This is Info file ../info/emacs, produced by Makeinfo-1.63 from the
input file emacs.texi.


File: emacs,  Node: Multi-User Branching,  Prev: Creating Branches,  Up: Branches

Multi-User Branching
....................

   It is sometimes useful for multiple developers to work simultaneously
on different branches of a file.  This is possible if you create
multiple source directories.  Each source directory should have a link
named `RCS' which points to a common directory of RCS master files.
Then each source directory can have its own choice of versions checked
out, but all share the same common RCS records.

   This technique works reliably and automatically, provided that the
source files contain RCS version headers (*note Version Headers::.).
The headers enable Emacs to be sure, at all times, which version number
is present in the work file.

   If the files do not have version headers, you must instead tell Emacs
explicitly in each session which branch you are working on.  To do this,
first find the file, then type `C-u C-x C-q' and specify the correct
branch number.  This ensures that Emacs knows which branch it is using
during this particular editing session.


File: emacs,  Node: Status in VC,  Next: Renaming and VC,  Prev: Branches,  Up: Version Control

VC Status Commands
------------------

   To view the detailed version control status and history of a file,
type `C-x v l' (`vc-print-log').  It displays the history of changes to
the current file, including the text of the log entries.  The output
appears in a separate window.

   When you are working on a large program, it's often useful to find
all the files that are currently locked, or all the files maintained in
version control at all.  You can use `C-x v d' (`vc-directory') to show
all the locked files in or beneath a certain directory.  This includes
all files that are locked by any user.  `C-u C-x v d' lists all files
in or beneath the specified directory that are maintained with version
control.

   The list of files is displayed as a buffer that uses an augmented
Dired mode.  The names of the users locking various files are shown (in
parentheses) in place of the owner and group.  (With CVS, a more
detailed status is shown for each file.)  All the normal Dired commands
work in this buffer.  Most interactive VC commands work also, and apply
to the file name on the current line.

   The `C-x v v' command (`vc-next-action'), when used in the augmented
Dired buffer, operates on all the marked files (or the file on the
current line).  If it operates on more than one file, it handles each
file according to its current state; thus, it may check out one file
and check in another (because it is already checked out).  If it has to
check in any files, it reads a single log entry, then uses that text
for all the files being checked in.  This can be convenient for
registering or checking in several files at once, as part of the same
change.


File: emacs,  Node: Renaming and VC,  Next: Snapshots,  Prev: Status in VC,  Up: Version Control

Renaming VC Work Files and Master Files
---------------------------------------

   When you rename a registered file, you must also rename its master
file correspondingly to get proper results.  Use `vc-rename-file' to
rename the source file as you specify, and rename its master file
accordingly.  It also updates any snapshots (*note Snapshots::.) that
mention the file, so that they use the new name; despite this, the
snapshot thus modified may not completely work (*note Snapshot
Caveats::.).

   You cannot use `vc-rename-file' on a file that is locked by someone
else.


File: emacs,  Node: Snapshots,  Next: Version Headers,  Prev: Renaming and VC,  Up: Version Control

Snapshots
---------

   A "snapshot" is a named set of file versions (one for each
registered file) that you can treat as a unit.  One important kind of
snapshot is a "release", a (theoretically) stable version of the system
that is ready for distribution to users.

* Menu:

* Making Snapshots::		The snapshot facilities.
* Snapshot Caveats::		Things to be careful of when using snapshots.


File: emacs,  Node: Making Snapshots,  Next: Snapshot Caveats,  Up: Snapshots

Making and Using Snapshots
..........................

   There are two basic commands for snapshots; one makes a snapshot
with a given name, the other retrieves a named snapshot.

`C-x v s NAME RET'
     Define the last saved versions of every registered file in or
     under the current directory as a snapshot named NAME
     (`vc-create-snapshot').

`C-x v r NAME RET'
     Check out all registered files at or below the current directory
     level using whatever versions correspond to the snapshot NAME
     (`vc-retrieve-snapshot').

     This command reports an error if any files are locked at or below
     the current directory, without changing anything; this is to avoid
     overwriting work in progress.

   A snapshot uses a very small amount of resources--just enough to
record the list of file names and which version belongs to the
snapshot.  Thus, you need not hesitate to create snapshots whenever
they are useful.

   You can give a snapshot name as an argument to `C-x v =' or `C-x v
~' (*note Old Versions::.).  Thus, you can use it to compare a snapshot
against the current files, or two snapshots against each other, or a
snapshot against a named version.


File: emacs,  Node: Snapshot Caveats,  Prev: Making Snapshots,  Up: Snapshots

Snapshot Caveats
................

   VC's snapshot facilities are modeled on RCS's named-configuration
support.  They use RCS's native facilities for this, so under VC
snapshots made using RCS are visible even when you bypass VC.

   For SCCS, VC implements snapshots itself.  The files it uses contain
name/file/version-number triples.  These snapshots are visible only
through VC.

   A snapshot is a set of checked-in versions.  So make sure that all
the files are checked in and not locked when you make a snapshot.

   File renaming and deletion can create some difficulties with
snapshots.  This is not a VC-specific problem, but a general design
issue in version control systems that no one has solved very well yet.

   If you rename a registered file, you need to rename its master along
with it (the command `vc-rename-file' does this automatically).  If you
are using SCCS, you must also update the records of the snapshot, to
mention the file by its new name (`vc-rename-file' does this, too).  An
old snapshot that refers to a master file that no longer exists under
the recorded name is invalid; VC can no longer retrieve it.  It would
be beyond the scope of this manual to explain enough about RCS and SCCS
to explain how to update the snapshots by hand.

   Using `vc-rename-file' makes the snapshot remain valid for
retrieval, but it does not solve all problems.  For example, some of the
files in the program probably refer to others by name.  At the very
least, the makefile probably mentions the file that you renamed.  If you
retrieve an old snapshot, the renamed file is retrieved under its new
name, which is not the name that the makefile expects.  So the program
won't really work as retrieved.


File: emacs,  Node: Version Headers,  Next: Customizing VC,  Prev: Snapshots,  Up: Version Control

Inserting Version Control Headers
---------------------------------

   Sometimes it is convenient to put version identification strings
directly into working files.  Certain special strings called "version
headers" are replaced in each successive version by the number of that
version.

   If you are using RCS, and version headers are present in your working
files, Emacs can use them to determine the current version and the
locking state of the files.  This is more reliable than referring to the
master files, which is done when there are no version headers.  Note
that in a multi-branch environment, version headers are necessary to
make VC behave correctly (*note Multi-User Branching::.).

   Searching for version headers is controlled by the variable
`vc-consult-headers'.  If it is non-`nil', Emacs searches for headers
to determine the version number you are editing.  Setting it to `nil'
disables this feature.

   You can use the `C-x v h' command (`vc-insert-headers') to insert a
suitable header string.

`C-x v h'
     Insert headers in a file for use with your version-control system.

   The default header string is `$Id$' for RCS and `%W%' for SCCS.  You
can specify other headers to insert by setting the variable
`vc-header-alist'.  Its value is a list of elements of the form
`(PROGRAM . STRING)' where PROGRAM is `RCS' or `SCCS' and STRING is the
string to use.

   Instead of a single string, you can specify a list of strings; then
each string in the list is inserted as a separate header on a line of
its own.

   It is often necessary to use "superfluous" backslashes when writing
the strings that you put in this variable.  This is to prevent the
string in the constant from being interpreted as a header itself if the
Emacs Lisp file containing it is maintained with version control.

   Each header is inserted surrounded by tabs, inside comment
delimiters, on a new line at the start of the buffer.  Normally the
ordinary comment start and comment end strings of the current mode are
used, but for certain modes, there are special comment delimiters for
this purpose; the variable `vc-comment-alist' specifies them.  Each
element of this list has the form `(MODE STARTER ENDER)'.

   The variable `vc-static-header-alist' specifies further strings to
add based on the name of the buffer.  Its value should be a list of
elements of the form `(REGEXP . FORMAT)'.  Whenever REGEXP matches the
buffer name, FORMAT is inserted as part of the header.  A header line
is inserted for each element that matches the buffer name, and for each
string specified by `vc-header-alist'.  The header line is made by
processing the string from `vc-header-alist' with the format taken from
the element.  The default value for `vc-static-header-alist' is as
follows:

     (("\\.c$" .
       "\n#ifndef lint\nstatic char vcid[] = \"\%s\";\n\
     #endif /* lint */\n"))

It specifies insertion of text of this form:


     #ifndef lint
     static char vcid[] = "STRING";
     #endif /* lint */

Note that the text above starts with a blank line.

   If you use more than one version header in a file, put them close
together in the file.  The mechanism in `revert-buffer' that preserves
markers may not handle markers positioned between two version headers.


File: emacs,  Node: Customizing VC,  Prev: Version Headers,  Up: Version Control

Customizing VC
--------------

   There are many ways of customizing VC.  The variables that control
its behavior fall into three categories, described in the following
sections.

* Menu:

* VC Workfile Handling::  Various options concerning working files.
* VC Status Retrieval::   How VC finds the version control status of a file,
                            and how to customize this.
* VC Command Execution::  Which commands VC should run, and how.


File: emacs,  Node: VC Workfile Handling,  Next: VC Status Retrieval,  Up: Customizing VC

VC Workfile Handling
....................

   Emacs normally does not save backup files for source files that are
maintained with version control.  If you want to make backup files even
for files that use version control, set the variable
`vc-make-backup-files' to a non-`nil' value.

   Normally the work file exists all the time, whether it is locked or
not.  If you set `vc-keep-workfiles' to `nil', then checking in a new
version with `C-x C-q' deletes the work file; but any attempt to visit
the file with Emacs creates it again.  (With CVS, work files are always
kept.)

   Editing a version-controlled file through a symbolic link can be
dangerous.  It bypasses the version control system--you can edit the
file without checking it out, and fail to check your changes in.  Also,
your changes might overwrite those of another user.  To protect against
this, VC checks each symbolic link that you visit, to see if it points
to a file under version control.

   The variable `vc-follow-symlinks' controls what to do when a
symbolic link points to a version-controlled file.  If it is `nil', VC
only displays a warning message.  If it is `t', VC automatically
follows the link, and visits the real file instead, telling you about
this in the echo area.  If the value is `ask' (the default), VC asks
you each time whether to follow the link.


File: emacs,  Node: VC Status Retrieval,  Next: VC Command Execution,  Prev: VC Workfile Handling,  Up: Customizing VC

VC Status Retrieval
...................

   When deducing the locked/unlocked state of a file, VC first looks for
an RCS version header string in the file (*note Version Headers::.).  If
there is no header string (or if the backend system is SCCS), VC
normally looks at the file permissions of the work file; this is fast.
But there might be situations when the file permissions cannot be
trusted.  In this case the master file has to be consulted, which is
rather expensive.  Also the master file can only tell you *if* there's
any lock on the file, but not whether your work file really contains
that locked version.

   You can tell VC not to use version headers to determine lock status
by setting `vc-consult-headers' to `nil'.  VC then always uses the file
permissions (if it can trust them), or else checks the master file.

   You can specify the criterion for whether to trust the file
permissions by setting the variable `vc-mistrust-permissions'.  Its
value may be `t' (always mistrust the file permissions and check the
master file), `nil' (always trust the file permissions), or a function
of one argument which makes the decision.  The argument is the
directory name of the `RCS', `CVS' or `SCCS' subdirectory.  A non-`nil'
value from the function says to mistrust the file permissions.  If you
find that the file permissions of work files are changed erroneously,
set `vc-mistrust-permissions' to `t'.  Then VC always checks the master
file to determine the file's status.


File: emacs,  Node: VC Command Execution,  Prev: VC Status Retrieval,  Up: Customizing VC

VC Command Execution
....................

   If `vc-suppress-confirm' is non-`nil', then `C-x C-q' and `C-x v i'
can save the current buffer without asking, and `C-x v u' also operates
without asking for confirmation.  (This variable does not affect `C-x v
c'; that operation is so drastic that it should always ask for
confirmation.)

   VC mode does much of its work by running the shell commands for RCS,
CVS and SCCS.  If `vc-command-messages' is non-`nil', VC displays
messages to indicate which shell commands it runs, and additional
messages when the commands finish.

   You can specify additional directories to search for version control
programs by setting the variable `vc-path'.  These directories are
searched before the usual search path.  But the proper files are usually
found automatically.


File: emacs,  Node: Directories,  Next: Comparing Files,  Prev: Version Control,  Up: Files

File Directories
================

   The file system groups files into "directories".  A "directory
listing" is a list of all the files in a directory.  Emacs provides
commands to create and delete directories, and to make directory
listings in brief format (file names only) and verbose format (sizes,
dates, and authors included).  There is also a directory browser called
Dired; see *Note Dired::.

`C-x C-d DIR-OR-PATTERN RET'
     Display a brief directory listing (`list-directory').

`C-u C-x C-d DIR-OR-PATTERN RET'
     Display a verbose directory listing.

`M-x make-directory RET DIRNAME RET'
     Create a new directory named DIRNAME.

`M-x delete-directory RET DIRNAME RET'
     Delete the directory named DIRNAME.  It must be empty, or you get
     an error.

   The command to display a directory listing is `C-x C-d'
(`list-directory').  It reads using the minibuffer a file name which is
either a directory to be listed or a wildcard-containing pattern for
the files to be listed.  For example,

     C-x C-d /u2/emacs/etc RET

lists all the files in directory `/u2/emacs/etc'.  Here is an example
of specifying a file name pattern:

     C-x C-d /u2/emacs/src/*.c RET

   Normally, `C-x C-d' prints a brief directory listing containing just
file names.  A numeric argument (regardless of value) tells it to make
a verbose listing including sizes, dates, and authors (like `ls -l').

   The text of a directory listing is obtained by running `ls' in an
inferior process.  Two Emacs variables control the switches passed to
`ls': `list-directory-brief-switches' is a string giving the switches
to use in brief listings (`"-CF"' by default), and
`list-directory-verbose-switches' is a string giving the switches to
use in a verbose listing (`"-l"' by default).


File: emacs,  Node: Comparing Files,  Next: Misc File Ops,  Prev: Directories,  Up: Files

Comparing Files
===============

   The command `M-x diff' compares two files, displaying the
differences in an Emacs buffer named `*Diff*'.  It works by running the
`diff' program, using options taken from the variable `diff-switches',
whose value should be a string.

   The buffer `*Diff*' has Compilation mode as its major mode, so you
can use `C-x `' to visit successive changed locations in the two source
files.  You can also move to a particular hunk of changes and type RET
or `C-c C-c', or click `Mouse-2' on it, to move to the corresponding
source location.  You can also use the other special commands of
Compilation mode: SPC and DEL for scrolling, and `M-p' and `M-n' for
cursor motion.  *Note Compilation::.

   The command `M-x diff-backup' compares a specified file with its most
recent backup.  If you specify the name of a backup file, `diff-backup'
compares it with the source file that it is a backup of.

   The command `M-x compare-windows' compares the text in the current
window with that in the next window.  Comparison starts at point in each
window, and each starting position is pushed on the mark ring in its
respective buffer.  Then point moves forward in each window, a character
at a time, until a mismatch between the two windows is reached.  Then
the command is finished.  For more information about windows in Emacs,
*Note Windows::.

   With a numeric argument, `compare-windows' ignores changes in
whitespace.  If the variable `compare-ignore-case' is non-`nil', it
ignores differences in case as well.

   See also *Note Emerge::, for convenient facilities for merging two
similar files.


File: emacs,  Node: Misc File Ops,  Next: Compressed Files,  Prev: Comparing Files,  Up: Files

Miscellaneous File Operations
=============================

   Emacs has commands for performing many other operations on files.
All operate on one file; they do not accept wild card file names.

   `M-x view-file' allows you to scan or read a file by sequential
screenfuls.  It reads a file name argument using the minibuffer.  After
reading the file into an Emacs buffer, `view-file' displays the
beginning.  You can then type SPC to scroll forward one windowful, or
DEL to scroll backward.  Various other commands are provided for moving
around in the file, but none for changing it; type `?' while viewing
for a list of them.  They are mostly the same as normal Emacs cursor
motion commands.  To exit from viewing, type `q'.  The commands for
viewing are defined by a special major mode called View mode.

   A related command, `M-x view-buffer', views a buffer already present
in Emacs.  *Note Misc Buffer::.

   `M-x insert-file' inserts a copy of the contents of the specified
file into the current buffer at point, leaving point unchanged before
the contents and the mark after them.

   `M-x write-region' is the inverse of `M-x insert-file'; it copies
the contents of the region into the specified file.  `M-x
append-to-file' adds the text of the region to the end of the specified
file.  *Note Accumulating Text::.

   `M-x delete-file' deletes the specified file, like the `rm' command
in the shell.  If you are deleting many files in one directory, it may
be more convenient to use Dired (*note Dired::.).

   `M-x rename-file' reads two file names OLD and NEW using the
minibuffer, then renames file OLD as NEW.  If a file named NEW already
exists, you must confirm with `yes' or renaming is not done; this is
because renaming causes the old meaning of the name NEW to be lost.  If
OLD and NEW are on different file systems, the file OLD is copied and
deleted.

   The similar command `M-x add-name-to-file' is used to add an
additional name to an existing file without removing its old name.  The
new name must belong on the same file system that the file is on.

   `M-x copy-file' reads the file OLD and writes a new file named NEW
with the same contents.  Confirmation is required if a file named NEW
already exists, because copying has the consequence of overwriting the
old contents of the file NEW.

   `M-x make-symbolic-link' reads two file names OLD and LINKNAME, then
creates a symbolic link named LINKNAME and pointing at OLD.  The effect
is that future attempts to open file LINKNAME will refer to whatever
file is named OLD at the time the opening is done, or will get an error
if the name OLD is not in use at that time.  This command does not
expand the argument FILENAME, so that it allows you to specify a
relative name as the target of the link.

   Confirmation is required when creating the link if LINKNAME is in
use.  Note that not all systems support symbolic links.


File: emacs,  Node: Compressed Files,  Prev: Misc File Ops,  Up: Files

Accessing Compressed Files
==========================

   Emacs comes with a library that can automatically uncompress
compressed files when you visit them, and automatically recompress them
if you alter them and save them.  To enable this feature, type the
command `M-x auto-compression-mode'.

   When automatic compression (which implies automatic uncompression as
well) is enabled, Emacs recognizes compressed files by their file names.
File names ending in `.gz' indicate a file compressed with `gzip'.
Other endings indicate other compression programs.

   Automatic uncompression and compression apply to all the operations
in which Emacs uses the contents of a file.  This includes visiting it,
saving it, inserting its contents into a buffer, loading it, and byte
compiling it.


File: emacs,  Node: Buffers,  Next: Windows,  Prev: Files,  Up: Top

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
(*note 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
(*note 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.  *Note Locals::.

* 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-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.


File: emacs,  Node: Select Buffer,  Next: List Buffers,  Up: Buffers

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 (*note
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' (*note 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.  *Note
Visiting::.

   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.


File: emacs,  Node: List Buffers,  Next: Misc Buffer,  Prev: Select Buffer,  Up: Buffers

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' (*note 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/'.


File: emacs,  Node: Misc Buffer,  Next: Kill Buffer,  Prev: List Buffers,  Up: Buffers

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.  *Note 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' (*note 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.  *Note Accumulating
Text::.


File: emacs,  Node: Kill Buffer,  Next: Several Buffers,  Prev: Misc Buffer,  Up: Buffers

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 (*note 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' (*note
Hooks::.).


File: emacs,  Node: Several Buffers,  Next: Indirect Buffers,  Prev: Kill Buffer,  Up: Buffers

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.  *Note Select 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.


File: emacs,  Node: Indirect Buffers,  Prev: Several Buffers,  Up: Buffers

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.  *Note Outline Views::.


File: emacs,  Node: Windows,  Next: Frames,  Prev: Buffers,  Up: Top

Multiple Windows
****************

   Emacs can split a frame into two or many windows.  Multiple windows
can display parts of different buffers, or different parts of one
buffer.  Multiple frames always imply multiple windows, because each
frame has its own set of windows.  Each window belongs to one and only
one frame.

* Menu:

* Basic Window::       Introduction to Emacs windows.
* Split Window::       New windows are made by splitting existing windows.
* Other Window::       Moving to another window or doing something to it.
* Pop Up Window::      Finding a file or buffer in another window.
* Force Same Window::  Forcing certain buffers to appear in the selected
                         window rather than in another window.
* Change Window::      Deleting windows and changing their sizes.


File: emacs,  Node: Basic Window,  Next: Split Window,  Up: Windows

Concepts of Emacs Windows
=========================

   Each Emacs window displays one Emacs buffer at any time.  A single
buffer may appear in more than one window; if it does, any changes in
its text are displayed in all the windows where it appears.  But the
windows showing the same buffer can show different parts of it, because
each window has its own value of point.

   At any time, one of the windows is the "selected window"; the buffer
this window is displaying is the current buffer.  The terminal's cursor
shows the location of point in this window.  Each other window has a
location of point as well, but since the terminal has only one cursor
there is no way to show where those locations are.  When multiple
frames are visible in X Windows, each frame has a cursor which appears
in the frame's selected window.  The cursor in the selected frame is
solid; the cursor in other frames is a hollow box.

   Commands to move point affect the value of point for the selected
Emacs window only.  They do not change the value of point in any other
Emacs window, even one showing the same buffer.  The same is true for
commands such as `C-x b' to change the selected buffer in the selected
window; they do not affect other windows at all.  However, there are
other commands such as `C-x 4 b' that select a different window and
switch buffers in it.  Also, all commands that display information in a
window, including (for example) `C-h f' (`describe-function') and `C-x
C-b' (`list-buffers'), work by switching buffers in a nonselected window
without affecting the selected window.

   When multiple windows show the same buffer, they can have different
regions, because they can have different values of point.  This means
that in Transient Mark mode, each window highlights a different part of
the buffer.  The part that is highlighted in the selected window is the
region that editing commands use.

   Each window has its own mode line, which displays the buffer name,
modification status and major and minor modes of the buffer that is
displayed in the window.  *Note Mode Line::, for full details on the
mode line.


File: emacs,  Node: Split Window,  Next: Other Window,  Prev: Basic Window,  Up: Windows

Splitting Windows
=================

`C-x 2'
     Split the selected window into two windows, one above the other
     (`split-window-vertically').

`C-x 3'
     Split the selected window into two windows positioned side by side
     (`split-window-horizontally').

`C-Mouse-2'
     In the mode line or scroll bar of a window, split that window.

   The command `C-x 2' (`split-window-vertically') breaks the selected
window into two windows, one above the other.  Both windows start out
displaying the same buffer, with the same value of point.  By default
the two windows each get half the height of the window that was split; a
numeric argument specifies how many lines to give to the top window.

   `C-x 3' (`split-window-horizontally') breaks the selected window
into two side-by-side windows.  A numeric argument specifies how many
columns to give the one on the left.  A line of vertical bars separates
the two windows.  Windows that are not the full width of the screen
have mode lines, but they are truncated; also, they do not always
appear in inverse video, because the Emacs display routines have not
been taught how to display a region of inverse video that is only part
of a line on the screen.

   You can split a window horizontally or vertically by clicking
`C-Mouse-2' in the mode line or the scroll bar.  The line of splitting
goes through the place where you click: if you click on the mode line,
the new scroll bar goes above the spot; if you click in the scroll bar,
the mode line of the split window is side by side with your click.

   When a window is less than the full width, text lines too long to
fit are frequent.  Continuing all those lines might be confusing.  The
variable `truncate-partial-width-windows' can be set non-`nil' to force
truncation in all windows less than the full width of the screen,
independent of the buffer being displayed and its value for
`truncate-lines'.  *Note Continuation Lines::.

   Horizontal scrolling is often used in side-by-side windows.  *Note
Display::.

   If `split-window-keep-point' is non-nil, `C-x 2' tries to avoid
shifting any text on the screen by putting point in whichever window
happens to contain the screen line the cursor is already on.  The
default is that `split-window-keep-point' is non-nil on slow terminals.


File: emacs,  Node: Other Window,  Next: Pop Up Window,  Prev: Split Window,  Up: Windows

Using Other Windows
===================

`C-x o'
     Select another window (`other-window').  That is `o', not zero.

`C-M-v'
     Scroll the next window (`scroll-other-window').

`M-x compare-windows'
     Find next place where the text in the selected window does not
     match the text in the next window.

`Mouse-1'
     `Mouse-1', in a window's mode line, selects that window but does
     not move point in it (`mouse-select-region').

   To select a different window, click with `Mouse-1' on its mode line.
With the keyboard, you can switch windows by typing `C-x o'
(`other-window').  That is an `o', for `other', not a zero.  When there
are more than two windows, this command moves through all the windows
in a cyclic order, generally top to bottom and left to right.  After
the rightmost and bottommost window, it goes back to the one at the
upper left corner.  A numeric argument means to move several steps in
the cyclic order of windows.  A negative argument moves around the
cycle in the opposite order.  When the minibuffer is active, the
minibuffer is the last window in the cycle; you can switch from the
minibuffer window to one of the other windows, and later switch back and
finish supplying the minibuffer argument that is requested.  *Note
Minibuffer Edit::.

   The usual scrolling commands (*note Display::.) apply to the selected
window only, but there is one command to scroll the next window.
`C-M-v' (`scroll-other-window') scrolls the window that `C-x o' would
select.  It takes arguments, positive and negative, like `C-v'.  (In
the minibuffer, `C-M-v' scrolls the window that contains the minibuffer
help display, if any, rather than the next window in the standard
cyclic order.)

   The command `M-x compare-windows' lets you compare two files or
buffers visible in two windows, by moving through them to the next
mismatch.  *Note Comparing Files::, for details.


File: emacs,  Node: Pop Up Window,  Next: Force Same Window,  Prev: Other Window,  Up: Windows

Displaying in Another Window
============================

   `C-x 4' is a prefix key for commands that select another window
(splitting the window if there is only one) and select a buffer in that
window.  Different `C-x 4' commands have different ways of finding the
buffer to select.

`C-x 4 b BUFNAME RET'
     Select buffer BUFNAME in another window.  This runs
     `switch-to-buffer-other-window'.

`C-x 4 C-o BUFNAME RET'
     Display buffer BUFNAME in another window, but don't select that
     buffer or that window.  This runs `display-buffer'.

`C-x 4 f FILENAME RET'
     Visit file FILENAME and select its buffer in another window.  This
     runs `find-file-other-window'.  *Note Visiting::.

`C-x 4 d DIRECTORY RET'
     Select a Dired buffer for directory DIRECTORY in another window.
     This runs `dired-other-window'.  *Note Dired::.

`C-x 4 m'
     Start composing a mail message in another window.  This runs
     `mail-other-window'; its same-window analogue is `C-x m' (*note
     Sending Mail::.).

`C-x 4 .'
     Find a tag in the current tags table, in another window.  This runs
     `find-tag-other-window', the multiple-window variant of `M-.'
     (*note Tags::.).

`C-x 4 r FILENAME RET'
     Visit file FILENAME read-only, and select its buffer in another
     window.  This runs `find-file-read-only-other-window'.  *Note
     Visiting::.


File: emacs,  Node: Force Same Window,  Next: Change Window,  Prev: Pop Up Window,  Up: Windows

Forcing Display in the Same Window
==================================

   Certain Emacs commands switch to a specific buffer with special
contents.  For example, `M-x shell' switches to a buffer named
`*Shell*'.  By convention, all these commands are written to pop up the
buffer in a separate window.  But you can specify that certain of these
buffers should appear in the selected window.

   If you add a buffer name to the list `same-window-buffer-names', the
effect is that such commands display that particular buffer by
switching to it in the selected window.  For example, if you add the
element `"*grep*"' to the list, the `grep' command will display its
output buffer in the selected window.

   The default value of `same-window-buffer-names' is not `nil'.  It
specifies the buffers `*info*', `*mail*' and `*shell*'.  This is why
`M-x shell' normally switches to the `*shell*' buffer in the selected
window.  If you delete this element from the value of
`same-window-buffer-names', the behavior of `M-x shell' will change--it
will pop up the buffer in another window instead.

   You can specify these buffers more generally with the variable
`same-window-regexps'.  Set it to a list of regular expressions; then
any buffer whose name matches one of those regular expressions is
displayed by switching to it in the selected window.  (Once again, this
applies only to buffers that normally get displayed for you in a
separate window.)  The default value of this variable specifies Telnet
and rlogin buffers.

   An analogous feature lets you specify buffers which should be
displayed in their own individual frames.  *Note Special Buffer
Frames::.

