1 Using Multiple Buffers

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 (@pxref{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 (@pxref{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. @xref{Locals}.

1.1 Creating and Selecting Buffers

C-x b buffer <RET>

Select or create a buffer named buffer (switch-to-buffer).

C-x 4 b buffer <RET>

Similar, but select buffer in another window (switch-to-buffer-other-window).

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 (@pxref{Completion}). An empty argument to C-x b specifies the most recently selected buffer that is not displayed in any window.

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 default-major-mode (@pxref{Major Modes}).

Note that C-x C-f, and any other command for visiting a file, can also be used to switch buffers. @xref{Visiting}.

1.2 Listing Existing Buffers

C-x C-b

List the existing buffers (list-buffers).

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 (@pxref{Saving}). ‘%’ 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 directory ‘/u2/emacs/man/’.

1.3 Miscellaneous Buffer Operations

C-x C-q

Toggle read-only status of buffer (toggle-read-only).

M-x rename-buffer <RET> name <RET>

Change the name of the current buffer.

M-x rename-uniquely

Rename the current buffer by adding ‘<number>’ to the end.

M-x view-buffer <RET> buffer <RET>

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 ‘%%’ near the left margin.

Read-only buffers are made by subsystems such as Dired and Rmail that have special commands to operate on the text; also if you visit a file that is protected so 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. 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 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 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*’, then do M-x shell again, it makes a new shell buffer named ‘*Shell*’; meanwhile, the old shell buffer continues to exist under its altered name. This method is also good for mail buffers, compilation buffers, and any Emacs feature which creates a special buffer with a particular name.

M-x view-buffer is much like M-x view-file (@pxref{Misc File Ops}) 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. @xref{Accumulating Text}.

1.4 Killing Buffers

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. There are several commands for killing buffers:

C-x k bufname <RET>

Kill buffer bufname (kill-buffer).

M-x kill-some-buffers

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 is selected; one that has been selected recently but does not appear in any window now. If you ask to kill a 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.

If you want to do something special every time a buffer is killed, you can add hook functions to the hook kill-buffer-hook (@pxref{Hooks}).

1.5 Operating on Several Buffers

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.

M-x buffer-menu

Begin editing a buffer listing all Emacs buffers.

The command 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.

d

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.

C-d

Like d but move up afterwards instead of down.

s

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.

x

Perform previously requested deletions and saves.

u

Remove any request made for the current line, and move down.

<DEL>

Move to previous line and remove any request made for that 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:

~

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.

t

Visit the buffer as a tag table.

There are also commands to select another buffer or buffers:

q

Quit the buffer menu—immediately display the most recent formerly visible buffer in its place.

f

Immediately select this line’s buffer in place of the ‘*Buffer List*’ buffer.

o

Immediately select this line’s buffer in another window as if by C-x 4 b, leaving ‘*Buffer List*’ visible.

C-o

Immediately display this line’s buffer in another window, but don’t select the window.

1

Immediately select this line’s buffer in a full-screen window.

2

Immediately set up two windows, with this line’s buffer in one, and the previously selected buffer (aside from the buffer ‘*Buffer List*’) in the other.

m

Mark this line’s buffer to be displayed in another window if the q command is used. The request shows as a ‘>’ at the beginning of the line. The same buffer may not have both a delete request and a display request.

v

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.

All that 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 and list-buffers is that 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; 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 repeat the buffer-menu command.

About This Document

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