@c This is part of the Emacs manual.
@c Copyright (C) 1985--1987, 1993--1995, 1997, 2000--2020 Free Software
@c 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 Usenet news, host and network security,
viewing PDFs and other such documents, web
browsing, running shell commands and shell subprocesses, using a
single shared Emacs for utilities that expect to run an editor as a
subprocess, printing, sorting text, editing binary files, saving an
Emacs session for later resumption, recursive editing level, following
hyperlinks, and various diversions and amusements.

@end iftex

@ifnottex
@raisesections
@end ifnottex

@node Gnus
@section Email and Usenet News with Gnus
@cindex Gnus
@cindex Usenet news
@cindex newsreader

  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---email, 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{C-h i} and then select the Gnus
manual.
@end iftex

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

@node Buffers of Gnus
@subsection Gnus Buffers

  Gnus uses several buffers to display information and to receive
commands.  The three most commonly-used Gnus buffers are the
@dfn{group buffer}, the @dfn{summary buffer} and the @dfn{article
buffer}.

  The @dfn{group buffer} contains a list of article sources (e.g.,
newsgroups and email inboxes), which are collectively referred to as
@dfn{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.  From this buffer, you can select a
group to read.

  The @dfn{summary buffer} lists the articles in a single group,
showing one article per line.  By default, it displays each article's
author, subject, and line
@iftex
number.
@end iftex
@ifnottex
number, but this is customizable; @xref{Summary Buffer Format,,, gnus,
The Gnus Manual}.
@end ifnottex
The summary buffer is created when you select a group in the group
buffer, and is killed when you exit the group.

  From the summary buffer, you can choose an article to view.  The
article is displayed in the @dfn{article buffer}.  In normal Gnus
usage, you view this buffer but do not select it---all useful Gnus
commands can be invoked from the summary buffer.  But you can select
the article buffer, and execute Gnus commands from it, if you wish.

@node Gnus Startup
@subsection When Gnus Starts Up

@findex gnus
@cindex @file{.newsrc} file
  If your system has been set up for reading Usenet news, getting
started with Gnus is easy---just type @kbd{M-x gnus}.

  On starting up, Gnus reads your @dfn{news initialization file}: a
file named @file{.newsrc} in your home directory which lists your
Usenet newsgroups and subscriptions (this file is not unique to Gnus;
it is used by many other newsreader programs).  It then tries to
contact the system's default news server, which is typically specified
by the @env{NNTPSERVER} environment variable.

  If your system does not have a default news server, or if you wish
to use Gnus for reading email, then before invoking @kbd{M-x gnus} you
need to tell Gnus where to get news and/or mail.  To do this,
customize the variables @code{gnus-select-method} and/or
@code{gnus-secondary-select-methods}.
@iftex
See the Gnus manual for details.
@end iftex
@ifnottex
@xref{Finding the News,,, gnus, The Gnus Manual}.
@end ifnottex

  Once Gnus has started up, it displays the group buffer.  By default,
the group buffer shows only a small number of @dfn{subscribed groups}.
Groups with other statuses---@dfn{unsubscribed}, @dfn{killed}, or
@dfn{zombie}---are hidden.  The first time you start Gnus, any group
to which you are not subscribed is made into a killed group; any group
that subsequently appears on the news server becomes a zombie group.

  To proceed, you must select a group in the group buffer to open the
summary buffer for that group; then, select an article in the summary
buffer to view its article buffer in a separate window.  The following
sections explain how to use the group and summary buffers to do this.

  To quit Gnus, type @kbd{q} in the group buffer.  This automatically
records your group statuses in the files @file{.newsrc} and
@file{.newsrc.eld}, so that they take effect in subsequent Gnus
sessions.

@node Gnus Group Buffer
@subsection Using the Gnus Group Buffer

  The following commands are available in the Gnus group buffer:

@table @kbd
@kindex SPC @r{(Gnus Group mode)}
@findex gnus-group-read-group
@item @key{SPC}
Switch to the summary buffer for the group on the current line
(@code{gnus-group-read-group}).

@kindex l @r{(Gnus Group mode)}
@kindex A s @r{(Gnus Group mode)}
@findex gnus-group-list-groups
@item l
@itemx A s
In the group buffer, list only the groups to which you subscribe and
which contain unread articles (@code{gnus-group-list-groups}; this is
the default listing).

@kindex L @r{(Gnus Group mode)}
@kindex A u @r{(Gnus Group mode)}
@findex gnus-group-list-all-groups
@item L
@itemx A u
List all subscribed and unsubscribed groups, but not killed or zombie
groups (@code{gnus-group-list-all-groups}).

@kindex A k @r{(Gnus Group mode)}
@findex gnus-group-list-killed
@item A k
List killed groups (@code{gnus-group-list-killed}).

@kindex A z @r{(Gnus Group mode)}
@findex gnus-group-list-zombies
@item A z
List zombie groups (@code{gnus-group-list-zombies}).

@kindex u @r{(Gnus Group mode)}
@findex gnus-group-unsubscribe-current-group
@cindex subscribe groups
@cindex unsubscribe groups
@item u
Toggle the subscription status of the group
(@code{gnus-group-unsubscribe-current-group}) on the current line
(i.e., turn a subscribed group into an unsubscribed group, or vice
versa).  Invoking this on a killed or zombie group turns it into an
unsubscribed group.

@kindex C-k @r{(Gnus Group mode)}
@findex gnus-group-kill-group
@item C-k
Kill the group on the current line (@code{gnus-group-kill-group}).
Killed groups are not recorded in the @file{.newsrc} file, and they
are not shown in the @kbd{l} or @kbd{L} listings.

@kindex DEL @r{(Gnus Group mode)}
@item @key{DEL}
Move point to the previous group containing unread articles
(@code{gnus-group-prev-unread-group}).

@kindex n @r{(Gnus Group mode)}
@findex gnus-group-next-unread-group
@item n
Move point to the next unread group
(@code{gnus-group-next-unread-group}).

@kindex p @r{(Gnus Group mode)}
@findex gnus-group-prev-unread-group
@item p
Move point to the previous unread group
(@code{gnus-group-prev-unread-group}).

@kindex q @r{(Gnus Group mode)}
@findex gnus-group-exit
@item q
Update your Gnus settings, and quit Gnus (@code{gnus-group-exit}).
@end table

@node Gnus Summary Buffer
@subsection Using the Gnus Summary Buffer

  The following commands are available in the Gnus summary buffer:

@table @kbd
@kindex SPC @r{(Gnus Summary mode)}
@findex gnus-summary-next-page
@item @key{SPC}
If there is no article selected, select the article on the current
line and display its article buffer.  Otherwise, try scrolling the
selected article buffer in its window; on reaching the end of the
buffer, select the next unread article (@code{gnus-summary-next-page}).

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

@kindex DEL @r{(Gnus Summary mode)}
@findex gnus-summary-prev-page
@item @key{DEL}
Scroll the text of the article backwards
(@code{gnus-summary-prev-page}).

@kindex n @r{(Gnus Summary mode)}
@findex gnus-summary-next-unread-article
@item n
Select the next unread article
(@code{gnus-summary-next-unread-article}).

@kindex p @r{(Gnus Summary mode)}
@findex gnus-summary-prev-unread-article
@item p
Select the previous unread article
(@code{gnus-summary-prev-unread-article}).

@kindex s @r{(Gnus Summary mode)}
@findex gnus-summary-isearch-article
@item s
Do an incremental search on the selected article buffer
(@code{gnus-summary-isearch-article}), as if you switched to the
buffer and typed @kbd{C-s} (@pxref{Incremental Search}).

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

@kindex M-r @r{(Gnus Summary mode)}
@findex gnus-summary-search-article-backward
@item M-r @var{regexp} @key{RET}
Search back for articles containing a match for @var{regexp}
(@code{gnus-summary-search-article-backward}).

@kindex q @r{(Gnus Summary mode)}
@item q
Exit the summary buffer and return to the group buffer
(@code{gnus-summary-exit}).
@end table

@node Host Security
@section Host Security
@cindex security

Emacs runs inside an operating system such as GNU/Linux, and relies on
the operating system to check security constraints such as accesses to
files.  The default settings for Emacs are designed for typical use;
they may require some tailoring in environments where security is more
of a concern, or less of a concern, than usual.  For example,
file-local variables can be risky, and you can set the variable
@code{enable-local-variables} to @code{:safe} or (even more
conservatively) to @code{nil}; conversely, if your files can all be
trusted and the default checking for these variables is irritating,
you can set @code{enable-local-variables} to @code{:all}.  @xref{Safe
File Variables}.

@xref{Security Considerations,,, elisp, The Emacs Lisp Reference
Manual}, for more information about security considerations when using
Emacs as part of a larger application.

@node Network Security
@section Network Security
@cindex network security manager
@cindex NSM
@cindex encryption
@cindex SSL
@cindex TLS
@cindex Transport Layer Security
@cindex STARTTLS

Whenever Emacs establishes any network connection, it passes the
established connection to the @dfn{Network Security Manager}
(@acronym{NSM}).  @acronym{NSM} is responsible for enforcing the
network security under your control.  Currently, this works by using
the Transport Layer Security (@acronym{TLS}) features.

@vindex network-security-level
The @code{network-security-level} variable determines the security
level that @acronym{NSM} enforces.  If its value is @code{low}, no
security checks are performed.  This is not recommended, and will
basically mean that your network connections can't be trusted.
However, the setting can be useful in limited circumstances, as when
testing network issues.

If this variable is @code{medium} (which is the default), a number of
checks will be performed.  If as result @acronym{NSM} determines that
the network connection might not be trustworthy, it will make you
aware of that, and will ask you what to do about the network
connection.

You can decide to register a permanent security exception for an
unverified connection, a temporary exception, or refuse the connection
entirely.

@vindex network-security-protocol-checks
In addition to the basic certificate correctness checks, several
@acronym{TLS} algorithm checks are available.  Some encryption
technologies that were previously thought to be secure have shown
themselves to be fragile, so Emacs (by default) warns you about some
of these problems.

The protocol network checks is controlled via the
@code{network-security-protocol-checks} variable.

It's an alist where the first element of each association is the name
of the check, and the second element is the security level where the
check should be used.

An element like @code{(rc4 medium)} will result in the function
@code{nsm-protocol-check--rc4} being called like thus:
@w{@code{(nsm-protocol-check--rc4 host port status settings)}}.
The function should return non-@code{nil} if the connection should
proceed and @code{nil} otherwise.

Below is a list of the checks done on the default @code{medium} level.

@table @asis

@item unable to verify a @acronym{TLS} certificate
If the connection is a @acronym{TLS}, @acronym{SSL} or
@acronym{STARTTLS} connection, @acronym{NSM} will check whether
the certificate used to establish the identity of the server we're
connecting to can be verified.

While an invalid certificate is often the cause for concern (there
could be a Man-in-the-Middle hijacking your network connection and
stealing your password), there may be valid reasons for going ahead
with the connection anyway.  For instance, the server may be using a
self-signed certificate, or the certificate may have expired.  It's up
to you to determine whether it's acceptable to continue with the
connection.

@item a self-signed certificate has changed
If you've previously accepted a self-signed certificate, but it has
now changed, that could mean that the server has just changed the
certificate, but it might also mean that the network connection has
been hijacked.

@item previously encrypted connection now unencrypted
If the connection is unencrypted, but it was encrypted in previous
sessions, this might mean that there is a proxy between you and the
server that strips away @acronym{STARTTLS} announcements, leaving the
connection unencrypted.  This is usually very suspicious.

@item talking to an unencrypted service when sending a password
When connecting to an @acronym{IMAP} or @acronym{POP3} server, these
should usually be encrypted, because it's common to send passwords
over these connections.  Similarly, if you're sending email via
@acronym{SMTP} that requires a password, you usually want that
connection to be encrypted.  If the connection isn't encrypted,
@acronym{NSM} will warn you.

@item Diffie-Hellman low prime bits
When doing the public key exchange, the number of prime bits should be
high enough to ensure that the channel can't be eavesdropped on by third
parties.  If this number is too low, Emacs will warn you.  (This is the
@code{diffie-hellman-prime-bits} check in
@code{network-security-protocol-checks}).

@item @acronym{RC4} stream cipher
The @acronym{RC4} stream cipher is believed to be of low quality and
may allow eavesdropping by third parties.  (This is the @code{rc4}
check in @code{network-security-protocol-checks}).

@item @acronym{SHA1} in the host certificate or in intermediate certificates
It is believed that if an intermediate certificate uses the
@acronym{SHA1} hashing algorithm, then third parties can issue
certificates pretending to be that issuing instance.  These
connections are therefore vulnerable to man-in-the-middle attacks.
(These are the @code{signature-sha1} and @code{intermediate-sha1}
checks in @code{network-security-protocol-checks}).

@item @acronym{SSL1}, @acronym{SSL2} and @acronym{SSL3}
The protocols older than @acronym{TLS1.0} are believed to be
vulnerable to a variety of attacks, and you may want to avoid using
these if what you're doing requires higher security.  (This is the
@code{ssl} check in @code{network-security-protocol-checks}).

@end table

If @code{network-security-level} is @code{high}, the following checks
will be made, in addition to the above:

@table @asis
@item @acronym{3DES} cipher
The @acronym{3DES} stream cipher provides at most 112 bits of
effective security, which is considered to be towards the low end.
(This is the @code{3des} check in
@code{network-security-protocol-checks}).

@item a validated certificate changes the public key
Servers change their keys occasionally, and that is normally nothing
to be concerned about.  However, if you are worried that your network
connections are being hijacked by agencies who have access to pliable
Certificate Authorities which issue new certificates for third-party
services, you may want to keep track of these changes.

@end table

Finally, if @code{network-security-level} is @code{paranoid}, you will
also be notified the first time @acronym{NSM} sees any new
certificate.  This will allow you to inspect all the certificates from
all the connections that Emacs makes.

The following additional variables can be used to control details of
@acronym{NSM} operation:

@table @code
@item nsm-settings-file
@vindex nsm-settings-file
This is the file where @acronym{NSM} stores details about connections.
It defaults to @file{~/.emacs.d/network-security.data}.

@item nsm-save-host-names
@vindex nsm-save-host-names
By default, host names will not be saved for non-@code{STARTTLS}
connections.  Instead a host/port hash is used to identify connections.
This means that one can't casually read the settings file to see what
servers the user has connected to.  If this variable is @code{t},
@acronym{NSM} will also save host names in the
@code{nsm-settings-file}.

@end table


@node Document View
@section Document Viewing
@cindex DVI file
@cindex PDF file
@cindex PS file
@cindex PostScript file
@cindex OpenDocument file
@cindex Microsoft Office file
@cindex DocView mode
@cindex mode, DocView
@cindex document viewer (DocView)
@findex doc-view-mode

  DocView mode is a major mode for viewing DVI, PostScript (PS), PDF,
OpenDocument, and Microsoft Office documents.  It provides features
such as slicing, zooming, and searching inside documents.  It works by
converting the document to a set of images using the @command{gs}
(GhostScript) or @command{mudraw}/@command{pdfdraw} (MuPDF) commands
and other external tools @footnote{For PostScript files, GhostScript
is a hard requirement.  For DVI files, @code{dvipdf} or @code{dvipdfm}
is needed.  For OpenDocument and Microsoft Office documents, the
@code{unoconv} tool is needed.}, and displaying those images.

@findex doc-view-toggle-display
@findex doc-view-minor-mode
  When you visit a document file that can be displayed with DocView
mode, Emacs automatically uses that mode @footnote{The needed
external tools for the document type must be available, and Emacs must
be running in a graphical frame and have PNG image support.  If these
requirements is not fulfilled, Emacs falls back to another major
mode.}.  As an exception, when you visit a PostScript file, Emacs
switches to PS mode, a major mode for editing PostScript files as
text; however, it also enables DocView minor mode, so you can type
@kbd{C-c C-c} to view the document with DocView.  In either DocView
mode or DocView minor mode, repeating @kbd{C-c C-c}
(@code{doc-view-toggle-display}) toggles between DocView and the
underlying file contents.

@findex doc-view-open-text
  When you visit a file which would normally be handled by DocView
mode but some requirement is not met (e.g., you operate in a terminal
frame or Emacs has no PNG support), you are queried if you want to
view the document's contents as plain text.  If you confirm, the
buffer is put in text mode and DocView minor mode is activated.  Thus,
by typing @kbd{C-c C-c} you switch to the fallback mode.  With another
@kbd{C-c C-c} you return to DocView mode.  The plain text contents can
also be displayed from within DocView mode by typing @kbd{C-c C-t}
(@code{doc-view-open-text}).

  You can explicitly enable DocView mode with the command @kbd{M-x
doc-view-mode}.  You can toggle DocView minor mode with @kbd{M-x
doc-view-minor-mode}.

  When DocView mode starts, it displays a welcome screen and begins
formatting the file, page by page.  It displays the first page once
that has been formatted.

  To kill the DocView buffer, type @kbd{k}
(@code{doc-view-kill-proc-and-buffer}).  To bury it, type @kbd{q}
(@code{quit-window}).

@menu
* Navigation: DocView Navigation.  Navigating DocView buffers.
* Searching: DocView Searching.    Searching inside documents.
* Slicing: DocView Slicing.        Specifying which part of a page is displayed.
* Conversion: DocView Conversion.  Influencing and triggering conversion.
@end menu

@node DocView Navigation
@subsection DocView Navigation

  In DocView mode, you can scroll the current page using the usual
Emacs movement keys: @kbd{C-p}, @kbd{C-n}, @kbd{C-b}, @kbd{C-f}, and
the arrow keys.

@vindex doc-view-continuous
  By default, the line-motion keys @kbd{C-p} and @kbd{C-n} stop
scrolling at the beginning and end of the current page, respectively.
However, if you change the variable @code{doc-view-continuous} to a
non-@code{nil} value, then @kbd{C-p} displays the previous page if you
are already at the beginning of the current page, and @kbd{C-n}
displays the next page if you are at the end of the current page.

@findex doc-view-next-page
@findex doc-view-previous-page
@kindex n @r{(DocView mode)}
@kindex p @r{(DocView mode)}
@kindex PageDown @r{(DocView mode)}
@kindex PageUp @r{(DocView mode)}
@kindex next @r{(DocView mode)}
@kindex prior @r{(DocView mode)}
@kindex C-x ] @r{(DocView mode)}
@kindex C-x [ @r{(DocView mode)}
  You can also display the next page by typing @kbd{n},
@key{PageDown}, @key{next} or @kbd{C-x ]} (@code{doc-view-next-page}).
To display the previous page, type @kbd{p}, @key{PageUp}, @key{prior}
or @kbd{C-x [} (@code{doc-view-previous-page}).

@findex doc-view-scroll-up-or-next-page
@findex doc-view-scroll-down-or-previous-page
@kindex SPC @r{(DocView mode)}
@kindex DEL @r{(DocView mode)}
  @key{SPC} (@code{doc-view-scroll-up-or-next-page}) is a convenient
way to advance through the document.  It scrolls within the current
page or advances to the next.  @key{DEL} moves backwards in a similar
way (@code{doc-view-scroll-down-or-previous-page}).

@findex doc-view-first-page
@findex doc-view-last-page
@findex doc-view-goto-page
@kindex M-< @r{(DocView mode)}
@kindex M-> @r{(DocView mode)}
  To go to the first page, type @kbd{M-<}
(@code{doc-view-first-page}); to go to the last one, type @kbd{M->}
(@code{doc-view-last-page}).  To jump to a page by its number, type
@kbd{M-g M-g} or @kbd{M-g g} (@code{doc-view-goto-page}).

@findex doc-view-enlarge
@findex doc-view-shrink
@vindex doc-view-resolution
@vindex doc-view-scale-internally
@kindex + @r{(DocView mode)}
@kindex - @r{(DocView mode)}
  You can enlarge or shrink the document with @kbd{+}
(@code{doc-view-enlarge}) and @kbd{-} (@code{doc-view-shrink}).  By
default, these commands just rescale the already-rendered image.  If
you instead want the image to be re-rendered at the new size, set
@code{doc-view-scale-internally} to @code{nil}.  To specify the
default size for DocView, customize the variable
@code{doc-view-resolution}.

@node DocView Searching
@subsection DocView Searching

  In DocView mode, you can search the file's text for a regular
expression (@pxref{Regexps}).  The interface for searching is inspired
by @code{isearch} (@pxref{Incremental Search}).

@findex doc-view-search
@findex doc-view-search-backward
@findex doc-view-show-tooltip
  To begin a search, type @kbd{C-s} (@code{doc-view-search}) or
@kbd{C-r} (@code{doc-view-search-backward}).  This reads a regular
expression using a minibuffer, then echoes the number of matches found
within the document.  You can move forward and back among the matches
by typing @kbd{C-s} and @kbd{C-r}.  DocView mode has no way to show
the match inside the page image; instead, it displays a tooltip (at
the mouse position) listing all matching lines in the current page.
To force display of this tooltip, type @kbd{C-t}
(@code{doc-view-show-tooltip}).

  To start a new search, use the search command with a prefix
argument; i.e., @kbd{C-u C-s} for a forward search or @kbd{C-u C-r}
for a backward search.

@node DocView Slicing
@subsection DocView Slicing

Documents often have wide margins for printing.  They are annoying
when reading the document on the screen, because they use up screen
space and can cause inconvenient scrolling.

@findex doc-view-set-slice
@findex doc-view-set-slice-using-mouse
  With DocView you can hide these margins by selecting a @dfn{slice}
of pages to display.  A slice is a rectangle within the page area;
once you specify a slice in DocView, it applies to whichever page you
look at.

  To specify the slice numerically, type @kbd{c s}
(@code{doc-view-set-slice}); then enter the top left pixel position
and the slice's width and height.
@c ??? how does this work?

  A more convenient graphical way to specify the slice is with @kbd{c
m} (@code{doc-view-set-slice-using-mouse}), where you use the mouse to
select the slice.  Simply press and hold the left mouse button at the
upper-left corner of the region you want to have in the slice, then
move the mouse pointer to the lower-right corner and release the
button.

  The most convenient way is to set the optimal slice by using
BoundingBox information automatically determined from the document by
typing @kbd{c b} (@code{doc-view-set-slice-from-bounding-box}).

@findex doc-view-reset-slice
  To cancel the selected slice, type @kbd{c r}
(@code{doc-view-reset-slice}).  Then DocView shows the entire page
including its entire margins.

@node DocView Conversion
@subsection DocView Conversion

@vindex doc-view-cache-directory
@findex doc-view-clear-cache
  For efficiency, DocView caches the images produced by @command{gs}.
The name of the directory where it caches images is given by the variable
@code{doc-view-cache-directory}.  You can clear the cache directory by
typing @kbd{M-x doc-view-clear-cache}.

@findex doc-view-kill-proc
@findex doc-view-kill-proc-and-buffer
  To force reconversion of the currently viewed document, type @kbd{r}
or @kbd{g} (@code{revert-buffer}).  To kill the converter process
associated with the current buffer, type @kbd{K}
(@code{doc-view-kill-proc}).  The command @kbd{k}
(@code{doc-view-kill-proc-and-buffer}) kills the converter process and
the DocView buffer.

@node Shell
@section Running Shell Commands from Emacs
@cindex subshell
@cindex shell commands

  Emacs has commands for passing single command lines to shell
subprocesses, and for running a shell interactively with input and
output to an Emacs buffer, and for running a shell in a terminal
emulator window.

@table @kbd
@item M-! @var{cmd} @key{RET}
Run the shell command @var{cmd} and display the output
(@code{shell-command}).
@item M-| @var{cmd} @key{RET}
Run the shell command @var{cmd} with region contents as input;
optionally replace the region with the output
(@code{shell-command-on-region}).
@item M-& @var{cmd} @key{RET}
Run the shell command @var{cmd} asynchronously, and display the output
(@code{async-shell-command}).
@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

@vindex exec-path
  Whenever you specify a relative file name for an executable program
(either in the @var{cmd} argument to one of the above commands, or in
other contexts), Emacs searches for the program in the directories
specified by the variable @code{exec-path}.  The value of this
variable must be a list of directories; the default value is
initialized from the environment variable @env{PATH} when Emacs is
started (@pxref{General Variables}).

  @kbd{M-x eshell} invokes a shell implemented entirely in Emacs.  It
is documented in its own manual.
@ifnottex
@xref{Top,Eshell,Eshell, eshell, Eshell: The Emacs Shell}.
@end ifnottex
@iftex
See the Eshell Info manual, which is distributed with Emacs.
@end iftex

@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.
* 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
@file{*Shell Command Output*}, displayed in another window (if the
output is long).  The variables @code{resize-mini-windows} and
@code{max-mini-window-height} (@pxref{Minibuffer Edit}) control when
Emacs should consider the output to be too long for the echo area.

  For instance, one way to decompress a file named @file{foo.gz} 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 to @code{shell-command}, e.g., @kbd{M-1 M-!},
causes it to insert terminal output into the current buffer instead of
a separate buffer.  By default, it puts point before the output, and
sets the mark after the output (but a non-default value of
@code{shell-command-dont-erase-buffer} can change that, see below).
For instance, @kbd{M-1 M-! gunzip < foo.gz @key{RET}} would insert the
uncompressed form of the file @file{foo.gz} into the current buffer.

  Provided the specified shell command does not end with @samp{&}, it
runs @dfn{synchronously}, and you must wait for it to exit before
continuing to use Emacs.  To stop waiting, type @kbd{C-g} to quit;
this sends a @code{SIGINT} signal to terminate the shell command (this
is 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.

@kindex M-&
@findex async-shell-command
  A shell command that ends in @samp{&} is executed
@dfn{asynchronously}, and you can continue to use Emacs as it runs.
You can also type @kbd{M-&} (@code{async-shell-command}) to execute a
shell command asynchronously; this is exactly like calling @kbd{M-!}
with a trailing @samp{&}, except that you do not need the @samp{&}.
The default output buffer for asynchronous shell commands is named
@samp{*Async Shell Command*}.  Emacs inserts the output into this
buffer as it comes in, whether or not the buffer is visible in a
window.

@vindex async-shell-command-buffer
  If you want to run more than one asynchronous shell command at the
same time, they could end up competing for the output buffer.  The
option @code{async-shell-command-buffer} specifies what to do about
this; e.g., whether to rename the pre-existing output buffer, or to
use a different buffer for the new command.  Consult the variable's
documentation for more possibilities.

@vindex async-shell-command-display-buffer
  If you want the output buffer for asynchronous shell commands to be
displayed only when the command generates output, set
@code{async-shell-command-display-buffer} to @code{nil}.

@vindex async-shell-command-width
  The option @code{async-shell-command-width} defines the number of display
columns available for output of asynchronous shell commands.
A positive integer tells the shell to use that number of columns for
command output.  The default value is @code{nil} that means to use
the same number of columns as provided by the shell.

@vindex shell-command-prompt-show-cwd
  To make the above commands show the current directory in their
prompts, customize the variable @code{shell-command-prompt-show-cwd}
to a non-@code{nil} value.

@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, it deletes the
old region and replaces it with the output from the shell command.

  For example, you can use @kbd{M-|} with the @command{gpg} program to
see what keys are in the buffer.  If the buffer contains a GnuPG key,
type @kbd{C-x h M-| gpg @key{RET}} to feed the entire buffer contents
to @command{gpg}.  This will output the list of keys to the
@file{*Shell Command Output*} buffer.

@vindex shell-file-name
  The above commands use the shell specified by the variable
@code{shell-file-name}.  Its default value is determined by the
@env{SHELL} environment variable when Emacs is started.  If the file
name is relative, Emacs searches the directories listed in
@code{exec-path} (@pxref{Shell}).

  If the default directory is remote (@pxref{Remote Files}), the
default value is @file{/bin/sh}.  This can be changed by declaring
@code{shell-file-name} connection-local (@pxref{Connection Variables}).

  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
  By default, error output is intermixed with the regular output in
the output buffer.  But if you change the value of the variable
@code{shell-command-default-error-buffer} to a string, error output is
inserted into a buffer of that name.

@vindex shell-command-dont-erase-buffer
  By default, the output buffer is erased between shell commands, except
when the output goes to the current buffer.  If you change the value
of the option @code{shell-command-dont-erase-buffer} to @code{erase},
then the output buffer is always erased.  Other non-@code{nil} values
prevent erasing of the output buffer, and---if the output buffer is
not the current buffer---also control where to put point after
inserting the output of the shell command:

@table @code
@item beg-last-out
Puts point at the beginning of the last shell-command output.
@item end-last-out
Puts point at the end of the last shell-command output, i.e.@: at the
end of the output buffer.
@item save-point
Restores the position of point as it was before inserting the
shell-command output.
@end table

@node Interactive Shell
@subsection Interactive Subshell

@findex shell
  To run a subshell interactively, type @kbd{M-x shell}.  This creates
(or reuses) a buffer named @file{*shell*}, and runs a shell subprocess
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}.

  By default, when the subshell is invoked interactively, the
@file{*shell*} buffer is displayed in a new window, unless the current
window already shows the @file{*shell*} buffer.  This behavior can
be customized via @code{display-buffer-alist} (@pxref{Window Choice}).

  While the subshell is waiting or running a command, you can switch
windows or buffers and perform other editing in Emacs.  Emacs inserts
the output from the subshell into the Shell buffer whenever it has
time to process it (e.g., while waiting for keyboard input).

@cindex @code{comint-highlight-input} face
@cindex @code{comint-highlight-prompt} face
  In the Shell buffer, prompts are displayed with the face
@code{comint-highlight-prompt}, and submitted input lines are
displayed with the face @code{comint-highlight-input}.  This makes it
easier to distinguish input lines from the shell output.
@xref{Faces}.

  To make multiple subshells, invoke @kbd{M-x shell} with a prefix
argument (e.g., @kbd{C-u M-x shell}).  Then the command will read a
buffer name, and create (or reuse) a subshell in that buffer.  You can
also rename the @file{*shell*} buffer using @kbd{M-x rename-uniquely},
then create a new @file{*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
  To specify the shell file name used by @kbd{M-x shell}, customize
the variable @code{explicit-shell-file-name}.  If this is @code{nil}
(the default), Emacs uses the environment variable @env{ESHELL} if it
exists.  Otherwise, it usually uses the variable
@code{shell-file-name} (@pxref{Single Shell}); but if the default
directory is remote (@pxref{Remote Files}), it prompts you for the
shell file name.  @xref{Minibuffer File}, for hints how to type remote
file names effectively.

  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 with
@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 @samp{@var{version},comint}, where @var{version} is the
Emacs version (e.g., @samp{24.1}).  Programs can check this variable
to determine whether they are running inside an Emacs subshell.

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

  The major mode for Shell buffers is Shell mode.  Many of its special
commands are bound to the @kbd{C-c} prefix, and resemble the usual
editing and job control characters present in ordinary shells, except
that you must type @kbd{C-c} first.  Here is a list of Shell mode
commands:

@table @kbd
@item @key{RET}
@kindex RET @r{(Shell mode)}
@findex comint-send-input
Send the current line as input to the subshell
(@code{comint-send-input}).  Any shell prompt at the beginning of the
line is omitted (@pxref{Shell Prompts}).  If point is at the end of
buffer, this is like submitting the command line in an ordinary
interactive shell.  However, you can also invoke @key{RET} elsewhere
in the shell buffer to submit the current line as input.

@item @key{TAB}
@kindex TAB @r{(Shell mode)}
@findex completion-at-point@r{, in Shell Mode}
@cindex shell completion
Complete the command name or file name before point in the shell
buffer (@code{completion-at-point}).  This uses the usual Emacs
completion rules (@pxref{Completion}), with the completion
alternatives being file names, environment variable names, the shell
command history, and history references (@pxref{History References}).
For options controlling the completion, @pxref{Shell Options}.

@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 (@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, this sends @acronym{EOF} to the subshell.  Typed at any other
position in the buffer, this 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
(@code{comint-accumulate}).  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.

@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 last line 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 for its working directory, and update the Shell buffer's
default directory.  @xref{Directory Tracking}.

@item M-x comint-send-invisible @key{RET} @var{text} @key{RET}
@findex comint-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 (@pxref{Lisp Eval}) 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.  To pass arguments to the program, use
@kbd{C-u M-x comint-run}.

@node Shell Prompts
@subsection Shell Prompts

@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)
automatically figures out which part of the buffer is a prompt, based
on the output of the subprocess.  (Specifically, it assumes that any
received output line which doesn't end with a newline is a prompt.)

  Comint mode divides the buffer into two types of @dfn{fields}: input
fields (where user input is typed) and output fields (everywhere
else).  Prompts are part of the output fields.  Most Emacs motion
commands do not cross field boundaries, unless they move over multiple
lines.  For instance, when point is in the input field on a shell
command line, @kbd{C-a} puts point at the beginning of the input
field, after the prompt.  Internally, the fields are implemented using
the @code{field} text property (@pxref{Text Properties,,, elisp, the
Emacs Lisp Reference Manual}).

@vindex comint-use-prompt-regexp
@vindex shell-prompt-pattern
  If you change the variable @code{comint-use-prompt-regexp} to a
non-@code{nil} value, then Comint mode will recognize prompts using a
regular expression (@pxref{Regexps}).  In Shell mode, the regular
expression is specified by the variable @code{shell-prompt-pattern}.
The default value of @code{comint-use-prompt-regexp} is @code{nil},
because this method for recognizing prompts is unreliable, but you may
want to set it to a non-@code{nil} value in unusual circumstances.  In
that case, Emacs does not divide the Comint buffer into fields, so the
general motion commands behave as they normally do in buffers without
special text properties.  However, you can use the paragraph motion
commands to conveniently navigate the buffer (@pxref{Paragraphs}); in
Shell mode, Emacs uses @code{shell-prompt-pattern} as paragraph
boundaries.

@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
(@code{comint-previous-input}).

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

@kindex M-r @r{(Shell mode)}
@findex comint-history-isearch-backward-regexp
@item M-r
Begin an incremental regexp search of old shell commands
(@code{comint-history-isearch-backward-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
(@code{comint-get-next-from-history}).

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

@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}, and @kbd{M-r}.  These work
similar to the minibuffer history commands (@pxref{Minibuffer
History}), except that they operate within the Shell buffer rather
than the minibuffer, and @code{M-r} in a Shell buffer invokes
incremental search through shell command history.

  @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 command @kbd{M-r} begins an incremental regular
expression search of previous shell commands.  After typing @kbd{M-r},
start typing the desired string or regular expression; the last
matching shell command will be displayed in the current line.
Incremental search commands have their usual effects---for instance,
@kbd{C-s} and @kbd{C-r} search forward and backward for the next match
(@pxref{Incremental Search}).  When you find the desired input, type
@key{RET} to terminate the search.  This puts the input in the command
line.  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-insert-previous-argument})
copies an individual argument from a previous command, like
@kbd{@key{ESC} .}@: in Bash and @command{zsh}.  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 commands, always
using the same value of @var{n}  (don't give a prefix argument when
you repeat the @kbd{C-c .} command).

@vindex comint-insert-previous-argument-from-end
  If you set @code{comint-insert-previous-argument-from-end} to a
non-@code{nil} value, @kbd{C-c .}@: will instead copy the @var{n}th
argument counting from the last one; this emulates @kbd{@key{ESC} .}@:
in @command{zsh}.

  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 comint-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.

@vindex tramp-histfile-override
  If you run the shell on a remote host, this setting might be
overwritten by the variable @code{tramp-histfile-override}.  It is
recommended to set this variable to @code{nil}.

@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 at point, 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}.  @xref{Rebinding}.

  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 subshell, in order to keep the Shell buffer's
default directory (@pxref{File Names}) the same as the shell's working
directory.  It recognizes these commands by examining lines of input
that you send.

  If you use aliases for these commands, you can tell Emacs to
recognize them also, by setting the variables
@code{shell-pushd-regexp}, @code{shell-popd-regexp}, and
@code{shell-cd-regexp} to the appropriate regular expressions
(@pxref{Regexps}).  For example, if @code{shell-pushd-regexp} matches
the beginning of a shell command line, that line is regarded as a
@code{pushd} command.  These commands are recognized only at the
beginning of a shell command line.

@findex dirs
  If Emacs gets confused about changes in the working directory of the
subshell, type @kbd{M-x dirs}.  This command asks the shell for its
working directory and updates the default directory accordingly.  It
works for shells that support the most common command syntax, but may
not work for unusual shells.

@findex dirtrack-mode
@cindex Dirtrack mode
@cindex mode, Dirtrack
@vindex dirtrack-list
  You can also use Dirtrack mode, a buffer-local minor mode that
implements an alternative method of tracking the shell's working
directory.  To use this method, your shell prompt must contain the
working directory at all times, and you must supply a regular
expression for recognizing which part of the prompt contains the
working directory; see the documentation of the variable
@code{dirtrack-list} for details.  To use Dirtrack mode, type @kbd{M-x
dirtrack-mode} in the Shell buffer, or add @code{dirtrack-mode} to
@code{shell-mode-hook} (@pxref{Hooks}).

@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.

@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.

@findex shell-dynamic-complete-command
Some implementation details of the shell command completion may also be found
in the lisp documentation of the @code{shell-dynamic-complete-command}
function.

@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.

@vindex comint-terminfo-terminal
@vindex TERM@r{, environment variable, in sub-shell}
Comint mode sets the @env{TERM} environment variable to a safe default
value, but this value disables some useful features.  For example,
color is disabled in applications that use @env{TERM} to determine if
color is supported.  Therefore, Emacs provides an option
@code{comint-terminfo-terminal}, which you can set to a terminal that
is present in your system's terminfo database, in order to take
advantage of advanced features of that terminal.

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

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

@cindex line mode @r{(terminal emulator)}
@cindex char mode @r{(terminal emulator)}
  The terminal emulator uses Term mode, which has two input modes.  In
@dfn{line mode}, Term basically acts like Shell mode (@pxref{Shell
Mode}).  In @dfn{char mode}, each character is sent directly to the
subshell, as terminal input; the sole exception is the terminal escape
character, which by default is @kbd{C-c} (@pxref{Term Mode}).  Any
echoing of your input is the responsibility of the subshell; any
terminal output from the subshell goes into the buffer, advancing
point.

  Some programs (such as Emacs itself) need to control the appearance
of the terminal screen in detail.  They do this by emitting special
control codes.  Term mode recognizes and handles ANSI-standard
VT100-style escape sequences, which are accepted by most modern
terminals, including @command{xterm}.  (Hence, you can actually run
Emacs inside an Emacs Term window.)

  The @code{term} face specifies the default appearance of text
in the terminal emulator (the default is the same appearance as the
@code{default} face).  When terminal control codes are used to change
the appearance of text, these are represented in the terminal emulator
by the faces @code{term-color-black}, @code{term-color-red},
@code{term-color-green}, @code{term-color-yellow}
@code{term-color-blue}, @code{term-color-magenta},
@code{term-color-cyan}, @code{term-color-white},
@code{term-color-underline}, and @code{term-color-bold}.
@xref{Faces}.

  You can also use Term mode to communicate with a device connected to
a serial port.  @xref{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 @file{*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

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

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

@kindex C-c C-k @r{(Term mode)}
@findex term-char-mode
@item C-c C-k
Switch to char mode (@code{term-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 @kbd{C-c} to the sub-shell
(@code{term-interrupt-subjob}).

@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

@cindex paging in Term mode
  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 (@code{term-pager-toggle}).  This
command works in both line and char modes.  When the feature is
enabled, the mode-line displays the word @samp{page}, and each time
Term receives more than a screenful of output, it pauses and displays
@samp{**MORE**} in the mode-line.  Type @key{SPC} to display the next
screenful of output, or @kbd{?} to see your other options.  The
interface is similar to the @code{more} program.
@end table

@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 @command{ssh} or
@command{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 a separating comma.)  Terminal types
@samp{ansi} or @samp{vt100} will work on most systems.

@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 communicate with it by typing @kbd{M-x serial-term}.  This
command asks for a serial port name and speed, and switches to a new
Term mode buffer.  Emacs communicates with the serial device through
this buffer just like it does with a terminal in ordinary 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 @samp{8N1} in
the mode line.  By default, a serial port is configured as @samp{8N1},
which means that each byte consists of 8 data bits, No parity check
bit, and 1 stopbit.

  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
@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 can invoke your choice of editor to edit a
particular piece of text.  For instance, version control programs
invoke an editor to enter version control logs (@pxref{Version
Control}), and the Unix @command{mail} utility invokes an editor to
enter a message to send.  By convention, your choice of editor is
specified by the environment variable @env{EDITOR}.  If you set
@env{EDITOR} to @samp{emacs}, Emacs would be invoked, but in an
inconvenient way---by starting a new Emacs process.  This is
inconvenient because the new Emacs process doesn't share buffers, a
command history, or other kinds of information with any existing Emacs
process.

  You can solve this problem by setting up Emacs as an @dfn{edit
server}, so that it ``listens'' for external edit requests and acts
accordingly.  There are various ways to start an Emacs server:

@itemize
@findex server-start
@item
Run the command @code{server-start} in an existing Emacs process:
either type @kbd{M-x server-start}, or put the expression
@code{(server-start)} in your init file (@pxref{Init File}).  The
existing Emacs process is the server; when you exit Emacs, the server
dies with the Emacs process.

@cindex daemon, Emacs
@item
Run Emacs as a @dfn{daemon}, using one of the @samp{--daemon} command-line
options.  @xref{Initial Options}.  When Emacs is started this way, it
calls @code{server-start} after initialization and does not open an
initial frame.  It then waits for edit requests from clients.

@cindex systemd unit file
@item
If your operating system uses @command{systemd} to manage startup,
you can automatically start Emacs in daemon mode when you login
using the supplied @dfn{systemd unit file}.  To activate this:
@example
systemctl --user enable emacs
@end example
(If your Emacs was installed into a non-standard location, you may
need to copy the @file{emacs.service} file to a standard directory
such as @file{~/.config/systemd/user/}.)

@cindex socket activation, systemd, Emacs
@item
An external process can invoke the Emacs server when a connection
event occurs upon a specified socket and pass the socket to the new
Emacs server process.  An instance of this is the socket functionality
of @command{systemd}: the @command{systemd} service creates a socket and
listens for connections on it; when @command{emacsclient} connects to
it for the first time, @command{systemd} can launch the Emacs server
and hand over the socket to it for servicing @command{emacsclient}
connections.  A setup to use this functionality could be:

@file{~/.config/systemd/user/emacs.socket}:
@example
[Socket]
ListenStream=/path/to/.emacs.socket

[Install]
WantedBy=sockets.target
@end example

(The @file{emacs.service} file described above must also be installed.)

The @code{ListenStream} path will be the path that Emacs listens for
connections from @command{emacsclient}; this is a file of your choice.
@end itemize

@cindex @env{TEXEDIT} environment variable
  Once an Emacs server is started, you can use a shell
command called @command{emacsclient} to connect to the Emacs process
and tell it to visit a file.  You can then set the @env{EDITOR}
environment variable to @samp{emacsclient}, so that external programs
will use the existing Emacs process for editing.@footnote{Some
programs use a different environment variable; for example, to make
@TeX{} use @samp{emacsclient}, set the @env{TEXEDIT} environment
variable to @samp{emacsclient +%d %s}.}

@vindex server-name
  You can run multiple Emacs servers on the same machine by giving
each one a unique @dfn{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} or the @samp{-f} option (@pxref{emacsclient
Options}), depending on whether or not the server uses a TCP socket
(@pxref{TCP Emacs server}).

  If you want to run multiple Emacs daemons (@pxref{Initial Options}),
you can give each daemon its own server name like this:

@example
  emacs --daemon=foo
@end example

@findex server-eval-at
  If you have defined a server by a unique server name, it is possible
to connect to the server from another Emacs instance and evaluate Lisp
expressions on the server, using the @code{server-eval-at} function.
For instance, @code{(server-eval-at "foo" '(+ 1 2))} evaluates the
expression @code{(+ 1 2)} on the @samp{foo} server, and returns
@code{3}.  (If there is no server with that name, an error is
signaled.)  Currently, this feature is mainly useful for developers.

@menu
* TCP Emacs server::     Listening to a TCP socket.
* Invoking emacsclient:: Connecting to the Emacs server.
* emacsclient Options::  Emacs client startup options.
@end menu

@node TCP Emacs server
@subsection TCP Emacs server
@cindex TCP Emacs server

@vindex server-use-tcp
  An Emacs server usually listens to connections on a local Unix
domain socket.  Some operating systems, such as MS-Windows, do not
support local sockets; in that case, the server uses TCP sockets
instead.  In some cases it is useful to have the server listen on a
TCP socket even if local sockets are supported, e.g., if you need to
contact the Emacs server from a remote machine.  You can set
@code{server-use-tcp} to non-@code{nil} to have Emacs listen on a TCP
socket instead of a local socket.  This is the default if your OS does
not support local sockets.

@vindex server-host
@vindex server-port
  If the Emacs server is set to use TCP, it will by default listen on
a random port on the localhost interface.  This can be changed to
another interface and/or a fixed port using the variables
@code{server-host} and @code{server-port}.

@vindex server-auth-key
  A TCP socket is not subject to file system permissions.  To retain
some control over which users can talk to an Emacs server over TCP
sockets, the @command{emacsclient} program must send an authorization
key to the server.  This key is normally randomly generated by the
Emacs server.  This is the recommended mode of operation.

@findex server-generate-key
  If needed, you can set the authorization key to a static value by
setting the @code{server-auth-key} variable.  The key must consist of
64 ASCII printable characters except for space (this means characters
from @samp{!} to @samp{~}, or from decimal code 33 to 126).  You can
use @kbd{M-x server-generate-key} to get a random key.

@vindex server-auth-dir
@cindex server file
  When you start a TCP Emacs server, Emacs creates a @dfn{server file}
containing the TCP information to be used by @command{emacsclient} to
connect to the server.  The variable @code{server-auth-dir} specifies
the default directory containing the server file; by default, this is
@file{~/.emacs.d/server/}.  In the absence of a local socket with file
permissions, the permissions of this directory determine which users
can have their @command{emacsclient} processes talk to the Emacs
server.  If @code{server-name} is an absolute file name, the server
file is created where specified by that file name.

@vindex EMACS_SERVER_FILE@r{, environment variable}
  To tell @command{emacsclient} to connect to the server over TCP with
a specific server file, use the @samp{-f} or @samp{--server-file}
option, or set the @env{EMACS_SERVER_FILE} environment variable
(@pxref{emacsclient Options}).  If @code{server-auth-dir} is set to a
non-standard value, or if @code{server-name} is set to an absolute
file name, @command{emacsclient} needs an absolute file name to the
server file, as the default @code{server-auth-dir} is hard-coded in
@command{emacsclient} to be used as the directory for resolving
relative filenames.

@node Invoking emacsclient
@subsection Invoking @code{emacsclient}
@cindex @code{emacsclient} invocation

  The simplest way to use the @command{emacsclient} program is to run
the shell command @samp{emacsclient @var{file}}, where @var{file} is a
file name.  This connects to an Emacs server, and tells that Emacs
process to visit @var{file} in one of its existing frames---either a
graphical frame, or one in a text terminal (@pxref{Frames}).  You
can then select that frame to begin editing.

  If there is no Emacs server, the @command{emacsclient} program halts
with an error message (you can prevent this from happening by using
the @samp{--alternate-editor=""} option to @command{emacsclient},
@pxref{emacsclient Options}).  If the Emacs process has no existing
frame---which can happen if it was started as a daemon (@pxref{Emacs
Server})---then Emacs opens a frame on the terminal in which you
called @command{emacsclient}.

  You can also force @command{emacsclient} to open a new frame on a
graphical display using the @samp{-c} option, or on a text terminal
using the @samp{-t} option.  @xref{emacsclient Options}.

  If you are running on a single text terminal, you can switch between
@command{emacsclient}'s shell and the Emacs server using one of two
methods: (i) run the Emacs server and @command{emacsclient} on
different virtual terminals, and switch to the Emacs server's virtual
terminal after calling @command{emacsclient}; or (ii) call
@command{emacsclient} from within the Emacs server itself, using Shell
mode (@pxref{Interactive Shell}) or Term mode (@pxref{Term Mode});
@command{emacsclient} blocks only the subshell under Emacs, and you can
still use Emacs to edit the file.

@kindex C-x #
@findex server-edit
  When you finish editing @var{file} in the Emacs server, type
@kbd{C-x #} (@code{server-edit}) in its buffer.  This saves the file
and sends a message back to the @command{emacsclient} program, telling
it to exit.  Programs that use @env{EDITOR} usually wait for the
editor---in this case @command{emacsclient}---to exit before doing
something else.

  You can also call @command{emacsclient} with multiple file name
arguments: @samp{emacsclient @var{file1} @var{file2} ...} tells the
Emacs server to visit @var{file1}, @var{file2}, and so forth.  Emacs
selects the buffer visiting @var{file1}, and buries the other buffers
at the bottom of the buffer list (@pxref{Buffers}).  The
@command{emacsclient} program exits once all the specified files are
finished (i.e., once you have typed @kbd{C-x #} in each server
buffer).

@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 was 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.

  Each @kbd{C-x #} 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 tell
@command{emacsclient} that you are finished.

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

@node emacsclient Options
@subsection @code{emacsclient} Options
@cindex @code{emacsclient} options

  You can pass some optional arguments to the @command{emacsclient}
program, such as:

@example
emacsclient -c +12 @var{file1} +4:3 @var{file2}
@end example

@noindent
The @samp{+@var{line}} or @samp{+@var{line}:@var{column}} arguments
specify line numbers, or line and column numbers, for the next file
argument.  These behave like the command line arguments for Emacs
itself.  @xref{Action Arguments}.

  The other optional arguments recognized by @command{emacsclient} are
listed below:

@table @samp
@item -a @var{command}
@itemx --alternate-editor=@var{command}
Specify a shell command to run if @command{emacsclient} fails to
contact Emacs.  This is useful when running @code{emacsclient} in a
script.  The command may include arguments, which may be quoted "like
this".  Currently, escaping of quotes is not supported.

As a special exception, if @var{command} is the empty string, then
@command{emacsclient} starts Emacs in daemon mode (as @samp{emacs
--daemon}) and then tries connecting again.

@cindex @env{ALTERNATE_EDITOR} environment variable
The environment variable @env{ALTERNATE_EDITOR} has the same effect as
the @samp{-a} option.  If both are present, the latter takes
precedence.

@cindex client frame
@item -c
@itemx --create-frame
Create a new graphical @dfn{client frame}, instead of using an
existing Emacs frame.  See below for the special behavior of @kbd{C-x
C-c} in a client frame.  If Emacs cannot create a new graphical frame
(e.g., if it cannot connect to the X server), it tries to create a
text terminal client frame, as though you had supplied the @samp{-t}
option instead.

On MS-Windows, a single Emacs session cannot display frames on both
graphical and text terminals, nor on multiple text terminals.  Thus,
if the Emacs server is running on a text terminal, the @samp{-c}
option, like the @samp{-t} option, creates a new frame in the server's
current text terminal.  @xref{Windows Startup}.

If you omit a filename argument while supplying the @samp{-c} option,
the new frame displays the @file{*scratch*} buffer by default.  You
can customize this behavior with the variable @code{initial-buffer-choice}
(@pxref{Entering Emacs}).

@item -F @var{alist}
@itemx --frame-parameters=@var{alist}
Set the parameters for a newly-created graphical frame
(@pxref{Frame Parameters}).

@item -d @var{display}
@itemx --display=@var{display}
Tell Emacs to open the given files on the X display @var{display}
(assuming there is more than one X display available).

@item -e
@itemx --eval
Tell Emacs to evaluate some Emacs Lisp code, instead of visiting some
files.  When this option is given, the arguments to
@command{emacsclient} are interpreted as a list of expressions to
evaluate, @emph{not} as a list of files to visit.

@item -f @var{server-file}
@itemx --server-file=@var{server-file}
Specify a server file (@pxref{TCP Emacs server}) for connecting to an
Emacs server via TCP@.  Alternatively, you can set the
@env{EMACS_SERVER_FILE} environment variable to point to the server
file.  (The command-line option overrides the environment variable.)

An Emacs server usually uses a local socket to listen for connections,
but also supports connections over TCP@.  To connect to a TCP Emacs
server, @command{emacsclient} needs to read a @dfn{server file}
containing the connection details of the Emacs server.  The name of
this file is specified with this option, either as a file name
relative to @file{~/.emacs.d/server} or as an absolute file name.
@xref{TCP Emacs server}.

@item -n
@itemx --no-wait
Let @command{emacsclient} exit immediately, instead of waiting until
all server buffers are finished.  You can take as long as you like to
edit the server buffers within Emacs, and they are @emph{not} killed
when you type @kbd{C-x #} in them.

@item --parent-id @var{id}
Open an @command{emacsclient} frame as a client frame in the parent X
window with id @var{id}, via the XEmbed protocol.  Currently, this
option is mainly useful for developers.

@item -q
@itemx --quiet
Do not let @command{emacsclient} display messages about waiting for
Emacs or connecting to remote server sockets.

@item -u
@itemx --suppress-output
Do not let @command{emacsclient} display results returned from the
server.  Mostly useful in combination with @samp{-e} when the
evaluation performed is for side-effect rather than result.

@item -s @var{server-name}
@itemx --socket-name=@var{server-name}
Connect to the Emacs server named @var{server-name}.  (This option is
not supported on MS-Windows.)  The server name is given by the
variable @code{server-name} on the Emacs server.  If this option is
omitted, @command{emacsclient} connects to the first server it finds.
If you set @code{server-name} of the Emacs server to an absolute file
name, give the same absolute file name as @var{server-name} to this
option to instruct @command{emacsclient} to connect to that server.
You need to use this option if you started Emacs as daemon
(@pxref{Initial Options}) and specified the name for the server
started by the daemon.

Alternatively, you can set the @env{EMACS_SOCKET_NAME} environment
variable to point to the server socket.  (The command-line option
overrides the environment variable.)

@item -t
@itemx --tty
@itemx -nw
Create a new client frame on the current text terminal, instead of
using an existing Emacs frame.  This behaves just like the @samp{-c}
option, described above, except that it creates a text terminal frame
(@pxref{Non-Window Terminals}).

On MS-Windows, @samp{-t} behaves just like @samp{-c} if the Emacs
server is using the graphical display, but if the Emacs server is
running on a text terminal, it creates a new frame in the current text
terminal.

@item -T @var{tramp-prefix}
@itemx --tramp-prefix=@var{tramp-prefix}
Set the prefix to add to filenames for Emacs to locate files on remote
machines (@pxref{Remote Files}) using TRAMP (@pxref{Top, The Tramp
Manual,, tramp, The Tramp Manual}).  This is mostly useful in
combination with using the Emacs server over TCP (@pxref{TCP Emacs
server}).  By ssh-forwarding the listening port and making the
@var{server-file} available on a remote machine, programs on the
remote machine can use @command{emacsclient} as the value for the
@env{EDITOR} and similar environment variables, but instead of talking
to an Emacs server on the remote machine, the files will be visited in
the local Emacs session using TRAMP.

@vindex EMACSCLIENT_TRAMP@r{, environment variable}
Setting the environment variable @env{EMACSCLIENT_TRAMP} has the same
effect as using the @samp{-T} option.  If both are specified, the
command-line option takes precedence.

For example, assume two hosts, @samp{local} and @samp{remote}, and
that the local Emacs listens on tcp port 12345.  Assume further that
@file{/home} is on a shared file system, so that the server file
@file{~/.emacs.d/server/server} is readable on both hosts.

@example
local$ ssh -R12345:localhost:12345 remote
remote$ export EDITOR="emacsclient \
        --server-file=server \
        --tramp=/ssh:remote:"
remote$ $EDITOR /tmp/foo.txt #Should open in local emacs.
@end example

@end table

  The new graphical or text terminal frames created by the @samp{-c}
or @samp{-t} options are considered @dfn{client frames}.  Any new
frame that you create from a client frame is also considered a client
frame.  If you type @kbd{C-x C-c} (@code{save-buffers-kill-terminal})
in a client frame, that command does not kill the Emacs session as it
normally does (@pxref{Exiting}).  Instead, Emacs deletes the client
frame; furthermore, if the client frame has an @command{emacsclient}
waiting to regain control (i.e., if you did not supply the @samp{-n}
option), Emacs deletes all other frames of the same client, and marks
the client's server buffers as finished, as though you had typed
@kbd{C-x #} in all of them.  If it so happens that there are no
remaining frames after the client frame(s) are deleted, the Emacs
session exits.

  As an exception, when Emacs is started as a daemon, all frames are
considered client frames, and @kbd{C-x C-c} never kills Emacs.  To
kill a daemon session, type @kbd{M-x kill-emacs}.

  Note that the @samp{-t} and @samp{-n} options are contradictory:
@samp{-t} says to take control of the current text terminal to create
a new client frame, while @samp{-n} says not to take control of the
text terminal.  If you supply both options, Emacs visits the specified
files(s) in an existing frame rather than a new client frame, negating
the effect of @samp{-t}.

@node Printing
@section Printing Hard Copies
@cindex hardcopy
@cindex printing

  Emacs provides commands for printing hardcopies of either an entire
buffer or part of one.  You can invoke the printing commands directly,
as detailed below, or using the @samp{File} menu on the menu bar.

@findex htmlfontify-buffer
  Aside from the commands described in this section, you can also
print hardcopies from Dired (@pxref{Operating on Files}) and the diary
(@pxref{Displaying the Diary}).  You can also ``print'' an Emacs
buffer to HTML with the command @kbd{M-x htmlfontify-buffer}, which
converts the current buffer to a HTML file, replacing Emacs faces with
CSS-based markup.  Furthermore, Org mode allows you to print Org
files to a variety of formats, such as PDF (@pxref{Org Mode}).

@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
@vindex lpr-commands
  On most operating systems, the above hardcopy commands submit files
for printing by calling the @command{lpr} program.  To change the
printer program, customize the variable @code{lpr-command}.  To
specify extra switches to give the printer program, customize the list
variable @code{lpr-switches}.  Its value should be a list of option
strings, each of which should start with @samp{-} (e.g., the option
string @code{"-w80"} specifies a line width of 80 columns).  The
default is the empty list, @code{nil}.

@vindex printer-name
@vindex lpr-printer-switch
  To specify the printer to use, set the variable @code{printer-name}.
The default, @code{nil}, specifies the default printer.  If you set it
to a printer name (a string), that name is passed to @command{lpr}
with the @samp{-P} switch; if you are not using @command{lpr}, you
should specify the switch with @code{lpr-printer-switch}.

@vindex lpr-headers-switches
@vindex lpr-add-switches
  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 @command{lpr}) to the printer program:
@code{nil} means don't add them (this should be the value if your
printer program is not compatible with @command{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
@subsection 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 and spool a PostScript image for the current buffer text.
@item M-x ps-spool-region
Generate and spool a PostScript image for the current region.
@item M-x ps-spool-buffer-with-faces
Generate and spool a PostScript image for the current buffer, showing the faces used.
@item M-x ps-spool-region-with-faces
Generate and spool a PostScript image for the current region, showing the faces used.
@item M-x ps-despool
Send the spooled PostScript to the printer.
@item M-x handwrite
Generate/print 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 @code{ps-print-buffer} and @code{ps-print-region} commands print
buffer contents in PostScript form.  One command prints the entire
buffer; the other, just the region.  The commands
@code{ps-print-buffer-with-faces} and
@code{ps-print-region-with-faces} behave similarly, but use PostScript
features to show the faces (fonts and colors) of the buffer text.

  Interactively, when you use a prefix argument (@kbd{C-u}), these commands
prompt the user for a file name, and save the PostScript image in that file
instead of sending it to the printer.

@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 ps-despool
  Use the command @code{ps-despool} to send the spooled images to the
printer.  This command sends the PostScript generated by
@samp{-spool-} commands (see commands above) to the printer.  With a
prefix argument (@kbd{C-u}), it prompts for a file name, and saves the
spooled PostScript image in that file 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.

@node PostScript Variables
@subsection 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.

  Alternatively, you can set @code{ps-print-color-p} to @code{black-white} to
print colors on black/white printers.

@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 and defaults to 8.5 points.  The value of
@code{ps-font-size} can also be a cons of 2 floats: one for landscape
mode, the other for portrait mode.

@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
@subsection 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 @key{RET}}; this creates a
@file{*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 @key{RET}).  For
further information on the various options, use the @samp{Interface
Help} button.

@node Sorting
@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 @samp{A}
through @samp{Z} come before lower-case @samp{a}, in accordance with the
@acronym{ASCII} character sequence (but @code{sort-fold-case},
described below, can change that).

  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.; the default is 1.  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.  With a
prefix argument, sort in reverse order.  See below for more details
on this command.

@findex reverse-region
@item M-x reverse-region
Reverse the order of the lines in the region.  This is useful for
sorting into descending order by fields, 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}.

@c Picture Mode documentation
@ifnottex
@include picture-xtra.texi
@end ifnottex


@node Editing Binary Files
@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.

  Inserting text always overwrites in Hexl mode.  This is to reduce
the risk of accidentally spoiling the alignment of data in the file.
Ordinary text characters insert themselves (i.e., overwrite with
themselves).  There are commands for insertion of special characters
by their code.  Most cursor motion keys, as well as @kbd{C-x C-s}, are
bound in Hexl mode to commands that produce the same effect.  Here is
a list of other important commands special to 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-M-a
Move to the beginning of a 512-byte page.

@item C-M-e
Move to the end of a 512-byte page.

@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
@section Saving Emacs Sessions
@cindex saving sessions
@cindex restore session
@cindex remember editing session
@cindex reload files
@cindex desktop

@vindex desktop-restore-frames
   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.  By default,
the desktop also tries to save the frame and window configuration.
To disable this, set @code{desktop-restore-frames} to @code{nil}.
(See that variable's documentation for some related options
that you can customize to fine-tune this behavior.)

@vindex desktop-files-not-to-save
Information about buffers visiting remote files is not saved by
default.  Customize the variable @code{desktop-files-not-to-save} to
change this.

@vindex frameset-filter-alist
   When the desktop restores the frame and window configuration, it
uses the recorded values of frame parameters, disregarding any
settings for those parameters you have in your init file (@pxref{Init
File}).  This means that frame parameters such as fonts and faces for
the restored frames will come from the desktop file, where they were
saved when you exited your previous Emacs session; any settings for
those parameters in your init file will be ignored.  To disable this,
customize the value of @code{frameset-filter-alist} to filter out the
frame parameters you don't want to be restored.

@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 init file (@pxref{Init File}):

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

@findex desktop-change-dir
@findex desktop-revert
@vindex desktop-path
  If you turn on @code{desktop-save-mode} in your init file, then when
Emacs starts, it looks for a saved desktop in the current directory.
(More precisely, it looks in the directories specified by
@code{desktop-path}, and uses the first desktop it finds.)
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 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 in 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.

@vindex desktop-auto-save-timeout
  While Emacs runs with @code{desktop-save-mode} turned on, it by
default auto-saves the desktop whenever any of it changes.  The
variable @code{desktop-auto-save-timeout} determines how frequently
Emacs checks for modifications to your desktop.

@vindex desktop-load-locked-desktop
  The file in which Emacs saves the desktop is locked while the
session runs, to avoid inadvertently overwriting it from another Emacs
session.  That lock is normally removed when Emacs exits, but if Emacs
or your system crashes, the lock stays, and when you restart Emacs, it
will by default ask you whether to use the locked desktop file.  You
can avoid the question by customizing the variable
@code{desktop-load-locked-desktop} to either @code{nil}, which means
never load the desktop in this case, or @code{t}, which means load the
desktop without asking.

@cindex desktop restore in daemon mode
  When Emacs starts in daemon mode, it cannot ask you any questions,
so if it finds the desktop file locked, it will not load it, unless
@code{desktop-load-locked-desktop} is @code{t}.  Note that restoring
the desktop in daemon mode is somewhat problematic for other reasons:
e.g., the daemon cannot use GUI features, so parameters such as frame
position, size, and decorations cannot be restored.  For that reason,
you may wish to delay restoring the desktop in daemon mode until the
first client connects, by calling @code{desktop-read} in a hook
function that you add to @code{server-after-make-frame-hook}
(@pxref{Creating Frames,,, elisp, The Emacs Lisp Reference Manual}).

@node Recursive Edit
@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}.  @xref{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.  It also exits the minibuffer, if it is active.

  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.

@ignore
@c Apart from edt and viper, this is all obsolete.
@c (Can't believe we were saying "most other editors" into 2014!)
@c There seems no point having a node just for those, which both have
@c their own manuals.
@node Emulation
@section Emulation
@cindex emulating other editors
@cindex other editors
@cindex EDT
@cindex vi
@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
@kbd{M-x crisp-mode} enables key bindings to emulate the CRiSP/Brief
editor.  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 @kbd{M-x edt-emulation-on}; restore normal
command bindings with @kbd{M-x edt-emulation-off}.

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 an 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
@end ignore


@node Hyperlinking
@section Hyperlinking and Web Navigation Features

  The following subsections describe convenience features for handling
URLs and other types of links occurring in Emacs buffer text.

@menu
* EWW::                         A web browser in Emacs.
* Embedded WebKit Widgets::     Embedding browser widgets in Emacs buffers.
* Browse-URL::                  Following URLs.
* Goto Address mode::           Activating URLs.
* FFAP::                        Finding files etc. at point.
@end menu

@node EWW
@subsection Web Browsing with EWW

@findex eww
@findex eww-open-file
  @dfn{EWW}, the Emacs Web Wowser, is a web browser package for Emacs.
It allows browsing URLs within an Emacs buffer.  The command @kbd{M-x
eww} will open a URL or search the web.  You can open a file
using the command @kbd{M-x eww-open-file}.  You can use EWW as the
web browser for @code{browse-url}, @pxref{Browse-URL}.  For full
details, @pxref{Top, EWW,, eww, The Emacs Web Wowser Manual}.

@node Embedded WebKit Widgets
@subsection Embedded WebKit Widgets
@cindex xwidget
@cindex webkit widgets
@cindex embedded widgets

@findex xwidget-webkit-browse-url
@findex xwidget-webkit-mode
@cindex Xwidget-WebKit mode
  If Emacs was compiled with the appropriate support packages, it is
able to show browser widgets in its buffers.  The command @kbd{M-x
xwidget-webkit-browse-url} asks for a URL to display in the browser
widget.  The URL normally defaults to the URL at or before point, but
if there is an active region (@pxref{Mark}), the default URL comes
from the region instead, after removing any whitespace from it.  The
command then creates a new buffer with the embedded browser showing
the specified URL@.  The buffer is put in the Xwidget-WebKit mode
(similar to Image mode, @pxref{Image Mode}), which provides
one-key commands for scrolling the widget, changing its size, and
reloading it.  Type @w{@kbd{C-h b}} in that buffer to see the key
bindings.

@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 allows you to easily follow URLs from within
Emacs.  Most URLs are followed by invoking a web browser;
@samp{mailto:} URLs are followed by invoking the @code{compose-mail}
Emacs command to send mail to the specified address (@pxref{Sending
Mail}).

  The command @kbd{M-x browse-url} prompts for a URL, and follows it.
If point is located near a plausible URL, that URL is offered as the
default.  The Browse-URL package also provides other commands which
you might like to bind to keys, such as @code{browse-url-at-point} and
@code{browse-url-at-mouse}.

@vindex browse-url-mailto-function
@vindex browse-url-browser-function
  You can customize Browse-URL's behavior via various options in the
@code{browse-url} Customize group.  In particular, the option
@code{browse-url-mailto-function} lets you define how to follow
@samp{mailto:} URLs, while @code{browse-url-browser-function} lets you
define how to follow other types of URLs.  For more information, view
the package commentary by typing @kbd{C-h P browse-url @key{RET}}.

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

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

@kindex C-c RET @r{(Goto Address mode)}
@findex goto-address-at-point
  You can make Emacs mark out URLs specially in the current buffer, by
typing @kbd{M-x goto-address-mode}.  When this buffer-local minor mode
is enabled, it finds all the URLs in the buffer, highlights them, and
turns them into clickable buttons.  You can follow the URL by typing
@kbd{C-c @key{RET}} (@code{goto-address-at-point}) while point is on
its text; or by clicking with @kbd{mouse-2}, or by clicking
@kbd{mouse-1} quickly (@pxref{Mouse References}).  Following a URL is
done by calling @code{browse-url} as a subroutine
(@pxref{Browse-URL}).

  It can be useful to add @code{goto-address-mode} to mode hooks and
hooks for displaying an incoming message
(e.g., @code{rmail-show-message-hook} for Rmail).  This is not needed
for Gnus or MH-E, which have similar features of their 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

  The FFAP package replaces certain key bindings for finding files,
such as @kbd{C-x C-f}, with commands that provide more sensible
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 (@pxref{Browse-URL}).

  This feature is useful for following references in mail or news
buffers, @file{README} files, @file{MANIFEST} files, and so on.  For
more information, view the package commentary by typing @kbd{C-h P
ffap @key{RET}}.

@cindex FFAP minor mode
@findex ffap-mode
  To enable FFAP, type @kbd{M-x ffap-bindings}.  This makes the
following key bindings, and also installs hooks for additional FFAP
functionality 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 @var{filename} @key{RET}
@kindex C-x C-r @r{(FFAP)}
@code{ffap-read-only}, analogous to @code{find-file-read-only}.
@item C-x C-v @var{filename} @key{RET}
@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 at
point (@code{dired-at-point}).
@item C-x C-d @var{directory} @key{RET}
@code{ffap-list-directory}, analogous to @code{list-directory}.
@item C-x 4 f @var{filename} @key{RET}
@kindex C-x 4 f @r{(FFAP)}
@code{ffap-other-window}, analogous to @code{find-file-other-window}.
@item C-x 4 r @var{filename} @key{RET}
@code{ffap-read-only-other-window}, analogous to
@code{find-file-read-only-other-window}.
@item C-x 4 d @var{directory} @key{RET}
@code{ffap-dired-other-window}, like @code{dired-other-window}.
@item C-x 5 f @var{filename} @key{RET}
@kindex C-x 5 f @r{(FFAP)}
@code{ffap-other-frame}, analogous to @code{find-file-other-frame}.
@item C-x 5 r @var{filename} @key{RET}
@code{ffap-read-only-other-frame}, analogous to
@code{find-file-read-only-other-frame}.
@item C-x 5 d @var{directory} @key{RET}
@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 Amusements
@section Games and Other Amusements
@cindex boredom
@cindex games

@findex animate-birthday-present
@cindex animate
  The @code{animate} package makes text dance (e.g., @kbd{M-x
animate-birthday-present}).

@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 bubbles
@cindex bubbles
  @kbd{M-x bubbles} is a game in which the object is to remove as many
bubbles as you can in the smallest number of moves.

@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 dissociated-press
  @kbd{M-x dissociated-press} scrambles the text in the current Emacs
buffer, word by word or character by character, writing its output to
a buffer named @file{*Dissociation*}.  A positive argument 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.  Dissociated Press produces
results fairly like those of a Markov chain, but is however, an
independent, ignoriginal invention; it techniquitously copies several
consecutive characters from the sample text between random jumps,
unlike a Markov chain which would jump randomly after each word or
character.  Keep dissociwords out of your documentation, if you want
it to be well userenced and properbose.

@findex dunnet
@cindex dunnet
  @kbd{M-x dunnet} runs a text-based adventure game.

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

@cindex tower of Hanoi
@findex 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.

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

@findex morse-region
@findex unmorse-region
@findex nato-region
@cindex Morse code
@cindex --/---/.-./.../.
  @kbd{M-x morse-region} converts the text in the region to Morse
code; @kbd{M-x unmorse-region} converts it back.  @kbd{M-x
nato-region} converts the text in the region to NATO phonetic
alphabet; @kbd{M-x denato-region} converts it back.

@findex pong
@cindex Pong game
@findex tetris
@cindex Tetris
@findex snake
@cindex Snake
  @kbd{M-x pong}, @kbd{M-x snake} and @kbd{M-x tetris} are
implementations of the well-known Pong, Snake and Tetris games.

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

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

@findex butterfly
@cindex butterfly
  ``Real Programmers'' deploy @kbd{M-x butterfly}, which uses butterflies
to flip a bit on the drive platter, see @uref{https://xkcd.com/378}.

@findex doctor
@cindex Eliza
  Finally, if you find yourself frustrated, try describing your
problems to the famous psychotherapist Eliza.  Just do @kbd{M-x
doctor}.  End each input by typing @key{RET} twice.

@ifnottex
@lowersections
@end ifnottex