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@c This is part of the Emacs manual.
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@c Copyright (C) 1985, 86, 87, 93, 94, 95, 97, 2000
@c   Free Software Foundation, Inc.
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@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, emulating other editors, and
various diversions and amusements.

@end iftex
@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.
@ifinfo
For full details, see @ref{Top, Gnus,, gnus, The Gnus Manual}.
@end ifinfo
@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

As opposed to most normal Emacs packages, Gnus uses a number of
different buffers to display information and to receive commands.  The
three buffers users spend most of their time in are the @dfn{group
buffer}, the @dfn{summary buffer} and the @dfn{article buffer}.  

The @dfn{group buffer} contains a list of groups.  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 don't select this buffer---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; however, 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
@ifinfo
additional topics:

@end ifinfo
@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
@ifinfo
@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 ifinfo
@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*}.

@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.
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@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.
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@end table

@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.
* History: Shell History.  Repeating previous commands in a shell buffer.
* Options: Shell Options.  Options for customizing Shell mode.
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* 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.
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* Remote Host::            Connecting to another computer.
@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 goes into
an Emacs buffer named @samp{*Shell Command Output*}, which is displayed
in another window but not selected.  A numeric argument, as in @kbd{M-1
M-!}, directs this command to insert any output into the current buffer.
In that case, point is left before the output and the mark is set after
the output.

  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.

@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.  If a numeric argument is used, meaning
insert the output in the current buffer, then the old region is deleted
first and the output replaces it as the contents of the region.  It
returns the command's exit status when it is called from a Lisp program.

@vindex shell-file-name
@cindex environment
  Both @kbd{M-!} and @kbd{M-|} use @code{shell-file-name} to specify the
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shell to use.  This variable is initialized based on your @env{SHELL}
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environment variable when Emacs is started.  If the file name does not
specify a directory, the directories in the list @code{exec-path} are
searched; this list is initialized based on the environment variable
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@env{PATH} when Emacs is started.  Your @file{.emacs} file can override
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either or both of these default initializations.@refill

  Both @kbd{M-!} and @kbd{M-|} wait for the shell command to complete.
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 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.

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

@vindex shell-command-default-error-buffer
  Error output from the command is normally intermixed with the regular
output.  If you set the variable
@code{shell-command-default-error-buffer} to a string, which is a buffer
name, error output is inserted before point in the buffer of that name.

@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.

  To make multiple subshells, rename the buffer @samp{*shell*} to
something different using @kbd{M-x rename-uniquely}.  Then type @kbd{M-x
shell} again to create a new buffer @samp{*shell*} with its own
subshell.  If you rename this buffer as well, you can create a third
one, and so on.  All the subshells run independently and in parallel.

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

  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
specify a coding system after starting the shell by using @kbd{C-x
@key{RET} p} in the shell buffer.  @xref{Specify Coding}.

  As soon as the subshell is started, it is sent as input the contents
of the file @file{~/.emacs_@var{shellname}}, if that file 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}.

@vindex shell-pushd-regexp
@vindex shell-popd-regexp
@vindex shell-cd-regexp
  @code{cd}, @code{pushd} and @code{popd} commands given to the inferior
shell are watched by Emacs so it can keep the @samp{*shell*} buffer's
default directory the same as the shell's working directory.  These
commands are recognized 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.@refill

@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}).

@findex dirs
  If Emacs does not properly track 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 and more aggressive method of tracking changes in the
current directory.

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  Emacs defines the environment variable @env{EMACS} in the subshell,
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with value @code{t}.  A shell script can check this variable to
determine whether it has been run from an Emacs subshell.

@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}).  When a line is
copied, any text at the beginning of the line that matches the variable
@code{shell-prompt-pattern} is left out; this variable's value should be
a regexp string that matches the prompts that your shell uses.

@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
ignores 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
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Either delete a character or send @sc{eof}
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(@code{comint-delchar-or-maybe-eof}).  Typed at the end of the shell
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buffer, @kbd{C-d} sends @sc{eof} to the subshell.  Typed at any other
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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
Move to the beginning of the line, but after the prompt if any
(@code{comint-bol}).  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}).

@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-kill-output
Kill the last batch of output from a shell command
(@code{comint-kill-output}).  This is useful if a shell command spews
out lots of output that just gets in the way.

@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 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}).

@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.

Alternatively, you can arrange for Emacs to notice password prompts
and turn off echoing for them, as follows:

@example
(add-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

  Shell mode also customizes the paragraph commands so that only shell
prompts start new paragraphs.  Thus, a paragraph consists of an input
command plus the output that follows it in the buffer.

@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 in
particular include the choice of regular expression for detecting
prompts, 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 History
@subsection Shell Command History

  Shell buffers support three ways of repeating earlier commands.  You
can use the same keys used in the minibuffer; 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
Fetch the next earlier old shell command.

@kindex M-n @r{(Shell mode)}
@findex comint-next-input
@item M-n
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 @r{(Shell mode)}
@findex comint-get-next-from-history
Fetch the next subsequent command from the history.
@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.

  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-r}.  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.

  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.

  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 previous 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.
@end table

  Moving to a previous input and then copying it with @kbd{C-c
@key{RET}} 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 can understand these
constructs and 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 shell-prompt-pattern
@vindex comint-prompt-regexp
  History references take effect only following a shell prompt.  The
variable @code{shell-prompt-pattern} specifies how to recognize a shell
prompt.  Comint modes in general use the variable
@code{comint-prompt-regexp} to specify how to find a prompt; Shell mode
uses @code{shell-prompt-pattern} to set up the local value of
@code{comint-prompt-regexp}.

@vindex comint-input-autoexpand
  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}.

@findex comint-magic-space
  You can make @key{SPC} perform history expansion by binding @key{SPC} to
the command @code{comint-magic-space}.

@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.

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

@vindex comint-scroll-to-bottom-on-output
  By setting @code{comint-scroll-to-bottom-on-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-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.

@findex comint-dynamic-complete-variable
  The command @code{comint-dynamic-complete-variable} does variable-name
completion using the environment variables as set within Emacs.  The
variables controlling file name completion apply to variable-name
completion too.  This command is normally available through the menu
bar.

@vindex shell-command-execonly
  Command completion normally considers only executable files.
If you set @code{shell-command-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.

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@node Terminal emulator
@subsection Interactive Inferior Shell with 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{*term*} and runs a subshell with input coming from your keyboard and
output going to that buffer.

All the normal keys that you type are sent without any interpretation
by Emacs directly to the subshell, as ``terminal input''.
Any ``echo'' of your input is the responsibility of the subshell.
(The exception is the terminal escape character,
which by default is @kbd{C-c}.  @xref{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 also understands these escape sequences,
and for each control code does the appropriate thing
to change the buffer so that the appearance of the window
matches what it would be on a real terminal.
Thus you can actually run Emacs inside an Emacs Term window!

   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.

   To make multiple terminal emulators, rename the buffer @samp{*term*}
to something different using @kbd{M-x rename-uniquely},
just as with Shell mode.

   The file name used to load the subshell is determined
the same way as for Shell mode.

Unlike Shell mode, Term mode does not track the current directory
by examining your input.  Instead, if you use a programmable
shell, you can have it 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

  Term uses Term mode, which has two input modes:
In line mode, Term basically acts like Shell mode.  @xref{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-k @r{(Term mode)}
@findex term-char-mode
@item C-c C-k
Switch to line mode.  Do nothing if already in line mode.

@kindex C-c C-j @r{(Term mode)}
@findex term-line-mode
@item C-c C-j
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 C-x
A prefix command to access the global @key{C-x} commands conveniently.
For example, @kbd{C-c C-x o} invokes the global binding of
@kbd{C-x o}, which is normally @samp{other-window}.
@end table

@node Paging in Term
@subsection Paging in the terminal emulator

Term mode has a pager feature.  When the pager is enabled,
term mode will 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
Toggles the pager feature:  Disables the pager if it is enabled,
and vice versa.  This works in both line and char modes.
If the pager enabled, the mode-line contains the word @samp{page}.
@end table

If the pager is enabled, and Term receives more than a screenful
of output since your last input, Term will enter More break mode.
This is indicated by @samp{**MORE**} in the mode-line.
Type a @kbd{Space} to display the next screenful of output.
Type @kbd{?} to see your other options.  The interface is similar
to the Unix @code{more} program.

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

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  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
will be 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 your using.  Terminal types @samp{ansi}
or @samp{vt100} will work on most systems.

@c   If you are talking to a Bourne-compatible
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@c shell, and your system understands the @env{TERMCAP} variable,
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@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.

You cannot log into to a remove comuter 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
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and communicating with it through an Emacs buffer.

@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.

@node Emacs Server, Hardcopy, Shell, Top
@section Using Emacs as a Server
@pindex emacsclient
@cindex Emacs as a server
@cindex server, using Emacs as
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@cindex @env{EDITOR} environment variable
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  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
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variable @env{EDITOR} to specify which editor to run.  If you set
@env{EDITOR} to @samp{emacs}, they invoke Emacs---but in an
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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 in the 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 and Emacs server
programs.  Here is how.

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@cindex @env{TEXEDIT} environment variable
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  First, the preparation.  Within Emacs, call the function
@code{server-start}.  (Your @file{.emacs} file can do this automatically
if you add the expression @code{(server-start)} to it.)  Then, outside
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Emacs, set the @env{EDITOR} environment variable to @samp{emacsclient}.
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(Note that some programs use a different environment variable; for
example, to make @TeX{} use @samp{emacsclient}, you should set the
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@env{TEXEDIT} environment variable to @samp{emacsclient +%d %s}.)
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@kindex C-x #
@findex server-edit
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  Then, whenever any program invokes your specified @env{EDITOR}
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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.

  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
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use @env{EDITOR} wait for the ``editor'' (actually, @code{emacsclient})
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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 only way to
say that you are ``finished'' with one.

@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.

  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
two 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
Use Shell 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

@vindex server-temp-file-regexp
  Some programs write temporary files for you to edit.  After you edit
the temporary file, the program reads it back and deletes it.  If the
Emacs server is later asked to edit the same file name, it should assume
this has nothing to do with the previous occasion for that file name.
The server accomplishes this by killing the temporary file's buffer when
you finish with the file.  Use the variable
@code{server-temp-file-regexp} to specify which files are temporary in
this sense; its value should be a regular expression that matches file
names that are temporary.

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@vindex server-kill-new-buffers
  If the variable @code{server-kill-new-buffers} is set to non-nil,
buffers which still have a client are killed when you are done with
them, unless they were already present before Emacs Server visited
them.  This overrides the effect of the @code{server-temp-file-regexp}
variable.  By default, @code{server-kill-new-buffers} has a non-nil
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value; set it to nil if you want the old behavior governed by
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@code{server-temp-file-regexp}.

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  If you run @code{emacsclient} with the option @samp{--no-wait}, it
returns immediately without waiting for you to ``finish'' the buffer in
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Emacs.  Note that it this case, buffers for temporary files will not be
killed automatically with the default value of
@code{server-kill-new-buffers}, since those buffers will not have a
client.
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  If you have forgotten to start Emacs, then the option
@samp{--alternate-editor=@var{command}} may be useful.  It specifies a
command to run if @code{emacsclient} fails to contact Emacs.  For
example, the following setting for the @var{EDITOR} environment variable
will always give an editor, even if Emacs is not running.

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

The environment variable @var{ALTERNATE_EDITOR} has the same effect, but
the value of the @samp{--alternate-editor} takes precedence.

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@pindex emacs.bash
Alternatively, the file @file{etc/emacs.bash} defines a function for
@command{bash} which will use a running Emacs server or start one if
none exists.

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@menu
* Invoking emacsclient::
@end menu

@node Invoking emacsclient,, Emacs Server, Emacs Server
@section Invoking @code{emacsclient}

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

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

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.

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.

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.)


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@node Hardcopy, PostScript, Emacs Server, Top
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@section Hardcopy Output
@cindex hardcopy

  The Emacs commands for making hardcopy let you print either an entire
buffer or just part of one, either with or without page headers.
See also the hardcopy commands of Dired (@pxref{Misc File Ops})
and the diary (@pxref{Diary Commands}).

@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}.

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@node PostScript, PostScript Variables, Hardcopy, Top
@section PostScript Hardcopy
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  These commands convert buffer contents to PostScript,
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either printing it or leaving it in another Emacs buffer.

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

@findex ps-print-region
@findex ps-print-buffer
@findex ps-print-region-with-faces
@findex ps-print-buffer-with-faces
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  The PostScript commands, @code{ps-print-buffer} and
@code{ps-print-region}, print buffer contents in PostScript form.  One
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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},
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use PostScript features to show the faces (fonts and colors) in the text
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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}
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generate the PostScript output in an Emacs buffer instead of sending
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it to the printer.

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@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}.

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

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@node PostScript Variables, Sorting, PostScript, Top
@section Variables for PostScript Hardcopy
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@vindex ps-lpr-command
@vindex ps-lpr-switches
@vindex ps-printer-name
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  All the PostScript hardcopy commands use the variables
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@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
@vindex ps-print-color-p
  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.  You can turn off color processing by setting
@code{ps-print-color-p} to @code{nil}.

@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.

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

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@node Sorting, Narrowing, PostScript Variables, Top
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@section Sorting Text
@cindex sorting

  Emacs provides several commands for sorting text in the buffer.  All
operate on the contents of the region (the text between point and the
mark).  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 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
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@vindex sort-numeric-base
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@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 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
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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.
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@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 amount of narrowing in effect in a buffer at
any time is 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 restrict the
range of operation of a replace command or repeating keyboard macro.

@c WideCommands
@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
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@cindex hex editing
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  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

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


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@node Saving Emacs Sessions, Recursive Edit, Editing Binary Files, Top
@section Saving Emacs Sessions
@cindex saving sessions
@cindex desktop

  You can use the Desktop library to save the state of Emacs from one
session to another.  Saving the state means that Emacs starts up with
the same set of buffers, major modes, buffer positions, and so on that
the previous Emacs session had.

@vindex desktop-enable
  To use Desktop, you should use the Customization buffer (@pxref{Easy
Customization}) to set @code{desktop-enable} to a non-@code{nil} value,
or add these lines at the end of your @file{.emacs} file:

@example
(desktop-load-default)
(desktop-read)
@end example

@noindent
@findex desktop-save
The first time you save the state of the Emacs session, you must do it
manually, with the command @kbd{M-x desktop-save}.  Once you have done
that, exiting Emacs will save the state again---not only the present
Emacs session, but also subsequent sessions.  You can also save the
state at any time, without exiting Emacs, by typing @kbd{M-x
desktop-save} again.

  In order for Emacs to recover the state from a previous session, you
must start it with the same current directory as you used when you
started the previous session.  This is because @code{desktop-read} looks
in the current directory for the file to read.  This means that you can
have separate saved sessions in different directories; the directory in
which you start Emacs will control which saved session to use.

@vindex desktop-files-not-to-save
  The variable @code{desktop-files-not-to-save} controls which files are
excluded from state saving.  Its value is a regular expression that
matches the files to exclude.  By default, remote (ftp-accessed) files
are excluded; this is because visiting them again in the subsequent
session would be slow.  If you want to include these files in state
saving, set @code{desktop-files-not-to-save} to @code{"^$"}.
@xref{Remote Files}.

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@vindex save-place
@cindex Saveplace
@findex toggle-save-place
There is a simpler mechanism provided by Saveplace library which records
your position in each file when you kill its buffer (or kill Emacs), and
jumps to the same position when you visit the file again (even in
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another Emacs session).  Use @kbd{M-x toggle-save-place} to turn on
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place-saving in a given file.  Customize the option @code{save-place} to
turn it on for all files in each session.

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@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.

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@node Emulation, Hyperlinking, Recursive Edit, Top
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@section Emulation
@cindex emulating other editors
@cindex other editors
@cindex EDT
@cindex vi
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@cindex CRiSP
@cindex Brief
@cindex PC keybindings
@cindex scrolling all windows
@cindex PC selecion
@cindex Motif keybindings
@cindex Macintosh keybindings
@cindex WordStar
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  GNU Emacs can be programmed to emulate (more or less) most other
editors.  Standard facilities can emulate these:

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

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@item `PC' bindings
@findex pc-bindings-mode
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@cindex `PC' key bindings
The command @kbd{M-x pc-bindings-mode} sets up certain key bindings for
`PC compatibility'---what people are often used to on PCs---as follows:
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@kbd{Delete} and its variants) delete forward instead of backward,
@kbd{C-Backspace} kills backward a word (as @kbd{C-Delete} normally
would), @kbd{M-Backspace} does undo, @kbd{Home} and @kbd{End} move to
beginning and end of line, @kbd{C-Home} and @kbd{C-End} move to
beginning and end of buffer and @kbd{C-Escape} does @code{list-buffers}.

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@item PC Selection mode
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@findex pc-selection-mode
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@cindex PC Selection minor mode
@cindex mode, PC selection
@cindex selection, `PC'
The command @kbd{M-x pc-selction-mode} turns on a global minor mode
which emulates the mark, copy, cut and paste
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look-and-feel of Motif programs (which is the same as the Macintosh GUI
and MS-Windows).  It makes the keybindings of PC mode and also modifies
the bindings of the cursor keys and the @kbd{next}, @kbd{prior},
@kbd{home} and @kbd{end} keys.  It does not provide the full set of CUA
keybindings---the fundamental Emacs keys @kbd{C-c}, @kbd{C-v} and
@kbd{C-x} are not rebound.

The standard keys for moving around (@kbd{right}, @kbd{left}, @kbd{up},
@kbd{down}, @kbd{home}, @kbd{end}, @kbd{prior}, @kbd{next}, called
``move-keys'') will always de-activate the mark.  Using @kbd{Shift}
together with the ``move keys'' activates the region over which they
move.  The copy, cut and paste functions (as in many other programs)
operate on the active region, bound to @kbd{C-insert}, @kbd{S-delete}
and @kbd{S-insert} respectively.

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@cindex s-region package
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The @code{s-region} package provides similar, but less complete,
facilities.

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@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.

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

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

@cindex hyperlinking
@cindex URLs
@cindex navigation
Various modes documented elsewhere have hypertext features whereby you
can follow links, usually with @kbd{mouse-2} or @kbd{RET} on the text of
the link.  Info mode, Help mode and the Dired-like modes are examples.
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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}.
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Other non-mode-specific facilities described in this section enable
following links from the current buffer in a context-sensitive fashion.
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@menu
* Browse-URL::                  Following URLs.
* Goto-address::                Activating URLs.
* FFAP::                        Finding files etc. at point.
* Find-func::                   Finding function and variable definitions.
@end menu

@node Browse-URL
@subsection  Following URLs
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@cindex World Wide Web
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@cindex Web
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@findex browse-url
@findex browse-url-at-point
@findex browse-url-at-mouse
@cindex Browse-URL
@cindex URLs
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@table @kbd
@item M-x browse-url @key{RET} @var{url} @key{ret}
Load a URL into a Web browser.
@end table

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The Browse-URL package provides facilities for following URLs specifying
links on the World Wide Web.  Usually this works by invoking a web
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browser but you can, for instance, arrange to invoke @code{compose-mail}
from @samp{mailto:} URLs.  Packages such as Gnus may make active links
from URLs themselves.  Otherwise you can use @kbd{M-x browse-url} to
follow a link, defaulting to the URL at point.  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}.
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@vindex browse-url-browser-function
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You can customize Browse-URL's behaviour via various options in the
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@code{browse-url} Customize group, particularly
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@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}
provides more information.  Packages with facilities for following URLs
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should use Browse-URL, so customizing options in the @code{browse-url}
group should be sufficient to determine how they all work in that
respect.