@c This is part of the Emacs manual. @c Copyright (C) 1985-1987, 1993-1995, 1997, 2000-2012 @c Free Software Foundation, Inc. @c See file emacs.texi for copying conditions. @node Buffers @chapter Using Multiple Buffers @cindex buffers The text you are editing in Emacs resides in an object called a @dfn{buffer}. Each time you visit a file, a buffer is used to hold the file's text. Each time you invoke Dired, a buffer is used to hold the directory listing. If you send a message with @kbd{C-x m}, a buffer is used to hold the text of the message. When you ask for a command's documentation, that appears in a buffer named @file{*Help*}. Each buffer has a unique name, which can be of any length. When a buffer is displayed in a window, its name is shown in the mode line (@pxref{Mode Line}). The distinction between upper and lower case matters in buffer names. Most buffers are made by visiting files, and their names are derived from the files' names; however, you can also create an empty buffer with any name you want. A newly started Emacs has several buffers, including one named @file{*scratch*}, which can be used for evaluating Lisp expressions and is not associated with any file (@pxref{Lisp Interaction}). @cindex selected buffer @cindex current buffer At any time, one and only one buffer is @dfn{selected}; we call it the @dfn{current buffer}. We sometimes say that a command operates on ``the buffer''; this really means that it operates on the current buffer. When there is only one Emacs window, the buffer displayed in that window is current. When there are multiple windows, the buffer displayed in the @dfn{selected window} is current. @xref{Windows}. Aside from its textual contents, each buffer records several pieces of information, such as what file it is visiting (if any), whether it is modified, and what major mode and minor modes are in effect (@pxref{Modes}). These are stored in @dfn{buffer-local variables}---variables that can have a different value in each buffer. @xref{Locals}. @cindex buffer size, maximum A buffer's size cannot be larger than some maximum, which is defined by the largest buffer position representable by @dfn{Emacs integers}. This is because Emacs tracks buffer positions using that data type. For typical 64-bit machines, this maximum buffer size is @math{2^61 - 2} bytes, or about 2 EiB. For typical 32-bit machines, the maximum is usually @math{2^29 - 2} bytes, or about 512 MiB. Buffer sizes are also limited by the amount of memory in the system. @menu * 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-onlyness; 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. * Buffer Convenience:: Convenience and customization features for buffer handling. @end menu @node Select Buffer @section Creating and Selecting Buffers @cindex change buffers @cindex switch buffers @table @kbd @item C-x b @var{buffer} @key{RET} Select or create a buffer named @var{buffer} (@code{switch-to-buffer}). @item C-x 4 b @var{buffer} @key{RET} Similar, but select @var{buffer} in another window (@code{switch-to-buffer-other-window}). @item C-x 5 b @var{buffer} @key{RET} Similar, but select @var{buffer} in a separate frame (@code{switch-to-buffer-other-frame}). @item C-x @key{LEFT} Select the previous buffer in the buffer list (@code{previous-buffer}). @item C-x @key{RIGHT} Select the next buffer in the buffer list (@code{next-buffer}). @item C-u M-g M-g @itemx C-u M-g g Read a number @var{n} and move to line @var{n} in the most recently selected buffer other than the current buffer. @end table @kindex C-x b @findex switch-to-buffer The @kbd{C-x b} (@code{switch-to-buffer}) command reads a buffer name using the minibuffer. Then it makes that buffer current, and displays it in the currently-selected window. An empty input specifies the buffer that was current most recently among those not now displayed in any window. While entering the buffer name, you can use the usual completion and history commands (@pxref{Minibuffer}). Note that @kbd{C-x b}, and related commands, use ``permissive completion with confirmation'' for minibuffer completion: if you type @key{RET} immediately after completing up to a nonexistent buffer name, Emacs prints @samp{[Confirm]} and you must type a second @key{RET} to submit that buffer name. @xref{Completion Exit}, for details. If you specify a buffer that does not exist, @kbd{C-x b} creates a new, empty buffer that is not visiting any file, and selects it for editing. The default value of the variable @code{major-mode} determines the new buffer's major mode; the default value is Fundamental mode. @xref{Major Modes}. One reason to create a new buffer is to use it for making temporary notes. If you try to save it, Emacs asks for the file name to use, and the buffer's major mode is re-established taking that file name into account (@pxref{Choosing Modes}). @kindex C-x @key{LEFT} @kindex C-x @key{RIGHT} @findex next-buffer @findex previous-buffer For conveniently switching between a few buffers, use the commands @kbd{C-x @key{LEFT}} and @kbd{C-x @key{RIGHT}}. @kbd{C-x @key{LEFT}} (@code{previous-buffer}) selects the previous buffer (following the order of most recent selection in the current frame), while @kbd{C-x @key{RIGHT}} (@code{next-buffer}) moves through buffers in the reverse direction. @kindex C-x 4 b @findex switch-to-buffer-other-window To select a buffer in a window other than the current one, type @kbd{C-x 4 b} (@code{switch-to-buffer-other-window}). This prompts for a buffer name using the minibuffer, displays that buffer in another window, and selects that window. @kindex C-x 5 b @findex switch-to-buffer-other-frame Similarly, @kbd{C-x 5 b} (@code{switch-to-buffer-other-frame}) prompts for a buffer name, displays that buffer in another frame, and selects that frame. If the buffer is already being shown in a window on another frame, Emacs selects that window and frame instead of creating a new frame. @xref{Displaying Buffers}, for how the @kbd{C-x 4 b} and @kbd{C-x 5 b} commands get the window and/or frame to display in. In addition, @kbd{C-x C-f}, and any other command for visiting a file, can also be used to switch to an existing file-visiting buffer. @xref{Visiting}. @findex goto-line @kbd{C-u M-g M-g}, that is @code{goto-line} with a plain prefix argument, reads a number @var{n} using the minibuffer, selects the most recently selected buffer other than the current buffer in another window, and then moves point to the beginning of line number @var{n} in that buffer. This is mainly useful in a buffer that refers to line numbers in another buffer: if point is on or just after a number, @code{goto-line} uses that number as the default for @var{n}. Note that prefix arguments other than just @kbd{C-u} behave differently. @kbd{C-u 4 M-g M-g} goes to line 4 in the @emph{current} buffer, without reading a number from the minibuffer. (Remember that @kbd{M-g M-g} without prefix argument reads a number @var{n} and then moves to line number @var{n} in the current buffer. @xref{Moving Point}.) Emacs uses buffer names that start with a space for internal purposes. It treats these buffers specially in minor ways---for example, by default they do not record undo information. It is best to avoid using such buffer names yourself. @node List Buffers @section Listing Existing Buffers @table @kbd @item C-x C-b List the existing buffers (@code{list-buffers}). @end table @cindex listing current buffers @kindex C-x C-b @findex list-buffers To display a list of existing buffers, type @kbd{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 that they were current; the buffers that were current most recently come first. @samp{.} in the first field of a line indicates that the buffer is current. @samp{%} indicates a read-only buffer. @samp{*} indicates that the buffer is ``modified''. If several buffers are modified, it may be time to save some with @kbd{C-x s} (@pxref{Save Commands}). Here is an example of a buffer list: @smallexample CRM Buffer Size Mode File . * .emacs 3294 Emacs-Lisp ~/.emacs % *Help* 101 Help search.c 86055 C ~/cvs/emacs/src/search.c % src 20959 Dired by name ~/cvs/emacs/src/ * *mail* 42 Mail % HELLO 1607 Fundamental ~/cvs/emacs/etc/HELLO % NEWS 481184 Outline ~/cvs/emacs/etc/NEWS *scratch* 191 Lisp Interaction * *Messages* 1554 Fundamental @end smallexample @noindent The buffer @file{*Help*} was made by a help request (@pxref{Help}); it is not visiting any file. The buffer @code{src} was made by Dired on the directory @file{~/cvs/emacs/src/}. You can list only buffers that are visiting files by giving the command a prefix argument, as in @kbd{C-u C-x C-b}. @code{list-buffers} omits buffers whose names begin with a space, unless they visit files: such buffers are used internally by Emacs. @node Misc Buffer @section Miscellaneous Buffer Operations @table @kbd @item C-x C-q Toggle read-only status of buffer (@code{toggle-read-only}). @item M-x rename-buffer @key{RET} @var{name} @key{RET} Change the name of the current buffer. @item M-x rename-uniquely Rename the current buffer by adding @samp{<@var{number}>} to the end. @item M-x view-buffer @key{RET} @var{buffer} @key{RET} Scroll through buffer @var{buffer}. @xref{View Mode}. @end table @kindex C-x C-q @vindex buffer-read-only @cindex read-only buffer A buffer can be @dfn{read-only}, which means that commands to change its contents are not allowed. The mode line indicates read-only buffers with @samp{%%} or @samp{%*} 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. @findex toggle-read-only The command @kbd{C-x C-q} (@code{toggle-read-only}) makes a read-only buffer writable, and makes a writable buffer read-only. This works by setting the variable @code{buffer-read-only}, which has a local value in each buffer and makes the buffer read-only if its value is non-@code{nil}. @findex rename-buffer @kbd{M-x rename-buffer} changes the name of the current buffer. You 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. @findex rename-uniquely @kbd{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 @file{*shell*} buffer, then do @kbd{M-x shell} again, it makes a new shell buffer named @file{*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. (With some of these features, such as @kbd{M-x compile}, @kbd{M-x grep}, you need to switch to some other buffer before using the command again, otherwise it will reuse the current buffer despite the name change.) The commands @kbd{M-x append-to-buffer} and @kbd{M-x insert-buffer} can also be used to copy text from one buffer to another. @xref{Accumulating Text}. @node Kill Buffer @section Killing Buffers @cindex 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 @dfn{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: @table @kbd @item C-x k @var{bufname} @key{RET} Kill buffer @var{bufname} (@code{kill-buffer}). @item M-x kill-some-buffers Offer to kill each buffer, one by one. @item M-x kill-matching-buffers Offer to kill all buffers matching a regular expression. @end table @findex kill-buffer @kindex C-x k @kbd{C-x k} (@code{kill-buffer}) kills one buffer, whose name you specify in the minibuffer. The default, used if you type just @key{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 @kbd{yes} before the buffer is killed. @findex kill-some-buffers The command @kbd{M-x kill-some-buffers} asks about each buffer, one by one. An answer of @kbd{y} means to kill the buffer, just like @code{kill-buffer}. This command ignores buffers whose names begin with a space, which are used internally by Emacs. @findex kill-matching-buffers The command @kbd{M-x kill-matching-buffers} prompts for a regular expression and kills all buffers whose names match that expression. @xref{Regexps}. Like @code{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 @code{kill-matching-buffers} with a prefix argument. The buffer menu feature is also convenient for killing various buffers. @xref{Several Buffers}. @vindex kill-buffer-hook If you want to do something special every time a buffer is killed, you can add hook functions to the hook @code{kill-buffer-hook} (@pxref{Hooks}). @findex clean-buffer-list 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 @kbd{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. @cindex Midnight mode @vindex midnight-mode @vindex midnight-hook 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 @code{clean-buffer-list}, or whichever functions you have placed in the normal hook @code{midnight-hook} (@pxref{Hooks}). To enable Midnight mode, use the Customization buffer to set the variable @code{midnight-mode} to @code{t}. @xref{Easy Customization}. @node Several Buffers @section Operating on Several Buffers @cindex buffer menu @table @kbd @item M-x buffer-menu Begin editing a buffer listing all Emacs buffers. @item M-x buffer-menu-other-window. Similar, but do it in another window. @end table The @dfn{buffer menu} opened by @kbd{C-x C-b} (@pxref{List Buffers}) does not merely list buffers. It also allows you to perform various operations on buffers, through an interface similar to Dired (@pxref{Dired}). You can save buffers, kill them (here called @dfn{deleting} them, for consistency with Dired), or display them. @findex buffer-menu @findex buffer-menu-other-window To use the buffer menu, type @kbd{C-x C-b} and switch to the window displaying the @file{*Buffer List*} buffer. You can also type @kbd{M-x buffer-menu} to open the buffer menu in the selected window. Alternatively, the command @kbd{M-x buffer-menu-other-window} opens the buffer menu in another window, and selects that window. The buffer menu is a read-only buffer, and can be changed only through the special commands described in this section. The usual cursor motion commands can be used in this buffer. The following commands apply to the buffer described on the current line: @table @kbd @item d Request to delete (kill) the buffer, then move down. The request shows as a @samp{D} on the line, before the buffer name. Requested deletions take place when you type the @kbd{x} command. @item C-d Like @kbd{d} but move up afterwards instead of down. @item s Request to save the buffer. The request shows as an @samp{S} on the line. Requested saves take place when you type the @kbd{x} command. You may request both saving and deletion for the same buffer. @item x Perform previously requested deletions and saves. @item u Remove any request made for the current line, and move down. @item @key{DEL} Move to previous line and remove any request made for that line. @end table The @kbd{d}, @kbd{C-d}, @kbd{s} and @kbd{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: @table @kbd @item ~ Mark the buffer ``unmodified''. The command @kbd{~} does this immediately when you type it. @item % Toggle the buffer's read-only flag. The command @kbd{%} does this immediately when you type it. @item t Visit the buffer as a tags table. @xref{Select Tags Table}. @end table There are also commands to select another buffer or buffers: @table @kbd @item q Quit the buffer menu---immediately display the most recent formerly visible buffer in its place. @item @key{RET} @itemx f Immediately select this line's buffer in place of the @file{*Buffer List*} buffer. @item o Immediately select this line's buffer in another window as if by @kbd{C-x 4 b}, leaving @file{*Buffer List*} visible. @item C-o Immediately display this line's buffer in another window, but don't select the window. @item 1 Immediately select this line's buffer in a full-screen window. @item 2 Immediately set up two windows, with this line's buffer selected in one, and the previously current buffer (aside from the buffer @file{*Buffer List*}) displayed in the other. @item b Bury the buffer listed on this line. @item m Mark this line's buffer to be displayed in another window if you exit with the @kbd{v} command. The request shows as a @samp{>} at the beginning of the line. (A single buffer may not have both a delete request and a display request.) @item v Immediately select this line's buffer, and also display in other windows any buffers previously marked with the @kbd{m} command. If you have not marked any buffers, this command is equivalent to @kbd{1}. @end table There is also a command that affects the entire buffer list: @table @kbd @item T Delete, or reinsert, lines for non-file buffers. This command toggles the inclusion of such buffers in the buffer list. @end table What @code{buffer-menu} actually does is create and switch to a suitable buffer, and turn on Buffer Menu mode in it. 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 @file{*Buffer List*} buffer to another Emacs buffer, and edit there. You can reselect the @file{*Buffer List*} buffer later, to perform the operations already requested, or you can kill it, or pay no further attention to it. Normally, the buffer @file{*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 @file{*Buffer List*} to show what you have done is to type @kbd{g} (@code{revert-buffer}). You can make this happen regularly every @code{auto-revert-interval} seconds if you enable Auto Revert mode in this buffer, as long as it is not marked modified. Global Auto Revert mode applies to the @file{*Buffer List*} buffer only if @code{global-auto-revert-non-file-buffers} is non-@code{nil}. @iftex @inforef{Autorevert,, emacs-xtra}, for details. @end iftex @ifnottex @xref{Autorevert, global-auto-revert-non-file-buffers}, for details. @end ifnottex @node Indirect Buffers @section Indirect Buffers @cindex indirect buffer @cindex base buffer An @dfn{indirect buffer} shares the text of some other buffer, which is called the @dfn{base buffer} of the indirect buffer. In some ways it is a buffer analogue of a symbolic link between files. @table @kbd @findex make-indirect-buffer @item M-x make-indirect-buffer @key{RET} @var{base-buffer} @key{RET} @var{indirect-name} @key{RET} Create an indirect buffer named @var{indirect-name} with base buffer @var{base-buffer}. @findex clone-indirect-buffer @item M-x clone-indirect-buffer @key{RET} Create an indirect buffer that is a twin copy of the current buffer. @item C-x 4 c @kindex C-x 4 c @findex clone-indirect-buffer-other-window Create an indirect buffer that is a twin copy of the current buffer, and select it in another window (@code{clone-indirect-buffer-other-window}). @end table 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 can 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. @xref{Outline Views}. @vindex clone-indirect-buffer-hook A quick and handy way to make an indirect buffer is with the command @kbd{M-x clone-indirect-buffer}. It creates and selects an indirect buffer whose base buffer is the current buffer. With a numeric argument, it prompts for the name of the indirect buffer; otherwise it uses the name of the current buffer, with a @samp{<@var{n}>} suffix added. @kbd{C-x 4 c} (@code{clone-indirect-buffer-other-window}) works like @kbd{M-x clone-indirect-buffer}, but it selects the new buffer in another window. These functions run the hook @code{clone-indirect-buffer-hook} after creating the indirect buffer. The more general way to make an indirect buffer is with the command @kbd{M-x make-indirect-buffer}. It creates an indirect buffer named @var{indirect-name} from a buffer @var{base-buffer}, prompting for both using the minibuffer. @node Buffer Convenience @section Convenience Features and Customization of Buffer Handling This section describes several modes and features that make it more convenient to switch between buffers. @menu * Uniquify:: Making buffer names unique with directory parts. * Iswitchb:: Switching between buffers with substrings. * Buffer Menus:: Configurable buffer menu. @end menu @node Uniquify @subsection Making Buffer Names Unique @cindex unique buffer names @cindex directories in buffer names When several buffers visit identically-named files, Emacs must give the buffers distinct names. The usual method for making buffer names unique adds @samp{<2>}, @samp{<3>}, etc. to the end of the buffer names (all but one of them). @vindex uniquify-buffer-name-style Other methods work by adding parts of each file's directory to the buffer name. To select one, load the library @file{uniquify} (e.g. using @code{(require 'uniquify)}), and customize the variable @code{uniquify-buffer-name-style} (@pxref{Easy Customization}). To begin with, the @code{forward} naming method includes part of the file's directory name at the beginning of the buffer name; using this method, buffers visiting the files @file{/u/rms/tmp/Makefile} and @file{/usr/projects/zaphod/Makefile} would be named @samp{tmp/Makefile} and @samp{zaphod/Makefile}, respectively (instead of @samp{Makefile} and @samp{Makefile<2>}). In contrast, the @code{post-forward} naming method would call the buffers @samp{Makefile|tmp} and @samp{Makefile|zaphod}, and the @code{reverse} naming method would call them @samp{Makefile\tmp} and @samp{Makefile\zaphod}. The nontrivial difference between @code{post-forward} and @code{reverse} occurs when just one directory name is not enough to distinguish two files; then @code{reverse} puts the directory names in reverse order, so that @file{/top/middle/file} becomes @samp{file\middle\top}, while @code{post-forward} puts them in forward order after the file name, as in @samp{file|top/middle}. Which rule to follow for putting the directory names in the buffer name is not very important if you are going to @emph{look} at the buffer names before you type one. But as an experienced user, if you know the rule, you won't have to look. And then you may find that one rule or another is easier for you to remember and apply quickly. @node Iswitchb @subsection Switching Between Buffers using Substrings @findex iswitchb-mode @cindex Iswitchb mode @cindex mode, Iswitchb @kindex C-x b @r{(Iswitchb mode)} @kindex C-x 4 b @r{(Iswitchb mode)} @kindex C-x 5 b @r{(Iswitchb mode)} @kindex C-x 4 C-o @r{(Iswitchb mode)} Iswitchb global minor mode provides convenient switching between buffers using substrings of their names. It replaces the normal definitions of @kbd{C-x b}, @kbd{C-x 4 b}, @kbd{C-x 5 b}, and @kbd{C-x 4 C-o} with alternative commands that are somewhat ``smarter''. When one of these commands prompts you for a buffer name, you can type in just a substring of the name you want to choose. As you enter the substring, Iswitchb mode continuously displays a list of buffers that match the substring you have typed. At any time, you can type @key{RET} to select the first buffer in the list. So the way to select a particular buffer is to make it the first in the list. There are two ways to do this. You can type more of the buffer name and thus narrow down the list, excluding unwanted buffers above the desired one. Alternatively, you can use @kbd{C-s} and @kbd{C-r} to rotate the list until the desired buffer is first. @key{TAB} while entering the buffer name performs completion on the string you have entered, based on the displayed list of buffers. To enable Iswitchb mode, type @kbd{M-x iswitchb-mode}, or customize the variable @code{iswitchb-mode} to @code{t} (@pxref{Easy Customization}). @node Buffer Menus @subsection Customizing Buffer Menus @findex bs-show @cindex buffer list, customizable @table @kbd @item M-x bs-show Make a list of buffers similarly to @kbd{M-x list-buffers} but customizable. @end table @kbd{M-x bs-show} pops up a buffer list similar to the one normally displayed by @kbd{C-x C-b} but which you can customize. If you prefer this to the usual buffer list, you can bind this command to @kbd{C-x C-b}. To customize this buffer list, use the @code{bs} Custom group (@pxref{Easy Customization}). @findex msb-mode @cindex mode, MSB @cindex MSB mode @cindex buffer menu @findex mouse-buffer-menu @kindex C-Down-Mouse-1 MSB global minor mode (``MSB'' stands for ``mouse select buffer'') provides a different and customizable mouse buffer menu which you may prefer. It replaces the bindings of @code{mouse-buffer-menu}, normally on @kbd{C-Down-Mouse-1}, and the menu bar buffer menu. You can customize the menu in the @code{msb} Custom group.