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
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 value of
To display 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
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 (
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.
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 (
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 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.
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:
There are also commands to select another buffer or buffers:
The only difference between
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 (
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.
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