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1 @c This is part of the Emacs manual.
2 @c Copyright (C) 1985, 86, 87, 93, 94, 95, 1997 Free Software Foundation, Inc.
3 @c See file emacs.texi for copying conditions.
4 @node Buffers, Windows, Files, Top
5 @chapter Using Multiple Buffers
6
7 @cindex buffers
8 The text you are editing in Emacs resides in an object called a
9 @dfn{buffer}. Each time you visit a file, a buffer is created to hold the
10 file's text. Each time you invoke Dired, a buffer is created to hold the
11 directory listing. If you send a message with @kbd{C-x m}, a buffer named
12 @samp{*mail*} is used to hold the text of the message. When you ask for a
13 command's documentation, that appears in a buffer called @samp{*Help*}.
14
15 @cindex selected buffer
16 @cindex current buffer
17 At any time, one and only one buffer is @dfn{selected}. It is also
18 called the @dfn{current buffer}. Often we say that a command operates on
19 ``the buffer'' as if there were only one; but really this means that the
20 command operates on the selected buffer (most commands do).
21
22 When Emacs has multiple windows, each window has a chosen buffer which
23 is displayed there, but at any time only one of the windows is selected and
24 its chosen buffer is the selected buffer. Each window's mode line displays
25 the name of the buffer that the window is displaying (@pxref{Windows}).
26
27 Each buffer has a name, which can be of any length, and you can select
28 any buffer by giving its name. Most buffers are made by visiting files,
29 and their names are derived from the files' names. But you can also create
30 an empty buffer with any name you want. A newly started Emacs has a buffer
31 named @samp{*scratch*} which can be used for evaluating Lisp expressions in
32 Emacs. The distinction between upper and lower case matters in buffer
33 names.
34
35 Each buffer records individually what file it is visiting, whether it is
36 modified, and what major mode and minor modes are in effect in it
37 (@pxref{Major Modes}). Any Emacs variable can be made @dfn{local to} a
38 particular buffer, meaning its value in that buffer can be different from
39 the value in other buffers. @xref{Locals}.
40
41 @menu
42 * Select Buffer:: Creating a new buffer or reselecting an old one.
43 * List Buffers:: Getting a list of buffers that exist.
44 * Misc Buffer:: Renaming; changing read-onlyness; copying text.
45 * Kill Buffer:: Killing buffers you no longer need.
46 * Several Buffers:: How to go through the list of all buffers
47 and operate variously on several of them.
48 * Indirect Buffers:: An indirect buffer shares the text of another buffer.
49 @end menu
50
51 @node Select Buffer
52 @section Creating and Selecting Buffers
53 @cindex change buffers
54 @cindex switch buffers
55
56 @table @kbd
57 @item C-x b @var{buffer} @key{RET}
58 Select or create a buffer named @var{buffer} (@code{switch-to-buffer}).
59 @item C-x 4 b @var{buffer} @key{RET}
60 Similar, but select @var{buffer} in another window
61 (@code{switch-to-buffer-other-window}).
62 @item C-x 5 b @var{buffer} @key{RET}
63 Similar, but select @var{buffer} in a separate frame
64 (@code{switch-to-buffer-other-frame}).
65 @end table
66
67 @kindex C-x 4 b
68 @findex switch-to-buffer-other-window
69 @kindex C-x 5 b
70 @findex switch-to-buffer-other-frame
71 @kindex C-x b
72 @findex switch-to-buffer
73 To select the buffer named @var{bufname}, type @kbd{C-x b @var{bufname}
74 @key{RET}}. This runs the command @code{switch-to-buffer} with argument
75 @var{bufname}. You can use completion on an abbreviation for the buffer
76 name you want (@pxref{Completion}). An empty argument to @kbd{C-x b}
77 specifies the most recently selected buffer that is not displayed in any
78 window.@refill
79
80 Most buffers are created by visiting files, or by Emacs commands that
81 want to display some text, but you can also create a buffer explicitly
82 by typing @kbd{C-x b @var{bufname} @key{RET}}. This makes a new, empty
83 buffer that is not visiting any file, and selects it for editing. Such
84 buffers are used for making notes to yourself. If you try to save one,
85 you are asked for the file name to use. The new buffer's major mode is
86 determined by the value of @code{default-major-mode} (@pxref{Major
87 Modes}).
88
89 Note that @kbd{C-x C-f}, and any other command for visiting a file,
90 can also be used to switch to an existing file-visiting buffer.
91 @xref{Visiting}.
92
93 Emacs uses buffer names that start with a space for internal purposes.
94 It treats these buffers specially in minor ways---for example, by
95 default they do not record undo information. It is best to avoid using
96 such buffer names yourself.
97
98 @node List Buffers
99 @section Listing Existing Buffers
100
101 @table @kbd
102 @item C-x C-b
103 List the existing buffers (@code{list-buffers}).
104 @end table
105
106 @cindex listing current buffers
107 @kindex C-x C-b
108 @findex list-buffers
109 To display a list of all the buffers that exist, type @kbd{C-x C-b}.
110 Each line in the list shows one buffer's name, major mode and visited
111 file. The buffers are listed in the order that they were current; the
112 buffers that were current most recently come first.
113
114 @samp{*} at the beginning of a line indicates the buffer is ``modified.''
115 If several buffers are modified, it may be time to save some with @kbd{C-x s}
116 (@pxref{Saving}). @samp{%} indicates a read-only buffer. @samp{.} marks the
117 selected buffer. Here is an example of a buffer list:@refill
118
119 @smallexample
120 MR Buffer Size Mode File
121 -- ------ ---- ---- ----
122 .* emacs.tex 383402 Texinfo /u2/emacs/man/emacs.tex
123 *Help* 1287 Fundamental
124 files.el 23076 Emacs-Lisp /u2/emacs/lisp/files.el
125 % RMAIL 64042 RMAIL /u/rms/RMAIL
126 *% man 747 Dired /u2/emacs/man/
127 net.emacs 343885 Fundamental /u/rms/net.emacs
128 fileio.c 27691 C /u2/emacs/src/fileio.c
129 NEWS 67340 Text /u2/emacs/etc/NEWS
130 *scratch* 0 Lisp Interaction
131 @end smallexample
132
133 @noindent
134 Note that the buffer @samp{*Help*} was made by a help request; it is not
135 visiting any file. The buffer @code{man} was made by Dired on the
136 directory @file{/u2/emacs/man/}.
137
138 @need 2000
139 @node Misc Buffer
140 @section Miscellaneous Buffer Operations
141
142 @table @kbd
143 @item C-x C-q
144 Toggle read-only status of buffer (@code{vc-toggle-read-only}).
145 @item M-x rename-buffer @key{RET} @var{name} @key{RET}
146 Change the name of the current buffer.
147 @item M-x rename-uniquely
148 Rename the current buffer by adding @samp{<@var{number}>} to the end.
149 @item M-x view-buffer @key{RET} @var{buffer} @key{RET}
150 Scroll through buffer @var{buffer}.
151 @end table
152
153 @kindex C-x C-q
154 @findex vc-toggle-read-only
155 @vindex buffer-read-only
156 @cindex read-only buffer
157 A buffer can be @dfn{read-only}, which means that commands to change
158 its contents are not allowed. The mode line indicates read-only buffers
159 with @samp{%%} or @samp{%*} near the left margin. Read-only buffers are
160 usually made by subsystems such as Dired and Rmail that have special
161 commands to operate on the text; also by visiting a file whose access
162 control says you cannot write it.
163
164 If you wish to make changes in a read-only buffer, use the command
165 @kbd{C-x C-q} (@code{vc-toggle-read-only}). It makes a read-only buffer
166 writable, and makes a writable buffer read-only. In most cases, this
167 works by setting the variable @code{buffer-read-only}, which has a local
168 value in each buffer and makes the buffer read-only if its value is
169 non-@code{nil}. If the file is maintained with version control,
170 @kbd{C-x C-q} works through the version control system to change the
171 read-only status of the file as well as the buffer. @xref{Version
172 Control}.
173
174 @findex rename-buffer
175 @kbd{M-x rename-buffer} changes the name of the current buffer. Specify
176 the new name as a minibuffer argument. There is no default. If you
177 specify a name that is in use for some other buffer, an error happens and
178 no renaming is done.
179
180 @kbd{M-x rename-uniquely} renames the current buffer to a similar name
181 with a numeric suffix added to make it both different and unique. This
182 command does not need an argument. It is useful for creating multiple
183 shell buffers: if you rename the @samp{*Shell*} buffer, then do @kbd{M-x
184 shell} again, it makes a new shell buffer named @samp{*Shell*};
185 meanwhile, the old shell buffer continues to exist under its new name.
186 This method is also good for mail buffers, compilation buffers, and most
187 Emacs features that create special buffers with particular names.
188
189 @findex view-buffer
190 @kbd{M-x view-buffer} is much like @kbd{M-x view-file} (@pxref{Misc
191 File Ops}) except that it examines an already existing Emacs buffer.
192 View mode provides commands for scrolling through the buffer
193 conveniently but not for changing it. When you exit View mode with
194 @kbd{q}, that switches back to the buffer (and the position) which was
195 previously displayed in the window. Alternatively, if you exit View
196 mode with @kbd{e}, the buffer and the value of point that resulted from
197 your perusal remain in effect.
198
199 The commands @kbd{M-x append-to-buffer} and @kbd{M-x insert-buffer}
200 can be used to copy text from one buffer to another. @xref{Accumulating
201 Text}.@refill
202
203 @node Kill Buffer
204 @section Killing Buffers
205
206 @cindex killing buffers
207 If you continue an Emacs session for a while, you may accumulate a
208 large number of buffers. You may then find it convenient to @dfn{kill}
209 the buffers you no longer need. On most operating systems, killing a
210 buffer releases its space back to the operating system so that other
211 programs can use it. Here are some commands for killing buffers:
212
213 @c WideCommands
214 @table @kbd
215 @item C-x k @var{bufname} @key{RET}
216 Kill buffer @var{bufname} (@code{kill-buffer}).
217 @item M-x kill-some-buffers
218 Offer to kill each buffer, one by one.
219 @end table
220
221 @findex kill-buffer
222 @findex kill-some-buffers
223 @kindex C-x k
224
225 @kbd{C-x k} (@code{kill-buffer}) kills one buffer, whose name you
226 specify in the minibuffer. The default, used if you type just @key{RET}
227 in the minibuffer, is to kill the current buffer. If you kill the
228 current buffer, another buffer is selected; one that has been selected
229 recently but does not appear in any window now. If you ask to kill a
230 file-visiting buffer that is modified (has unsaved editing), then you
231 must confirm with @kbd{yes} before the buffer is killed.
232
233 The command @kbd{M-x kill-some-buffers} asks about each buffer, one by
234 one. An answer of @kbd{y} means to kill the buffer. Killing the current
235 buffer or a buffer containing unsaved changes selects a new buffer or asks
236 for confirmation just like @code{kill-buffer}.
237
238 The buffer menu feature (@pxref{Several Buffers}) is also convenient
239 for killing various buffers.
240
241 @vindex kill-buffer-hook
242 If you want to do something special every time a buffer is killed, you
243 can add hook functions to the hook @code{kill-buffer-hook} (@pxref{Hooks}).
244
245 @findex clean-buffer-list
246 If you run one Emacs session for a period of days, as many people do,
247 it can fill up with buffers that you used several days ago. The command
248 @kbd{M-x clean-buffer-list} is a convenient way to purge them; it kills
249 all the unmodified buffers that you have not used for a long time. An
250 ordinary buffer is killed if it has not been displayed for three days;
251 however, you can specify certain buffers that should never be killed
252 automatically, and others that should be killed if they have been unused
253 for a mere hour.
254
255 @cindex Midnight mode
256 @vindex midnight-mode
257 @vindex midnight-hook
258 You can also have this buffer purging done for you, every day at
259 midnight, by enabling Midnight mode. Midnight mode operates each day at
260 midnight; at that time, it runs @code{clean-buffer-list}, or whichever
261 functions you have placed in the normal hook @code{midnight-hook}
262 (@pxref{Hooks}).
263
264 To enable Midnight mode, use the Customization buffer to set the
265 variable @code{midnight-mode} to @code{t}. @xref{Easy Customization}.
266
267 @node Several Buffers
268 @section Operating on Several Buffers
269 @cindex buffer menu
270
271 The @dfn{buffer-menu} facility is like a ``Dired for buffers''; it allows
272 you to request operations on various Emacs buffers by editing an Emacs
273 buffer containing a list of them. You can save buffers, kill them
274 (here called @dfn{deleting} them, for consistency with Dired), or display
275 them.
276
277 @table @kbd
278 @item M-x buffer-menu
279 Begin editing a buffer listing all Emacs buffers.
280 @end table
281
282 @findex buffer-menu
283 The command @code{buffer-menu} writes a list of all Emacs buffers into
284 the buffer @samp{*Buffer List*}, and selects that buffer in Buffer Menu
285 mode. The buffer is read-only, and can be changed only through the
286 special commands described in this section. The usual Emacs cursor
287 motion commands can be used in the @samp{*Buffer List*} buffer. The
288 following commands apply to the buffer described on the current line.
289
290 @table @kbd
291 @item d
292 Request to delete (kill) the buffer, then move down. The request
293 shows as a @samp{D} on the line, before the buffer name. Requested
294 deletions take place when you type the @kbd{x} command.
295 @item C-d
296 Like @kbd{d} but move up afterwards instead of down.
297 @item s
298 Request to save the buffer. The request shows as an @samp{S} on the
299 line. Requested saves take place when you type the @kbd{x} command.
300 You may request both saving and deletion for the same buffer.
301 @item x
302 Perform previously requested deletions and saves.
303 @item u
304 Remove any request made for the current line, and move down.
305 @item @key{DEL}
306 Move to previous line and remove any request made for that line.
307 @end table
308
309 The @kbd{d}, @kbd{C-d}, @kbd{s} and @kbd{u} commands to add or remove
310 flags also move down (or up) one line. They accept a numeric argument
311 as a repeat count.
312
313 These commands operate immediately on the buffer listed on the current
314 line:
315
316 @table @kbd
317 @item ~
318 Mark the buffer ``unmodified.'' The command @kbd{~} does this
319 immediately when you type it.
320 @item %
321 Toggle the buffer's read-only flag. The command @kbd{%} does
322 this immediately when you type it.
323 @item t
324 Visit the buffer as a tags table. @xref{Select Tags Table}.
325 @end table
326
327 There are also commands to select another buffer or buffers:
328
329 @table @kbd
330 @item q
331 Quit the buffer menu---immediately display the most recent formerly
332 visible buffer in its place.
333 @item @key{RET}
334 @itemx f
335 Immediately select this line's buffer in place of the @samp{*Buffer
336 List*} buffer.
337 @item o
338 Immediately select this line's buffer in another window as if by
339 @kbd{C-x 4 b}, leaving @samp{*Buffer List*} visible.
340 @item C-o
341 Immediately display this line's buffer in another window, but don't
342 select the window.
343 @item 1
344 Immediately select this line's buffer in a full-screen window.
345 @item 2
346 Immediately set up two windows, with this line's buffer in one, and the
347 previously selected buffer (aside from the buffer @samp{*Buffer List*})
348 in the other.
349 @item b
350 Bury the buffer listed on this line.
351 @item m
352 Mark this line's buffer to be displayed in another window if you exit
353 with the @kbd{v} command. The request shows as a @samp{>} at the
354 beginning of the line. (A single buffer may not have both a delete
355 request and a display request.)
356 @item v
357 Immediately select this line's buffer, and also display in other windows
358 any buffers previously marked with the @kbd{m} command. If you have not
359 marked any buffers, this command is equivalent to @kbd{1}.
360 @end table
361
362 All that @code{buffer-menu} does directly is create and switch to a
363 suitable buffer, and turn on Buffer Menu mode. Everything else
364 described above is implemented by the special commands provided in
365 Buffer Menu mode. One consequence of this is that you can switch from
366 the @samp{*Buffer List*} buffer to another Emacs buffer, and edit there.
367 You can reselect the @samp{*Buffer List*} buffer later, to perform the
368 operations already requested, or you can kill it, or pay no further
369 attention to it.
370
371 The only difference between @code{buffer-menu} and @code{list-buffers}
372 is that @code{buffer-menu} switches to the @samp{*Buffer List*} buffer
373 in the selected window; @code{list-buffers} displays it in another
374 window. If you run @code{list-buffers} (that is, type @kbd{C-x C-b})
375 and select the buffer list manually, you can use all of the commands
376 described here.
377
378 The buffer @samp{*Buffer List*} is not updated automatically when
379 buffers are created and killed; its contents are just text. If you have
380 created, deleted or renamed buffers, the way to update @samp{*Buffer
381 List*} to show what you have done is to type @kbd{g}
382 (@code{revert-buffer}) or repeat the @code{buffer-menu} command.
383
384 @node Indirect Buffers
385 @section Indirect Buffers
386 @cindex indirect buffer
387 @cindex base buffer
388
389 An @dfn{indirect buffer} shares the text of some other buffer, which
390 is called the @dfn{base buffer} of the indirect buffer. In some ways it
391 is the analogue, for buffers, of a symbolic link between files.
392
393 @table @kbd
394 @findex make-indirect-buffer
395 @item M-x make-indirect-buffer @var{base-buffer} @key{RET} @var{indirect-name} @key{RET}
396 Create an indirect buffer named @var{indirect-name} whose base buffer
397 is @var{base-buffer}.
398 @end table
399
400 The text of the indirect buffer is always identical to the text of its
401 base buffer; changes made by editing either one are visible immediately
402 in the other. But in all other respects, the indirect buffer and its
403 base buffer are completely separate. They have different names,
404 different values of point, different narrowing, different markers,
405 different major modes, and different local variables.
406
407 An indirect buffer cannot visit a file, but its base buffer can. If
408 you try to save the indirect buffer, that actually works by saving the
409 base buffer. Killing the base buffer effectively kills the indirect
410 buffer, but killing an indirect buffer has no effect on its base buffer.
411
412 One way to use indirect buffers is to display multiple views of an
413 outline. @xref{Outline Views}.