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The text you are editing in Emacs resides in an object called a buffer. Each time you visit a file, a buffer is created to hold the file's text. Each time you invoke Dired, a buffer is created to hold the directory listing. If you send a message with C-x m, a buffer named `*mail*' is used to hold the text of the message. When you ask for a command's documentation, that appears in a buffer called `*Help*'.
At any time, one and only one buffer is current. It is also called the selected buffer. Often we say that a command operates on "the buffer" as if there were only one; but really this means that the command operates on the current buffer (most commands do).
When Emacs has multiple windows, each window has its own chosen buffer and displays it; at any time, only one of the windows is selected, and its chosen buffer is the current buffer. Each window's mode line normally displays the name of the window's chosen buffer (see section Multiple Windows).
Each buffer has a name, which can be of any length, and you can select any buffer by giving its name. Most buffers are made by visiting files, and their names are derived from the files' names. But you can also create an empty buffer with any name you want. A newly started Emacs has a buffer named `*scratch*' which can be used for evaluating Lisp expressions in Emacs. The distinction between upper and lower case matters in buffer names.
Each buffer records individually what file it is visiting, whether it is modified, and what major mode and minor modes are in effect in it (see section Major Modes). Any Emacs variable can be made local to a particular buffer, meaning its value in that buffer can be different from the value in other buffers. See section Local Variables.
A buffer's size cannot be larger than some maximum, which is defined by the largest buffer position representable by the Emacs integer data type. This is because Emacs tracks buffer positions using that data type. For 32-bit machines, the largest buffer size is 256 megabytes.
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Select or create a buffer named buffer (switch-to-buffer).
Similar, but select buffer in another window
(switch-to-buffer-other-window).
Similar, but select buffer in a separate frame
(switch-to-buffer-other-frame).
Select the previous buffer in the list of existing buffers.
Select the next buffer in the list of existing buffers.
Read a number n and move to line n in the most recently selected buffer other than the current buffer.
To select the buffer named bufname, type C-x b bufname
RET. This runs the command switch-to-buffer with argument
bufname. You can use completion to enter the buffer
name (see section Completion). An empty argument to C-x b
specifies the buffer that was current most recently among those not
now displayed in any window.
For conveniently switching between a few buffers, use the commands
C-x LEFT and C-x RIGHT. C-x RIGHT
(previous-buffer) selects the previous buffer (following the order
of most recent selection in the current frame), while C-x LEFT
(next-buffer) moves through buffers in the reverse direction.
To select a buffer in a window other than the current one, type
C-x 4 b bufname RET. This runs the command
switch-to-buffer-other-window which displays the buffer
bufname in another window. By default, if displaying the buffer
causes two vertically adjacent windows to be displayed, the heights of
those windows are evened out; to countermand that and preserve the
window configuration, set the variable even-window-heights to
nil.
Similarly, C-x 5 b buffer RET runs the command
switch-to-buffer-other-frame which selects a buffer in another
frame.
You can control how certain buffers are handled by these commands by
customizing the variables special-display-buffer-names,
special-display-regexps, same-window-buffer-names, and
same-window-regexps. See Forcing Display in the Same Window, and
Special Buffer Frames, for more about these variables. In
addition, if the value of display-buffer-reuse-frames is
non-nil, and the buffer you want to switch to is already
displayed in some frame, Emacs will just raise that frame.
Most buffers are created by visiting files, or by Emacs commands that
want to display some text, but you can also create a buffer explicitly
by typing C-x b bufname RET. This makes a new, empty
buffer that is not visiting any file, and selects it for editing. Such
buffers are used for making notes to yourself. If you try to save one,
you are asked for the file name to use. The new buffer's major mode is
determined by the value of default-major-mode (see section Major Modes).
Note that C-x C-f, and any other command for visiting a file, can also be used to switch to an existing file-visiting buffer. See section Visiting Files.
C-u M-g M-g, that is goto-line with a prefix argument
of just C-u, reads a number n using the minibuffer,
selects the most recently selected buffer other than the current
buffer in another window, and then moves point to the beginning of
line number n in that buffer. This is mainly useful in a buffer
that refers to line numbers in another buffer: if point is on or just
after a number, goto-line uses that number as the default for
n. Note that prefix arguments other than just C-u behave
differently. C-u 4 M-g M-g goes to line 4 in the current
buffer, without reading a number from the minibuffer. (Remember that
M-g M-g without prefix argument reads a number n and then
moves to line number n in the current buffer.)
Emacs uses buffer names that start with a space for internal purposes. It treats these buffers specially in minor ways--for example, by default they do not record undo information. It is best to avoid using such buffer names yourself.
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List the existing buffers (list-buffers).
To display a list of existing buffers, type C-x C-b. Each line in the list shows one buffer's name, major mode and visited file. The buffers are listed in the order that they were current; the buffers that were current most recently come first.
`*' in the first field of a line indicates the buffer is "modified." If several buffers are modified, it may be time to save some with C-x s (see section Commands for Saving Files). `%' indicates a read-only buffer. `.' marks the current buffer. Here is an example of a buffer list:
CRM Buffer Size Mode File
. * .emacs 3294 Emacs-Lisp ~/.emacs
% *Help* 101 Help
search.c 86055 C ~/cvs/emacs/src/search.c
% src 20959 Dired by name ~/cvs/emacs/src/
* *mail* 42 Mail
% HELLO 1607 Fundamental ~/cvs/emacs/etc/HELLO
% NEWS 481184 Outline ~/cvs/emacs/etc/NEWS
*scratch* 191 Lisp Interaction
* *Messages* 1554 Fundamental
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Note that the buffer `*Help*' was made by a help request; it is
not visiting any file. The buffer src was made by Dired on the
directory `~/cvs/emacs/src/'. You can list only buffers that are
visiting files by giving the command a prefix argument, as in
C-u C-x C-b.
list-buffers omits buffers whose names begin with a space,
unless they visit files: such buffers are used internally by Emacs.
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Toggle read-only status of buffer (toggle-read-only).
Change the name of the current buffer.
Rename the current buffer by adding `<number>' to the end.
Scroll through buffer buffer.
A buffer can be read-only, which means that commands to change its contents are not allowed. The mode line indicates read-only buffers with `%%' or `%*' near the left margin. Read-only buffers are usually made by subsystems such as Dired and Rmail that have special commands to operate on the text; also by visiting a file whose access control says you cannot write it.
If you wish to make changes in a read-only buffer, use the command
C-x C-q (toggle-read-only). It makes a read-only buffer
writable, and makes a writable buffer read-only. This
works by setting the variable buffer-read-only, which has a local
value in each buffer and makes the buffer read-only if its value is
non-nil. If you have files under version control, you may find
it convenient to bind C-x C-q to vc-toggle-read-only
instead. Then, typing C-x C-q not only changes the read-only
flag, but it also checks the file in or out. See section Version Control.
M-x rename-buffer changes the name of the current buffer. You specify the new name as a minibuffer argument; there is no default. If you specify a name that is in use for some other buffer, an error happens and no renaming is done.
M-x rename-uniquely renames the current buffer to a similar name with a numeric suffix added to make it both different and unique. This command does not need an argument. It is useful for creating multiple shell buffers: if you rename the `*shell*' buffer, then do M-x shell again, it makes a new shell buffer named `*shell*'; meanwhile, the old shell buffer continues to exist under its new name. This method is also good for mail buffers, compilation buffers, and most Emacs features that create special buffers with particular names. (With some of these features, such as M-x compile, M-x grep an M-x info, you need to switch to some other buffer before using the command, in order for it to make a different buffer.)
M-x view-buffer is much like M-x view-file (see section Miscellaneous File Operations) except that it examines an already existing Emacs buffer. View mode provides commands for scrolling through the buffer conveniently but not for changing it. When you exit View mode with q, that switches back to the buffer (and the position) which was previously displayed in the window. Alternatively, if you exit View mode with e, the buffer and the value of point that resulted from your perusal remain in effect.
The commands M-x append-to-buffer and M-x insert-buffer can be used to copy text from one buffer to another. See section Accumulating Text.
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If you continue an Emacs session for a while, you may accumulate a large number of buffers. You may then find it convenient to kill the buffers you no longer need. On most operating systems, killing a buffer releases its space back to the operating system so that other programs can use it. Here are some commands for killing buffers:
Kill buffer bufname (kill-buffer).
Offer to kill each buffer, one by one.
C-x k (kill-buffer) kills one buffer, whose name you
specify in the minibuffer. The default, used if you type just
RET in the minibuffer, is to kill the current buffer. If you
kill the current buffer, another buffer becomes current: one that was
current in the recent past but is not displayed in any window now. If
you ask to kill a file-visiting buffer that is modified (has unsaved
editing), then you must confirm with yes before the buffer is
killed.
The command M-x kill-some-buffers asks about each buffer, one by
one. An answer of y means to kill the buffer. Killing the current
buffer or a buffer containing unsaved changes selects a new buffer or asks
for confirmation just like kill-buffer.
The buffer menu feature (see section Operating on Several Buffers) is also convenient for killing various buffers.
If you want to do something special every time a buffer is killed, you
can add hook functions to the hook kill-buffer-hook (see section Hooks).
If you run one Emacs session for a period of days, as many people do, it can fill up with buffers that you used several days ago. The command M-x clean-buffer-list is a convenient way to purge them; it kills all the unmodified buffers that you have not used for a long time. An ordinary buffer is killed if it has not been displayed for three days; however, you can specify certain buffers that should never be killed automatically, and others that should be killed if they have been unused for a mere hour.
You can also have this buffer purging done for you, every day at
midnight, by enabling Midnight mode. Midnight mode operates each day at
midnight; at that time, it runs clean-buffer-list, or whichever
functions you have placed in the normal hook midnight-hook
(see section Hooks).
To enable Midnight mode, use the Customization buffer to set the
variable midnight-mode to t. See section Easy Customization Interface.
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The buffer-menu facility is like a "Dired for buffers"; it allows you to request operations on various Emacs buffers by editing an Emacs buffer containing a list of them. You can save buffers, kill them (here called deleting them, for consistency with Dired), or display them.
Begin editing a buffer listing all Emacs buffers.
Similar, but do it in another window.
The command buffer-menu writes a list of all Emacs
buffers(3) into the
buffer `*Buffer List*', and selects that buffer in Buffer Menu
mode.
The buffer is read-only, and can be changed only through the special commands described in this section. The usual Emacs cursor motion commands can be used in the `*Buffer List*' buffer. The following commands apply to the buffer described on the current line.
Request to delete (kill) the buffer, then move down. The request shows as a `D' on the line, before the buffer name. Requested deletions take place when you type the x command.
Like d but move up afterwards instead of down.
Request to save the buffer. The request shows as an `S' on the line. Requested saves take place when you type the x command. You may request both saving and deletion for the same buffer.
Perform previously requested deletions and saves.
Remove any request made for the current line, and move down.
Move to previous line and remove any request made for that line.
The d, C-d, s and u commands to add or remove flags also move down (or up) one line. They accept a numeric argument as a repeat count.
These commands operate immediately on the buffer listed on the current line:
Mark the buffer "unmodified." The command ~ does this immediately when you type it.
Toggle the buffer's read-only flag. The command % does this immediately when you type it.
Visit the buffer as a tags table. See section Selecting a Tags Table.
There are also commands to select another buffer or buffers:
Quit the buffer menu--immediately display the most recent formerly visible buffer in its place.
Immediately select this line's buffer in place of the `*Buffer List*' buffer.
Immediately select this line's buffer in another window as if by C-x 4 b, leaving `*Buffer List*' visible.
Immediately display this line's buffer in another window, but don't select the window.
Immediately select this line's buffer in a full-screen window.
Immediately set up two windows, with this line's buffer selected in one, and the previously current buffer (aside from the buffer `*Buffer List*') displayed in the other.
Bury the buffer listed on this line.
Mark this line's buffer to be displayed in another window if you exit with the v command. The request shows as a `>' at the beginning of the line. (A single buffer may not have both a delete request and a display request.)
Immediately select this line's buffer, and also display in other windows any buffers previously marked with the m command. If you have not marked any buffers, this command is equivalent to 1.
There is also a command that affects the entire buffer list:
Delete, or reinsert, lines for non-file buffers. This command toggles the inclusion of such buffers in the buffer list.
What buffer-menu actually does is create and switch to a
suitable buffer, and turn on Buffer Menu mode in it. Everything else
described above is implemented by the special commands provided in
Buffer Menu mode. One consequence of this is that you can switch from
the `*Buffer List*' buffer to another Emacs buffer, and edit
there. You can reselect the `*Buffer List*' buffer later, to
perform the operations already requested, or you can kill it, or pay
no further attention to it.
The list in the `*Buffer List*' buffer looks exactly like the
buffer list described in Listing Existing Buffers, because they really are
the same. The only difference between buffer-menu and
list-buffers is that buffer-menu switches to the
`*Buffer List*' buffer in the selected window;
list-buffers displays the same buffer in another window. If
you run list-buffers (that is, type C-x C-b) and select
the buffer list manually, you can use all of the commands described
here.
Normally, the buffer `*Buffer List*' is not updated
automatically when buffers are created and killed; its contents are
just text. If you have created, deleted or renamed buffers, the way
to update `*Buffer List*' to show what you have done is to type
g (revert-buffer). You can make this happen regularly
every auto-revert-interval seconds if you enable Auto Revert
mode in this buffer, as long as it is not marked modified. Global
Auto Revert mode applies to the `*Buffer List*' buffer only if
global-auto-revert-non-file-buffers is non-nil.
See section global-auto-revert-non-file-buffers, for details.
The command buffer-menu-other-window works the same as
buffer-menu, except that it displays the buffers list in
another window.
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An indirect buffer shares the text of some other buffer, which is called the base buffer of the indirect buffer. In some ways it is the analogue, for buffers, of a symbolic link between files.
Create an indirect buffer named indirect-name whose base buffer is base-buffer.
Create an indirect buffer that is a twin copy of the current buffer.
Create an indirect buffer that is a twin copy of the current buffer, and
select it in another window (clone-indirect-buffer-other-window).
The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. But in all other respects, the indirect buffer and its base buffer are completely separate. They have different names, different values of point, different narrowing, different markers, different major modes, and different local variables.
An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually works by saving the base buffer. Killing the base buffer effectively kills the indirect buffer, but killing an indirect buffer has no effect on its base buffer.
One way to use indirect buffers is to display multiple views of an outline. See section Viewing One Outline in Multiple Views.
A quick and handy way to make an indirect buffer is with the command
M-x clone-indirect-buffer. It creates and selects an indirect
buffer whose base buffer is the current buffer. With a numeric
argument, it prompts for the name of the indirect buffer; otherwise it
uses the name of the current buffer, with a `<n>' suffix
added. C-x 4 c (clone-indirect-buffer-other-window)
works like M-x clone-indirect-buffer, but it selects the new
buffer in another window.
The more general way to make an indirect buffer is with the command M-x make-indirect-buffer. It creates an indirect buffer from buffer base-buffer, under the name indirect-name. It prompts for both base-buffer and indirect-name using the minibuffer.
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This section describes several modes and features that make it more convenient to switch between buffers.
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When several buffers visit identically-named files, Emacs must give the buffers distinct names. The usual method for making buffer names unique adds `<2>', `<3>', etc. to the end of the buffer names (all but one of them).
Other methods work by adding parts of each file's directory to the
buffer name. To select one, customize the variable
uniquify-buffer-name-style (see section Easy Customization Interface).
To begin with, the forward naming method includes part of the
file's directory name at the beginning of the buffer name; using this
method, buffers visiting the files `/u/rms/tmp/Makefile' and
`/usr/projects/zaphod/Makefile' would be named
`tmp/Makefile' and `zaphod/Makefile', respectively (instead
of `Makefile' and `Makefile<2>').
In contrast, the post-forward naming method would call the
buffers `Makefile|tmp' and `Makefile|zaphod', and the
reverse naming method would call them `Makefile\tmp' and
`Makefile\zaphod'. The nontrivial difference between
post-forward and reverse occurs when just one directory
name is not enough to distinguish two files; then reverse puts
the directory names in reverse order, so that `/top/middle/file'
becomes `file\middle\top', while post-forward puts them in
forward order after the file name, as in `file|top/middle'.
Which rule to follow for putting the directory names in the buffer name is not very important if you are going to look at the buffer names before you type one. But as an experienced user, if you know the rule, you won't have to look. And then you may find that one rule or another is easier for you to remember and apply quickly.
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Iswitchb global minor mode provides convenient switching between buffers using substrings of their names. It replaces the normal definitions of C-x b, C-x 4 b, C-x 5 b, and C-x 4 C-o with alternative commands that are somewhat "smarter."
When one of these commands prompts you for a buffer name, you can type in just a substring of the name you want to choose. As you enter the substring, Iswitchb mode continuously displays a list of buffers that match the substring you have typed.
At any time, you can type RET to select the first buffer in the list. So the way to select a particular buffer is to make it the first in the list. There are two ways to do this. You can type more of the buffer name and thus narrow down the list, excluding unwanted buffers above the desired one. Alternatively, you can use C-s and C-r to rotate the list until the desired buffer is first.
TAB while entering the buffer name performs completion on the string you have entered, based on the displayed list of buffers.
To enable Iswitchb mode, type M-x iswitchb-mode, or customize
the variable iswitchb-mode to t (see section Easy Customization Interface).
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Make a list of buffers similarly to M-x list-buffers but customizable.
M-x bs-show pops up a buffer list similar to the one normally
displayed by C-x C-b but which you can customize. If you prefer
this to the usual buffer list, you can bind this command to C-x
C-b. To customize this buffer list, use the bs Custom group
(see section Easy Customization Interface).
MSB global minor mode ("MSB" stands for "mouse select buffer")
provides a different and customizable mouse buffer menu which you may
prefer. It replaces the bindings of mouse-buffer-menu,
normally on C-Down-Mouse-1, and the menu bar buffer menu. You
can customize the menu in the msb Custom group.
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This document was generated by Mark Kaminski on July, 3 2008 using texi2html 1.70.