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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 (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.

  • Select Buffer: Creating a new buffer or reselecting an old one.
  • List Buffers: Getting a list of buffers that exist.
  • Misc Buffer: Renaming; changing read-onliness; copying text.
  • Kill Buffer: Killing buffers you no longer need.
  • Several Buffers: How to go through the list of all buffers and operate variously on several of them.
  • Indirect Buffers: An indirect buffer shares the text of another buffer.

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). C-x 5 b buffer RET Similar, but select buffer in a separate frame (switch-to-buffer-other-frame).

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 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 (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.

Listing Existing Buffers

C-x C-b List the existing buffers (list-buffers).

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

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/.

Miscellaneous Buffer Operations

C-x C-q Toggle read-only status of buffer (vc-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 %% 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 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 file as well as the buffer. See section Version Control.

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.

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. Here are some 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 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).

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, 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. t Visit the buffer as a tags table. See section Selecting a Tags 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. RET 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 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.) 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 switch to 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 List* 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 switches to the *Buffer List* buffer in the selected window; list-buffers displays it 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.

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 buffer-menu command.

Indirect Buffers

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.

M-x make-indirect-buffer base-buffer RET indirect-name RET Create an indirect buffer named indirect-name whose base buffer is base-buffer.

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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