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. (Some other editors call this operation close, and talk about “closing the buffer” or “closing the file” visited in the buffer.) 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 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, 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, just like
kill-buffer. This command ignores buffers whose names begin
with a space, which are used internally by Emacs.
The command M-x kill-matching-buffers prompts for a regular
expression and kills all buffers whose names match that expression.
See Regexps. Like
kill-some-buffers, it asks for
confirmation before each kill. This command normally ignores buffers
whose names begin with a space, which are used internally by Emacs.
To kill internal buffers as well, call
with a prefix argument.
The Buffer Menu feature is also convenient for killing various buffers. See Several 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 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, once a day,
by enabling Midnight mode. Midnight mode operates each day
at midnight; at that time, it runs
whichever functions you have placed in the normal hook
midnight-hook (see Hooks). To enable Midnight mode, use
the Customization buffer to set the variable
t. See Easy Customization.