Merge from emacs--rel--22

[gnu-emacs] / doc / emacs / misc.texi

@c This is part of the Emacs manual.
@c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 2000, 2001,
@c   2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@iftex
@chapter Miscellaneous Commands

  This chapter contains several brief topics that do not fit anywhere
else: reading netnews, running shell commands and shell subprocesses,
using a single shared Emacs for utilities that expect to run an editor
as a subprocess, printing hardcopy, sorting text, narrowing display to
part of the buffer, editing double-column files and binary files,
saving an Emacs session for later resumption, following hyperlinks,
browsing images, emulating other editors, and various diversions and
amusements.

@end iftex

@ifnottex
@raisesections
@end ifnottex

@node Gnus, Shell, Calendar/Diary, Top
@section Gnus
@cindex Gnus
@cindex reading netnews

Gnus is an Emacs package primarily designed for reading and posting
Usenet news.  It can also be used to read and respond to messages from a
number of other sources---mail, remote directories, digests, and so on.

Here we introduce Gnus and describe several basic features.
@ifnottex
For full details, see @ref{Top, Gnus,, gnus, The Gnus Manual}.
@end ifnottex
@iftex
For full details on Gnus, type @kbd{M-x info} and then select the Gnus
manual.
@end iftex

@findex gnus
To start Gnus, type @kbd{M-x gnus @key{RET}}.

@menu
* Buffers of Gnus::     The group, summary, and article buffers.
* Gnus Startup::        What you should know about starting Gnus.
* Summary of Gnus::     A short description of the basic Gnus commands.
@end menu

@node Buffers of Gnus
@subsection Gnus Buffers

Unlike most Emacs packages, Gnus uses several buffers to display
information and to receive commands.  The three Gnus buffers users use
most are the @dfn{group buffer}, the @dfn{summary buffer} and the
@dfn{article buffer}.

The @dfn{group buffer} contains a list of newsgroups.  This is the
first buffer Gnus displays when it starts up.  It normally displays
only the groups to which you subscribe and that contain unread
articles.  Use this buffer to select a specific group.

The @dfn{summary buffer} lists one line for each article in a single
group.  By default, the author, the subject and the line number are
displayed for each article, but this is customizable, like most aspects
of Gnus display.  The summary buffer is created when you select a group
in the group buffer, and is killed when you exit the group.  Use this
buffer to select an article.

The @dfn{article buffer} displays the article.  In normal Gnus usage,
you see this buffer but you don't select it---all useful
article-oriented commands work in the summary buffer.  But you can
select the article buffer, and execute all Gnus commands from that
buffer, if you want to.

@node Gnus Startup
@subsection When Gnus Starts Up

At startup, Gnus reads your @file{.newsrc} news initialization file
and attempts to communicate with the local news server, which is a
repository of news articles.  The news server need not be the same
computer you are logged in on.

If you start Gnus and connect to the server, but do not see any
newsgroups listed in the group buffer, type @kbd{L} or @kbd{A k} to get
a listing of all the groups.  Then type @kbd{u} to toggle
subscription to groups.

The first time you start Gnus, Gnus subscribes you to a few selected
groups.  All other groups start out as @dfn{killed groups} for you; you
can list them with @kbd{A k}.  All new groups that subsequently come to
exist at the news server become @dfn{zombie groups} for you; type @kbd{A
z} to list them.  You can subscribe to a group shown in these lists
using the @kbd{u} command.

When you quit Gnus with @kbd{q}, it automatically records in your
@file{.newsrc} and @file{.newsrc.eld} initialization files the
subscribed or unsubscribed status of all groups.  You should normally
not edit these files manually, but you may if you know how.

@node Summary of Gnus
@subsection Summary of Gnus Commands

Reading news is a two-step process:

@enumerate
@item
Choose a group in the group buffer.

@item
Select articles from the summary buffer.  Each article selected is
displayed in the article buffer in a large window, below the summary
buffer in its small window.
@end enumerate

  Each Gnus buffer has its own special commands; the meanings of any
given key in the various Gnus buffers are usually analogous, even if
not identical.  Here are commands for the group and summary buffers:

@table @kbd
@kindex q @r{(Gnus Group mode)}
@findex gnus-group-exit
@item q
In the group buffer, update your @file{.newsrc} initialization file
and quit Gnus.

In the summary buffer, exit the current group and return to the
group buffer.  Thus, typing @kbd{q} twice quits Gnus.

@kindex L @r{(Gnus Group mode)}
@findex gnus-group-list-all-groups
@item L
In the group buffer, list all the groups available on your news
server (except those you have killed).  This may be a long list!

@kindex l @r{(Gnus Group mode)}
@findex gnus-group-list-groups
@item l
In the group buffer, list only the groups to which you subscribe and
which contain unread articles.

@kindex u @r{(Gnus Group mode)}
@findex gnus-group-unsubscribe-current-group
@cindex subscribe groups
@cindex unsubscribe groups
@item u
In the group buffer, unsubscribe from (or subscribe to) the group listed
in the line that point is on.  When you quit Gnus by typing @kbd{q},
Gnus lists in your @file{.newsrc} file which groups you have subscribed
to.  The next time you start Gnus, you won't see this group,
because Gnus normally displays only subscribed-to groups.

@kindex C-k @r{(Gnus)}
@findex gnus-group-kill-group
@item C-k
In the group buffer, ``kill'' the current line's group---don't
even list it in @file{.newsrc} from now on.  This affects future
Gnus sessions as well as the present session.

When you quit Gnus by typing @kbd{q}, Gnus writes information
in the file @file{.newsrc} describing all newsgroups except those you
have ``killed.''

@kindex SPC @r{(Gnus)}
@findex gnus-group-read-group
@item @key{SPC}
In the group buffer, select the group on the line under the cursor
and display the first unread article in that group.

@need 1000
In the summary buffer,

@itemize @bullet
@item
Select the article on the line under the cursor if none is selected.

@item
Scroll the text of the selected article (if there is one).

@item
Select the next unread article if at the end of the current article.
@end itemize

Thus, you can move through all the articles by repeatedly typing @key{SPC}.

@kindex DEL @r{(Gnus)}
@item @key{DEL}
In the group buffer, move point to the previous group containing
unread articles.

@findex gnus-summary-prev-page
In the summary buffer, scroll the text of the article backwards.

@kindex n @r{(Gnus)}
@findex gnus-group-next-unread-group
@findex gnus-summary-next-unread-article
@item n
Move point to the next unread group, or select the next unread article.

@kindex p @r{(Gnus)}
@findex gnus-group-prev-unread-group
@findex gnus-summary-prev-unread-article
@item p
Move point to the previous unread group, or select the previous
unread article.

@kindex C-n @r{(Gnus Group mode)}
@findex gnus-group-next-group
@kindex C-p @r{(Gnus Group mode)}
@findex gnus-group-prev-group
@kindex C-n @r{(Gnus Summary mode)}
@findex gnus-summary-next-subject
@kindex C-p @r{(Gnus Summary mode)}
@findex gnus-summary-prev-subject
@item C-n
@itemx C-p
Move point to the next or previous item, even if it is marked as read.
This does not select the article or group on that line.

@kindex s @r{(Gnus Summary mode)}
@findex gnus-summary-isearch-article
@item s
In the summary buffer, do an incremental search of the current text in
the article buffer, just as if you switched to the article buffer and
typed @kbd{C-s}.

@kindex M-s @r{(Gnus Summary mode)}
@findex gnus-summary-search-article-forward
@item M-s @var{regexp} @key{RET}
In the summary buffer, search forward for articles containing a match
for @var{regexp}.

@end table

@ignore
@node Where to Look
@subsection Where to Look Further

@c Too many references to the name of the manual if done with xref in TeX!
Gnus is powerful and customizable.  Here are references to a few
@ifnottex
additional topics:

@end ifnottex
@iftex
additional topics in @cite{The Gnus Manual}:

@itemize @bullet
@item
Follow discussions on specific topics.@*
See section ``Threading.''

@item
Read digests.  See section ``Document Groups.''

@item
Refer to and jump to the parent of the current article.@*
See section ``Finding the Parent.''

@item
Refer to articles by using Message-IDs included in the messages.@*
See section ``Article Keymap.''

@item
Save articles.  See section ``Saving Articles.''

@item
Have Gnus score articles according to various criteria, like author
name, subject, or string in the body of the articles.@*
See section ``Scoring.''

@item
Send an article to a newsgroup.@*
See section ``Composing Messages.''
@end itemize
@end iftex
@ifnottex
@itemize @bullet
@item
Follow discussions on specific topics.@*
@xref{Threading, , Reading Based on Conversation Threads,
gnus, The Gnus Manual}.

@item
Read digests. @xref{Document Groups, , , gnus, The Gnus Manual}.

@item
Refer to and jump to the parent of the current article.@*
@xref{Finding the Parent, , , gnus, The Gnus Manual}.

@item
Refer to articles by using Message-IDs included in the messages.@*
@xref{Article Keymap, , , gnus, The Gnus Manual}.

@item
Save articles. @xref{Saving Articles, , , gnus, The Gnus Manual}.

@item
Have Gnus score articles according to various criteria, like author
name, subject, or string in the body of the articles.@*
@xref{Scoring, , , gnus, The Gnus Manual}.

@item
Send an article to a newsgroup.@*
@xref{Composing Messages, , , gnus, The Gnus Manual}.
@end itemize
@end ifnottex
@end ignore

@node Shell, Emacs Server, Gnus, Top
@section Running Shell Commands from Emacs
@cindex subshell
@cindex shell commands

  Emacs has commands for passing single command lines to inferior shell
processes; it can also run a shell interactively with input and output
to an Emacs buffer named @samp{*shell*} or run a shell inside a terminal
emulator window.

@table @kbd
@item M-! @var{cmd} @key{RET}
Run the shell command line @var{cmd} and display the output
(@code{shell-command}).
@item M-| @var{cmd} @key{RET}
Run the shell command line @var{cmd} with region contents as input;
optionally replace the region with the output
(@code{shell-command-on-region}).
@item M-x shell
Run a subshell with input and output through an Emacs buffer.
You can then give commands interactively.
@item M-x term
Run a subshell with input and output through an Emacs buffer.
You can then give commands interactively.
Full terminal emulation is available.
@end table

  @kbd{M-x eshell} invokes a shell implemented entirely in Emacs.  It
is documented in a separate manual.  @xref{Top,Eshell,Eshell, eshell,
Eshell: The Emacs Shell}.

@menu
* Single Shell::           How to run one shell command and return.
* Interactive Shell::      Permanent shell taking input via Emacs.
* Shell Mode::             Special Emacs commands used with permanent shell.
* Shell Prompts::          Two ways to recognize shell prompts.
* History: Shell History.  Repeating previous commands in a shell buffer.
* Directory Tracking::     Keeping track when the subshell changes directory.
* Options: Shell Options.  Options for customizing Shell mode.
* Terminal emulator::      An Emacs window as a terminal emulator.
* Term Mode::              Special Emacs commands used in Term mode.
* Paging in Term::         Paging in the terminal emulator.
* Remote Host::            Connecting to another computer.
* Serial Terminal::        Connecting to a serial port.
@end menu

@node Single Shell
@subsection Single Shell Commands

@kindex M-!
@findex shell-command
  @kbd{M-!} (@code{shell-command}) reads a line of text using the
minibuffer and executes it as a shell command in a subshell made just
for that command.  Standard input for the command comes from the null
device.  If the shell command produces any output, the output appears
either in the echo area (if it is short), or in an Emacs buffer named
@samp{*Shell Command Output*}, which is displayed in another window
but not selected (if the output is long).

  For instance, one way to decompress a file @file{foo.gz} from Emacs
is to type @kbd{M-! gunzip foo.gz @key{RET}}.  That shell command
normally creates the file @file{foo} and produces no terminal output.

  A numeric argument, as in @kbd{M-1 M-!}, says to insert terminal
output into the current buffer instead of a separate buffer.  It puts
point before the output, and sets the mark after the output.  For
instance, @kbd{M-1 M-! gunzip < foo.gz @key{RET}} would insert the
uncompressed equivalent of @file{foo.gz} into the current buffer.

  If the shell command line ends in @samp{&}, it runs asynchronously.
For a synchronous shell command, @code{shell-command} returns the
command's exit status (0 means success), when it is called from a Lisp
program.  You do not get any status information for an asynchronous
command, since it hasn't finished yet when @code{shell-command} returns.

@kindex M-|
@findex shell-command-on-region
  @kbd{M-|} (@code{shell-command-on-region}) is like @kbd{M-!} but
passes the contents of the region as the standard input to the shell
command, instead of no input.  With a numeric argument, meaning insert
the output in the current buffer, it deletes the old region and the
output replaces it as the contents of the region.  It returns the
command's exit status, like @kbd{M-!}.

  One use for @kbd{M-|} is to run @code{gpg} to see what keys are in
the buffer.  For instance, if the buffer contains a GPG key, type
@kbd{C-x h M-| gpg @key{RET}} to feed the entire buffer contents to
the @code{gpg} program.  That program will ignore everything except
the encoded keys, and will output a list of the keys the buffer
contains.

@vindex shell-file-name
  Both @kbd{M-!} and @kbd{M-|} use @code{shell-file-name} to specify
the shell to use.  This variable is initialized based on your
@env{SHELL} environment variable when Emacs is started.  If the file
name is relative, Emacs searches the directories in the list
@code{exec-path}; this list is initialized based on the environment
variable @env{PATH} when Emacs is started.  Your @file{.emacs} file
can override either or both of these default initializations.

  Both @kbd{M-!} and @kbd{M-|} wait for the shell command to complete,
unless you end the command with @samp{&} to make it asynchronous.  To
stop waiting, type @kbd{C-g} to quit; that terminates the shell
command with the signal @code{SIGINT}---the same signal that @kbd{C-c}
normally generates in the shell.  Emacs then waits until the command
actually terminates.  If the shell command doesn't stop (because it
ignores the @code{SIGINT} signal), type @kbd{C-g} again; this sends
the command a @code{SIGKILL} signal which is impossible to ignore.

  Asynchronous commands ending in @samp{&} feed their output into
the buffer @samp{*Async Shell Command*}.  Output arrives in that
buffer regardless of whether it is visible in a window.

  To specify a coding system for @kbd{M-!} or @kbd{M-|}, use the command
@kbd{C-x @key{RET} c} immediately beforehand.  @xref{Communication Coding}.

@vindex shell-command-default-error-buffer
  Error output from these commands is normally intermixed with the
regular output.  But if the variable
@code{shell-command-default-error-buffer} has a string as value, and
it's the name of a buffer, @kbd{M-!} and @kbd{M-|} insert error output
before point in that buffer.

@node Interactive Shell
@subsection Interactive Inferior Shell

@findex shell
  To run a subshell interactively, putting its typescript in an Emacs
buffer, use @kbd{M-x shell}.  This creates (or reuses) a buffer named
@samp{*shell*} and runs a subshell with input coming from and output going
to that buffer.  That is to say, any ``terminal output'' from the subshell
goes into the buffer, advancing point, and any ``terminal input'' for
the subshell comes from text in the buffer.  To give input to the subshell,
go to the end of the buffer and type the input, terminated by @key{RET}.

  Emacs does not wait for the subshell to do anything.  You can switch
windows or buffers and edit them while the shell is waiting, or while it is
running a command.  Output from the subshell waits until Emacs has time to
process it; this happens whenever Emacs is waiting for keyboard input or
for time to elapse.

@cindex @code{comint-highlight-input} face
@cindex @code{comint-highlight-prompt} face
  Input lines, once you submit them, are displayed using the face
@code{comint-highlight-input}, and prompts are displayed using the
face @code{comint-highlight-prompt}.  This makes it easier to see
previous input lines in the buffer.  @xref{Faces}.

  To make multiple subshells, you can invoke @kbd{M-x shell} with a
prefix argument (e.g. @kbd{C-u M-x shell}), which will read a buffer
name and create (or reuse) a subshell in that buffer.  You can also
rename the @samp{*shell*} buffer using @kbd{M-x rename-uniquely}, then
create a new @samp{*shell*} buffer using plain @kbd{M-x shell}.
Subshells in different buffers run independently and in parallel.

@vindex explicit-shell-file-name
@cindex environment variables for subshells
@cindex @env{ESHELL} environment variable
@cindex @env{SHELL} environment variable
  The file name used to load the subshell is the value of the variable
@code{explicit-shell-file-name}, if that is non-@code{nil}.  Otherwise,
the environment variable @env{ESHELL} is used, or the environment
variable @env{SHELL} if there is no @env{ESHELL}.  If the file name
specified is relative, the directories in the list @code{exec-path} are
searched; this list is initialized based on the environment variable
@env{PATH} when Emacs is started.  Your @file{.emacs} file can override
either or both of these default initializations.

  Emacs sends the new shell the contents of the file
@file{~/.emacs_@var{shellname}} as input, if it exists, where
@var{shellname} is the name of the file that the shell was loaded
from.  For example, if you use bash, the file sent to it is
@file{~/.emacs_bash}.  If this file is not found, Emacs tries to fallback
on @file{~/.emacs.d/init_@var{shellname}.sh}.

  To specify a coding system for the shell, you can use the command
@kbd{C-x @key{RET} c} immediately before @kbd{M-x shell}.  You can
also change the coding system for a running subshell by typing
@kbd{C-x @key{RET} p} in the shell buffer.  @xref{Communication
Coding}.

@cindex @env{INSIDE_EMACS} environment variable
  Emacs sets the environment variable @env{INSIDE_EMACS} in the
subshell to a comma-separated list including the Emacs version.
Programs can check this variable to determine whether they are running
inside an Emacs subshell.

@cindex @env{EMACS} environment variable
  Emacs also sets the @env{EMACS} environment variable (to @code{t}) if
it is not already defined.  @strong{Warning:} This environment
variable is deprecated.  Programs that check this variable should be
changed to check @env{INSIDE_EMACS} instead.

@node Shell Mode
@subsection Shell Mode
@cindex Shell mode
@cindex mode, Shell

  Shell buffers use Shell mode, which defines several special keys
attached to the @kbd{C-c} prefix.  They are chosen to resemble the usual
editing and job control characters present in shells that are not under
Emacs, except that you must type @kbd{C-c} first.  Here is a complete list
of the special key bindings of Shell mode:

@table @kbd
@item @key{RET}
@kindex RET @r{(Shell mode)}
@findex comint-send-input
At end of buffer send line as input; otherwise, copy current line to
end of buffer and send it (@code{comint-send-input}).  Copying a line
in this way omits any prompt at the beginning of the line (text output
by programs preceding your input).  @xref{Shell Prompts}, for how
Shell mode recognizes prompts.

@item @key{TAB}
@kindex TAB @r{(Shell mode)}
@findex comint-dynamic-complete
Complete the command name or file name before point in the shell buffer
(@code{comint-dynamic-complete}).  @key{TAB} also completes history
references (@pxref{History References}) and environment variable names.

@vindex shell-completion-fignore
@vindex comint-completion-fignore
The variable @code{shell-completion-fignore} specifies a list of file
name extensions to ignore in Shell mode completion.  The default
setting is @code{nil}, but some users prefer @code{("~" "#" "%")} to
ignore file names ending in @samp{~}, @samp{#} or @samp{%}.  Other
related Comint modes use the variable @code{comint-completion-fignore}
instead.

@item M-?
@kindex M-? @r{(Shell mode)}
@findex comint-dynamic-list-filename@dots{}
Display temporarily a list of the possible completions of the file name
before point in the shell buffer
(@code{comint-dynamic-list-filename-completions}).

@item C-d
@kindex C-d @r{(Shell mode)}
@findex comint-delchar-or-maybe-eof
Either delete a character or send @acronym{EOF}
(@code{comint-delchar-or-maybe-eof}).  Typed at the end of the shell
buffer, @kbd{C-d} sends @acronym{EOF} to the subshell.  Typed at any other
position in the buffer, @kbd{C-d} deletes a character as usual.

@item C-c C-a
@kindex C-c C-a @r{(Shell mode)}
@findex comint-bol-or-process-mark
Move to the beginning of the line, but after the prompt if any
(@code{comint-bol-or-process-mark}).  If you repeat this command twice
in a row, the second time it moves back to the process mark, which is
the beginning of the input that you have not yet sent to the subshell.
(Normally that is the same place---the end of the prompt on this
line---but after @kbd{C-c @key{SPC}} the process mark may be in a
previous line.)

@item C-c @key{SPC}
Accumulate multiple lines of input, then send them together.  This
command inserts a newline before point, but does not send the preceding
text as input to the subshell---at least, not yet.  Both lines, the one
before this newline and the one after, will be sent together (along with
the newline that separates them), when you type @key{RET}.

@item C-c C-u
@kindex C-c C-u @r{(Shell mode)}
@findex comint-kill-input
Kill all text pending at end of buffer to be sent as input
(@code{comint-kill-input}).  If point is not at end of buffer,
this only kills the part of this text that precedes point.

@item C-c C-w
@kindex C-c C-w @r{(Shell mode)}
Kill a word before point (@code{backward-kill-word}).

@item C-c C-c
@kindex C-c C-c @r{(Shell mode)}
@findex comint-interrupt-subjob
Interrupt the shell or its current subjob if any
(@code{comint-interrupt-subjob}).  This command also kills
any shell input pending in the shell buffer and not yet sent.

@item C-c C-z
@kindex C-c C-z @r{(Shell mode)}
@findex comint-stop-subjob
Stop the shell or its current subjob if any (@code{comint-stop-subjob}).
This command also kills any shell input pending in the shell buffer and
not yet sent.

@item C-c C-\
@findex comint-quit-subjob
@kindex C-c C-\ @r{(Shell mode)}
Send quit signal to the shell or its current subjob if any
(@code{comint-quit-subjob}).  This command also kills any shell input
pending in the shell buffer and not yet sent.

@item C-c C-o
@kindex C-c C-o @r{(Shell mode)}
@findex comint-delete-output
Delete the last batch of output from a shell command
(@code{comint-delete-output}).  This is useful if a shell command spews
out lots of output that just gets in the way.  This command used to be
called @code{comint-kill-output}.

@item C-c C-s
@kindex C-c C-s @r{(Shell mode)}
@findex comint-write-output
Write the last batch of output from a shell command to a file
(@code{comint-write-output}).  With a prefix argument, the file is
appended to instead.  Any prompt at the end of the output is not
written.

@item C-c C-r
@itemx C-M-l
@kindex C-c C-r @r{(Shell mode)}
@kindex C-M-l @r{(Shell mode)}
@findex comint-show-output
Scroll to display the beginning of the last batch of output at the top
of the window; also move the cursor there (@code{comint-show-output}).

@item C-c C-e
@kindex C-c C-e @r{(Shell mode)}
@findex comint-show-maximum-output
Scroll to put the end of the buffer at the bottom of the window
(@code{comint-show-maximum-output}).

@item C-c C-f
@kindex C-c C-f @r{(Shell mode)}
@findex shell-forward-command
@vindex shell-command-regexp
Move forward across one shell command, but not beyond the current line
(@code{shell-forward-command}).  The variable @code{shell-command-regexp}
specifies how to recognize the end of a command.

@item C-c C-b
@kindex C-c C-b @r{(Shell mode)}
@findex shell-backward-command
Move backward across one shell command, but not beyond the current line
(@code{shell-backward-command}).

@item M-x dirs
Ask the shell what its current directory is, so that Emacs can agree
with the shell.

@item M-x send-invisible @key{RET} @var{text} @key{RET}
@findex send-invisible
Send @var{text} as input to the shell, after reading it without
echoing.  This is useful when a shell command runs a program that asks
for a password.

Please note that Emacs will not echo passwords by default.  If you
really want them to be echoed, evaluate the following Lisp
expression:

@example
(remove-hook 'comint-output-filter-functions
             'comint-watch-for-password-prompt)
@end example

@item M-x comint-continue-subjob
@findex comint-continue-subjob
Continue the shell process.  This is useful if you accidentally suspend
the shell process.@footnote{You should not suspend the shell process.
Suspending a subjob of the shell is a completely different matter---that
is normal practice, but you must use the shell to continue the subjob;
this command won't do it.}

@item M-x comint-strip-ctrl-m
@findex comint-strip-ctrl-m
Discard all control-M characters from the current group of shell output.
The most convenient way to use this command is to make it run
automatically when you get output from the subshell.  To do that,
evaluate this Lisp expression:

@example
(add-hook 'comint-output-filter-functions
          'comint-strip-ctrl-m)
@end example

@item M-x comint-truncate-buffer
@findex comint-truncate-buffer
This command truncates the shell buffer to a certain maximum number of
lines, specified by the variable @code{comint-buffer-maximum-size}.
Here's how to do this automatically each time you get output from the
subshell:

@example
(add-hook 'comint-output-filter-functions
          'comint-truncate-buffer)
@end example
@end table

@cindex Comint mode
@cindex mode, Comint
  Shell mode is a derivative of Comint mode, a general-purpose mode for
communicating with interactive subprocesses.  Most of the features of
Shell mode actually come from Comint mode, as you can see from the
command names listed above.  The special features of Shell mode include
the directory tracking feature, and a few user commands.

  Other Emacs features that use variants of Comint mode include GUD
(@pxref{Debuggers}) and @kbd{M-x run-lisp} (@pxref{External Lisp}).

@findex comint-run
  You can use @kbd{M-x comint-run} to execute any program of your choice
in a subprocess using unmodified Comint mode---without the
specializations of Shell mode.

@node Shell Prompts
@subsection Shell Prompts

@vindex shell-prompt-pattern
@vindex comint-prompt-regexp
@vindex comint-use-prompt-regexp
@cindex prompt, shell
  A prompt is text output by a program to show that it is ready to
accept new user input.  Normally, Comint mode (and thus Shell mode)
considers the prompt to be any text output by a program at the
beginning of an input line.  However, if the variable
@code{comint-use-prompt-regexp} is non-@code{nil}, then Comint mode
uses a regular expression to recognize prompts.  In Shell mode,
@code{shell-prompt-pattern} specifies the regular expression.

  The value of @code{comint-use-prompt-regexp} also affects many
motion and paragraph commands.  If the value is non-@code{nil}, the
general Emacs motion commands behave as they normally do in buffers
without special text properties.  However, if the value is @code{nil},
the default, then Comint mode divides the buffer into two types of
``fields'' (ranges of consecutive characters having the same
@code{field} text property): input and output.  Prompts are part of
the output.  Most Emacs motion commands do not cross field boundaries,
unless they move over multiple lines.  For instance, when point is in
input on the same line as a prompt, @kbd{C-a} puts point at the
beginning of the input if @code{comint-use-prompt-regexp} is
@code{nil} and at the beginning of the line otherwise.

  In Shell mode, only shell prompts start new paragraphs.  Thus, a
paragraph consists of a prompt and the input and output that follow
it.  However, if @code{comint-use-prompt-regexp} is @code{nil}, the
default, most paragraph commands do not cross field boundaries.  This
means that prompts, ranges of input, and ranges of non-prompt output
behave mostly like separate paragraphs; with this setting, numeric
arguments to most paragraph commands yield essentially undefined
behavior.  For the purpose of finding paragraph boundaries, Shell mode
uses @code{shell-prompt-pattern}, regardless of
@code{comint-use-prompt-regexp}.

@node Shell History
@subsection Shell Command History

  Shell buffers support three ways of repeating earlier commands.  You
can use keys like those used for the minibuffer history; these work
much as they do in the minibuffer, inserting text from prior commands
while point remains always at the end of the buffer.  You can move
through the buffer to previous inputs in their original place, then
resubmit them or copy them to the end.  Or you can use a
@samp{!}-style history reference.

@menu
* Ring: Shell Ring.             Fetching commands from the history list.
* Copy: Shell History Copying.  Moving to a command and then copying it.
* History References::          Expanding @samp{!}-style history references.
@end menu

@node Shell Ring
@subsubsection Shell History Ring

@table @kbd
@findex comint-previous-input
@kindex M-p @r{(Shell mode)}
@item M-p
@itemx C-@key{UP}
Fetch the next earlier old shell command.

@kindex M-n @r{(Shell mode)}
@findex comint-next-input
@item M-n
@itemx C-@key{DOWN}
Fetch the next later old shell command.

@kindex M-r @r{(Shell mode)}
@kindex M-s @r{(Shell mode)}
@findex comint-previous-matching-input
@findex comint-next-matching-input
@item M-r @var{regexp} @key{RET}
@itemx M-s @var{regexp} @key{RET}
Search backwards or forwards for old shell commands that match @var{regexp}.

@item C-c C-x
@kindex C-c C-x @r{(Shell mode)}
@findex comint-get-next-from-history
Fetch the next subsequent command from the history.

@item C-c .
@kindex C-c . @r{(Shell mode)}
@findex comint-input-previous-argument
Fetch one argument from an old shell command.

@item C-c C-l
@kindex C-c C-l @r{(Shell mode)}
@findex comint-dynamic-list-input-ring
Display the buffer's history of shell commands in another window
(@code{comint-dynamic-list-input-ring}).
@end table

  Shell buffers provide a history of previously entered shell commands.  To
reuse shell commands from the history, use the editing commands @kbd{M-p},
@kbd{M-n}, @kbd{M-r} and @kbd{M-s}.  These work just like the minibuffer
history commands except that they operate on the text at the end of the
shell buffer, where you would normally insert text to send to the shell.

  @kbd{M-p} fetches an earlier shell command to the end of the shell
buffer.  Successive use of @kbd{M-p} fetches successively earlier
shell commands, each replacing any text that was already present as
potential shell input.  @kbd{M-n} does likewise except that it finds
successively more recent shell commands from the buffer.
@kbd{C-@key{UP}} works like @kbd{M-p}, and @kbd{C-@key{DOWN}} like
@kbd{M-n}.

  The history search commands @kbd{M-r} and @kbd{M-s} read a regular
expression and search through the history for a matching command.  Aside
from the choice of which command to fetch, they work just like @kbd{M-p}
and @kbd{M-n}.  If you enter an empty regexp, these commands reuse the
same regexp used last time.

  When you find the previous input you want, you can resubmit it by
typing @key{RET}, or you can edit it first and then resubmit it if you
wish.  Any partial input you were composing before navigating the
history list is restored when you go to the beginning or end of the
history ring.

  Often it is useful to reexecute several successive shell commands that
were previously executed in sequence.  To do this, first find and
reexecute the first command of the sequence.  Then type @kbd{C-c C-x};
that will fetch the following command---the one that follows the command
you just repeated.  Then type @key{RET} to reexecute this command.  You
can reexecute several successive commands by typing @kbd{C-c C-x
@key{RET}} over and over.

  The command @kbd{C-c .}@: (@code{comint-input-previous-argument})
copies an individual argument from a previous command, like @kbd{ESC
.} in Bash.  The simplest use copies the last argument from the
previous shell command.  With a prefix argument @var{n}, it copies the
@var{n}th argument instead.  Repeating @kbd{C-c .} copies from an
earlier shell command instead, always using the same value of @var{n}
(don't give a prefix argument when you repeat the @kbd{C-c .}
command).

  These commands get the text of previous shell commands from a special
history list, not from the shell buffer itself.  Thus, editing the shell
buffer, or even killing large parts of it, does not affect the history
that these commands access.

@vindex shell-input-ring-file-name
  Some shells store their command histories in files so that you can
refer to commands from previous shell sessions.  Emacs reads
the command history file for your chosen shell, to initialize its own
command history.  The file name is @file{~/.bash_history} for bash,
@file{~/.sh_history} for ksh, and @file{~/.history} for other shells.

@node Shell History Copying
@subsubsection Shell History Copying

@table @kbd
@kindex C-c C-p @r{(Shell mode)}
@findex comint-previous-prompt
@item C-c C-p
Move point to the previous prompt (@code{comint-previous-prompt}).

@kindex C-c C-n @r{(Shell mode)}
@findex comint-next-prompt
@item C-c C-n
Move point to the following prompt (@code{comint-next-prompt}).

@kindex C-c RET @r{(Shell mode)}
@findex comint-copy-old-input
@item C-c @key{RET}
Copy the input command which point is in, inserting the copy at the end
of the buffer (@code{comint-copy-old-input}).  This is useful if you
move point back to a previous command.  After you copy the command, you
can submit the copy as input with @key{RET}.  If you wish, you can
edit the copy before resubmitting it.  If you use this command on an
output line, it copies that line to the end of the buffer.

@item Mouse-2
If @code{comint-use-prompt-regexp} is @code{nil} (the default), copy
the old input command that you click on, inserting the copy at the end
of the buffer (@code{comint-insert-input}).  If
@code{comint-use-prompt-regexp} is non-@code{nil}, or if the click is
not over old input, just yank as usual.
@end table

  Moving to a previous input and then copying it with @kbd{C-c
@key{RET}} or @kbd{Mouse-2} produces the same results---the same
buffer contents---that you would get by using @kbd{M-p} enough times
to fetch that previous input from the history list.  However, @kbd{C-c
@key{RET}} copies the text from the buffer, which can be different
from what is in the history list if you edit the input text in the
buffer after it has been sent.

@node History References
@subsubsection Shell History References
@cindex history reference

  Various shells including csh and bash support @dfn{history
references} that begin with @samp{!} and @samp{^}.  Shell mode
recognizes these constructs, and can perform the history substitution
for you.

  If you insert a history reference and type @key{TAB}, this searches
the input history for a matching command, performs substitution if
necessary, and places the result in the buffer in place of the history
reference.  For example, you can fetch the most recent command
beginning with @samp{mv} with @kbd{! m v @key{TAB}}.  You can edit the
command if you wish, and then resubmit the command to the shell by
typing @key{RET}.

@vindex comint-input-autoexpand
@findex comint-magic-space
  Shell mode can optionally expand history references in the buffer
when you send them to the shell.  To request this, set the variable
@code{comint-input-autoexpand} to @code{input}.  You can make
@key{SPC} perform history expansion by binding @key{SPC} to the
command @code{comint-magic-space}.

  Shell mode recognizes history references when they follow a prompt.
@xref{Shell Prompts}, for how Shell mode recognizes prompts.

@node Directory Tracking
@subsection Directory Tracking
@cindex directory tracking

@vindex shell-pushd-regexp
@vindex shell-popd-regexp
@vindex shell-cd-regexp
  Shell mode keeps track of @samp{cd}, @samp{pushd} and @samp{popd}
commands given to the inferior shell, so it can keep the
@samp{*shell*} buffer's default directory the same as the shell's
working directory.  It recognizes these commands syntactically, by
examining lines of input that are sent.

  If you use aliases for these commands, you can tell Emacs to
recognize them also.  For example, if the value of the variable
@code{shell-pushd-regexp} matches the beginning of a shell command
line, that line is regarded as a @code{pushd} command.  Change this
variable when you add aliases for @samp{pushd}.  Likewise,
@code{shell-popd-regexp} and @code{shell-cd-regexp} are used to
recognize commands with the meaning of @samp{popd} and @samp{cd}.
These commands are recognized only at the beginning of a shell command
line.

@ignore  @c This seems to have been deleted long ago.
@vindex shell-set-directory-error-hook
  If Emacs gets an error while trying to handle what it believes is a
@samp{cd}, @samp{pushd} or @samp{popd} command, it runs the hook
@code{shell-set-directory-error-hook} (@pxref{Hooks}).
@end ignore

@findex dirs
  If Emacs gets confused about changes in the current directory of the
subshell, use the command @kbd{M-x dirs} to ask the shell what its
current directory is.  This command works for shells that support the
most common command syntax; it may not work for unusual shells.

@findex dirtrack-mode
  You can also use @kbd{M-x dirtrack-mode} to enable (or disable) an
alternative method of tracking changes in the current directory.  This
method relies on your shell prompt containing the full current working
directory at all times.

@node Shell Options
@subsection Shell Mode Options

@vindex comint-scroll-to-bottom-on-input
  If the variable @code{comint-scroll-to-bottom-on-input} is
non-@code{nil}, insertion and yank commands scroll the selected window
to the bottom before inserting.  The default is @code{nil}.

@vindex comint-scroll-show-maximum-output
  If @code{comint-scroll-show-maximum-output} is non-@code{nil}, then
arrival of output when point is at the end tries to scroll the last
line of text to the bottom line of the window, showing as much useful
text as possible.  (This mimics the scrolling behavior of most
terminals.)  The default is @code{t}.

@vindex comint-move-point-for-output
  By setting @code{comint-move-point-for-output}, you can opt for
having point jump to the end of the buffer whenever output arrives---no
matter where in the buffer point was before.  If the value is
@code{this}, point jumps in the selected window.  If the value is
@code{all}, point jumps in each window that shows the Comint buffer.  If
the value is @code{other}, point jumps in all nonselected windows that
show the current buffer.  The default value is @code{nil}, which means
point does not jump to the end.

@vindex comint-prompt-read-only
  If you set @code{comint-prompt-read-only}, the prompts in the Comint
buffer are read-only.

@vindex comint-input-ignoredups
  The variable @code{comint-input-ignoredups} controls whether successive
identical inputs are stored in the input history.  A non-@code{nil}
value means to omit an input that is the same as the previous input.
The default is @code{nil}, which means to store each input even if it is
equal to the previous input.

@vindex comint-completion-addsuffix
@vindex comint-completion-recexact
@vindex comint-completion-autolist
  Three variables customize file name completion.  The variable
@code{comint-completion-addsuffix} controls whether completion inserts a
space or a slash to indicate a fully completed file or directory name
(non-@code{nil} means do insert a space or slash).
@code{comint-completion-recexact}, if non-@code{nil}, directs @key{TAB}
to choose the shortest possible completion if the usual Emacs completion
algorithm cannot add even a single character.
@code{comint-completion-autolist}, if non-@code{nil}, says to list all
the possible completions whenever completion is not exact.

@vindex shell-completion-execonly
  Command completion normally considers only executable files.
If you set @code{shell-completion-execonly} to @code{nil},
it considers nonexecutable files as well.

@findex shell-pushd-tohome
@findex shell-pushd-dextract
@findex shell-pushd-dunique
  You can configure the behavior of @samp{pushd}.  Variables control
whether @samp{pushd} behaves like @samp{cd} if no argument is given
(@code{shell-pushd-tohome}), pop rather than rotate with a numeric
argument (@code{shell-pushd-dextract}), and only add directories to the
directory stack if they are not already on it
(@code{shell-pushd-dunique}).  The values you choose should match the
underlying shell, of course.

  If you want Shell mode to handle color output from shell commands,
you can enable ANSI Color mode.  Here is how to do this:

@example
(add-hook 'shell-mode-hook 'ansi-color-for-comint-mode-on)
@end example

@node Terminal emulator
@subsection Emacs Terminal Emulator
@findex term

  To run a subshell in a terminal emulator, putting its typescript in
an Emacs buffer, use @kbd{M-x term}.  This creates (or reuses) a
buffer named @samp{*terminal*}, and runs a subshell with input coming
from your keyboard, and output going to that buffer.

  The terminal emulator uses Term mode, which has two input modes.  In
line mode, Term basically acts like Shell mode; see @ref{Shell Mode}.

  In char mode, each character is sent directly to the inferior
subshell, as ``terminal input.''  Any ``echoing'' of your input is the
responsibility of the subshell.  The sole exception is the terminal
escape character, which by default is @kbd{C-c} (@pxref{Term Mode}).
Any ``terminal output'' from the subshell goes into the buffer,
advancing point.

  Some programs (such as Emacs itself) need to control the appearance
on the terminal screen in detail.  They do this by sending special
control codes.  The exact control codes needed vary from terminal to
terminal, but nowadays most terminals and terminal emulators
(including @code{xterm}) understand the ANSI-standard (VT100-style)
escape sequences.  Term mode recognizes these escape sequences, and
handles each one appropriately, changing the buffer so that the
appearance of the window matches what it would be on a real terminal.
You can actually run Emacs inside an Emacs Term window.

  You can use Term mode to communicate with a device connected to a
serial port of your computer, see @ref{Serial Terminal}.

  The file name used to load the subshell is determined the same way
as for Shell mode.  To make multiple terminal emulators, rename the
buffer @samp{*terminal*} to something different using @kbd{M-x
rename-uniquely}, just as with Shell mode.

  Unlike Shell mode, Term mode does not track the current directory by
examining your input.  But some shells can tell Term what the current
directory is.  This is done automatically by @code{bash} version 1.15
and later.

@node Term Mode
@subsection Term Mode
@cindex Term mode
@cindex mode, Term

  The terminal emulator uses Term mode, which has two input modes.  In
line mode, Term basically acts like Shell mode; see @ref{Shell Mode}.
In char mode, each character is sent directly to the inferior
subshell, except for the Term escape character, normally @kbd{C-c}.

  To switch between line and char mode, use these commands:

@table @kbd
@kindex C-c C-j @r{(Term mode)}
@findex term-char-mode
@item C-c C-j
Switch to line mode.  Do nothing if already in line mode.

@kindex C-c C-k @r{(Term mode)}
@findex term-line-mode
@item C-c C-k
Switch to char mode.  Do nothing if already in char mode.
@end table

  The following commands are only available in char mode:

@table @kbd
@item C-c C-c
Send a literal @key{C-c} to the sub-shell.

@item C-c @var{char}
This is equivalent to @kbd{C-x @var{char}} in normal Emacs.  For
example, @kbd{C-c o} invokes the global binding of @kbd{C-x o}, which
is normally @samp{other-window}.
@end table

@node Paging in Term
@subsection Page-At-A-Time Output
@cindex page-at-a-time

  Term mode has a page-at-a-time feature.  When enabled it makes
output pause at the end of each screenful.

@table @kbd
@kindex C-c C-q @r{(Term mode)}
@findex term-pager-toggle
@item C-c C-q
Toggle the page-at-a-time feature.  This command works in both line
and char modes.  When page-at-a-time is enabled, the mode-line
displays the word @samp{page}.
@end table

  With page-at-a-time enabled, whenever Term receives more than a
screenful of output since your last input, it pauses, displaying
@samp{**MORE**} in the mode-line.  Type @key{SPC} to display the next
screenful of output.  Type @kbd{?} to see your other options.  The
interface is similar to the @code{more} program.

@node Remote Host
@subsection Remote Host Shell
@cindex remote host
@cindex connecting to remote host
@cindex Telnet
@cindex Rlogin

  You can login to a remote computer, using whatever commands you
would from a regular terminal (e.g.@: using the @code{telnet} or
@code{rlogin} commands), from a Term window.

  A program that asks you for a password will normally suppress
echoing of the password, so the password will not show up in the
buffer.  This will happen just as if you were using a real terminal,
if the buffer is in char mode.  If it is in line mode, the password is
temporarily visible, but will be erased when you hit return.  (This
happens automatically; there is no special password processing.)

  When you log in to a different machine, you need to specify the type
of terminal you're using, by setting the @env{TERM} environment
variable in the environment for the remote login command.  (If you use
bash, you do that by writing the variable assignment before the remote
login command, without separating comma.)  Terminal types @samp{ansi}
or @samp{vt100} will work on most systems.

@c   If you are talking to a Bourne-compatible
@c shell, and your system understands the @env{TERMCAP} variable,
@c you can use the command @kbd{M-x shell-send-termcap}, which
@c sends a string specifying the terminal type and size.
@c (This command is also useful after the window has changed size.)

@c You can of course run @samp{gdb} on that remote computer.  One useful
@c trick:  If you invoke gdb with the @code{--fullname} option,
@c it will send special commands to Emacs that will cause Emacs to
@c pop up the source files you're debugging.  This will work
@c whether or not gdb is running on a different computer than Emacs,
@c as long as Emacs can access the source files specified by gdb.

@ignore
  You cannot log in to a remote computer using the Shell mode.
@c (This will change when Shell is re-written to use Term.)
Instead, Emacs provides two commands for logging in to another computer
and communicating with it through an Emacs buffer using Comint mode:

@table @kbd
@item M-x telnet @key{RET} @var{hostname} @key{RET}
Set up a Telnet connection to the computer named @var{hostname}.
@item M-x rlogin @key{RET} @var{hostname} @key{RET}
Set up an Rlogin connection to the computer named @var{hostname}.
@end table

@findex telnet
  Use @kbd{M-x telnet} to set up a Telnet connection to another
computer.  (Telnet is the standard Internet protocol for remote login.)
It reads the host name of the other computer as an argument with the
minibuffer.  Once the connection is established, talking to the other
computer works like talking to a subshell: you can edit input with the
usual Emacs commands, and send it a line at a time by typing @key{RET}.
The output is inserted in the Telnet buffer interspersed with the input.

@findex rlogin
@vindex rlogin-explicit-args
  Use @kbd{M-x rlogin} to set up an Rlogin connection.  Rlogin is
another remote login communication protocol, essentially much like the
Telnet protocol but incompatible with it, and supported only by certain
systems.  Rlogin's advantages are that you can arrange not to have to
give your user name and password when communicating between two machines
you frequently use, and that you can make an 8-bit-clean connection.
(To do that in Emacs, set @code{rlogin-explicit-args} to @code{("-8")}
before you run Rlogin.)

  @kbd{M-x rlogin} sets up the default file directory of the Emacs
buffer to access the remote host via FTP (@pxref{File Names}), and it
tracks the shell commands that change the current directory, just like
Shell mode.

@findex rlogin-directory-tracking-mode
  There are two ways of doing directory tracking in an Rlogin
buffer---either with remote directory names
@file{/@var{host}:@var{dir}/} or with local names (that works if the
``remote'' machine shares file systems with your machine of origin).
You can use the command @code{rlogin-directory-tracking-mode} to switch
modes.  No argument means use remote directory names, a positive
argument means use local names, and a negative argument means turn
off directory tracking.

@end ignore

@node Serial Terminal
@subsection Serial Terminal
@cindex terminal, serial
@findex serial-term

  If you have a device connected to a serial port of your computer,
you can use Emacs to communicate with it.  @kbd{M-x serial-term} will
ask you for a serial port name and speed and will then open a new
window in @ref{Term Mode}.

  The speed of the serial port is measured in bits per second.  The
most common speed is 9600 bits per second.  You can change the speed
interactively by clicking on the mode line.

  A serial port can be configured even more by clicking on ``8N1'' in
the mode line.  By default, a serial port is configured as ``8N1'',
which means that each byte consists of 8 data bits, No parity check
bit, and 1 stopbit.

  When you have opened the serial port connection, you will see output
from the device in the window.  Also, what you type in the window is
sent to the device.

  If the speed or the configuration is wrong, you cannot communicate
with your device and will probably only see garbage output in the
window.

@node Emacs Server, Printing, Shell, Top
@section Using Emacs as a Server
@pindex emacsclient
@cindex Emacs as a server
@cindex server, using Emacs as
@cindex @env{EDITOR} environment variable

  Various programs such as @code{mail} can invoke your choice of editor
to edit a particular piece of text, such as a message that you are
sending.  By convention, most of these programs use the environment
variable @env{EDITOR} to specify which editor to run.  If you set
@env{EDITOR} to @samp{emacs}, they invoke Emacs---but in an
inconvenient fashion, by starting a new, separate Emacs process.  This
is inconvenient because it takes time and because the new Emacs process
doesn't share the buffers with any existing Emacs process.

  You can arrange to use your existing Emacs process as the editor for
programs like @code{mail} by using the Emacs client program and the
server that is part of Emacs.  Here is how.

@cindex @env{TEXEDIT} environment variable
@findex server-start
  First, the preparations.  Within Emacs, call the function
@code{server-start}.  (Your @file{.emacs} init file can do this
automatically if you add the expression @code{(server-start)} to it,
see @ref{Init File}.)  Then, outside Emacs, set the @env{EDITOR}
environment variable to @samp{emacsclient}.  (Note that some programs
use a different environment variable; for example, to make @TeX{} use
@samp{emacsclient}, you should set the @env{TEXEDIT} environment
variable to @samp{emacsclient +%d %s}.)

@pindex emacs.bash
@cindex Bash command to use Emacs server
  As an alternative to using @code{emacsclient}, the file
@file{etc/emacs.bash} defines a Bash command @code{edit} which will
communicate with a running Emacs session, or start one if none exist.

@kindex C-x #
@findex server-edit
  Now, whenever any program invokes your specified @env{EDITOR}
program, the effect is to send a message to your principal Emacs telling
it to visit a file.  (That's what the program @code{emacsclient} does.)
Emacs displays the buffer immediately and you can immediately begin
editing it in the already running Emacs session.

  When you've finished editing that buffer, type @kbd{C-x #}
(@code{server-edit}).  This saves the file and sends a message back to
the @code{emacsclient} program telling it to exit.  The programs that
use @env{EDITOR} wait for the ``editor'' (actually, @code{emacsclient})
to exit.  @kbd{C-x #} also checks for other pending external requests
to edit various files, and selects the next such file.

  You can switch to a server buffer manually if you wish; you don't
have to arrive at it with @kbd{C-x #}.  But @kbd{C-x #} is the way to
say that you are finished with one.

@vindex server-kill-new-buffers
@vindex server-temp-file-regexp
  Finishing with a server buffer also kills the buffer, unless it
already existed in the Emacs session before the server asked to create
it.  However, if you set @code{server-kill-new-buffers} to @code{nil},
then a different criterion is used: finishing with a server buffer
kills it if the file name matches the regular expression
@code{server-temp-file-regexp}.  This is set up to distinguish certain
``temporary'' files.

@vindex server-window
  If you set the variable @code{server-window} to a window or a frame,
@kbd{C-x #} displays the server buffer in that window or in that frame.

@vindex server-name
  You can run multiple Emacs servers on the same machine by giving
each one a unique ``server name'', using the variable
@code{server-name}.  For example, @kbd{M-x set-variable @key{RET}
server-name @key{RET} foo @key{RET}} sets the server name to
@samp{foo}.  The @code{emacsclient} program can specify a server by
name using the @samp{-s} option.  @xref{Invoking emacsclient}.

  While @code{mail} or another application is waiting for
@code{emacsclient} to finish, @code{emacsclient} does not read terminal
input.  So the terminal that @code{mail} was using is effectively
blocked for the duration.  In order to edit with your principal Emacs,
you need to be able to use it without using that terminal.  There are
three ways to do this:

@itemize @bullet
@item
Using a window system, run @code{mail} and the principal Emacs in two
separate windows.  While @code{mail} is waiting for @code{emacsclient},
the window where it was running is blocked, but you can use Emacs by
switching windows.

@item
Using virtual terminals, run @code{mail} in one virtual terminal
and run Emacs in another.

@item
Use Shell mode or Term mode in Emacs to run the other program such as
@code{mail}; then, @code{emacsclient} blocks only the subshell under
Emacs, and you can still use Emacs to edit the file.
@end itemize

  If you run @code{emacsclient} with the option @samp{--no-wait}, it
returns immediately without waiting for you to ``finish'' the buffer
in Emacs.  Note that server buffers created in this way are not killed
automatically when you finish with them.

@menu
* Invoking emacsclient:: Emacs client startup options.
@end menu

@node Invoking emacsclient,, Emacs Server, Emacs Server
@subsection Invoking @code{emacsclient}
@cindex @code{emacsclient} invocation and options

  To run the @code{emacsclient} program, specify file names as arguments,
and optionally line numbers as well, like this:

@example
emacsclient @r{@{}@r{[}+@var{line}@r{[}@var{column}@r{]}@r{]} @var{filename}@r{@}}@dots{}
@end example

@noindent
This tells Emacs to visit each of the specified files; if you specify a
line number for a certain file, Emacs moves to that line in the file.
If you specify a column number as well, Emacs puts point on that column
in the line.

  Ordinarily, @code{emacsclient} does not return until you use the
@kbd{C-x #} command on each of these buffers.  When that happens,
Emacs sends a message to the @code{emacsclient} program telling it to
return.

  If you invoke @code{emacsclient} for more than one file, the
additional client buffers are buried at the bottom of the buffer list
(@pxref{Buffers}).  If you call @kbd{C-x #} after you are done editing
a client buffer, the next client buffer is automatically selected.

  But if you use the option @samp{-n} or @samp{--no-wait} when running
@code{emacsclient}, then it returns immediately.  (You can take as
long as you like to edit the files in Emacs.)

  The option @samp{-a @var{command}} or
@samp{--alternate-editor=@var{command}} specifies a command to run if
@code{emacsclient} fails to contact Emacs.  This is useful when
running @code{emacsclient} in a script.  For example, the following
setting for the @env{EDITOR} environment variable will always give you
an editor, even if no Emacs server is running:

@example
EDITOR="emacsclient --alternate-editor emacs +%d %s"
@end example

@noindent
@cindex @env{ALTERNATE_EDITOR} environment variable
The environment variable @env{ALTERNATE_EDITOR} has the same effect, with
the value of the @samp{--alternate-editor} option taking precedence.

If you use several displays, you can tell Emacs on which display to
open the given files with the @samp{-d @var{display}} or
@samp{--display=@var{display}} option to @code{emacsclient}.  This is
handy when connecting from home to an Emacs session running on your
machine at your workplace.

If there is more than one Emacs server running, you can specify a
server name with the @samp{-s @var{name}} or
@samp{--socket-name=@var{name}} option to @code{emacsclient}.  (This
option is not supported on MS-Windows.)

You can also use @code{emacsclient} to execute any piece of Emacs Lisp
code, using the @samp{-e} or @samp{--eval} option.  When this option
is given, the rest of the arguments is interpreted as a list of
expressions to evaluate, not a list of files to visit.

@cindex @env{EMACS_SERVER_FILE} environment variable
When you start the Emacs server (by calling @code{server-start}),
Emacs creates a file with information about TCP connection to the
server: the host where Emacs is running, the port where it is
listening, and an authentication string.  @code{emacsclient} uses this
information if it needs to connect to the server via TCP.  By default,
the file goes in the @file{~/.emacs.d/server/} directory@footnote{On
MS-Windows, if @env{HOME} is not set or the TCP configuration file
cannot be found there, Emacs also looks for the file in the
@file{.emacs.d/server/} subdirectory of the directory pointed to by
the @env{APPDATA} environment variable.}.  You can specify the file
name to use with the @samp{-f @var{file}} or
@samp{--server-file=@var{file}} options, or by setting
@env{EMACS_SERVER_FILE} environment variable to the file name.

@node Printing, Sorting, Emacs Server, Top
@section Printing Hard Copies
@cindex hardcopy
@cindex printing

  Emacs provides commands for printing hard copies of either an entire
buffer or just part of one, with or without page headers.  You can
invoke the printing commands directly, as detailed in the following
section, or using the @samp{File} menu on the menu bar.  See also the
hardcopy commands of Dired (@pxref{Misc File Ops}) and the diary
(@pxref{Displaying the Diary}).

@table @kbd
@item M-x print-buffer
Print hardcopy of current buffer with page headings containing the file
name and page number.
@item M-x lpr-buffer
Print hardcopy of current buffer without page headings.
@item M-x print-region
Like @code{print-buffer} but print only the current region.
@item M-x lpr-region
Like @code{lpr-buffer} but print only the current region.
@end table

@findex print-buffer
@findex print-region
@findex lpr-buffer
@findex lpr-region
@vindex lpr-switches
  The hardcopy commands (aside from the PostScript commands) pass extra
switches to the @code{lpr} program based on the value of the variable
@code{lpr-switches}.  Its value should be a list of strings, each string
an option starting with @samp{-}.  For example, to specify a line width
of 80 columns for all the printing you do in Emacs, set
@code{lpr-switches} like this:

@example
(setq lpr-switches '("-w80"))
@end example

@vindex printer-name
  You can specify the printer to use by setting the variable
@code{printer-name}.

@vindex lpr-headers-switches
@vindex lpr-commands
@vindex lpr-add-switches
  The variable @code{lpr-command} specifies the name of the printer
program to run; the default value depends on your operating system type.
On most systems, the default is @code{"lpr"}.  The variable
@code{lpr-headers-switches} similarly specifies the extra switches to
use to make page headers.  The variable @code{lpr-add-switches} controls
whether to supply @samp{-T} and @samp{-J} options (suitable for
@code{lpr}) to the printer program: @code{nil} means don't add them.
@code{lpr-add-switches} should be @code{nil} if your printer program is
not compatible with @code{lpr}.

@menu
* PostScript::           Printing buffers or regions as PostScript.
* PostScript Variables:: Customizing the PostScript printing commands.
* Printing Package::     An optional advanced printing interface.
@end menu

@node PostScript, PostScript Variables,, Printing
@section PostScript Hardcopy

  These commands convert buffer contents to PostScript,
either printing it or leaving it in another Emacs buffer.

@table @kbd
@item M-x ps-print-buffer
Print hardcopy of the current buffer in PostScript form.
@item M-x ps-print-region
Print hardcopy of the current region in PostScript form.
@item M-x ps-print-buffer-with-faces
Print hardcopy of the current buffer in PostScript form, showing the
faces used in the text by means of PostScript features.
@item M-x ps-print-region-with-faces
Print hardcopy of the current region in PostScript form, showing the
faces used in the text.
@item M-x ps-spool-buffer
Generate PostScript for the current buffer text.
@item M-x ps-spool-region
Generate PostScript for the current region.
@item M-x ps-spool-buffer-with-faces
Generate PostScript for the current buffer, showing the faces used.
@item M-x ps-spool-region-with-faces
Generate PostScript for the current region, showing the faces used.
@item M-x handwrite
Generates/prints PostScript for the current buffer as if handwritten.
@end table

@findex ps-print-region
@findex ps-print-buffer
@findex ps-print-region-with-faces
@findex ps-print-buffer-with-faces
  The PostScript commands, @code{ps-print-buffer} and
@code{ps-print-region}, print buffer contents in PostScript form.  One
command prints the entire buffer; the other, just the region.  The
corresponding @samp{-with-faces} commands,
@code{ps-print-buffer-with-faces} and @code{ps-print-region-with-faces},
use PostScript features to show the faces (fonts and colors) in the text
properties of the text being printed.

  If you are using a color display, you can print a buffer of program
code with color highlighting by turning on Font-Lock mode in that
buffer, and using @code{ps-print-buffer-with-faces}.

@findex ps-spool-region
@findex ps-spool-buffer
@findex ps-spool-region-with-faces
@findex ps-spool-buffer-with-faces
  The commands whose names have @samp{spool} instead of @samp{print}
generate the PostScript output in an Emacs buffer instead of sending
it to the printer.

@findex handwrite
@cindex handwriting
@kbd{M-x handwrite} is more frivolous.  It generates a PostScript
rendition of the current buffer as a cursive handwritten document.  It
can be customized in group @code{handwrite}.  This function only
supports ISO 8859-1 characters.

@ifnottex
  The following section describes variables for customizing these commands.
@end ifnottex

@node PostScript Variables, Printing Package, PostScript, Printing
@section Variables for PostScript Hardcopy

@vindex ps-lpr-command
@vindex ps-lpr-switches
@vindex ps-printer-name
  All the PostScript hardcopy commands use the variables
@code{ps-lpr-command} and @code{ps-lpr-switches} to specify how to print
the output.  @code{ps-lpr-command} specifies the command name to run,
@code{ps-lpr-switches} specifies command line options to use, and
@code{ps-printer-name} specifies the printer.  If you don't set the
first two variables yourself, they take their initial values from
@code{lpr-command} and @code{lpr-switches}.  If @code{ps-printer-name}
is @code{nil}, @code{printer-name} is used.

@vindex ps-print-header
  The variable @code{ps-print-header} controls whether these commands
add header lines to each page---set it to @code{nil} to turn headers
off.

@cindex color emulation on black-and-white printers
@vindex ps-print-color-p
  If your printer doesn't support colors, you should turn off color
processing by setting @code{ps-print-color-p} to @code{nil}.  By
default, if the display supports colors, Emacs produces hardcopy output
with color information; on black-and-white printers, colors are emulated
with shades of gray.  This might produce illegible output, even if your
screen colors only use shades of gray.

@vindex ps-use-face-background
  By default, PostScript printing ignores the background colors of the
faces, unless the variable @code{ps-use-face-background} is
non-@code{nil}.  This is to avoid unwanted interference with the zebra
stripes and background image/text.

@vindex ps-paper-type
@vindex ps-page-dimensions-database
  The variable @code{ps-paper-type} specifies which size of paper to
format for; legitimate values include @code{a4}, @code{a3},
@code{a4small}, @code{b4}, @code{b5}, @code{executive}, @code{ledger},
@code{legal}, @code{letter}, @code{letter-small}, @code{statement},
@code{tabloid}.  The default is @code{letter}.  You can define
additional paper sizes by changing the variable
@code{ps-page-dimensions-database}.

@vindex ps-landscape-mode
  The variable @code{ps-landscape-mode} specifies the orientation of
printing on the page.  The default is @code{nil}, which stands for
``portrait'' mode.  Any non-@code{nil} value specifies ``landscape''
mode.

@vindex ps-number-of-columns
  The variable @code{ps-number-of-columns} specifies the number of
columns; it takes effect in both landscape and portrait mode.  The
default is 1.

@vindex ps-font-family
@vindex ps-font-size
@vindex ps-font-info-database
  The variable @code{ps-font-family} specifies which font family to use
for printing ordinary text.  Legitimate values include @code{Courier},
@code{Helvetica}, @code{NewCenturySchlbk}, @code{Palatino} and
@code{Times}.  The variable @code{ps-font-size} specifies the size of
the font for ordinary text.  It defaults to 8.5 points.

@vindex ps-multibyte-buffer
@cindex Intlfonts for PostScript printing
@cindex fonts for PostScript printing
  Emacs supports more scripts and characters than a typical PostScript
printer.  Thus, some of the characters in your buffer might not be
printable using the fonts built into your printer.  You can augment
the fonts supplied with the printer with those from the GNU Intlfonts
package, or you can instruct Emacs to use Intlfonts exclusively.  The
variable @code{ps-multibyte-buffer} controls this: the default value,
@code{nil}, is appropriate for printing @acronym{ASCII} and Latin-1
characters; a value of @code{non-latin-printer} is for printers which
have the fonts for @acronym{ASCII}, Latin-1, Japanese, and Korean
characters built into them.  A value of @code{bdf-font} arranges for
the BDF fonts from the Intlfonts package to be used for @emph{all}
characters.  Finally, a value of @code{bdf-font-except-latin}
instructs the printer to use built-in fonts for @acronym{ASCII} and Latin-1
characters, and Intlfonts BDF fonts for the rest.

@vindex bdf-directory-list
  To be able to use the BDF fonts, Emacs needs to know where to find
them.  The variable @code{bdf-directory-list} holds the list of
directories where Emacs should look for the fonts; the default value
includes a single directory @file{/usr/local/share/emacs/fonts/bdf}.

  Many other customization variables for these commands are defined and
described in the Lisp files @file{ps-print.el} and @file{ps-mule.el}.

@node Printing Package,, PostScript Variables, Printing
@section Printing Package
@cindex Printing package

  The basic Emacs facilities for printing hardcopy can be extended
using the Printing package.  This provides an easy-to-use interface
for choosing what to print, previewing PostScript files before
printing, and setting various printing options such as print headers,
landscape or portrait modes, duplex modes, and so forth.  On GNU/Linux
or Unix systems, the Printing package relies on the @file{gs} and
@file{gv} utilities, which are distributed as part of the GhostScript
program.  On MS-Windows, the @file{gstools} port of Ghostscript can be
used.

@findex pr-interface
  To use the Printing package, add @code{(require 'printing)} to your
init file (@pxref{Init File}), followed by @code{(pr-update-menus)}.
This function replaces the usual printing commands in the menu bar
with a @samp{Printing} submenu that contains various printing options.
You can also type @kbd{M-x pr-interface RET}; this creates a
@samp{*Printing Interface*} buffer, similar to a customization buffer,
where you can set the printing options.  After selecting what and how
to print, you start the print job using the @samp{Print} button (click
@kbd{mouse-2} on it, or move point over it and type @kbd{RET}).  For
further information on the various options, use the @samp{Interface
Help} button.

@node Sorting, Narrowing, Printing, Top
@section Sorting Text
@cindex sorting

  Emacs provides several commands for sorting text in the buffer.  All
operate on the contents of the region.
They divide the text of the region into many @dfn{sort records},
identify a @dfn{sort key} for each record, and then reorder the records
into the order determined by the sort keys.  The records are ordered so
that their keys are in alphabetical order, or, for numeric sorting, in
numeric order.  In alphabetic sorting, all upper-case letters `A' through
`Z' come before lower-case `a', in accord with the @acronym{ASCII} character
sequence.

  The various sort commands differ in how they divide the text into sort
records and in which part of each record is used as the sort key.  Most of
the commands make each line a separate sort record, but some commands use
paragraphs or pages as sort records.  Most of the sort commands use each
entire sort record as its own sort key, but some use only a portion of the
record as the sort key.

@findex sort-lines
@findex sort-paragraphs
@findex sort-pages
@findex sort-fields
@findex sort-numeric-fields
@vindex sort-numeric-base
@table @kbd
@item M-x sort-lines
Divide the region into lines, and sort by comparing the entire
text of a line.  A numeric argument means sort into descending order.

@item M-x sort-paragraphs
Divide the region into paragraphs, and sort by comparing the entire
text of a paragraph (except for leading blank lines).  A numeric
argument means sort into descending order.

@item M-x sort-pages
Divide the region into pages, and sort by comparing the entire
text of a page (except for leading blank lines).  A numeric
argument means sort into descending order.

@item M-x sort-fields
Divide the region into lines, and sort by comparing the contents of
one field in each line.  Fields are defined as separated by
whitespace, so the first run of consecutive non-whitespace characters
in a line constitutes field 1, the second such run constitutes field
2, etc.

Specify which field to sort by with a numeric argument: 1 to sort by
field 1, etc.  A negative argument means count fields from the right
instead of from the left; thus, minus 1 means sort by the last field.
If several lines have identical contents in the field being sorted, they
keep the same relative order that they had in the original buffer.

@item M-x sort-numeric-fields
Like @kbd{M-x sort-fields} except the specified field is converted
to an integer for each line, and the numbers are compared.  @samp{10}
comes before @samp{2} when considered as text, but after it when
considered as a number.  By default, numbers are interpreted according
to @code{sort-numeric-base}, but numbers beginning with @samp{0x} or
@samp{0} are interpreted as hexadecimal and octal, respectively.

@item M-x sort-columns
Like @kbd{M-x sort-fields} except that the text within each line
used for comparison comes from a fixed range of columns.  See below
for an explanation.

@item M-x reverse-region
Reverse the order of the lines in the region.  This is useful for
sorting into descending order by fields or columns, since those sort
commands do not have a feature for doing that.
@end table

  For example, if the buffer contains this:

@smallexample
On systems where clash detection (locking of files being edited) is
implemented, Emacs also checks the first time you modify a buffer
whether the file has changed on disk since it was last visited or
saved.  If it has, you are asked to confirm that you want to change
the buffer.
@end smallexample

@noindent
applying @kbd{M-x sort-lines} to the entire buffer produces this:

@smallexample
On systems where clash detection (locking of files being edited) is
implemented, Emacs also checks the first time you modify a buffer
saved.  If it has, you are asked to confirm that you want to change
the buffer.
whether the file has changed on disk since it was last visited or
@end smallexample

@noindent
where the upper-case @samp{O} sorts before all lower-case letters.  If
you use @kbd{C-u 2 M-x sort-fields} instead, you get this:

@smallexample
implemented, Emacs also checks the first time you modify a buffer
saved.  If it has, you are asked to confirm that you want to change
the buffer.
On systems where clash detection (locking of files being edited) is
whether the file has changed on disk since it was last visited or
@end smallexample

@noindent
where the sort keys were @samp{Emacs}, @samp{If}, @samp{buffer},
@samp{systems} and @samp{the}.

@findex sort-columns
  @kbd{M-x sort-columns} requires more explanation.  You specify the
columns by putting point at one of the columns and the mark at the other
column.  Because this means you cannot put point or the mark at the
beginning of the first line of the text you want to sort, this command
uses an unusual definition of ``region'': all of the line point is in is
considered part of the region, and so is all of the line the mark is in,
as well as all the lines in between.

  For example, to sort a table by information found in columns 10 to 15,
you could put the mark on column 10 in the first line of the table, and
point on column 15 in the last line of the table, and then run
@code{sort-columns}.  Equivalently, you could run it with the mark on
column 15 in the first line and point on column 10 in the last line.

  This can be thought of as sorting the rectangle specified by point and
the mark, except that the text on each line to the left or right of the
rectangle moves along with the text inside the rectangle.
@xref{Rectangles}.

@vindex sort-fold-case
  Many of the sort commands ignore case differences when comparing, if
@code{sort-fold-case} is non-@code{nil}.

@node Narrowing, Two-Column, Sorting, Top
@section Narrowing
@cindex widening
@cindex restriction
@cindex narrowing
@cindex accessible portion

  @dfn{Narrowing} means focusing in on some portion of the buffer,
making the rest temporarily inaccessible.  The portion which you can
still get to is called the @dfn{accessible portion}.  Canceling the
narrowing, which makes the entire buffer once again accessible, is
called @dfn{widening}.  The bounds of narrowing in effect in a buffer
are called the buffer's @dfn{restriction}.

  Narrowing can make it easier to concentrate on a single subroutine or
paragraph by eliminating clutter.  It can also be used to limit the
range of operation of a replace command or repeating keyboard macro.

@table @kbd
@item C-x n n
Narrow down to between point and mark (@code{narrow-to-region}).
@item C-x n w
Widen to make the entire buffer accessible again (@code{widen}).
@item C-x n p
Narrow down to the current page (@code{narrow-to-page}).
@item C-x n d
Narrow down to the current defun (@code{narrow-to-defun}).
@end table

  When you have narrowed down to a part of the buffer, that part appears
to be all there is.  You can't see the rest, you can't move into it
(motion commands won't go outside the accessible part), you can't change
it in any way.  However, it is not gone, and if you save the file all
the inaccessible text will be saved.  The word @samp{Narrow} appears in
the mode line whenever narrowing is in effect.

@kindex C-x n n
@findex narrow-to-region
  The primary narrowing command is @kbd{C-x n n} (@code{narrow-to-region}).
It sets the current buffer's restrictions so that the text in the current
region remains accessible, but all text before the region or after the
region is inaccessible.  Point and mark do not change.

@kindex C-x n p
@findex narrow-to-page
@kindex C-x n d
@findex narrow-to-defun
  Alternatively, use @kbd{C-x n p} (@code{narrow-to-page}) to narrow
down to the current page.  @xref{Pages}, for the definition of a page.
@kbd{C-x n d} (@code{narrow-to-defun}) narrows down to the defun
containing point (@pxref{Defuns}).

@kindex C-x n w
@findex widen
  The way to cancel narrowing is to widen with @kbd{C-x n w}
(@code{widen}).  This makes all text in the buffer accessible again.

  You can get information on what part of the buffer you are narrowed down
to using the @kbd{C-x =} command.  @xref{Position Info}.

  Because narrowing can easily confuse users who do not understand it,
@code{narrow-to-region} is normally a disabled command.  Attempting to use
this command asks for confirmation and gives you the option of enabling it;
if you enable the command, confirmation will no longer be required for
it.  @xref{Disabling}.

@node Two-Column, Editing Binary Files, Narrowing, Top
@section Two-Column Editing
@cindex two-column editing
@cindex splitting columns
@cindex columns, splitting

  Two-column mode lets you conveniently edit two side-by-side columns of
text.  It uses two side-by-side windows, each showing its own
buffer.

  There are three ways to enter two-column mode:

@table @asis
@item @kbd{@key{F2} 2} or @kbd{C-x 6 2}
@kindex F2 2
@kindex C-x 6 2
@findex 2C-two-columns
Enter two-column mode with the current buffer on the left, and on the
right, a buffer whose name is based on the current buffer's name
(@code{2C-two-columns}).  If the right-hand buffer doesn't already
exist, it starts out empty; the current buffer's contents are not
changed.

This command is appropriate when the current buffer is empty or contains
just one column and you want to add another column.

@item @kbd{@key{F2} s} or @kbd{C-x 6 s}
@kindex F2 s
@kindex C-x 6 s
@findex 2C-split
Split the current buffer, which contains two-column text, into two
buffers, and display them side by side (@code{2C-split}).  The current
buffer becomes the left-hand buffer, but the text in the right-hand
column is moved into the right-hand buffer.  The current column
specifies the split point.  Splitting starts with the current line and
continues to the end of the buffer.

This command is appropriate when you have a buffer that already contains
two-column text, and you wish to separate the columns temporarily.

@item @kbd{@key{F2} b @var{buffer} @key{RET}}
@itemx @kbd{C-x 6 b @var{buffer} @key{RET}}
@kindex F2 b
@kindex C-x 6 b
@findex 2C-associate-buffer
Enter two-column mode using the current buffer as the left-hand buffer,
and using buffer @var{buffer} as the right-hand buffer
(@code{2C-associate-buffer}).
@end table

  @kbd{@key{F2} s} or @kbd{C-x 6 s} looks for a column separator, which
is a string that appears on each line between the two columns.  You can
specify the width of the separator with a numeric argument to
@kbd{@key{F2} s}; that many characters, before point, constitute the
separator string.  By default, the width is 1, so the column separator
is the character before point.

  When a line has the separator at the proper place, @kbd{@key{F2} s}
puts the text after the separator into the right-hand buffer, and
deletes the separator.  Lines that don't have the column separator at
the proper place remain unsplit; they stay in the left-hand buffer, and
the right-hand buffer gets an empty line to correspond.  (This is the
way to write a line that ``spans both columns while in two-column
mode'': write it in the left-hand buffer, and put an empty line in the
right-hand buffer.)

@kindex F2 RET
@kindex C-x 6 RET
@findex 2C-newline
  The command @kbd{C-x 6 @key{RET}} or @kbd{@key{F2} @key{RET}}
(@code{2C-newline}) inserts a newline in each of the two buffers at
corresponding positions.  This is the easiest way to add a new line to
the two-column text while editing it in split buffers.

@kindex F2 1
@kindex C-x 6 1
@findex 2C-merge
  When you have edited both buffers as you wish, merge them with
@kbd{@key{F2} 1} or @kbd{C-x 6 1} (@code{2C-merge}).  This copies the
text from the right-hand buffer as a second column in the other buffer.
To go back to two-column editing, use @kbd{@key{F2} s}.

@kindex F2 d
@kindex C-x 6 d
@findex 2C-dissociate
  Use @kbd{@key{F2} d} or @kbd{C-x 6 d} to dissociate the two buffers,
leaving each as it stands (@code{2C-dissociate}).  If the other buffer,
the one not current when you type @kbd{@key{F2} d}, is empty,
@kbd{@key{F2} d} kills it.

@node Editing Binary Files, Saving Emacs Sessions, Two-Column, Top
@section Editing Binary Files

@cindex Hexl mode
@cindex mode, Hexl
@cindex editing binary files
@cindex hex editing
  There is a special major mode for editing binary files: Hexl mode.  To
use it, use @kbd{M-x hexl-find-file} instead of @kbd{C-x C-f} to visit
the file.  This command converts the file's contents to hexadecimal and
lets you edit the translation.  When you save the file, it is converted
automatically back to binary.

  You can also use @kbd{M-x hexl-mode} to translate an existing buffer
into hex.  This is useful if you visit a file normally and then discover
it is a binary file.

  Ordinary text characters overwrite in Hexl mode.  This is to reduce
the risk of accidentally spoiling the alignment of data in the file.
There are special commands for insertion.  Here is a list of the
commands of Hexl mode:

@c I don't think individual index entries for these commands are useful--RMS.
@table @kbd
@item C-M-d
Insert a byte with a code typed in decimal.

@item C-M-o
Insert a byte with a code typed in octal.

@item C-M-x
Insert a byte with a code typed in hex.

@item C-x [
Move to the beginning of a 1k-byte ``page.''

@item C-x ]
Move to the end of a 1k-byte ``page.''

@item M-g
Move to an address specified in hex.

@item M-j
Move to an address specified in decimal.

@item C-c C-c
Leave Hexl mode, going back to the major mode this buffer had before you
invoked @code{hexl-mode}.
@end table

@noindent
Other Hexl commands let you insert strings (sequences) of binary
bytes, move by @code{short}s or @code{int}s, etc.; type @kbd{C-h a
hexl-@key{RET}} for details.


@node Saving Emacs Sessions, Recursive Edit, Editing Binary Files, Top
@section Saving Emacs Sessions
@cindex saving sessions
@cindex restore session
@cindex remember editing session
@cindex reload files
@cindex desktop

   Use the desktop library to save the state of Emacs from one session
to another.  Once you save the Emacs @dfn{desktop}---the buffers,
their file names, major modes, buffer positions, and so on---then
subsequent Emacs sessions reload the saved desktop.

@findex desktop-save
@vindex desktop-save-mode
  You can save the desktop manually with the command @kbd{M-x
desktop-save}.  You can also enable automatic saving of the desktop
when you exit Emacs, and automatic restoration of the last saved
desktop when Emacs starts: use the Customization buffer (@pxref{Easy
Customization}) to set @code{desktop-save-mode} to @code{t} for future
sessions, or add this line in your @file{~/.emacs} file:

@example
(desktop-save-mode 1)
@end example

@findex desktop-change-dir
@findex desktop-revert
  If you turn on @code{desktop-save-mode} in your @file{~/.emacs},
then when Emacs starts, it looks for a saved desktop in the current
directory.  Thus, you can have separate saved desktops in different
directories, and the starting directory determines which one Emacs
reloads.  You can save the current desktop and reload one saved in
another directory by typing @kbd{M-x desktop-change-dir}.  Typing
@kbd{M-x desktop-revert} reverts to the desktop previously reloaded.

  Specify the option @samp{--no-desktop} on the command line when you
don't want it to reload any saved desktop.  This turns off
@code{desktop-save-mode} for the current session.  Starting Emacs with
the @samp{--no-init-file} option also disables desktop reloading,
since it bypasses the @file{.emacs} init file, where
@code{desktop-save-mode} is usually turned on.

@vindex desktop-restore-eager
  By default, all the buffers in the desktop are restored at one go.
However, this may be slow if there are a lot of buffers in the
desktop.  You can specify the maximum number of buffers to restore
immediately with the variable @code{desktop-restore-eager}; the
remaining buffers are restored ``lazily,'' when Emacs is idle.

@findex desktop-clear
@vindex desktop-globals-to-clear
@vindex desktop-clear-preserve-buffers-regexp
  Type @kbd{M-x desktop-clear} to empty the Emacs desktop.  This kills
all buffers except for internal ones, and clears the global variables
listed in @code{desktop-globals-to-clear}.  If you want this to
preserve certain buffers, customize the variable
@code{desktop-clear-preserve-buffers-regexp}, whose value is a regular
expression matching the names of buffers not to kill.

  If you want to save minibuffer history from one session to
another, use the @code{savehist} library.

@node Recursive Edit, Emulation, Saving Emacs Sessions, Top
@section Recursive Editing Levels
@cindex recursive editing level
@cindex editing level, recursive

  A @dfn{recursive edit} is a situation in which you are using Emacs
commands to perform arbitrary editing while in the middle of another
Emacs command.  For example, when you type @kbd{C-r} inside of a
@code{query-replace}, you enter a recursive edit in which you can change
the current buffer.  On exiting from the recursive edit, you go back to
the @code{query-replace}.

@kindex C-M-c
@findex exit-recursive-edit
@cindex exiting recursive edit
  @dfn{Exiting} the recursive edit means returning to the unfinished
command, which continues execution.  The command to exit is @kbd{C-M-c}
(@code{exit-recursive-edit}).

  You can also @dfn{abort} the recursive edit.  This is like exiting,
but also quits the unfinished command immediately.  Use the command
@kbd{C-]} (@code{abort-recursive-edit}) to do this.  @xref{Quitting}.

  The mode line shows you when you are in a recursive edit by displaying
square brackets around the parentheses that always surround the major and
minor mode names.  Every window's mode line shows this in the same way,
since being in a recursive edit is true of Emacs as a whole rather than
any particular window or buffer.

  It is possible to be in recursive edits within recursive edits.  For
example, after typing @kbd{C-r} in a @code{query-replace}, you may type a
command that enters the debugger.  This begins a recursive editing level
for the debugger, within the recursive editing level for @kbd{C-r}.
Mode lines display a pair of square brackets for each recursive editing
level currently in progress.

  Exiting the inner recursive edit (such as with the debugger @kbd{c}
command) resumes the command running in the next level up.  When that
command finishes, you can then use @kbd{C-M-c} to exit another recursive
editing level, and so on.  Exiting applies to the innermost level only.
Aborting also gets out of only one level of recursive edit; it returns
immediately to the command level of the previous recursive edit.  If you
wish, you can then abort the next recursive editing level.

  Alternatively, the command @kbd{M-x top-level} aborts all levels of
recursive edits, returning immediately to the top-level command reader.

  The text being edited inside the recursive edit need not be the same text
that you were editing at top level.  It depends on what the recursive edit
is for.  If the command that invokes the recursive edit selects a different
buffer first, that is the buffer you will edit recursively.  In any case,
you can switch buffers within the recursive edit in the normal manner (as
long as the buffer-switching keys have not been rebound).  You could
probably do all the rest of your editing inside the recursive edit,
visiting files and all.  But this could have surprising effects (such as
stack overflow) from time to time.  So remember to exit or abort the
recursive edit when you no longer need it.

  In general, we try to minimize the use of recursive editing levels in
GNU Emacs.  This is because they constrain you to ``go back'' in a
particular order---from the innermost level toward the top level.  When
possible, we present different activities in separate buffers so that
you can switch between them as you please.  Some commands switch to a
new major mode which provides a command to switch back.  These
approaches give you more flexibility to go back to unfinished tasks in
the order you choose.

@node Emulation, Hyperlinking, Recursive Edit, Top
@section Emulation
@cindex emulating other editors
@cindex other editors
@cindex EDT
@cindex vi
@cindex PC key bindings
@cindex scrolling all windows
@cindex PC selection
@cindex Motif key bindings
@cindex Macintosh key bindings
@cindex WordStar

  GNU Emacs can be programmed to emulate (more or less) most other
editors.  Standard facilities can emulate these:

@table @asis
@item CRiSP/Brief (PC editor)
@findex crisp-mode
@vindex crisp-override-meta-x
@findex scroll-all-mode
@cindex CRiSP mode
@cindex Brief emulation
@cindex emulation of Brief
@cindex mode, CRiSP
You can turn on key bindings to emulate the CRiSP/Brief editor with
@kbd{M-x crisp-mode}.  Note that this rebinds @kbd{M-x} to exit Emacs
unless you set the variable @code{crisp-override-meta-x}.  You can
also use the command @kbd{M-x scroll-all-mode} or set the variable
@code{crisp-load-scroll-all} to emulate CRiSP's scroll-all feature
(scrolling all windows together).

@item EDT (DEC VMS editor)
@findex edt-emulation-on
@findex edt-emulation-off
Turn on EDT emulation with the command @kbd{M-x edt-emulation-on},
while @kbd{M-x edt-emulation-off} restores normal Emacs command
bindings.

Most of the EDT emulation commands are keypad keys, and most standard
Emacs key bindings are still available.  The EDT emulation rebindings
are done in the global keymap, so there is no problem switching
buffers or major modes while in EDT emulation.

@item TPU (DEC VMS editor)
@findex tpu-edt-on
@cindex TPU
@kbd{M-x tpu-edt-on} turns on emulation of the TPU editor emulating EDT.

@item vi (Berkeley editor)
@findex viper-mode
Viper is the newest emulator for vi.  It implements several levels of
emulation; level 1 is closest to vi itself, while level 5 departs
somewhat from strict emulation to take advantage of the capabilities of
Emacs.  To invoke Viper, type @kbd{M-x viper-mode}; it will guide you
the rest of the way and ask for the emulation level.  @inforef{Top,
Viper, viper}.

@item vi (another emulator)
@findex vi-mode
@kbd{M-x vi-mode} enters a major mode that replaces the previously
established major mode.  All of the vi commands that, in real vi, enter
``input'' mode are programmed instead to return to the previous major
mode.  Thus, ordinary Emacs serves as vi's ``input'' mode.

Because vi emulation works through major modes, it does not work
to switch buffers during emulation.  Return to normal Emacs first.

If you plan to use vi emulation much, you probably want to bind a key
to the @code{vi-mode} command.

@item vi (alternate emulator)
@findex vip-mode
@kbd{M-x vip-mode} invokes another vi emulator, said to resemble real vi
more thoroughly than @kbd{M-x vi-mode}.  ``Input'' mode in this emulator
is changed from ordinary Emacs so you can use @key{ESC} to go back to
emulated vi command mode.  To get from emulated vi command mode back to
ordinary Emacs, type @kbd{C-z}.

This emulation does not work through major modes, and it is possible
to switch buffers in various ways within the emulator.  It is not
so necessary to assign a key to the command @code{vip-mode} as
it is with @code{vi-mode} because terminating insert mode does
not use it.

@inforef{Top, VIP, vip}, for full information.

@item WordStar (old wordprocessor)
@findex wordstar-mode
@kbd{M-x wordstar-mode} provides a major mode with WordStar-like
key bindings.
@end table

@node Hyperlinking, Dissociated Press, Emulation, Top
@section Hyperlinking and Navigation Features

@cindex hyperlinking
@cindex navigation
  Various modes documented elsewhere have hypertext features so that
you can follow links, usually by clicking @kbd{Mouse-2} on the link or
typing @key{RET} while point is on the link.  Clicking @kbd{Mouse-1}
quickly on the link also follows it.  (Hold @kbd{Mouse-1} for longer
if you want to set point instead.)

  Info mode, Help mode and the Dired-like modes are examples of modes
that have links in the buffer.  The Tags facility links between uses
and definitions in source files, see @ref{Tags}.  Imenu provides
navigation amongst items indexed in the current buffer, see
@ref{Imenu}.  Info-lookup provides mode-specific lookup of definitions
in Info indexes, see @ref{Documentation}.  Speedbar maintains a frame
in which links to files, and locations in files are displayed, see
@ref{Speedbar}.

  Other non-mode-specific facilities described in this section enable
following links from the current buffer in a context-sensitive
fashion.

@menu
* Browse-URL::                  Following URLs.
* Goto-address::                Activating URLs.
* FFAP::                        Finding files etc. at point.
@end menu

@node Browse-URL
@subsection  Following URLs
@cindex World Wide Web
@cindex Web
@findex browse-url
@findex browse-url-at-point
@findex browse-url-at-mouse
@cindex Browse-URL
@cindex URLs

@table @kbd
@item M-x browse-url @key{RET} @var{url} @key{RET}
Load a URL into a Web browser.
@end table

The Browse-URL package provides facilities for following URLs specifying
links on the World Wide Web.  Usually this works by invoking a web
browser, but you can, for instance, arrange to invoke @code{compose-mail}
from @samp{mailto:} URLs.

  The general way to use this feature is to type @kbd{M-x browse-url},
which displays a specified URL.  If point is located near a plausible
URL, that URL is used as the default.  Other commands are available
which you might like to bind to keys, such as
@code{browse-url-at-point} and @code{browse-url-at-mouse}.

@vindex browse-url-browser-function
  You can customize Browse-URL's behavior via various options in the
@code{browse-url} Customize group, particularly
@code{browse-url-browser-function}.  You can invoke actions dependent
on the type of URL by defining @code{browse-url-browser-function} as
an association list.  The package's commentary available via @kbd{C-h
p} under the @samp{hypermedia} keyword provides more information.
Packages with facilities for following URLs should always go through
Browse-URL, so that the customization options for Browse-URL will
affect all browsing in Emacs.

@node Goto-address
@subsection Activating URLs
@findex goto-address
@cindex Goto-address
@cindex URLs, activating

@table @kbd
@item M-x goto-address
Activate URLs and e-mail addresses in the current buffer.
@end table

  You can make URLs in the current buffer active with @kbd{M-x
goto-address}.  This finds all the URLs in the buffer, and establishes
bindings for @kbd{Mouse-2} and @kbd{C-c @key{RET}} on them.  After
activation, if you click on a URL with @kbd{Mouse-2}, or move to a URL
and type @kbd{C-c @key{RET}}, that will display the web page that the URL
specifies.  For a @samp{mailto} URL, it sends mail instead, using your
selected mail-composition method (@pxref{Mail Methods}).

  It can be useful to add @code{goto-address} to mode hooks and the
hooks used to display an incoming message.
@code{rmail-show-message-hook} is the appropriate hook for Rmail, and
@code{mh-show-mode-hook} for MH-E.  This is not needed for Gnus,
which has a similar feature of its own.


@node FFAP
@subsection Finding Files and URLs at Point
@findex find-file-at-point
@findex ffap
@findex dired-at-point
@findex ffap-next
@findex ffap-menu
@cindex finding file at point

  FFAP mode replaces certain key bindings for finding files, including
@kbd{C-x C-f}, with commands that provide more sensitive defaults.
These commands behave like the ordinary ones when given a prefix
argument.  Otherwise, they get the default file name or URL from the
text around point.  If what is found in the buffer has the form of a
URL rather than a file name, the commands use @code{browse-url} to
view it.

  This feature is useful for following references in mail or news
buffers, @file{README} files, @file{MANIFEST} files, and so on.  The
@samp{ffap} package's commentary available via @kbd{C-h p} under the
@samp{files} keyword and the @code{ffap} Custom group provide details.

@cindex FFAP minor mode
@findex ffap-mode
  You can turn on FFAP minor mode by calling @code{ffap-bindings} to
make the following key bindings and to install hooks for using
@code{ffap} in Rmail, Gnus and VM article buffers.

@table @kbd
@item C-x C-f @var{filename} @key{RET}
@kindex C-x C-f @r{(FFAP)}
Find @var{filename}, guessing a default from text around point
(@code{find-file-at-point}).
@item C-x C-r
@kindex C-x C-r @r{(FFAP)}
@code{ffap-read-only}, analogous to @code{find-file-read-only}.
@item C-x C-v
@kindex C-x C-v @r{(FFAP)}
@code{ffap-alternate-file}, analogous to @code{find-alternate-file}.
@item C-x d @var{directory} @key{RET}
@kindex C-x d @r{(FFAP)}
Start Dired on @var{directory}, defaulting to the directory name at
point (@code{dired-at-point}).
@item C-x C-d
@code{ffap-list-directory}, analogous to @code{list-directory}.
@item C-x 4 f
@kindex C-x 4 f @r{(FFAP)}
@code{ffap-other-window}, analogous to @code{find-file-other-window}.
@item C-x 4 r
@code{ffap-read-only-other-window}, analogous to
@code{find-file-read-only-other-window}.
@item C-x 4 d
@code{ffap-dired-other-window}, analogous to @code{dired-other-window}.
@item C-x 5 f
@kindex C-x 5 f @r{(FFAP)}
@code{ffap-other-frame}, analogous to @code{find-file-other-frame}.
@item C-x 5 r
@code{ffap-read-only-other-frame}, analogous to
@code{find-file-read-only-other-frame}.
@item C-x 5 d
@code{ffap-dired-other-frame}, analogous to @code{dired-other-frame}.
@item M-x ffap-next
Search buffer for next file name or URL, then find that file or URL.
@item S-Mouse-3
@kindex S-Mouse-3 @r{(FFAP)}
@code{ffap-at-mouse} finds the file guessed from text around the position
of a mouse click.
@item C-S-Mouse-3
@kindex C-S-Mouse-3 @r{(FFAP)}
Display a menu of files and URLs mentioned in current buffer, then
find the one you select (@code{ffap-menu}).
@end table

@node Dissociated Press, Amusements, Hyperlinking, Top
@section Dissociated Press

@findex dissociated-press
  @kbd{M-x dissociated-press} is a command for scrambling a file of text
either word by word or character by character.  Starting from a buffer of
straight English, it produces extremely amusing output.  The input comes
from the current Emacs buffer.  Dissociated Press writes its output in a
buffer named @samp{*Dissociation*}, and redisplays that buffer after every
couple of lines (approximately) so you can read the output as it comes out.

  Dissociated Press asks every so often whether to continue generating
output.  Answer @kbd{n} to stop it.  You can also stop at any time by
typing @kbd{C-g}.  The dissociation output remains in the
@samp{*Dissociation*} buffer for you to copy elsewhere if you wish.

@cindex presidentagon
  Dissociated Press operates by jumping at random from one point in the
buffer to another.  In order to produce plausible output rather than
gibberish, it insists on a certain amount of overlap between the end of
one run of consecutive words or characters and the start of the next.
That is, if it has just output `president' and then decides to jump
to a different point in the file, it might spot the `ent' in `pentagon'
and continue from there, producing `presidentagon'.@footnote{This
dissociword actually appeared during the Vietnam War, when it was very
appropriate.  Bush has made it appropriate again.}  Long sample texts
produce the best results.

@cindex againformation
  A positive argument to @kbd{M-x dissociated-press} tells it to operate
character by character, and specifies the number of overlap characters.  A
negative argument tells it to operate word by word, and specifies the number
of overlap words.  In this mode, whole words are treated as the elements to
be permuted, rather than characters.  No argument is equivalent to an
argument of two.  For your againformation, the output goes only into the
buffer @samp{*Dissociation*}.  The buffer you start with is not changed.

@cindex Markov chain
@cindex ignoriginal
@cindex techniquitous
  Dissociated Press produces results fairly like those of a Markov
chain based on a frequency table constructed from the sample text.  It
is, however, an independent, ignoriginal invention.  Dissociated Press
techniquitously copies several consecutive characters from the sample
between random choices, whereas a Markov chain would choose randomly
for each word or character.  This makes for more plausible sounding
results, and runs faster.

@cindex outragedy
@cindex buggestion
@cindex properbose
@cindex mustatement
@cindex developediment
@cindex userenced
  It is a mustatement that too much use of Dissociated Press can be a
developediment to your real work, sometimes to the point of outragedy.
And keep dissociwords out of your documentation, if you want it to be well
userenced and properbose.  Have fun.  Your buggestions are welcome.

@node Amusements, Customization, Dissociated Press, Top
@section Other Amusements
@cindex boredom
@findex hanoi
@findex yow
@findex gomoku
@cindex tower of Hanoi

  If you are a little bit bored, you can try @kbd{M-x hanoi}.  If you are
considerably bored, give it a numeric argument.  If you are very, very
bored, try an argument of 9.  Sit back and watch.

@cindex Go Moku
  If you want a little more personal involvement, try @kbd{M-x gomoku},
which plays the game Go Moku with you.

@findex blackbox
@findex mpuz
@findex 5x5
@cindex puzzles
  @kbd{M-x blackbox}, @kbd{M-x mpuz} and @kbd{M-x 5x5} are puzzles.
@code{blackbox} challenges you to determine the location of objects
inside a box by tomography.  @code{mpuz} displays a multiplication
puzzle with letters standing for digits in a code that you must
guess---to guess a value, type a letter and then the digit you think it
stands for.  The aim of @code{5x5} is to fill in all the squares.

@findex decipher
@cindex ciphers
@cindex cryptanalysis
@kbd{M-x decipher} helps you to cryptanalyze a buffer which is encrypted
in a simple monoalphabetic substitution cipher.

@findex dunnet
  @kbd{M-x dunnet} runs an adventure-style exploration game, which is
a bigger sort of puzzle.

@findex lm
@cindex landmark game
@kbd{M-x lm} runs a relatively non-participatory game in which a robot
attempts to maneuver towards a tree at the center of the window based on
unique olfactory cues from each of the four directions.

@findex life
@cindex Life
@kbd{M-x life} runs Conway's ``Life'' cellular automaton.

@findex morse-region
@findex unmorse-region
@cindex Morse code
@cindex --/---/.-./.../.
@kbd{M-x morse-region} converts text in a region to Morse code and
@kbd{M-x unmorse-region} converts it back.  No cause for remorse.

@findex pong
@cindex Pong game
@kbd{M-x pong} plays a Pong-like game, bouncing the ball off opposing
bats.

@findex solitaire
@cindex solitaire
@kbd{M-x solitaire} plays a game of solitaire in which you jump pegs
across other pegs.

@findex studlify-region
@cindex StudlyCaps
@kbd{M-x studlify-region} studlify-cases the region, producing
text like this:

@example
M-x stUdlIfY-RegioN stUdlIfY-CaSeS thE region.
@end example

@findex tetris
@cindex Tetris
@findex snake
@cindex Snake
@kbd{M-x tetris} runs an implementation of the well-known Tetris game.
Likewise, @kbd{M-x snake} provides an implementation of Snake.

  When you are frustrated, try the famous Eliza program.  Just do
@kbd{M-x doctor}.  End each input by typing @key{RET} twice.

@cindex Zippy
  When you are feeling strange, type @kbd{M-x yow}.

@findex zone
The command @kbd{M-x zone} plays games with the display when Emacs is
idle.

@ifnottex
@lowersections
@end ifnottex

@ignore
   arch-tag: 8f094220-c0d5-4e9e-af7d-3e0da8187474
@end ignore