1 @c This is part of the Emacs manual.
2 @c Copyright (C) 1985, 86, 87, 93, 94, 95, 97, 2000, 2001, 2004
3 @c Free Software Foundation, Inc.
4 @c See file emacs.texi for copying conditions.
5 @node Buffers, Windows, Files, Top
6 @chapter Using Multiple Buffers
9 The text you are editing in Emacs resides in an object called a
10 @dfn{buffer}. Each time you visit a file, a buffer is created to hold the
11 file's text. Each time you invoke Dired, a buffer is created to hold the
12 directory listing. If you send a message with @kbd{C-x m}, a buffer named
13 @samp{*mail*} is used to hold the text of the message. When you ask for a
14 command's documentation, that appears in a buffer called @samp{*Help*}.
16 @cindex selected buffer
17 @cindex current buffer
18 At any time, one and only one buffer is @dfn{current}. It is also
19 called the @dfn{selected buffer}. Often we say that a command operates on
20 ``the buffer'' as if there were only one; but really this means that the
21 command operates on the current buffer (most commands do).
23 When Emacs has multiple windows, each window has its own chosen
24 buffer and displays it; at any time, only one of the windows is
25 selected, and its chosen buffer is the current buffer. Each window's
26 mode line normally displays the name of the window's chosen buffer
29 Each buffer has a name, which can be of any length, and you can select
30 any buffer by giving its name. Most buffers are made by visiting files,
31 and their names are derived from the files' names. But you can also create
32 an empty buffer with any name you want. A newly started Emacs has a buffer
33 named @samp{*scratch*} which can be used for evaluating Lisp expressions in
34 Emacs. The distinction between upper and lower case matters in buffer
37 Each buffer records individually what file it is visiting, whether it is
38 modified, and what major mode and minor modes are in effect in it
39 (@pxref{Major Modes}). Any Emacs variable can be made @dfn{local to} a
40 particular buffer, meaning its value in that buffer can be different from
41 the value in other buffers. @xref{Locals}.
43 @cindex buffer size, maximum
44 A buffer's size cannot be larger than some maximum, which is defined
45 by the largest buffer position representable by the @dfn{Emacs integer}
46 data type. This is because Emacs tracks buffer positions using that
47 data type. For 32-bit machines, the largest buffer size is 256
51 * Select Buffer:: Creating a new buffer or reselecting an old one.
52 * List Buffers:: Getting a list of buffers that exist.
53 * Misc Buffer:: Renaming; changing read-onlyness; copying text.
54 * Kill Buffer:: Killing buffers you no longer need.
55 * Several Buffers:: How to go through the list of all buffers
56 and operate variously on several of them.
57 * Indirect Buffers:: An indirect buffer shares the text of another buffer.
58 * Buffer Convenience:: Convenience and customization features for
63 @section Creating and Selecting Buffers
64 @cindex change buffers
65 @cindex switch buffers
68 @item C-x b @var{buffer} @key{RET}
69 Select or create a buffer named @var{buffer} (@code{switch-to-buffer}).
70 @item C-x 4 b @var{buffer} @key{RET}
71 Similar, but select @var{buffer} in another window
72 (@code{switch-to-buffer-other-window}).
73 @item C-x 5 b @var{buffer} @key{RET}
74 Similar, but select @var{buffer} in a separate frame
75 (@code{switch-to-buffer-other-frame}).
79 @findex switch-to-buffer
80 To select the buffer named @var{bufname}, type @kbd{C-x b @var{bufname}
81 @key{RET}}. This runs the command @code{switch-to-buffer} with argument
82 @var{bufname}. You can use completion on an abbreviation for the buffer
83 name you want (@pxref{Completion}). An empty argument to @kbd{C-x b}
84 specifies the buffer that was current most recently among those not
85 now displayed in any window.
88 @findex switch-to-buffer-other-window
89 @vindex even-window-heights
90 To select a buffer in a window other than the current one, type
91 @kbd{C-x 4 b @var{bufname} @key{RET}}. This runs the command
92 @code{switch-to-buffer-other-window} which displays the buffer
93 @var{bufname} in another window. By default, if displaying the buffer
94 causes two vertically adjacent windows to be displayed, the heights of
95 those windows are evened out; to countermand that and preserve the
96 window configuration, set the variable @code{even-window-heights} to
100 @findex switch-to-buffer-other-frame
101 Similarly, @kbd{C-x 5 b @var{buffer} @key{RET}} runs the command
102 @code{switch-to-buffer-other-frame} which selects a buffer in another
105 @vindex display-buffer-reuse-frames
106 You can control how certain buffers are handled by these commands by
107 customizing the variables @code{special-display-buffer-names},
108 @code{special-display-regexps}, @code{same-window-buffer-names}, and
109 @code{same-window-regexps}. See @ref{Force Same Window}, and
110 @ref{Special Buffer Frames}, for more about these variables. In
111 addition, if the value of @code{display-buffer-reuse-frames} is
112 non-@code{nil}, and the buffer you want to switch to is already
113 displayed in some frame, Emacs will raise that frame.
115 Most buffers are created by visiting files, or by Emacs commands that
116 want to display some text, but you can also create a buffer explicitly
117 by typing @kbd{C-x b @var{bufname} @key{RET}}. This makes a new, empty
118 buffer that is not visiting any file, and selects it for editing. Such
119 buffers are used for making notes to yourself. If you try to save one,
120 you are asked for the file name to use. The new buffer's major mode is
121 determined by the value of @code{default-major-mode} (@pxref{Major
124 Note that @kbd{C-x C-f}, and any other command for visiting a file,
125 can also be used to switch to an existing file-visiting buffer.
128 Emacs uses buffer names that start with a space for internal purposes.
129 It treats these buffers specially in minor ways---for example, by
130 default they do not record undo information. It is best to avoid using
131 such buffer names yourself.
134 @section Listing Existing Buffers
138 List the existing buffers (@code{list-buffers}).
141 @cindex listing current buffers
144 To display a list of all the buffers that exist, type @kbd{C-x C-b}.
145 Each line in the list shows one buffer's name, major mode and visited
146 file. The buffers are listed in the order that they were current; the
147 buffers that were current most recently come first.
149 @samp{*} in the first field of a line indicates the buffer is ``modified.''
150 If several buffers are modified, it may be time to save some with @kbd{C-x s}
151 (@pxref{Saving}). @samp{%} indicates a read-only buffer. @samp{.} marks the
152 current buffer. Here is an example of a buffer list:@refill
155 CRM Buffer Size Mode File
156 . * .emacs 3294 Emacs-Lisp ~/.emacs
158 search.c 86055 C ~/cvs/emacs/src/search.c
159 % src 20959 Dired by name ~/cvs/emacs/src/
161 % HELLO 1607 Fundamental ~/cvs/emacs/etc/HELLO
162 % NEWS 481184 Outline ~/cvs/emacs/etc/NEWS
163 *scratch* 191 Lisp Interaction
164 * *Messages* 1554 Fundamental
168 Note that the buffer @samp{*Help*} was made by a help request; it is
169 not visiting any file. The buffer @code{src} was made by Dired on the
170 directory @file{~/cvs/emacs/src/}. You can list only buffers that are
171 visiting files by giving the command a prefix; for instance, by typing
174 @code{list-buffers} omits buffers whose name begins with a blank,
175 unless they visit files: such buffers are used internally by Emacs.
179 @section Miscellaneous Buffer Operations
183 Toggle read-only status of buffer (@code{toggle-read-only}).
184 @item M-x rename-buffer @key{RET} @var{name} @key{RET}
185 Change the name of the current buffer.
186 @item M-x rename-uniquely
187 Rename the current buffer by adding @samp{<@var{number}>} to the end.
188 @item M-x view-buffer @key{RET} @var{buffer} @key{RET}
189 Scroll through buffer @var{buffer}.
193 @vindex buffer-read-only
194 @cindex read-only buffer
195 A buffer can be @dfn{read-only}, which means that commands to change
196 its contents are not allowed. The mode line indicates read-only
197 buffers with @samp{%%} or @samp{%*} near the left margin. Read-only
198 buffers are usually made by subsystems such as Dired and Rmail that
199 have special commands to operate on the text; also by visiting a file
200 whose access control says you cannot write it.
202 @findex toggle-read-only
203 If you wish to make changes in a read-only buffer, use the command
204 @kbd{C-x C-q} (@code{toggle-read-only}). It makes a read-only buffer
205 writable, and makes a writable buffer read-only. This
206 works by setting the variable @code{buffer-read-only}, which has a local
207 value in each buffer and makes the buffer read-only if its value is
208 non-@code{nil}. If you have files under version control, you may find
209 it convenient to bind @kbd{C-x C-q} to @code{vc-toggle-read-only}
210 instead. Then, typing @kbd{C-x C-q} not only changes the read-only
211 flag, but it also checks the file in or out. @xref{Version
214 @findex rename-buffer
215 @kbd{M-x rename-buffer} changes the name of the current buffer. Specify
216 the new name as a minibuffer argument. There is no default. If you
217 specify a name that is in use for some other buffer, an error happens and
220 @findex rename-uniquely
221 @kbd{M-x rename-uniquely} renames the current buffer to a similar
222 name with a numeric suffix added to make it both different and unique.
223 This command does not need an argument. It is useful for creating
224 multiple shell buffers: if you rename the @samp{*Shell*} buffer, then
225 do @kbd{M-x shell} again, it makes a new shell buffer named
226 @samp{*Shell*}; meanwhile, the old shell buffer continues to exist
227 under its new name. This method is also good for mail buffers,
228 compilation buffers, and most Emacs features that create special
229 buffers with particular names. (With some of these features, such as
230 @kbd{M-x compile}, @kbd{M-x grep} an @kbd{M-x info}, you need to
231 switch to some other buffer before using the command, in order for it
232 to make a different buffer.)
235 @kbd{M-x view-buffer} is much like @kbd{M-x view-file} (@pxref{Misc
236 File Ops}) except that it examines an already existing Emacs buffer.
237 View mode provides commands for scrolling through the buffer
238 conveniently but not for changing it. When you exit View mode with
239 @kbd{q}, that switches back to the buffer (and the position) which was
240 previously displayed in the window. Alternatively, if you exit View
241 mode with @kbd{e}, the buffer and the value of point that resulted from
242 your perusal remain in effect.
244 The commands @kbd{M-x append-to-buffer} and @kbd{M-x insert-buffer}
245 can be used to copy text from one buffer to another. @xref{Accumulating
249 @section Killing Buffers
251 @cindex killing buffers
252 If you continue an Emacs session for a while, you may accumulate a
253 large number of buffers. You may then find it convenient to @dfn{kill}
254 the buffers you no longer need. On most operating systems, killing a
255 buffer releases its space back to the operating system so that other
256 programs can use it. Here are some commands for killing buffers:
259 @item C-x k @var{bufname} @key{RET}
260 Kill buffer @var{bufname} (@code{kill-buffer}).
261 @item M-x kill-some-buffers
262 Offer to kill each buffer, one by one.
266 @findex kill-some-buffers
269 @kbd{C-x k} (@code{kill-buffer}) kills one buffer, whose name you
270 specify in the minibuffer. The default, used if you type just
271 @key{RET} in the minibuffer, is to kill the current buffer. If you
272 kill the current buffer, another buffer becomes current: one that was
273 current in the recent past but is not displayed in any window now. If
274 you ask to kill a file-visiting buffer that is modified (has unsaved
275 editing), then you must confirm with @kbd{yes} before the buffer is
278 The command @kbd{M-x kill-some-buffers} asks about each buffer, one by
279 one. An answer of @kbd{y} means to kill the buffer. Killing the current
280 buffer or a buffer containing unsaved changes selects a new buffer or asks
281 for confirmation just like @code{kill-buffer}.
283 The buffer menu feature (@pxref{Several Buffers}) is also convenient
284 for killing various buffers.
286 @vindex kill-buffer-hook
287 If you want to do something special every time a buffer is killed, you
288 can add hook functions to the hook @code{kill-buffer-hook} (@pxref{Hooks}).
290 @findex clean-buffer-list
291 If you run one Emacs session for a period of days, as many people do,
292 it can fill up with buffers that you used several days ago. The command
293 @kbd{M-x clean-buffer-list} is a convenient way to purge them; it kills
294 all the unmodified buffers that you have not used for a long time. An
295 ordinary buffer is killed if it has not been displayed for three days;
296 however, you can specify certain buffers that should never be killed
297 automatically, and others that should be killed if they have been unused
300 @cindex Midnight mode
301 @vindex midnight-mode
302 @vindex midnight-hook
303 You can also have this buffer purging done for you, every day at
304 midnight, by enabling Midnight mode. Midnight mode operates each day at
305 midnight; at that time, it runs @code{clean-buffer-list}, or whichever
306 functions you have placed in the normal hook @code{midnight-hook}
309 To enable Midnight mode, use the Customization buffer to set the
310 variable @code{midnight-mode} to @code{t}. @xref{Easy Customization}.
312 @node Several Buffers
313 @section Operating on Several Buffers
316 The @dfn{buffer-menu} facility is like a ``Dired for buffers''; it allows
317 you to request operations on various Emacs buffers by editing an Emacs
318 buffer containing a list of them. You can save buffers, kill them
319 (here called @dfn{deleting} them, for consistency with Dired), or display
323 @item M-x buffer-menu
324 Begin editing a buffer listing all Emacs buffers.
325 @item M-x buffer-menu-other-window.
326 Similar, but do it in another window.
330 @findex buffer-menu-other-window
331 The command @code{buffer-menu} writes a list of all Emacs
332 buffers@footnote{Buffers which don't visit files and whose names begin
333 with a space are omitted: these are used internally by Emacs.} into the
334 buffer @samp{*Buffer List*}, and selects that buffer in Buffer Menu
335 mode. The list in the @samp{*Buffer List*} buffer looks exactly as
336 described in @ref{List Buffers}. The buffer is read-only, and can be
337 changed only through the special commands described in this section.
338 The usual Emacs cursor motion commands can be used in the @samp{*Buffer
339 List*} buffer. The following commands apply to the buffer described on
344 Request to delete (kill) the buffer, then move down. The request
345 shows as a @samp{D} on the line, before the buffer name. Requested
346 deletions take place when you type the @kbd{x} command.
348 Like @kbd{d} but move up afterwards instead of down.
350 Request to save the buffer. The request shows as an @samp{S} on the
351 line. Requested saves take place when you type the @kbd{x} command.
352 You may request both saving and deletion for the same buffer.
354 Perform previously requested deletions and saves.
356 Remove any request made for the current line, and move down.
358 Move to previous line and remove any request made for that line.
361 The @kbd{d}, @kbd{C-d}, @kbd{s} and @kbd{u} commands to add or remove
362 flags also move down (or up) one line. They accept a numeric argument
365 These commands operate immediately on the buffer listed on the current
370 Mark the buffer ``unmodified.'' The command @kbd{~} does this
371 immediately when you type it.
373 Toggle the buffer's read-only flag. The command @kbd{%} does
374 this immediately when you type it.
376 Visit the buffer as a tags table. @xref{Select Tags Table}.
379 There are also commands to select another buffer or buffers:
383 Quit the buffer menu---immediately display the most recent formerly
384 visible buffer in its place.
387 Immediately select this line's buffer in place of the @samp{*Buffer
390 Immediately select this line's buffer in another window as if by
391 @kbd{C-x 4 b}, leaving @samp{*Buffer List*} visible.
393 Immediately display this line's buffer in another window, but don't
396 Immediately select this line's buffer in a full-screen window.
398 Immediately set up two windows, with this line's buffer selected in
399 one, and the previously current buffer (aside from the buffer
400 @samp{*Buffer List*}) displayed in the other.
402 Bury the buffer listed on this line.
404 Mark this line's buffer to be displayed in another window if you exit
405 with the @kbd{v} command. The request shows as a @samp{>} at the
406 beginning of the line. (A single buffer may not have both a delete
407 request and a display request.)
409 Immediately select this line's buffer, and also display in other windows
410 any buffers previously marked with the @kbd{m} command. If you have not
411 marked any buffers, this command is equivalent to @kbd{1}.
414 All that @code{buffer-menu} does directly is create and switch to a
415 suitable buffer, and turn on Buffer Menu mode. Everything else
416 described above is implemented by the special commands provided in
417 Buffer Menu mode. One consequence of this is that you can switch from
418 the @samp{*Buffer List*} buffer to another Emacs buffer, and edit there.
419 You can reselect the @samp{*Buffer List*} buffer later, to perform the
420 operations already requested, or you can kill it, or pay no further
423 The only difference between @code{buffer-menu} and @code{list-buffers}
424 is that @code{buffer-menu} switches to the @samp{*Buffer List*} buffer
425 in the selected window; @code{list-buffers} displays it in another
426 window. If you run @code{list-buffers} (that is, type @kbd{C-x C-b})
427 and select the buffer list manually, you can use all of the commands
430 Normally, the buffer @samp{*Buffer List*} is not updated automatically when
431 buffers are created and killed; its contents are just text. If you have
432 created, deleted or renamed buffers, the way to update @samp{*Buffer
433 List*} to show what you have done is to type @kbd{g}
434 (@code{revert-buffer}) or repeat the @code{buffer-menu} command.
436 The @samp{*Buffer List*} buffer does automatically update every
437 @code{auto-revert-interval} seconds if you enable Auto Revert mode in
438 it. (As long as it is not marked modified.) Global Auto Revert mode
439 does not update the @samp{*Buffer List*} buffer by default, but it
440 does if @code{global-auto-revert-non-file-buffers} is non-@code{nil}.
441 @inforef{Autorevert,, emacs-xtra}, for details.
443 The command @code{buffer-menu-other-window} works the same as
444 @code{buffer-menu}, except that it displays the buffers list in
447 @node Indirect Buffers
448 @section Indirect Buffers
449 @cindex indirect buffer
452 An @dfn{indirect buffer} shares the text of some other buffer, which
453 is called the @dfn{base buffer} of the indirect buffer. In some ways it
454 is the analogue, for buffers, of a symbolic link between files.
457 @findex make-indirect-buffer
458 @item M-x make-indirect-buffer @key{RET} @var{base-buffer} @key{RET} @var{indirect-name} @key{RET}
459 Create an indirect buffer named @var{indirect-name} whose base buffer
460 is @var{base-buffer}.
461 @findex clone-indirect-buffer
462 @item M-x clone-indirect-buffer @key{RET}
463 Create an indirect buffer that is a twin copy of the current buffer.
466 @findex clone-indirect-buffer-other-window
467 Create an indirect buffer that is a twin copy of the current buffer, and
468 select it in another window (@code{clone-indirect-buffer-other-window}).
471 The text of the indirect buffer is always identical to the text of its
472 base buffer; changes made by editing either one are visible immediately
473 in the other. But in all other respects, the indirect buffer and its
474 base buffer are completely separate. They have different names,
475 different values of point, different narrowing, different markers,
476 different major modes, and different local variables.
478 An indirect buffer cannot visit a file, but its base buffer can. If
479 you try to save the indirect buffer, that actually works by saving the
480 base buffer. Killing the base buffer effectively kills the indirect
481 buffer, but killing an indirect buffer has no effect on its base buffer.
483 One way to use indirect buffers is to display multiple views of an
484 outline. @xref{Outline Views}.
486 A quick and handy way to make an indirect buffer is with the command
487 @kbd{M-x clone-indirect-buffer}. It creates and selects an indirect
488 buffer whose base buffer is the current buffer. With a numeric
489 argument, it prompts for the name of the indirect buffer; otherwise it
490 defaults to the name of the current buffer, modifying it by adding a
491 @samp{<@var{n}>} suffix if required. @kbd{C-x 4 c}
492 (@code{clone-indirect-buffer-other-window}) works like @kbd{M-x
493 clone-indirect-buffer}, but it selects the new buffer in another
496 The more general way to make an indirect buffer is with the command
497 @kbd{M-x make-indirect-buffer}. It creates an indirect buffer from
498 buffer @var{base-buffer}, under the name @var{indirect-name}. It
499 prompts for both @var{base-buffer} and @var{indirect-name} using the
502 @node Buffer Convenience
503 @section Convenience Features and Customization of Buffer Handling
505 This section describes several modes and features that make it more
506 convenient to switch between buffers.
509 * Uniquify:: Buffer names can contain directory parts.
510 * Iswitchb:: Switching between buffers with substrings.
511 * Buffer Menus:: Configurable buffer menu.
515 @subsection Making Buffer Names Unique
517 @cindex unique buffer names
518 @cindex directories in buffer names
519 When several buffers visit identically-named files, Emacs must give
520 the buffers distinct names. The usual method for making buffer names
521 unique adds @samp{<2>}, @samp{<3>}, etc. to the end of the buffer
522 names (all but one of them).
524 @vindex uniquify-buffer-name-style
525 Other methods work by adding parts of each file's directory to the
526 buffer name. To select one, customize the variable
527 @code{uniquify-buffer-name-style} (@pxref{Easy Customization}).
529 For instance, the @code{forward} naming method puts part of the
530 directory name at the beginning of the buffer name; using this method,
531 buffers visiting @file{/u/mernst/tmp/Makefile} and
532 @file{/usr/projects/zaphod/Makefile} would be named
533 @samp{tmp/Makefile} and @samp{zaphod/Makefile}, respectively (instead
534 of @samp{Makefile} and @samp{Makefile<2>}).
536 By contrast, the @code{post-forward} naming method would call the
537 buffers @samp{Makefile|tmp} and @samp{Makefile|zaphod}, and the
538 @code{reverse} naming method would call them @samp{Makefile\tmp} and
539 @samp{Makefile\zaphod}. The nontrivial difference between
540 @code{post-forward} and @code{reverse} occurs when just one directory
541 name is not enough to distinguish two files; then @code{reverse} puts
542 the directory names in reverse order, so that @file{/top/middle/file}
543 becomes @samp{file\middle\top}, while @code{post-forward} puts them in
544 forward order after the file name, as in @samp{file|top/middle}.
546 Which rule to follow for putting the directory names in the buffer
547 name is not very important if you are going to @emph{look} at the
548 buffer names before you type one. But as an experienced user, if you
549 know the rule, you won't have to look. And then you may find that one
550 rule or another is easier for you to remember and utilize fast.
553 @subsection Switching Between Buffers using Substrings
555 @findex iswitchb-mode
556 @cindex Iswitchb mode
557 @cindex mode, Iswitchb
558 @kindex C-x b @r{(Iswitchb mode)}
559 @kindex C-x 4 b @r{(Iswitchb mode)}
560 @kindex C-x 5 b @r{(Iswitchb mode)}
561 @kindex C-x 4 C-o @r{(Iswitchb mode)}
563 Iswitchb global minor mode provides convenient switching between
564 buffers using substrings of their names. It replaces the normal
565 definitions of @kbd{C-x b}, @kbd{C-x 4 b}, @kbd{C-x 5 b}, and @kbd{C-x
566 4 C-o} with alternative commands that are somewhat ``smarter.''
568 When one of these commands prompts you for a buffer name, you can
569 type in just a substring of the name you want to choose. As you enter
570 the substring, Iswitchb mode continuously displays a list of buffers
571 that match the substring you have typed.
573 At any time, you can type @key{RET} to select the first buffer in
574 the list. So the way to select a particular buffer is to make it the
575 first in the list. There are two ways to do this. You can type more
576 of the buffer name and thus narrow down the list, excluding unwanted
577 buffers above the desired one. Alternatively, you can use @kbd{C-s}
578 and @kbd{C-r} to rotate the list until the desired buffer is first.
580 @key{TAB} while entering the buffer name performs completion on the
581 string you have entered, based on the displayed list of buffers.
583 To enable Iswitchb mode, type @kbd{M-x iswitchb-mode}, or customize
584 the variable @code{iswitchb-mode} to @code{t} (@pxref{Easy
588 @subsection Customizing Buffer Menus
591 @cindex buffer list, customizable
594 Make a list of buffers similarly to @kbd{M-x list-buffers} but
598 @kbd{M-x bs-show} pops up a buffer list similar to the one normally
599 displayed by @kbd{C-x C-b} but which you can customize. If you prefer
600 this to the usual buffer list, you can bind this command to @kbd{C-x
601 C-b}. To customize this buffer list, use the @code{bs} Custom group
602 (@pxref{Easy Customization}).
608 @findex mouse-buffer-menu
609 @kindex C-Down-Mouse-1
610 MSB global minor mode (``MSB'' stands for ``mouse select buffer'')
611 provides a different and customizable mouse buffer menu which you may
612 prefer. It replaces the bindings of @code{mouse-buffer-menu},
613 normally on @kbd{C-Down-Mouse-1}, and the menu bar buffer menu. You
614 can customize the menu in the @code{msb} Custom group.
617 arch-tag: 08c43460-f4f4-4b43-9cb5-1ea9ad991695