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 creating files
217 What if you want to create a new file? Just visit it. Emacs prints
218 @samp{(New File)} in the echo area, but in other respects behaves as if
219 you had visited an existing empty file. If you make any changes and
220 save them, the file is created.
222 Emacs recognizes from the contents of a file which convention it uses
223 to separate lines---newline (used on GNU/Linux and on Unix),
224 carriage-return linefeed (used on Microsoft systems), or just
225 carriage-return (used on the Macintosh)---and automatically converts the
226 contents to the normal Emacs convention, which is that the newline
227 character separates lines. This is a part of the general feature of
228 coding system conversion (@pxref{Coding Systems}), and makes it possible
229 to edit files imported from various different operating systems with
230 equal convenience. If you change the text and save the file, Emacs
231 performs the inverse conversion, changing newlines back into
232 carriage-return linefeed or just carriage-return if appropriate.
234 @vindex find-file-run-dired
235 If the file you specify is actually a directory, @kbd{C-x C-f} invokes
236 Dired, the Emacs directory browser, so that you can ``edit'' the contents
237 of the directory (@pxref{Dired}). Dired is a convenient way to delete,
238 look at, or operate on the files in the directory. However, if the
239 variable @code{find-file-run-dired} is @code{nil}, then it is an error
240 to try to visit a directory.
242 Files which are actually collections of other files, or @dfn{file
243 archives}, are visited in special modes which invoke a Dired-like
244 environment to allow operations on archive members. @xref{File
245 Archives}, for more about these features.
247 @cindex wildcard characters in file names
248 @vindex find-file-wildcards
249 If the file name you specify contains shell-style wildcard
250 characters, Emacs visits all the files that match it. Wildcards
251 comprise @samp{?}, @samp{*} and @samp{[@dots{}]} sequences.
252 @xref{Quoted File Names}, for how to visit a file whose name actually
253 contains wildcard characters. You can disable the wildcard feature by
254 customizing @code{find-file-wildcards}.
256 If you visit a file that the operating system won't let you modify,
257 Emacs makes the buffer read-only, so that you won't go ahead and make
258 changes that you'll have trouble saving afterward. You can make the
259 buffer writable with @kbd{C-x C-q} (@code{vc-toggle-read-only}).
263 @findex find-file-read-only
264 Occasionally you might want to visit a file as read-only in order to
265 protect yourself from entering changes accidentally; do so by visiting
266 the file with the command @kbd{C-x C-r} (@code{find-file-read-only}).
269 @findex find-alternate-file
270 If you visit a nonexistent file unintentionally (because you typed the
271 wrong file name), use the @kbd{C-x C-v} command
272 (@code{find-alternate-file}) to visit the file you really wanted.
273 @kbd{C-x C-v} is similar to @kbd{C-x C-f}, but it kills the current
274 buffer (after first offering to save it if it is modified). When it
275 reads the file name to visit, it inserts the entire default file name in
276 the buffer, with point just after the directory part; this is convenient
277 if you made a slight error in typing the name.
279 If you find a file which exists but cannot be read, @kbd{C-x C-f}
283 @findex find-file-other-window
284 @kbd{C-x 4 f} (@code{find-file-other-window}) is like @kbd{C-x C-f}
285 except that the buffer containing the specified file is selected in another
286 window. The window that was selected before @kbd{C-x 4 f} continues to
287 show the same buffer it was already showing. If this command is used when
288 only one window is being displayed, that window is split in two, with one
289 window showing the same buffer as before, and the other one showing the
290 newly requested file. @xref{Windows}.
293 @findex find-file-other-frame
294 @kbd{C-x 5 f} (@code{find-file-other-frame}) is similar, but opens a
295 new frame, or makes visible any existing frame showing the file you
296 seek. This feature is available only when you are using a window
297 system. @xref{Frames}.
299 @findex find-file-literally
300 If you wish to edit a file as a sequence of ASCII characters with no special
301 encoding or conversion, use the @kbd{M-x find-file-literally} command.
302 It visits a file, like @kbd{C-x C-f}, but does not do format conversion
303 (@pxref{Formatted Text}), character code conversion (@pxref{Coding
304 Systems}), or automatic uncompression (@pxref{Compressed Files}), and
305 does not add a final newline because of @code{require-final-newline}.
306 If you already have visited the same file in the usual (non-literal)
307 manner, this command asks you whether to visit it literally instead.
309 @vindex find-file-hooks
310 @vindex find-file-not-found-hooks
311 Two special hook variables allow extensions to modify the operation of
312 visiting files. Visiting a file that does not exist runs the functions
313 in the list @code{find-file-not-found-hooks}; this variable holds a list
314 of functions, and the functions are called one by one (with no
315 arguments) until one of them returns non-@code{nil}. This is not a
316 normal hook, and the name ends in @samp{-hooks} rather than @samp{-hook}
317 to indicate that fact.
319 Any visiting of a file, whether extant or not, expects
320 @code{find-file-hooks} to contain a list of functions, and calls them
321 all, one by one, with no arguments. This variable is really a normal
322 hook, but it has an abnormal name for historical compatibility. In the
323 case of a nonexistent file, the @code{find-file-not-found-hooks} are run
326 There are several ways to specify automatically the major mode for
327 editing the file (@pxref{Choosing Modes}), and to specify local
328 variables defined for that file (@pxref{File Variables}).
331 @section Saving Files
333 @dfn{Saving} a buffer in Emacs means writing its contents back into the file
334 that was visited in the buffer.
338 Save the current buffer in its visited file (@code{save-buffer}).
340 Save any or all buffers in their visited files (@code{save-some-buffers}).
342 Forget that the current buffer has been changed (@code{not-modified}).
343 With prefix argument (@kbd{C-u}), mark the current buffer as changed.
345 Save the current buffer in a specified file (@code{write-file}).
346 @item M-x set-visited-file-name
347 Change the file name under which the current buffer will be saved.
352 When you wish to save the file and make your changes permanent, type
353 @kbd{C-x C-s} (@code{save-buffer}). After saving is finished, @kbd{C-x C-s}
354 displays a message like this:
357 Wrote /u/rms/gnu/gnu.tasks
361 If the selected buffer is not modified (no changes have been made in it
362 since the buffer was created or last saved), saving is not really done,
363 because it would have no effect. Instead, @kbd{C-x C-s} displays a message
364 like this in the echo area:
367 (No changes need to be saved)
371 @findex save-some-buffers
372 The command @kbd{C-x s} (@code{save-some-buffers}) offers to save any
373 or all modified buffers. It asks you what to do with each buffer. The
374 possible responses are analogous to those of @code{query-replace}:
378 Save this buffer and ask about the rest of the buffers.
380 Don't save this buffer, but ask about the rest of the buffers.
382 Save this buffer and all the rest with no more questions.
383 @c following generates acceptable underfull hbox
385 Terminate @code{save-some-buffers} without any more saving.
387 Save this buffer, then exit @code{save-some-buffers} without even asking
390 View the buffer that you are currently being asked about. When you exit
391 View mode, you get back to @code{save-some-buffers}, which asks the
394 Display a help message about these options.
397 @kbd{C-x C-c}, the key sequence to exit Emacs, invokes
398 @code{save-some-buffers} and therefore asks the same questions.
402 If you have changed a buffer but you do not want to save the changes,
403 you should take some action to prevent it. Otherwise, each time you use
404 @kbd{C-x s} or @kbd{C-x C-c}, you are liable to save this buffer by
405 mistake. One thing you can do is type @kbd{M-~} (@code{not-modified}),
406 which clears out the indication that the buffer is modified. If you do
407 this, none of the save commands will believe that the buffer needs to be
408 saved. (@samp{~} is often used as a mathematical symbol for `not'; thus
409 @kbd{M-~} is `not', metafied.) You could also use
410 @code{set-visited-file-name} (see below) to mark the buffer as visiting
411 a different file name, one which is not in use for anything important.
412 Alternatively, you can cancel all the changes made since the file was
413 visited or saved, by reading the text from the file again. This is
414 called @dfn{reverting}. @xref{Reverting}. You could also undo all the
415 changes by repeating the undo command @kbd{C-x u} until you have undone
416 all the changes; but reverting is easier.
418 @findex set-visited-file-name
419 @kbd{M-x set-visited-file-name} alters the name of the file that the
420 current buffer is visiting. It reads the new file name using the
421 minibuffer. Then it specifies the visited file name and changes the
422 buffer name correspondingly (as long as the new name is not in use).
423 @code{set-visited-file-name} does not save the buffer in the newly
424 visited file; it just alters the records inside Emacs in case you do
425 save later. It also marks the buffer as ``modified'' so that @kbd{C-x
426 C-s} in that buffer @emph{will} save.
430 If you wish to mark the buffer as visiting a different file and save it
431 right away, use @kbd{C-x C-w} (@code{write-file}). It is precisely
432 equivalent to @code{set-visited-file-name} followed by @kbd{C-x C-s}.
433 @kbd{C-x C-s} used on a buffer that is not visiting a file has the
434 same effect as @kbd{C-x C-w}; that is, it reads a file name, marks the
435 buffer as visiting that file, and saves it there. The default file name in
436 a buffer that is not visiting a file is made by combining the buffer name
437 with the buffer's default directory.
439 If the new file name implies a major mode, then @kbd{C-x C-w} switches
440 to that major mode, in most cases. The command
441 @code{set-visited-file-name} also does this. @xref{Choosing Modes}.
443 If Emacs is about to save a file and sees that the date of the latest
444 version on disk does not match what Emacs last read or wrote, Emacs
445 notifies you of this fact, because it probably indicates a problem caused
446 by simultaneous editing and requires your immediate attention.
447 @xref{Interlocking,, Simultaneous Editing}.
449 @vindex require-final-newline
450 If the value of the variable @code{require-final-newline} is @code{t},
451 Emacs silently puts a newline at the end of any file that doesn't
452 already end in one, every time a file is saved or written. If the value
453 is @code{nil}, Emacs leaves the end of the file unchanged; if it's
454 neither @code{nil} nor @code{t}, Emacs asks you whether to add a
455 newline. The default is @code{nil}.
458 * Backup:: How Emacs saves the old version of your file.
459 * Interlocking:: How Emacs protects against simultaneous editing
460 of one file by two users.
461 * Shadowing: File Shadowing.
462 Copying files to "shadows" automatically.
463 * Time Stamps:: Emacs can update time stamps on saved files.
467 @subsection Backup Files
469 @vindex make-backup-files
470 @vindex vc-make-backup-files
472 On most operating systems, rewriting a file automatically destroys all
473 record of what the file used to contain. Thus, saving a file from Emacs
474 throws away the old contents of the file---or it would, except that
475 Emacs carefully copies the old contents to another file, called the
476 @dfn{backup} file, before actually saving.
478 For most files, the variable @code{make-backup-files} determines
479 whether to make backup files. On most operating systems, its default
480 value is @code{t}, so that Emacs does write backup files.
482 For files managed by a version control system (@pxref{Version
483 Control}), the variable @code{vc-make-backup-files} determines whether
484 to make backup files. By default, it is @code{nil}, since backup files
485 are redundant when you store all the previous versions in a version
486 control system. @xref{General VC Options}.
488 @vindex backup-enable-predicate
489 @vindex temporary-file-directory
490 @vindex small-temporary-file-directory
491 The default value of the @code{backup-enable-predicate} variable
492 prevents backup files being written for files in the directories used
493 for temporary files, specified by @code{temporary-file-directory} or
494 @code{small-temporary-file-directory}.
496 At your option, Emacs can keep either a single backup file or a series of
497 numbered backup files for each file that you edit.
499 Emacs makes a backup for a file only the first time the file is saved
500 from one buffer. No matter how many times you save a file, its backup file
501 continues to contain the contents from before the file was visited.
502 Normally this means that the backup file contains the contents from before
503 the current editing session; however, if you kill the buffer and then visit
504 the file again, a new backup file will be made by the next save.
506 You can also explicitly request making another backup file from a
507 buffer even though it has already been saved at least once. If you save
508 the buffer with @kbd{C-u C-x C-s}, the version thus saved will be made
509 into a backup file if you save the buffer again. @kbd{C-u C-u C-x C-s}
510 saves the buffer, but first makes the previous file contents into a new
511 backup file. @kbd{C-u C-u C-u C-x C-s} does both things: it makes a
512 backup from the previous contents, and arranges to make another from the
513 newly saved contents, if you save again.
516 * Names: Backup Names. How backup files are named;
517 choosing single or numbered backup files.
518 * Deletion: Backup Deletion. Emacs deletes excess numbered backups.
519 * Copying: Backup Copying. Backups can be made by copying or renaming.
523 @subsubsection Single or Numbered Backups
525 If you choose to have a single backup file (this is the default),
526 the backup file's name is normally constructed by appending @samp{~} to the
527 file name being edited; thus, the backup file for @file{eval.c} would
530 @vindex make-backup-file-name-function
531 @vindex backup-directory-alist
532 You can change this behaviour by defining the variable
533 @code{make-backup-file-name-function} to a suitable function.
534 Alternatively you can customize the variable
535 @var{backup-directory-alist} to specify that files matching certain
536 patterns should be backed up in specific directories.
538 A typical use is to add an element @code{("." . @var{dir})} to make
539 all backups in the directory with absolute name @var{dir}; Emacs
540 modifies the backup file names to avoid clashes between files with the
541 same names originating in different directories. Alternatively,
542 adding, say, @code{("." ".~")} would make backups in the invisible
543 subdirectory @file{.~} of the original file's directory. Emacs
544 creates the directory, if necessary, to make the backup.
546 If access control stops Emacs from writing backup files under the usual
547 names, it writes the backup file as @file{%backup%~} in your home
548 directory. Only one such file can exist, so only the most recently
549 made such backup is available.
551 If you choose to have a series of numbered backup files, backup file
552 names contain @samp{.~}, the number, and another @samp{~} after the
553 original file name. Thus, the backup files of @file{eval.c} would be
554 called @file{eval.c.~1~}, @file{eval.c.~2~}, and so on, all the way
555 through names like @file{eval.c.~259~} and beyond. The variable
556 @code{backup-directory-alist} applies to numbered backups just as
559 @vindex version-control
560 The choice of single backup or numbered backups is controlled by the
561 variable @code{version-control}. Its possible values are
565 Make numbered backups.
567 Make numbered backups for files that have numbered backups already.
568 Otherwise, make single backups.
570 Never make numbered backups; always make single backups.
574 You can set @code{version-control} locally in an individual buffer to
575 control the making of backups for that buffer's file. For example,
576 Rmail mode locally sets @code{version-control} to @code{never} to make sure
577 that there is only one backup for an Rmail file. @xref{Locals}.
579 @cindex @env{VERSION_CONTROL} environment variable
580 If you set the environment variable @env{VERSION_CONTROL}, to tell
581 various GNU utilities what to do with backup files, Emacs also obeys the
582 environment variable by setting the Lisp variable @code{version-control}
583 accordingly at startup. If the environment variable's value is @samp{t}
584 or @samp{numbered}, then @code{version-control} becomes @code{t}; if the
585 value is @samp{nil} or @samp{existing}, then @code{version-control}
586 becomes @code{nil}; if it is @samp{never} or @samp{simple}, then
587 @code{version-control} becomes @code{never}.
589 @node Backup Deletion
590 @subsubsection Automatic Deletion of Backups
592 To prevent unlimited consumption of disk space, Emacs can delete numbered
593 backup versions automatically. Generally Emacs keeps the first few backups
594 and the latest few backups, deleting any in between. This happens every
595 time a new backup is made.
597 @vindex kept-old-versions
598 @vindex kept-new-versions
599 The two variables @code{kept-old-versions} and
600 @code{kept-new-versions} control this deletion. Their values are,
601 respectively the number of oldest (lowest-numbered) backups to keep and
602 the number of newest (highest-numbered) ones to keep, each time a new
603 backup is made. Recall that these values are used just after a new
604 backup version is made; that newly made backup is included in the count
605 in @code{kept-new-versions}. By default, both variables are 2.
607 @vindex delete-old-versions
608 If @code{delete-old-versions} is non-@code{nil}, the excess
609 middle versions are deleted without a murmur. If it is @code{nil}, the
610 default, then you are asked whether the excess middle versions should
613 Dired's @kbd{.} (Period) command can also be used to delete old versions.
614 @xref{Dired Deletion}.
617 @subsubsection Copying vs.@: Renaming
619 Backup files can be made by copying the old file or by renaming it. This
620 makes a difference when the old file has multiple names. If the old file
621 is renamed into the backup file, then the alternate names become names for
622 the backup file. If the old file is copied instead, then the alternate
623 names remain names for the file that you are editing, and the contents
624 accessed by those names will be the new contents.
626 The method of making a backup file may also affect the file's owner
627 and group. If copying is used, these do not change. If renaming is used,
628 you become the file's owner, and the file's group becomes the default
629 (different operating systems have different defaults for the group).
631 Having the owner change is usually a good idea, because then the owner
632 always shows who last edited the file. Also, the owners of the backups
633 show who produced those versions. Occasionally there is a file whose
634 owner should not change; it is a good idea for such files to contain
635 local variable lists to set @code{backup-by-copying-when-mismatch}
636 locally (@pxref{File Variables}).
638 @vindex backup-by-copying
639 @vindex backup-by-copying-when-linked
640 @vindex backup-by-copying-when-mismatch
641 @vindex backup-by-copying-when-privileged-mismatch
642 @cindex file ownership, and backup
643 @cindex backup, and user-id
644 The choice of renaming or copying is controlled by four variables.
645 Renaming is the default choice. If the variable
646 @code{backup-by-copying} is non-@code{nil}, copying is used. Otherwise,
647 if the variable @code{backup-by-copying-when-linked} is non-@code{nil},
648 then copying is used for files that have multiple names, but renaming
649 may still be used when the file being edited has only one name. If the
650 variable @code{backup-by-copying-when-mismatch} is non-@code{nil}, then
651 copying is used if renaming would cause the file's owner or group to
652 change. @code{backup-by-copying-when-mismatch} is @code{t} by default
653 if you start Emacs as the superuser. The fourth variable,
654 @code{backup-by-copying-when-privileged-mismatch}, gives the highest
655 numeric user-id for which @code{backup-by-copying-when-mismatch} will be
656 forced on. This is useful when low-numbered user-id are assigned to
657 special system users, such as @code{root}, @code{bin}, @code{daemon},
658 etc., which must maintain ownership of files.
660 When a file is managed with a version control system (@pxref{Version
661 Control}), Emacs does not normally make backups in the usual way for
662 that file. But check-in and check-out are similar in some ways to
663 making backups. One unfortunate similarity is that these operations
664 typically break hard links, disconnecting the file name you visited from
665 any alternate names for the same file. This has nothing to do with
666 Emacs---the version control system does it.
669 @subsection Protection against Simultaneous Editing
672 @cindex simultaneous editing
673 Simultaneous editing occurs when two users visit the same file, both
674 make changes, and then both save them. If nobody were informed that
675 this was happening, whichever user saved first would later find that his
678 On some systems, Emacs notices immediately when the second user starts
679 to change the file, and issues an immediate warning. On all systems,
680 Emacs checks when you save the file, and warns if you are about to
681 overwrite another user's changes. You can prevent loss of the other
682 user's work by taking the proper corrective action instead of saving the
685 @findex ask-user-about-lock
686 @cindex locking files
687 When you make the first modification in an Emacs buffer that is
688 visiting a file, Emacs records that the file is @dfn{locked} by you.
689 (It does this by creating a symbolic link in the same directory with a
690 different name.) Emacs removes the lock when you save the changes. The
691 idea is that the file is locked whenever an Emacs buffer visiting it has
695 If you begin to modify the buffer while the visited file is locked by
696 someone else, this constitutes a @dfn{collision}. When Emacs detects a
697 collision, it asks you what to do, by calling the Lisp function
698 @code{ask-user-about-lock}. You can redefine this function for the sake
699 of customization. The standard definition of this function asks you a
700 question and accepts three possible answers:
704 Steal the lock. Whoever was already changing the file loses the lock,
705 and you gain the lock.
707 Proceed. Go ahead and edit the file despite its being locked by someone else.
709 Quit. This causes an error (@code{file-locked}) and the modification you
710 were trying to make in the buffer does not actually take place.
713 Note that locking works on the basis of a file name; if a file has
714 multiple names, Emacs does not realize that the two names are the same file
715 and cannot prevent two users from editing it simultaneously under different
716 names. However, basing locking on names means that Emacs can interlock the
717 editing of new files that will not really exist until they are saved.
719 Some systems are not configured to allow Emacs to make locks, and
720 there are cases where lock files cannot be written. In these cases,
721 Emacs cannot detect trouble in advance, but it still can detect the
722 collision when you try to save a file and overwrite someone else's
725 If Emacs or the operating system crashes, this may leave behind lock
726 files which are stale, so you may occasionally get warnings about
727 spurious collisions. When you determine that the collision is spurious,
728 just use @kbd{p} to tell Emacs to go ahead anyway.
730 Every time Emacs saves a buffer, it first checks the last-modification
731 date of the existing file on disk to verify that it has not changed since the
732 file was last visited or saved. If the date does not match, it implies
733 that changes were made in the file in some other way, and these changes are
734 about to be lost if Emacs actually does save. To prevent this, Emacs
735 prints a warning message and asks for confirmation before saving.
736 Occasionally you will know why the file was changed and know that it does
737 not matter; then you can answer @kbd{yes} and proceed. Otherwise, you should
738 cancel the save with @kbd{C-g} and investigate the situation.
740 The first thing you should do when notified that simultaneous editing
741 has already taken place is to list the directory with @kbd{C-u C-x C-d}
742 (@pxref{Directories}). This shows the file's current author. You
743 should attempt to contact him to warn him not to continue editing.
744 Often the next step is to save the contents of your Emacs buffer under a
745 different name, and use @code{diff} to compare the two files.@refill
748 @subsection Shadowing Files
753 @item M-x shadow-initialize
754 Set up file shadowing.
755 @item M-x shadow-define-literal-group
756 Declare a single file to be shared between sites.
757 @item M-x shadow-define-regexp-group
758 Make all files that match each of a group of files be shared between hosts.
759 @item M-x shadow-define-cluster @key{RET} @var{name} @key{RET}
760 Define a shadow file cluster @var{name}.
761 @item M-x shadow-copy-files
762 Copy all pending shadow files.
763 @item M-x shadow-cancel
764 Cancel the instruction to shadow some files.
767 You can arrange to keep identical @dfn{shadow} copies of certain files
768 in more than one place---possibly on different machines. To do this,
769 first you must set up a @dfn{shadow file group}, which is a set of
770 identically-named files shared between a list of sites. The file
771 group is permanent and applies to further Emacs sessions as well as
772 the current one. Once the group is set up, every time you exit Emacs,
773 it will copy the file you edited to the other files in its group. You
774 can also do the copying without exiting Emacs, by typing @kbd{M-x
777 To set up a file group, use @kbd{M-x shadow-define-literal-group} or
778 @kbd{M-x shadow-define-regexp-group}. See their documentation strings
779 for further information.
781 Before copying a file to its shadows, Emacs asks for confirmation.
782 You can answer ``no'' to bypass copying of this file, this time. If
783 you want to cancel the shadowing permanently for a certain file, use
784 @kbd{M-x shadow-cancel} to eliminate or change the shadow file group.
786 A @dfn{shadow cluster} is a group of hosts that share directories, so
787 that copying to or from one of them is sufficient to update the file
788 on all of them. Each shadow cluster has a name, and specifies the
789 network address of a primary host (the one we copy files to), and a
790 regular expression that matches the hostnames of all the other hosts
791 in the cluster. You can define a shadow cluster with @kbd{M-x
792 shadow-define-cluster}.
795 @subsection Updating Time Stamps Automatically
798 @cindex modification dates
799 @cindex locale, date format
801 You can arrange put a time stamp in a file, so that it will be updated
802 automatically each time you edit and save the file. The time stamp
803 has to be in the first eight lines of the file, and you should
817 Then add the hook function @code{time-stamp} to the hook
818 @code{write-file-hooks}; that hook function will automatically update
819 the time stamp, inserting the current date and time when you save the
820 file. You can also use the command @kbd{M-x time-stamp} to update the
821 time stamp manually. For other customizations, see the Custom group
822 @code{time-stamp}. Note that non-numeric fields in the time stamp are
823 formatted according to your locale setting (@pxref{Environment}).
826 @section Reverting a Buffer
827 @findex revert-buffer
828 @cindex drastic changes
829 @cindex reread a file
831 If you have made extensive changes to a file and then change your mind
832 about them, you can get rid of them by reading in the previous version
833 of the file. To do this, use @kbd{M-x revert-buffer}, which operates on
834 the current buffer. Since reverting a buffer unintentionally could lose
835 a lot of work, you must confirm this command with @kbd{yes}.
837 @code{revert-buffer} keeps point at the same distance (measured in
838 characters) from the beginning of the file. If the file was edited only
839 slightly, you will be at approximately the same piece of text after
840 reverting as before. If you have made drastic changes, the same value of
841 point in the old file may address a totally different piece of text.
843 Reverting marks the buffer as ``not modified'' until another change is
846 Some kinds of buffers whose contents reflect data bases other than files,
847 such as Dired buffers, can also be reverted. For them, reverting means
848 recalculating their contents from the appropriate data base. Buffers
849 created explicitly with @kbd{C-x b} cannot be reverted; @code{revert-buffer}
850 reports an error when asked to do so.
852 @vindex revert-without-query
853 When you edit a file that changes automatically and frequently---for
854 example, a log of output from a process that continues to run---it may be
855 useful for Emacs to revert the file without querying you, whenever you
856 visit the file again with @kbd{C-x C-f}.
858 To request this behavior, set the variable @code{revert-without-query}
859 to a list of regular expressions. When a file name matches one of these
860 regular expressions, @code{find-file} and @code{revert-buffer} will
861 revert it automatically if it has changed---provided the buffer itself
862 is not modified. (If you have edited the text, it would be wrong to
863 discard your changes.)
866 @section Auto-Saving: Protection Against Disasters
867 @cindex Auto Save mode
868 @cindex mode, Auto Save
871 Emacs saves all the visited files from time to time (based on counting
872 your keystrokes) without being asked. This is called @dfn{auto-saving}.
873 It prevents you from losing more than a limited amount of work if the
876 When Emacs determines that it is time for auto-saving, each buffer is
877 considered, and is auto-saved if auto-saving is turned on for it and it
878 has been changed since the last time it was auto-saved. The message
879 @samp{Auto-saving...} is displayed in the echo area during auto-saving,
880 if any files are actually auto-saved. Errors occurring during
881 auto-saving are caught so that they do not interfere with the execution
882 of commands you have been typing.
885 * Files: Auto Save Files. The file where auto-saved changes are
886 actually made until you save the file.
887 * Control: Auto Save Control. Controlling when and how often to auto-save.
888 * Recover:: Recovering text from auto-save files.
891 @node Auto Save Files
892 @subsection Auto-Save Files
894 Auto-saving does not normally save in the files that you visited, because
895 it can be very undesirable to save a program that is in an inconsistent
896 state when you have made half of a planned change. Instead, auto-saving
897 is done in a different file called the @dfn{auto-save file}, and the
898 visited file is changed only when you request saving explicitly (such as
901 Normally, the auto-save file name is made by appending @samp{#} to the
902 front and rear of the visited file name. Thus, a buffer visiting file
903 @file{foo.c} is auto-saved in a file @file{#foo.c#}. Most buffers that
904 are not visiting files are auto-saved only if you request it explicitly;
905 when they are auto-saved, the auto-save file name is made by appending
906 @samp{#%} to the front and @samp{#} to the rear of buffer name. For
907 example, the @samp{*mail*} buffer in which you compose messages to be
908 sent is auto-saved in a file named @file{#%*mail*#}. Auto-save file
909 names are made this way unless you reprogram parts of Emacs to do
910 something different (the functions @code{make-auto-save-file-name} and
911 @code{auto-save-file-name-p}). The file name to be used for auto-saving
912 in a buffer is calculated when auto-saving is turned on in that buffer.
914 When you delete a substantial part of the text in a large buffer, auto
915 save turns off temporarily in that buffer. This is because if you
916 deleted the text unintentionally, you might find the auto-save file more
917 useful if it contains the deleted text. To reenable auto-saving after
918 this happens, save the buffer with @kbd{C-x C-s}, or use @kbd{C-u 1 M-x
921 @vindex auto-save-visited-file-name
922 If you want auto-saving to be done in the visited file, set the variable
923 @code{auto-save-visited-file-name} to be non-@code{nil}. In this mode,
924 there is really no difference between auto-saving and explicit saving.
926 @vindex delete-auto-save-files
927 A buffer's auto-save file is deleted when you save the buffer in its
928 visited file. To inhibit this, set the variable @code{delete-auto-save-files}
929 to @code{nil}. Changing the visited file name with @kbd{C-x C-w} or
930 @code{set-visited-file-name} renames any auto-save file to go with
931 the new visited name.
933 @node Auto Save Control
934 @subsection Controlling Auto-Saving
936 @vindex auto-save-default
937 @findex auto-save-mode
938 Each time you visit a file, auto-saving is turned on for that file's
939 buffer if the variable @code{auto-save-default} is non-@code{nil} (but not
940 in batch mode; @pxref{Entering Emacs}). The default for this variable is
941 @code{t}, so auto-saving is the usual practice for file-visiting buffers.
942 Auto-saving can be turned on or off for any existing buffer with the
943 command @kbd{M-x auto-save-mode}. Like other minor mode commands, @kbd{M-x
944 auto-save-mode} turns auto-saving on with a positive argument, off with a
945 zero or negative argument; with no argument, it toggles.
947 @vindex auto-save-interval
948 Emacs does auto-saving periodically based on counting how many characters
949 you have typed since the last time auto-saving was done. The variable
950 @code{auto-save-interval} specifies how many characters there are between
951 auto-saves. By default, it is 300.
953 @vindex auto-save-timeout
954 Auto-saving also takes place when you stop typing for a while. The
955 variable @code{auto-save-timeout} says how many seconds Emacs should
956 wait before it does an auto save (and perhaps also a garbage
957 collection). (The actual time period is longer if the current buffer is
958 long; this is a heuristic which aims to keep out of your way when you
959 are editing long buffers, in which auto-save takes an appreciable amount
960 of time.) Auto-saving during idle periods accomplishes two things:
961 first, it makes sure all your work is saved if you go away from the
962 terminal for a while; second, it may avoid some auto-saving while you
965 Emacs also does auto-saving whenever it gets a fatal error. This
966 includes killing the Emacs job with a shell command such as @samp{kill
967 %emacs}, or disconnecting a phone line or network connection.
970 You can request an auto-save explicitly with the command @kbd{M-x
974 @subsection Recovering Data from Auto-Saves
977 You can use the contents of an auto-save file to recover from a loss
978 of data with the command @kbd{M-x recover-file @key{RET} @var{file}
979 @key{RET}}. This visits @var{file} and then (after your confirmation)
980 restores the contents from its auto-save file @file{#@var{file}#}.
981 You can then save with @kbd{C-x C-s} to put the recovered text into
982 @var{file} itself. For example, to recover file @file{foo.c} from its
983 auto-save file @file{#foo.c#}, do:@refill
986 M-x recover-file @key{RET} foo.c @key{RET}
991 Before asking for confirmation, @kbd{M-x recover-file} displays a
992 directory listing describing the specified file and the auto-save file,
993 so you can compare their sizes and dates. If the auto-save file
994 is older, @kbd{M-x recover-file} does not offer to read it.
996 @findex recover-session
997 If Emacs or the computer crashes, you can recover all the files you
998 were editing from their auto save files with the command @kbd{M-x
999 recover-session}. This first shows you a list of recorded interrupted
1000 sessions. Move point to the one you choose, and type @kbd{C-c C-c}.
1002 Then @code{recover-session} asks about each of the files that were
1003 being edited during that session, asking whether to recover that file.
1004 If you answer @kbd{y}, it calls @code{recover-file}, which works in its
1005 normal fashion. It shows the dates of the original file and its
1006 auto-save file, and asks once again whether to recover that file.
1008 When @code{recover-session} is done, the files you've chosen to
1009 recover are present in Emacs buffers. You should then save them. Only
1010 this---saving them---updates the files themselves.
1012 @vindex auto-save-list-file-prefix
1013 Emacs records interrupted sessions for later recovery in files named
1014 @file{~/.emacs.d/auto-save-list/.saves-@var{pid}-@var{hostname}}. The
1015 @samp{~/.emacs.d/auto-save-list/.saves-} portion of these names comes
1016 from the value of @code{auto-save-list-file-prefix}. You can record
1017 sessions in a different place by customizing that variable. If you
1018 set @code{auto-save-list-file-prefix} to @code{nil} in your
1019 @file{.emacs} file, sessions are not recorded for recovery.
1022 @section File Name Aliases
1024 Symbolic links and hard links both make it possible for several file
1025 names to refer to the same file. Hard links are alternate names that
1026 refer directly to the file; all the names are equally valid, and no one
1027 of them is preferred. By contrast, a symbolic link is a kind of defined
1028 alias: when @file{foo} is a symbolic link to @file{bar}, you can use
1029 either name to refer to the file, but @file{bar} is the real name, while
1030 @file{foo} is just an alias. More complex cases occur when symbolic
1031 links point to directories.
1033 If you visit two names for the same file, normally Emacs makes
1034 two different buffers, but it warns you about the situation.
1036 @vindex find-file-existing-other-name
1037 Normally, if you visit a file which Emacs is already visiting under
1038 a different name, Emacs displays a message in the echo area and uses
1039 the existing buffer visiting that file. This can happen on systems
1040 that support symbolic links, or if you use a long file name on a
1041 system that truncates long file names. You can disable this feature
1042 by setting the variable @code{find-file-existing-other-name} to
1043 @code{nil}. Then if you visit the same file under two different names,
1044 you get a separate buffer for each file name.
1046 @vindex find-file-visit-truename
1047 @cindex truenames of files
1048 @cindex file truenames
1049 If the variable @code{find-file-visit-truename} is non-@code{nil},
1050 then the file name recorded for a buffer is the file's @dfn{truename}
1051 (made by replacing all symbolic links with their target names), rather
1052 than the name you specify. Setting @code{find-file-visit-truename} also
1053 implies the effect of @code{find-file-existing-other-name}.
1055 @node Version Control
1056 @section Version Control
1057 @cindex version control
1059 @dfn{Version control systems} are packages that can record multiple
1060 versions of a source file, usually storing the unchanged parts of the
1061 file just once. Version control systems also record history information
1062 such as the creation time of each version, who created it, and a
1063 description of what was changed in that version.
1065 The Emacs version control interface is called VC. Its commands work
1066 with three version control systems---RCS, CVS, and SCCS. The GNU
1067 project recommends RCS and CVS, which are free software and available
1068 from the Free Software Foundation. We also have free software to
1069 replace SCCS, known as CSSC; if you are using SCCS and don't want to
1070 make the incompatible change to RCS or CVS, you can switch to CSSC.
1073 * Introduction to VC:: How version control works in general.
1074 * VC Mode Line:: How the mode line shows version control status.
1075 * Basic VC Editing:: How to edit a file under version control.
1076 * Old Versions:: Examining and comparing old versions.
1077 * Secondary VC Commands:: The commands used a little less frequently.
1078 * Branches:: Multiple lines of development.
1079 * Remote Repositories:: Efficient access to remote CVS servers.
1080 * Snapshots:: Sets of file versions treated as a unit.
1081 * Miscellaneous VC:: Various other commands and features of VC.
1082 * Customizing VC:: Variables that change VC's behavior.
1085 @node Introduction to VC
1086 @subsection Introduction to Version Control
1088 VC allows you to use a version control system from within Emacs,
1089 integrating the version control operations smoothly with editing. VC
1090 provides a uniform interface to version control, so that regardless of
1091 which version control system is in use, you can use it the same way.
1093 This section provides a general overview of version control, and
1094 describes the version control systems that VC supports. You can skip
1095 this section if you are already familiar with the version control system
1099 * Version Systems:: Supported version control back-end systems.
1100 * VC Concepts:: Words and concepts related to version control.
1103 @node Version Systems
1104 @subsubsection Supported Version Control Systems
1107 @cindex back end (version control)
1108 VC currently works with three different version control systems or
1109 ``back ends'': RCS, CVS, and SCCS.
1111 RCS is a free version control system that is available from the Free
1112 Software Foundation. It is perhaps the most mature of the supported
1113 back ends, and the VC commands are conceptually closest to RCS. Almost
1114 everything you can do with RCS can be done through VC.
1117 CVS is built on top of RCS, and extends the features of RCS, allowing
1118 for more sophisticated release management, and concurrent multi-user
1119 development. VC supports basic editing operations under CVS, but for
1120 some less common tasks you still need to call CVS from the command line.
1121 Note also that before using CVS you must set up a repository, which is a
1122 subject too complex to treat here.
1125 SCCS is a proprietary but widely used version control system. In
1126 terms of capabilities, it is the weakest of the three that VC
1127 supports. VC compensates for certain features missing in SCCS
1128 (snapshots, for example) by implementing them itself, but some other VC
1129 features, such as multiple branches, are not available with SCCS. You
1130 should use SCCS only if for some reason you cannot use RCS.
1133 @subsubsection Concepts of Version Control
1136 @cindex registered file
1137 When a file is under version control, we also say that it is
1138 @dfn{registered} in the version control system. Each registered file
1139 has a corresponding @dfn{master file} which represents the file's
1140 present state plus its change history---enough to reconstruct the
1141 current version or any earlier version. Usually the master file also
1142 records a @dfn{log entry} for each version, describing in words what was
1143 changed in that version.
1146 @cindex checking out files
1147 The file that is maintained under version control is sometimes called
1148 the @dfn{work file} corresponding to its master file. You edit the work
1149 file and make changes in it, as you would with an ordinary file. (With
1150 SCCS and RCS, you must @dfn{lock} the file before you start to edit it.)
1151 After you are done with a set of changes, you @dfn{check the file in},
1152 which records the changes in the master file, along with a log entry for
1155 With CVS, there are usually multiple work files corresponding to a
1156 single master file---often each user has his own copy. It is also
1157 possible to use RCS in this way, but this is not the usual way to use
1160 @cindex locking and version control
1161 A version control system typically has some mechanism to coordinate
1162 between users who want to change the same file. One method is
1163 @dfn{locking} (analogous to the locking that Emacs uses to detect
1164 simultaneous editing of a file, but distinct from it). The other method
1165 is to merge your changes with other people's changes when you check them
1168 With version control locking, work files are normally read-only so
1169 that you cannot change them. You ask the version control system to make
1170 a work file writable for you by locking it; only one user can do
1171 this at any given time. When you check in your changes, that unlocks
1172 the file, making the work file read-only again. This allows other users
1173 to lock the file to make further changes. SCCS always uses locking, and
1176 The other alternative for RCS is to let each user modify the work file
1177 at any time. In this mode, locking is not required, but it is
1178 permitted; check-in is still the way to record a new version.
1180 CVS normally allows each user to modify his own copy of the work file
1181 at any time, but requires merging with changes from other users at
1182 check-in time. However, CVS can also be set up to require locking.
1183 (@pxref{CVS Options}).
1186 @subsection Version Control and the Mode Line
1188 When you visit a file that is under version control, Emacs indicates
1189 this on the mode line. For example, @samp{RCS-1.3} says that RCS is
1190 used for that file, and the current version is 1.3.
1192 The character between the back-end name and the version number
1193 indicates the version control status of the file. @samp{-} means that
1194 the work file is not locked (if locking is in use), or not modified (if
1195 locking is not in use). @samp{:} indicates that the file is locked, or
1196 that it is modified. If the file is locked by some other user (for
1197 instance, @samp{jim}), that is displayed as @samp{RCS:jim:1.3}.
1199 @node Basic VC Editing
1200 @subsection Basic Editing under Version Control
1202 The principal VC command is an all-purpose command that performs
1203 either locking or check-in, depending on the situation.
1208 Perform the next logical version control operation on this file.
1211 @findex vc-next-action
1212 @findex vc-toggle-read-only
1214 @kindex C-x C-q @r{(Version Control)}
1215 Strictly speaking, the command for this job is @code{vc-next-action},
1216 bound to @kbd{C-x v v}. However, the normal meaning of @kbd{C-x C-q} is
1217 to make a read-only buffer writable, or vice versa; we have extended it
1218 to do the same job properly for files managed by version control, by
1219 performing the appropriate version control operations. When you type
1220 @kbd{C-x C-q} on a registered file, it acts like @kbd{C-x v v}.
1222 The precise action of this command depends on the state of the file,
1223 and whether the version control system uses locking or not. SCCS and
1224 RCS normally use locking; CVS normally does not use locking.
1227 * VC with Locking:: RCS in its default mode, SCCS, and optionally CVS.
1228 * Without Locking:: Without locking: default mode for CVS.
1229 * Advanced C-x C-q:: Advanced features available with a prefix argument.
1230 * Log Buffer:: Features available in log entry buffers.
1233 @node VC with Locking
1234 @subsubsection Basic Version Control with Locking
1236 If locking is used for the file (as with SCCS, and RCS in its default
1237 mode), @kbd{C-x C-q} can either lock a file or check it in:
1241 If the file is not locked, @kbd{C-x C-q} locks it, and
1242 makes it writable so that you can change it.
1245 If the file is locked by you, and contains changes, @kbd{C-x C-q} checks
1246 in the changes. In order to do this, it first reads the log entry
1247 for the new version. @xref{Log Buffer}.
1250 If the file is locked by you, but you have not changed it since you
1251 locked it, @kbd{C-x C-q} releases the lock and makes the file read-only
1255 If the file is locked by some other user, @kbd{C-x C-q} asks you whether
1256 you want to ``steal the lock'' from that user. If you say yes, the file
1257 becomes locked by you, but a message is sent to the person who had
1258 formerly locked the file, to inform him of what has happened.
1261 These rules also apply when you use CVS in locking mode, except
1262 that there is no such thing as stealing a lock.
1264 @node Without Locking
1265 @subsubsection Basic Version Control without Locking
1267 When there is no locking---the default for CVS---work files are always
1268 writable; you do not need to do anything before you begin to edit a
1269 file. The status indicator on the mode line is @samp{-} if the file is
1270 unmodified; it flips to @samp{:} as soon as you save any changes in the
1273 Here is what @kbd{C-x C-q} does when using CVS:
1277 If some other user has checked in changes into the master file, Emacs
1278 asks you whether you want to merge those changes into your own work
1279 file. You must do this before you can check in your own changes. (To
1280 pick up any recent changes from the master file @emph{without} trying
1281 to commit your own changes, type @kbd{C-x v m @key{RET}}.)
1285 If there are no new changes in the master file, but you have made
1286 modifications in your work file, @kbd{C-x C-q} checks in your changes.
1287 In order to do this, it first reads the log entry for the new version.
1291 If the file is not modified, the @kbd{C-x C-q} does nothing.
1294 These rules also apply when you use RCS in the mode that does not
1295 require locking, except that automatic merging of changes from the
1296 master file is not implemented. Unfortunately, this means that nothing
1297 informs you if another user has checked in changes in the same file
1298 since you began editing it, and when this happens, his changes will be
1299 effectively removed when you check in your version (though they will
1300 remain in the master file, so they will not be entirely lost). You must
1301 therefore verify the current version is unchanged, before you check in your
1302 changes. We hope to eliminate this risk and provide automatic merging
1303 with RCS in a future Emacs version.
1305 In addition, locking is possible with RCS even in this mode, although
1306 it is not required; @kbd{C-x C-q} with an unmodified file locks the
1307 file, just as it does with RCS in its normal (locking) mode.
1309 @node Advanced C-x C-q
1310 @subsubsection Advanced Control in @kbd{C-x C-q}
1312 When you give a prefix argument to @code{vc-next-action} (@kbd{C-u
1313 C-x C-q}), it still performs the next logical version control
1314 operation, but accepts additional arguments to specify precisely how
1315 to do the operation.
1319 If the file is modified (or locked), you can specify the version
1320 number to use for the new verion that you check-in. This is one way
1321 to create a new branch (@pxref{Branches}).
1324 If the file is not modified (and unlocked), you can specify the
1325 version to select; this lets you start working from an older version,
1326 or on another branch. If you do not enter any version, that takes you
1327 to the highest version on the current branch; therefore @kbd{C-u C-x
1328 C-q @key{RET}} is a convenient way to get the latest version of a file from
1332 Instead of the version number, you can also specify the name of a
1333 version control system. This is useful when one file is being managed
1334 with two version control systems at the same time file (@pxref{Local
1339 @subsubsection Features of the Log Entry Buffer
1341 When you check in changes, @kbd{C-x C-q} first reads a log entry. It
1342 pops up a buffer called @samp{*VC-Log*} for you to enter the log entry.
1343 When you are finished, type @kbd{C-c C-c} in the @samp{*VC-Log*} buffer.
1344 That is when check-in really happens.
1346 To abort check-in, just @strong{don't} type @kbd{C-c C-c} in that
1347 buffer. You can switch buffers and do other editing. As long as you
1348 don't try to check in another file, the entry you were editing remains
1349 in the @samp{*VC-Log*} buffer, and you can go back to that buffer at any
1350 time to complete the check-in.
1352 If you change several source files for the same reason, it is often
1353 convenient to specify the same log entry for many of the files. To do
1354 this, use the history of previous log entries. The commands @kbd{M-n},
1355 @kbd{M-p}, @kbd{M-s} and @kbd{M-r} for doing this work just like the
1356 minibuffer history commands (except that these versions are used outside
1359 @vindex vc-log-mode-hook
1360 Each time you check in a file, the log entry buffer is put into VC Log
1361 mode, which involves running two hooks: @code{text-mode-hook} and
1362 @code{vc-log-mode-hook}. @xref{Hooks}.
1365 @subsection Examining And Comparing Old Versions
1367 One of the convenient features of version control is the ability
1368 to examine any version of a file, or compare two versions.
1371 @item C-x v ~ @var{version} @key{RET}
1372 Examine version @var{version} of the visited file, in a buffer of its
1376 Compare the current buffer contents with the latest checked-in version
1379 @item C-u C-x v = @var{file} @key{RET} @var{oldvers} @key{RET} @var{newvers} @key{RET}
1380 Compare the specified two versions of @var{file}.
1383 Display the result of the CVS annotate command using colors.
1386 @findex vc-version-other-window
1388 To examine an old version in toto, visit the file and then type
1389 @kbd{C-x v ~ @var{version} @key{RET}} (@code{vc-version-other-window}).
1390 This puts the text of version @var{version} in a file named
1391 @file{@var{filename}.~@var{version}~}, and visits it in its own buffer
1392 in a separate window. (In RCS, you can also select an old version
1393 and create a branch from it. @xref{Branches}.)
1397 It is usually more convenient to compare two versions of the file,
1398 with the command @kbd{C-x v =} (@code{vc-diff}). Plain @kbd{C-x v =}
1399 compares the current buffer contents (saving them in the file if
1400 necessary) with the last checked-in version of the file. @kbd{C-u C-x
1401 v =}, with a numeric argument, reads a file name and two version
1402 numbers, then compares those versions of the specified file. Both
1403 forms display the output in a special buffer in another window.
1405 You can specify a checked-in version by its number; an empty input
1406 specifies the current contents of the work file (which may be different
1407 from all the checked-in versions). You can also specify a snapshot name
1408 (@pxref{Snapshots}) instead of one or both version numbers.
1410 If you supply a directory name instead of the name of a registered
1411 file, this command compares the two specified versions of all registered
1412 files in that directory and its subdirectories.
1414 @vindex diff-switches
1415 @vindex vc-diff-switches
1416 @kbd{C-x v =} works by running a variant of the @code{diff} utility
1417 designed to work with the version control system in use. Emacs passes
1418 the contents of the variable @code{diff-switches} to it; you can
1419 specify comparison options for version control in
1420 @code{vc-diff-switches}, and there are similar variables for each
1421 specific system---@code{vc-rcs-diff-switches}, and so on.
1423 Unlike the @kbd{M-x diff} command, @kbd{C-x v =} does not try to
1424 locate the changes in the old and new versions. This is because
1425 normally one or both versions do not exist as files when you compare
1426 them; they exist only in the records of the master file.
1427 @xref{Comparing Files}, for more information about @kbd{M-x diff}.
1431 For CVS-controlled files, you can display the result of the CVS
1432 annotate command, using colors to enhance the visual appearance. Use
1433 the command @kbd{M-x vc-annotate} to do this. Red means new, blue means
1434 old, and intermediate colors indicate intermediate ages. A prefix
1435 argument @var{n} specifies a stretch factor for the time scale; it makes
1436 each color cover a period @var{n} times as long.
1438 @node Secondary VC Commands
1439 @subsection The Secondary Commands of VC
1441 This section explains the secondary commands of VC; those that you might
1445 * Registering:: Putting a file under version control.
1446 * VC Status:: Viewing the VC status of files.
1447 * VC Undo:: Cancelling changes before or after check-in.
1448 * VC Dired Mode:: Listing files managed by version control.
1449 * VC Dired Commands:: Commands to use in a VC Dired buffer.
1453 @subsubsection Registering a File for Version Control
1457 You can put any file under version control by simply visiting it, and
1458 then typing @w{@kbd{C-x v i}} (@code{vc-register}).
1462 Register the visited file for version control.
1465 To register the file, Emacs must choose which version control system
1466 to use for it. If the file's directory already contains files
1467 registered in a version control system, Emacs uses that system. If
1468 there is more than one system in use for a directory, Emacs uses the one
1469 that appears first in @var{vc-handled-backends} (@pxref{Customizing VC}).
1470 On the other hand, if there are no files already registered,
1471 Emacs uses the first system from @var{vc-handled-backends} that could
1472 register the file---for example, you cannot register a file under CVS if
1473 its directory is not already part of a CVS tree.
1475 With the default value of @var{vc-handled-backends}, this means that
1476 Emacs uses RCS if there are any files under RCS control, or CVS if
1477 there are any files under CVS, or RCS as the ultimate default.
1479 If locking is in use, @kbd{C-x v i} leaves the file unlocked and
1480 read-only. Type @kbd{C-x C-q} if you wish to start editing it. After
1481 registering a file with CVS, you must subsequently commit the initial
1482 version by typing @kbd{C-x C-q}.
1484 @vindex vc-default-init-version
1485 The initial version number for a newly registered file is 1.1, by
1486 default. You can specify a different default by setting the variable
1487 @code{vc-default-init-version}, or you can give @kbd{C-x v i} a numeric
1488 argument; then it reads the initial version number for this particular
1489 file using the minibuffer.
1491 @vindex vc-initial-comment
1492 If @code{vc-initial-comment} is non-@code{nil}, @kbd{C-x v i} reads an
1493 initial comment to describe the purpose of this source file. Reading
1494 the initial comment works like reading a log entry (@pxref{Log Buffer}).
1497 @subsubsection VC Status Commands
1501 Display version control state and change history.
1505 @findex vc-print-log
1506 To view the detailed version control status and history of a file,
1507 type @kbd{C-x v l} (@code{vc-print-log}). It displays the history of
1508 changes to the current file, including the text of the log entries. The
1509 output appears in a separate window.
1512 @subsubsection Undoing Version Control Actions
1516 Revert the buffer and the file to the last checked-in version.
1519 Remove the last-entered change from the master for the visited file.
1520 This undoes your last check-in.
1524 @findex vc-revert-buffer
1525 If you want to discard your current set of changes and revert to the
1526 last version checked in, use @kbd{C-x v u} (@code{vc-revert-buffer}).
1527 This leaves the file unlocked; if locking is in use, you must first lock
1528 the file again before you change it again. @kbd{C-x v u} requires
1529 confirmation, unless it sees that you haven't made any changes since the
1530 last checked-in version.
1532 @kbd{C-x v u} is also the command to unlock a file if you lock it and
1533 then decide not to change it.
1536 @findex vc-cancel-version
1537 To cancel a change that you already checked in, use @kbd{C-x v c}
1538 (@code{vc-cancel-version}). This command discards all record of the
1539 most recent checked-in version. @kbd{C-x v c} also offers to revert
1540 your work file and buffer to the previous version (the one that precedes
1541 the version that is deleted).
1543 If you answer @kbd{no}, VC keeps your changes in the buffer, and locks
1544 the file. The no-revert option is useful when you have checked in a
1545 change and then discover a trivial error in it; you can cancel the
1546 erroneous check-in, fix the error, and check the file in again.
1548 When @kbd{C-x v c} does not revert the buffer, it unexpands all
1549 version control headers in the buffer instead (@pxref{Version Headers}).
1550 This is because the buffer no longer corresponds to any existing
1551 version. If you check it in again, the check-in process will expand the
1552 headers properly for the new version number.
1554 However, it is impossible to unexpand the RCS @samp{@w{$}Log$} header
1555 automatically. If you use that header feature, you have to unexpand it
1556 by hand---by deleting the entry for the version that you just canceled.
1558 Be careful when invoking @kbd{C-x v c}, as it is easy to lose a lot of
1559 work with it. To help you be careful, this command always requires
1560 confirmation with @kbd{yes}. Note also that this command is disabled
1561 under CVS, because canceling versions is very dangerous and discouraged
1565 @subsubsection Dired under VC
1569 @cindex CVS Dired Mode
1570 The VC Dired Mode described here works with all the version control
1571 systems that VC supports. Another more powerful facility, designed
1572 specifically for CVS, is called PCL-CVS. @xref{Top, , About PCL-CVS,
1573 pcl-cvs, PCL-CVS --- The Emacs Front-End to CVS}.
1576 @findex vc-directory
1577 When you are working on a large program, it is often useful to find
1578 out which files have changed within an entire directory tree, or to view
1579 the status of all files under version control at once, and to perform
1580 version control operations on collections of files. You can use the
1581 command @kbd{C-x v d} (@code{vc-directory}) to make a directory listing
1582 that includes only files relevant for version control.
1584 @vindex vc-dired-terse-display
1585 @kbd{C-x v d} creates a buffer which uses VC Dired Mode. This looks
1586 much like an ordinary Dired buffer (@pxref{Dired}); however, normally it
1587 shows only the noteworthy files (those locked or not up-to-date). This
1588 is called @dfn{terse display}. If you set the variable
1589 @code{vc-dired-terse-display} to @code{nil}, then VC Dired shows all
1590 relevant files---those managed under version control, plus all
1591 subdirectories (@dfn{full display}). The command @kbd{v t} in a VC
1592 Dired buffer toggles between terse display and full display (@pxref{VC
1595 @vindex vc-dired-recurse
1596 By default, VC Dired produces a recursive listing of noteworthy or
1597 relevant files at or below the given directory. You can change this by
1598 setting the variable @code{vc-dired-recurse} to @code{nil}; then VC
1599 Dired shows only the files in the given directory.
1601 The line for an individual file shows the version control state in the
1602 place of the hard link count, owner, group, and size of the file. If
1603 the file is unmodified, in sync with the master file, the version
1604 control state shown is blank. Otherwise it consists of text in
1605 parentheses. Under RCS and SCCS, the name of the user locking the file
1606 is shown; under CVS, an abbreviated version of the @samp{cvs status}
1607 output is used. Here is an example using RCS:
1613 -rw-r--r-- (jim) Apr 2 23:39 file1
1614 -r--r--r-- Apr 5 20:21 file2
1619 The files @samp{file1} and @samp{file2} are under version control,
1620 @samp{file1} is locked by user jim, and @samp{file2} is unlocked.
1622 Here is an example using CVS:
1628 -rw-r--r-- (modified) Aug 2 1997 file1.c
1629 -rw-r--r-- Apr 4 20:09 file2.c
1630 -rw-r--r-- (merge) Sep 13 1996 file3.c
1634 Here @samp{file1.c} is modified with respect to the repository, and
1635 @samp{file2.c} is not. @samp{file3.c} is modified, but other changes
1636 have also been checked in to the repository---you need to merge them
1637 with the work file before you can check it in.
1639 @vindex vc-directory-exclusion-list
1640 When VC Dired displays subdirectories (in the ``full'' display mode),
1641 it omits some that should never contain any files under version control.
1642 By default, this includes Version Control subdirectories such as
1643 @samp{RCS} and @samp{CVS}; you can customize this by setting the
1644 variable @code{vc-directory-exclusion-list}.
1646 You can fine-tune VC Dired's format by typing @kbd{C-u C-x v d}---as in
1647 ordinary Dired, that allows you to specify additional switches for the
1650 @node VC Dired Commands
1651 @subsubsection VC Dired Commands
1653 All the usual Dired commands work normally in VC Dired mode, except
1654 for @kbd{v}, which is redefined as the version control prefix. You can
1655 invoke VC commands such as @code{vc-diff} and @code{vc-print-log} by
1656 typing @kbd{v =}, or @kbd{v l}, and so on. Most of these commands apply
1657 to the file name on the current line.
1659 The command @kbd{v v} (@code{vc-next-action}) operates on all the
1660 marked files, so that you can lock or check in several files at once.
1661 If it operates on more than one file, it handles each file according to
1662 its current state; thus, it might lock one file, but check in another
1663 file. This could be confusing; it is up to you to avoid confusing
1664 behavior by marking a set of files that are in a similar state.
1666 If any files call for check-in, @kbd{v v} reads a single log entry,
1667 then uses it for all the files being checked in. This is convenient for
1668 registering or checking in several files at once, as part of the same
1671 @findex vc-dired-toggle-terse-mode
1672 @findex vc-dired-mark-locked
1673 You can toggle between terse display (only locked files, or files not
1674 up-to-date) and full display at any time by typing @kbd{v t}
1675 @code{vc-dired-toggle-terse-mode}. There is also a special command
1676 @kbd{* l} (@code{vc-dired-mark-locked}), which marks all files currently
1677 locked (or, with CVS, all files not up-to-date). Thus, typing @kbd{* l
1678 t k} is another way to delete from the buffer all files except those
1682 @subsection Multiple Branches of a File
1683 @cindex branch (version control)
1684 @cindex trunk (version control)
1686 One use of version control is to maintain multiple ``current''
1687 versions of a file. For example, you might have different versions of a
1688 program in which you are gradually adding various unfinished new
1689 features. Each such independent line of development is called a
1690 @dfn{branch}. VC allows you to create branches, switch between
1691 different branches, and merge changes from one branch to another.
1692 Please note, however, that branches are only supported for RCS at the
1695 A file's main line of development is usually called the @dfn{trunk}.
1696 The versions on the trunk are normally numbered 1.1, 1.2, 1.3, etc. At
1697 any such version, you can start an independent branch. A branch
1698 starting at version 1.2 would have version number 1.2.1.1, and consecutive
1699 versions on this branch would have numbers 1.2.1.2, 1.2.1.3, 1.2.1.4,
1700 and so on. If there is a second branch also starting at version 1.2, it
1701 would consist of versions 1.2.2.1, 1.2.2.2, 1.2.2.3, etc.
1703 @cindex head version
1704 If you omit the final component of a version number, that is called a
1705 @dfn{branch number}. It refers to the highest existing version on that
1706 branch---the @dfn{head version} of that branch. The branches in the
1707 example above have branch numbers 1.2.1 and 1.2.2.
1710 * Switching Branches:: How to get to another existing branch.
1711 * Creating Branches:: How to start a new branch.
1712 * Merging:: Transferring changes between branches.
1713 * Multi-User Branching:: Multiple users working at multiple branches
1717 @node Switching Branches
1718 @subsubsection Switching between Branches
1720 To switch between branches, type @kbd{C-u C-x C-q} and specify the
1721 version number you want to select. This version is then visited
1722 @emph{unlocked} (write-protected), so you can examine it before locking
1723 it. Switching branches in this way is allowed only when the file is not
1726 You can omit the minor version number, thus giving only the branch
1727 number; this takes you to the head version on the chosen branch. If you
1728 only type @key{RET}, Emacs goes to the highest version on the trunk.
1730 After you have switched to any branch (including the main branch), you
1731 stay on it for subsequent VC commands, until you explicitly select some
1734 @node Creating Branches
1735 @subsubsection Creating New Branches
1737 To create a new branch from a head version (one that is the latest in
1738 the branch that contains it), first select that version if necessary,
1739 lock it with @kbd{C-x C-q}, and make whatever changes you want. Then,
1740 when you check in the changes, use @kbd{C-u C-x C-q}. This lets you
1741 specify the version number for the new version. You should specify a
1742 suitable branch number for a branch starting at the current version.
1743 For example, if the current version is 2.5, the branch number should be
1744 2.5.1, 2.5.2, and so on, depending on the number of existing branches at
1747 To create a new branch at an older version (one that is no longer the
1748 head of a branch), first select that version (@pxref{Switching
1749 Branches}), then lock it with @kbd{C-x C-q}. You'll be asked to
1750 confirm, when you lock the old version, that you really mean to create a
1751 new branch---if you say no, you'll be offered a chance to lock the
1752 latest version instead.
1754 Then make your changes and type @kbd{C-x C-q} again to check in a new
1755 version. This automatically creates a new branch starting from the
1756 selected version. You need not specially request a new branch, because
1757 that's the only way to add a new version at a point that is not the head
1760 After the branch is created, you ``stay'' on it. That means that
1761 subsequent check-ins create new versions on that branch. To leave the
1762 branch, you must explicitly select a different version with @kbd{C-u C-x
1763 C-q}. To transfer changes from one branch to another, use the merge
1764 command, described in the next section.
1767 @subsubsection Merging Branches
1769 @cindex merging changes
1770 When you have finished the changes on a certain branch, you will
1771 often want to incorporate them into the file's main line of development
1772 (the trunk). This is not a trivial operation, because development might
1773 also have proceeded on the trunk, so that you must @dfn{merge} the
1774 changes into a file that has already been changed otherwise. VC allows
1775 you to do this (and other things) with the @code{vc-merge} command.
1778 @item C-x v m (vc-merge)
1779 Merge changes into the work file.
1784 @kbd{C-x v m} (@code{vc-merge}) takes a set of changes and merges it
1785 into the current version of the work file. It firsts asks you in the
1786 minibuffer where the changes should come from. If you just type
1787 @key{RET}, Emacs merges any changes that were made on the same branch
1788 since you checked the file out (we call this @dfn{merging the news}).
1789 This is the common way to pick up recent changes from the repository,
1790 regardless of whether you have already changed the file yourself.
1792 You can also enter a branch number or a pair of version numbers in
1793 the minibuffer. Then it finds the changes from that branch, or between
1794 the two versions you specified, and merges them into the current version
1795 of the current file.
1797 As an example, suppose that you have finished a certain feature on
1798 branch 1.3.1. In the meantime, development on the trunk has proceeded
1799 to version 1.5. To merge the changes from the branch to the trunk,
1800 first go to the head version of the trunk, by typing @kbd{C-u C-x C-q
1801 @key{RET}}. Version 1.5 is now current. If locking is used for the file,
1802 type @kbd{C-x C-q} to lock version 1.5 so that you can change it. Next,
1803 type @kbd{C-x v m 1.3.1 @key{RET}}. This takes the entire set of changes on
1804 branch 1.3.1 (relative to version 1.3, where the branch started, up to
1805 the last version on the branch) and merges it into the current version
1806 of the work file. You can now check in the changed file, thus creating
1807 version 1.6 containing the changes from the branch.
1809 It is possible to do further editing after merging the branch, before
1810 the next check-in. But it is usually wiser to check in the merged
1811 version, then lock it and make the further changes. This will keep
1812 a better record of the history of changes.
1815 @cindex resolving conflicts
1816 When you merge changes into a file that has itself been modified, the
1817 changes might overlap. We call this situation a @dfn{conflict}, and
1818 reconciling the conflicting changes is called @dfn{resolving a
1821 Whenever conflicts occur during merging, VC detects them, tells you
1822 about them in the echo area, and asks whether you want help in merging.
1823 If you say yes, it starts an Ediff session (@pxref{Top,
1824 Ediff, Ediff, ediff, The Ediff Manual}).
1826 If you say no, the conflicting changes are both inserted into the
1827 file, surrounded by @dfn{conflict markers}. The example below shows how
1828 a conflict region looks; the file is called @samp{name} and the current
1829 master file version with user B's changes in it is 1.11.
1831 @c @w here is so CVS won't think this is a conflict.
1835 @var{User A's version}
1837 @var{User B's version}
1842 @cindex vc-resolve-conflicts
1843 Then you can resolve the conflicts by editing the file manually. Or
1844 you can type @code{M-x vc-resolve-conflicts} after visiting the file.
1845 This starts an Ediff session, as described above.
1847 @node Multi-User Branching
1848 @subsubsection Multi-User Branching
1850 It is often useful for multiple developers to work simultaneously on
1851 different branches of a file. CVS allows this by default; for RCS, it
1852 is possible if you create multiple source directories. Each source
1853 directory should have a link named @file{RCS} which points to a common
1854 directory of RCS master files. Then each source directory can have its
1855 own choice of selected versions, but all share the same common RCS
1858 This technique works reliably and automatically, provided that the
1859 source files contain RCS version headers (@pxref{Version Headers}). The
1860 headers enable Emacs to be sure, at all times, which version number is
1861 present in the work file.
1863 If the files do not have version headers, you must instead tell Emacs
1864 explicitly in each session which branch you are working on. To do this,
1865 first find the file, then type @kbd{C-u C-x C-q} and specify the correct
1866 branch number. This ensures that Emacs knows which branch it is using
1867 during this particular editing session.
1869 @node Remote Repositories
1870 @subsection Remote Repositories
1871 @cindex remote repositories (CVS)
1873 A common way of using CVS is to set up a central CVS repository on
1874 some Internet host, then have each developer check out a personal
1875 working copy of the files on his local machine. Committing changes to
1876 the repository, and picking up changes from other users into one's own
1877 working area, then works by direct interactions with the CVS server.
1879 One difficulty is that access to the CVS server is often slow, and
1880 that developers might need to work offline as well. VC is designed
1881 to reduce the amount of network interaction necessary.
1884 * Version Backups:: Keeping local copies of repository versions.
1885 * Local Version Control:: Using another version system for local editing.
1888 @node Version Backups
1889 @subsubsection Version Backups
1890 @cindex version backups
1892 @cindex automatic version backups
1893 When VC sees that the CVS repository for a file is on a remote
1894 machine, it automatically makes local backups of unmodified versions
1895 of the file---@dfn{automatic version backups}. This means that you
1896 can compare the file to the repository version (@kbd{C-x v =}), or
1897 revert to that version (@kbd{C-x v u}), without any network
1900 The local copy of the unmodified file is called a @dfn{version
1901 backup} to indicate that it corresponds exactly to a version that is
1902 stored in the repository. Note that version backups are not the same
1903 as ordinary Emacs backup files (@pxref{Backup}). But they follow a
1904 similar naming convention.
1906 For a file that comes from a remote CVS repository, VC makes a
1907 version backup whenever you save the first changes to the file, and
1908 removes it after you have committed your modified version to the
1909 repository. You can disable the making of automatic version backups by
1910 setting @code{vc-cvs-stay-local} to @code{nil} (@pxref{CVS Options}).
1912 @cindex manual version backups
1913 The name of the automatic version backup for version @var{version}
1914 of file @var{file} is @code{@var{file}.~@var{version}.~}. This is
1915 almost the same as the name used by @kbd{C-x v ~} (@pxref{Old
1916 Versions}), the only difference being the additional dot (@samp{.})
1917 after the version number. This similarity is intentional, because
1918 both kinds of files store the same kind of information. The file made
1919 by @kbd{C-x v ~} acts as a @dfn{manual version backup}.
1921 All the VC commands that operate on old versions of a file can use
1922 both kinds of version backups. For instance, @kbd{C-x v ~} uses
1923 either an automatic or a manual version backup, if possible, to get
1924 the contents of the version you request. Likewise, @kbd{C-x v =} and
1925 @kbd{C-x v u} use either an automatic or a manual version backup, if
1926 one of them exists, to get the contents of a version to compare or
1927 revert to. If you changed a file outside of Emacs, so that no
1928 automatic version backup was created for the previous text, you can
1929 create a manual backup of that version using @kbd{C-x v ~}, and thus
1930 obtain the benefit of the local copy for Emacs commands.
1932 The only difference in Emacs's handling of manual and automatic
1933 version backups, once they exist, is that Emacs deletes automatic
1934 version backups when you commit to the repository. By contrast,
1935 manual version backups remain until you delete them.
1937 @node Local Version Control
1938 @subsubsection Local Version Control
1939 @cindex local version control
1940 @cindex local back end (version control)
1942 When you make many changes to a file that comes from a remote
1943 repository, it can be convenient to have version control on your local
1944 machine as well. You can then record intermediate versions, revert to
1945 a previous state, etc., before you actually commit your changes to the
1948 VC lets you do this by putting a file under a second, local version
1949 control system, so that the file is effectively registered in two
1950 systems at the same time. For the description here, we will assume
1951 that the remote system is CVS, and you use RCS locally, although the
1952 mechanism works with any combination of version control systems
1955 To make it work with other back ends, you must make sure that the
1956 ``more local'' back end comes before the ``more remote'' back end in
1957 the setting of @var{vc-handled-backends} (@pxref{Customizing VC}). By
1958 default, this variable is set up so that you can use remote CVS and
1959 local RCS as described here.
1961 To start using local RCS for a file that comes from a remote CVS
1962 server, you must @emph{register the file in RCS}, by typing @kbd{C-u
1963 C-x v v rcs @key{RET}}. (In other words, use @code{vc-next-action} with a
1964 prefix argument, and specify RCS as the back end.)
1966 You can do this at any time; it does not matter whether you have
1967 already modified the file with respect to the version in the CVS
1968 repository. If possible, VC tries to make the RCS master start with
1969 the unmodified repository version, then checking in any local changes
1970 as a new version. This works if you have not made any changes yet, or
1971 if the unmodified repository version exists locally as a version
1972 backup (@pxref{Version Backups}). If the unmodified version is not
1973 available locally, the RCS master starts with the modified version;
1974 the only drawback of this is that you cannot compare your changes
1975 locally to what is stored in the repository.
1977 The version number of the RCS master is derived from the current CVS
1978 version, starting a branch from it. For example, if the current CVS
1979 version is 1.23, the local RCS branch will be 1.23.1. Version 1.23 in
1980 the RCS master will be identical to version 1.23 under CVS; your first
1981 changes are checked in as 1.23.1.1. (If the unmodified file is not
1982 available locally, VC will check in the modified file twice, both as
1983 1.23 and 1.23.1.1, to make the revision numbers consistent.)
1985 If you do not use locking under CVS (the default), locking is also
1986 disabled for RCS, so that editing under RCS works exactly as under
1989 When you are done with local editing, you can commit the final version
1990 back to the CVS repository by typing @kbd{C-u C-x v v cvs @key{RET}}.
1991 This initializes the log entry buffer (@pxref{Log Buffer}) to contain
1992 all the log entries you have recorded in the RCS master; you can edit
1993 them as you wish, and then commit in CVS by typing @kbd{C-c C-c}. If
1994 the commit is successful, VC removes the RCS master, so that the file
1995 is once again registered under CVS only. (The RCS master is not
1996 actually deleted, just renamed by appending @samp{~} to the name, so
1997 that you can refer to it later if you wish.)
1999 While using local RCS, you can pick up recent changes from the CVS
2000 repository into your local file, or commit some of your changes back
2001 to CVS, without terminating local RCS version control. To do this,
2002 switch to the CVS backend temporarily, with the @kbd{C-x v b} command:
2006 Switch to another back end that the current file is registered
2007 under (@code{vc-switch-backend}).
2009 @item C-u C-x v b @var{backend} @key{RET}
2010 Switch to @var{backend} for the current file.
2014 @findex vc-switch-backend
2015 @kbd{C-x v b} does not change the buffer contents, or any files; it
2016 only changes VC's perspective on how to handle the file. Any
2017 subsequent VC commands for that file will operate on the back end that
2018 is currently selected.
2020 If the current file is registered in more than one back end, typing
2021 @kbd{C-x v b} ``cycles'' through all of these back ends. With a
2022 prefix argument, it asks for the back end to use in the minibuffer.
2024 Thus, if you are using local RCS, and you want to pick up some recent
2025 changes in the file from remote CVS, first visit the file, then type
2026 @kbd{C-x v b} to switch to CVS, and finally use @kbd{C-x v m
2027 @key{RET}} to merge the news (@pxref{Merging}). You can then switch
2028 back to RCS by typing @kbd{C-x v b} again, and continue to edit
2031 But if you do this, the revision numbers in the RCS master no longer
2032 correspond to those of CVS. Technically, this is not a problem, but
2033 it can become difficult to keep track of what is in the CVS repository
2034 and what is not. So we suggest that you return from time to time to
2035 CVS-only operation, using @kbd{C-u C-x v v cvs @key{RET}}.
2038 @subsection Snapshots
2039 @cindex snapshots and version control
2041 A @dfn{snapshot} is a named set of file versions (one for each
2042 registered file) that you can treat as a unit. One important kind of
2043 snapshot is a @dfn{release}, a (theoretically) stable version of the
2044 system that is ready for distribution to users.
2047 * Making Snapshots:: The snapshot facilities.
2048 * Snapshot Caveats:: Things to be careful of when using snapshots.
2051 @node Making Snapshots
2052 @subsubsection Making and Using Snapshots
2054 There are two basic commands for snapshots; one makes a
2055 snapshot with a given name, the other retrieves a named snapshot.
2059 @findex vc-create-snapshot
2060 @item C-x v s @var{name} @key{RET}
2061 Define the last saved versions of every registered file in or under the
2062 current directory as a snapshot named @var{name}
2063 (@code{vc-create-snapshot}).
2066 @findex vc-retrieve-snapshot
2067 @item C-x v r @var{name} @key{RET}
2068 For all registered files at or below the current directory level, select
2069 whatever versions correspond to the snapshot @var{name}
2070 (@code{vc-retrieve-snapshot}).
2072 This command reports an error if any files are locked at or below the
2073 current directory, without changing anything; this is to avoid
2074 overwriting work in progress.
2077 A snapshot uses a very small amount of resources---just enough to record
2078 the list of file names and which version belongs to the snapshot. Thus,
2079 you need not hesitate to create snapshots whenever they are useful.
2081 You can give a snapshot name as an argument to @kbd{C-x v =} or
2082 @kbd{C-x v ~} (@pxref{Old Versions}). Thus, you can use it to compare a
2083 snapshot against the current files, or two snapshots against each other,
2084 or a snapshot against a named version.
2086 @node Snapshot Caveats
2087 @subsubsection Snapshot Caveats
2089 @cindex named configurations (RCS)
2090 VC's snapshot facilities are modeled on RCS's named-configuration
2091 support. They use RCS's native facilities for this, so under VC
2092 snapshots made using RCS are visible even when you bypass VC.
2094 @c worded verbosely to avoid overfull hbox.
2095 For SCCS, VC implements snapshots itself. The files it uses contain
2096 name/file/version-number triples. These snapshots are visible only
2099 A snapshot is a set of checked-in versions. So make sure that all the
2100 files are checked in and not locked when you make a snapshot.
2102 File renaming and deletion can create some difficulties with snapshots.
2103 This is not a VC-specific problem, but a general design issue in version
2104 control systems that no one has solved very well yet.
2106 If you rename a registered file, you need to rename its master along
2107 with it (the command @code{vc-rename-file} does this automatically). If
2108 you are using SCCS, you must also update the records of the snapshot, to
2109 mention the file by its new name (@code{vc-rename-file} does this,
2110 too). An old snapshot that refers to a master file that no longer
2111 exists under the recorded name is invalid; VC can no longer retrieve
2112 it. It would be beyond the scope of this manual to explain enough about
2113 RCS and SCCS to explain how to update the snapshots by hand.
2115 Using @code{vc-rename-file} makes the snapshot remain valid for
2116 retrieval, but it does not solve all problems. For example, some of the
2117 files in the program probably refer to others by name. At the very
2118 least, the makefile probably mentions the file that you renamed. If you
2119 retrieve an old snapshot, the renamed file is retrieved under its new
2120 name, which is not the name that the makefile expects. So the program
2121 won't really work as retrieved.
2123 @node Miscellaneous VC
2124 @subsection Miscellaneous Commands and Features of VC
2126 This section explains the less-frequently-used features of VC.
2129 * Change Logs and VC:: Generating a change log file from log entries.
2130 * Renaming and VC:: A command to rename both the source and master
2132 * Version Headers:: Inserting version control headers into working files.
2135 @node Change Logs and VC
2136 @subsubsection Change Logs and VC
2138 If you use RCS or CVS for a program and also maintain a change log
2139 file for it (@pxref{Change Log}), you can generate change log entries
2140 automatically from the version control log entries:
2145 @findex vc-update-change-log
2146 Visit the current directory's change log file and, for registered files
2147 in that directory, create new entries for versions checked in since the
2148 most recent entry in the change log file.
2149 (@code{vc-update-change-log}).
2151 This command works with RCS or CVS only, not with SCCS.
2154 As above, but only find entries for the current buffer's file.
2157 As above, but find entries for all the currently visited files that are
2158 maintained with version control. This works only with RCS, and it puts
2159 all entries in the log for the default directory, which may not be
2163 For example, suppose the first line of @file{ChangeLog} is dated
2164 1999-04-10, and that the only check-in since then was by Nathaniel
2165 Bowditch to @file{rcs2log} on 1999-05-22 with log text @samp{Ignore log
2166 messages that start with `#'.}. Then @kbd{C-x v a} visits
2167 @file{ChangeLog} and inserts text like this:
2174 1999-05-22 Nathaniel Bowditch <nat@@apn.org>
2176 * rcs2log: Ignore log messages that start with `#'.
2184 You can then edit the new change log entry further as you wish.
2186 Some of the new change log entry may duplicate what's already in
2187 ChangeLog. You will have to remove these duplicates by hand.
2189 Normally, the log entry for file @file{foo} is displayed as @samp{*
2190 foo: @var{text of log entry}}. The @samp{:} after @file{foo} is omitted
2191 if the text of the log entry starts with @w{@samp{(@var{functionname}):
2192 }}. For example, if the log entry for @file{vc.el} is
2193 @samp{(vc-do-command): Check call-process status.}, then the text in
2194 @file{ChangeLog} looks like this:
2201 1999-05-06 Nathaniel Bowditch <nat@@apn.org>
2203 * vc.el (vc-do-command): Check call-process status.
2210 When @kbd{C-x v a} adds several change log entries at once, it groups
2211 related log entries together if they all are checked in by the same
2212 author at nearly the same time. If the log entries for several such
2213 files all have the same text, it coalesces them into a single entry.
2214 For example, suppose the most recent check-ins have the following log
2218 @bullet{} For @file{vc.texinfo}: @samp{Fix expansion typos.}
2219 @bullet{} For @file{vc.el}: @samp{Don't call expand-file-name.}
2220 @bullet{} For @file{vc-hooks.el}: @samp{Don't call expand-file-name.}
2224 They appear like this in @file{ChangeLog}:
2231 1999-04-01 Nathaniel Bowditch <nat@@apn.org>
2233 * vc.texinfo: Fix expansion typos.
2235 * vc.el, vc-hooks.el: Don't call expand-file-name.
2242 Normally, @kbd{C-x v a} separates log entries by a blank line, but you
2243 can mark several related log entries to be clumped together (without an
2244 intervening blank line) by starting the text of each related log entry
2245 with a label of the form @w{@samp{@{@var{clumpname}@} }}. The label
2246 itself is not copied to @file{ChangeLog}. For example, suppose the log
2250 @bullet{} For @file{vc.texinfo}: @samp{@{expand@} Fix expansion typos.}
2251 @bullet{} For @file{vc.el}: @samp{@{expand@} Don't call expand-file-name.}
2252 @bullet{} For @file{vc-hooks.el}: @samp{@{expand@} Don't call expand-file-name.}
2256 Then the text in @file{ChangeLog} looks like this:
2263 1999-04-01 Nathaniel Bowditch <nat@@apn.org>
2265 * vc.texinfo: Fix expansion typos.
2266 * vc.el, vc-hooks.el: Don't call expand-file-name.
2273 A log entry whose text begins with @samp{#} is not copied to
2274 @file{ChangeLog}. For example, if you merely fix some misspellings in
2275 comments, you can log the change with an entry beginning with @samp{#}
2276 to avoid putting such trivia into @file{ChangeLog}.
2278 @node Renaming and VC
2279 @subsubsection Renaming VC Work Files and Master Files
2281 @findex vc-rename-file
2282 When you rename a registered file, you must also rename its master
2283 file correspondingly to get proper results. Use @code{vc-rename-file}
2284 to rename the source file as you specify, and rename its master file
2285 accordingly. It also updates any snapshots (@pxref{Snapshots}) that
2286 mention the file, so that they use the new name; despite this, the
2287 snapshot thus modified may not completely work (@pxref{Snapshot
2290 You cannot use @code{vc-rename-file} on a file that is locked by
2293 @node Version Headers
2294 @subsubsection Inserting Version Control Headers
2296 Sometimes it is convenient to put version identification strings
2297 directly into working files. Certain special strings called
2298 @dfn{version headers} are replaced in each successive version by the
2299 number of that version.
2301 If you are using RCS, and version headers are present in your working
2302 files, Emacs can use them to determine the current version and the
2303 locking state of the files. This is more reliable than referring to the
2304 master files, which is done when there are no version headers. Note
2305 that in a multi-branch environment, version headers are necessary to
2306 make VC behave correctly (@pxref{Multi-User Branching}).
2308 Searching for version headers is controlled by the variable
2309 @code{vc-consult-headers}. If it is non-@code{nil}, Emacs searches for
2310 headers to determine the version number you are editing. Setting it to
2311 @code{nil} disables this feature.
2314 @findex vc-insert-headers
2315 You can use the @kbd{C-x v h} command (@code{vc-insert-headers}) to
2316 insert a suitable header string.
2320 Insert headers in a file for use with your version-control system.
2323 @vindex vc-header-alist
2324 The default header string is @samp{@w{$}Id$} for RCS and
2325 @samp{@w{%}W%} for SCCS. You can specify other headers to insert by
2326 setting the variable @code{vc-header-alist}. Its value is a list of
2327 elements of the form @code{(@var{program} . @var{string})} where
2328 @var{program} is @code{RCS} or @code{SCCS} and @var{string} is the
2331 Instead of a single string, you can specify a list of strings; then
2332 each string in the list is inserted as a separate header on a line of
2335 It is often necessary to use ``superfluous'' backslashes when writing
2336 the strings that you put in this variable. This is to prevent the
2337 string in the constant from being interpreted as a header itself if the
2338 Emacs Lisp file containing it is maintained with version control.
2340 @vindex vc-comment-alist
2341 Each header is inserted surrounded by tabs, inside comment delimiters,
2342 on a new line at point. Normally the ordinary comment
2343 start and comment end strings of the current mode are used, but for
2344 certain modes, there are special comment delimiters for this purpose;
2345 the variable @code{vc-comment-alist} specifies them. Each element of
2346 this list has the form @code{(@var{mode} @var{starter} @var{ender})}.
2348 @vindex vc-static-header-alist
2349 The variable @code{vc-static-header-alist} specifies further strings
2350 to add based on the name of the buffer. Its value should be a list of
2351 elements of the form @code{(@var{regexp} . @var{format})}. Whenever
2352 @var{regexp} matches the buffer name, @var{format} is inserted as part
2353 of the header. A header line is inserted for each element that matches
2354 the buffer name, and for each string specified by
2355 @code{vc-header-alist}. The header line is made by processing the
2356 string from @code{vc-header-alist} with the format taken from the
2357 element. The default value for @code{vc-static-header-alist} is as follows:
2362 "\n#ifndef lint\nstatic char vcid[] = \"\%s\";\n\
2363 #endif /* lint */\n"))
2368 It specifies insertion of text of this form:
2374 static char vcid[] = "@var{string}";
2380 Note that the text above starts with a blank line.
2382 If you use more than one version header in a file, put them close
2383 together in the file. The mechanism in @code{revert-buffer} that
2384 preserves markers may not handle markers positioned between two version
2387 @node Customizing VC
2388 @subsection Customizing VC
2390 @vindex vc-handled-backends
2391 The variable @var{vc-handled-backends} determines which version
2392 control systems VC should handle. The default value is @code{(RCS CVS
2393 SCCS)}, so it contains all three version systems that are currently
2394 supported. If you want VC to ignore one or more of these systems,
2395 exclude its name from the list.
2397 The order of systems in the list is significant: when you visit a file
2398 is registered in more than one system (@pxref{Local Version Control}),
2399 VC uses the system that comes first in @var{vc-handled-backends} by
2400 default. The order is also significant when you register a file for
2401 the first time, @pxref{Registering} for details.
2404 * General VC Options:: Options that apply to multiple back ends.
2405 * RCS and SCCS:: Options for RCS and SCCS.
2406 * CVS Options:: Options for CVS.
2409 @node General VC Options
2410 @subsubsection General Options
2412 @vindex vc-make-backup-files
2413 Emacs normally does not save backup files for source files that are
2414 maintained with version control. If you want to make backup files even
2415 for files that use version control, set the variable
2416 @code{vc-make-backup-files} to a non-@code{nil} value.
2418 @vindex vc-keep-workfiles
2419 Normally the work file exists all the time, whether it is locked or
2420 not. If you set @code{vc-keep-workfiles} to @code{nil}, then checking
2421 in a new version with @kbd{C-x C-q} deletes the work file; but any
2422 attempt to visit the file with Emacs creates it again. (With CVS, work
2423 files are always kept.)
2425 @vindex vc-follow-symlinks
2426 Editing a version-controlled file through a symbolic link can be
2427 dangerous. It bypasses the version control system---you can edit the
2428 file without locking it, and fail to check your changes in. Also,
2429 your changes might overwrite those of another user. To protect against
2430 this, VC checks each symbolic link that you visit, to see if it points
2431 to a file under version control.
2433 The variable @code{vc-follow-symlinks} controls what to do when a
2434 symbolic link points to a version-controlled file. If it is @code{nil},
2435 VC only displays a warning message. If it is @code{t}, VC automatically
2436 follows the link, and visits the real file instead, telling you about
2437 this in the echo area. If the value is @code{ask} (the default), VC
2438 asks you each time whether to follow the link.
2440 @vindex vc-suppress-confirm
2441 If @code{vc-suppress-confirm} is non-@code{nil}, then @kbd{C-x C-q}
2442 and @kbd{C-x v i} can save the current buffer without asking, and
2443 @kbd{C-x v u} also operates without asking for confirmation. (This
2444 variable does not affect @kbd{C-x v c}; that operation is so drastic
2445 that it should always ask for confirmation.)
2447 @vindex vc-command-messages
2448 VC mode does much of its work by running the shell commands for RCS,
2449 CVS and SCCS. If @code{vc-command-messages} is non-@code{nil}, VC
2450 displays messages to indicate which shell commands it runs, and
2451 additional messages when the commands finish.
2454 You can specify additional directories to search for version control
2455 programs by setting the variable @code{vc-path}. These directories
2456 are searched before the usual search path. It is rarely necessary to
2457 set this variable, because VC normally finds the proper files
2461 @subsubsection Options for RCS and SCCS
2463 @cindex non-strict locking (RCS)
2464 @cindex locking, non-strict (RCS)
2465 By default, RCS uses locking to coordinate the activities of several
2466 users, but there is a mode called @dfn{non-strict locking} in which
2467 you can check-in changes without locking the file first. Use
2468 @samp{rcs -U} to switch to non-strict locking for a particular file,
2469 see the @code{rcs} manpage for details.
2471 When deducing the version control state of an RCS file, VC first
2472 looks for an RCS version header string in the file (@pxref{Version
2473 Headers}). If there is no header string, VC normally looks at the
2474 file permissions of the work file; this is fast. But there might be
2475 situations when the file permissions cannot be trusted. In this case
2476 the master file has to be consulted, which is rather expensive. Also
2477 the master file can only tell you @emph{if} there's any lock on the
2478 file, but not whether your work file really contains that locked
2481 @vindex vc-consult-headers
2482 You can tell VC not to use version headers to determine the file
2483 status by setting @code{vc-consult-headers} to @code{nil}. VC then
2484 always uses the file permissions (if it is supposed to trust them), or
2485 else checks the master file.
2487 @vindex vc-mistrust-permissions
2488 You can specify the criterion for whether to trust the file
2489 permissions by setting the variable @code{vc-mistrust-permissions}.
2490 Its value can be @code{t} (always mistrust the file permissions and
2491 check the master file), @code{nil} (always trust the file
2492 permissions), or a function of one argument which makes the decision.
2493 The argument is the directory name of the @file{RCS} subdirectory. A
2494 non-@code{nil} value from the function says to mistrust the file
2495 permissions. If you find that the file permissions of work files are
2496 changed erroneously, set @code{vc-mistrust-permissions} to @code{t}.
2497 Then VC always checks the master file to determine the file's status.
2499 VC determines the version control state of files under SCCS much as
2500 with RCS. It does not consider SCCS version headers, though. Thus,
2501 the variable @var{vc-mistrust-permissions} affects SCCS use, but
2502 @var{vc-consult-headers} does not.
2505 @subsubsection Options specific for CVS
2507 @cindex locking (CVS)
2508 By default, CVS does not use locking to coordinate the activities of
2509 several users; anyone can change a work file at any time. However,
2510 there are ways to restrict this, resulting in behavior that resembles
2513 @cindex CVSREAD environment variable (CVS)
2514 For one thing, you can set the @env{CVSREAD} environment variable
2515 (the value you use makes no difference). If this variable is defined,
2516 CVS makes your work files read-only by default. In Emacs, you must
2517 type @kbd{C-x C-q} to make the file writeable, so that editing works
2518 in fact similar as if locking was used. Note however, that no actual
2519 locking is performed, so several users can make their files writeable
2520 at the same time. When setting @env{CVSREAD} for the first time, make
2521 sure to check out all your modules anew, so that the file protections
2524 @cindex cvs watch feature
2525 @cindex watching files (CVS)
2526 Another way to achieve something similar to locking is to use the
2527 @dfn{watch} feature of CVS. If a file is being watched, CVS makes it
2528 read-only by default, and you must also use @kbd{C-x C-q} in Emacs to
2529 make it writable. VC calls @code{cvs edit} to make the file writeable,
2530 and CVS takes care to notify other developers of the fact that you
2531 intend to change the file. See the CVS documentation for details on
2532 using the watch feature.
2534 @vindex vc-cvs-stay-local
2535 @cindex remote repositories (CVS)
2536 When a file's repository is on a remote machine, VC tries to keep
2537 network interactions to a minimum. This is controlled by the variable
2538 @var{vc-cvs-stay-local}. If it is @code{t} (the default), then VC uses
2539 only the entry in the local CVS subdirectory to determine the file's
2540 state (and possibly information returned by previous CVS commands). One
2541 consequence of this is that when you have modified a file, and somebody
2542 else has already checked in other changes to the file, you are not
2543 notified of it until you actually try to commit. (But you can try to
2544 pick up any recent changes from the repository first, using @kbd{C-x v m
2545 @key{RET}}, @pxref{Merging}).
2547 When @var{vc-cvs-stay-local} is @code{t}, VC also makes local
2548 version backups, so that simple diff and revert operations are
2549 completely local (@pxref{Version Backups}).
2551 On the other hand, if you set @var{vc-cvs-stay-local} to @code{nil},
2552 then VC queries the remote repository @emph{before} it decides what to
2553 do in @code{vc-next-action} (@kbd{C-x v v}), just as it does for local
2554 repositories. It also does not make any version backups.
2556 You can also set @var{vc-cvs-stay-local} to a regular expression
2557 that is matched against the repository hostname; VC then stays local
2558 only for repositories from hosts that match the pattern.
2561 @section File Directories
2563 @cindex file directory
2564 @cindex directory listing
2565 The file system groups files into @dfn{directories}. A @dfn{directory
2566 listing} is a list of all the files in a directory. Emacs provides
2567 commands to create and delete directories, and to make directory
2568 listings in brief format (file names only) and verbose format (sizes,
2569 dates, and authors included). There is also a directory browser called
2570 Dired; see @ref{Dired}.
2573 @item C-x C-d @var{dir-or-pattern} @key{RET}
2574 Display a brief directory listing (@code{list-directory}).
2575 @item C-u C-x C-d @var{dir-or-pattern} @key{RET}
2576 Display a verbose directory listing.
2577 @item M-x make-directory @key{RET} @var{dirname} @key{RET}
2578 Create a new directory named @var{dirname}.
2579 @item M-x delete-directory @key{RET} @var{dirname} @key{RET}
2580 Delete the directory named @var{dirname}. It must be empty,
2581 or you get an error.
2584 @findex list-directory
2586 The command to display a directory listing is @kbd{C-x C-d}
2587 (@code{list-directory}). It reads using the minibuffer a file name
2588 which is either a directory to be listed or a wildcard-containing
2589 pattern for the files to be listed. For example,
2592 C-x C-d /u2/emacs/etc @key{RET}
2596 lists all the files in directory @file{/u2/emacs/etc}. Here is an
2597 example of specifying a file name pattern:
2600 C-x C-d /u2/emacs/src/*.c @key{RET}
2603 Normally, @kbd{C-x C-d} prints a brief directory listing containing
2604 just file names. A numeric argument (regardless of value) tells it to
2605 make a verbose listing including sizes, dates, and authors (like
2608 @vindex list-directory-brief-switches
2609 @vindex list-directory-verbose-switches
2610 The text of a directory listing is obtained by running @code{ls} in an
2611 inferior process. Two Emacs variables control the switches passed to
2612 @code{ls}: @code{list-directory-brief-switches} is a string giving the
2613 switches to use in brief listings (@code{"-CF"} by default), and
2614 @code{list-directory-verbose-switches} is a string giving the switches to
2615 use in a verbose listing (@code{"-l"} by default).
2617 @node Comparing Files
2618 @section Comparing Files
2619 @cindex comparing files
2622 @vindex diff-switches
2623 The command @kbd{M-x diff} compares two files, displaying the
2624 differences in an Emacs buffer named @samp{*Diff*}. It works by running
2625 the @code{diff} program, using options taken from the variable
2626 @code{diff-switches}, whose value should be a string.
2628 The buffer @samp{*Diff*} has Compilation mode as its major mode, so
2629 you can use @kbd{C-x `} to visit successive changed locations in the two
2630 source files. You can also move to a particular hunk of changes and
2631 type @key{RET} or @kbd{C-c C-c}, or click @kbd{Mouse-2} on it, to move
2632 to the corresponding source location. You can also use the other
2633 special commands of Compilation mode: @key{SPC} and @key{DEL} for
2634 scrolling, and @kbd{M-p} and @kbd{M-n} for cursor motion.
2638 The command @kbd{M-x diff-backup} compares a specified file with its most
2639 recent backup. If you specify the name of a backup file,
2640 @code{diff-backup} compares it with the source file that it is a backup
2643 @findex compare-windows
2644 The command @kbd{M-x compare-windows} compares the text in the current
2645 window with that in the next window. Comparison starts at point in each
2646 window, and each starting position is pushed on the mark ring in its
2647 respective buffer. Then point moves forward in each window, a character
2648 at a time, until a mismatch between the two windows is reached. Then
2649 the command is finished. For more information about windows in Emacs,
2652 @vindex compare-ignore-case
2653 With a numeric argument, @code{compare-windows} ignores changes in
2654 whitespace. If the variable @code{compare-ignore-case} is
2655 non-@code{nil}, it ignores differences in case as well.
2661 Differences between versions of files are often distributed as
2662 @dfn{patches}, which are the output from @command{diff} or a version
2663 control system that uses @command{diff}. @kbd{M-x diff-mode} turns on
2664 Diff mode, a major mode for viewing and editing patches, either as
2665 ``unified diffs'' or ``context diffs.''
2669 @cindex failed merges
2670 @cindex merges, failed
2671 @cindex comparing 3 files (@code{diff3})
2672 You can use @kbd{M-x smerge-mode} to turn on Smerge mode, a minor
2673 mode for editing output from the @command{diff3} program. This is
2674 typically the result of a failed merge from a version control system
2675 ``update'' outside VC, due to conflicting changes to a file. Smerge
2676 mode provides commands to resolve conflicts by selecting specific
2679 See also @ref{Emerge}, and @ref{Top,,, ediff, The Ediff Manual}, for
2680 convenient facilities for merging two similar files.
2683 @section Miscellaneous File Operations
2685 Emacs has commands for performing many other operations on files.
2686 All operate on one file; they do not accept wildcard file names.
2692 @kbd{M-x view-file} allows you to scan or read a file by sequential
2693 screenfuls. It reads a file name argument using the minibuffer. After
2694 reading the file into an Emacs buffer, @code{view-file} displays the
2695 beginning. You can then type @key{SPC} to scroll forward one windowful,
2696 or @key{DEL} to scroll backward. Various other commands are provided
2697 for moving around in the file, but none for changing it; type @kbd{?}
2698 while viewing for a list of them. They are mostly the same as normal
2699 Emacs cursor motion commands. To exit from viewing, type @kbd{q}.
2700 The commands for viewing are defined by a special major mode called View
2703 A related command, @kbd{M-x view-buffer}, views a buffer already present
2704 in Emacs. @xref{Misc Buffer}.
2707 @kbd{M-x insert-file} inserts a copy of the contents of the specified
2708 file into the current buffer at point, leaving point unchanged before the
2709 contents and the mark after them.
2711 @findex write-region
2712 @kbd{M-x write-region} is the inverse of @kbd{M-x insert-file}; it
2713 copies the contents of the region into the specified file. @kbd{M-x
2714 append-to-file} adds the text of the region to the end of the specified
2715 file. @xref{Accumulating Text}.
2718 @cindex deletion (of files)
2719 @kbd{M-x delete-file} deletes the specified file, like the @code{rm}
2720 command in the shell. If you are deleting many files in one directory, it
2721 may be more convenient to use Dired (@pxref{Dired}).
2724 @kbd{M-x rename-file} reads two file names @var{old} and @var{new} using
2725 the minibuffer, then renames file @var{old} as @var{new}. If a file named
2726 @var{new} already exists, you must confirm with @kbd{yes} or renaming is not
2727 done; this is because renaming causes the old meaning of the name @var{new}
2728 to be lost. If @var{old} and @var{new} are on different file systems, the
2729 file @var{old} is copied and deleted.
2731 @findex add-name-to-file
2732 The similar command @kbd{M-x add-name-to-file} is used to add an
2733 additional name to an existing file without removing its old name.
2734 The new name must belong on the same file system that the file is on.
2737 @cindex copying files
2738 @kbd{M-x copy-file} reads the file @var{old} and writes a new file named
2739 @var{new} with the same contents. Confirmation is required if a file named
2740 @var{new} already exists, because copying has the consequence of overwriting
2741 the old contents of the file @var{new}.
2743 @findex make-symbolic-link
2744 @kbd{M-x make-symbolic-link} reads two file names @var{target} and
2745 @var{linkname}, then creates a symbolic link named @var{linkname} and
2746 pointing at @var{target}. The effect is that future attempts to open file
2747 @var{linkname} will refer to whatever file is named @var{target} at the
2748 time the opening is done, or will get an error if the name @var{target} is
2749 not in use at that time. This command does not expand the argument
2750 @var{target}, so that it allows you to specify a relative name
2751 as the target of the link.
2753 Confirmation is required when creating the link if @var{linkname} is
2754 in use. Note that not all systems support symbolic links.
2756 @node Compressed Files
2757 @section Accessing Compressed Files
2759 @cindex uncompression
2760 @cindex Auto Compression mode
2761 @cindex mode, Auto Compression
2764 @findex auto-compression-mode
2765 @vindex auto-compression-mode
2766 Emacs comes with a library that can automatically uncompress
2767 compressed files when you visit them, and automatically recompress them
2768 if you alter them and save them. To enable this feature, type the
2769 command @kbd{M-x auto-compression-mode}. You can enable it permanently
2770 by customizing the option @var{auto-compression-mode}.
2772 When automatic compression (which implies automatic uncompression as
2773 well) is enabled, Emacs recognizes compressed files by their file names.
2774 File names ending in @samp{.gz} indicate a file compressed with
2775 @code{gzip}. Other endings indicate other compression programs.
2777 Automatic uncompression and compression apply to all the operations in
2778 which Emacs uses the contents of a file. This includes visiting it,
2779 saving it, inserting its contents into a buffer, loading it, and byte
2783 @section File Archives
2786 @cindex file archives
2788 A file whose name ends in @samp{.tar} is normally an @dfn{archive}
2789 made by the @code{tar} program. Emacs views these files in a special
2790 mode called Tar mode which provides a Dired-like list of the contents
2791 (@pxref{Dired}). You can move around through the list just as you
2792 would in Dired, and visit the subfiles contained in the archive.
2793 However, not all Dired commands are available in Tar mode.
2795 If you enable Auto Compression mode (@pxref{Compressed Files}), then
2796 Tar mode is used also for compressed archives---files with extensions
2797 @samp{.tgz}, @code{.tar.Z} and @code{.tar.gz}.
2799 The keys @kbd{e}, @kbd{f} and @key{RET} all extract a component file
2800 into its own buffer. You can edit it there and when you save the buffer
2801 the edited version will replace the version in the Tar buffer. @kbd{v}
2802 extracts a file into a buffer in View mode. @kbd{o} extracts the file
2803 and displays it in another window, so you could edit the file and
2804 operate on the archive simultaneously. @kbd{d} marks a file for
2805 deletion when you later use @kbd{x}, and @kbd{u} unmarks a file, as in
2806 Dired. @kbd{C} copies a file from the archive to disk and @kbd{R}
2807 renames a file. @kbd{g} reverts the buffer from the archive on disk.
2809 The keys @kbd{M}, @kbd{G}, and @kbd{O} change the file's permission
2810 bits, group, and owner, respectively.
2812 If your display supports colors and the mouse, moving the mouse
2813 pointer across a file name highlights that file name, indicating that
2814 you can click on it. Clicking @kbd{Mouse-2} on the highlighted file
2815 name extracts the file into a buffer and displays that buffer.
2817 Saving the Tar buffer writes a new version of the archive to disk with
2818 the changes you made to the components.
2820 You don't need the @code{tar} program to use Tar mode---Emacs reads
2821 the archives directly. However, accessing compressed archives
2822 requires the appropriate uncompression program.
2824 @cindex Archive mode
2825 @cindex mode, archive
2836 @cindex Java class archives
2837 @cindex unzip archives
2838 A separate but similar Archive mode is used for archives produced by
2839 the programs @code{arc}, @code{jar}, @code{lzh}, @code{zip}, and
2840 @code{zoo}, which have extensions corresponding to the program names.
2842 The keybindings of Archive mode are similar to those in Tar mode,
2843 with the addition of the @kbd{m} key which marks a file for subsequent
2844 operations, and @kbd{M-@key{DEL}} which unmarks all the marked files.
2845 Also, the @kbd{a} key toggles the display of detailed file
2846 information, for those archive types where it won't fit in a single
2847 line. Operations such as renaming a subfile, or changing its mode or
2848 owner, are supported only for some of the archive formats.
2850 Unlike Tar mode, Archive mode runs the archiving program to unpack
2851 and repack archives. Details of the program names and their options
2852 can be set in the @samp{Archive} Customize group. However, you don't
2853 need these programs to the archive table of contents, only to extract
2854 or manipulate the subfiles in the archive.
2857 @section Remote Files
2860 @cindex remote file access
2861 You can refer to files on other machines using a special file name syntax:
2865 /@var{host}:@var{filename}
2866 /@var{user}@@@var{host}:@var{filename}
2867 /@var{user}@@@var{host}#@var{port}:@var{filename}
2872 When you do this, Emacs uses the FTP program to read and write files on
2873 the specified host. It logs in through FTP using your user name or the
2874 name @var{user}. It may ask you for a password from time to time; this
2875 is used for logging in on @var{host}. The form using @var{port} allows
2876 you to access servers running on a non-default TCP port.
2878 @cindex backups for remote files
2879 @vindex ange-ftp-make-backup-files
2880 If you want to disable backups for remote files, set the variable
2881 @code{ange-ftp-make-backup-files} to @code{nil}.
2884 @vindex ange-ftp-default-user
2885 @cindex user name for remote file access
2886 Normally, if you do not specify a user name in a remote file name,
2887 that means to use your own user name. But if you set the variable
2888 @code{ange-ftp-default-user} to a string, that string is used instead.
2889 (The Emacs package that implements FTP file access is called
2892 @cindex anonymous FTP
2893 @vindex ange-ftp-generate-anonymous-password
2894 To visit files accessible by anonymous FTP, you use special user
2895 names @samp{anonymous} or @samp{ftp}. Passwords for these user names
2896 are handled specially. The variable
2897 @code{ange-ftp-generate-anonymous-password} controls what happens: if
2898 the value of this variable is a string, then that string is used as
2899 the password; if non-@code{nil} (the default), then the value of
2900 @code{user-mail-address} is used; if @code{nil}, the user is prompted
2901 for a password as normal.
2903 @cindex firewall, and accessing remote files
2904 @cindex gateway, and remote file access with @code{ange-ftp}
2905 @vindex ange-ftp-smart-gateway
2906 @vindex ange-ftp-gateway-host
2907 Sometimes you may be unable to access files on a remote machine
2908 because a @dfn{firewall} in between blocks the connection for security
2909 reasons. If you can log in on a @dfn{gateway} machine from which the
2910 target files @emph{are} accessible, and whose FTP server supports
2911 gatewaying features, you can still use remote file names; all you have
2912 to do is specify the name of the gateway machine by setting the
2913 variable @code{ange-ftp-gateway-host}, and set
2914 @code{ange-ftp-smart-gateway} to @code{t}. Otherwise you may be able
2915 to make remote file names work, but the procedure is complex. You can
2916 read the instructions by typing @kbd{M-x finder-commentary @key{RET}
2917 ange-ftp @key{RET}}.
2919 @vindex file-name-handler-alist
2920 @cindex disabling remote files
2921 You can entirely turn off the FTP file name feature by removing the
2922 entries @var{ange-ftp-completion-hook-function} and
2923 @var{ange-ftp-hook-function} from the variable
2924 @code{file-name-handler-alist}. You can turn off the feature in
2925 individual cases by quoting the file name with @samp{/:} (@pxref{Quoted
2928 @node Quoted File Names
2929 @section Quoted File Names
2931 @cindex quoting file names
2932 You can @dfn{quote} an absolute file name to prevent special
2933 characters and syntax in it from having their special effects.
2934 The way to do this is to add @samp{/:} at the beginning.
2936 For example, you can quote a local file name which appears remote, to
2937 prevent it from being treated as a remote file name. Thus, if you have
2938 a directory named @file{/foo:} and a file named @file{bar} in it, you
2939 can refer to that file in Emacs as @samp{/:/foo:/bar}.
2941 @samp{/:} can also prevent @samp{~} from being treated as a special
2942 character for a user's home directory. For example, @file{/:/tmp/~hack}
2943 refers to a file whose name is @file{~hack} in directory @file{/tmp}.
2945 Likewise, quoting with @samp{/:} is one way to enter in the minibuffer
2946 a file name that contains @samp{$}. However, the @samp{/:} must be at
2947 the beginning of the buffer in order to quote @samp{$}.
2949 You can also quote wildcard characters with @samp{/:}, for visiting.
2950 For example, @file{/:/tmp/foo*bar} visits the file @file{/tmp/foo*bar}.
2951 However, in most cases you can simply type the wildcard characters for
2952 themselves. For example, if the only file name in @file{/tmp} that
2953 starts with @samp{foo} and ends with @samp{bar} is @file{foo*bar}, then
2954 specifying @file{/tmp/foo*bar} will visit just @file{/tmp/foo*bar}.
2955 Another way is to specify @file{/tmp/foo[*]bar}.
2957 @node File Name Cache
2958 @section File Name Cache
2960 @cindex file name caching
2961 @cindex cache of file names
2964 @findex file-cache-minibuffer-complete
2965 You can use the @dfn{file name cache} to make it easy to locate a
2966 file by name, without having to remember exactly where it is located.
2967 When typing a file name in the minibuffer, @kbd{C-@key{tab}}
2968 (@code{file-cache-minibuffer-complete}) completes it using the file
2969 name cache. If you repeat @kbd{C-@key{tab}}, that cycles through the
2970 possible completions of what you had originally typed. Note that the
2971 @kbd{C-@key{tab}} character cannot be typed on most text-only
2974 The file name cache does not fill up automatically. Instead, you
2975 load file names into the cache using these commands:
2977 @findex file-cache-add-directory
2979 @item M-x file-cache-add-directory @key{RET} @var{directory} @key{RET}
2980 Add each file name in @var{directory} to the file name cache.
2981 @item M-x file-cache-add-directory-using-find @key{RET} @var{directory} @key{RET}
2982 Add each file name in @var{directory} and all of its nested
2983 subdirectories to the file name cache.
2984 @item M-x file-cache-add-directory-using-locate @key{RET} @var{directory} @key{RET}
2985 Add each file name in @var{directory} and all of its nested
2986 subdirectories to the file name cache, using @command{locate} to find
2988 @item M-x file-cache-add-directory-list @key{RET} @var{variable} @key{RET}
2989 Add each file name in each directory listed in @var{variable}
2990 to the file name cache. @var{variable} should be a Lisp variable
2991 such as @code{load-path} or @code{exec-path}, whose value is a list
2993 @item M-x file-cache-clear-cache @key{RET}
2994 Clear the cache; that is, remove all file names from it.
2997 @node File Conveniences
2998 @section Convenience Features for Finding Files
3000 @findex recentf-mode
3001 @vindex recentf-mode
3002 @findex recentf-save-list
3003 @findex recentf-edit-list
3004 If you enable Recentf mode, with @kbd{M-x recentf-mode}, the
3005 @samp{Files} menu includes a submenu containing a list of recently
3006 opened files. @kbd{M-x recentf-save-list} saves the current
3007 recent-file-list to a file, and @kbd{M-x recentf-edit-list} edits it.
3009 @findex auto-image-file-mode
3010 @findex mode, auto-image-file
3011 @cindex images, visiting
3012 @cindex visiting image files
3013 @vindex image-file-name-regexps
3014 @vindex image-file-name-extensions
3015 When Auto-image-file minor mode is enabled, visiting an image file
3016 displays it as an image, not as text. Likewise, inserting an image
3017 file into a buffer inserts it as an image. This works only when Emacs
3018 can display the relevant image type. The variables
3019 @code{image-file-name-extensions} or @code{image-file-name-regexps}
3020 control which file names are recognized as containing images.
3022 The @kbd{M-x ffap} command generalizes @code{find-file} with more
3023 powerful heuristic defaults (@pxref{FFAP}), often based on the text at
3024 point. Partial Completion mode offers other features extending
3025 @code{find-file}, which can be used with @code{ffap}.
3026 @xref{Completion Options}.