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