1 @c This is part of the Emacs manual.
2 @c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 1999, 2000,
3 @c 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
4 @c See file emacs.texi for copying conditions.
5 @node Files, Buffers, Keyboard Macros, 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.
40 * Filesets:: Handling sets of files.
47 Most Emacs commands that operate on a file require you to specify the
48 file name. (Saving and reverting are exceptions; the buffer knows which
49 file name to use for them.) You enter the file name using the
50 minibuffer (@pxref{Minibuffer}). @dfn{Completion} is available
51 (@pxref{Completion}) to make it easier to specify long file names. When
52 completing file names, Emacs ignores those whose file-name extensions
53 appear in the variable @code{completion-ignored-extensions}; see
54 @ref{Completion Options}.
56 For most operations, there is a @dfn{default file name} which is used
57 if you type just @key{RET} to enter an empty argument. Normally the
58 default file name is the name of the file visited in the current buffer;
59 this makes it easy to operate on that file with any of the Emacs file
62 @vindex default-directory
63 Each buffer has a default directory which is normally the same as the
64 directory of the file visited in that buffer. When you enter a file
65 name without a directory, the default directory is used. If you specify
66 a directory in a relative fashion, with a name that does not start with
67 a slash, it is interpreted with respect to the default directory. The
68 default directory is kept in the variable @code{default-directory},
69 which has a separate value in every buffer.
73 The command @kbd{M-x pwd} displays the current buffer's default
74 directory, and the command @kbd{M-x cd} sets it (to a value read using
75 the minibuffer). A buffer's default directory changes only when the
76 @code{cd} command is used. A file-visiting buffer's default directory
77 is initialized to the directory of the file it visits. If you create
78 a buffer with @kbd{C-x b}, its default directory is copied from that
79 of the buffer that was current at the time.
81 For example, if the default file name is @file{/u/rms/gnu/gnu.tasks}
82 then the default directory is normally @file{/u/rms/gnu/}. If you
83 type just @samp{foo}, which does not specify a directory, it is short
84 for @file{/u/rms/gnu/foo}. @samp{../.login} would stand for
85 @file{/u/rms/.login}. @samp{new/foo} would stand for the file name
86 @file{/u/rms/gnu/new/foo}.
88 @vindex insert-default-directory
89 The default directory actually appears in the minibuffer when the
90 minibuffer becomes active to read a file name. This serves two
91 purposes: it @emph{shows} you what the default is, so that you can type
92 a relative file name and know with certainty what it will mean, and it
93 allows you to @emph{edit} the default to specify a different directory.
94 This insertion of the default directory is inhibited if the variable
95 @code{insert-default-directory} is set to @code{nil}.
97 Note that it is legitimate to type an absolute file name after you
98 enter the minibuffer, ignoring the presence of the default directory
99 name as part of the text. The final minibuffer contents may look
100 invalid, but that is not so. For example, if the minibuffer starts out
101 with @samp{/usr/tmp/} and you add @samp{/x1/rms/foo}, you get
102 @samp{/usr/tmp//x1/rms/foo}; but Emacs ignores everything through the
103 first slash in the double slash; the result is @samp{/x1/rms/foo}.
104 @xref{Minibuffer File}.
106 @cindex home directory shorthand
107 You can use @file{~/} in a file name to mean your home directory,
108 or @file{~@var{user-id}/} to mean the home directory of a user whose
109 login name is @code{user-id}. (On DOS and Windows systems, where a user
110 doesn't have a home directory, Emacs substitutes @file{~/} with the
111 value of the environment variable @code{HOME}; see @ref{General
114 @cindex environment variables in file names
115 @cindex expansion of environment variables
116 @cindex @code{$} in file names
117 @anchor{File Names with $}@samp{$} in a file name is used to
118 substitute an environment variable. The environment variable name
119 consists of all the alphanumeric characters after the @samp{$};
120 alternatively, it can be enclosed in braces after the @samp{$}. For
121 example, if you have used the shell command @command{export
122 FOO=rms/hacks} to set up an environment variable named @env{FOO}, then
123 you can use @file{/u/$FOO/test.c} or @file{/u/$@{FOO@}/test.c} as an
124 abbreviation for @file{/u/rms/hacks/test.c}. If the environment
125 variable is not defined, no substitution occurs: @file{/u/$notdefined}
126 stands for itself (assuming the environment variable @env{notdefined}
129 Note that shell commands to set environment variables affect Emacs
130 only when done before Emacs is started.
132 To access a file with @samp{$} in its name, if the @samp{$} causes
133 expansion, type @samp{$$}. This pair is converted to a single
134 @samp{$} at the same time as variable substitution is performed for a
135 single @samp{$}. Alternatively, quote the whole file name with
136 @samp{/:} (@pxref{Quoted File Names}). File names which begin with a
137 literal @samp{~} should also be quoted with @samp{/:}.
139 @findex substitute-in-file-name
140 The Lisp function that performs the @samp{$}-substitution is called
141 @code{substitute-in-file-name}. The substitution is performed only on
142 file names read as such using the minibuffer.
144 You can include non-@acronym{ASCII} characters in file names if you set the
145 variable @code{file-name-coding-system} to a non-@code{nil} value.
146 @xref{File Name Coding}.
149 @section Visiting Files
150 @cindex visiting files
154 Visit a file (@code{find-file}).
156 Visit a file for viewing, without allowing changes to it
157 (@code{find-file-read-only}).
159 Visit a different file instead of the one visited last
160 (@code{find-alternate-file}).
162 Visit a file, in another window (@code{find-file-other-window}). Don't
163 alter what is displayed in the selected window.
165 Visit a file, in a new frame (@code{find-file-other-frame}). Don't
166 alter what is displayed in the selected frame.
167 @item M-x find-file-literally
168 Visit a file with no conversion of the contents.
171 @cindex files, visiting and saving
173 @dfn{Visiting} a file means copying its contents into an Emacs
174 buffer so you can edit them. Emacs makes a new buffer for each file
175 that you visit. We often say that this buffer ``is visiting'' that
176 file, or that the buffer's ``visited file'' is that file. Emacs
177 constructs the buffer name from the file name by throwing away the
178 directory, keeping just the name proper. For example, a file named
179 @file{/usr/rms/emacs.tex} would get a buffer named @samp{emacs.tex}.
180 If there is already a buffer with that name, Emacs constructs a unique
181 name---the normal method is to append @samp{<2>}, @samp{<3>}, and so
182 on, but you can select other methods (@pxref{Uniquify}).
184 Each window's mode line shows the name of the buffer that is being displayed
185 in that window, so you can always tell what buffer you are editing.
187 The changes you make with editing commands are made in the Emacs
188 buffer. They do not take effect in the file that you visited, or any
189 permanent place, until you @dfn{save} the buffer. Saving the buffer
190 means that Emacs writes the current contents of the buffer into its
191 visited file. @xref{Saving}.
193 @cindex modified (buffer)
194 If a buffer contains changes that have not been saved, we say the
195 buffer is @dfn{modified}. This is important because it implies that
196 some changes will be lost if the buffer is not saved. The mode line
197 displays two stars near the left margin to indicate that the buffer is
202 To visit a file, use the command @kbd{C-x C-f} (@code{find-file}). Follow
203 the command with the name of the file you wish to visit, terminated by a
206 The file name is read using the minibuffer (@pxref{Minibuffer}), with
207 defaulting and completion in the standard manner (@pxref{File Names}).
208 While in the minibuffer, you can abort @kbd{C-x C-f} by typing
209 @kbd{C-g}. File-name completion ignores certain filenames; for more
210 about this, see @ref{Completion Options}.
212 Your confirmation that @kbd{C-x C-f} has completed successfully is
213 the appearance of new text on the screen and a new buffer name in the
214 mode line. If the specified file does not exist and you could not
215 create it, or exists but you can't read it, then you get an error,
216 with an error message displayed in the echo area.
218 If you visit a file that is already in Emacs, @kbd{C-x C-f} does not make
219 another copy. It selects the existing buffer containing that file.
220 However, before doing so, it checks whether the file itself has changed
221 since you visited or saved it last. If the file has changed, Emacs offers
224 @vindex large-file-warning-threshold
225 @cindex maximum buffer size exceeded, error message
226 If you try to visit a file larger than
227 @code{large-file-warning-threshold} (the default is 10000000, which is
228 about 10 megabytes), Emacs will ask you for confirmation first. You
229 can answer @kbd{y} to proceed with visiting the file. Note, however,
230 that Emacs cannot visit files that are larger than the maximum Emacs
231 buffer size, which is around 256 megabytes on 32-bit machines
232 (@pxref{Buffers}). If you try, Emacs will display an error message
233 saying that the maximum buffer size has been exceeded.
235 @cindex file selection dialog
236 On graphical displays there are two additional methods for
237 visiting files. Firstly, when Emacs is built with a suitable GUI
238 toolkit, commands invoked with the mouse (by clicking on the menu bar
239 or tool bar) use the toolkit's standard File Selection dialog instead
240 of prompting for the file name in the minibuffer. On Unix and
241 GNU/Linux platforms, Emacs does that when built with GTK, LessTif, and
242 Motif toolkits; on MS-Windows and Mac, the GUI version does that by default.
243 For information on how to customize this, see @ref{Dialog Boxes}.
245 Secondly, Emacs supports ``drag and drop''; dropping a file into an
246 ordinary Emacs window visits the file using that window. However,
247 dropping a file into a window displaying a Dired buffer moves or
248 copies the file into the displayed directory. For details, see
249 @ref{Drag and Drop}, and @ref{Misc Dired Features}.
251 @cindex creating files
252 What if you want to create a new file? Just visit it. Emacs displays
253 @samp{(New file)} in the echo area, but in other respects behaves as if
254 you had visited an existing empty file. If you make any changes and
255 save them, the file is created.
257 Emacs recognizes from the contents of a file which convention it uses
258 to separate lines---newline (used on GNU/Linux and on Unix),
259 carriage-return linefeed (used on Microsoft systems), or just
260 carriage-return (used on the Macintosh)---and automatically converts the
261 contents to the normal Emacs convention, which is that the newline
262 character separates lines. This is a part of the general feature of
263 coding system conversion (@pxref{Coding Systems}), and makes it possible
264 to edit files imported from different operating systems with
265 equal convenience. If you change the text and save the file, Emacs
266 performs the inverse conversion, changing newlines back into
267 carriage-return linefeed or just carriage-return if appropriate.
269 @vindex find-file-run-dired
270 If the file you specify is actually a directory, @kbd{C-x C-f} invokes
271 Dired, the Emacs directory browser, so that you can ``edit'' the contents
272 of the directory (@pxref{Dired}). Dired is a convenient way to view, delete,
273 or operate on the files in the directory. However, if the variable
274 @code{find-file-run-dired} is @code{nil}, then it is an error to try
275 to visit a directory.
277 Files which are actually collections of other files, or @dfn{file
278 archives}, are visited in special modes which invoke a Dired-like
279 environment to allow operations on archive members. @xref{File
280 Archives}, for more about these features.
282 @cindex wildcard characters in file names
283 @vindex find-file-wildcards
284 If the file name you specify contains shell-style wildcard
285 characters, Emacs visits all the files that match it. Wildcards
286 include @samp{?}, @samp{*}, and @samp{[@dots{}]} sequences. To enter
287 the wild card @samp{?} in a file name in the minibuffer, you need to
288 type @kbd{C-q ?}. @xref{Quoted File Names}, for information on how to
289 visit a file whose name actually contains wildcard characters. You
290 can disable the wildcard feature by customizing
291 @code{find-file-wildcards}.
293 If you visit a file that the operating system won't let you modify,
294 or that is marked read-only, Emacs makes the buffer read-only too, so
295 that you won't go ahead and make changes that you'll have trouble
296 saving afterward. You can make the buffer writable with @kbd{C-x C-q}
297 (@code{toggle-read-only}). @xref{Misc Buffer}.
300 @findex find-file-read-only
301 If you want to visit a file as read-only in order to protect
302 yourself from entering changes accidentally, visit it with the command
303 @kbd{C-x C-r} (@code{find-file-read-only}) instead of @kbd{C-x C-f}.
306 @findex find-alternate-file
307 If you visit a nonexistent file unintentionally (because you typed the
308 wrong file name), use the @kbd{C-x C-v} command
309 (@code{find-alternate-file}) to visit the file you really wanted.
310 @kbd{C-x C-v} is similar to @kbd{C-x C-f}, but it kills the current
311 buffer (after first offering to save it if it is modified). When
312 @kbd{C-x C-v} reads the file name to visit, it inserts the entire
313 default file name in the buffer, with point just after the directory
314 part; this is convenient if you made a slight error in typing the name.
317 @findex find-file-other-window
318 @kbd{C-x 4 f} (@code{find-file-other-window}) is like @kbd{C-x C-f}
319 except that the buffer containing the specified file is selected in another
320 window. The window that was selected before @kbd{C-x 4 f} continues to
321 show the same buffer it was already showing. If this command is used when
322 only one window is being displayed, that window is split in two, with one
323 window showing the same buffer as before, and the other one showing the
324 newly requested file. @xref{Windows}.
327 @findex find-file-other-frame
328 @kbd{C-x 5 f} (@code{find-file-other-frame}) is similar, but opens a
329 new frame, or makes visible any existing frame showing the file you
330 seek. This feature is available only when you are using a window
331 system. @xref{Frames}.
333 @findex find-file-literally
334 If you wish to edit a file as a sequence of @acronym{ASCII} characters with no special
335 encoding or conversion, use the @kbd{M-x find-file-literally} command.
336 It visits a file, like @kbd{C-x C-f}, but does not do format conversion
337 (@pxref{Formatted Text}), character code conversion (@pxref{Coding
338 Systems}), or automatic uncompression (@pxref{Compressed Files}), and
339 does not add a final newline because of @code{require-final-newline}.
340 If you already have visited the same file in the usual (non-literal)
341 manner, this command asks you whether to visit it literally instead.
343 @vindex find-file-hook
344 @vindex find-file-not-found-functions
345 Two special hook variables allow extensions to modify the operation of
346 visiting files. Visiting a file that does not exist runs the functions
347 in the list @code{find-file-not-found-functions}; this variable holds a list
348 of functions, and the functions are called one by one (with no
349 arguments) until one of them returns non-@code{nil}. This is not a
350 normal hook, and the name ends in @samp{-functions} rather than @samp{-hook}
351 to indicate that fact.
353 Successful visiting of any file, whether existing or not, calls the
354 functions in the list @code{find-file-hook}, with no arguments.
355 This variable is a normal hook. In the case of a nonexistent file, the
356 @code{find-file-not-found-functions} are run first. @xref{Hooks}.
358 There are several ways to specify automatically the major mode for
359 editing the file (@pxref{Choosing Modes}), and to specify local
360 variables defined for that file (@pxref{File Variables}).
363 @section Saving Files
365 @dfn{Saving} a buffer in Emacs means writing its contents back into the file
366 that was visited in the buffer.
369 * Save Commands:: Commands for saving files.
370 * Backup:: How Emacs saves the old version of your file.
371 * Customize Save:: Customizing the saving of files.
372 * Interlocking:: How Emacs protects against simultaneous editing
373 of one file by two users.
374 * Shadowing: File Shadowing. Copying files to "shadows" automatically.
375 * Time Stamps:: Emacs can update time stamps on saved files.
379 @subsection Commands for Saving Files
381 These are the commands that relate to saving and writing files.
385 Save the current buffer in its visited file on disk (@code{save-buffer}).
387 Save any or all buffers in their visited files (@code{save-some-buffers}).
389 Forget that the current buffer has been changed (@code{not-modified}).
390 With prefix argument (@kbd{C-u}), mark the current buffer as changed.
392 Save the current buffer with a specified file name (@code{write-file}).
393 @item M-x set-visited-file-name
394 Change the file name under which the current buffer will be saved.
399 When you wish to save the file and make your changes permanent, type
400 @kbd{C-x C-s} (@code{save-buffer}). After saving is finished, @kbd{C-x C-s}
401 displays a message like this:
404 Wrote /u/rms/gnu/gnu.tasks
408 If the selected buffer is not modified (no changes have been made in it
409 since the buffer was created or last saved), saving is not really done,
410 because it would have no effect. Instead, @kbd{C-x C-s} displays a message
411 like this in the echo area:
414 (No changes need to be saved)
418 @findex save-some-buffers
419 The command @kbd{C-x s} (@code{save-some-buffers}) offers to save any
420 or all modified buffers. It asks you what to do with each buffer. The
421 possible responses are analogous to those of @code{query-replace}:
425 Save this buffer and ask about the rest of the buffers.
427 Don't save this buffer, but ask about the rest of the buffers.
429 Save this buffer and all the rest with no more questions.
430 @c following generates acceptable underfull hbox
432 Terminate @code{save-some-buffers} without any more saving.
434 Save this buffer, then exit @code{save-some-buffers} without even asking
437 View the buffer that you are currently being asked about. When you exit
438 View mode, you get back to @code{save-some-buffers}, which asks the
441 Diff the buffer against its corresponding file, so you can see
442 what changes you would be saving.
444 Display a help message about these options.
447 @kbd{C-x C-c}, the key sequence to exit Emacs, invokes
448 @code{save-some-buffers} and therefore asks the same questions.
452 If you have changed a buffer but you do not want to save the changes,
453 you should take some action to prevent it. Otherwise, each time you use
454 @kbd{C-x s} or @kbd{C-x C-c}, you are liable to save this buffer by
455 mistake. One thing you can do is type @kbd{M-~} (@code{not-modified}),
456 which clears out the indication that the buffer is modified. If you do
457 this, none of the save commands will believe that the buffer needs to be
458 saved. (@samp{~} is often used as a mathematical symbol for `not'; thus
459 @kbd{M-~} is `not', metafied.) You could also use
460 @code{set-visited-file-name} (see below) to mark the buffer as visiting
461 a different file name, one which is not in use for anything important.
462 Alternatively, you can cancel all the changes made since the file was
463 visited or saved, by reading the text from the file again. This is
464 called @dfn{reverting}. @xref{Reverting}. (You could also undo all the
465 changes by repeating the undo command @kbd{C-x u} until you have undone
466 all the changes; but reverting is easier.) You can also kill the buffer.
468 @findex set-visited-file-name
469 @kbd{M-x set-visited-file-name} alters the name of the file that the
470 current buffer is visiting. It reads the new file name using the
471 minibuffer. Then it marks the buffer as visiting that file name, and
472 changes the buffer name correspondingly. @code{set-visited-file-name}
473 does not save the buffer in the newly visited file; it just alters the
474 records inside Emacs in case you do save later. It also marks the
475 buffer as ``modified'' so that @kbd{C-x C-s} in that buffer
480 If you wish to mark the buffer as visiting a different file and save it
481 right away, use @kbd{C-x C-w} (@code{write-file}). It is
482 equivalent to @code{set-visited-file-name} followed by @kbd{C-x C-s}
483 (except that @kbd{C-x C-w} asks for confirmation if the file exists).
484 @kbd{C-x C-s} used on a buffer that is not visiting a file has the
485 same effect as @kbd{C-x C-w}; that is, it reads a file name, marks the
486 buffer as visiting that file, and saves it there. The default file name in
487 a buffer that is not visiting a file is made by combining the buffer name
488 with the buffer's default directory (@pxref{File Names}).
490 If the new file name implies a major mode, then @kbd{C-x C-w} switches
491 to that major mode, in most cases. The command
492 @code{set-visited-file-name} also does this. @xref{Choosing Modes}.
494 If Emacs is about to save a file and sees that the date of the latest
495 version on disk does not match what Emacs last read or wrote, Emacs
496 notifies you of this fact, because it probably indicates a problem caused
497 by simultaneous editing and requires your immediate attention.
498 @xref{Interlocking,, Simultaneous Editing}.
501 @subsection Backup Files
503 @vindex make-backup-files
504 @vindex vc-make-backup-files
506 On most operating systems, rewriting a file automatically destroys all
507 record of what the file used to contain. Thus, saving a file from Emacs
508 throws away the old contents of the file---or it would, except that
509 Emacs carefully copies the old contents to another file, called the
510 @dfn{backup} file, before actually saving.
512 For most files, the variable @code{make-backup-files} determines
513 whether to make backup files. On most operating systems, its default
514 value is @code{t}, so that Emacs does write backup files.
516 For files managed by a version control system (@pxref{Version
517 Control}), the variable @code{vc-make-backup-files} determines whether
518 to make backup files. By default it is @code{nil}, since backup files
519 are redundant when you store all the previous versions in a version
520 control system. @xref{General VC Options}.
522 At your option, Emacs can keep either a single backup for each file,
523 or make a series of numbered backup files for each file that you edit.
525 @vindex backup-enable-predicate
526 @vindex temporary-file-directory
527 @vindex small-temporary-file-directory
528 The default value of the @code{backup-enable-predicate} variable
529 prevents backup files being written for files in the directories used
530 for temporary files, specified by @code{temporary-file-directory} or
531 @code{small-temporary-file-directory}.
533 Emacs makes a backup for a file only the first time the file is saved
534 from one buffer. No matter how many times you save a file, its backup file
535 continues to contain the contents from before the file was visited.
536 Normally this means that the backup file contains the contents from before
537 the current editing session; however, if you kill the buffer and then visit
538 the file again, a new backup file will be made by the next save.
540 You can also explicitly request making another backup file from a
541 buffer even though it has already been saved at least once. If you save
542 the buffer with @kbd{C-u C-x C-s}, the version thus saved will be made
543 into a backup file if you save the buffer again. @kbd{C-u C-u C-x C-s}
544 saves the buffer, but first makes the previous file contents into a new
545 backup file. @kbd{C-u C-u C-u C-x C-s} does both things: it makes a
546 backup from the previous contents, and arranges to make another from the
547 newly saved contents if you save again.
550 * One or Many: Numbered Backups. Whether to make one backup file or many.
551 * Names: Backup Names. How backup files are named.
552 * Deletion: Backup Deletion. Emacs deletes excess numbered backups.
553 * Copying: Backup Copying. Backups can be made by copying or renaming.
556 @node Numbered Backups
557 @subsubsection Numbered Backups
559 @vindex version-control
560 The choice of single backup file or multiple numbered backup files
561 is controlled by the variable @code{version-control}. Its possible
566 Make numbered backups.
568 Make numbered backups for files that have numbered backups already.
569 Otherwise, make single backups.
571 Never make numbered backups; always make single backups.
575 The usual way to set this variable is globally, through your
576 @file{.emacs} file or the customization buffer. However, you can set
577 @code{version-control} locally in an individual buffer to control the
578 making of backups for that buffer's file. For example, Rmail mode
579 locally sets @code{version-control} to @code{never} to make sure that
580 there is only one backup for an Rmail file. @xref{Locals}.
582 @cindex @env{VERSION_CONTROL} environment variable
583 If you set the environment variable @env{VERSION_CONTROL}, to tell
584 various GNU utilities what to do with backup files, Emacs also obeys the
585 environment variable by setting the Lisp variable @code{version-control}
586 accordingly at startup. If the environment variable's value is @samp{t}
587 or @samp{numbered}, then @code{version-control} becomes @code{t}; if the
588 value is @samp{nil} or @samp{existing}, then @code{version-control}
589 becomes @code{nil}; if it is @samp{never} or @samp{simple}, then
590 @code{version-control} becomes @code{never}.
593 @subsubsection Single or Numbered Backups
595 When Emacs makes a single backup file, its name is normally
596 constructed by appending @samp{~} to the file name being edited; thus,
597 the backup file for @file{eval.c} would be @file{eval.c~}.
599 @vindex make-backup-file-name-function
600 @vindex backup-directory-alist
601 You can change this behavior by defining the variable
602 @code{make-backup-file-name-function} to a suitable function.
603 Alternatively you can customize the variable
604 @code{backup-directory-alist} to specify that files matching certain
605 patterns should be backed up in specific directories.
607 A typical use is to add an element @code{("." . @var{dir})} to make
608 all backups in the directory with absolute name @var{dir}; Emacs
609 modifies the backup file names to avoid clashes between files with the
610 same names originating in different directories. Alternatively,
611 adding, say, @code{("." . ".~")} would make backups in the invisible
612 subdirectory @file{.~} of the original file's directory. Emacs
613 creates the directory, if necessary, to make the backup.
615 If access control stops Emacs from writing backup files under the usual
616 names, it writes the backup file as @file{%backup%~} in your home
617 directory. Only one such file can exist, so only the most recently
618 made such backup is available.
620 If you choose to have a series of numbered backup files, backup file
621 names contain @samp{.~}, the number, and another @samp{~} after the
622 original file name. Thus, the backup files of @file{eval.c} would be
623 called @file{eval.c.~1~}, @file{eval.c.~2~}, and so on, all the way
624 through names like @file{eval.c.~259~} and beyond. The variable
625 @code{backup-directory-alist} applies to numbered backups just as
628 @node Backup Deletion
629 @subsubsection Automatic Deletion of Backups
631 To prevent excessive consumption of disk space, Emacs can delete numbered
632 backup versions automatically. Generally Emacs keeps the first few backups
633 and the latest few backups, deleting any in between. This happens every
634 time a new backup is made.
636 @vindex kept-old-versions
637 @vindex kept-new-versions
638 The two variables @code{kept-old-versions} and
639 @code{kept-new-versions} control this deletion. Their values are,
640 respectively, the number of oldest (lowest-numbered) backups to keep
641 and the number of newest (highest-numbered) ones to keep, each time a
642 new backup is made. The backups in the middle (excluding those oldest
643 and newest) are the excess middle versions---those backups are
644 deleted. These variables' values are used when it is time to delete
645 excess versions, just after a new backup version is made; the newly
646 made backup is included in the count in @code{kept-new-versions}. By
647 default, both variables are 2.
649 @vindex delete-old-versions
650 If @code{delete-old-versions} is @code{t}, Emacs deletes the excess
651 backup files silently. If it is @code{nil}, the default, Emacs asks
652 you whether it should delete the excess backup versions. If it has
653 any other value, then Emacs never automatically deletes backups.
655 Dired's @kbd{.} (Period) command can also be used to delete old versions.
656 @xref{Dired Deletion}.
659 @subsubsection Copying vs.@: Renaming
661 Backup files can be made by copying the old file or by renaming it.
662 This makes a difference when the old file has multiple names (hard
663 links). If the old file is renamed into the backup file, then the
664 alternate names become names for the backup file. If the old file is
665 copied instead, then the alternate names remain names for the file
666 that you are editing, and the contents accessed by those names will be
669 The method of making a backup file may also affect the file's owner
670 and group. If copying is used, these do not change. If renaming is used,
671 you become the file's owner, and the file's group becomes the default
672 (different operating systems have different defaults for the group).
674 Having the owner change is usually a good idea, because then the owner
675 always shows who last edited the file. Also, the owners of the backups
676 show who produced those versions. Occasionally there is a file whose
677 owner should not change; it is a good idea for such files to contain
678 local variable lists to set @code{backup-by-copying-when-mismatch}
679 locally (@pxref{File Variables}).
681 @vindex backup-by-copying
682 @vindex backup-by-copying-when-linked
683 @vindex backup-by-copying-when-mismatch
684 @vindex backup-by-copying-when-privileged-mismatch
685 @cindex file ownership, and backup
686 @cindex backup, and user-id
687 The choice of renaming or copying is controlled by four variables.
688 Renaming is the default choice. If the variable
689 @code{backup-by-copying} is non-@code{nil}, copying is used. Otherwise,
690 if the variable @code{backup-by-copying-when-linked} is non-@code{nil},
691 then copying is used for files that have multiple names, but renaming
692 may still be used when the file being edited has only one name. If the
693 variable @code{backup-by-copying-when-mismatch} is non-@code{nil}, then
694 copying is used if renaming would cause the file's owner or group to
695 change. @code{backup-by-copying-when-mismatch} is @code{t} by default
696 if you start Emacs as the superuser. The fourth variable,
697 @code{backup-by-copying-when-privileged-mismatch}, gives the highest
698 numeric user-id for which @code{backup-by-copying-when-mismatch} will be
699 forced on. This is useful when low-numbered user-ids are assigned to
700 special system users, such as @code{root}, @code{bin}, @code{daemon},
701 etc., which must maintain ownership of files.
703 When a file is managed with a version control system (@pxref{Version
704 Control}), Emacs does not normally make backups in the usual way for
705 that file. But check-in and check-out are similar in some ways to
706 making backups. One unfortunate similarity is that these operations
707 typically break hard links, disconnecting the file name you visited from
708 any alternate names for the same file. This has nothing to do with
709 Emacs---the version control system does it.
712 @subsection Customizing Saving of Files
714 @vindex require-final-newline
715 If the value of the variable @code{require-final-newline} is
716 @code{t}, saving or writing a file silently puts a newline at the end
717 if there isn't already one there. If the value is @code{visit}, Emacs
718 adds a newline at the end of any file that doesn't have one, just
719 after it visits the file. (This marks the buffer as modified, and you
720 can undo it.) If the value is @code{visit-save}, that means to add
721 newlines both on visiting and on saving. If the value is @code{nil},
722 Emacs leaves the end of the file unchanged; if it's neither @code{nil}
723 nor @code{t}, Emacs asks you whether to add a newline. The default is
726 @vindex mode-require-final-newline
727 Many major modes are designed for specific kinds of files that are
728 always supposed to end in newlines. These major modes set the
729 variable @code{require-final-newline} according to
730 @code{mode-require-final-newline}. By setting the latter variable,
731 you can control how these modes handle final newlines.
733 @vindex write-region-inhibit-fsync
734 When Emacs saves a file, it invokes the @code{fsync} system call to
735 force the data immediately out to disk. This is important for safety
736 if the system crashes or in case of power outage. However, it can be
737 disruptive on laptops using power saving, because it requires the disk
738 to spin up each time you save a file. Setting
739 @code{write-region-inhibit-fsync} to a non-@code{nil} value disables
740 this synchronization. Be careful---this means increased risk of data
744 @subsection Protection against Simultaneous Editing
747 @cindex simultaneous editing
748 Simultaneous editing occurs when two users visit the same file, both
749 make changes, and then both save them. If nobody were informed that
750 this was happening, whichever user saved first would later find that his
753 On some systems, Emacs notices immediately when the second user starts
754 to change the file, and issues an immediate warning. On all systems,
755 Emacs checks when you save the file, and warns if you are about to
756 overwrite another user's changes. You can prevent loss of the other
757 user's work by taking the proper corrective action instead of saving the
760 @findex ask-user-about-lock
761 @cindex locking files
762 When you make the first modification in an Emacs buffer that is
763 visiting a file, Emacs records that the file is @dfn{locked} by you.
764 (It does this by creating a symbolic link in the same directory with a
765 different name.) Emacs removes the lock when you save the changes. The
766 idea is that the file is locked whenever an Emacs buffer visiting it has
770 If you begin to modify the buffer while the visited file is locked by
771 someone else, this constitutes a @dfn{collision}. When Emacs detects a
772 collision, it asks you what to do, by calling the Lisp function
773 @code{ask-user-about-lock}. You can redefine this function for the sake
774 of customization. The standard definition of this function asks you a
775 question and accepts three possible answers:
779 Steal the lock. Whoever was already changing the file loses the lock,
780 and you gain the lock.
782 Proceed. Go ahead and edit the file despite its being locked by someone else.
784 Quit. This causes an error (@code{file-locked}), and the buffer
785 contents remain unchanged---the modification you were trying to make
786 does not actually take place.
789 Note that locking works on the basis of a file name; if a file has
790 multiple names, Emacs does not realize that the two names are the same file
791 and cannot prevent two users from editing it simultaneously under different
792 names. However, basing locking on names means that Emacs can interlock the
793 editing of new files that will not really exist until they are saved.
795 Some systems are not configured to allow Emacs to make locks, and
796 there are cases where lock files cannot be written. In these cases,
797 Emacs cannot detect trouble in advance, but it still can detect the
798 collision when you try to save a file and overwrite someone else's
801 If Emacs or the operating system crashes, this may leave behind lock
802 files which are stale, so you may occasionally get warnings about
803 spurious collisions. When you determine that the collision is spurious,
804 just use @kbd{p} to tell Emacs to go ahead anyway.
806 Every time Emacs saves a buffer, it first checks the last-modification
807 date of the existing file on disk to verify that it has not changed since the
808 file was last visited or saved. If the date does not match, it implies
809 that changes were made in the file in some other way, and these changes are
810 about to be lost if Emacs actually does save. To prevent this, Emacs
811 displays a warning message and asks for confirmation before saving.
812 Occasionally you will know why the file was changed and know that it does
813 not matter; then you can answer @kbd{yes} and proceed. Otherwise, you should
814 cancel the save with @kbd{C-g} and investigate the situation.
816 The first thing you should do when notified that simultaneous editing
817 has already taken place is to list the directory with @kbd{C-u C-x C-d}
818 (@pxref{Directories}). This shows the file's current author. You
819 should attempt to contact him to warn him not to continue editing.
820 Often the next step is to save the contents of your Emacs buffer under a
821 different name, and use @code{diff} to compare the two files.@refill
824 @subsection Shadowing Files
827 @findex shadow-initialize
830 @item M-x shadow-initialize
831 Set up file shadowing.
832 @item M-x shadow-define-literal-group
833 Declare a single file to be shared between sites.
834 @item M-x shadow-define-regexp-group
835 Make all files that match each of a group of files be shared between hosts.
836 @item M-x shadow-define-cluster @key{RET} @var{name} @key{RET}
837 Define a shadow file cluster @var{name}.
838 @item M-x shadow-copy-files
839 Copy all pending shadow files.
840 @item M-x shadow-cancel
841 Cancel the instruction to shadow some files.
844 You can arrange to keep identical @dfn{shadow} copies of certain files
845 in more than one place---possibly on different machines. To do this,
846 first you must set up a @dfn{shadow file group}, which is a set of
847 identically-named files shared between a list of sites. The file
848 group is permanent and applies to further Emacs sessions as well as
849 the current one. Once the group is set up, every time you exit Emacs,
850 it will copy the file you edited to the other files in its group. You
851 can also do the copying without exiting Emacs, by typing @kbd{M-x
854 To set up a shadow file group, use @kbd{M-x
855 shadow-define-literal-group} or @kbd{M-x shadow-define-regexp-group}.
856 See their documentation strings for further information.
858 Before copying a file to its shadows, Emacs asks for confirmation.
859 You can answer ``no'' to bypass copying of this file, this time. If
860 you want to cancel the shadowing permanently for a certain file, use
861 @kbd{M-x shadow-cancel} to eliminate or change the shadow file group.
863 A @dfn{shadow cluster} is a group of hosts that share directories, so
864 that copying to or from one of them is sufficient to update the file
865 on all of them. Each shadow cluster has a name, and specifies the
866 network address of a primary host (the one we copy files to), and a
867 regular expression that matches the host names of all the other hosts
868 in the cluster. You can define a shadow cluster with @kbd{M-x
869 shadow-define-cluster}.
872 @subsection Updating Time Stamps Automatically
874 @cindex modification dates
875 @cindex locale, date format
877 You can arrange to put a time stamp in a file, so that it will be updated
878 automatically each time you edit and save the file. The time stamp
879 has to be in the first eight lines of the file, and you should
894 Then add the hook function @code{time-stamp} to the hook
895 @code{before-save-hook}; that hook function will automatically update
896 the time stamp, inserting the current date and time when you save the
897 file. You can also use the command @kbd{M-x time-stamp} to update the
898 time stamp manually. For other customizations, see the Custom group
899 @code{time-stamp}. Note that non-numeric fields in the time stamp are
900 formatted according to your locale setting (@pxref{Environment}).
903 @section Reverting a Buffer
904 @findex revert-buffer
905 @cindex drastic changes
906 @cindex reread a file
908 If you have made extensive changes to a file and then change your mind
909 about them, you can get rid of them by reading in the previous version
910 of the file. To do this, use @kbd{M-x revert-buffer}, which operates on
911 the current buffer. Since reverting a buffer unintentionally could lose
912 a lot of work, you must confirm this command with @kbd{yes}.
914 @code{revert-buffer} tries to position point in such a way that, if
915 the file was edited only slightly, you will be at approximately the
916 same piece of text after reverting as before. However, if you have made
917 drastic changes, point may wind up in a totally different piece of text.
919 Reverting marks the buffer as ``not modified'' until another change is
922 Some kinds of buffers whose contents reflect data bases other than files,
923 such as Dired buffers, can also be reverted. For them, reverting means
924 recalculating their contents from the appropriate data base. Buffers
925 created explicitly with @kbd{C-x b} cannot be reverted; @code{revert-buffer}
926 reports an error when asked to do so.
928 @vindex revert-without-query
929 When you edit a file that changes automatically and frequently---for
930 example, a log of output from a process that continues to run---it may be
931 useful for Emacs to revert the file without querying you, whenever you
932 visit the file again with @kbd{C-x C-f}.
934 To request this behavior, set the variable @code{revert-without-query}
935 to a list of regular expressions. When a file name matches one of these
936 regular expressions, @code{find-file} and @code{revert-buffer} will
937 revert it automatically if it has changed---provided the buffer itself
938 is not modified. (If you have edited the text, it would be wrong to
939 discard your changes.)
941 @cindex Global Auto-Revert mode
942 @cindex mode, Global Auto-Revert
943 @cindex Auto-Revert mode
944 @cindex mode, Auto-Revert
945 @findex global-auto-revert-mode
946 @findex auto-revert-mode
947 @findex auto-revert-tail-mode
949 You may find it useful to have Emacs revert files automatically when
950 they change. Three minor modes are available to do this.
952 @kbd{M-x global-auto-revert-mode} enables Global Auto-Revert mode,
953 which periodically checks all file buffers and reverts when the
954 corresponding file has changed. @kbd{M-x auto-revert-mode} enables a
955 local version, Auto-Revert mode, which applies only to the current
958 You can use Auto-Revert mode to ``tail'' a file such as a system
959 log, so that changes made to that file by other programs are
960 continuously displayed. To do this, just move the point to the end of
961 the buffer, and it will stay there as the file contents change.
962 However, if you are sure that the file will only change by growing at
963 the end, use Auto-Revert Tail mode instead
964 (@code{auto-revert-tail-mode}). It is more efficient for this.
966 @vindex auto-revert-interval
967 The variable @code{auto-revert-interval} controls how often to check
968 for a changed file. Since checking a remote file is too slow, these
969 modes do not check or revert remote files.
971 @xref{VC Mode Line}, for Auto Revert peculiarities in buffers that
972 visit files under version control.
975 @section Auto-Saving: Protection Against Disasters
976 @cindex Auto Save mode
977 @cindex mode, Auto Save
980 Emacs saves all the visited files from time to time (based on counting
981 your keystrokes) without being asked. This is called @dfn{auto-saving}.
982 It prevents you from losing more than a limited amount of work if the
985 When Emacs determines that it is time for auto-saving, it considers
986 each buffer, and each is auto-saved if auto-saving is enabled for it
987 and it has been changed since the last time it was auto-saved. The
988 message @samp{Auto-saving...} is displayed in the echo area during
989 auto-saving, if any files are actually auto-saved. Errors occurring
990 during auto-saving are caught so that they do not interfere with the
991 execution of commands you have been typing.
994 * Files: Auto Save Files. The file where auto-saved changes are
995 actually made until you save the file.
996 * Control: Auto Save Control. Controlling when and how often to auto-save.
997 * Recover:: Recovering text from auto-save files.
1000 @node Auto Save Files
1001 @subsection Auto-Save Files
1003 Auto-saving does not normally save in the files that you visited, because
1004 it can be very undesirable to save a program that is in an inconsistent
1005 state when you have made half of a planned change. Instead, auto-saving
1006 is done in a different file called the @dfn{auto-save file}, and the
1007 visited file is changed only when you request saving explicitly (such as
1008 with @kbd{C-x C-s}).
1010 Normally, the auto-save file name is made by appending @samp{#} to the
1011 front and rear of the visited file name. Thus, a buffer visiting file
1012 @file{foo.c} is auto-saved in a file @file{#foo.c#}. Most buffers that
1013 are not visiting files are auto-saved only if you request it explicitly;
1014 when they are auto-saved, the auto-save file name is made by appending
1015 @samp{#} to the front and rear of buffer name, then
1016 adding digits and letters at the end for uniqueness. For
1017 example, the @samp{*mail*} buffer in which you compose messages to be
1018 sent might be auto-saved in a file named @file{#*mail*#704juu}. Auto-save file
1019 names are made this way unless you reprogram parts of Emacs to do
1020 something different (the functions @code{make-auto-save-file-name} and
1021 @code{auto-save-file-name-p}). The file name to be used for auto-saving
1022 in a buffer is calculated when auto-saving is turned on in that buffer.
1024 @cindex auto-save for remote files
1025 @vindex auto-save-file-name-transforms
1026 The variable @code{auto-save-file-name-transforms} allows a degree
1027 of control over the auto-save file name. It lets you specify a series
1028 of regular expressions and replacements to transform the auto save
1029 file name. The default value puts the auto-save files for remote
1030 files (@pxref{Remote Files}) into the temporary file directory on the
1033 When you delete a substantial part of the text in a large buffer, auto
1034 save turns off temporarily in that buffer. This is because if you
1035 deleted the text unintentionally, you might find the auto-save file more
1036 useful if it contains the deleted text. To reenable auto-saving after
1037 this happens, save the buffer with @kbd{C-x C-s}, or use @kbd{C-u 1 M-x
1040 @vindex auto-save-visited-file-name
1041 If you want auto-saving to be done in the visited file rather than
1042 in a separate auto-save file, set the variable
1043 @code{auto-save-visited-file-name} to a non-@code{nil} value. In this
1044 mode, there is no real difference between auto-saving and explicit
1047 @vindex delete-auto-save-files
1048 A buffer's auto-save file is deleted when you save the buffer in its
1049 visited file. (You can inhibit this by setting the variable
1050 @code{delete-auto-save-files} to @code{nil}.) Changing the visited
1051 file name with @kbd{C-x C-w} or @code{set-visited-file-name} renames
1052 any auto-save file to go with the new visited name.
1054 @node Auto Save Control
1055 @subsection Controlling Auto-Saving
1057 @vindex auto-save-default
1058 @findex auto-save-mode
1059 Each time you visit a file, auto-saving is turned on for that file's
1060 buffer if the variable @code{auto-save-default} is non-@code{nil} (but not
1061 in batch mode; @pxref{Entering Emacs}). The default for this variable is
1062 @code{t}, so auto-saving is the usual practice for file-visiting buffers.
1063 Auto-saving can be turned on or off for any existing buffer with the
1064 command @kbd{M-x auto-save-mode}. Like other minor mode commands, @kbd{M-x
1065 auto-save-mode} turns auto-saving on with a positive argument, off with a
1066 zero or negative argument; with no argument, it toggles.
1068 @vindex auto-save-interval
1069 Emacs does auto-saving periodically based on counting how many characters
1070 you have typed since the last time auto-saving was done. The variable
1071 @code{auto-save-interval} specifies how many characters there are between
1072 auto-saves. By default, it is 300. Emacs doesn't accept values that are
1073 too small: if you customize @code{auto-save-interval} to a value less
1074 than 20, Emacs will behave as if the value is 20.
1076 @vindex auto-save-timeout
1077 Auto-saving also takes place when you stop typing for a while. The
1078 variable @code{auto-save-timeout} says how many seconds Emacs should
1079 wait before it does an auto save (and perhaps also a garbage
1080 collection). (The actual time period is longer if the current buffer is
1081 long; this is a heuristic which aims to keep out of your way when you
1082 are editing long buffers, in which auto-save takes an appreciable amount
1083 of time.) Auto-saving during idle periods accomplishes two things:
1084 first, it makes sure all your work is saved if you go away from the
1085 terminal for a while; second, it may avoid some auto-saving while you
1086 are actually typing.
1088 Emacs also does auto-saving whenever it gets a fatal error. This
1089 includes killing the Emacs job with a shell command such as @samp{kill
1090 %emacs}, or disconnecting a phone line or network connection.
1092 @findex do-auto-save
1093 You can request an auto-save explicitly with the command @kbd{M-x
1097 @subsection Recovering Data from Auto-Saves
1099 @findex recover-file
1100 You can use the contents of an auto-save file to recover from a loss
1101 of data with the command @kbd{M-x recover-file @key{RET} @var{file}
1102 @key{RET}}. This visits @var{file} and then (after your confirmation)
1103 restores the contents from its auto-save file @file{#@var{file}#}.
1104 You can then save with @kbd{C-x C-s} to put the recovered text into
1105 @var{file} itself. For example, to recover file @file{foo.c} from its
1106 auto-save file @file{#foo.c#}, do:@refill
1109 M-x recover-file @key{RET} foo.c @key{RET}
1114 Before asking for confirmation, @kbd{M-x recover-file} displays a
1115 directory listing describing the specified file and the auto-save file,
1116 so you can compare their sizes and dates. If the auto-save file
1117 is older, @kbd{M-x recover-file} does not offer to read it.
1119 @findex recover-session
1120 If Emacs or the computer crashes, you can recover all the files you
1121 were editing from their auto save files with the command @kbd{M-x
1122 recover-session}. This first shows you a list of recorded interrupted
1123 sessions. Move point to the one you choose, and type @kbd{C-c C-c}.
1125 Then @code{recover-session} asks about each of the files that were
1126 being edited during that session, asking whether to recover that file.
1127 If you answer @kbd{y}, it calls @code{recover-file}, which works in its
1128 normal fashion. It shows the dates of the original file and its
1129 auto-save file, and asks once again whether to recover that file.
1131 When @code{recover-session} is done, the files you've chosen to
1132 recover are present in Emacs buffers. You should then save them. Only
1133 this---saving them---updates the files themselves.
1135 @vindex auto-save-list-file-prefix
1136 Emacs records interrupted sessions for later recovery in files named
1137 @file{~/.emacs.d/auto-save-list/.saves-@var{pid}-@var{hostname}}. All
1138 of this name except @file{@var{pid}-@var{hostname}} comes from the
1139 value of @code{auto-save-list-file-prefix}. You can record sessions
1140 in a different place by customizing that variable. If you set
1141 @code{auto-save-list-file-prefix} to @code{nil} in your @file{.emacs}
1142 file, sessions are not recorded for recovery.
1145 @section File Name Aliases
1146 @cindex symbolic links (visiting)
1147 @cindex hard links (visiting)
1149 Symbolic links and hard links both make it possible for several file
1150 names to refer to the same file. Hard links are alternate names that
1151 refer directly to the file; all the names are equally valid, and no one
1152 of them is preferred. By contrast, a symbolic link is a kind of defined
1153 alias: when @file{foo} is a symbolic link to @file{bar}, you can use
1154 either name to refer to the file, but @file{bar} is the real name, while
1155 @file{foo} is just an alias. More complex cases occur when symbolic
1156 links point to directories.
1158 @vindex find-file-existing-other-name
1159 @vindex find-file-suppress-same-file-warnings
1161 Normally, if you visit a file which Emacs is already visiting under
1162 a different name, Emacs displays a message in the echo area and uses
1163 the existing buffer visiting that file. This can happen on systems
1164 that support hard or symbolic links, or if you use a long file name on
1165 a system that truncates long file names, or on a case-insensitive file
1166 system. You can suppress the message by setting the variable
1167 @code{find-file-suppress-same-file-warnings} to a non-@code{nil}
1168 value. You can disable this feature entirely by setting the variable
1169 @code{find-file-existing-other-name} to @code{nil}: then if you visit
1170 the same file under two different names, you get a separate buffer for
1173 @vindex find-file-visit-truename
1174 @cindex truenames of files
1175 @cindex file truenames
1176 If the variable @code{find-file-visit-truename} is non-@code{nil},
1177 then the file name recorded for a buffer is the file's @dfn{truename}
1178 (made by replacing all symbolic links with their target names), rather
1179 than the name you specify. Setting @code{find-file-visit-truename} also
1180 implies the effect of @code{find-file-existing-other-name}.
1182 @node Version Control
1183 @section Version Control
1184 @cindex version control
1186 @dfn{Version control systems} are packages that can record multiple
1187 versions of a source file, usually storing the unchanged parts of the
1188 file just once. Version control systems also record history information
1189 such as the creation time of each version, who created it, and a
1190 description of what was changed in that version.
1192 The Emacs version control interface is called VC. Its commands work
1193 with different version control systems---currently, it supports CVS,
1194 GNU Arch, RCS, Meta-CVS, Subversion, and SCCS. Of these, the GNU
1195 project distributes CVS, GNU Arch, and RCS; we recommend that you use
1196 either CVS or GNU Arch for your projects, and RCS for individual
1197 files. We also have free software to replace SCCS, known as CSSC; if
1198 you are using SCCS and don't want to make the incompatible change to
1199 RCS or CVS, you can switch to CSSC.
1201 VC is enabled by default in Emacs. To disable it, set the
1202 customizable variable @code{vc-handled-backends} to @code{nil}
1203 (@pxref{Customizing VC}).
1206 * Introduction to VC:: How version control works in general.
1207 * VC Mode Line:: How the mode line shows version control status.
1208 * Basic VC Editing:: How to edit a file under version control.
1209 * Old Versions:: Examining and comparing old versions.
1210 * Secondary VC Commands:: The commands used a little less frequently.
1211 * Branches:: Multiple lines of development.
1212 * Remote Repositories:: Efficient access to remote CVS servers.
1213 * Snapshots:: Sets of file versions treated as a unit.
1214 * Miscellaneous VC:: Various other commands and features of VC.
1215 * Customizing VC:: Variables that change VC's behavior.
1218 @node Introduction to VC
1219 @subsection Introduction to Version Control
1221 VC allows you to use a version control system from within Emacs,
1222 integrating the version control operations smoothly with editing. VC
1223 provides a uniform interface to version control, so that regardless of
1224 which version control system is in use, you can use it the same way.
1226 This section provides a general overview of version control, and
1227 describes the version control systems that VC supports. You can skip
1228 this section if you are already familiar with the version control system
1232 * Version Systems:: Supported version control back-end systems.
1233 * VC Concepts:: Words and concepts related to version control.
1234 * Types of Log File:: The per-file VC log in contrast to the ChangeLog.
1237 @node Version Systems
1238 @subsubsection Supported Version Control Systems
1240 @cindex back end (version control)
1241 VC currently works with six different version control systems or
1242 ``back ends'': CVS, GNU Arch, RCS, Meta-CVS, Subversion, and SCCS.
1245 CVS is a free version control system that is used for the majority
1246 of free software projects today. It allows concurrent multi-user
1247 development either locally or over the network. Some of its
1248 shortcomings, corrected by newer systems such as GNU Arch, are that it
1249 lacks atomic commits or support for renaming files. VC supports all
1250 basic editing operations under CVS, but for some less common tasks you
1251 still need to call CVS from the command line. Note also that before
1252 using CVS you must set up a repository, which is a subject too complex
1257 GNU Arch is a new version control system that is designed for
1258 distributed work. It differs in many ways from old well-known
1259 systems, such as CVS and RCS. It supports different transports for
1260 interoperating between users, offline operations, and it has good
1261 branching and merging features. It also supports atomic commits, and
1262 history of file renaming and moving. VC does not support all
1263 operations provided by GNU Arch, so you must sometimes invoke it from
1264 the command line, or use a specialized module.
1267 RCS is the free version control system around which VC was initially
1268 built. The VC commands are therefore conceptually closest to RCS.
1269 Almost everything you can do with RCS can be done through VC. You
1270 cannot use RCS over the network though, and it only works at the level
1271 of individual files, rather than projects. You should use it if you
1272 want a simple, yet reliable tool for handling individual files.
1276 Subversion is a free version control system designed to be similar
1277 to CVS but without CVS's problems. Subversion supports atomic commits,
1278 and versions directories, symbolic links, meta-data, renames, copies,
1279 and deletes. It can be used via http or via its own protocol.
1283 Meta-CVS is another attempt to solve problems arising in CVS. It
1284 supports directory structure versioning, improved branching and
1285 merging, and use of symbolic links and meta-data in repositories.
1288 SCCS is a proprietary but widely used version control system. In
1289 terms of capabilities, it is the weakest of the six that VC supports.
1290 VC compensates for certain features missing in SCCS (snapshots, for
1291 example) by implementing them itself, but some other VC features, such
1292 as multiple branches, are not available with SCCS. Since SCCS is
1293 non-free, not respecting its users freedom, you should not use it;
1294 use its free replacement CSSC instead. But you should use CSSC only
1295 if for some reason you cannot use RCS, or one of the higher-level
1296 systems such as CVS or GNU Arch.
1298 In the following, we discuss mainly RCS, SCCS and CVS. Nearly
1299 everything said about CVS applies to GNU Arch, Subversion and Meta-CVS
1303 @subsubsection Concepts of Version Control
1306 @cindex registered file
1307 When a file is under version control, we also say that it is
1308 @dfn{registered} in the version control system. Each registered file
1309 has a corresponding @dfn{master file} which represents the file's
1310 present state plus its change history---enough to reconstruct the
1311 current version or any earlier version. Usually the master file also
1312 records a @dfn{log entry} for each version, describing in words what was
1313 changed in that version.
1316 @cindex checking out files
1317 The file that is maintained under version control is sometimes called
1318 the @dfn{work file} corresponding to its master file. You edit the work
1319 file and make changes in it, as you would with an ordinary file. (With
1320 SCCS and RCS, you must @dfn{lock} the file before you start to edit it.)
1321 After you are done with a set of changes, you @dfn{check the file in},
1322 which records the changes in the master file, along with a log entry for
1325 With CVS, there are usually multiple work files corresponding to a
1326 single master file---often each user has his own copy. It is also
1327 possible to use RCS in this way, but this is not the usual way to use
1330 @cindex locking and version control
1331 A version control system typically has some mechanism to coordinate
1332 between users who want to change the same file. One method is
1333 @dfn{locking} (analogous to the locking that Emacs uses to detect
1334 simultaneous editing of a file, but distinct from it). The other method
1335 is to merge your changes with other people's changes when you check them
1338 With version control locking, work files are normally read-only so
1339 that you cannot change them. You ask the version control system to make
1340 a work file writable for you by locking it; only one user can do
1341 this at any given time. When you check in your changes, that unlocks
1342 the file, making the work file read-only again. This allows other users
1343 to lock the file to make further changes. SCCS always uses locking, and
1346 The other alternative for RCS is to let each user modify the work file
1347 at any time. In this mode, locking is not required, but it is
1348 permitted; check-in is still the way to record a new version.
1350 CVS normally allows each user to modify his own copy of the work file
1351 at any time, but requires merging with changes from other users at
1352 check-in time. However, CVS can also be set up to require locking.
1353 (@pxref{CVS Options}).
1355 @node Types of Log File
1356 @subsubsection Types of Log File
1357 @cindex types of log file
1358 @cindex log File, types of
1359 @cindex version control log
1361 Projects that use a revision control system can have @emph{two}
1362 types of log for changes. One is the per-file log maintained by the
1363 revision control system: each time you check in a change, you must
1364 fill out a @dfn{log entry} for the change (@pxref{Log Buffer}). This
1365 kind of log is called the @dfn{version control log}, also the
1366 @dfn{revision control log}, @dfn{RCS log}, or @dfn{CVS log}.
1368 The other kind of log is the file @file{ChangeLog} (@pxref{Change
1369 Log}). It provides a chronological record of all changes to a large
1370 portion of a program---typically one directory and its subdirectories.
1371 A small program would use one @file{ChangeLog} file; a large program
1372 may well merit a @file{ChangeLog} file in each major directory.
1375 A project maintained with version control can use just the per-file
1376 log, or it can use both kinds of logs. It can handle some files one
1377 way and some files the other way. Each project has its policy, which
1380 When the policy is to use both, you typically want to write an entry
1381 for each change just once, then put it into both logs. You can write
1382 the entry in @file{ChangeLog}, then copy it to the log buffer when you
1383 check in the change. Or you can write the entry in the log buffer
1384 while checking in the change, and later use the @kbd{C-x v a} command
1385 to copy it to @file{ChangeLog} (@pxref{Change Logs and VC}).
1388 @subsection Version Control and the Mode Line
1390 When you visit a file that is under version control, Emacs indicates
1391 this on the mode line. For example, @samp{RCS-1.3} says that RCS is
1392 used for that file, and the current version is 1.3.
1394 The character between the back-end name and the version number
1395 indicates the version control status of the file. @samp{-} means that
1396 the work file is not locked (if locking is in use), or not modified (if
1397 locking is not in use). @samp{:} indicates that the file is locked, or
1398 that it is modified. If the file is locked by some other user (for
1399 instance, @samp{jim}), that is displayed as @samp{RCS:jim:1.3}.
1401 @vindex auto-revert-check-vc-info
1402 When Auto Revert mode (@pxref{Reverting}) reverts a buffer that is
1403 under version control, it updates the version control information in
1404 the mode line. However, Auto Revert mode may not properly update this
1405 information if the version control status changes without changes to
1406 the work file, from outside the current Emacs session. If you set
1407 @code{auto-revert-check-vc-info} to @code{t}, Auto Revert mode updates
1408 the version control status information every
1409 @code{auto-revert-interval} seconds, even if the work file itself is
1410 unchanged. The resulting CPU usage depends on the version control
1411 system, but is usually not excessive.
1413 @node Basic VC Editing
1414 @subsection Basic Editing under Version Control
1416 The principal VC command is an all-purpose command that performs
1417 either locking or check-in, depending on the situation.
1421 Perform the next logical version control operation on this file.
1424 @findex vc-next-action
1426 The precise action of this command depends on the state of the file,
1427 and whether the version control system uses locking or not. SCCS and
1428 RCS normally use locking; CVS normally does not use locking.
1430 @findex vc-toggle-read-only
1431 @kindex C-x C-q @r{(Version Control)}
1432 As a special convenience that is particularly useful for files with
1433 locking, you can let Emacs check a file in or out whenever you change
1434 its read-only flag. This means, for example, that you cannot
1435 accidentally edit a file without properly checking it out first. To
1436 achieve this, bind the key @kbd{C-x C-q} to @kbd{vc-toggle-read-only}
1437 in your @file{~/.emacs} file. (@xref{Init Rebinding}.)
1440 * VC with Locking:: RCS in its default mode, SCCS, and optionally CVS.
1441 * Without Locking:: Without locking: default mode for CVS.
1442 * Advanced C-x v v:: Advanced features available with a prefix argument.
1443 * Log Buffer:: Features available in log entry buffers.
1446 @node VC with Locking
1447 @subsubsection Basic Version Control with Locking
1449 If locking is used for the file (as with SCCS, and RCS in its default
1450 mode), @kbd{C-x v v} can either lock a file or check it in:
1454 If the file is not locked, @kbd{C-x v v} locks it, and
1455 makes it writable so that you can change it.
1458 If the file is locked by you, and contains changes, @kbd{C-x v v} checks
1459 in the changes. In order to do this, it first reads the log entry
1460 for the new version. @xref{Log Buffer}.
1463 If the file is locked by you, but you have not changed it since you
1464 locked it, @kbd{C-x v v} releases the lock and makes the file read-only
1468 If the file is locked by some other user, @kbd{C-x v v} asks you whether
1469 you want to ``steal the lock'' from that user. If you say yes, the file
1470 becomes locked by you, but a message is sent to the person who had
1471 formerly locked the file, to inform him of what has happened.
1474 These rules also apply when you use CVS in locking mode, except
1475 that there is no such thing as stealing a lock.
1477 @node Without Locking
1478 @subsubsection Basic Version Control without Locking
1480 When there is no locking---the default for CVS---work files are always
1481 writable; you do not need to do anything before you begin to edit a
1482 file. The status indicator on the mode line is @samp{-} if the file is
1483 unmodified; it flips to @samp{:} as soon as you save any changes in the
1486 Here is what @kbd{C-x v v} does when using CVS:
1490 If some other user has checked in changes into the master file, Emacs
1491 asks you whether you want to merge those changes into your own work
1492 file. You must do this before you can check in your own changes. (To
1493 pick up any recent changes from the master file @emph{without} trying
1494 to commit your own changes, type @kbd{C-x v m @key{RET}}.)
1498 If there are no new changes in the master file, but you have made
1499 modifications in your work file, @kbd{C-x v v} checks in your changes.
1500 In order to do this, it first reads the log entry for the new version.
1504 If the file is not modified, the @kbd{C-x v v} does nothing.
1507 These rules also apply when you use RCS in the mode that does not
1508 require locking, except that automatic merging of changes from the
1509 master file is not implemented. Unfortunately, this means that nothing
1510 informs you if another user has checked in changes in the same file
1511 since you began editing it, and when this happens, his changes will be
1512 effectively removed when you check in your version (though they will
1513 remain in the master file, so they will not be entirely lost). You must
1514 therefore verify that the current version is unchanged, before you
1515 check in your changes. We hope to eliminate this risk and provide
1516 automatic merging with RCS in a future Emacs version.
1518 In addition, locking is possible with RCS even in this mode, although
1519 it is not required; @kbd{C-x v v} with an unmodified file locks the
1520 file, just as it does with RCS in its normal (locking) mode.
1522 @node Advanced C-x v v
1523 @subsubsection Advanced Control in @kbd{C-x v v}
1525 @cindex version number to check in/out
1526 When you give a prefix argument to @code{vc-next-action} (@kbd{C-u
1527 C-x v v}), it still performs the next logical version control
1528 operation, but accepts additional arguments to specify precisely how
1529 to do the operation.
1533 If the file is modified (or locked), you can specify the version
1534 number to use for the new version that you check in. This is one way
1535 to create a new branch (@pxref{Branches}).
1538 If the file is not modified (and unlocked), you can specify the
1539 version to select; this lets you start working from an older version,
1540 or on another branch. If you do not enter any version, that takes you
1541 to the highest version on the current branch; therefore @kbd{C-u C-x
1542 v v @key{RET}} is a convenient way to get the latest version of a file from
1546 @cindex specific version control system
1547 Instead of the version number, you can also specify the name of a
1548 version control system. This is useful when one file is being managed
1549 with two version control systems at the same time (@pxref{Local
1554 @subsubsection Features of the Log Entry Buffer
1556 When you check in changes, @kbd{C-x v v} first reads a log entry. It
1557 pops up a buffer called @samp{*VC-Log*} for you to enter the log entry.
1559 Sometimes the @samp{*VC-Log*} buffer contains default text when you enter it,
1560 typically the last log message entered. If it does, mark and point
1561 are set around the entire contents of the buffer so that it is easy to
1562 kill the contents of the buffer with @kbd{C-w}.
1564 @findex log-edit-insert-changelog
1565 If you work by writing entries in the @file{ChangeLog}
1566 (@pxref{Change Log}) and then commit the change under revision
1567 control, you can generate the Log Edit text from the ChangeLog using
1568 @kbd{C-c C-a} (@kbd{log-edit-insert-changelog}). This looks for
1569 entries for the file(s) concerned in the top entry in the ChangeLog
1570 and uses those paragraphs as the log text. This text is only inserted
1571 if the top entry was made under your user name on the current date.
1572 @xref{Change Logs and VC}, for the opposite way of
1573 working---generating ChangeLog entries from the revision control log.
1575 In the @samp{*VC-Log*} buffer, @kbd{C-c C-f} (@kbd{M-x log-edit-show-files})
1576 shows the list of files to be committed in case you need to check
1577 that. (This can be a list of more than one file if you use VC Dired
1578 mode or PCL-CVS. @xref{VC Dired Mode}, and @ref{Top, , About PCL-CVS,
1579 pcl-cvs, PCL-CVS --- The Emacs Front-End to CVS}.)
1581 When you have finished editing the log message, type @kbd{C-c C-c} to
1582 exit the buffer and commit the change.
1584 To abort check-in, just @strong{don't} type @kbd{C-c C-c} in that
1585 buffer. You can switch buffers and do other editing. As long as you
1586 don't try to check in another file, the entry you were editing remains
1587 in the @samp{*VC-Log*} buffer, and you can go back to that buffer at any
1588 time to complete the check-in.
1590 If you change several source files for the same reason, it is often
1591 convenient to specify the same log entry for many of the files. To do
1592 this, use the history of previous log entries. The commands @kbd{M-n},
1593 @kbd{M-p}, @kbd{M-s} and @kbd{M-r} for doing this work just like the
1594 minibuffer history commands (except that these versions are used outside
1597 @vindex vc-log-mode-hook
1598 Each time you check in a file, the log entry buffer is put into VC Log
1599 mode, which involves running two hooks: @code{text-mode-hook} and
1600 @code{vc-log-mode-hook}. @xref{Hooks}.
1603 @subsection Examining And Comparing Old Versions
1605 One of the convenient features of version control is the ability
1606 to examine any version of a file, or compare two versions.
1609 @item C-x v ~ @var{version} @key{RET}
1610 Examine version @var{version} of the visited file, in a buffer of its
1614 Compare the current buffer contents with the master version from which
1615 you started editing.
1617 @item C-u C-x v = @var{file} @key{RET} @var{oldvers} @key{RET} @var{newvers} @key{RET}
1618 Compare the specified two versions of @var{file}.
1621 Display the file with per-line version information and using colors.
1624 @findex vc-version-other-window
1626 To examine an old version in its entirety, visit the file and then type
1627 @kbd{C-x v ~ @var{version} @key{RET}} (@code{vc-version-other-window}).
1628 This puts the text of version @var{version} in a file named
1629 @file{@var{filename}.~@var{version}~}, and visits it in its own buffer
1630 in a separate window. (In RCS, you can also select an old version
1631 and create a branch from it. @xref{Branches}.)
1635 It is usually more convenient to compare two versions of the file,
1636 with the command @kbd{C-x v =} (@code{vc-diff}). Plain @kbd{C-x v =}
1637 compares the current buffer contents (saving them in the file if
1638 necessary) with the master version from which you started editing the
1639 file (this is not necessarily the latest version of the file).
1640 @kbd{C-u C-x v =}, with a numeric argument, reads a file name and two
1641 version numbers, then compares those versions of the specified file.
1642 Both forms display the output in a special buffer in another window.
1644 You can specify a checked-in version by its number; an empty input
1645 specifies the current contents of the work file (which may be different
1646 from all the checked-in versions). You can also specify a snapshot name
1647 (@pxref{Snapshots}) instead of one or both version numbers.
1649 If you supply a directory name instead of the name of a registered
1650 file, this command compares the two specified versions of all registered
1651 files in that directory and its subdirectories.
1653 @vindex vc-diff-switches
1654 @vindex vc-rcs-diff-switches
1655 @kbd{C-x v =} works by running a variant of the @code{diff} utility
1656 designed to work with the version control system in use. When you
1657 invoke @code{diff} this way, in addition to the options specified by
1658 @code{diff-switches} (@pxref{Comparing Files}), it receives those
1659 specified by @code{vc-diff-switches}, plus those specified for the
1660 specific back end by @code{vc-@var{backend}-diff-switches}. For
1661 instance, when the version control back end is RCS, @code{diff} uses
1662 the options in @code{vc-rcs-diff-switches}. The
1663 @samp{vc@dots{}diff-switches} variables are @code{nil} by default.
1665 The buffer produced by @kbd{C-x v =} supports the commands of
1666 Compilation mode (@pxref{Compilation Mode}), such as @kbd{C-x `} and
1667 @kbd{C-c C-c}, in both the ``old'' and ``new'' text, and they always
1668 find the corresponding locations in the current work file. (Older
1669 versions are not, in general, present as files on your disk.)
1673 For some back ends, you can display the file @dfn{annotated} with
1674 per-line version information and using colors to enhance the visual
1675 appearance, with the command @kbd{M-x vc-annotate}.
1676 It creates a new buffer (the ``annotate buffer'') displaying the
1677 file's text, with each part colored to show how old it is. Text
1678 colored red is new, blue means old, and intermediate colors indicate
1679 intermediate ages. By default, the time scale is 360 days, so that
1680 everything more than one year old is shown in blue.
1682 When you give a prefix argument to this command, it uses the
1683 minibuffer to read two arguments: which version number to display and
1684 annotate (instead of the current file contents), and a stretch factor
1685 for the time scale. A stretch factor of 0.1 means that the color
1686 range from red to blue spans the past 36 days instead of 360 days. A
1687 stretch factor greater than 1 means the color range spans more than a
1690 From the annotate buffer, you can use the following keys to browse the
1691 annotations of past revisions, view diffs, or view log entries:
1695 Annotate the previous revision, that is to say, the revision before
1696 the one currently annotated. A numeric prefix argument is a repeat
1697 count, so @kbd{C-u 10 P} would take you back 10 revisions.
1700 Annotate the next revision---the one after the revision currently
1701 annotated. A numeric prefix argument is a repeat count.
1704 Annotate the revision indicated by the current line.
1707 Annotate the revision before the one indicated by the current line.
1708 This is useful to see the state the file was in before the change on
1709 the current line was made.
1712 Display the diff between the current line's revision and the previous
1713 revision. This is useful to see what the current line's revision
1714 actually changed in the file.
1717 Show the log of the current line's revision. This is useful to see
1718 the author's description of the changes in the revision on the current
1722 Annotate the workfile version--the one you are editing. If you used
1723 @kbd{P} and @kbd{N} to browse to other revisions, use this key to
1724 return to your current version.
1727 @node Secondary VC Commands
1728 @subsection The Secondary Commands of VC
1730 This section explains the secondary commands of VC; those that you might
1734 * Registering:: Putting a file under version control.
1735 * VC Status:: Viewing the VC status of files.
1736 * VC Undo:: Canceling changes before or after check-in.
1737 * VC Dired Mode:: Listing files managed by version control.
1738 * VC Dired Commands:: Commands to use in a VC Dired buffer.
1742 @subsubsection Registering a File for Version Control
1746 You can put any file under version control by simply visiting it, and
1747 then typing @w{@kbd{C-x v i}} (@code{vc-register}).
1751 Register the visited file for version control.
1754 To register the file, Emacs must choose which version control system
1755 to use for it. If the file's directory already contains files
1756 registered in a version control system, Emacs uses that system. If
1757 there is more than one system in use for a directory, Emacs uses the one
1758 that appears first in @code{vc-handled-backends} (@pxref{Customizing VC}).
1759 On the other hand, if there are no files already registered,
1760 Emacs uses the first system from @code{vc-handled-backends} that could
1761 register the file (for example, you cannot register a file under CVS if
1762 its directory is not already part of a CVS tree); with the default
1763 value of @code{vc-handled-backends}, this means that Emacs uses RCS in
1766 If locking is in use, @kbd{C-x v i} leaves the file unlocked and
1767 read-only. Type @kbd{C-x v v} if you wish to start editing it. After
1768 registering a file with CVS, you must subsequently commit the initial
1769 version by typing @kbd{C-x v v}. Until you do that, the version
1770 appears as @samp{@@@@} in the mode line.
1772 @vindex vc-default-init-version
1773 @cindex initial version number to register
1774 The initial version number for a newly registered file is 1.1, by
1775 default. You can specify a different default by setting the variable
1776 @code{vc-default-init-version}, or you can give @kbd{C-x v i} a numeric
1777 argument; then it reads the initial version number for this particular
1778 file using the minibuffer.
1780 @vindex vc-initial-comment
1781 If @code{vc-initial-comment} is non-@code{nil}, @kbd{C-x v i} reads an
1782 initial comment to describe the purpose of this source file. Reading
1783 the initial comment works like reading a log entry (@pxref{Log Buffer}).
1786 @subsubsection VC Status Commands
1790 Display version control state and change history.
1794 @findex vc-print-log
1795 To view the detailed version control status and history of a file,
1796 type @kbd{C-x v l} (@code{vc-print-log}). It displays the history of
1797 changes to the current file, including the text of the log entries. The
1798 output appears in a separate window. The point is centered at the
1799 revision of the file that is currently being visited.
1801 In the change log buffer, you can use the following keys to move
1802 between the logs of revisions and of files, to view past revisions, and
1807 Move to the previous revision-item in the buffer. (Revision entries in the log
1808 buffer are usually in reverse-chronological order, so the previous
1809 revision-item usually corresponds to a newer revision.) A numeric
1810 prefix argument is a repeat count.
1813 Move to the next revision-item (which most often corresponds to the
1814 previous revision of the file). A numeric prefix argument is a repeat
1818 Move to the log of the previous file, when the logs of multiple files
1819 are in the log buffer (@pxref{VC Dired Mode}). Otherwise, just move
1820 to the beginning of the log. A numeric prefix argument is a repeat
1821 count, so @kbd{C-u 10 P} would move backward 10 files.
1824 Move to the log of the next file, when the logs of multiple files are
1825 in the log buffer (@pxref{VC Dired Mode}). It also takes a numeric
1826 prefix argument as a repeat count.
1829 Visit the revision indicated at the current line, like typing @kbd{C-x
1830 v ~} and specifying this revision's number (@pxref{Old Versions}).
1833 Display the diff (@pxref{Comparing Files}) between the revision
1834 indicated at the current line and the next earlier revision. This is
1835 useful to see what actually changed when the revision indicated on the
1836 current line was committed.
1840 @subsubsection Undoing Version Control Actions
1844 Revert the buffer and the file to the version from which you started
1848 Remove the last-entered change from the master for the visited file.
1849 This undoes your last check-in.
1853 @findex vc-revert-buffer
1854 If you want to discard your current set of changes and revert to the
1855 version from which you started editing the file, use @kbd{C-x v u}
1856 (@code{vc-revert-buffer}). This leaves the file unlocked; if locking
1857 is in use, you must first lock the file again before you change it
1858 again. @kbd{C-x v u} requires confirmation, unless it sees that you
1859 haven't made any changes with respect to the master version.
1861 @kbd{C-x v u} is also the command to unlock a file if you lock it and
1862 then decide not to change it.
1865 @findex vc-cancel-version
1866 To cancel a change that you already checked in, use @kbd{C-x v c}
1867 (@code{vc-cancel-version}). This command discards all record of the
1868 most recent checked-in version, but only if your work file corresponds
1869 to that version---you cannot use @kbd{C-x v c} to cancel a version
1870 that is not the latest on its branch. @kbd{C-x v c} also offers to
1871 revert your work file and buffer to the previous version (the one that
1872 precedes the version that is deleted).
1874 If you answer @kbd{no}, VC keeps your changes in the buffer, and locks
1875 the file. The no-revert option is useful when you have checked in a
1876 change and then discover a trivial error in it; you can cancel the
1877 erroneous check-in, fix the error, and check the file in again.
1879 When @kbd{C-x v c} does not revert the buffer, it unexpands all
1880 version control headers in the buffer instead (@pxref{Version Headers}).
1881 This is because the buffer no longer corresponds to any existing
1882 version. If you check it in again, the check-in process will expand the
1883 headers properly for the new version number.
1885 However, it is impossible to unexpand the RCS @samp{@w{$}Log$} header
1886 automatically. If you use that header feature, you have to unexpand it
1887 by hand---by deleting the entry for the version that you just canceled.
1889 Be careful when invoking @kbd{C-x v c}, as it is easy to lose a lot of
1890 work with it. To help you be careful, this command always requires
1891 confirmation with @kbd{yes}. Note also that this command is disabled
1892 under CVS, because canceling versions is very dangerous and discouraged
1896 @subsubsection Dired under VC
1900 @cindex CVS Dired Mode
1901 The VC Dired Mode described here works with all the version control
1902 systems that VC supports. Another more powerful facility, designed
1903 specifically for CVS, is called PCL-CVS. @xref{Top, , About PCL-CVS,
1904 pcl-cvs, PCL-CVS --- The Emacs Front-End to CVS}.
1907 @findex vc-directory
1908 When you are working on a large program, it is often useful to find
1909 out which files have changed within an entire directory tree, or to view
1910 the status of all files under version control at once, and to perform
1911 version control operations on collections of files. You can use the
1912 command @kbd{C-x v d} (@code{vc-directory}) to make a directory listing
1913 that includes only files relevant for version control.
1915 @vindex vc-dired-terse-display
1916 @kbd{C-x v d} creates a buffer which uses VC Dired Mode. This looks
1917 much like an ordinary Dired buffer (@pxref{Dired}); however, normally it
1918 shows only the noteworthy files (those locked or not up-to-date). This
1919 is called @dfn{terse display}. If you set the variable
1920 @code{vc-dired-terse-display} to @code{nil}, then VC Dired shows all
1921 relevant files---those managed under version control, plus all
1922 subdirectories (@dfn{full display}). The command @kbd{v t} in a VC
1923 Dired buffer toggles between terse display and full display (@pxref{VC
1926 @vindex vc-dired-recurse
1927 By default, VC Dired produces a recursive listing of noteworthy or
1928 relevant files at or below the given directory. You can change this by
1929 setting the variable @code{vc-dired-recurse} to @code{nil}; then VC
1930 Dired shows only the files in the given directory.
1932 The line for an individual file shows the version control state in the
1933 place of the hard link count, owner, group, and size of the file. If
1934 the file is unmodified, in sync with the master file, the version
1935 control state shown is blank. Otherwise it consists of text in
1936 parentheses. Under RCS and SCCS, the name of the user locking the file
1937 is shown; under CVS, an abbreviated version of the @samp{cvs status}
1938 output is used. Here is an example using RCS:
1944 -rw-r--r-- (jim) Apr 2 23:39 file1
1945 -r--r--r-- Apr 5 20:21 file2
1950 The files @samp{file1} and @samp{file2} are under version control,
1951 @samp{file1} is locked by user jim, and @samp{file2} is unlocked.
1953 Here is an example using CVS:
1959 -rw-r--r-- (modified) Aug 2 1997 file1.c
1960 -rw-r--r-- Apr 4 20:09 file2.c
1961 -rw-r--r-- (merge) Sep 13 1996 file3.c
1965 Here @samp{file1.c} is modified with respect to the repository, and
1966 @samp{file2.c} is not. @samp{file3.c} is modified, but other changes
1967 have also been checked in to the repository---you need to merge them
1968 with the work file before you can check it in.
1970 @vindex{vc-stay-local}
1971 @vindex{vc-cvs-stay-local}
1972 In the above, if the repository were on a remote machine, VC would
1973 only contact it when the variable @code{vc-stay-local} (or
1974 @code{vc-cvs-stay-local}) is nil (@pxref{CVS Options}). This is
1975 because access to the repository may be slow, or you may be working
1976 offline and not have access to the repository at all. As a
1977 consequence, VC would not be able to tell you that @samp{file3.c} is
1978 in the ``merge'' state; you would learn that only when you try to
1979 check-in your modified copy of the file, or use a command such as
1982 In practice, this is not a problem because CVS handles this case
1983 consistently whenever it arises. In VC, you'll simply get prompted to
1984 merge the remote changes into your work file first. The benefits of
1985 less network communication usually outweigh the disadvantage of not
1986 seeing remote changes immediately.
1988 @vindex vc-directory-exclusion-list
1989 When VC Dired displays subdirectories (in the ``full'' display mode),
1990 it omits some that should never contain any files under version control.
1991 By default, this includes Version Control subdirectories such as
1992 @samp{RCS} and @samp{CVS}; you can customize this by setting the
1993 variable @code{vc-directory-exclusion-list}.
1995 You can fine-tune VC Dired's format by typing @kbd{C-u C-x v d}---as in
1996 ordinary Dired, that allows you to specify additional switches for the
1999 @node VC Dired Commands
2000 @subsubsection VC Dired Commands
2002 All the usual Dired commands work normally in VC Dired mode, except
2003 for @kbd{v}, which is redefined as the version control prefix. You can
2004 invoke VC commands such as @code{vc-diff} and @code{vc-print-log} by
2005 typing @kbd{v =}, or @kbd{v l}, and so on. Most of these commands apply
2006 to the file name on the current line.
2008 The command @kbd{v v} (@code{vc-next-action}) operates on all the
2009 marked files, so that you can lock or check in several files at once.
2010 If it operates on more than one file, it handles each file according to
2011 its current state; thus, it might lock one file, but check in another
2012 file. This could be confusing; it is up to you to avoid confusing
2013 behavior by marking a set of files that are in a similar state. If no
2014 files are marked, @kbd{v v} operates on the file in the current line.
2016 If any files call for check-in, @kbd{v v} reads a single log entry,
2017 then uses it for all the files being checked in. This is convenient for
2018 registering or checking in several files at once, as part of the same
2021 @findex vc-dired-toggle-terse-mode
2022 @findex vc-dired-mark-locked
2023 You can toggle between terse display (only locked files, or files not
2024 up-to-date) and full display at any time by typing @kbd{v t}
2025 (@code{vc-dired-toggle-terse-mode}). There is also a special command
2026 @kbd{* l} (@code{vc-dired-mark-locked}), which marks all files currently
2027 locked (or, with CVS, all files not up-to-date). Thus, typing @kbd{* l
2028 t k} is another way to delete from the buffer all files except those
2032 @subsection Multiple Branches of a File
2033 @cindex branch (version control)
2034 @cindex trunk (version control)
2036 One use of version control is to maintain multiple ``current''
2037 versions of a file. For example, you might have different versions of a
2038 program in which you are gradually adding various unfinished new
2039 features. Each such independent line of development is called a
2040 @dfn{branch}. VC allows you to create branches, switch between
2041 different branches, and merge changes from one branch to another.
2042 Please note, however, that branches are not supported for SCCS.
2044 A file's main line of development is usually called the @dfn{trunk}.
2045 The versions on the trunk are normally numbered 1.1, 1.2, 1.3, etc. At
2046 any such version, you can start an independent branch. A branch
2047 starting at version 1.2 would have version number 1.2.1.1, and consecutive
2048 versions on this branch would have numbers 1.2.1.2, 1.2.1.3, 1.2.1.4,
2049 and so on. If there is a second branch also starting at version 1.2, it
2050 would consist of versions 1.2.2.1, 1.2.2.2, 1.2.2.3, etc.
2052 @cindex head version
2053 If you omit the final component of a version number, that is called a
2054 @dfn{branch number}. It refers to the highest existing version on that
2055 branch---the @dfn{head version} of that branch. The branches in the
2056 example above have branch numbers 1.2.1 and 1.2.2.
2059 * Switching Branches:: How to get to another existing branch.
2060 * Creating Branches:: How to start a new branch.
2061 * Merging:: Transferring changes between branches.
2062 * Multi-User Branching:: Multiple users working at multiple branches
2066 @node Switching Branches
2067 @subsubsection Switching between Branches
2069 To switch between branches, type @kbd{C-u C-x v v} and specify the
2070 version number you want to select. This version is then visited
2071 @emph{unlocked} (write-protected), so you can examine it before locking
2072 it. Switching branches in this way is allowed only when the file is not
2075 You can omit the minor version number, thus giving only the branch
2076 number; this takes you to the head version on the chosen branch. If you
2077 only type @key{RET}, Emacs goes to the highest version on the trunk.
2079 After you have switched to any branch (including the main branch), you
2080 stay on it for subsequent VC commands, until you explicitly select some
2083 @node Creating Branches
2084 @subsubsection Creating New Branches
2086 To create a new branch from a head version (one that is the latest in
2087 the branch that contains it), first select that version if necessary,
2088 lock it with @kbd{C-x v v}, and make whatever changes you want. Then,
2089 when you check in the changes, use @kbd{C-u C-x v v}. This lets you
2090 specify the version number for the new version. You should specify a
2091 suitable branch number for a branch starting at the current version.
2092 For example, if the current version is 2.5, the branch number should be
2093 2.5.1, 2.5.2, and so on, depending on the number of existing branches at
2096 To create a new branch at an older version (one that is no longer the
2097 head of a branch), first select that version (@pxref{Switching
2098 Branches}), then lock it with @kbd{C-x v v}. You'll be asked to
2099 confirm, when you lock the old version, that you really mean to create a
2100 new branch---if you say no, you'll be offered a chance to lock the
2101 latest version instead.
2103 Then make your changes and type @kbd{C-x v v} again to check in a new
2104 version. This automatically creates a new branch starting from the
2105 selected version. You need not specially request a new branch, because
2106 that's the only way to add a new version at a point that is not the head
2109 After the branch is created, you ``stay'' on it. That means that
2110 subsequent check-ins create new versions on that branch. To leave the
2111 branch, you must explicitly select a different version with @kbd{C-u C-x
2112 v v}. To transfer changes from one branch to another, use the merge
2113 command, described in the next section.
2116 @subsubsection Merging Branches
2118 @cindex merging changes
2119 When you have finished the changes on a certain branch, you will
2120 often want to incorporate them into the file's main line of development
2121 (the trunk). This is not a trivial operation, because development might
2122 also have proceeded on the trunk, so that you must @dfn{merge} the
2123 changes into a file that has already been changed otherwise. VC allows
2124 you to do this (and other things) with the @code{vc-merge} command.
2127 @item C-x v m (vc-merge)
2128 Merge changes into the work file.
2133 @kbd{C-x v m} (@code{vc-merge}) takes a set of changes and merges it
2134 into the current version of the work file. It firsts asks you in the
2135 minibuffer where the changes should come from. If you just type
2136 @key{RET}, Emacs merges any changes that were made on the same branch
2137 since you checked the file out (we call this @dfn{merging the news}).
2138 This is the common way to pick up recent changes from the repository,
2139 regardless of whether you have already changed the file yourself.
2141 You can also enter a branch number or a pair of version numbers in
2142 the minibuffer. Then @kbd{C-x v m} finds the changes from that
2143 branch, or the differences between the two versions you specified, and
2144 merges them into the current version of the current file.
2146 As an example, suppose that you have finished a certain feature on
2147 branch 1.3.1. In the meantime, development on the trunk has proceeded
2148 to version 1.5. To merge the changes from the branch to the trunk,
2149 first go to the head version of the trunk, by typing @kbd{C-u C-x v v
2150 @key{RET}}. Version 1.5 is now current. If locking is used for the file,
2151 type @kbd{C-x v v} to lock version 1.5 so that you can change it. Next,
2152 type @kbd{C-x v m 1.3.1 @key{RET}}. This takes the entire set of changes on
2153 branch 1.3.1 (relative to version 1.3, where the branch started, up to
2154 the last version on the branch) and merges it into the current version
2155 of the work file. You can now check in the changed file, thus creating
2156 version 1.6 containing the changes from the branch.
2158 It is possible to do further editing after merging the branch, before
2159 the next check-in. But it is usually wiser to check in the merged
2160 version, then lock it and make the further changes. This will keep
2161 a better record of the history of changes.
2164 @cindex resolving conflicts
2165 When you merge changes into a file that has itself been modified, the
2166 changes might overlap. We call this situation a @dfn{conflict}, and
2167 reconciling the conflicting changes is called @dfn{resolving a
2170 Whenever conflicts occur during merging, VC detects them, tells you
2171 about them in the echo area, and asks whether you want help in merging.
2172 If you say yes, it starts an Ediff session (@pxref{Top,
2173 Ediff, Ediff, ediff, The Ediff Manual}).
2175 If you say no, the conflicting changes are both inserted into the
2176 file, surrounded by @dfn{conflict markers}. The example below shows how
2177 a conflict region looks; the file is called @samp{name} and the current
2178 master file version with user B's changes in it is 1.11.
2180 @c @w here is so CVS won't think this is a conflict.
2184 @var{User A's version}
2186 @var{User B's version}
2191 @cindex vc-resolve-conflicts
2192 Then you can resolve the conflicts by editing the file manually. Or
2193 you can type @code{M-x vc-resolve-conflicts} after visiting the file.
2194 This starts an Ediff session, as described above. Don't forget to
2195 check in the merged version afterwards.
2197 @node Multi-User Branching
2198 @subsubsection Multi-User Branching
2200 It is often useful for multiple developers to work simultaneously on
2201 different branches of a file. CVS allows this by default; for RCS, it
2202 is possible if you create multiple source directories. Each source
2203 directory should have a link named @file{RCS} which points to a common
2204 directory of RCS master files. Then each source directory can have its
2205 own choice of selected versions, but all share the same common RCS
2208 This technique works reliably and automatically, provided that the
2209 source files contain RCS version headers (@pxref{Version Headers}). The
2210 headers enable Emacs to be sure, at all times, which version number is
2211 present in the work file.
2213 If the files do not have version headers, you must instead tell Emacs
2214 explicitly in each session which branch you are working on. To do this,
2215 first find the file, then type @kbd{C-u C-x v v} and specify the correct
2216 branch number. This ensures that Emacs knows which branch it is using
2217 during this particular editing session.
2219 @node Remote Repositories
2220 @subsection Remote Repositories
2221 @cindex remote repositories (CVS)
2223 A common way of using CVS is to set up a central CVS repository on
2224 some Internet host, then have each developer check out a personal
2225 working copy of the files on his local machine. Committing changes to
2226 the repository, and picking up changes from other users into one's own
2227 working area, then works by direct interactions with the CVS server.
2229 One difficulty is that access to the CVS server is often slow, and
2230 that developers might need to work off-line as well. VC is designed
2231 to reduce the amount of network interaction necessary.
2234 * Version Backups:: Keeping local copies of repository versions.
2235 * Local Version Control:: Using another version system for local editing.
2238 @node Version Backups
2239 @subsubsection Version Backups
2240 @cindex version backups
2242 @cindex automatic version backups
2243 When VC sees that the CVS repository for a file is on a remote
2244 machine, it automatically makes local backups of unmodified versions
2245 of the file---@dfn{automatic version backups}. This means that you
2246 can compare the file to the repository version (@kbd{C-x v =}), or
2247 revert to that version (@kbd{C-x v u}), without any network
2250 The local copy of the unmodified file is called a @dfn{version
2251 backup} to indicate that it corresponds exactly to a version that is
2252 stored in the repository. Note that version backups are not the same
2253 as ordinary Emacs backup files (@pxref{Backup}). But they follow a
2254 similar naming convention.
2256 For a file that comes from a remote CVS repository, VC makes a
2257 version backup whenever you save the first changes to the file, and
2258 removes it after you have committed your modified version to the
2259 repository. You can disable the making of automatic version backups by
2260 setting @code{vc-cvs-stay-local} to @code{nil} (@pxref{CVS Options}).
2262 @cindex manual version backups
2263 The name of the automatic version backup for version @var{version}
2264 of file @var{file} is @code{@var{file}.~@var{version}.~}. This is
2265 almost the same as the name used by @kbd{C-x v ~} (@pxref{Old
2266 Versions}), the only difference being the additional dot (@samp{.})
2267 after the version number. This similarity is intentional, because
2268 both kinds of files store the same kind of information. The file made
2269 by @kbd{C-x v ~} acts as a @dfn{manual version backup}.
2271 All the VC commands that operate on old versions of a file can use
2272 both kinds of version backups. For instance, @kbd{C-x v ~} uses
2273 either an automatic or a manual version backup, if possible, to get
2274 the contents of the version you request. Likewise, @kbd{C-x v =} and
2275 @kbd{C-x v u} use either an automatic or a manual version backup, if
2276 one of them exists, to get the contents of a version to compare or
2277 revert to. If you changed a file outside of Emacs, so that no
2278 automatic version backup was created for the previous text, you can
2279 create a manual backup of that version using @kbd{C-x v ~}, and thus
2280 obtain the benefit of the local copy for Emacs commands.
2282 The only difference in Emacs's handling of manual and automatic
2283 version backups, once they exist, is that Emacs deletes automatic
2284 version backups when you commit to the repository. By contrast,
2285 manual version backups remain until you delete them.
2287 @node Local Version Control
2288 @subsubsection Local Version Control
2289 @cindex local version control
2290 @cindex local back end (version control)
2292 When you make many changes to a file that comes from a remote
2293 repository, it can be convenient to have version control on your local
2294 machine as well. You can then record intermediate versions, revert to
2295 a previous state, etc., before you actually commit your changes to the
2298 VC lets you do this by putting a file under a second, local version
2299 control system, so that the file is effectively registered in two
2300 systems at the same time. For the description here, we will assume
2301 that the remote system is CVS, and you use RCS locally, although the
2302 mechanism works with any combination of version control systems
2305 To make it work with other back ends, you must make sure that the
2306 ``more local'' back end comes before the ``more remote'' back end in
2307 the setting of @code{vc-handled-backends} (@pxref{Customizing VC}). By
2308 default, this variable is set up so that you can use remote CVS and
2309 local RCS as described here.
2311 To start using local RCS for a file that comes from a remote CVS
2312 server, you must @emph{register the file in RCS}, by typing @kbd{C-u
2313 C-x v v rcs @key{RET}}. (In other words, use @code{vc-next-action} with a
2314 prefix argument, and specify RCS as the back end.)
2316 You can do this at any time; it does not matter whether you have
2317 already modified the file with respect to the version in the CVS
2318 repository. If possible, VC tries to make the RCS master start with
2319 the unmodified repository version, then checks in any local changes
2320 as a new version. This works if you have not made any changes yet, or
2321 if the unmodified repository version exists locally as a version
2322 backup (@pxref{Version Backups}). If the unmodified version is not
2323 available locally, the RCS master starts with the modified version;
2324 the only drawback to this is that you cannot compare your changes
2325 locally to what is stored in the repository.
2327 The version number of the RCS master is derived from the current CVS
2328 version, starting a branch from it. For example, if the current CVS
2329 version is 1.23, the local RCS branch will be 1.23.1. Version 1.23 in
2330 the RCS master will be identical to version 1.23 under CVS; your first
2331 changes are checked in as 1.23.1.1. (If the unmodified file is not
2332 available locally, VC will check in the modified file twice, both as
2333 1.23 and 1.23.1.1, to make the revision numbers consistent.)
2335 If you do not use locking under CVS (the default), locking is also
2336 disabled for RCS, so that editing under RCS works exactly as under
2339 When you are done with local editing, you can commit the final version
2340 back to the CVS repository by typing @kbd{C-u C-x v v cvs @key{RET}}.
2341 This initializes the log entry buffer (@pxref{Log Buffer}) to contain
2342 all the log entries you have recorded in the RCS master; you can edit
2343 them as you wish, and then commit in CVS by typing @kbd{C-c C-c}. If
2344 the commit is successful, VC removes the RCS master, so that the file
2345 is once again registered under CVS only. (The RCS master is not
2346 actually deleted, just renamed by appending @samp{~} to the name, so
2347 that you can refer to it later if you wish.)
2349 While using local RCS, you can pick up recent changes from the CVS
2350 repository into your local file, or commit some of your changes back
2351 to CVS, without terminating local RCS version control. To do this,
2352 switch to the CVS back end temporarily, with the @kbd{C-x v b} command:
2356 Switch to another back end that the current file is registered
2357 under (@code{vc-switch-backend}).
2359 @item C-u C-x v b @var{backend} @key{RET}
2360 Switch to @var{backend} for the current file.
2364 @findex vc-switch-backend
2365 @kbd{C-x v b} does not change the buffer contents, or any files; it
2366 only changes VC's perspective on how to handle the file. Any
2367 subsequent VC commands for that file will operate on the back end that
2368 is currently selected.
2370 If the current file is registered in more than one back end, typing
2371 @kbd{C-x v b} ``cycles'' through all of these back ends. With a
2372 prefix argument, it asks for the back end to use in the minibuffer.
2374 Thus, if you are using local RCS, and you want to pick up some recent
2375 changes in the file from remote CVS, first visit the file, then type
2376 @kbd{C-x v b} to switch to CVS, and finally use @kbd{C-x v m
2377 @key{RET}} to merge the news (@pxref{Merging}). You can then switch
2378 back to RCS by typing @kbd{C-x v b} again, and continue to edit
2381 But if you do this, the revision numbers in the RCS master no longer
2382 correspond to those of CVS. Technically, this is not a problem, but
2383 it can become difficult to keep track of what is in the CVS repository
2384 and what is not. So we suggest that you return from time to time to
2385 CVS-only operation, by committing your local changes back to the
2386 repository using @kbd{C-u C-x v v cvs @key{RET}}.
2389 @subsection Snapshots
2390 @cindex snapshots and version control
2392 A @dfn{snapshot} is a named set of file versions (one for each
2393 registered file) that you can treat as a unit. One important kind of
2394 snapshot is a @dfn{release}, a (theoretically) stable version of the
2395 system that is ready for distribution to users.
2398 * Making Snapshots:: The snapshot facilities.
2399 * Snapshot Caveats:: Things to be careful of when using snapshots.
2402 @node Making Snapshots
2403 @subsubsection Making and Using Snapshots
2405 There are two basic commands for snapshots; one makes a
2406 snapshot with a given name, the other retrieves a named snapshot.
2410 @findex vc-create-snapshot
2411 @item C-x v s @var{name} @key{RET}
2412 Define the last saved versions of every registered file in or under the
2413 current directory as a snapshot named @var{name}
2414 (@code{vc-create-snapshot}).
2417 @findex vc-retrieve-snapshot
2418 @item C-x v r @var{name} @key{RET}
2419 For all registered files at or below the current directory level, select
2420 whatever versions correspond to the snapshot @var{name}
2421 (@code{vc-retrieve-snapshot}).
2423 This command reports an error if any files are locked at or below the
2424 current directory, without changing anything; this is to avoid
2425 overwriting work in progress.
2428 A snapshot uses a very small amount of resources---just enough to record
2429 the list of file names and which version belongs to the snapshot. Thus,
2430 you need not hesitate to create snapshots whenever they are useful.
2432 You can give a snapshot name as an argument to @kbd{C-x v =} or
2433 @kbd{C-x v ~} (@pxref{Old Versions}). Thus, you can use it to compare a
2434 snapshot against the current files, or two snapshots against each other,
2435 or a snapshot against a named version.
2437 @node Snapshot Caveats
2438 @subsubsection Snapshot Caveats
2440 @cindex named configurations (RCS)
2441 VC's snapshot facilities are modeled on RCS's named-configuration
2442 support. They use RCS's native facilities for this, so
2443 snapshots made using RCS through VC are visible even when you bypass VC.
2445 With CVS, Meta-CVS, and Subversion, VC also uses the native
2446 mechanism provided by that back end to make snapshots and retrieve them
2447 (@dfn{tags} for CVS and Meta-CVS, @dfn{copies} for Subversion).
2449 @c worded verbosely to avoid overfull hbox.
2450 For SCCS, VC implements snapshots itself. The files it uses contain
2451 name/file/version-number triples. These snapshots are visible only
2454 There is no support for VC snapshots using GNU Arch yet.
2456 A snapshot is a set of checked-in versions. So make sure that all the
2457 files are checked in and not locked when you make a snapshot.
2459 File renaming and deletion can create some difficulties with snapshots.
2460 This is not a VC-specific problem, but a general design issue in version
2461 control systems that no one has solved very well yet.
2463 If you rename a registered file, you need to rename its master along
2464 with it (the command @code{vc-rename-file} does this automatically). If
2465 you are using SCCS, you must also update the records of the snapshot, to
2466 mention the file by its new name (@code{vc-rename-file} does this,
2467 too). An old snapshot that refers to a master file that no longer
2468 exists under the recorded name is invalid; VC can no longer retrieve
2469 it. It would be beyond the scope of this manual to explain enough about
2470 RCS and SCCS to explain how to update the snapshots by hand.
2472 Using @code{vc-rename-file} makes the snapshot remain valid for
2473 retrieval, but it does not solve all problems. For example, some of the
2474 files in your program probably refer to others by name. At the very
2475 least, the makefile probably mentions the file that you renamed. If you
2476 retrieve an old snapshot, the renamed file is retrieved under its new
2477 name, which is not the name that the makefile expects. So the program
2478 won't really work as retrieved.
2480 @node Miscellaneous VC
2481 @subsection Miscellaneous Commands and Features of VC
2483 This section explains the less-frequently-used features of VC.
2486 * Change Logs and VC:: Generating a change log file from log entries.
2487 * Renaming and VC:: A command to rename both the source and master
2489 * Version Headers:: Inserting version control headers into working files.
2492 @node Change Logs and VC
2493 @subsubsection Change Logs and VC
2495 If you use RCS or CVS for a program and also maintain a change log
2496 file for it (@pxref{Change Log}), you can generate change log entries
2497 automatically from the version control log entries:
2502 @findex vc-update-change-log
2503 Visit the current directory's change log file and, for registered files
2504 in that directory, create new entries for versions checked in since the
2505 most recent entry in the change log file.
2506 (@code{vc-update-change-log}).
2508 This command works with RCS or CVS only, not with any of the other
2512 As above, but only find entries for the current buffer's file.
2515 As above, but find entries for all the currently visited files that are
2516 maintained with version control. This works only with RCS, and it puts
2517 all entries in the log for the default directory, which may not be
2521 For example, suppose the first line of @file{ChangeLog} is dated
2522 1999-04-10, and that the only check-in since then was by Nathaniel
2523 Bowditch to @file{rcs2log} on 1999-05-22 with log text @samp{Ignore log
2524 messages that start with `#'.}. Then @kbd{C-x v a} visits
2525 @file{ChangeLog} and inserts text like this:
2532 1999-05-22 Nathaniel Bowditch <nat@@apn.org>
2534 * rcs2log: Ignore log messages that start with `#'.
2542 You can then edit the new change log entry further as you wish.
2544 Some of the new change log entries may duplicate what's already in
2545 ChangeLog. You will have to remove these duplicates by hand.
2547 Normally, the log entry for file @file{foo} is displayed as @samp{*
2548 foo: @var{text of log entry}}. The @samp{:} after @file{foo} is omitted
2549 if the text of the log entry starts with @w{@samp{(@var{functionname}):
2550 }}. For example, if the log entry for @file{vc.el} is
2551 @samp{(vc-do-command): Check call-process status.}, then the text in
2552 @file{ChangeLog} looks like this:
2559 1999-05-06 Nathaniel Bowditch <nat@@apn.org>
2561 * vc.el (vc-do-command): Check call-process status.
2568 When @kbd{C-x v a} adds several change log entries at once, it groups
2569 related log entries together if they all are checked in by the same
2570 author at nearly the same time. If the log entries for several such
2571 files all have the same text, it coalesces them into a single entry.
2572 For example, suppose the most recent check-ins have the following log
2576 @bullet{} For @file{vc.texinfo}: @samp{Fix expansion typos.}
2577 @bullet{} For @file{vc.el}: @samp{Don't call expand-file-name.}
2578 @bullet{} For @file{vc-hooks.el}: @samp{Don't call expand-file-name.}
2582 They appear like this in @file{ChangeLog}:
2589 1999-04-01 Nathaniel Bowditch <nat@@apn.org>
2591 * vc.texinfo: Fix expansion typos.
2593 * vc.el, vc-hooks.el: Don't call expand-file-name.
2600 Normally, @kbd{C-x v a} separates log entries by a blank line, but you
2601 can mark several related log entries to be clumped together (without an
2602 intervening blank line) by starting the text of each related log entry
2603 with a label of the form @w{@samp{@{@var{clumpname}@} }}. The label
2604 itself is not copied to @file{ChangeLog}. For example, suppose the log
2608 @bullet{} For @file{vc.texinfo}: @samp{@{expand@} Fix expansion typos.}
2609 @bullet{} For @file{vc.el}: @samp{@{expand@} Don't call expand-file-name.}
2610 @bullet{} For @file{vc-hooks.el}: @samp{@{expand@} Don't call expand-file-name.}
2614 Then the text in @file{ChangeLog} looks like this:
2621 1999-04-01 Nathaniel Bowditch <nat@@apn.org>
2623 * vc.texinfo: Fix expansion typos.
2624 * vc.el, vc-hooks.el: Don't call expand-file-name.
2631 A log entry whose text begins with @samp{#} is not copied to
2632 @file{ChangeLog}. For example, if you merely fix some misspellings in
2633 comments, you can log the change with an entry beginning with @samp{#}
2634 to avoid putting such trivia into @file{ChangeLog}.
2636 @node Renaming and VC
2637 @subsubsection Renaming VC Work Files and Master Files
2639 @findex vc-rename-file
2640 When you rename a registered file, you must also rename its master
2641 file correspondingly to get proper results. Use @code{vc-rename-file}
2642 to rename the source file as you specify, and rename its master file
2643 accordingly. It also updates any snapshots (@pxref{Snapshots}) that
2644 mention the file, so that they use the new name; despite this, the
2645 snapshot thus modified may not completely work (@pxref{Snapshot
2648 Some back ends do not provide an explicit rename operation to their
2649 repositories. After issuing @code{vc-rename-file}, use @kbd{C-x v v}
2650 on the original and renamed buffers and provide the necessary edit
2653 You cannot use @code{vc-rename-file} on a file that is locked by
2656 @node Version Headers
2657 @subsubsection Inserting Version Control Headers
2659 Sometimes it is convenient to put version identification strings
2660 directly into working files. Certain special strings called
2661 @dfn{version headers} are replaced in each successive version by the
2662 number of that version, the name of the user who created it, and other
2663 relevant information. All of the back ends that VC supports have such
2664 a mechanism, except GNU Arch.
2666 VC does not normally use the information contained in these headers.
2667 The exception is RCS---with RCS, version headers are sometimes more
2668 reliable than the master file to determine which version of the file
2669 you are editing. Note that in a multi-branch environment, version
2670 headers are necessary to make VC behave correctly (@pxref{Multi-User
2673 Searching for RCS version headers is controlled by the variable
2674 @code{vc-consult-headers}. If it is non-@code{nil} (the default),
2675 Emacs searches for headers to determine the version number you are
2676 editing. Setting it to @code{nil} disables this feature.
2678 Note that although CVS uses the same kind of version headers as RCS
2679 does, VC never searches for these headers if you are using CVS,
2680 regardless of the above setting.
2683 @findex vc-insert-headers
2684 You can use the @kbd{C-x v h} command (@code{vc-insert-headers}) to
2685 insert a suitable header string.
2689 Insert headers in a file for use with your version-control system.
2692 @vindex vc-@var{backend}-header
2693 The default header string is @samp{@w{$}Id$} for RCS and
2694 @samp{@w{%}W%} for SCCS. You can specify other headers to insert by
2695 setting the variables @code{vc-@var{backend}-header} where
2696 @var{backend} is @code{rcs} or @code{sccs}.
2698 Instead of a single string, you can specify a list of strings; then
2699 each string in the list is inserted as a separate header on a line of
2702 It may be necessary to use apparently-superfluous backslashes when
2703 writing the strings that you put in this variable. For instance, you
2704 might write @code{"$Id\$"} rather than @code{"$Id@w{$}"}. The extra
2705 backslash prevents the string constant from being interpreted as a
2706 header, if the Emacs Lisp file containing it is maintained with
2709 @vindex vc-comment-alist
2710 Each header is inserted surrounded by tabs, inside comment delimiters,
2711 on a new line at point. Normally the ordinary comment
2712 start and comment end strings of the current mode are used, but for
2713 certain modes, there are special comment delimiters for this purpose;
2714 the variable @code{vc-comment-alist} specifies them. Each element of
2715 this list has the form @code{(@var{mode} @var{starter} @var{ender})}.
2717 @vindex vc-static-header-alist
2718 The variable @code{vc-static-header-alist} specifies further strings
2719 to add based on the name of the buffer. Its value should be a list of
2720 elements of the form @code{(@var{regexp} . @var{format})}. Whenever
2721 @var{regexp} matches the buffer name, @var{format} is inserted as part
2722 of the header. A header line is inserted for each element that matches
2723 the buffer name, and for each string specified by
2724 @code{vc-@var{backend}-header}. The header line is made by processing the
2725 string from @code{vc-@var{backend}-header} with the format taken from the
2726 element. The default value for @code{vc-static-header-alist} is as follows:
2731 "\n#ifndef lint\nstatic char vcid[] = \"\%s\";\n\
2732 #endif /* lint */\n"))
2737 It specifies insertion of text of this form:
2743 static char vcid[] = "@var{string}";
2749 Note that the text above starts with a blank line.
2751 If you use more than one version header in a file, put them close
2752 together in the file. The mechanism in @code{revert-buffer} that
2753 preserves markers may not handle markers positioned between two version
2756 @node Customizing VC
2757 @subsection Customizing VC
2759 @vindex vc-handled-backends
2760 The variable @code{vc-handled-backends} determines which version
2761 control systems VC should handle. The default value is @code{(RCS CVS
2762 SVN SCCS Arch MCVS)}, so it contains all six version systems that are
2763 currently supported. If you want VC to ignore one or more of these
2764 systems, exclude its name from the list. To disable VC entirely, set
2765 this variable to @code{nil}.
2767 The order of systems in the list is significant: when you visit a file
2768 registered in more than one system (@pxref{Local Version Control}),
2769 VC uses the system that comes first in @code{vc-handled-backends} by
2770 default. The order is also significant when you register a file for
2771 the first time, @pxref{Registering} for details.
2774 * General VC Options:: Options that apply to multiple back ends.
2775 * RCS and SCCS:: Options for RCS and SCCS.
2776 * CVS Options:: Options for CVS.
2779 @node General VC Options
2780 @subsubsection General Options
2782 @vindex vc-make-backup-files
2783 Emacs normally does not save backup files for source files that are
2784 maintained with version control. If you want to make backup files even
2785 for files that use version control, set the variable
2786 @code{vc-make-backup-files} to a non-@code{nil} value.
2788 @vindex vc-keep-workfiles
2789 Normally the work file exists all the time, whether it is locked or
2790 not. If you set @code{vc-keep-workfiles} to @code{nil}, then checking
2791 in a new version with @kbd{C-x v v} deletes the work file; but any
2792 attempt to visit the file with Emacs creates it again. (With CVS, work
2793 files are always kept.)
2795 @vindex vc-follow-symlinks
2796 Editing a version-controlled file through a symbolic link can be
2797 dangerous. It bypasses the version control system---you can edit the
2798 file without locking it, and fail to check your changes in. Also,
2799 your changes might overwrite those of another user. To protect against
2800 this, VC checks each symbolic link that you visit, to see if it points
2801 to a file under version control.
2803 The variable @code{vc-follow-symlinks} controls what to do when a
2804 symbolic link points to a version-controlled file. If it is @code{nil},
2805 VC only displays a warning message. If it is @code{t}, VC automatically
2806 follows the link, and visits the real file instead, telling you about
2807 this in the echo area. If the value is @code{ask} (the default), VC
2808 asks you each time whether to follow the link.
2810 @vindex vc-suppress-confirm
2811 If @code{vc-suppress-confirm} is non-@code{nil}, then @kbd{C-x v v}
2812 and @kbd{C-x v i} can save the current buffer without asking, and
2813 @kbd{C-x v u} also operates without asking for confirmation. (This
2814 variable does not affect @kbd{C-x v c}; that operation is so drastic
2815 that it should always ask for confirmation.)
2817 @vindex vc-command-messages
2818 VC mode does much of its work by running the shell commands for RCS,
2819 CVS and SCCS. If @code{vc-command-messages} is non-@code{nil}, VC
2820 displays messages to indicate which shell commands it runs, and
2821 additional messages when the commands finish.
2824 You can specify additional directories to search for version control
2825 programs by setting the variable @code{vc-path}. These directories
2826 are searched before the usual search path. It is rarely necessary to
2827 set this variable, because VC normally finds the proper files
2831 @subsubsection Options for RCS and SCCS
2833 @cindex non-strict locking (RCS)
2834 @cindex locking, non-strict (RCS)
2835 By default, RCS uses locking to coordinate the activities of several
2836 users, but there is a mode called @dfn{non-strict locking} in which
2837 you can check-in changes without locking the file first. Use
2838 @samp{rcs -U} to switch to non-strict locking for a particular file,
2839 see the @code{rcs} manual page for details.
2841 When deducing the version control state of an RCS file, VC first
2842 looks for an RCS version header string in the file (@pxref{Version
2843 Headers}). If there is no header string, VC normally looks at the
2844 file permissions of the work file; this is fast. But there might be
2845 situations when the file permissions cannot be trusted. In this case
2846 the master file has to be consulted, which is rather expensive. Also
2847 the master file can only tell you @emph{if} there's any lock on the
2848 file, but not whether your work file really contains that locked
2851 @vindex vc-consult-headers
2852 You can tell VC not to use version headers to determine the file
2853 status by setting @code{vc-consult-headers} to @code{nil}. VC then
2854 always uses the file permissions (if it is supposed to trust them), or
2855 else checks the master file.
2857 @vindex vc-mistrust-permissions
2858 You can specify the criterion for whether to trust the file
2859 permissions by setting the variable @code{vc-mistrust-permissions}.
2860 Its value can be @code{t} (always mistrust the file permissions and
2861 check the master file), @code{nil} (always trust the file
2862 permissions), or a function of one argument which makes the decision.
2863 The argument is the directory name of the @file{RCS} subdirectory. A
2864 non-@code{nil} value from the function says to mistrust the file
2865 permissions. If you find that the file permissions of work files are
2866 changed erroneously, set @code{vc-mistrust-permissions} to @code{t}.
2867 Then VC always checks the master file to determine the file's status.
2869 VC determines the version control state of files under SCCS much as
2870 with RCS. It does not consider SCCS version headers, though. Thus,
2871 the variable @code{vc-mistrust-permissions} affects SCCS use, but
2872 @code{vc-consult-headers} does not.
2875 @subsubsection Options specific for CVS
2877 @cindex locking (CVS)
2878 By default, CVS does not use locking to coordinate the activities of
2879 several users; anyone can change a work file at any time. However,
2880 there are ways to restrict this, resulting in behavior that resembles
2883 @cindex CVSREAD environment variable (CVS)
2884 For one thing, you can set the @env{CVSREAD} environment variable
2885 (the value you use makes no difference). If this variable is defined,
2886 CVS makes your work files read-only by default. In Emacs, you must
2887 type @kbd{C-x v v} to make the file writable, so that editing works
2888 in fact similar as if locking was used. Note however, that no actual
2889 locking is performed, so several users can make their files writable
2890 at the same time. When setting @env{CVSREAD} for the first time, make
2891 sure to check out all your modules anew, so that the file protections
2894 @cindex cvs watch feature
2895 @cindex watching files (CVS)
2896 Another way to achieve something similar to locking is to use the
2897 @dfn{watch} feature of CVS. If a file is being watched, CVS makes it
2898 read-only by default, and you must also use @kbd{C-x v v} in Emacs to
2899 make it writable. VC calls @code{cvs edit} to make the file writable,
2900 and CVS takes care to notify other developers of the fact that you
2901 intend to change the file. See the CVS documentation for details on
2902 using the watch feature.
2904 @vindex vc-stay-local
2905 @vindex vc-cvs-stay-local
2906 @cindex remote repositories (CVS)
2907 When a file's repository is on a remote machine, VC tries to keep
2908 network interactions to a minimum. This is controlled by the variable
2909 @code{vc-cvs-stay-local}. There is another variable,
2910 @code{vc-stay-local}, which enables the feature also for other back
2911 ends that support it, including CVS. In the following, we will talk
2912 only about @code{vc-cvs-stay-local}, but everything applies to
2913 @code{vc-stay-local} as well.
2915 If @code{vc-cvs-stay-local} is @code{t} (the default), then VC uses
2916 only the entry in the local CVS subdirectory to determine the file's
2917 state (and possibly information returned by previous CVS commands).
2918 One consequence of this is that when you have modified a file, and
2919 somebody else has already checked in other changes to the file, you
2920 are not notified of it until you actually try to commit. (But you can
2921 try to pick up any recent changes from the repository first, using
2922 @kbd{C-x v m @key{RET}}, @pxref{Merging}).
2924 When @code{vc-cvs-stay-local} is @code{t}, VC also makes local
2925 version backups, so that simple diff and revert operations are
2926 completely local (@pxref{Version Backups}).
2928 On the other hand, if you set @code{vc-cvs-stay-local} to @code{nil},
2929 then VC queries the remote repository @emph{before} it decides what to
2930 do in @code{vc-next-action} (@kbd{C-x v v}), just as it does for local
2931 repositories. It also does not make any version backups.
2933 You can also set @code{vc-cvs-stay-local} to a regular expression
2934 that is matched against the repository host name; VC then stays local
2935 only for repositories from hosts that match the pattern.
2937 @vindex vc-cvs-global-switches
2938 You can specify additional command line options to pass to all CVS
2939 operations in the variable @code{vc-cvs-global-switches}. These
2940 switches are inserted immediately after the @code{cvs} command, before
2941 the name of the operation to invoke.
2944 @section File Directories
2946 @cindex file directory
2947 @cindex directory listing
2948 The file system groups files into @dfn{directories}. A @dfn{directory
2949 listing} is a list of all the files in a directory. Emacs provides
2950 commands to create and delete directories, and to make directory
2951 listings in brief format (file names only) and verbose format (sizes,
2952 dates, and authors included). Emacs also includes a directory browser
2953 feature called Dired; see @ref{Dired}.
2956 @item C-x C-d @var{dir-or-pattern} @key{RET}
2957 Display a brief directory listing (@code{list-directory}).
2958 @item C-u C-x C-d @var{dir-or-pattern} @key{RET}
2959 Display a verbose directory listing.
2960 @item M-x make-directory @key{RET} @var{dirname} @key{RET}
2961 Create a new directory named @var{dirname}.
2962 @item M-x delete-directory @key{RET} @var{dirname} @key{RET}
2963 Delete the directory named @var{dirname}. It must be empty,
2964 or you get an error.
2967 @findex list-directory
2969 The command to display a directory listing is @kbd{C-x C-d}
2970 (@code{list-directory}). It reads using the minibuffer a file name
2971 which is either a directory to be listed or a wildcard-containing
2972 pattern for the files to be listed. For example,
2975 C-x C-d /u2/emacs/etc @key{RET}
2979 lists all the files in directory @file{/u2/emacs/etc}. Here is an
2980 example of specifying a file name pattern:
2983 C-x C-d /u2/emacs/src/*.c @key{RET}
2986 Normally, @kbd{C-x C-d} displays a brief directory listing containing
2987 just file names. A numeric argument (regardless of value) tells it to
2988 make a verbose listing including sizes, dates, and owners (like
2991 @vindex list-directory-brief-switches
2992 @vindex list-directory-verbose-switches
2993 The text of a directory listing is mostly obtained by running
2994 @code{ls} in an inferior process. Two Emacs variables control the
2995 switches passed to @code{ls}: @code{list-directory-brief-switches} is
2996 a string giving the switches to use in brief listings (@code{"-CF"} by
2997 default), and @code{list-directory-verbose-switches} is a string
2998 giving the switches to use in a verbose listing (@code{"-l"} by
3001 @vindex directory-free-space-program
3002 @vindex directory-free-space-args
3003 In verbose directory listings, Emacs adds information about the
3004 amount of free space on the disk that contains the directory. To do
3005 this, it runs the program specified by
3006 @code{directory-free-space-program} with arguments
3007 @code{directory-free-space-args}.
3009 @node Comparing Files
3010 @section Comparing Files
3011 @cindex comparing files
3014 @vindex diff-switches
3015 The command @kbd{M-x diff} compares two files, displaying the
3016 differences in an Emacs buffer named @samp{*diff*}. It works by
3017 running the @code{diff} program, using options taken from the variable
3018 @code{diff-switches}. The value of @code{diff-switches} should be a
3019 string; the default is @code{"-c"} to specify a context diff.
3022 The command @kbd{M-x diff-backup} compares a specified file with its most
3023 recent backup. If you specify the name of a backup file,
3024 @code{diff-backup} compares it with the source file that it is a backup
3027 @findex diff-goto-source
3030 The @samp{*diff*} buffer uses Diff mode, which enables you to use
3031 @kbd{C-x `} to visit successive changed locations in the two source
3032 files, as in Compilation mode (@pxref{Compilation Mode}.) You can
3033 also move to a particular hunk of changes and type @kbd{C-c C-c}
3034 (@code{diff-goto-source}) to visit the corresponding source location.
3037 Differences between versions of files are often distributed as
3038 patches, which are the output from the @command{diff} program. You
3039 can use Diff mode to operate on a patch by typing @kbd{M-x diff-mode}.
3041 @findex compare-windows
3042 The command @kbd{M-x compare-windows} compares the text in the
3043 current window with that in the next window. (For more information
3044 about windows in Emacs, @ref{Windows}.) Comparison starts at point in
3045 each window, after pushing each initial point value on the mark ring
3046 in its respective buffer. Then it moves point forward in each window,
3047 one character at a time, until it reaches characters that don't match.
3048 Then the command exits.
3050 If point in the two windows is followed by non-matching text when
3051 the command starts, @kbd{M-x compare-windows} tries heuristically to
3052 advance up to matching text in the two windows, and then exits. So if
3053 you use @kbd{M-x compare-windows} repeatedly, each time it either
3054 skips one matching range or finds the start of another.
3056 @vindex compare-ignore-case
3057 @vindex compare-ignore-whitespace
3058 With a numeric argument, @code{compare-windows} ignores changes in
3059 whitespace. If the variable @code{compare-ignore-case} is
3060 non-@code{nil}, the comparison ignores differences in case as well.
3061 If the variable @code{compare-ignore-whitespace} is non-@code{nil},
3062 @code{compare-windows} normally ignores changes in whitespace, and a
3063 prefix argument turns that off.
3067 @cindex failed merges
3068 @cindex merges, failed
3069 @cindex comparing 3 files (@code{diff3})
3070 You can use @kbd{M-x smerge-mode} to turn on Smerge mode, a minor
3071 mode for editing output from the @command{diff3} program. This is
3072 typically the result of a failed merge from a version control system
3073 ``update'' outside VC, due to conflicting changes to a file. Smerge
3074 mode provides commands to resolve conflicts by selecting specific
3077 @inforef{Emerge,, emacs-xtra} for the Emerge facility, which
3078 provides a powerful interface for merging files.
3081 @section Miscellaneous File Operations
3083 Emacs has commands for performing many other operations on files.
3084 All operate on one file; they do not accept wildcard file names.
3090 @kbd{M-x view-file} allows you to scan or read a file by sequential
3091 screenfuls. It reads a file name argument using the minibuffer. After
3092 reading the file into an Emacs buffer, @code{view-file} displays the
3093 beginning. You can then type @key{SPC} to scroll forward one windowful,
3094 or @key{DEL} to scroll backward. Various other commands are provided
3095 for moving around in the file, but none for changing it; type @kbd{?}
3096 while viewing for a list of them. They are mostly the same as normal
3097 Emacs cursor motion commands. To exit from viewing, type @kbd{q}.
3098 The commands for viewing are defined by a special minor mode called View
3101 A related command, @kbd{M-x view-buffer}, views a buffer already present
3102 in Emacs. @xref{Misc Buffer}.
3106 @kbd{M-x insert-file} (also @kbd{C-x i}) inserts a copy of the
3107 contents of the specified file into the current buffer at point,
3108 leaving point unchanged before the contents and the mark after them.
3110 @findex write-region
3111 @kbd{M-x write-region} is the inverse of @kbd{M-x insert-file}; it
3112 copies the contents of the region into the specified file. @kbd{M-x
3113 append-to-file} adds the text of the region to the end of the
3114 specified file. @xref{Accumulating Text}. The variable
3115 @code{write-region-inhibit-fsync} applies to these commands, as well
3116 as saving files; see @ref{Customize Save}.
3119 @cindex deletion (of files)
3120 @kbd{M-x delete-file} deletes the specified file, like the @code{rm}
3121 command in the shell. If you are deleting many files in one directory, it
3122 may be more convenient to use Dired (@pxref{Dired}).
3125 @kbd{M-x rename-file} reads two file names @var{old} and @var{new} using
3126 the minibuffer, then renames file @var{old} as @var{new}. If the file name
3127 @var{new} already exists, you must confirm with @kbd{yes} or renaming is not
3128 done; this is because renaming causes the old meaning of the name @var{new}
3129 to be lost. If @var{old} and @var{new} are on different file systems, the
3130 file @var{old} is copied and deleted.
3132 If the argument @var{new} is just a directory name, the real new
3133 name is in that directory, with the same non-directory component as
3134 @var{old}. For example, @kbd{M-x rename-file RET ~/foo RET /tmp RET}
3135 renames @file{~/foo} to @file{/tmp/foo}. The same rule applies to all
3136 the remaining commands in this section. All of them ask for
3137 confirmation when the new file name already exists, too.
3139 @findex add-name-to-file
3140 @cindex hard links (creation)
3141 The similar command @kbd{M-x add-name-to-file} is used to add an
3142 additional name to an existing file without removing its old name.
3143 The new name is created as a ``hard link'' to the existing file.
3144 The new name must belong on the same file system that the file is on.
3145 On MS-Windows, this command works only if the file resides in an NTFS
3146 file system. On MS-DOS, it works by copying the file.
3149 @cindex copying files
3150 @kbd{M-x copy-file} reads the file @var{old} and writes a new file
3151 named @var{new} with the same contents.
3153 @findex make-symbolic-link
3154 @cindex symbolic links (creation)
3155 @kbd{M-x make-symbolic-link} reads two file names @var{target} and
3156 @var{linkname}, then creates a symbolic link named @var{linkname},
3157 which points at @var{target}. The effect is that future attempts to
3158 open file @var{linkname} will refer to whatever file is named
3159 @var{target} at the time the opening is done, or will get an error if
3160 the name @var{target} is nonexistent at that time. This command does
3161 not expand the argument @var{target}, so that it allows you to specify
3162 a relative name as the target of the link.
3164 Not all systems support symbolic links; on systems that don't
3165 support them, this command is not defined.
3167 @node Compressed Files
3168 @section Accessing Compressed Files
3170 @cindex uncompression
3171 @cindex Auto Compression mode
3172 @cindex mode, Auto Compression
3175 Emacs automatically uncompresses compressed files when you visit
3176 them, and automatically recompresses them if you alter them and save
3177 them. Emacs recognizes compressed files by their file names. File
3178 names ending in @samp{.gz} indicate a file compressed with
3179 @code{gzip}. Other endings indicate other compression programs.
3181 Automatic uncompression and compression apply to all the operations in
3182 which Emacs uses the contents of a file. This includes visiting it,
3183 saving it, inserting its contents into a buffer, loading it, and byte
3186 @findex auto-compression-mode
3187 @vindex auto-compression-mode
3188 To disable this feature, type the command @kbd{M-x
3189 auto-compression-mode}. You can disenable it permanently by
3190 customizing the variable @code{auto-compression-mode}.
3193 @section File Archives
3196 @cindex file archives
3198 A file whose name ends in @samp{.tar} is normally an @dfn{archive}
3199 made by the @code{tar} program. Emacs views these files in a special
3200 mode called Tar mode which provides a Dired-like list of the contents
3201 (@pxref{Dired}). You can move around through the list just as you
3202 would in Dired, and visit the subfiles contained in the archive.
3203 However, not all Dired commands are available in Tar mode.
3205 If Auto Compression mode is enabled (@pxref{Compressed Files}), then
3206 Tar mode is used also for compressed archives---files with extensions
3207 @samp{.tgz}, @code{.tar.Z} and @code{.tar.gz}.
3209 The keys @kbd{e}, @kbd{f} and @key{RET} all extract a component file
3210 into its own buffer. You can edit it there, and if you save the
3211 buffer, the edited version will replace the version in the Tar buffer.
3212 @kbd{v} extracts a file into a buffer in View mode. @kbd{o} extracts
3213 the file and displays it in another window, so you could edit the file
3214 and operate on the archive simultaneously. @kbd{d} marks a file for
3215 deletion when you later use @kbd{x}, and @kbd{u} unmarks a file, as in
3216 Dired. @kbd{C} copies a file from the archive to disk and @kbd{R}
3217 renames a file within the archive. @kbd{g} reverts the buffer from
3218 the archive on disk.
3220 The keys @kbd{M}, @kbd{G}, and @kbd{O} change the file's permission
3221 bits, group, and owner, respectively.
3223 If your display supports colors and the mouse, moving the mouse
3224 pointer across a file name highlights that file name, indicating that
3225 you can click on it. Clicking @kbd{Mouse-2} on the highlighted file
3226 name extracts the file into a buffer and displays that buffer.
3228 Saving the Tar buffer writes a new version of the archive to disk with
3229 the changes you made to the components.
3231 You don't need the @code{tar} program to use Tar mode---Emacs reads
3232 the archives directly. However, accessing compressed archives
3233 requires the appropriate uncompression program.
3235 @cindex Archive mode
3236 @cindex mode, archive
3247 @cindex Java class archives
3248 @cindex unzip archives
3249 A separate but similar Archive mode is used for archives produced by
3250 the programs @code{arc}, @code{jar}, @code{lzh}, @code{zip}, and
3251 @code{zoo}, which have extensions corresponding to the program names.
3253 The key bindings of Archive mode are similar to those in Tar mode,
3254 with the addition of the @kbd{m} key which marks a file for subsequent
3255 operations, and @kbd{M-@key{DEL}} which unmarks all the marked files.
3256 Also, the @kbd{a} key toggles the display of detailed file
3257 information, for those archive types where it won't fit in a single
3258 line. Operations such as renaming a subfile, or changing its mode or
3259 owner, are supported only for some of the archive formats.
3261 Unlike Tar mode, Archive mode runs the archiving program to unpack
3262 and repack archives. Details of the program names and their options
3263 can be set in the @samp{Archive} Customize group. However, you don't
3264 need these programs to look at the archive table of contents, only to
3265 extract or manipulate the subfiles in the archive.
3268 @section Remote Files
3272 @cindex remote file access
3273 You can refer to files on other machines using a special file name
3278 /@var{host}:@var{filename}
3279 /@var{user}@@@var{host}:@var{filename}
3280 /@var{user}@@@var{host}#@var{port}:@var{filename}
3281 /@var{method}:@var{user}@@@var{host}:@var{filename}
3282 /@var{method}:@var{user}@@@var{host}#@var{port}:@var{filename}
3287 To carry out this request, Emacs uses either the FTP program or a
3288 remote-login program such as @command{ssh}, @command{rlogin}, or
3289 @command{telnet}. You can always specify in the file name which
3290 method to use---for example,
3291 @file{/ftp:@var{user}@@@var{host}:@var{filename}} uses FTP, whereas
3292 @file{/ssh:@var{user}@@@var{host}:@var{filename}} uses @command{ssh}.
3293 When you don't specify a method in the file name, Emacs chooses
3294 the method as follows:
3298 If the host name starts with @samp{ftp.} (with dot), then Emacs uses
3301 If the user name is @samp{ftp} or @samp{anonymous}, then Emacs uses
3304 Otherwise, Emacs uses @command{ssh}.
3308 Remote file access through FTP is handled by the Ange-FTP package, which
3309 is documented in the following. Remote file access through the other
3310 methods is handled by the Tramp package, which has its own manual.
3311 @xref{Top, The Tramp Manual,, tramp, The Tramp Manual}.
3313 When the Ange-FTP package is used, Emacs logs in through FTP using your
3314 user name or the name @var{user}. It may ask you for a password from
3315 time to time; this is used for logging in on @var{host}. The form using
3316 @var{port} allows you to access servers running on a non-default TCP
3319 @cindex backups for remote files
3320 @vindex ange-ftp-make-backup-files
3321 If you want to disable backups for remote files, set the variable
3322 @code{ange-ftp-make-backup-files} to @code{nil}.
3324 By default, the auto-save files (@pxref{Auto Save Files}) for remote
3325 files are made in the temporary file directory on the local machine.
3326 This is achieved using the variable @code{auto-save-file-name-transforms}.
3329 @vindex ange-ftp-default-user
3330 @cindex user name for remote file access
3331 Normally, if you do not specify a user name in a remote file name,
3332 that means to use your own user name. But if you set the variable
3333 @code{ange-ftp-default-user} to a string, that string is used instead.
3335 @cindex anonymous FTP
3336 @vindex ange-ftp-generate-anonymous-password
3337 To visit files accessible by anonymous FTP, you use special user
3338 names @samp{anonymous} or @samp{ftp}. Passwords for these user names
3339 are handled specially. The variable
3340 @code{ange-ftp-generate-anonymous-password} controls what happens: if
3341 the value of this variable is a string, then that string is used as
3342 the password; if non-@code{nil} (the default), then the value of
3343 @code{user-mail-address} is used; if @code{nil}, then Emacs prompts
3344 you for a password as usual.
3346 @cindex firewall, and accessing remote files
3347 @cindex gateway, and remote file access with @code{ange-ftp}
3348 @vindex ange-ftp-smart-gateway
3349 @vindex ange-ftp-gateway-host
3350 Sometimes you may be unable to access files on a remote machine
3351 because a @dfn{firewall} in between blocks the connection for security
3352 reasons. If you can log in on a @dfn{gateway} machine from which the
3353 target files @emph{are} accessible, and whose FTP server supports
3354 gatewaying features, you can still use remote file names; all you have
3355 to do is specify the name of the gateway machine by setting the
3356 variable @code{ange-ftp-gateway-host}, and set
3357 @code{ange-ftp-smart-gateway} to @code{t}. Otherwise you may be able
3358 to make remote file names work, but the procedure is complex. You can
3359 read the instructions by typing @kbd{M-x finder-commentary @key{RET}
3360 ange-ftp @key{RET}}.
3362 @vindex file-name-handler-alist
3363 @cindex disabling remote files
3364 You can entirely turn off the FTP file name feature by removing the
3365 entries @code{ange-ftp-completion-hook-function} and
3366 @code{ange-ftp-hook-function} from the variable
3367 @code{file-name-handler-alist}. You can turn off the feature in
3368 individual cases by quoting the file name with @samp{/:} (@pxref{Quoted
3371 @node Quoted File Names
3372 @section Quoted File Names
3374 @cindex quoting file names
3375 @cindex file names, quote special characters
3376 You can @dfn{quote} an absolute file name to prevent special
3377 characters and syntax in it from having their special effects.
3378 The way to do this is to add @samp{/:} at the beginning.
3380 For example, you can quote a local file name which appears remote, to
3381 prevent it from being treated as a remote file name. Thus, if you have
3382 a directory named @file{/foo:} and a file named @file{bar} in it, you
3383 can refer to that file in Emacs as @samp{/:/foo:/bar}.
3385 @samp{/:} can also prevent @samp{~} from being treated as a special
3386 character for a user's home directory. For example, @file{/:/tmp/~hack}
3387 refers to a file whose name is @file{~hack} in directory @file{/tmp}.
3389 Quoting with @samp{/:} is also a way to enter in the minibuffer a
3390 file name that contains @samp{$}. In order for this to work, the
3391 @samp{/:} must be at the beginning of the minibuffer contents. (You
3392 can also double each @samp{$}; see @ref{File Names with $}.)
3394 You can also quote wildcard characters with @samp{/:}, for visiting.
3395 For example, @file{/:/tmp/foo*bar} visits the file
3396 @file{/tmp/foo*bar}.
3398 Another method of getting the same result is to enter
3399 @file{/tmp/foo[*]bar}, which is a wildcard specification that matches
3400 only @file{/tmp/foo*bar}. However, in many cases there is no need to
3401 quote the wildcard characters because even unquoted they give the
3402 right result. For example, if the only file name in @file{/tmp} that
3403 starts with @samp{foo} and ends with @samp{bar} is @file{foo*bar},
3404 then specifying @file{/tmp/foo*bar} will visit only
3405 @file{/tmp/foo*bar}.
3407 @node File Name Cache
3408 @section File Name Cache
3410 @cindex file name caching
3411 @cindex cache of file names
3414 @findex file-cache-minibuffer-complete
3415 You can use the @dfn{file name cache} to make it easy to locate a
3416 file by name, without having to remember exactly where it is located.
3417 When typing a file name in the minibuffer, @kbd{C-@key{tab}}
3418 (@code{file-cache-minibuffer-complete}) completes it using the file
3419 name cache. If you repeat @kbd{C-@key{tab}}, that cycles through the
3420 possible completions of what you had originally typed. Note that the
3421 @kbd{C-@key{tab}} character cannot be typed on most text-only
3424 The file name cache does not fill up automatically. Instead, you
3425 load file names into the cache using these commands:
3427 @findex file-cache-add-directory
3429 @item M-x file-cache-add-directory @key{RET} @var{directory} @key{RET}
3430 Add each file name in @var{directory} to the file name cache.
3431 @item M-x file-cache-add-directory-using-find @key{RET} @var{directory} @key{RET}
3432 Add each file name in @var{directory} and all of its nested
3433 subdirectories to the file name cache.
3434 @item M-x file-cache-add-directory-using-locate @key{RET} @var{directory} @key{RET}
3435 Add each file name in @var{directory} and all of its nested
3436 subdirectories to the file name cache, using @command{locate} to find
3438 @item M-x file-cache-add-directory-list @key{RET} @var{variable} @key{RET}
3439 Add each file name in each directory listed in @var{variable}
3440 to the file name cache. @var{variable} should be a Lisp variable
3441 such as @code{load-path} or @code{exec-path}, whose value is a list
3443 @item M-x file-cache-clear-cache @key{RET}
3444 Clear the cache; that is, remove all file names from it.
3447 @node File Conveniences
3448 @section Convenience Features for Finding Files
3450 In this section, we introduce some convenient facilities for finding
3451 recently-opened files, reading file names from a buffer, and viewing
3454 @findex recentf-mode
3455 @vindex recentf-mode
3456 @findex recentf-save-list
3457 @findex recentf-edit-list
3458 If you enable Recentf mode, with @kbd{M-x recentf-mode}, the
3459 @samp{File} menu includes a submenu containing a list of recently
3460 opened files. @kbd{M-x recentf-save-list} saves the current
3461 @code{recent-file-list} to a file, and @kbd{M-x recentf-edit-list}
3464 The @kbd{M-x ffap} command generalizes @code{find-file} with more
3465 powerful heuristic defaults (@pxref{FFAP}), often based on the text at
3466 point. Partial Completion mode offers other features extending
3467 @code{find-file}, which can be used with @code{ffap}.
3468 @xref{Completion Options}.
3471 @findex image-toggle-display
3472 @cindex images, viewing
3473 Visiting image files automatically selects Image mode. This major
3474 mode allows you to toggle between displaying the file as an image in
3475 the Emacs buffer, and displaying its underlying text representation,
3476 using the command @kbd{C-c C-c} (@code{image-toggle-display}). This
3477 works only when Emacs can display the specific image type.
3480 @findex mode, thumbs
3481 Thumbs mode is a major mode for viewing directories containing many
3482 image files. To use it, type @kbd{M-x thumbs} and specify the
3483 directory to view. The images in that directory will be displayed in
3484 a @samp{Thumbs} buffer as @dfn{thumbnails}; type @kbd{RET} on a
3485 thumbnail to view the full-size image. Thumbs mode requires the
3486 @file{convert} program, which is part of the ImageMagick software
3493 @findex filesets-init
3494 If you regularly edit a certain group of files, you can define them
3495 as a @dfn{fileset}. This lets you perform certain operations, such as
3496 visiting, @code{query-replace}, and shell commands on all the files
3497 at once. To make use of filesets, you must first add the expression
3498 @code{(filesets-init)} to your @file{.emacs} file (@pxref{Init File}).
3499 This adds a @samp{Filesets} menu to the menu bar.
3501 @findex filesets-add-buffer
3502 @findex filesets-remove-buffer
3503 The simplest way to define a fileset is by adding files to it one
3504 at a time. To add a file to fileset @var{name}, visit the file and
3505 type @kbd{M-x filesets-add-buffer @kbd{RET} @var{name} @kbd{RET}}. If
3506 there is no fileset @var{name}, this creates a new one, which
3507 initially creates only the current file. The command @kbd{M-x
3508 filesets-remove-buffer} removes the current file from a fileset.
3510 You can also edit the list of filesets directly, with @kbd{M-x
3511 filesets-edit} (or by choosing @samp{Edit Filesets} from the
3512 @samp{Filesets} menu). The editing is performed in a Customize buffer
3513 (@pxref{Easy Customization}). Filesets need not be a simple list of
3514 files---you can also define filesets using regular expression matching
3515 file names. Some examples of these more complicated filesets are
3516 shown in the Customize buffer. Remember to select @samp{Save for
3517 future sessions} if you want to use the same filesets in future Emacs
3520 You can use the command @kbd{M-x filesets-open} to visit all the
3521 files in a fileset, and @kbd{M-x filesets-close} to close them. Use
3522 @kbd{M-x filesets-run-cmd} to run a shell command on all the files in
3523 a fileset. These commands are also available from the @samp{Filesets}
3524 menu, where each existing fileset is represented by a submenu.
3527 arch-tag: 768d32cb-e15a-4cc1-b7bf-62c00ee12250