Compare and round more carefully

[emacs.git] / doc / emacs / buffers.texi

@c This is part of the Emacs manual.
@c Copyright (C) 1985-1987, 1993-1995, 1997, 2000-2017 Free Software
@c 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-only status; 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 @dfn{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, size, 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  Messages
@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{read-only-mode}).
@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.  @xref{Mode
Line}.  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 read-only-mode
@vindex view-read-only
 The command @kbd{C-x C-q} (@code{read-only-mode}) 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}.  If you change the option @code{view-read-only} to a
non-@code{nil} value, making the buffer read-only with @kbd{C-x C-q}
also enables View mode in the buffer (@pxref{View Mode}).

@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
@cindex close buffer
@cindex close file
  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.  (Some other editors call this
operation @dfn{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:

@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
@findex Buffer-menu-delete
@kindex d @r{(Buffer Menu)}
Flag the buffer for deletion (killing), then move point to the next
line (@code{Buffer-menu-delete}).  The deletion flag is indicated by
the character @samp{D} on the line, before the buffer name.  The
deletion occurs only when you type the @kbd{x} command (see below).

@item C-d
@findex Buffer-menu-delete-backwards
@kindex C-d @r{(Buffer Menu)}
Like @kbd{d}, but move point up instead of down
(@code{Buffer-menu-delete-backwards}).

@item s
@findex Buffer-menu-save
@kindex s @r{(Buffer Menu)}
Flag the buffer for saving (@code{Buffer-menu-save}).  The save flag
is indicated by the character @samp{S} on the line, before the buffer
name.  The saving occurs only when you type @kbd{x}.  You may request
both saving and deletion for the same buffer.

@item x
@findex Buffer-menu-execute
@kindex x @r{(Buffer Menu)}
Perform all flagged deletions and saves (@code{Buffer-menu-execute}).

@item u
@findex Buffer-menu-unmark
@kindex u @r{(Buffer Menu)}
Remove all flags from the current line, and move down
(@code{Buffer-menu-unmark}).

@item @key{DEL}
@findex Buffer-menu-backup-unmark
@kindex DEL @r{(Buffer Menu)}
Move to the previous line and remove all flags on that line
(@code{Buffer-menu-backup-unmark}).

@item M-@key{DEL}
@findex Buffer-menu-unmark-all-buffers
@kindex M-DEL @r{(Buffer Menu)}
Remove a particular flag from all lines
(@code{Buffer-menu-unmark-all-buffers}).

@item U
@findex Buffer-menu-unmark-all
@kindex U @r{(Buffer Menu)}
Remove all flags from all the lines
(@code{Buffer-menu-unmark-all}).
@end table

@noindent
The commands for adding or removing flags, @kbd{d}, @kbd{C-d}, @kbd{s}
and @kbd{u}, all accept a numeric argument as a repeat count.

  The following commands operate immediately on the buffer listed on
the current line.  They also accept a numeric argument as a repeat
count.

@table @kbd
@item ~
@findex Buffer-menu-not-modified
@kindex ~ @r{(Buffer Menu)}
Mark the buffer as unmodified (@code{Buffer-menu-not-modified}).
@xref{Save Commands}.

@item %
@findex Buffer-menu-toggle-read-only
@kindex % @r{(Buffer Menu)}
Toggle the buffer's read-only status
(@code{Buffer-menu-toggle-read-only}).  @xref{Misc Buffer}.

@item t
@findex Buffer-menu-visit-tags-table
@kindex % @r{(Buffer Menu)}
Visit the buffer as a tags table
(@code{Buffer-menu-visit-tags-table}).  @xref{Select Tags Table}.
@end table

  The following commands are used to select another buffer or buffers:

@table @kbd
@item q
@findex quit-window
@kindex q @r{(Buffer Menu)}
Quit the Buffer Menu (@code{quit-window}).  The most recent formerly
visible buffer is displayed in its place.

@item @key{RET}
@itemx f
@findex Buffer-menu-this-window
@kindex f @r{(Buffer Menu)}
@kindex RET @r{(Buffer Menu)}
Select this line's buffer, replacing the @file{*Buffer List*} buffer
in its window (@code{Buffer-menu-this-window}).

@item o
@findex Buffer-menu-other-window
@kindex o @r{(Buffer Menu)}
Select this line's buffer in another window, as if by @kbd{C-x 4 b},
leaving @file{*Buffer List*} visible
(@code{Buffer-menu-other-window}).

@item C-o
@findex Buffer-menu-switch-other-window
@kindex C-o @r{(Buffer Menu)}
Display this line's buffer in another window, without selecting it
(@code{Buffer-menu-switch-other-window}).

@item 1
@findex Buffer-menu-1-window
@kindex 1 @r{(Buffer Menu)}
Select this line's buffer in a full-frame window
(@code{Buffer-menu-1-window}).

@item 2
@findex Buffer-menu-2-window
@kindex 2 @r{(Buffer Menu)}
Set up two windows on the current frame, with this line's buffer
selected in one, and a previously current buffer (aside from
@file{*Buffer List*}) in the other (@code{Buffer-menu-2-window}).

@item b
@findex Buffer-menu-bury
@kindex b @r{(Buffer Menu)}
Bury this line's buffer (@code{Buffer-menu-bury}).

@item m
@findex Buffer-menu-mark
@kindex m @r{(Buffer Menu)}
Mark this line's buffer to be displayed in another window if you exit
with the @kbd{v} command (@code{Buffer-menu-mark}).  The display flag
is indicated by the character @samp{>} at the beginning of the line.
(A single buffer may not have both deletion and display flags.)

@item v
@findex Buffer-menu-select
@kindex v @r{(Buffer Menu)}
Select this line's buffer, and also display in other windows any
buffers flagged with the @kbd{m} command (@code{Buffer-menu-select}).
If you have not flagged any buffers, this command is equivalent to
@kbd{1}.
@end table

  The following commands affect the entire buffer list:

@table @kbd
@item S
@findex tabulated-list-sort
@kindex S @r{(Buffer Menu)}
Sort the Buffer Menu entries according to their values in the column
at point.  With a numeric prefix argument @var{n}, sort according to
the @var{n}-th column (@code{tabulated-list-sort}).

@item T
@findex Buffer-menu-toggle-files-only
@kindex T @r{(Buffer Menu)}
Delete, or reinsert, lines for non-file buffers
(@code{Buffer-menu-toggle-files-only}).  This command toggles the
inclusion of such buffers in the buffer list.
@end table

  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.
* Icomplete::              Fast minibuffer selection.
* 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 default method adds a suffix based on
the names of the directories that contain the files.  For example, if
you visit files @file{/foo/bar/mumble/name} and
@file{/baz/quux/mumble/name} at the same time, their buffers will be
named @samp{name<bar/mumble>} and @samp{name<quux/mumble>}, respectively.
Emacs adds as many directory parts as are needed to make a unique name.

@vindex uniquify-buffer-name-style
  You can choose from several different styles for constructing unique
buffer names, by customizing the option @code{uniquify-buffer-name-style}.

  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}.

  In contrast, the @code{post-forward} naming method would call the
buffers @samp{Makefile|tmp} and @samp{Makefile|zaphod}.  The default
method @code{post-forward-angle-brackets} is like @code{post-forward},
except that it encloses the unique path in angle brackets.  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}.  If
@code{uniquify-buffer-name-style} is set to @code{nil}, the buffer
names simply get @samp{<2>}, @samp{<3>}, etc.@: appended.

  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 Icomplete
@subsection Fast minibuffer selection

@findex icomplete-mode
@cindex Icomplete mode

  Icomplete global minor mode provides a convenient way to quickly select an
element among the possible completions in a minibuffer.  When enabled, typing
in the minibuffer continuously displays a list of possible completions that
match the string you have typed.

  At any time, you can type @kbd{C-j} to select the first completion in
the list.  So the way to select a particular completion is to make it the
first in the list.  There are two ways to do this.  You can type more
of the completion name and thus narrow down the list, excluding unwanted
completions above the desired one.  Alternatively, you can use @kbd{C-.}
and @kbd{C-,} to rotate the list until the desired buffer is first.

  @kbd{M-@key{TAB}} will select the first completion in the list, like
@kbd{C-j} but without exiting the minibuffer, so you can edit it
further.  This is typically used when entering a file name, where
@kbd{M-@key{TAB}} can be used a few times to descend in the hierarchy
of directories.

  To enable Icomplete mode, type @kbd{M-x icomplete-mode}, or customize
the variable @code{icomplete-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
@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 @kbd{C-@key{F10}}, and the menu
bar buffer menu.  You can customize the menu in the @code{msb} Custom
group.