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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 selected. It is also called the current 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 selected buffer (most commands do).
When Emacs has multiple windows, each window has a chosen buffer which is displayed there, but at any time only one of the windows is selected and its chosen buffer is the selected buffer. Each window's mode line displays the name of the buffer that the window is displaying (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.
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 on an abbreviation for the buffer
name you want (see section Completion). An empty argument to C-x b
specifies the most recently selected buffer that is not displayed in any
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 which
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
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.
To print a list of all the buffers that exist, 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, most recently visited first.
`*' at the beginning 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 Saving Files). `%' indicates a read-only buffer. `.' marks the selected buffer. Here is an example of a buffer list:
MR Buffer Size Mode File -- ------ ---- ---- ---- .* emacs.tex 383402 Texinfo /u2/emacs/man/emacs.tex *Help* 1287 Fundamental files.el 23076 Emacs-Lisp /u2/emacs/lisp/files.el % RMAIL 64042 RMAIL /u/rms/RMAIL *% man 747 Dired /u2/emacs/man/ net.emacs 343885 Fundamental /u/rms/net.emacs fileio.c 27691 C /u2/emacs/src/fileio.c NEWS 67340 Text /u2/emacs/etc/NEWS *scratch* 0 Lisp Interaction
Note that the buffer `*Help*' was made by a help request; it is not
visiting any file. The buffer
man was made by Dired on the
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 (
vc-toggle-read-only). It makes a read-only buffer
writable, and makes a writable buffer read-only. In most cases, 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
nil. If the file is maintained with version control,
C-x C-q works through the version control system to change the
read-only status of the file as well as the buffer.
M-x rename-buffer changes the name of the current buffer. 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.
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, the value of point that resulted from your perusal remains 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.
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:
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 is selected; one that has been selected
recently but does not appear 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
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).
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.
buffer-menu writes a list of all Emacs buffers 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.
The d, s and u commands to add or remove flags also move down a line. They accept a numeric argument as a repeat count.
These commands operate immediately on the buffer listed on the current line:
There are also commands to select another buffer or buffers:
buffer-menu does directly is create and select a suitable
buffer, and turn on Buffer Menu mode. 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-menu buffer later, to perform the operations already
requested, or you can kill it, or pay no further attention to it.
The only difference between
buffer-menu selects the `*Buffer List*' buffer and
list-buffers does not. 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.
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) or repeat the
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