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 @samp{$} in a file name is used to substitute environment variables.
101 For example, if you have used the shell command @command{export
102 FOO=rms/hacks} to set up an environment variable named @env{FOO}, then
103 you can use @file{/u/$FOO/test.c} or @file{/u/$@{FOO@}/test.c} as an
104 abbreviation for @file{/u/rms/hacks/test.c}. The environment variable
105 name consists of all the alphanumeric characters after the @samp{$};
106 alternatively, it may be enclosed in braces after the @samp{$}. Note
107 that shell commands to set environment variables affect Emacs only if
108 done before Emacs is started.
110 To access a file with @samp{$} in its name, type @samp{$$}. This pair
111 is converted to a single @samp{$} at the same time as variable
112 substitution is performed for single @samp{$}. Alternatively, quote the
113 whole file name with @samp{/:} (@pxref{Quoted File Names}).
115 @findex substitute-in-file-name
116 The Lisp function that performs the substitution is called
117 @code{substitute-in-file-name}. The substitution is performed only on
118 file names read as such using the minibuffer.
120 You can include non-ASCII characters in file names if you set the
121 variable @code{file-name-coding-system} to a non-@code{nil} value.
122 @xref{Specify Coding}.
125 @section Visiting Files
126 @cindex visiting files
131 Visit a file (@code{find-file}).
133 Visit a file for viewing, without allowing changes to it
134 (@code{find-file-read-only}).
136 Visit a different file instead of the one visited last
137 (@code{find-alternate-file}).
139 Visit a file, in another window (@code{find-file-other-window}). Don't
140 alter what is displayed in the selected window.
142 Visit a file, in a new frame (@code{find-file-other-frame}). Don't
143 alter what is displayed in the selected frame.
144 @item M-x find-file-literally
145 Visit a file with no conversion of the contents.
148 @cindex files, visiting and saving
149 @cindex visiting files
151 @dfn{Visiting} a file means copying its contents into an Emacs buffer
152 so you can edit them. Emacs makes a new buffer for each file that you
153 visit. We say that this buffer is visiting the file that it was created
154 to hold. Emacs constructs the buffer name from the file name by
155 throwing away the directory, keeping just the name proper. For example,
156 a file named @file{/usr/rms/emacs.tex} would get a buffer named
157 @samp{emacs.tex}. If there is already a buffer with that name, a unique
158 name is constructed by appending @samp{<2>}, @samp{<3>}, or so on, using
159 the lowest number that makes a name that is not already in use.
161 Each window's mode line shows the name of the buffer that is being displayed
162 in that window, so you can always tell what buffer you are editing.
164 The changes you make with editing commands are made in the Emacs
165 buffer. They do not take effect in the file that you visited, or any
166 place permanent, until you @dfn{save} the buffer. Saving the buffer
167 means that Emacs writes the current contents of the buffer into its
168 visited file. @xref{Saving}.
170 @cindex modified (buffer)
171 If a buffer contains changes that have not been saved, we say the
172 buffer is @dfn{modified}. This is important because it implies that
173 some changes will be lost if the buffer is not saved. The mode line
174 displays two stars near the left margin to indicate that the buffer is
179 To visit a file, use the command @kbd{C-x C-f} (@code{find-file}). Follow
180 the command with the name of the file you wish to visit, terminated by a
183 The file name is read using the minibuffer (@pxref{Minibuffer}), with
184 defaulting and completion in the standard manner (@pxref{File Names}).
185 While in the minibuffer, you can abort @kbd{C-x C-f} by typing @kbd{C-g}.
187 @cindex file selection dialog
188 When Emacs is built with a suitable GUI toolkit, it pops up the
189 standard File Selection dialog of that toolkit instead of prompting for
190 the file name in the minibuffer. On Unix and GNU/Linux platforms, Emacs
191 does that when built with LessTif and Motif toolkits; on MS-Windows, the
192 GUI version does that by default.
194 Your confirmation that @kbd{C-x C-f} has completed successfully is the
195 appearance of new text on the screen and a new buffer name in the mode
196 line. If the specified file does not exist and could not be created, or
197 cannot be read, then you get an error, with an error message displayed
200 If you visit a file that is already in Emacs, @kbd{C-x C-f} does not make
201 another copy. It selects the existing buffer containing that file.
202 However, before doing so, it checks that the file itself has not changed
203 since you visited or saved it last. If the file has changed, a warning
204 message is printed. @xref{Interlocking,,Simultaneous Editing}.
206 @cindex creating files
207 What if you want to create a new file? Just visit it. Emacs prints
208 @samp{(New File)} in the echo area, but in other respects behaves as if
209 you had visited an existing empty file. If you make any changes and
210 save them, the file is created.
212 Emacs recognizes from the contents of a file which convention it uses
213 to separate lines---newline (used on GNU/Linux and on Unix),
214 carriage-return linefeed (used on Microsoft systems), or just
215 carriage-return (used on the Macintosh)---and automatically converts the
216 contents to the normal Emacs convention, which is that the newline
217 character separates lines. This is a part of the general feature of
218 coding system conversion (@pxref{Coding Systems}), and makes it possible
219 to edit files imported from various different operating systems with
220 equal convenience. If you change the text and save the file, Emacs
221 performs the inverse conversion, changing newlines back into
222 carriage-return linefeed or just carriage-return if appropriate.
224 @vindex find-file-run-dired
225 If the file you specify is actually a directory, @kbd{C-x C-f} invokes
226 Dired, the Emacs directory browser, so that you can ``edit'' the contents
227 of the directory (@pxref{Dired}). Dired is a convenient way to delete,
228 look at, or operate on the files in the directory. However, if the
229 variable @code{find-file-run-dired} is @code{nil}, then it is an error
230 to try to visit a directory.
232 @cindex wildcard characters in file names
233 @vindex find-file-wildcards
234 If the file name you specify contains shell-style wildcard
235 characters, Emacs visits all the files that match it. Wildcards
236 comprise @samp{?}, @samp{*} and @samp{[@dots{}]} sequences.
237 @xref{Quoted File Names}, for how to visit a file whose name actually
238 contains wildcard characters. You can disable the wildcard feature by
239 customizing @code{find-file-wildcards}.
241 If you visit a file that the operating system won't let you modify,
242 Emacs makes the buffer read-only, so that you won't go ahead and make
243 changes that you'll have trouble saving afterward. You can make the
244 buffer writable with @kbd{C-x C-q} (@code{vc-toggle-read-only}).
248 @findex find-file-read-only
249 Occasionally you might want to visit a file as read-only in order to
250 protect yourself from entering changes accidentally; do so by visiting
251 the file with the command @kbd{C-x C-r} (@code{find-file-read-only}).
254 @findex find-alternate-file
255 If you visit a nonexistent file unintentionally (because you typed the
256 wrong file name), use the @kbd{C-x C-v} command
257 (@code{find-alternate-file}) to visit the file you really wanted.
258 @kbd{C-x C-v} is similar to @kbd{C-x C-f}, but it kills the current
259 buffer (after first offering to save it if it is modified). When it
260 reads the file name to visit, it inserts the entire default file name in
261 the buffer, with point just after the directory part; this is convenient
262 if you made a slight error in typing the name.
264 If you find a file which exists but cannot be read, @kbd{C-x C-f}
268 @findex find-file-other-window
269 @kbd{C-x 4 f} (@code{find-file-other-window}) is like @kbd{C-x C-f}
270 except that the buffer containing the specified file is selected in another
271 window. The window that was selected before @kbd{C-x 4 f} continues to
272 show the same buffer it was already showing. If this command is used when
273 only one window is being displayed, that window is split in two, with one
274 window showing the same buffer as before, and the other one showing the
275 newly requested file. @xref{Windows}.
278 @findex find-file-other-frame
279 @kbd{C-x 5 f} (@code{find-file-other-frame}) is similar, but opens a
280 new frame, or makes visible any existing frame showing the file you
281 seek. This feature is available only when you are using a window
282 system. @xref{Frames}.
284 @findex find-file-literally
285 If you wish to edit a file as a sequence of ASCII characters with no special
286 encoding or conversion, use the @kbd{M-x find-file-literally} command.
287 It visits a file, like @kbd{C-x C-f}, but does not do format conversion
288 (@pxref{Formatted Text}), character code conversion (@pxref{Coding
289 Systems}), or automatic uncompression (@pxref{Compressed Files}), and
290 does not add a final newline because of @code{require-final-newline}.
291 If you already have visited the same file in the usual (non-literal)
292 manner, this command asks you whether to visit it literally instead.
294 @vindex find-file-hooks
295 @vindex find-file-not-found-hooks
296 Two special hook variables allow extensions to modify the operation of
297 visiting files. Visiting a file that does not exist runs the functions
298 in the list @code{find-file-not-found-hooks}; this variable holds a list
299 of functions, and the functions are called one by one (with no
300 arguments) until one of them returns non-@code{nil}. This is not a
301 normal hook, and the name ends in @samp{-hooks} rather than @samp{-hook}
302 to indicate that fact.
304 Any visiting of a file, whether extant or not, expects
305 @code{find-file-hooks} to contain a list of functions, and calls them
306 all, one by one, with no arguments. This variable is really a normal
307 hook, but it has an abnormal name for historical compatibility. In the
308 case of a nonexistent file, the @code{find-file-not-found-hooks} are run
311 There are several ways to specify automatically the major mode for
312 editing the file (@pxref{Choosing Modes}), and to specify local
313 variables defined for that file (@pxref{File Variables}).
316 @section Saving Files
318 @dfn{Saving} a buffer in Emacs means writing its contents back into the file
319 that was visited in the buffer.
323 Save the current buffer in its visited file (@code{save-buffer}).
325 Save any or all buffers in their visited files (@code{save-some-buffers}).
327 Forget that the current buffer has been changed (@code{not-modified}).
328 With prefix argument (@kbd{C-u}), mark the current buffer as changed.
330 Save the current buffer in a specified file (@code{write-file}).
331 @item M-x set-visited-file-name
332 Change file the name under which the current buffer will be saved.
337 When you wish to save the file and make your changes permanent, type
338 @kbd{C-x C-s} (@code{save-buffer}). After saving is finished, @kbd{C-x C-s}
339 displays a message like this:
342 Wrote /u/rms/gnu/gnu.tasks
346 If the selected buffer is not modified (no changes have been made in it
347 since the buffer was created or last saved), saving is not really done,
348 because it would have no effect. Instead, @kbd{C-x C-s} displays a message
349 like this in the echo area:
352 (No changes need to be saved)
356 @findex save-some-buffers
357 The command @kbd{C-x s} (@code{save-some-buffers}) offers to save any
358 or all modified buffers. It asks you what to do with each buffer. The
359 possible responses are analogous to those of @code{query-replace}:
363 Save this buffer and ask about the rest of the buffers.
365 Don't save this buffer, but ask about the rest of the buffers.
367 Save this buffer and all the rest with no more questions.
368 @c following generates acceptable underfull hbox
370 Terminate @code{save-some-buffers} without any more saving.
372 Save this buffer, then exit @code{save-some-buffers} without even asking
375 View the buffer that you are currently being asked about. When you exit
376 View mode, you get back to @code{save-some-buffers}, which asks the
379 Display a help message about these options.
382 @kbd{C-x C-c}, the key sequence to exit Emacs, invokes
383 @code{save-some-buffers} and therefore asks the same questions.
387 If you have changed a buffer but you do not want to save the changes,
388 you should take some action to prevent it. Otherwise, each time you use
389 @kbd{C-x s} or @kbd{C-x C-c}, you are liable to save this buffer by
390 mistake. One thing you can do is type @kbd{M-~} (@code{not-modified}),
391 which clears out the indication that the buffer is modified. If you do
392 this, none of the save commands will believe that the buffer needs to be
393 saved. (@samp{~} is often used as a mathematical symbol for `not'; thus
394 @kbd{M-~} is `not', metafied.) You could also use
395 @code{set-visited-file-name} (see below) to mark the buffer as visiting
396 a different file name, one which is not in use for anything important.
397 Alternatively, you can cancel all the changes made since the file was
398 visited or saved, by reading the text from the file again. This is
399 called @dfn{reverting}. @xref{Reverting}. You could also undo all the
400 changes by repeating the undo command @kbd{C-x u} until you have undone
401 all the changes; but reverting is easier.
403 @findex set-visited-file-name
404 @kbd{M-x set-visited-file-name} alters the name of the file that the
405 current buffer is visiting. It reads the new file name using the
406 minibuffer. Then it specifies the visited file name and changes the
407 buffer name correspondingly (as long as the new name is not in use).
408 @code{set-visited-file-name} does not save the buffer in the newly
409 visited file; it just alters the records inside Emacs in case you do
410 save later. It also marks the buffer as ``modified'' so that @kbd{C-x
411 C-s} in that buffer @emph{will} save.
415 If you wish to mark the buffer as visiting a different file and save it
416 right away, use @kbd{C-x C-w} (@code{write-file}). It is precisely
417 equivalent to @code{set-visited-file-name} followed by @kbd{C-x C-s}.
418 @kbd{C-x C-s} used on a buffer that is not visiting a file has the
419 same effect as @kbd{C-x C-w}; that is, it reads a file name, marks the
420 buffer as visiting that file, and saves it there. The default file name in
421 a buffer that is not visiting a file is made by combining the buffer name
422 with the buffer's default directory.
424 If the new file name implies a major mode, then @kbd{C-x C-w} switches
425 to that major mode, in most cases. The command
426 @code{set-visited-file-name} also does this. @xref{Choosing Modes}.
428 If Emacs is about to save a file and sees that the date of the latest
429 version on disk does not match what Emacs last read or wrote, Emacs
430 notifies you of this fact, because it probably indicates a problem caused
431 by simultaneous editing and requires your immediate attention.
432 @xref{Interlocking,, Simultaneous Editing}.
434 @vindex require-final-newline
435 If the variable @code{require-final-newline} is non-@code{nil}, Emacs
436 puts a newline at the end of any file that doesn't already end in one,
437 every time a file is saved or written. The default is @code{nil}.
440 * Backup:: How Emacs saves the old version of your file.
441 * Interlocking:: How Emacs protects against simultaneous editing
442 of one file by two users.
443 * Shadowing: File Shadowing.
444 Copying files to "shadows" automatically.
445 * Time Stamps:: Emacs can update time stamps on saved files.
449 @subsection Backup Files
451 @vindex make-backup-files
452 @vindex vc-make-backup-files
454 On most operating systems, rewriting a file automatically destroys all
455 record of what the file used to contain. Thus, saving a file from Emacs
456 throws away the old contents of the file---or it would, except that
457 Emacs carefully copies the old contents to another file, called the
458 @dfn{backup} file, before actually saving.
460 For most files, the variable @code{make-backup-files} determines
461 whether to make backup files. On most operating systems, its default
462 value is @code{t}, so that Emacs does write backup files.
464 For files managed by a version control system (@pxref{Version
465 Control}), the variable @code{vc-make-backup-files} determines whether
466 to make backup files. By default, it is @code{nil}, since backup files
467 are redundant when you store all the previous versions in a version
468 control system. @xref{VC Workfile Handling}.
470 @vindex backup-enable-predicate
471 @vindex temporary-file-directory
472 @vindex small-temporary-file-directory
473 The default value of the @code{backup-enable-predicate} variable
474 prevents backup files being written for files in the directories used
475 for temporary files, specified by @code{temporary-file-directory} or
476 @code{small-temporary-file-directory}.
478 At your option, Emacs can keep either a single backup file or a series of
479 numbered backup files for each file that you edit.
481 Emacs makes a backup for a file only the first time the file is saved
482 from one buffer. No matter how many times you save a file, its backup file
483 continues to contain the contents from before the file was visited.
484 Normally this means that the backup file contains the contents from before
485 the current editing session; however, if you kill the buffer and then visit
486 the file again, a new backup file will be made by the next save.
488 You can also explicitly request making another backup file from a
489 buffer even though it has already been saved at least once. If you save
490 the buffer with @kbd{C-u C-x C-s}, the version thus saved will be made
491 into a backup file if you save the buffer again. @kbd{C-u C-u C-x C-s}
492 saves the buffer, but first makes the previous file contents into a new
493 backup file. @kbd{C-u C-u C-u C-x C-s} does both things: it makes a
494 backup from the previous contents, and arranges to make another from the
495 newly saved contents, if you save again.
498 * Names: Backup Names. How backup files are named;
499 choosing single or numbered backup files.
500 * Deletion: Backup Deletion. Emacs deletes excess numbered backups.
501 * Copying: Backup Copying. Backups can be made by copying or renaming.
505 @subsubsection Single or Numbered Backups
507 If you choose to have a single backup file (this is the default),
508 the backup file's name is normally constructed by appending @samp{~} to the
509 file name being edited; thus, the backup file for @file{eval.c} would
512 @vindex make-backup-file-name-function
513 @vindex backup-directory-alist
514 You can change this behaviour by defining the variable
515 @code{make-backup-file-name-function} to a suitable function.
516 Alternatively you can customize the variable
517 @var{backup-directory-alist} to specify that files matching certain
518 patterns should be backed up in specific directories.
520 A typical use is to add an element @code{("." . @var{dir})} to make
521 all backups in the directory with absolute name @var{dir}; Emacs
522 modifies the backup file names to avoid clashes between files with the
523 same names originating in different directories. Alternatively,
524 adding, say, @code{("." ".~")} would make backups in the invisible
525 subdirectory @file{.~} of the original file's directory. Emacs
526 creates the directory, if necessary, to make the backup.
528 If access control stops Emacs from writing backup files under the usual
529 names, it writes the backup file as @file{%backup%~} in your home
530 directory. Only one such file can exist, so only the most recently
531 made such backup is available.
533 If you choose to have a series of numbered backup files, backup file
534 names contain @samp{.~}, the number, and another @samp{~} after the
535 original file name. Thus, the backup files of @file{eval.c} would be
536 called @file{eval.c.~1~}, @file{eval.c.~2~}, and so on, all the way
537 through names like @file{eval.c.~259~} and beyond. The variable
538 @code{backup-directory-alist} applies to numbered backups just as
541 @vindex version-control
542 The choice of single backup or numbered backups is controlled by the
543 variable @code{version-control}. Its possible values are
547 Make numbered backups.
549 Make numbered backups for files that have numbered backups already.
550 Otherwise, make single backups.
552 Do not in any case make numbered backups; always make single backups.
556 You can set @code{version-control} locally in an individual buffer to
557 control the making of backups for that buffer's file. For example,
558 Rmail mode locally sets @code{version-control} to @code{never} to make sure
559 that there is only one backup for an Rmail file. @xref{Locals}.
561 @cindex @env{VERSION_CONTROL} environment variable
562 If you set the environment variable @env{VERSION_CONTROL}, to tell
563 various GNU utilities what to do with backup files, Emacs also obeys the
564 environment variable by setting the Lisp variable @code{version-control}
565 accordingly at startup. If the environment variable's value is @samp{t}
566 or @samp{numbered}, then @code{version-control} becomes @code{t}; if the
567 value is @samp{nil} or @samp{existing}, then @code{version-control}
568 becomes @code{nil}; if it is @samp{never} or @samp{simple}, then
569 @code{version-control} becomes @code{never}.
571 @node Backup Deletion
572 @subsubsection Automatic Deletion of Backups
574 To prevent unlimited consumption of disk space, Emacs can delete numbered
575 backup versions automatically. Generally Emacs keeps the first few backups
576 and the latest few backups, deleting any in between. This happens every
577 time a new backup is made.
579 @vindex kept-old-versions
580 @vindex kept-new-versions
581 The two variables @code{kept-old-versions} and
582 @code{kept-new-versions} control this deletion. Their values are,
583 respectively the number of oldest (lowest-numbered) backups to keep and
584 the number of newest (highest-numbered) ones to keep, each time a new
585 backup is made. Recall that these values are used just after a new
586 backup version is made; that newly made backup is included in the count
587 in @code{kept-new-versions}. By default, both variables are 2.
589 @vindex delete-old-versions
590 If @code{delete-old-versions} is non-@code{nil}, the excess
591 middle versions are deleted without a murmur. If it is @code{nil}, the
592 default, then you are asked whether the excess middle versions should
595 Dired's @kbd{.} (Period) command can also be used to delete old versions.
596 @xref{Dired Deletion}.
599 @subsubsection Copying vs.@: Renaming
601 Backup files can be made by copying the old file or by renaming it. This
602 makes a difference when the old file has multiple names. If the old file
603 is renamed into the backup file, then the alternate names become names for
604 the backup file. If the old file is copied instead, then the alternate
605 names remain names for the file that you are editing, and the contents
606 accessed by those names will be the new contents.
608 The method of making a backup file may also affect the file's owner
609 and group. If copying is used, these do not change. If renaming is used,
610 you become the file's owner, and the file's group becomes the default
611 (different operating systems have different defaults for the group).
613 Having the owner change is usually a good idea, because then the owner
614 always shows who last edited the file. Also, the owners of the backups
615 show who produced those versions. Occasionally there is a file whose
616 owner should not change; it is a good idea for such files to contain
617 local variable lists to set @code{backup-by-copying-when-mismatch}
618 locally (@pxref{File Variables}).
620 @vindex backup-by-copying
621 @vindex backup-by-copying-when-linked
622 @vindex backup-by-copying-when-mismatch
623 @vindex backup-by-copying-when-privileged-mismatch
624 @cindex file ownership, and backup
625 @cindex backup, and user-id
626 The choice of renaming or copying is controlled by four variables.
627 Renaming is the default choice. If the variable
628 @code{backup-by-copying} is non-@code{nil}, copying is used. Otherwise,
629 if the variable @code{backup-by-copying-when-linked} is non-@code{nil},
630 then copying is used for files that have multiple names, but renaming
631 may still be used when the file being edited has only one name. If the
632 variable @code{backup-by-copying-when-mismatch} is non-@code{nil}, then
633 copying is used if renaming would cause the file's owner or group to
634 change. @code{backup-by-copying-when-mismatch} is @code{t} by default
635 if you start Emacs as the superuser. The fourth variable,
636 @code{backup-by-copying-when-privileged-mismatch}, gives the highest
637 numeric user-id for which @code{backup-by-copying-when-mismatch} will be
638 forced on. This is useful when low-numbered user-id are assigned to
639 special system users, such as @code{root}, @code{bin}, @code{daemon},
640 etc., which must maintain ownership of files.
642 When a file is managed with a version control system (@pxref{Version
643 Control}), Emacs does not normally make backups in the usual way for
644 that file. But check-in and check-out are similar in some ways to
645 making backups. One unfortunate similarity is that these operations
646 typically break hard links, disconnecting the file name you visited from
647 any alternate names for the same file. This has nothing to do with
648 Emacs---the version control system does it.
651 @subsection Protection against Simultaneous Editing
654 @cindex simultaneous editing
655 Simultaneous editing occurs when two users visit the same file, both
656 make changes, and then both save them. If nobody were informed that
657 this was happening, whichever user saved first would later find that his
660 On some systems, Emacs notices immediately when the second user starts
661 to change the file, and issues an immediate warning. On all systems,
662 Emacs checks when you save the file, and warns if you are about to
663 overwrite another user's changes. You can prevent loss of the other
664 user's work by taking the proper corrective action instead of saving the
667 @findex ask-user-about-lock
668 @cindex locking files
669 When you make the first modification in an Emacs buffer that is
670 visiting a file, Emacs records that the file is @dfn{locked} by you.
671 (It does this by creating a symbolic link in the same directory with a
672 different name.) Emacs removes the lock when you save the changes. The
673 idea is that the file is locked whenever an Emacs buffer visiting it has
677 If you begin to modify the buffer while the visited file is locked by
678 someone else, this constitutes a @dfn{collision}. When Emacs detects a
679 collision, it asks you what to do, by calling the Lisp function
680 @code{ask-user-about-lock}. You can redefine this function for the sake
681 of customization. The standard definition of this function asks you a
682 question and accepts three possible answers:
686 Steal the lock. Whoever was already changing the file loses the lock,
687 and you gain the lock.
689 Proceed. Go ahead and edit the file despite its being locked by someone else.
691 Quit. This causes an error (@code{file-locked}) and the modification you
692 were trying to make in the buffer does not actually take place.
695 Note that locking works on the basis of a file name; if a file has
696 multiple names, Emacs does not realize that the two names are the same file
697 and cannot prevent two users from editing it simultaneously under different
698 names. However, basing locking on names means that Emacs can interlock the
699 editing of new files that will not really exist until they are saved.
701 Some systems are not configured to allow Emacs to make locks, and
702 there are cases where lock files cannot be written. In these cases,
703 Emacs cannot detect trouble in advance, but it still can detect the
704 collision when you try to save a file and overwrite someone else's
707 If Emacs or the operating system crashes, this may leave behind lock
708 files which are stale. So you may occasionally get warnings about
709 spurious collisions. When you determine that the collision is spurious,
710 just use @kbd{p} to tell Emacs to go ahead anyway.
712 Every time Emacs saves a buffer, it first checks the last-modification
713 date of the existing file on disk to verify that it has not changed since the
714 file was last visited or saved. If the date does not match, it implies
715 that changes were made in the file in some other way, and these changes are
716 about to be lost if Emacs actually does save. To prevent this, Emacs
717 prints a warning message and asks for confirmation before saving.
718 Occasionally you will know why the file was changed and know that it does
719 not matter; then you can answer @kbd{yes} and proceed. Otherwise, you should
720 cancel the save with @kbd{C-g} and investigate the situation.
722 The first thing you should do when notified that simultaneous editing
723 has already taken place is to list the directory with @kbd{C-u C-x C-d}
724 (@pxref{Directories}). This shows the file's current author. You
725 should attempt to contact him to warn him not to continue editing.
726 Often the next step is to save the contents of your Emacs buffer under a
727 different name, and use @code{diff} to compare the two files.@refill
730 @subsection Shadowing Files
735 @item M-x shadow-initialize
736 Set up file shadowing.
737 @item M-x shadow-define-literal-group
738 Declare a single file to be shared between sites.
739 @item M-x shadow-define-regexp-group
740 Make all files that match each of a group of files be shared between hosts.
741 @item M-x shadow-define-cluster @key{RET} @var{name} @key{RET}
742 Define a shadow file cluster @var{name}.
743 @item M-x shadow-copy-files
744 Copy all pending shadow files.
745 @item M-x shadow-cancel
746 Cancel the instruction to shadow some files.
749 You can arrange to keep identical @dfn{shadow} copies of certain files
750 in more than one place---possibly on different machines. To do this,
751 first you must set up a @dfn{shadow file group}, which is a set of
752 identically-named files shared between a list of sites. The file
753 group is permanent and applies to further Emacs sessions as well as
754 the current one. Once the group is set up, every time you exit Emacs,
755 it will copy the file you edited to the other files in its group. You
756 can also do the copying without exiting Emacs, by typing @kbd{M-x
759 To set up a file group, use @kbd{M-x shadow-define-literal-group} or
760 @kbd{M-x shadow-define-regexp-group}. See their documentation strings
761 for further information.
763 Before copying a file to its shadows, Emacs asks for confirmation.
764 You can answer ``no'' to bypass copying of this file, this time. If
765 you want to cancel the shadowing permanently for a certain file, use
766 @kbd{M-x shadow-cancel} to eliminate or change the shadow file group.
768 A @dfn{shadow cluster} is a group of hosts that share directories, so
769 that copying to or from one of them is sufficient to update the file
770 on all of them. Each shadow cluster has a name, and specifies the
771 network address of a primary host (the one we copy files to), and a
772 regular expression that matches the hostnames of all the other hosts
773 in the cluster. You can define a shadow cluster with @kbd{M-x
774 shadow-define-cluster}.
777 @subsection Updating Time Stamps Automatically
780 @cindex modification dates
781 @cindex locale, date format
783 You can arrange put a time stamp in a file, so that it will be updated
784 automatically each time you edit and save the file. The time stamp
785 has to be in the first eight lines of the file, and you should
799 Then add the hook function @code{time-stamp} to the hook
800 @code{write-file-hooks}; that hook function will automatically update
801 the time stamp, inserting the current date and time when you save the
802 file. You can also use the command @kbd{M-x time-stamp} to update the
803 time stamp manually. For other customizations, see the Custom group
804 @code{time-stamp}. Note that non-numeric fields in the time stamp are
805 formatted according to your locale setting (@pxref{Environment}).
808 @section Reverting a Buffer
809 @findex revert-buffer
810 @cindex drastic changes
812 If you have made extensive changes to a file and then change your mind
813 about them, you can get rid of them by reading in the previous version
814 of the file. To do this, use @kbd{M-x revert-buffer}, which operates on
815 the current buffer. Since reverting a buffer unintentionally could lose
816 a lot of work, you must confirm this command with @kbd{yes}.
818 @code{revert-buffer} keeps point at the same distance (measured in
819 characters) from the beginning of the file. If the file was edited only
820 slightly, you will be at approximately the same piece of text after
821 reverting as before. If you have made drastic changes, the same value of
822 point in the old file may address a totally different piece of text.
824 Reverting marks the buffer as ``not modified'' until another change is
827 Some kinds of buffers whose contents reflect data bases other than files,
828 such as Dired buffers, can also be reverted. For them, reverting means
829 recalculating their contents from the appropriate data base. Buffers
830 created explicitly with @kbd{C-x b} cannot be reverted; @code{revert-buffer}
831 reports an error when asked to do so.
833 @vindex revert-without-query
834 When you edit a file that changes automatically and frequently---for
835 example, a log of output from a process that continues to run---it may be
836 useful for Emacs to revert the file without querying you, whenever you
837 visit the file again with @kbd{C-x C-f}.
839 To request this behavior, set the variable @code{revert-without-query}
840 to a list of regular expressions. When a file name matches one of these
841 regular expressions, @code{find-file} and @code{revert-buffer} will
842 revert it automatically if it has changed---provided the buffer itself
843 is not modified. (If you have edited the text, it would be wrong to
844 discard your changes.)
847 @section Auto-Saving: Protection Against Disasters
848 @cindex Auto Save mode
849 @cindex mode, Auto Save
852 Emacs saves all the visited files from time to time (based on counting
853 your keystrokes) without being asked. This is called @dfn{auto-saving}.
854 It prevents you from losing more than a limited amount of work if the
857 When Emacs determines that it is time for auto-saving, each buffer is
858 considered, and is auto-saved if auto-saving is turned on for it and it
859 has been changed since the last time it was auto-saved. The message
860 @samp{Auto-saving...} is displayed in the echo area during auto-saving,
861 if any files are actually auto-saved. Errors occurring during
862 auto-saving are caught so that they do not interfere with the execution
863 of commands you have been typing.
866 * Files: Auto Save Files. The file where auto-saved changes are
867 actually made until you save the file.
868 * Control: Auto Save Control. Controlling when and how often to auto-save.
869 * Recover:: Recovering text from auto-save files.
872 @node Auto Save Files
873 @subsection Auto-Save Files
875 Auto-saving does not normally save in the files that you visited, because
876 it can be very undesirable to save a program that is in an inconsistent
877 state when you have made half of a planned change. Instead, auto-saving
878 is done in a different file called the @dfn{auto-save file}, and the
879 visited file is changed only when you request saving explicitly (such as
882 Normally, the auto-save file name is made by appending @samp{#} to the
883 front and rear of the visited file name. Thus, a buffer visiting file
884 @file{foo.c} is auto-saved in a file @file{#foo.c#}. Most buffers that
885 are not visiting files are auto-saved only if you request it explicitly;
886 when they are auto-saved, the auto-save file name is made by appending
887 @samp{#%} to the front and @samp{#} to the rear of buffer name. For
888 example, the @samp{*mail*} buffer in which you compose messages to be
889 sent is auto-saved in a file named @file{#%*mail*#}. Auto-save file
890 names are made this way unless you reprogram parts of Emacs to do
891 something different (the functions @code{make-auto-save-file-name} and
892 @code{auto-save-file-name-p}). The file name to be used for auto-saving
893 in a buffer is calculated when auto-saving is turned on in that buffer.
895 When you delete a substantial part of the text in a large buffer, auto
896 save turns off temporarily in that buffer. This is because if you
897 deleted the text unintentionally, you might find the auto-save file more
898 useful if it contains the deleted text. To reenable auto-saving after
899 this happens, save the buffer with @kbd{C-x C-s}, or use @kbd{C-u 1 M-x
902 @vindex auto-save-visited-file-name
903 If you want auto-saving to be done in the visited file, set the variable
904 @code{auto-save-visited-file-name} to be non-@code{nil}. In this mode,
905 there is really no difference between auto-saving and explicit saving.
907 @vindex delete-auto-save-files
908 A buffer's auto-save file is deleted when you save the buffer in its
909 visited file. To inhibit this, set the variable @code{delete-auto-save-files}
910 to @code{nil}. Changing the visited file name with @kbd{C-x C-w} or
911 @code{set-visited-file-name} renames any auto-save file to go with
912 the new visited name.
914 @node Auto Save Control
915 @subsection Controlling Auto-Saving
917 @vindex auto-save-default
918 @findex auto-save-mode
919 Each time you visit a file, auto-saving is turned on for that file's
920 buffer if the variable @code{auto-save-default} is non-@code{nil} (but not
921 in batch mode; @pxref{Entering Emacs}). The default for this variable is
922 @code{t}, so auto-saving is the usual practice for file-visiting buffers.
923 Auto-saving can be turned on or off for any existing buffer with the
924 command @kbd{M-x auto-save-mode}. Like other minor mode commands, @kbd{M-x
925 auto-save-mode} turns auto-saving on with a positive argument, off with a
926 zero or negative argument; with no argument, it toggles.
928 @vindex auto-save-interval
929 Emacs does auto-saving periodically based on counting how many characters
930 you have typed since the last time auto-saving was done. The variable
931 @code{auto-save-interval} specifies how many characters there are between
932 auto-saves. By default, it is 300.
934 @vindex auto-save-timeout
935 Auto-saving also takes place when you stop typing for a while. The
936 variable @code{auto-save-timeout} says how many seconds Emacs should
937 wait before it does an auto save (and perhaps also a garbage
938 collection). (The actual time period is longer if the current buffer is
939 long; this is a heuristic which aims to keep out of your way when you
940 are editing long buffers, in which auto-save takes an appreciable amount
941 of time.) Auto-saving during idle periods accomplishes two things:
942 first, it makes sure all your work is saved if you go away from the
943 terminal for a while; second, it may avoid some auto-saving while you
946 Emacs also does auto-saving whenever it gets a fatal error. This
947 includes killing the Emacs job with a shell command such as @samp{kill
948 %emacs}, or disconnecting a phone line or network connection.
951 You can request an auto-save explicitly with the command @kbd{M-x
955 @subsection Recovering Data from Auto-Saves
958 You can use the contents of an auto-save file to recover from a loss
959 of data with the command @kbd{M-x recover-file @key{RET} @var{file}
960 @key{RET}}. This visits @var{file} and then (after your confirmation)
961 restores the contents from its auto-save file @file{#@var{file}#}.
962 You can then save with @kbd{C-x C-s} to put the recovered text into
963 @var{file} itself. For example, to recover file @file{foo.c} from its
964 auto-save file @file{#foo.c#}, do:@refill
967 M-x recover-file @key{RET} foo.c @key{RET}
972 Before asking for confirmation, @kbd{M-x recover-file} displays a
973 directory listing describing the specified file and the auto-save file,
974 so you can compare their sizes and dates. If the auto-save file
975 is older, @kbd{M-x recover-file} does not offer to read it.
977 @findex recover-session
978 If Emacs or the computer crashes, you can recover all the files you
979 were editing from their auto save files with the command @kbd{M-x
980 recover-session}. This first shows you a list of recorded interrupted
981 sessions. Move point to the one you choose, and type @kbd{C-c C-c}.
983 Then @code{recover-session} asks about each of the files that were
984 being edited during that session, asking whether to recover that file.
985 If you answer @kbd{y}, it calls @code{recover-file}, which works in its
986 normal fashion. It shows the dates of the original file and its
987 auto-save file, and asks once again whether to recover that file.
989 When @code{recover-session} is done, the files you've chosen to
990 recover are present in Emacs buffers. You should then save them. Only
991 this---saving them---updates the files themselves.
993 @vindex auto-save-list-file-prefix
994 Emacs records interrupted sessions for later recovery in files named
995 @file{~/.emacs.d/auto-save-list/.saves-@var{pid}-@var{hostname}}. The
996 @samp{~/.emacs.d/auto-save-list/.saves-} portion of these names comes
997 from the value of @code{auto-save-list-file-prefix}. You can record
998 sessions in a different place by customizing that variable. If you
999 set @code{auto-save-list-file-prefix} to @code{nil} in your
1000 @file{.emacs} file, sessions are not recorded for recovery.
1003 @section File Name Aliases
1005 Symbolic links and hard links both make it possible for several file
1006 names to refer to the same file. Hard links are alternate names that
1007 refer directly to the file; all the names are equally valid, and no one
1008 of them is preferred. By contrast, a symbolic link is a kind of defined
1009 alias: when @file{foo} is a symbolic link to @file{bar}, you can use
1010 either name to refer to the file, but @file{bar} is the real name, while
1011 @file{foo} is just an alias. More complex cases occur when symbolic
1012 links point to directories.
1014 If you visit two names for the same file, normally Emacs makes
1015 two different buffers, but it warns you about the situation.
1017 @vindex find-file-existing-other-name
1018 Normally, if you visit a file which Emacs is already visiting under
1019 a different name, Emacs displays a message in the echo area and uses
1020 the existing buffer visiting that file. This can happen on systems
1021 that support symbolic links, or if you use a long file name on a
1022 system that truncates long file names. You can disable this feature
1023 by setting the variable @code{find-file-existing-other-name} to
1024 @code{nil}. Then if you visit the same file under two different names,
1025 you get a separate buffer for each file name.
1027 @vindex find-file-visit-truename
1028 @cindex truenames of files
1029 @cindex file truenames
1030 If the variable @code{find-file-visit-truename} is non-@code{nil},
1031 then the file name recorded for a buffer is the file's @dfn{truename}
1032 (made by replacing all symbolic links with their target names), rather
1033 than the name you specify. Setting @code{find-file-visit-truename} also
1034 implies the effect of @code{find-file-existing-other-name}.
1036 @node Version Control
1037 @section Version Control
1038 @cindex version control
1040 @dfn{Version control systems} are packages that can record multiple
1041 versions of a source file, usually storing the unchanged parts of the
1042 file just once. Version control systems also record history information
1043 such as the creation time of each version, who created it, and a
1044 description of what was changed in that version.
1046 The Emacs version control interface is called VC. Its commands work
1047 with three version control systems---RCS, CVS and SCCS. The GNU
1048 project recommends RCS and CVS, which are free software and available
1049 from the Free Software Foundation. We also have free software to
1050 replace SCCS, known as CSSC; if you are using SCCS and don't want to
1051 make the incompatible change to RCS or CVS, you can switch to CSSC.
1054 * Introduction to VC:: How version control works in general.
1055 * VC Mode Line:: How the mode line shows version control status.
1056 * Basic VC Editing:: How to edit a file under version control.
1057 * Old Versions:: Examining and comparing old versions.
1058 * Secondary VC Commands:: The commands used a little less frequently.
1059 * Branches:: Multiple lines of development.
1060 * Snapshots:: Sets of file versions treated as a unit.
1061 * Miscellaneous VC:: Various other commands and features of VC.
1062 * Customizing VC:: Variables that change VC's behavior.
1065 @node Introduction to VC
1066 @subsection Introduction to Version Control
1068 VC allows you to use a version control system from within Emacs,
1069 integrating the version control operations smoothly with editing. VC
1070 provides a uniform interface to version control, so that regardless of
1071 which version control system is in use, you can use it the same way.
1073 This section provides a general overview of version control, and
1074 describes the version control systems that VC supports. You can skip
1075 this section if you are already familiar with the version control system
1079 * Version Systems:: Supported version control back-end systems.
1080 * VC Concepts:: Words and concepts related to version control.
1083 @node Version Systems
1084 @subsubsection Supported Version Control Systems
1087 @cindex back end (version control)
1088 VC currently works with three different version control systems or
1089 ``back ends'': RCS, CVS, and SCCS.
1091 RCS is a free version control system that is available from the Free
1092 Software Foundation. It is perhaps the most mature of the supported
1093 back ends, and the VC commands are conceptually closest to RCS. Almost
1094 everything you can do with RCS can be done through VC.
1097 CVS is built on top of RCS, and extends the features of RCS, allowing
1098 for more sophisticated release management, and concurrent multi-user
1099 development. VC supports basic editing operations under CVS, but for
1100 some less common tasks you still need to call CVS from the command line.
1101 Note also that before using CVS you must set up a repository, which is a
1102 subject too complex to treat here.
1105 SCCS is a proprietary but widely used version control system. In
1106 terms of capabilities, it is the weakest of the three that VC
1107 supports. VC compensates for certain features missing in SCCS
1108 (snapshots, for example) by implementing them itself, but some other VC
1109 features, such as multiple branches, are not available with SCCS. You
1110 should use SCCS only if for some reason you cannot use RCS.
1113 @subsubsection Concepts of Version Control
1116 @cindex registered file
1117 When a file is under version control, we also say that it is
1118 @dfn{registered} in the version control system. Each registered file
1119 has a corresponding @dfn{master file} which represents the file's
1120 present state plus its change history---enough to reconstruct the
1121 current version or any earlier version. Usually the master file also
1122 records a @dfn{log entry} for each version, describing in words what was
1123 changed in that version.
1126 @cindex checking out files
1127 The file that is maintained under version control is sometimes called
1128 the @dfn{work file} corresponding to its master file. You edit the work
1129 file and make changes in it, as you would with an ordinary file. (With
1130 SCCS and RCS, you must @dfn{lock} the file before you start to edit it.)
1131 After you are done with a set of changes, you @dfn{check the file in},
1132 which records the changes in the master file, along with a log entry for
1135 With CVS, there are usually multiple work files corresponding to a
1136 single master file---often each user has his own copy. It is also
1137 possible to use RCS in this way, but this is not the usual way to use
1140 @cindex locking and version control
1141 A version control system typically has some mechanism to coordinate
1142 between users who want to change the same file. One method is
1143 @dfn{locking} (analogous to the locking that Emacs uses to detect
1144 simultaneous editing of a file, but distinct from it). The other method
1145 is to merge your changes with other people's changes when you check them
1148 With version control locking, work files are normally read-only so
1149 that you cannot change them. You ask the version control system to make
1150 a work file writable for you by locking it; only one user can do
1151 this at any given time. When you check in your changes, that unlocks
1152 the file, making the work file read-only again. This allows other users
1153 to lock the file to make further changes. SCCS always uses locking, and
1156 The other alternative for RCS is to let each user modify the work file
1157 at any time. In this mode, locking is not required, but it is
1158 permitted; check-in is still the way to record a new version.
1160 CVS normally allows each user to modify his own copy of the work file
1161 at any time, but requires merging with changes from other users at
1162 check-in time. However, CVS can also be set up to require locking.
1163 (@pxref{Backend Options}).
1166 @subsection Version Control and the Mode Line
1168 When you visit a file that is under version control, Emacs indicates
1169 this on the mode line. For example, @samp{RCS-1.3} says that RCS is
1170 used for that file, and the current version is 1.3.
1172 The character between the back-end name and the version number
1173 indicates the version control status of the file. @samp{-} means that
1174 the work file is not locked (if locking is in use), or not modified (if
1175 locking is not in use). @samp{:} indicates that the file is locked, or
1176 that it is modified. If the file is locked by some other user (for
1177 instance, @samp{jim}), that is displayed as @samp{RCS:jim:1.3}.
1179 @node Basic VC Editing
1180 @subsection Basic Editing under Version Control
1182 The principal VC command is an all-purpose command that performs
1183 either locking or check-in, depending on the situation.
1188 Perform the next logical version control operation on this file.
1191 @findex vc-next-action
1192 @findex vc-toggle-read-only
1194 @kindex C-x C-q @r{(Version Control)}
1195 Strictly speaking, the command for this job is @code{vc-next-action},
1196 bound to @kbd{C-x v v}. However, the normal meaning of @kbd{C-x C-q} is
1197 to make a read-only buffer writable, or vice versa; we have extended it
1198 to do the same job properly for files managed by version control, by
1199 performing the appropriate version control operations. When you type
1200 @kbd{C-x C-q} on a registered file, it acts like @kbd{C-x v v}.
1202 The precise action of this command depends on the state of the file,
1203 and whether the version control system uses locking or not. SCCS and
1204 RCS normally use locking; CVS normally does not use locking.
1207 * VC with Locking:: RCS in its default mode, SCCS, and optionally CVS.
1208 * Without Locking:: Without locking: default mode for CVS.
1209 * Log Buffer:: Features available in log entry buffers.
1212 @node VC with Locking
1213 @subsubsection Basic Version Control with Locking
1215 If locking is used for the file (as with SCCS, and RCS in its default
1216 mode), @kbd{C-x C-q} can either lock a file or check it in:
1220 If the file is not locked, @kbd{C-x C-q} locks it, and
1221 makes it writable so that you can change it.
1224 If the file is locked by you, and contains changes, @kbd{C-x C-q} checks
1225 in the changes. In order to do this, it first reads the log entry
1226 for the new version. @xref{Log Buffer}.
1229 If the file is locked by you, but you have not changed it since you
1230 locked it, @kbd{C-x C-q} releases the lock and makes the file read-only
1234 If the file is locked by some other user, @kbd{C-x C-q} asks you whether
1235 you want to ``steal the lock'' from that user. If you say yes, the file
1236 becomes locked by you, but a message is sent to the person who had
1237 formerly locked the file, to inform him of what has happened.
1240 These rules also apply when you use CVS in locking mode, except
1241 that there is no such thing as stealing a lock.
1243 @node Without Locking
1244 @subsubsection Basic Version Control without Locking
1246 When there is no locking---the default for CVS---work files are always
1247 writable; you do not need to do anything before you begin to edit a
1248 file. The status indicator on the mode line is @samp{-} if the file is
1249 unmodified; it flips to @samp{:} as soon as you save any changes in the
1252 Here is what @kbd{C-x C-q} does when using CVS:
1256 If some other user has checked in changes into the master file,
1257 Emacs asks you whether you want to merge those changes into your own
1258 work file (@pxref{Merging}). You must do this before you can check in
1262 If there are no new changes in the master file, but you have made
1263 modifications in your work file, @kbd{C-x C-q} checks in your changes.
1264 In order to do this, it first reads the log entry for the new version.
1268 If the file is not modified, the @kbd{C-x C-q} does nothing.
1271 These rules also apply when you use RCS in the mode that does not
1272 require locking, except that automatic merging of changes from the
1273 master file is not implemented. Unfortunately, this means that nothing
1274 informs you if another user has checked in changes in the same file
1275 since you began editing it, and when this happens, his changes will be
1276 effectively removed when you check in your version (though they will
1277 remain in the master file, so they will not be entirely lost). You must
1278 therefore verify the current version is unchanged, before you check in your
1279 changes. We hope to eliminate this risk and provide automatic merging
1280 with RCS in a future Emacs version.
1282 In addition, locking is possible with RCS even in this mode, although
1283 it is not required; @kbd{C-x C-q} with an unmodified file locks the
1284 file, just as it does with RCS in its normal (locking) mode.
1287 @subsubsection Features of the Log Entry Buffer
1289 When you check in changes, @kbd{C-x C-q} first reads a log entry. It
1290 pops up a buffer called @samp{*VC-Log*} for you to enter the log entry.
1291 When you are finished, type @kbd{C-c C-c} in the @samp{*VC-Log*} buffer.
1292 That is when check-in really happens.
1294 To abort check-in, just @strong{don't} type @kbd{C-c C-c} in that
1295 buffer. You can switch buffers and do other editing. As long as you
1296 don't try to check in another file, the entry you were editing remains
1297 in the @samp{*VC-Log*} buffer, and you can go back to that buffer at any
1298 time to complete the check-in.
1300 If you change several source files for the same reason, it is often
1301 convenient to specify the same log entry for many of the files. To do
1302 this, use the history of previous log entries. The commands @kbd{M-n},
1303 @kbd{M-p}, @kbd{M-s} and @kbd{M-r} for doing this work just like the
1304 minibuffer history commands (except that these versions are used outside
1307 @vindex vc-log-mode-hook
1308 Each time you check in a file, the log entry buffer is put into VC Log
1309 mode, which involves running two hooks: @code{text-mode-hook} and
1310 @code{vc-log-mode-hook}. @xref{Hooks}.
1313 @subsection Examining And Comparing Old Versions
1315 One of the convenient features of version control is the ability
1316 to examine any version of a file, or compare two versions.
1319 @item C-x v ~ @var{version} @key{RET}
1320 Examine version @var{version} of the visited file, in a buffer of its
1324 Compare the current buffer contents with the latest checked-in version
1327 @item C-u C-x v = @var{file} @key{RET} @var{oldvers} @key{RET} @var{newvers} @key{RET}
1328 Compare the specified two versions of @var{file}.
1331 Display the result of the CVS annotate command using colors.
1334 @findex vc-version-other-window
1336 To examine an old version in toto, visit the file and then type
1337 @kbd{C-x v ~ @var{version} @key{RET}} (@code{vc-version-other-window}).
1338 This puts the text of version @var{version} in a file named
1339 @file{@var{filename}.~@var{version}~}, and visits it in its own buffer
1340 in a separate window. (In RCS, you can also select an old version
1341 and create a branch from it. @xref{Branches}.)
1345 But usually it is more convenient to compare two versions of the file,
1346 with the command @kbd{C-x v =} (@code{vc-diff}). Plain @kbd{C-x v =}
1347 compares the current buffer contents (saving them in the file if
1348 necessary) with the last checked-in version of the file. @kbd{C-u C-x v
1349 =}, with a numeric argument, reads a file name and two version numbers,
1350 then compares those versions of the specified file.
1352 If you supply a directory name instead of the name of a registered
1353 file, this command compares the two specified versions of all registered
1354 files in that directory and its subdirectories.
1356 You can specify a checked-in version by its number; an empty input
1357 specifies the current contents of the work file (which may be different
1358 from all the checked-in versions). You can also specify a snapshot name
1359 (@pxref{Snapshots}) instead of one or both version numbers.
1361 This command works by running the @code{diff} utility, getting the
1362 options from the variable @code{diff-switches}. It displays the output
1363 in a special buffer in another window. Unlike the @kbd{M-x diff}
1364 command, @kbd{C-x v =} does not try to locate the changes in the old and
1365 new versions. This is because normally one or both versions do not
1366 exist as files when you compare them; they exist only in the records of
1367 the master file. @xref{Comparing Files}, for more information about
1372 For CVS-controlled files, you can display the result of the CVS
1373 annotate command, using colors to enhance the visual appearance. Use
1374 the command @kbd{M-x vc-annotate} to do this. Red means new, blue means
1375 old, and intermediate colors indicate intermediate ages. A prefix
1376 argument @var{n} specifies a stretch factor for the time scale; it makes
1377 each color cover a period @var{n} times as long.
1379 @node Secondary VC Commands
1380 @subsection The Secondary Commands of VC
1382 This section explains the secondary commands of VC; those that you might
1386 * Registering:: Putting a file under version control.
1387 * VC Status:: Viewing the VC status of files.
1388 * VC Undo:: Cancelling changes before or after check-in.
1389 * VC Dired Mode:: Listing files managed by version control.
1390 * VC Dired Commands:: Commands to use in a VC Dired buffer.
1394 @subsubsection Registering a File for Version Control
1398 You can put any file under version control by simply visiting it, and
1399 then typing @w{@kbd{C-x v i}} (@code{vc-register}).
1403 Register the visited file for version control.
1406 @vindex vc-default-back-end
1407 To register the file, Emacs must choose which version control system
1408 to use for it. You can specify your choice explicitly by setting
1409 @code{vc-default-back-end} to @code{RCS}, @code{CVS} or @code{SCCS}.
1410 Otherwise, if there is a subdirectory named @file{RCS}, @file{SCCS}, or
1411 @file{CVS}, Emacs uses the corresponding version control system. In the
1412 absence of any specification, the default choice is RCS if RCS is
1413 installed, otherwise SCCS.
1415 If locking is in use, @kbd{C-x v i} leaves the file unlocked and
1416 read-only. Type @kbd{C-x C-q} if you wish to start editing it. After
1417 registering a file with CVS, you must subsequently commit the initial
1418 version by typing @kbd{C-x C-q}.
1420 @vindex vc-default-init-version
1421 The initial version number for a newly registered file is 1.1, by
1422 default. You can specify a different default by setting the variable
1423 @code{vc-default-init-version}, or you can give @kbd{C-x v i} a numeric
1424 argument; then it reads the initial version number for this particular
1425 file using the minibuffer.
1427 @vindex vc-initial-comment
1428 If @code{vc-initial-comment} is non-@code{nil}, @kbd{C-x v i} reads an
1429 initial comment to describe the purpose of this source file. Reading
1430 the initial comment works like reading a log entry (@pxref{Log Buffer}).
1433 @subsubsection VC Status Commands
1437 Display version control state and change history.
1441 @findex vc-print-log
1442 To view the detailed version control status and history of a file,
1443 type @kbd{C-x v l} (@code{vc-print-log}). It displays the history of
1444 changes to the current file, including the text of the log entries. The
1445 output appears in a separate window.
1448 @subsubsection Undoing Version Control Actions
1452 Revert the buffer and the file to the last checked-in version.
1455 Remove the last-entered change from the master for the visited file.
1456 This undoes your last check-in.
1460 @findex vc-revert-buffer
1461 If you want to discard your current set of changes and revert to the
1462 last version checked in, use @kbd{C-x v u} (@code{vc-revert-buffer}).
1463 This leaves the file unlocked; if locking is in use, you must first lock
1464 the file again before you change it again. @kbd{C-x v u} requires
1465 confirmation, unless it sees that you haven't made any changes since the
1466 last checked-in version.
1468 @kbd{C-x v u} is also the command to unlock a file if you lock it and
1469 then decide not to change it.
1472 @findex vc-cancel-version
1473 To cancel a change that you already checked in, use @kbd{C-x v c}
1474 (@code{vc-cancel-version}). This command discards all record of the
1475 most recent checked-in version. @kbd{C-x v c} also offers to revert
1476 your work file and buffer to the previous version (the one that precedes
1477 the version that is deleted).
1479 If you answer @kbd{no}, VC keeps your changes in the buffer, and locks
1480 the file. The no-revert option is useful when you have checked in a
1481 change and then discover a trivial error in it; you can cancel the
1482 erroneous check-in, fix the error, and check the file in again.
1484 When @kbd{C-x v c} does not revert the buffer, it unexpands all
1485 version control headers in the buffer instead (@pxref{Version Headers}).
1486 This is because the buffer no longer corresponds to any existing
1487 version. If you check it in again, the check-in process will expand the
1488 headers properly for the new version number.
1490 However, it is impossible to unexpand the RCS @samp{@w{$}Log$} header
1491 automatically. If you use that header feature, you have to unexpand it
1492 by hand---by deleting the entry for the version that you just canceled.
1494 Be careful when invoking @kbd{C-x v c}, as it is easy to lose a lot of
1495 work with it. To help you be careful, this command always requires
1496 confirmation with @kbd{yes}. Note also that this command is disabled
1497 under CVS, because canceling versions is very dangerous and discouraged
1501 @subsubsection Dired under VC
1505 @cindex CVS Dired Mode
1506 The VC Dired Mode described here works with all the version control
1507 systems that VC supports. Another more powerful facility, designed
1508 specifically for CVS, is called PCL-CVS. @xref{Top, , About PCL-CVS,
1509 pcl-cvs, PCL-CVS --- The Emacs Front-End to CVS}.
1512 @findex vc-directory
1513 When you are working on a large program, it is often useful to find
1514 out which files have changed within an entire directory tree, or to view
1515 the status of all files under version control at once, and to perform
1516 version control operations on collections of files. You can use the
1517 command @kbd{C-x v d} (@code{vc-directory}) to make a directory listing
1518 that includes only files relevant for version control.
1520 @vindex vc-dired-terse-display
1521 @kbd{C-x v d} creates a buffer which uses VC Dired Mode. This looks
1522 much like an ordinary Dired buffer (@pxref{Dired}); however, normally it
1523 shows only the noteworthy files (those locked or not up-to-date). This
1524 is called @dfn{terse display}. If you set the variable
1525 @code{vc-dired-terse-display} to @code{nil}, then VC Dired shows all
1526 relevant files---those managed under version control, plus all
1527 subdirectories (@dfn{full display}). The command @kbd{v t} in a VC
1528 Dired buffer toggles between terse display and full display (@pxref{VC
1531 @vindex vc-dired-recurse
1532 By default, VC Dired produces a recursive listing of noteworthy or
1533 relevant files at or below the given directory. You can change this by
1534 setting the variable @code{vc-dired-recurse} to @code{nil}; then VC
1535 Dired shows only the files in the given directory.
1537 The line for an individual file shows the version control state in the
1538 place of the hard link count, owner, group, and size of the file. If
1539 the file is unmodified, in sync with the master file, the version
1540 control state shown is blank. Otherwise it consists of text in
1541 parentheses. Under RCS and SCCS, the name of the user locking the file
1542 is shown; under CVS, an abbreviated version of the @samp{cvs status}
1543 output is used. Here is an example using RCS:
1549 -rw-r--r-- (jim) Apr 2 23:39 file1
1550 -r--r--r-- Apr 5 20:21 file2
1555 The files @samp{file1} and @samp{file2} are under version control,
1556 @samp{file1} is locked by user jim, and @samp{file2} is unlocked.
1558 Here is an example using CVS:
1564 -rw-r--r-- (modified) Aug 2 1997 file1.c
1565 -rw-r--r-- Apr 4 20:09 file2.c
1566 -rw-r--r-- (merge) Sep 13 1996 file3.c
1570 Here @samp{file1.c} is modified with respect to the repository, and
1571 @samp{file2.c} is not. @samp{file3.c} is modified, but other changes
1572 have also been checked in to the repository---you need to merge them
1573 with the work file before you can check it in.
1575 @vindex vc-directory-exclusion-list
1576 When VC Dired displays subdirectories (in the ``full'' display mode),
1577 it omits some that should never contain any files under version control.
1578 By default, this includes Version Control subdirectories such as
1579 @samp{RCS} and @samp{CVS}; you can customize this by setting the
1580 variable @code{vc-directory-exclusion-list}.
1582 You can fine-tune VC Dired's format by typing @kbd{C-u C-x v d}---as in
1583 ordinary Dired, that allows you to specify additional switches for the
1586 @node VC Dired Commands
1587 @subsubsection VC Dired Commands
1589 All the usual Dired commands work normally in VC Dired mode, except
1590 for @kbd{v}, which is redefined as the version control prefix. You can
1591 invoke VC commands such as @code{vc-diff} and @code{vc-print-log} by
1592 typing @kbd{v =}, or @kbd{v l}, and so on. Most of these commands apply
1593 to the file name on the current line.
1595 The command @kbd{v v} (@code{vc-next-action}) operates on all the
1596 marked files, so that you can lock or check in several files at once.
1597 If it operates on more than one file, it handles each file according to
1598 its current state; thus, it might lock one file, but check in another
1599 file. This could be confusing; it is up to you to avoid confusing
1600 behavior by marking a set of files that are in a similar state.
1602 If any files call for check-in, @kbd{v v} reads a single log entry,
1603 then uses it for all the files being checked in. This is convenient for
1604 registering or checking in several files at once, as part of the same
1607 @findex vc-dired-toggle-terse-mode
1608 @findex vc-dired-mark-locked
1609 You can toggle between terse display (only locked files, or files not
1610 up-to-date) and full display at any time by typing @kbd{v t}
1611 @code{vc-dired-toggle-terse-mode}. There is also a special command
1612 @kbd{* l} (@code{vc-dired-mark-locked}), which marks all files currently
1613 locked (or, with CVS, all files not up-to-date). Thus, typing @kbd{* l
1614 t k} is another way to delete from the buffer all files except those
1618 @subsection Multiple Branches of a File
1619 @cindex branch (version control)
1620 @cindex trunk (version control)
1622 One use of version control is to maintain multiple ``current''
1623 versions of a file. For example, you might have different versions of a
1624 program in which you are gradually adding various unfinished new
1625 features. Each such independent line of development is called a
1626 @dfn{branch}. VC allows you to create branches, switch between
1627 different branches, and merge changes from one branch to another.
1628 Please note, however, that branches are only supported for RCS at the
1631 A file's main line of development is usually called the @dfn{trunk}.
1632 The versions on the trunk are normally numbered 1.1, 1.2, 1.3, etc. At
1633 any such version, you can start an independent branch. A branch
1634 starting at version 1.2 would have version number 1.2.1.1, and consecutive
1635 versions on this branch would have numbers 1.2.1.2, 1.2.1.3, 1.2.1.4,
1636 and so on. If there is a second branch also starting at version 1.2, it
1637 would consist of versions 1.2.2.1, 1.2.2.2, 1.2.2.3, etc.
1639 @cindex head version
1640 If you omit the final component of a version number, that is called a
1641 @dfn{branch number}. It refers to the highest existing version on that
1642 branch---the @dfn{head version} of that branch. The branches in the
1643 example above have branch numbers 1.2.1 and 1.2.2.
1646 * Switching Branches:: How to get to another existing branch.
1647 * Creating Branches:: How to start a new branch.
1648 * Merging:: Transferring changes between branches.
1649 * Multi-User Branching:: Multiple users working at multiple branches
1653 @node Switching Branches
1654 @subsubsection Switching between Branches
1656 To switch between branches, type @kbd{C-u C-x C-q} and specify the
1657 version number you want to select. This version is then visited
1658 @emph{unlocked} (write-protected), so you can examine it before locking
1659 it. Switching branches in this way is allowed only when the file is not
1662 You can omit the minor version number, thus giving only the branch
1663 number; this takes you to the head version on the chosen branch. If you
1664 only type @key{RET}, Emacs goes to the highest version on the trunk.
1666 After you have switched to any branch (including the main branch), you
1667 stay on it for subsequent VC commands, until you explicitly select some
1670 @node Creating Branches
1671 @subsubsection Creating New Branches
1673 To create a new branch from a head version (one that is the latest in
1674 the branch that contains it), first select that version if necessary,
1675 lock it with @kbd{C-x C-q}, and make whatever changes you want. Then,
1676 when you check in the changes, use @kbd{C-u C-x C-q}. This lets you
1677 specify the version number for the new version. You should specify a
1678 suitable branch number for a branch starting at the current version.
1679 For example, if the current version is 2.5, the branch number should be
1680 2.5.1, 2.5.2, and so on, depending on the number of existing branches at
1683 To create a new branch at an older version (one that is no longer the
1684 head of a branch), first select that version (@pxref{Switching
1685 Branches}), then lock it with @kbd{C-x C-q}. You'll be asked to
1686 confirm, when you lock the old version, that you really mean to create a
1687 new branch---if you say no, you'll be offered a chance to lock the
1688 latest version instead.
1690 Then make your changes and type @kbd{C-x C-q} again to check in a new
1691 version. This automatically creates a new branch starting from the
1692 selected version. You need not specially request a new branch, because
1693 that's the only way to add a new version at a point that is not the head
1696 After the branch is created, you ``stay'' on it. That means that
1697 subsequent check-ins create new versions on that branch. To leave the
1698 branch, you must explicitly select a different version with @kbd{C-u C-x
1699 C-q}. To transfer changes from one branch to another, use the merge
1700 command, described in the next section.
1703 @subsubsection Merging Branches
1705 @cindex merging changes
1706 When you have finished the changes on a certain branch, you will
1707 often want to incorporate them into the file's main line of development
1708 (the trunk). This is not a trivial operation, because development might
1709 also have proceeded on the trunk, so that you must @dfn{merge} the
1710 changes into a file that has already been changed otherwise. VC allows
1711 you to do this (and other things) with the @code{vc-merge} command.
1714 @item C-x v m (vc-merge)
1715 Merge changes into the work file.
1720 @kbd{C-x v m} (@code{vc-merge}) takes a set of changes and merges it
1721 into the current version of the work file. It first asks you for a
1722 branch number or a pair of version numbers in the minibuffer. Then it
1723 finds the changes from that branch, or between the two versions you
1724 specified, and merges them into the current version of the current file.
1726 As an example, suppose that you have finished a certain feature on
1727 branch 1.3.1. In the meantime, development on the trunk has proceeded
1728 to version 1.5. To merge the changes from the branch to the trunk,
1729 first go to the head version of the trunk, by typing @kbd{C-u C-x C-q
1730 RET}. Version 1.5 is now current. If locking is used for the file,
1731 type @kbd{C-x C-q} to lock version 1.5 so that you can change it. Next,
1732 type @kbd{C-x v m 1.3.1 RET}. This takes the entire set of changes on
1733 branch 1.3.1 (relative to version 1.3, where the branch started, up to
1734 the last version on the branch) and merges it into the current version
1735 of the work file. You can now check in the changed file, thus creating
1736 version 1.6 containing the changes from the branch.
1738 It is possible to do further editing after merging the branch, before
1739 the next check-in. But it is usually wiser to check in the merged
1740 version, then lock it and make the further changes. This will keep
1741 a better record of the history of changes.
1744 @cindex resolving conflicts
1745 When you merge changes into a file that has itself been modified, the
1746 changes might overlap. We call this situation a @dfn{conflict}, and
1747 reconciling the conflicting changes is called @dfn{resolving a
1750 Whenever conflicts occur during merging, VC detects them, tells you
1751 about them in the echo area, and asks whether you want help in merging.
1752 If you say yes, it starts an Ediff session (@pxref{Top,
1753 Ediff, Ediff, ediff, The Ediff Manual}).
1755 If you say no, the conflicting changes are both inserted into the
1756 file, surrounded by @dfn{conflict markers}. The example below shows how
1757 a conflict region looks; the file is called @samp{name} and the current
1758 master file version with user B's changes in it is 1.11.
1760 @c @w here is so CVS won't think this is a conflict.
1764 @var{User A's version}
1766 @var{User B's version}
1771 @cindex vc-resolve-conflicts
1772 Then you can resolve the conflicts by editing the file manually. Or
1773 you can type @code{M-x vc-resolve-conflicts} after visiting the file.
1774 This starts an Ediff session, as described above.
1776 @node Multi-User Branching
1777 @subsubsection Multi-User Branching
1779 It is often useful for multiple developers to work simultaneously on
1780 different branches of a file. CVS allows this by default; for RCS, it
1781 is possible if you create multiple source directories. Each source
1782 directory should have a link named @file{RCS} which points to a common
1783 directory of RCS master files. Then each source directory can have its
1784 own choice of selected versions, but all share the same common RCS
1787 This technique works reliably and automatically, provided that the
1788 source files contain RCS version headers (@pxref{Version Headers}). The
1789 headers enable Emacs to be sure, at all times, which version number is
1790 present in the work file.
1792 If the files do not have version headers, you must instead tell Emacs
1793 explicitly in each session which branch you are working on. To do this,
1794 first find the file, then type @kbd{C-u C-x C-q} and specify the correct
1795 branch number. This ensures that Emacs knows which branch it is using
1796 during this particular editing session.
1799 @subsection Snapshots
1800 @cindex snapshots and version control
1802 A @dfn{snapshot} is a named set of file versions (one for each
1803 registered file) that you can treat as a unit. One important kind of
1804 snapshot is a @dfn{release}, a (theoretically) stable version of the
1805 system that is ready for distribution to users.
1808 * Making Snapshots:: The snapshot facilities.
1809 * Snapshot Caveats:: Things to be careful of when using snapshots.
1812 @node Making Snapshots
1813 @subsubsection Making and Using Snapshots
1815 There are two basic commands for snapshots; one makes a
1816 snapshot with a given name, the other retrieves a named snapshot.
1820 @findex vc-create-snapshot
1821 @item C-x v s @var{name} @key{RET}
1822 Define the last saved versions of every registered file in or under the
1823 current directory as a snapshot named @var{name}
1824 (@code{vc-create-snapshot}).
1827 @findex vc-retrieve-snapshot
1828 @item C-x v r @var{name} @key{RET}
1829 For all registered files at or below the current directory level, select
1830 whatever versions correspond to the snapshot @var{name}
1831 (@code{vc-retrieve-snapshot}).
1833 This command reports an error if any files are locked at or below the
1834 current directory, without changing anything; this is to avoid
1835 overwriting work in progress.
1838 A snapshot uses a very small amount of resources---just enough to record
1839 the list of file names and which version belongs to the snapshot. Thus,
1840 you need not hesitate to create snapshots whenever they are useful.
1842 You can give a snapshot name as an argument to @kbd{C-x v =} or
1843 @kbd{C-x v ~} (@pxref{Old Versions}). Thus, you can use it to compare a
1844 snapshot against the current files, or two snapshots against each other,
1845 or a snapshot against a named version.
1847 @node Snapshot Caveats
1848 @subsubsection Snapshot Caveats
1850 @cindex named configurations (RCS)
1851 VC's snapshot facilities are modeled on RCS's named-configuration
1852 support. They use RCS's native facilities for this, so under VC
1853 snapshots made using RCS are visible even when you bypass VC.
1855 @c worded verbosely to avoid overfull hbox.
1856 For SCCS, VC implements snapshots itself. The files it uses contain
1857 name/file/version-number triples. These snapshots are visible only
1860 A snapshot is a set of checked-in versions. So make sure that all the
1861 files are checked in and not locked when you make a snapshot.
1863 File renaming and deletion can create some difficulties with snapshots.
1864 This is not a VC-specific problem, but a general design issue in version
1865 control systems that no one has solved very well yet.
1867 If you rename a registered file, you need to rename its master along
1868 with it (the command @code{vc-rename-file} does this automatically). If
1869 you are using SCCS, you must also update the records of the snapshot, to
1870 mention the file by its new name (@code{vc-rename-file} does this,
1871 too). An old snapshot that refers to a master file that no longer
1872 exists under the recorded name is invalid; VC can no longer retrieve
1873 it. It would be beyond the scope of this manual to explain enough about
1874 RCS and SCCS to explain how to update the snapshots by hand.
1876 Using @code{vc-rename-file} makes the snapshot remain valid for
1877 retrieval, but it does not solve all problems. For example, some of the
1878 files in the program probably refer to others by name. At the very
1879 least, the makefile probably mentions the file that you renamed. If you
1880 retrieve an old snapshot, the renamed file is retrieved under its new
1881 name, which is not the name that the makefile expects. So the program
1882 won't really work as retrieved.
1884 @node Miscellaneous VC
1885 @subsection Miscellaneous Commands and Features of VC
1887 This section explains the less-frequently-used features of VC.
1890 * Change Logs and VC:: Generating a change log file from log entries.
1891 * Renaming and VC:: A command to rename both the source and master
1893 * Version Headers:: Inserting version control headers into working files.
1896 @node Change Logs and VC
1897 @subsubsection Change Logs and VC
1899 If you use RCS or CVS for a program and also maintain a change log
1900 file for it (@pxref{Change Log}), you can generate change log entries
1901 automatically from the version control log entries:
1906 @findex vc-update-change-log
1907 Visit the current directory's change log file and, for registered files
1908 in that directory, create new entries for versions checked in since the
1909 most recent entry in the change log file.
1910 (@code{vc-update-change-log}).
1912 This command works with RCS or CVS only, not with SCCS.
1915 As above, but only find entries for the current buffer's file.
1918 As above, but find entries for all the currently visited files that are
1919 maintained with version control. This works only with RCS, and it puts
1920 all entries in the log for the default directory, which may not be
1924 For example, suppose the first line of @file{ChangeLog} is dated
1925 1999-04-10, and that the only check-in since then was by Nathaniel
1926 Bowditch to @file{rcs2log} on 1999-05-22 with log text @samp{Ignore log
1927 messages that start with `#'.}. Then @kbd{C-x v a} visits
1928 @file{ChangeLog} and inserts text like this:
1935 1999-05-22 Nathaniel Bowditch <nat@@apn.org>
1937 * rcs2log: Ignore log messages that start with `#'.
1945 You can then edit the new change log entry further as you wish.
1947 Unfortunately, timestamps in ChangeLog files are only dates, so some
1948 of the new change log entry may duplicate what's already in ChangeLog.
1949 You will have to remove these duplicates by hand.
1951 Normally, the log entry for file @file{foo} is displayed as @samp{*
1952 foo: @var{text of log entry}}. The @samp{:} after @file{foo} is omitted
1953 if the text of the log entry starts with @w{@samp{(@var{functionname}):
1954 }}. For example, if the log entry for @file{vc.el} is
1955 @samp{(vc-do-command): Check call-process status.}, then the text in
1956 @file{ChangeLog} looks like this:
1963 1999-05-06 Nathaniel Bowditch <nat@@apn.org>
1965 * vc.el (vc-do-command): Check call-process status.
1972 When @kbd{C-x v a} adds several change log entries at once, it groups
1973 related log entries together if they all are checked in by the same
1974 author at nearly the same time. If the log entries for several such
1975 files all have the same text, it coalesces them into a single entry.
1976 For example, suppose the most recent check-ins have the following log
1980 @bullet{} For @file{vc.texinfo}: @samp{Fix expansion typos.}
1981 @bullet{} For @file{vc.el}: @samp{Don't call expand-file-name.}
1982 @bullet{} For @file{vc-hooks.el}: @samp{Don't call expand-file-name.}
1986 They appear like this in @file{ChangeLog}:
1993 1999-04-01 Nathaniel Bowditch <nat@@apn.org>
1995 * vc.texinfo: Fix expansion typos.
1997 * vc.el, vc-hooks.el: Don't call expand-file-name.
2004 Normally, @kbd{C-x v a} separates log entries by a blank line, but you
2005 can mark several related log entries to be clumped together (without an
2006 intervening blank line) by starting the text of each related log entry
2007 with a label of the form @w{@samp{@{@var{clumpname}@} }}. The label
2008 itself is not copied to @file{ChangeLog}. For example, suppose the log
2012 @bullet{} For @file{vc.texinfo}: @samp{@{expand@} Fix expansion typos.}
2013 @bullet{} For @file{vc.el}: @samp{@{expand@} Don't call expand-file-name.}
2014 @bullet{} For @file{vc-hooks.el}: @samp{@{expand@} Don't call expand-file-name.}
2018 Then the text in @file{ChangeLog} looks like this:
2025 1999-04-01 Nathaniel Bowditch <nat@@apn.org>
2027 * vc.texinfo: Fix expansion typos.
2028 * vc.el, vc-hooks.el: Don't call expand-file-name.
2035 A log entry whose text begins with @samp{#} is not copied to
2036 @file{ChangeLog}. For example, if you merely fix some misspellings in
2037 comments, you can log the change with an entry beginning with @samp{#}
2038 to avoid putting such trivia into @file{ChangeLog}.
2040 @node Renaming and VC
2041 @subsubsection Renaming VC Work Files and Master Files
2043 @findex vc-rename-file
2044 When you rename a registered file, you must also rename its master
2045 file correspondingly to get proper results. Use @code{vc-rename-file}
2046 to rename the source file as you specify, and rename its master file
2047 accordingly. It also updates any snapshots (@pxref{Snapshots}) that
2048 mention the file, so that they use the new name; despite this, the
2049 snapshot thus modified may not completely work (@pxref{Snapshot
2052 You cannot use @code{vc-rename-file} on a file that is locked by
2055 @node Version Headers
2056 @subsubsection Inserting Version Control Headers
2058 Sometimes it is convenient to put version identification strings
2059 directly into working files. Certain special strings called
2060 @dfn{version headers} are replaced in each successive version by the
2061 number of that version.
2063 If you are using RCS, and version headers are present in your working
2064 files, Emacs can use them to determine the current version and the
2065 locking state of the files. This is more reliable than referring to the
2066 master files, which is done when there are no version headers. Note
2067 that in a multi-branch environment, version headers are necessary to
2068 make VC behave correctly (@pxref{Multi-User Branching}).
2070 Searching for version headers is controlled by the variable
2071 @code{vc-consult-headers}. If it is non-@code{nil}, Emacs searches for
2072 headers to determine the version number you are editing. Setting it to
2073 @code{nil} disables this feature.
2076 @findex vc-insert-headers
2077 You can use the @kbd{C-x v h} command (@code{vc-insert-headers}) to
2078 insert a suitable header string.
2082 Insert headers in a file for use with your version-control system.
2085 @vindex vc-header-alist
2086 The default header string is @samp{@w{$}Id$} for RCS and
2087 @samp{@w{%}W%} for SCCS. You can specify other headers to insert by
2088 setting the variable @code{vc-header-alist}. Its value is a list of
2089 elements of the form @code{(@var{program} . @var{string})} where
2090 @var{program} is @code{RCS} or @code{SCCS} and @var{string} is the
2093 Instead of a single string, you can specify a list of strings; then
2094 each string in the list is inserted as a separate header on a line of
2097 It is often necessary to use ``superfluous'' backslashes when writing
2098 the strings that you put in this variable. This is to prevent the
2099 string in the constant from being interpreted as a header itself if the
2100 Emacs Lisp file containing it is maintained with version control.
2102 @vindex vc-comment-alist
2103 Each header is inserted surrounded by tabs, inside comment delimiters,
2104 on a new line at point. Normally the ordinary comment
2105 start and comment end strings of the current mode are used, but for
2106 certain modes, there are special comment delimiters for this purpose;
2107 the variable @code{vc-comment-alist} specifies them. Each element of
2108 this list has the form @code{(@var{mode} @var{starter} @var{ender})}.
2110 @vindex vc-static-header-alist
2111 The variable @code{vc-static-header-alist} specifies further strings
2112 to add based on the name of the buffer. Its value should be a list of
2113 elements of the form @code{(@var{regexp} . @var{format})}. Whenever
2114 @var{regexp} matches the buffer name, @var{format} is inserted as part
2115 of the header. A header line is inserted for each element that matches
2116 the buffer name, and for each string specified by
2117 @code{vc-header-alist}. The header line is made by processing the
2118 string from @code{vc-header-alist} with the format taken from the
2119 element. The default value for @code{vc-static-header-alist} is as follows:
2124 "\n#ifndef lint\nstatic char vcid[] = \"\%s\";\n\
2125 #endif /* lint */\n"))
2130 It specifies insertion of text of this form:
2136 static char vcid[] = "@var{string}";
2142 Note that the text above starts with a blank line.
2144 If you use more than one version header in a file, put them close
2145 together in the file. The mechanism in @code{revert-buffer} that
2146 preserves markers may not handle markers positioned between two version
2149 @node Customizing VC
2150 @subsection Customizing VC
2152 There are many ways of customizing VC. The options you can set fall
2153 into four categories, described in the following sections.
2156 * Backend Options:: Customizing the back-end to your needs.
2157 * VC Workfile Handling:: Various options concerning working files.
2158 * VC Status Retrieval:: How VC finds the version control status of a file,
2159 and how to customize this.
2160 * VC Command Execution:: Which commands VC should run, and how.
2163 @node Backend Options
2164 @subsubsection Options for VC Backends
2166 @vindex vc-handled-backends
2167 By default, VC detects automatically which files are managed by RCS,
2168 which by CVS, and which by SCCS, and it tries to do the right thing in
2169 all three cases. If you want VC to ignore one or more of these
2170 backends, set @code{vc-handled-backends} to the list of backends that
2171 @emph{should} be handled.
2173 @cindex backend options (VC)
2174 @cindex locking under version control
2175 You can tell RCS and CVS whether to use locking for a file or not
2176 (@pxref{VC Concepts}, for a description of locking). VC automatically
2177 recognizes what you have chosen, and behaves accordingly.
2179 @cindex non-strict locking (RCS)
2180 @cindex locking, non-strict (RCS)
2181 For RCS, the default is to use locking, but there is a mode called
2182 @dfn{non-strict locking} in which you can check-in changes without
2183 locking the file first. Use @samp{rcs -U} to switch to non-strict
2184 locking for a particular file, see the @samp{rcs} manpage for details.
2186 @cindex locking (CVS)
2187 Under CVS, the default is not to use locking; anyone can change a work
2188 file at any time. However, there are ways to restrict this, resulting
2189 in behavior that resembles locking.
2191 @cindex CVSREAD environment variable (CVS)
2192 For one thing, you can set the @env{CVSREAD} environment variable to
2193 an arbitrary value. If this variable is defined, CVS makes your work
2194 files read-only by default. In Emacs, you must type @kbd{C-x C-q} to
2195 make the file writeable, so that editing works in fact similar as if
2196 locking was used. Note however, that no actual locking is performed, so
2197 several users can make their files writeable at the same time. When
2198 setting @env{CVSREAD} for the first time, make sure to check out all
2199 your modules anew, so that the file protections are set correctly.
2201 @cindex cvs watch feature
2202 @cindex watching files (CVS)
2203 Another way to achieve something similar to locking is to use the
2204 @dfn{watch} feature of CVS. If a file is being watched, CVS makes it
2205 read-only by default, and you must also use @kbd{C-x C-q} in Emacs to
2206 make it writable. VC calls @code{cvs edit} to make the file writeable,
2207 and CVS takes care to notify other developers of the fact that you
2208 intend to change the file. See the CVS documentation for details on
2209 using the watch feature.
2211 @node VC Workfile Handling
2212 @subsubsection VC Workfile Handling
2214 @vindex vc-make-backup-files
2215 Emacs normally does not save backup files for source files that are
2216 maintained with version control. If you want to make backup files even
2217 for files that use version control, set the variable
2218 @code{vc-make-backup-files} to a non-@code{nil} value.
2220 @vindex vc-keep-workfiles
2221 Normally the work file exists all the time, whether it is locked or
2222 not. If you set @code{vc-keep-workfiles} to @code{nil}, then checking
2223 in a new version with @kbd{C-x C-q} deletes the work file; but any
2224 attempt to visit the file with Emacs creates it again. (With CVS, work
2225 files are always kept.)
2227 @vindex vc-follow-symlinks
2228 Editing a version-controlled file through a symbolic link can be
2229 dangerous. It bypasses the version control system---you can edit the
2230 file without locking it, and fail to check your changes in. Also,
2231 your changes might overwrite those of another user. To protect against
2232 this, VC checks each symbolic link that you visit, to see if it points
2233 to a file under version control.
2235 The variable @code{vc-follow-symlinks} controls what to do when a
2236 symbolic link points to a version-controlled file. If it is @code{nil},
2237 VC only displays a warning message. If it is @code{t}, VC automatically
2238 follows the link, and visits the real file instead, telling you about
2239 this in the echo area. If the value is @code{ask} (the default), VC
2240 asks you each time whether to follow the link.
2242 @node VC Status Retrieval
2243 @subsubsection VC Status Retrieval
2244 @c There is no need to tell users about vc-master-templates.
2246 When deducing the locked/unlocked state of a file, VC first looks for
2247 an RCS version header string in the file (@pxref{Version Headers}). If
2248 there is no header string, or if you are using SCCS, VC normally looks
2249 at the file permissions of the work file; this is fast. But there might
2250 be situations when the file permissions cannot be trusted. In this case
2251 the master file has to be consulted, which is rather expensive. Also
2252 the master file can only tell you @emph{if} there's any lock on the
2253 file, but not whether your work file really contains that locked
2256 @vindex vc-consult-headers
2257 You can tell VC not to use version headers to determine lock status by
2258 setting @code{vc-consult-headers} to @code{nil}. VC then always uses
2259 the file permissions (if it can trust them), or else checks the master
2262 @vindex vc-mistrust-permissions
2263 You can specify the criterion for whether to trust the file
2264 permissions by setting the variable @code{vc-mistrust-permissions}. Its
2265 value can be @code{t} (always mistrust the file permissions and check
2266 the master file), @code{nil} (always trust the file permissions), or a
2267 function of one argument which makes the decision. The argument is the
2268 directory name of the @file{RCS}, @file{CVS} or @file{SCCS}
2269 subdirectory. A non-@code{nil} value from the function says to mistrust
2270 the file permissions. If you find that the file permissions of work
2271 files are changed erroneously, set @code{vc-mistrust-permissions} to
2272 @code{t}. Then VC always checks the master file to determine the file's
2275 @node VC Command Execution
2276 @subsubsection VC Command Execution
2278 @vindex vc-suppress-confirm
2279 If @code{vc-suppress-confirm} is non-@code{nil}, then @kbd{C-x C-q}
2280 and @kbd{C-x v i} can save the current buffer without asking, and
2281 @kbd{C-x v u} also operates without asking for confirmation. (This
2282 variable does not affect @kbd{C-x v c}; that operation is so drastic
2283 that it should always ask for confirmation.)
2285 @vindex vc-command-messages
2286 VC mode does much of its work by running the shell commands for RCS,
2287 CVS and SCCS. If @code{vc-command-messages} is non-@code{nil}, VC
2288 displays messages to indicate which shell commands it runs, and
2289 additional messages when the commands finish.
2292 You can specify additional directories to search for version control
2293 programs by setting the variable @code{vc-path}. These directories are
2294 searched before the usual search path. But the proper files are usually
2295 found automatically.
2298 @section File Directories
2300 @cindex file directory
2301 @cindex directory listing
2302 The file system groups files into @dfn{directories}. A @dfn{directory
2303 listing} is a list of all the files in a directory. Emacs provides
2304 commands to create and delete directories, and to make directory
2305 listings in brief format (file names only) and verbose format (sizes,
2306 dates, and authors included). There is also a directory browser called
2307 Dired; see @ref{Dired}.
2310 @item C-x C-d @var{dir-or-pattern} @key{RET}
2311 Display a brief directory listing (@code{list-directory}).
2312 @item C-u C-x C-d @var{dir-or-pattern} @key{RET}
2313 Display a verbose directory listing.
2314 @item M-x make-directory @key{RET} @var{dirname} @key{RET}
2315 Create a new directory named @var{dirname}.
2316 @item M-x delete-directory @key{RET} @var{dirname} @key{RET}
2317 Delete the directory named @var{dirname}. It must be empty,
2318 or you get an error.
2321 @findex list-directory
2323 The command to display a directory listing is @kbd{C-x C-d}
2324 (@code{list-directory}). It reads using the minibuffer a file name
2325 which is either a directory to be listed or a wildcard-containing
2326 pattern for the files to be listed. For example,
2329 C-x C-d /u2/emacs/etc @key{RET}
2333 lists all the files in directory @file{/u2/emacs/etc}. Here is an
2334 example of specifying a file name pattern:
2337 C-x C-d /u2/emacs/src/*.c @key{RET}
2340 Normally, @kbd{C-x C-d} prints a brief directory listing containing
2341 just file names. A numeric argument (regardless of value) tells it to
2342 make a verbose listing including sizes, dates, and authors (like
2345 @vindex list-directory-brief-switches
2346 @vindex list-directory-verbose-switches
2347 The text of a directory listing is obtained by running @code{ls} in an
2348 inferior process. Two Emacs variables control the switches passed to
2349 @code{ls}: @code{list-directory-brief-switches} is a string giving the
2350 switches to use in brief listings (@code{"-CF"} by default), and
2351 @code{list-directory-verbose-switches} is a string giving the switches to
2352 use in a verbose listing (@code{"-l"} by default).
2354 @node Comparing Files
2355 @section Comparing Files
2356 @cindex comparing files
2359 @vindex diff-switches
2360 The command @kbd{M-x diff} compares two files, displaying the
2361 differences in an Emacs buffer named @samp{*Diff*}. It works by running
2362 the @code{diff} program, using options taken from the variable
2363 @code{diff-switches}, whose value should be a string.
2365 The buffer @samp{*Diff*} has Compilation mode as its major mode, so
2366 you can use @kbd{C-x `} to visit successive changed locations in the two
2367 source files. You can also move to a particular hunk of changes and
2368 type @key{RET} or @kbd{C-c C-c}, or click @kbd{Mouse-2} on it, to move
2369 to the corresponding source location. You can also use the other
2370 special commands of Compilation mode: @key{SPC} and @key{DEL} for
2371 scrolling, and @kbd{M-p} and @kbd{M-n} for cursor motion.
2375 The command @kbd{M-x diff-backup} compares a specified file with its most
2376 recent backup. If you specify the name of a backup file,
2377 @code{diff-backup} compares it with the source file that it is a backup
2380 @findex compare-windows
2381 The command @kbd{M-x compare-windows} compares the text in the current
2382 window with that in the next window. Comparison starts at point in each
2383 window, and each starting position is pushed on the mark ring in its
2384 respective buffer. Then point moves forward in each window, a character
2385 at a time, until a mismatch between the two windows is reached. Then
2386 the command is finished. For more information about windows in Emacs,
2389 @vindex compare-ignore-case
2390 With a numeric argument, @code{compare-windows} ignores changes in
2391 whitespace. If the variable @code{compare-ignore-case} is
2392 non-@code{nil}, it ignores differences in case as well.
2398 Differences between versions of files are often distributed as
2399 @dfn{patches}, which are the output from @command{diff} or a version
2400 control system that uses @command{diff}. @kbd{M-x diff-mode} turns on
2401 Diff mode, a major mode for viewing and editing patches, either as
2402 ``unified diffs'' or ``context diffs.''
2406 @cindex failed merges
2407 @cindex merges, failed
2409 You can use @kbd{M-x smerge-mode} to turn on Smerge mode, a minor
2410 mode for editing output from the @command{diff3} program. This is
2411 typically the result of a failed merge from a version control system
2412 ``update'' outside VC, due to conflicting changes to a file. Smerge
2413 mode provides commands to resolve conflicts by selecting specific
2416 See also @ref{Emerge}, and @ref{Top,,, ediff, The Ediff Manual}, for
2417 convenient facilities for merging two similar files.
2420 @section Miscellaneous File Operations
2422 Emacs has commands for performing many other operations on files.
2423 All operate on one file; they do not accept wildcard file names.
2429 @kbd{M-x view-file} allows you to scan or read a file by sequential
2430 screenfuls. It reads a file name argument using the minibuffer. After
2431 reading the file into an Emacs buffer, @code{view-file} displays the
2432 beginning. You can then type @key{SPC} to scroll forward one windowful,
2433 or @key{DEL} to scroll backward. Various other commands are provided
2434 for moving around in the file, but none for changing it; type @kbd{?}
2435 while viewing for a list of them. They are mostly the same as normal
2436 Emacs cursor motion commands. To exit from viewing, type @kbd{q}.
2437 The commands for viewing are defined by a special major mode called View
2440 A related command, @kbd{M-x view-buffer}, views a buffer already present
2441 in Emacs. @xref{Misc Buffer}.
2444 @kbd{M-x insert-file} inserts a copy of the contents of the specified
2445 file into the current buffer at point, leaving point unchanged before the
2446 contents and the mark after them.
2448 @findex write-region
2449 @kbd{M-x write-region} is the inverse of @kbd{M-x insert-file}; it
2450 copies the contents of the region into the specified file. @kbd{M-x
2451 append-to-file} adds the text of the region to the end of the specified
2452 file. @xref{Accumulating Text}.
2455 @cindex deletion (of files)
2456 @kbd{M-x delete-file} deletes the specified file, like the @code{rm}
2457 command in the shell. If you are deleting many files in one directory, it
2458 may be more convenient to use Dired (@pxref{Dired}).
2461 @kbd{M-x rename-file} reads two file names @var{old} and @var{new} using
2462 the minibuffer, then renames file @var{old} as @var{new}. If a file named
2463 @var{new} already exists, you must confirm with @kbd{yes} or renaming is not
2464 done; this is because renaming causes the old meaning of the name @var{new}
2465 to be lost. If @var{old} and @var{new} are on different file systems, the
2466 file @var{old} is copied and deleted.
2468 @findex add-name-to-file
2469 The similar command @kbd{M-x add-name-to-file} is used to add an
2470 additional name to an existing file without removing its old name.
2471 The new name must belong on the same file system that the file is on.
2474 @cindex copying files
2475 @kbd{M-x copy-file} reads the file @var{old} and writes a new file named
2476 @var{new} with the same contents. Confirmation is required if a file named
2477 @var{new} already exists, because copying has the consequence of overwriting
2478 the old contents of the file @var{new}.
2480 @findex make-symbolic-link
2481 @kbd{M-x make-symbolic-link} reads two file names @var{target} and
2482 @var{linkname}, then creates a symbolic link named @var{linkname} and
2483 pointing at @var{target}. The effect is that future attempts to open file
2484 @var{linkname} will refer to whatever file is named @var{target} at the
2485 time the opening is done, or will get an error if the name @var{target} is
2486 not in use at that time. This command does not expand the argument
2487 @var{target}, so that it allows you to specify a relative name
2488 as the target of the link.
2490 Confirmation is required when creating the link if @var{linkname} is
2491 in use. Note that not all systems support symbolic links.
2493 @node Compressed Files
2494 @section Accessing Compressed Files
2496 @cindex uncompression
2497 @cindex Auto Compression mode
2498 @cindex mode, Auto Compression
2501 @findex auto-compression-mode
2502 @vindex auto-compression-mode
2503 Emacs comes with a library that can automatically uncompress
2504 compressed files when you visit them, and automatically recompress them
2505 if you alter them and save them. To enable this feature, type the
2506 command @kbd{M-x auto-compression-mode}. You can enable it permanently
2507 by customizing the option @var{auto-compression-mode}.
2509 When automatic compression (which implies automatic uncompression as
2510 well) is enabled, Emacs recognizes compressed files by their file names.
2511 File names ending in @samp{.gz} indicate a file compressed with
2512 @code{gzip}. Other endings indicate other compression programs.
2514 Automatic uncompression and compression apply to all the operations in
2515 which Emacs uses the contents of a file. This includes visiting it,
2516 saving it, inserting its contents into a buffer, loading it, and byte
2520 @section File Archives
2525 A file whose name ends in @samp{.tar} is normally an @dfn{archive}
2526 made by the @code{tar} program. Emacs views these files in a special
2527 mode called Tar mode which provides a Dired-like list of the contents
2528 (@pxref{Dired}). You can move around through the list just as you
2529 would in Dired, and visit the subfiles contained in the archive.
2530 However, not all Dired commands are available in Tar mode.
2532 If you enable Auto Compression mode (@pxref{Compressed Files}), then
2533 Tar mode is used also for compressed archives---files with extensions
2534 @samp{.tgz}, @code{.tar.Z} and @code{.tar.gz}.
2536 The keys @kbd{e}, @kbd{f} and @kbd{RET} all extract a component file
2537 into its own buffer. You can edit it there and when you save the buffer
2538 the edited version will replace the version in the Tar buffer. @kbd{v}
2539 extracts a file into a buffer in View mode. @kbd{o} extracts the file
2540 and displays it in another window, so you could edit the file and
2541 operate on the archive simultaneously. @kbd{d} marks a file for
2542 deletion when you later use @kbd{x}, and @kbd{u} unmarks a file, as in
2543 Dired. @kbd{C} copies a file from the archive to disk and @kbd{R}
2544 renames a file. @kbd{g} reverts the buffer from the archive on disk.
2546 The keys @kbd{M}, @kbd{G}, and @kbd{O} change the file's permission
2547 bits, group, and owner, respectively.
2549 If your display supports colors and the mouse, moving the mouse
2550 pointer across a file name highlights that file name, indicating that
2551 you can click on it. Clicking @kbd{Mouse-2} on the highlighted file
2552 name extracts the file into a buffer and displays that buffer.
2554 Saving the Tar buffer writes a new version of the archive to disk with
2555 the changes you made to the components.
2557 You don't need the @code{tar} program to use Tar mode---Emacs reads
2558 the archives directly. However, accessing compressed archives
2559 requires the appropriate uncompression program.
2561 @cindex Archive mode
2562 @cindex mode, archive
2573 @cindex Java class archives
2574 @cindex unzip archives
2575 A separate but similar Archive mode is used for archives produced by
2576 the programs @code{arc}, @code{jar}, @code{lzh}, @code{zip}, and
2577 @code{zoo}, which have extensions corresponding to the program names.
2579 The keybindings of Archive mode are similar to those in Tar mode,
2580 with the addition of the @kbd{m} key which marks a file for subsequent
2581 operations, and @kbd{M-@key{DEL}} which unmarks all the marked files.
2582 Also, the @kbd{a} key toggles the display of detailed file
2583 information, for those archive types where it won't fit in a single
2584 line. Operations such as renaming a subfile, or changing its mode or
2585 owner, are supported only for some of the archive formats.
2587 Unlike Tar mode, Archive mode runs the archiving program to unpack
2588 and repack archives. Details of the program names and their options
2589 can be set in the @samp{Archive} Customize group. However, you don't
2590 need these programs to the archive table of contents, only to extract
2591 or manipulate the subfiles in the archive.
2594 @section Remote Files
2597 @cindex remote file access
2598 You can refer to files on other machines using a special file name syntax:
2602 /@var{host}:@var{filename}
2603 /@var{user}@@@var{host}:@var{filename}
2604 /@var{user}@@@var{host}#@var{port}:@var{filename}
2609 When you do this, Emacs uses the FTP program to read and write files on
2610 the specified host. It logs in through FTP using your user name or the
2611 name @var{user}. It may ask you for a password from time to time; this
2612 is used for logging in on @var{host}. The form using @var{port} allows
2613 you to access servers running on a non-default TCP port.
2615 @cindex backups for remote files
2616 @vindex ange-ftp-make-backup-files
2617 If you want to disable backups for remote files, set the variable
2618 @code{ange-ftp-make-backup-files} to @code{nil}.
2621 @vindex ange-ftp-default-user
2622 @cindex user name for remote file access
2623 Normally, if you do not specify a user name in a remote file name,
2624 that means to use your own user name. But if you set the variable
2625 @code{ange-ftp-default-user} to a string, that string is used instead.
2626 (The Emacs package that implements FTP file access is called
2629 @cindex anonymous FTP
2630 @vindex ange-ftp-generate-anonymous-password
2631 To visit files accessible by anonymous FTP, you use special user
2632 names @samp{anonymous} or @samp{ftp}. Passwords for these user names
2633 are handled specially. The variable
2634 @code{ange-ftp-generate-anonymous-password} controls what happens: if
2635 the value of this variable is a string, then that string is used as
2636 the password; if non-@code{nil} (the default), then the value of
2637 @code{user-mail-address} is used; if @code{nil}, the user is prompted
2638 for a password as normal.
2640 @cindex firewall, and accessing remote files
2641 @cindex gateway, and remote file access with @code{ange-ftp}
2642 @vindex ange-ftp-smart-gateway
2643 @vindex ange-ftp-gateway-host
2644 Sometimes you may be unable to access files on a remote machine
2645 because a @dfn{firewall} in between blocks the connection for security
2646 reasons. If you can log in on a @dfn{gateway} machine from which the
2647 target files @emph{are} accessible, and whose FTP server supports
2648 gatewaying features, you can still use remote file names; all you have
2649 to do is specify the name of the gateway machine by setting the
2650 variable @code{ange-ftp-gateway-host}, and set
2651 @code{ange-ftp-smart-gateway} to @code{t}. Otherwise you may be able
2652 to make remote file names work, but the procedure is complex. You can
2653 read the instructions by typing @kbd{M-x finder-commentary @key{RET}
2654 ange-ftp @key{RET}}.
2656 @vindex file-name-handler-alist
2657 @cindex disabling remote files
2658 You can entirely turn off the FTP file name feature by removing the
2659 entries @var{ange-ftp-completion-hook-function} and
2660 @var{ange-ftp-hook-function} from the variable
2661 @code{file-name-handler-alist}. You can turn off the feature in
2662 individual cases by quoting the file name with @samp{/:} (@pxref{Quoted
2665 @node Quoted File Names
2666 @section Quoted File Names
2668 @cindex quoting file names
2669 You can @dfn{quote} an absolute file name to prevent special
2670 characters and syntax in it from having their special effects.
2671 The way to do this is to add @samp{/:} at the beginning.
2673 For example, you can quote a local file name which appears remote, to
2674 prevent it from being treated as a remote file name. Thus, if you have
2675 a directory named @file{/foo:} and a file named @file{bar} in it, you
2676 can refer to that file in Emacs as @samp{/:/foo:/bar}.
2678 @samp{/:} can also prevent @samp{~} from being treated as a special
2679 character for a user's home directory. For example, @file{/:/tmp/~hack}
2680 refers to a file whose name is @file{~hack} in directory @file{/tmp}.
2682 Likewise, quoting with @samp{/:} is one way to enter in the minibuffer
2683 a file name that contains @samp{$}. However, the @samp{/:} must be at
2684 the beginning of the buffer in order to quote @samp{$}.
2686 @cindex wildcard characters in file names
2687 You can also quote wildcard characters with @samp{/:}, for visiting.
2688 For example, @file{/:/tmp/foo*bar} visits the file @file{/tmp/foo*bar}.
2689 However, in most cases you can simply type the wildcard characters for
2690 themselves. For example, if the only file name in @file{/tmp} that
2691 starts with @samp{foo} and ends with @samp{bar} is @file{foo*bar}, then
2692 specifying @file{/tmp/foo*bar} will visit just @file{/tmp/foo*bar}.
2693 Another way is to specify @file{/tmp/foo[*]bar}.
2695 @node File Name Cache
2696 @section File Name Cache
2698 @cindex file name caching
2699 @cindex cache of file names
2702 @findex file-cache-minibuffer-complete
2703 You can use the @dfn{file name cache} to make it easy to locate a
2704 file by name, without having to remember exactly where it is located.
2705 When typing a file name in the minibuffer, @kbd{C-@key{tab}}
2706 (@code{file-cache-minibuffer-complete}) completes it using the file
2707 name cache. If you repeat @kbd{C-@key{tab}}, that cycles through the
2708 possible completions of what you had originally typed. Note that the
2709 @kbd{C-@key{tab}} character cannot be typed on most text-only
2712 The file name cache does not fill up automatically. Instead, you
2713 load file names into the cache using these commands:
2715 @findex file-cache-add-directory
2717 @item M-x file-cache-add-directory @key{RET} @var{directory} @key{RET}
2718 Add each file name in @var{directory} to the file name cache.
2719 @item M-x file-cache-add-directory-using-find @key{RET} @var{directory} @key{RET}
2720 Add each file name in @var{directory} and all of its nested
2721 subdirectories to the file name cache.
2722 @item M-x file-cache-add-directory-using-locate @key{RET} @var{directory} @key{RET}
2723 Add each file name in @var{directory} and all of its nested
2724 subdirectories to the file name cache, using @command{locate} to find
2726 @item M-x file-cache-add-directory-list @key{RET} @var{variable} @key{RET}
2727 Add each file name in each directory listed in @var{variable}
2728 to the file name cache. @var{variable} should be a Lisp variable
2729 such as @code{load-path} or @code{exec-path}, whose value is a list
2731 @item M-x file-cache-clear-cache @key{RET}
2732 Clear the cache; that is, remove all file names from it.
2735 @node File Conveniences
2736 @section Convenience Features for Finding Files
2738 @findex recentf-mode
2739 @vindex recentf-mode
2740 @findex recentf-save-list
2741 @findex recentf-edit-list
2742 If you enable Recentf mode, with @kbd{M-x recentf-mode}, the
2743 @samp{Files} menu includes a submenu containing a list of recently
2744 opened files. @kbd{M-x recentf-save-list} saves the current
2745 recent-file-list to a file, and @kbd{M-x recentf-edit-list} edits it.
2747 @findex auto-image-file-mode
2748 @findex mode, auto-image-file
2749 @cindex images, visiting
2750 @cindex visiting image files
2751 @vindex image-file-name-regexps
2752 @vindex image-file-name-extensions
2753 When Auto-image-file minor mode is enabled, visiting an image file
2754 displays it as an image, not as text. Likewise, inserting an image
2755 file into a buffer inserts it as an image. This works only when Emacs
2756 can display the relevant image type. The variables
2757 @code{image-file-name-extensions} or @code{image-file-name-regexps}
2758 control which file names are recognized as containing images.
2760 The @kbd{M-x ffap} command generalizes @code{find-file} with more
2761 powerful heuristic defaults (@pxref{FFAP}), often based on the text at
2762 point. Partial Completion mode offers other features extending
2763 @code{find-file}, which can be used with @code{ffap}.
2764 @xref{Completion Options}.