs and VC
2238 If you use RCS or CVS for a program and also maintain a change log
2239 file for it (@pxref{Change Log}), you can generate change log entries
2240 automatically from the version control log entries:
2245 @findex vc-update-change-log
2246 Visit the current directory's change log file and, for registered files
2247 in that directory, create new entries for versions checked in since the
2248 most recent entry in the change log file.
2249 (@code{vc-update-change-log}).
2251 This command works with RCS or CVS only, not with SCCS.
2254 As above, but only find entries for the current buffer's file.
2257 As above, but find entries for all the currently visited files that are
2258 maintained with version control. This works only with RCS, and it puts
2259 all entries in the log for the default directory, which may not be
2263 For example, suppose the first line of @file{ChangeLog} is dated
2264 1999-04-10, and that the only check-in since then was by Nathaniel
2265 Bowditch to @file{rcs2log} on 1999-05-22 with log text @samp{Ignore log
2266 messages that start with `#'.}. Then @kbd{C-x v a} visits
2267 @file{ChangeLog} and inserts text like this:
2274 1999-05-22 Nathaniel Bowditch <nat@@apn.org>
2276 * rcs2log: Ignore log messages that start with `#'.
2284 You can then edit the new change log entry further as you wish.
2286 Some of the new change log entries may duplicate what's already in
2287 ChangeLog. You will have to remove these duplicates by hand.
2289 Normally, the log entry for file @file{foo} is displayed as @samp{*
2290 foo: @var{text of log entry}}. The @samp{:} after @file{foo} is omitted
2291 if the text of the log entry starts with @w{@samp{(@var{functionname}):
2292 }}. For example, if the log entry for @file{vc.el} is
2293 @samp{(vc-do-command): Check call-process status.}, then the text in
2294 @file{ChangeLog} looks like this:
2301 1999-05-06 Nathaniel Bowditch <nat@@apn.org>
2303 * vc.el (vc-do-command): Check call-process status.
2310 When @kbd{C-x v a} adds several change log entries at once, it groups
2311 related log entries together if they all are checked in by the same
2312 author at nearly the same time. If the log entries for several such
2313 files all have the same text, it coalesces them into a single entry.
2314 For example, suppose the most recent check-ins have the following log
2318 @bullet{} For @file{vc.texinfo}: @samp{Fix expansion typos.}
2319 @bullet{} For @file{vc.el}: @samp{Don't call expand-file-name.}
2320 @bullet{} For @file{vc-hooks.el}: @samp{Don't call expand-file-name.}
2324 They appear like this in @file{ChangeLog}:
2331 1999-04-01 Nathaniel Bowditch <nat@@apn.org>
2333 * vc.texinfo: Fix expansion typos.
2335 * vc.el, vc-hooks.el: Don't call expand-file-name.
2342 Normally, @kbd{C-x v a} separates log entries by a blank line, but you
2343 can mark several related log entries to be clumped together (without an
2344 intervening blank line) by starting the text of each related log entry
2345 with a label of the form @w{@samp{@{@var{clumpname}@} }}. The label
2346 itself is not copied to @file{ChangeLog}. For example, suppose the log
2350 @bullet{} For @file{vc.texinfo}: @samp{@{expand@} Fix expansion typos.}
2351 @bullet{} For @file{vc.el}: @samp{@{expand@} Don't call expand-file-name.}
2352 @bullet{} For @file{vc-hooks.el}: @samp{@{expand@} Don't call expand-file-name.}
2356 Then the text in @file{ChangeLog} looks like this:
2363 1999-04-01 Nathaniel Bowditch <nat@@apn.org>
2365 * vc.texinfo: Fix expansion typos.
2366 * vc.el, vc-hooks.el: Don't call expand-file-name.
2373 A log entry whose text begins with @samp{#} is not copied to
2374 @file{ChangeLog}. For example, if you merely fix some misspellings in
2375 comments, you can log the change with an entry beginning with @samp{#}
2376 to avoid putting such trivia into @file{ChangeLog}.
2378 @node Renaming and VC
2379 @subsubsection Renaming VC Work Files and Master Files
2381 @findex vc-rename-file
2382 When you rename a registered file, you must also rename its master
2383 file correspondingly to get proper results. Use @code{vc-rename-file}
2384 to rename the source file as you specify, and rename its master file
2385 accordingly. It also updates any snapshots (@pxref{Snapshots}) that
2386 mention the file, so that they use the new name; despite this, the
2387 snapshot thus modified may not completely work (@pxref{Snapshot
2390 You cannot use @code{vc-rename-file} on a file that is locked by
2393 @node Version Headers
2394 @subsubsection Inserting Version Control Headers
2396 Sometimes it is convenient to put version identification strings
2397 directly into working files. Certain special strings called
2398 @dfn{version headers} are replaced in each successive version by the
2399 number of that version.
2401 If you are using RCS, and version headers are present in your working
2402 files, Emacs can use them to determine the current version and the
2403 locking state of the files. This is more reliable than referring to the
2404 master files, which is done when there are no version headers. Note
2405 that in a multi-branch environment, version headers are necessary to
2406 make VC behave correctly (@pxref{Multi-User Branching}).
2408 Searching for version headers is controlled by the variable
2409 @code{vc-consult-headers}. If it is non-@code{nil} (the default),
2410 Emacs searches for headers to determine the version number you are
2411 editing. Setting it to @code{nil} disables this feature.
2414 @findex vc-insert-headers
2415 You can use the @kbd{C-x v h} command (@code{vc-insert-headers}) to
2416 insert a suitable header string.
2420 Insert headers in a file for use with your version-control system.
2423 @vindex vc-header-alist
2424 The default header string is @samp{@w{$}Id$} for RCS and
2425 @samp{@w{%}W%} for SCCS. You can specify other headers to insert by
2426 setting the variable @code{vc-header-alist}. Its value is a list of
2427 elements of the form @code{(@var{program} . @var{string})} where
2428 @var{program} is @code{RCS} or @code{SCCS} and @var{string} is the
2431 Instead of a single string, you can specify a list of strings; then
2432 each string in the list is inserted as a separate header on a line of
2435 It is often necessary to use ``superfluous'' backslashes when
2436 writing the strings that you put in this variable. For instance, you
2437 might write @code{"$Id\$"} rather than @code{"$Id@w{$}"}. The extra
2438 backslash prevents the string constant from being interpreted as a
2439 header, if the Emacs Lisp file containing it is maintained with
2442 @vindex vc-comment-alist
2443 Each header is inserted surrounded by tabs, inside comment delimiters,
2444 on a new line at point. Normally the ordinary comment
2445 start and comment end strings of the current mode are used, but for
2446 certain modes, there are special comment delimiters for this purpose;
2447 the variable @code{vc-comment-alist} specifies them. Each element of
2448 this list has the form @code{(@var{mode} @var{starter} @var{ender})}.
2450 @vindex vc-static-header-alist
2451 The variable @code{vc-static-header-alist} specifies further strings
2452 to add based on the name of the buffer. Its value should be a list of
2453 elements of the form @code{(@var{regexp} . @var{format})}. Whenever
2454 @var{regexp} matches the buffer name, @var{format} is inserted as part
2455 of the header. A header line is inserted for each element that matches
2456 the buffer name, and for each string specified by
2457 @code{vc-header-alist}. The header line is made by processing the
2458 string from @code{vc-header-alist} with the format taken from the
2459 element. The default value for @code{vc-static-header-alist} is as follows:
2464 "\n#ifndef lint\nstatic char vcid[] = \"\%s\";\n\
2465 #endif /* lint */\n"))
2470 It specifies insertion of text of this form:
2476 static char vcid[] = "@var{string}";
2482 Note that the text above starts with a blank line.
2484 If you use more than one version header in a file, put them close
2485 together in the file. The mechanism in @code{revert-buffer} that
2486 preserves markers may not handle markers positioned between two version
2489 @node Customizing VC
2490 @subsection Customizing VC
2492 @vindex vc-handled-backends
2493 The variable @code{vc-handled-backends} determines which version
2494 control systems VC should handle. The default value is @code{(RCS CVS
2495 SCCS)}, so it contains all three version systems that are currently
2496 supported. If you want VC to ignore one or more of these systems,
2497 exclude its name from the list.
2499 The order of systems in the list is significant: when you visit a file
2500 registered in more than one system (@pxref{Local Version Control}),
2501 VC uses the system that comes first in @code{vc-handled-backends} by
2502 default. The order is also significant when you register a file for
2503 the first time, @pxref{Registering} for details.
2506 * General VC Options:: Options that apply to multiple back ends.
2507 * RCS and SCCS:: Options for RCS and SCCS.
2508 * CVS Options:: Options for CVS.
2511 @node General VC Options
2512 @subsubsection General Options
2514 @vindex vc-make-backup-files
2515 Emacs normally does not save backup files for source files that are
2516 maintained with version control. If you want to make backup files even
2517 for files that use version control, set the variable
2518 @code{vc-make-backup-files} to a non-@code{nil} value.
2520 @vindex vc-keep-workfiles
2521 Normally the work file exists all the time, whether it is locked or
2522 not. If you set @code{vc-keep-workfiles} to @code{nil}, then checking
2523 in a new version with @kbd{C-x C-q} deletes the work file; but any
2524 attempt to visit the file with Emacs creates it again. (With CVS, work
2525 files are always kept.)
2527 @vindex vc-follow-symlinks
2528 Editing a version-controlled file through a symbolic link can be
2529 dangerous. It bypasses the version control system---you can edit the
2530 file without locking it, and fail to check your changes in. Also,
2531 your changes might overwrite those of another user. To protect against
2532 this, VC checks each symbolic link that you visit, to see if it points
2533 to a file under version control.
2535 The variable @code{vc-follow-symlinks} controls what to do when a
2536 symbolic link points to a version-controlled file. If it is @code{nil},
2537 VC only displays a warning message. If it is @code{t}, VC automatically
2538 follows the link, and visits the real file instead, telling you about
2539 this in the echo area. If the value is @code{ask} (the default), VC
2540 asks you each time whether to follow the link.
2542 @vindex vc-suppress-confirm
2543 If @code{vc-suppress-confirm} is non-@code{nil}, then @kbd{C-x C-q}
2544 and @kbd{C-x v i} can save the current buffer without asking, and
2545 @kbd{C-x v u} also operates without asking for confirmation. (This
2546 variable does not affect @kbd{C-x v c}; that operation is so drastic
2547 that it should always ask for confirmation.)
2549 @vindex vc-command-messages
2550 VC mode does much of its work by running the shell commands for RCS,
2551 CVS and SCCS. If @code{vc-command-messages} is non-@code{nil}, VC
2552 displays messages to indicate which shell commands it runs, and
2553 additional messages when the commands finish.
2556 You can specify additional directories to search for version control
2557 programs by setting the variable @code{vc-path}. These directories
2558 are searched before the usual search path. It is rarely necessary to
2559 set this variable, because VC normally finds the proper files
2563 @subsubsection Options for RCS and SCCS
2565 @cindex non-strict locking (RCS)
2566 @cindex locking, non-strict (RCS)
2567 By default, RCS uses locking to coordinate the activities of several
2568 users, but there is a mode called @dfn{non-strict locking} in which
2569 you can check-in changes without locking the file first. Use
2570 @samp{rcs -U} to switch to non-strict locking for a particular file,
2571 see the @code{rcs} manual page for details.
2573 When deducing the version control state of an RCS file, VC first
2574 looks for an RCS version header string in the file (@pxref{Version
2575 Headers}). If there is no header string, VC normally looks at the
2576 file permissions of the work file; this is fast. But there might be
2577 situations when the file permissions cannot be trusted. In this case
2578 the master file has to be consulted, which is rather expensive. Also
2579 the master file can only tell you @emph{if} there's any lock on the
2580 file, but not whether your work file really contains that locked
2583 @vindex vc-consult-headers
2584 You can tell VC not to use version headers to determine the file
2585 status by setting @code{vc-consult-headers} to @code{nil}. VC then
2586 always uses the file permissions (if it is supposed to trust them), or
2587 else checks the master file.
2589 @vindex vc-mistrust-permissions
2590 You can specify the criterion for whether to trust the file
2591 permissions by setting the variable @code{vc-mistrust-permissions}.
2592 Its value can be @code{t} (always mistrust the file permissions and
2593 check the master file), @code{nil} (always trust the file
2594 permissions), or a function of one argument which makes the decision.
2595 The argument is the directory name of the @file{RCS} subdirectory. A
2596 non-@code{nil} value from the function says to mistrust the file
2597 permissions. If you find that the file permissions of work files are
2598 changed erroneously, set @code{vc-mistrust-permissions} to @code{t}.
2599 Then VC always checks the master file to determine the file's status.
2601 VC determines the version control state of files under SCCS much as
2602 with RCS. It does not consider SCCS version headers, though. Thus,
2603 the variable @code{vc-mistrust-permissions} affects SCCS use, but
2604 @code{vc-consult-headers} does not.
2607 @subsubsection Options specific for CVS
2609 @cindex locking (CVS)
2610 By default, CVS does not use locking to coordinate the activities of
2611 several users; anyone can change a work file at any time. However,
2612 there are ways to restrict this, resulting in behavior that resembles
2615 @cindex CVSREAD environment variable (CVS)
2616 For one thing, you can set the @env{CVSREAD} environment variable
2617 (the value you use makes no difference). If this variable is defined,
2618 CVS makes your work files read-only by default. In Emacs, you must
2619 type @kbd{C-x C-q} to make the file writable, so that editing works
2620 in fact similar as if locking was used. Note however, that no actual
2621 locking is performed, so several users can make their files writable
2622 at the same time. When setting @env{CVSREAD} for the first time, make
2623 sure to check out all your modules anew, so that the file protections
2626 @cindex cvs watch feature
2627 @cindex watching files (CVS)
2628 Another way to achieve something similar to locking is to use the
2629 @dfn{watch} feature of CVS. If a file is being watched, CVS makes it
2630 read-only by default, and you must also use @kbd{C-x C-q} in Emacs to
2631 make it writable. VC calls @code{cvs edit} to make the file writable,
2632 and CVS takes care to notify other developers of the fact that you
2633 intend to change the file. See the CVS documentation for details on
2634 using the watch feature.
2636 @vindex vc-cvs-stay-local
2637 @cindex remote repositories (CVS)
2638 When a file's repository is on a remote machine, VC tries to keep
2639 network interactions to a minimum. This is controlled by the variable
2640 @code{vc-cvs-stay-local}. If it is @code{t} (the default), then VC uses
2641 only the entry in the local CVS subdirectory to determine the file's
2642 state (and possibly information returned by previous CVS commands). One
2643 consequence of this is that when you have modified a file, and somebody
2644 else has already checked in other changes to the file, you are not
2645 notified of it until you actually try to commit. (But you can try to
2646 pick up any recent changes from the repository first, using @kbd{C-x v m
2647 @key{RET}}, @pxref{Merging}).
2649 When @code{vc-cvs-stay-local} is @code{t}, VC also makes local
2650 version backups, so that simple diff and revert operations are
2651 completely local (@pxref{Version Backups}).
2653 On the other hand, if you set @code{vc-cvs-stay-local} to @code{nil},
2654 then VC queries the remote repository @emph{before} it decides what to
2655 do in @code{vc-next-action} (@kbd{C-x v v}), just as it does for local
2656 repositories. It also does not make any version backups.
2658 You can also set @code{vc-cvs-stay-local} to a regular expression
2659 that is matched against the repository host name; VC then stays local
2660 only for repositories from hosts that match the pattern.
2663 @section File Directories
2665 @cindex file directory
2666 @cindex directory listing
2667 The file system groups files into @dfn{directories}. A @dfn{directory
2668 listing} is a list of all the files in a directory. Emacs provides
2669 commands to create and delete directories, and to make directory
2670 listings in brief format (file names only) and verbose format (sizes,
2671 dates, and authors included). There is also a directory browser called
2672 Dired; see @ref{Dired}.
2675 @item C-x C-d @var{dir-or-pattern} @key{RET}
2676 Display a brief directory listing (@code{list-directory}).
2677 @item C-u C-x C-d @var{dir-or-pattern} @key{RET}
2678 Display a verbose directory listing.
2679 @item M-x make-directory @key{RET} @var{dirname} @key{RET}
2680 Create a new directory named @var{dirname}.
2681 @item M-x delete-directory @key{RET} @var{dirname} @key{RET}
2682 Delete the directory named @var{dirname}. It must be empty,
2683 or you get an error.
2686 @findex list-directory
2688 The command to display a directory listing is @kbd{C-x C-d}
2689 (@code{list-directory}). It reads using the minibuffer a file name
2690 which is either a directory to be listed or a wildcard-containing
2691 pattern for the files to be listed. For example,
2694 C-x C-d /u2/emacs/etc @key{RET}
2698 lists all the files in directory @file{/u2/emacs/etc}. Here is an
2699 example of specifying a file name pattern:
2702 C-x C-d /u2/emacs/src/*.c @key{RET}
2705 Normally, @kbd{C-x C-d} displays a brief directory listing containing
2706 just file names. A numeric argument (regardless of value) tells it to
2707 make a verbose listing including sizes, dates, and owners (like
2710 @vindex list-directory-brief-switches
2711 @vindex list-directory-verbose-switches
2712 The text of a directory listing is obtained by running @code{ls} in an
2713 inferior process. Two Emacs variables control the switches passed to
2714 @code{ls}: @code{list-directory-brief-switches} is a string giving the
2715 switches to use in brief listings (@code{"-CF"} by default), and
2716 @code{list-directory-verbose-switches} is a string giving the switches to
2717 use in a verbose listing (@code{"-l"} by default).
2719 @node Comparing Files
2720 @section Comparing Files
2721 @cindex comparing files
2724 @vindex diff-switches
2725 The command @kbd{M-x diff} compares two files, displaying the
2726 differences in an Emacs buffer named @samp{*diff*}. It works by
2727 running the @code{diff} program, using options taken from the variable
2728 @code{diff-switches}. The value of @code{diff-switches} should be a
2729 string; the default is @code{"-c"} to specify a context diff.
2731 The buffer @samp{*diff*} has Compilation mode as its major mode, so
2732 you can use @kbd{C-x `} to visit successive changed locations in the two
2733 source files. You can also move to a particular hunk of changes and
2734 type @key{RET} or @kbd{C-c C-c}, or click @kbd{Mouse-2} on it, to move
2735 to the corresponding source location. You can also use the other
2736 special commands of Compilation mode: @key{SPC} and @key{DEL} for
2737 scrolling, and @kbd{M-p} and @kbd{M-n} for cursor motion.
2741 The command @kbd{M-x diff-backup} compares a specified file with its most
2742 recent backup. If you specify the name of a backup file,
2743 @code{diff-backup} compares it with the source file that it is a backup
2746 @findex compare-windows
2747 The command @kbd{M-x compare-windows} compares the text in the current
2748 window with that in the next window. Comparison starts at point in each
2749 window, and each starting position is pushed on the mark ring in its
2750 respective buffer. Then point moves forward in each window, a character
2751 at a time, until a mismatch between the two windows is reached. Then
2752 the command is finished. For more information about windows in Emacs,
2755 @vindex compare-ignore-case
2756 With a numeric argument, @code{compare-windows} ignores changes in
2757 whitespace. If the variable @code{compare-ignore-case} is
2758 non-@code{nil}, it ignores differences in case as well.
2764 Differences between versions of files are often distributed as
2765 @dfn{patches}, which are the output from @command{diff} or a version
2766 control system that uses @command{diff}. @kbd{M-x diff-mode} turns on
2767 Diff mode, a major mode for viewing and editing patches, either as
2768 ``unified diffs'' or ``context diffs.''
2772 @cindex failed merges
2773 @cindex merges, failed
2774 @cindex comparing 3 files (@code{diff3})
2775 You can use @kbd{M-x smerge-mode} to turn on Smerge mode, a minor
2776 mode for editing output from the @command{diff3} program. This is
2777 typically the result of a failed merge from a version control system
2778 ``update'' outside VC, due to conflicting changes to a file. Smerge
2779 mode provides commands to resolve conflicts by selecting specific
2782 See also @ref{Emerge}, and @ref{Top,,, ediff, The Ediff Manual}, for
2783 convenient facilities for merging two similar files.
2786 @section Miscellaneous File Operations
2788 Emacs has commands for performing many other operations on files.
2789 All operate on one file; they do not accept wildcard file names.
2795 @kbd{M-x view-file} allows you to scan or read a file by sequential
2796 screenfuls. It reads a file name argument using the minibuffer. After
2797 reading the file into an Emacs buffer, @code{view-file} displays the
2798 beginning. You can then type @key{SPC} to scroll forward one windowful,
2799 or @key{DEL} to scroll backward. Various other commands are provided
2800 for moving around in the file, but none for changing it; type @kbd{?}
2801 while viewing for a list of them. They are mostly the same as normal
2802 Emacs cursor motion commands. To exit from viewing, type @kbd{q}.
2803 The commands for viewing are defined by a special major mode called View
2806 A related command, @kbd{M-x view-buffer}, views a buffer already present
2807 in Emacs. @xref{Misc Buffer}.
2811 @kbd{M-x insert-file} (also @kbd{C-x i}) inserts a copy of the
2812 contents of the specified file into the current buffer at point,
2813 leaving point unchanged before the contents and the mark after them.
2815 @findex write-region
2816 @kbd{M-x write-region} is the inverse of @kbd{M-x insert-file}; it
2817 copies the contents of the region into the specified file. @kbd{M-x
2818 append-to-file} adds the text of the region to the end of the specified
2819 file. @xref{Accumulating Text}.
2822 @cindex deletion (of files)
2823 @kbd{M-x delete-file} deletes the specified file, like the @code{rm}
2824 command in the shell. If you are deleting many files in one directory, it
2825 may be more convenient to use Dired (@pxref{Dired}).
2828 @kbd{M-x rename-file} reads two file names @var{old} and @var{new} using
2829 the minibuffer, then renames file @var{old} as @var{new}. If the file name
2830 @var{new} already exists, you must confirm with @kbd{yes} or renaming is not
2831 done; this is because renaming causes the old meaning of the name @var{new}
2832 to be lost. If @var{old} and @var{new} are on different file systems, the
2833 file @var{old} is copied and deleted.
2835 @findex add-name-to-file
2836 @cindex hard links (creation)
2837 The similar command @kbd{M-x add-name-to-file} is used to add an
2838 additional name to an existing file without removing its old name.
2839 The new name is created as a ``hard link'' to the existing file.
2840 The new name must belong on the same file system that the file is on.
2841 On Windows, this command works only if the file resides in an NTFS
2842 file system. On MS-DOS, it works by copying the file.
2845 @cindex copying files
2846 @kbd{M-x copy-file} reads the file @var{old} and writes a new file named
2847 @var{new} with the same contents. Confirmation is required if a file named
2848 @var{new} already exists, because copying has the consequence of overwriting
2849 the old contents of the file @var{new}.
2851 @findex make-symbolic-link
2852 @kbd{M-x make-symbolic-link} reads two file names @var{target} and
2853 @var{linkname}, then creates a symbolic link named @var{linkname}, which
2854 points at @var{target}. The effect is that future attempts to open file
2855 @var{linkname} will refer to whatever file is named @var{target} at the
2856 time the opening is done, or will get an error if the name @var{target} is
2857 not in use at that time. This command does not expand the argument
2858 @var{target}, so that it allows you to specify a relative name
2859 as the target of the link.
2861 Confirmation is required when creating the link if @var{linkname} is
2862 in use. Note that not all systems support symbolic links; on systems
2863 that don't support them, this command is not defined.
2865 @node Compressed Files
2866 @section Accessing Compressed Files
2868 @cindex uncompression
2869 @cindex Auto Compression mode
2870 @cindex mode, Auto Compression
2873 @findex auto-compression-mode
2874 @vindex auto-compression-mode
2875 Emacs comes with a library that can automatically uncompress
2876 compressed files when you visit them, and automatically recompress them
2877 if you alter them and save them. To enable this feature, type the
2878 command @kbd{M-x auto-compression-mode}. You can enable it permanently
2879 by customizing the option @code{auto-compression-mode}.
2881 When automatic compression (which implies automatic uncompression as
2882 well) is enabled, Emacs recognizes compressed files by their file names.
2883 File names ending in @samp{.gz} indicate a file compressed with
2884 @code{gzip}. Other endings indicate other compression programs.
2886 Automatic uncompression and compression apply to all the operations in
2887 which Emacs uses the contents of a file. This includes visiting it,
2888 saving it, inserting its contents into a buffer, loading it, and byte
2892 @section File Archives
2895 @cindex file archives
2897 A file whose name ends in @samp{.tar} is normally an @dfn{archive}
2898 made by the @code{tar} program. Emacs views these files in a special
2899 mode called Tar mode which provides a Dired-like list of the contents
2900 (@pxref{Dired}). You can move around through the list just as you
2901 would in Dired, and visit the subfiles contained in the archive.
2902 However, not all Dired commands are available in Tar mode.
2904 If you enable Auto Compression mode (@pxref{Compressed Files}), then
2905 Tar mode is used also for compressed archives---files with extensions
2906 @samp{.tgz}, @code{.tar.Z} and @code{.tar.gz}.
2908 The keys @kbd{e}, @kbd{f} and @key{RET} all extract a component file
2909 into its own buffer. You can edit it there and when you save the buffer
2910 the edited version will replace the version in the Tar buffer. @kbd{v}
2911 extracts a file into a buffer in View mode. @kbd{o} extracts the file
2912 and displays it in another window, so you could edit the file and
2913 operate on the archive simultaneously. @kbd{d} marks a file for
2914 deletion when you later use @kbd{x}, and @kbd{u} unmarks a file, as in
2915 Dired. @kbd{C} copies a file from the archive to disk and @kbd{R}
2916 renames a file. @kbd{g} reverts the buffer from the archive on disk.
2918 The keys @kbd{M}, @kbd{G}, and @kbd{O} change the file's permission
2919 bits, group, and owner, respectively.
2921 If your display supports colors and the mouse, moving the mouse
2922 pointer across a file name highlights that file name, indicating that
2923 you can click on it. Clicking @kbd{Mouse-2} on the highlighted file
2924 name extracts the file into a buffer and displays that buffer.
2926 Saving the Tar buffer writes a new version of the archive to disk with
2927 the changes you made to the components.
2929 You don't need the @code{tar} program to use Tar mode---Emacs reads
2930 the archives directly. However, accessing compressed archives
2931 requires the appropriate uncompression program.
2933 @cindex Archive mode
2934 @cindex mode, archive
2945 @cindex Java class archives
2946 @cindex unzip archives
2947 A separate but similar Archive mode is used for archives produced by
2948 the programs @code{arc}, @code{jar}, @code{lzh}, @code{zip}, and
2949 @code{zoo}, which have extensions corresponding to the program names.
2951 The key bindings of Archive mode are similar to those in Tar mode,
2952 with the addition of the @kbd{m} key which marks a file for subsequent
2953 operations, and @kbd{M-@key{DEL}} which unmarks all the marked files.
2954 Also, the @kbd{a} key toggles the display of detailed file
2955 information, for those archive types where it won't fit in a single
2956 line. Operations such as renaming a subfile, or changing its mode or
2957 owner, are supported only for some of the archive formats.
2959 Unlike Tar mode, Archive mode runs the archiving program to unpack
2960 and repack archives. Details of the program names and their options
2961 can be set in the @samp{Archive} Customize group. However, you don't
2962 need these programs to look at the archive table of contents, only to
2963 extract or manipulate the subfiles in the archive.
2966 @section Remote Files
2969 @cindex remote file access
2970 You can refer to files on other machines using a special file name syntax:
2974 /@var{host}:@var{filename}
2975 /@var{user}@@@var{host}:@var{filename}
2976 /@var{user}@@@var{host}#@var{port}:@var{filename}
2981 When you do this, Emacs uses the FTP program to read and write files on
2982 the specified host. It logs in through FTP using your user name or the
2983 name @var{user}. It may ask you for a password from time to time; this
2984 is used for logging in on @var{host}. The form using @var{port} allows
2985 you to access servers running on a non-default TCP port.
2987 @cindex backups for remote files
2988 @vindex ange-ftp-make-backup-files
2989 If you want to disable backups for remote files, set the variable
2990 @code{ange-ftp-make-backup-files} to @code{nil}.
2993 @vindex ange-ftp-default-user
2994 @cindex user name for remote file access
2995 Normally, if you do not specify a user name in a remote file name,
2996 that means to use your own user name. But if you set the variable
2997 @code{ange-ftp-default-user} to a string, that string is used instead.
2998 (The Emacs package that implements FTP file access is called
3001 @cindex anonymous FTP
3002 @vindex ange-ftp-generate-anonymous-password
3003 To visit files accessible by anonymous FTP, you use special user
3004 names @samp{anonymous} or @samp{ftp}. Passwords for these user names
3005 are handled specially. The variable
3006 @code{ange-ftp-generate-anonymous-password} controls what happens: if
3007 the value of this variable is a string, then that string is used as
3008 the password; if non-@code{nil} (the default), then the value of
3009 @code{user-mail-address} is used; if @code{nil}, the user is prompted
3010 for a password as normal.
3012 @cindex firewall, and accessing remote files
3013 @cindex gateway, and remote file access with @code{ange-ftp}
3014 @vindex ange-ftp-smart-gateway
3015 @vindex ange-ftp-gateway-host
3016 Sometimes you may be unable to access files on a remote machine
3017 because a @dfn{firewall} in between blocks the connection for security
3018 reasons. If you can log in on a @dfn{gateway} machine from which the
3019 target files @emph{are} accessible, and whose FTP server supports
3020 gatewaying features, you can still use remote file names; all you have
3021 to do is specify the name of the gateway machine by setting the
3022 variable @code{ange-ftp-gateway-host}, and set
3023 @code{ange-ftp-smart-gateway} to @code{t}. Otherwise you may be able
3024 to make remote file names work, but the procedure is complex. You can
3025 read the instructions by typing @kbd{M-x finder-commentary @key{RET}
3026 ange-ftp @key{RET}}.
3028 @vindex file-name-handler-alist
3029 @cindex disabling remote files
3030 You can entirely turn off the FTP file name feature by removing the
3031 entries @code{ange-ftp-completion-hook-function} and
3032 @code{ange-ftp-hook-function} from the variable
3033 @code{file-name-handler-alist}. You can turn off the feature in
3034 individual cases by quoting the file name with @samp{/:} (@pxref{Quoted
3037 @node Quoted File Names
3038 @section Quoted File Names
3040 @cindex quoting file names
3041 You can @dfn{quote} an absolute file name to prevent special
3042 characters and syntax in it from having their special effects.
3043 The way to do this is to add @samp{/:} at the beginning.
3045 For example, you can quote a local file name which appears remote, to
3046 prevent it from being treated as a remote file name. Thus, if you have
3047 a directory named @file{/foo:} and a file named @file{bar} in it, you
3048 can refer to that file in Emacs as @samp{/:/foo:/bar}.
3050 @samp{/:} can also prevent @samp{~} from being treated as a special
3051 character for a user's home directory. For example, @file{/:/tmp/~hack}
3052 refers to a file whose name is @file{~hack} in directory @file{/tmp}.
3054 Likewise, quoting with @samp{/:} is one way to enter in the minibuffer
3055 a file name that contains @samp{$}. However, the @samp{/:} must be at
3056 the beginning of the minibuffer in order to quote @samp{$}.
3058 You can also quote wildcard characters with @samp{/:}, for visiting.
3059 For example, @file{/:/tmp/foo*bar} visits the file @file{/tmp/foo*bar}.
3060 However, in most cases you can simply type the wildcard characters for
3061 themselves. For example, if the only file name in @file{/tmp} that
3062 starts with @samp{foo} and ends with @samp{bar} is @file{foo*bar}, then
3063 specifying @file{/tmp/foo*bar} will visit just @file{/tmp/foo*bar}.
3064 Another way is to specify @file{/tmp/foo[*]bar}.
3066 @node File Name Cache
3067 @section File Name Cache
3069 @cindex file name caching
3070 @cindex cache of file names
3073 @findex file-cache-minibuffer-complete
3074 You can use the @dfn{file name cache} to make it easy to locate a
3075 file by name, without having to remember exactly where it is located.
3076 When typing a file name in the minibuffer, @kbd{C-@key{tab}}
3077 (@code{file-cache-minibuffer-complete}) completes it using the file
3078 name cache. If you repeat @kbd{C-@key{tab}}, that cycles through the
3079 possible completions of what you had originally typed. Note that the
3080 @kbd{C-@key{tab}} character cannot be typed on most text-only
3083 The file name cache does not fill up automatically. Instead, you
3084 load file names into the cache using these commands:
3086 @findex file-cache-add-directory
3088 @item M-x file-cache-add-directory @key{RET} @var{directory} @key{RET}
3089 Add each file name in @var{directory} to the file name cache.
3090 @item M-x file-cache-add-directory-using-find @key{RET} @var{directory} @key{RET}
3091 Add each file name in @var{directory} and all of its nested
3092 subdirectories to the file name cache.
3093 @item M-x file-cache-add-directory-using-locate @key{RET} @var{directory} @key{RET}
3094 Add each file name in @var{directory} and all of its nested
3095 subdirectories to the file name cache, using @command{locate} to find
3097 @item M-x file-cache-add-directory-list @key{RET} @var{variable} @key{RET}
3098 Add each file name in each directory listed in @var{variable}
3099 to the file name cache. @var{variable} should be a Lisp variable
3100 such as @code{load-path} or @code{exec-path}, whose value is a list
3102 @item M-x file-cache-clear-cache @key{RET}
3103 Clear the cache; that is, remove all file names from it.
3106 @node File Conveniences
3107 @section Convenience Features for Finding Files
3109 @findex recentf-mode
3110 @vindex recentf-mode
3111 @findex recentf-save-list
3112 @findex recentf-edit-list
3113 If you enable Recentf mode, with @kbd{M-x recentf-mode}, the
3114 @samp{File} menu includes a submenu containing a list of recently
3115 opened files. @kbd{M-x recentf-save-list} saves the current
3116 @code{recent-file-list} to a file, and @kbd{M-x recentf-edit-list}
3119 @findex auto-image-file-mode
3120 @findex mode, auto-image-file
3121 @cindex images, visiting
3122 @cindex visiting image files
3123 @vindex image-file-name-regexps
3124 @vindex image-file-name-extensions
3125 When Auto-image-file minor mode is enabled, visiting an image file
3126 displays it as an image, not as text. Likewise, inserting an image
3127 file into a buffer inserts it as an image. This works only when Emacs
3128 can display the relevant image type. The variables
3129 @code{image-file-name-extensions} or @code{image-file-name-regexps}
3130 control which file names are recognized as containing images.
3132 The @kbd{M-x ffap} command generalizes @code{find-file} with more
3133 powerful heuristic defaults (@pxref{FFAP}), often based on the text at
3134 point. Partial Completion mode offers other features extending
3135 @code{find-file}, which can be used with @code{ffap}.
3136 @xref{Completion Options}.