(shell-command-on-region): Handle errors and signals

[emacs.git] / man / help.texi

@c This is part of the Emacs manual.
@c Copyright (C) 1985, 86, 87, 93, 94, 95, 97, 2000, 2001
@c   Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Help, Mark, M-x, Top
@chapter Help
@kindex Help
@cindex help
@cindex self-documentation
@findex help-command
@kindex C-h
@kindex F1

  Emacs provides extensive help features accessible through a single
character, @kbd{C-h}.  @kbd{C-h} is a prefix key that is used for
commands that display documentation.  The characters that you can type after
@kbd{C-h} are called @dfn{help options}.  One help option is @kbd{C-h};
that is how you ask for help about using @kbd{C-h}.  To cancel, type
@kbd{C-g}.  The function key @key{F1} is equivalent to @kbd{C-h}.

@kindex C-h C-h
@findex help-for-help
  @kbd{C-h C-h} (@code{help-for-help}) displays a list of the possible
help options, each with a brief description.  Before you type a help
option, you can use @key{SPC} or @key{DEL} to scroll through the list.

  @kbd{C-h} or @key{F1} means ``help'' in various other contexts as
well.  For example, in the middle of @code{query-replace}, it describes
the options available for how to operate on the current match.  After a
prefix key, it displays a list of the alternatives that can follow the
prefix key.  (A few prefix keys don't support @kbd{C-h}, because they
define other meanings for it, but they all support @key{F1}.)

  Most help buffers use a special major mode, Help mode, which lets you
scroll conveniently with @key{SPC} and @key{DEL}.  It also offers
hyperlinks to further help regarding cross-referenced names, Info nodes,
customization buffers and the like.  @xref{Help Mode}.

@cindex searching documentation efficiently
@cindex looking for a subject in documentation
  If you are looking for a certain feature, but don't know where
exactly it is documented, and aren't sure of the name of a
related command or option, we recommend trying these methods.  Usually
it is best to start with an apropos command, then try searching the
manual index, then finally look in the FAQ and the package keywords.

@table @kbd
@item C-h a @var{topic} @key{RET}
This searches for commands whose names match @var{topic}, which should
be a regular expression (@pxref{Regexps}).  Browse the buffer that this
command displays to find what you are looking for.  @xref{Apropos}.

@item M-x apropos @key{RET} @var{topic} @key{RET}
This works like @kbd{C-h a}, but it also searches for user options and
other variables, in case the feature you are looking for is controlled
by an option, not a command.  @xref{Apropos}.

@item M-x apropos-documentation @key{RET} @var{topic} @key{RET}
This searches the @emph{documentation strings} (the built-in short
descriptions) of all variables and functions (not their names) for a
match for @var{topic}, a regular expression.  @xref{Apropos}.

@item C-h i d m emacs @key{RET} i @var{topic} @key{RET}
This looks up @var{topic} in the indices of the Emacs on-line manual.
If there are several matches, Emacs displays the first one.  You can then
press @key{,} to move to other matches, until you find what you are
looking for.

@item C-h i d m emacs @key{RET} s @var{topic} @key{RET}
Similar, but searches for @var{topic} (which can be a regular
expression) in the @emph{text} of the manual rather than in its
indices.

@item C-h F
This brings up the Emacs FAQ, where you can use the usual search
commands (@pxref{Search}) to find the information.

@item C-h p
Finally, you can try looking up a suitable package using keywords
pertinent to the feature you need.  @xref{Library Keywords}.
@end table

  To find the documentation of a key sequence or a menu item, type
@kbd{C-h C-k} and then type that key sequence or select the menu
item.  This looks up the description of the command invoked by the key
or the menu in the appropriate manual (not necessarily the Emacs
manual).  Likewise, use @kbd{C-h C-f} for reading documentation of a
command.

@menu
* Help Summary::        Brief list of all Help commands.
* Key Help::            Asking what a key does in Emacs.
* Name Help::           Asking about a command, variable or function name.
* Apropos::             Asking what pertains to a given topic.
* Library Keywords::    Finding Lisp libraries by keywords (topics).
* Language Help::       Help relating to international language support.
* Help Mode::           Special features of Help mode and Help buffers.
* Misc Help::           Other help commands.
* Help Echo::           Help on active text and tooltips (`balloon help')
@end menu

@iftex
@node Help Summary
@end iftex
@ifinfo
@node Help Summary
@section Help Summary
@end ifinfo

  Here is a summary of the defined help commands.

@table @kbd
@item C-h a @var{regexp} @key{RET}
Display a list of commands whose names match @var{regexp}
(@code{apropos-command}).
@item C-h b
Display a table of all key bindings in effect now, in this order: minor
mode bindings, major mode bindings, and global bindings
(@code{describe-bindings}).
@item C-h c @var{key}
Show the name of the command that @var{key} runs
(@code{describe-key-briefly}).  Here @kbd{c} stands for ``character.''
For more extensive information on @var{key}, use @kbd{C-h k}.
@item C-h f @var{function} @key{RET}
Display documentation on the Lisp function named @var{function}
(@code{describe-function}).  Since commands are Lisp functions,
a command name may be used.
@item C-h h
Display the @file{HELLO} file, which shows examples of various character
sets.
@item C-h i
Run Info, the program for browsing documentation files (@code{info}).
The complete Emacs manual is available on-line in Info.
@item C-h k @var{key}
Display the name and documentation of the command that @var{key} runs
(@code{describe-key}).
@item C-h l
Display a description of the last 100 characters you typed
(@code{view-lossage}).
@item C-h m
Display documentation of the current major mode (@code{describe-mode}).
@item C-h n
Display documentation of Emacs changes, most recent first
(@code{view-emacs-news}).
@item C-h P
Display info on known problems with Emacs and possible workarounds
(@code{view-emacs-problems}).
@item C-h p
Find packages by topic keyword (@code{finder-by-keyword}).
@item C-h s
Display the current contents of the syntax table, plus an explanation of
what they mean (@code{describe-syntax}).  @xref{Syntax}.
@item C-h t
Enter the Emacs interactive tutorial (@code{help-with-tutorial}).
@item C-h v @var{var} @key{RET}
Display the documentation of the Lisp variable @var{var}
(@code{describe-variable}).
@item C-h w @var{command} @key{RET}
Show which keys run the command named @var{command} (@code{where-is}).
@item C-h C @var{coding} @key{RET}
Describe coding system @var{coding}
(@code{describe-coding-system}).
@item C-h C @key{RET}
Describe the coding systems currently in use.
@item C-h I @var{method} @key{RET}
Describe an input method (@code{describe-input-method}).
@item C-h L @var{language-env} @key{RET}
Display information on the character sets, coding systems, and input
methods used for language environment @var{language-env}
(@code{describe-language-environment}).
@item C-h C-c
Display the copying conditions for GNU Emacs.
@item C-h C-d
Display information about getting new versions of GNU Emacs.
@item C-h C-f @var{function} @key{RET}
Enter Info and go to the node documenting the Emacs function @var{function}
(@code{Info-goto-emacs-command-node}).
@item C-h C-k @var{key}
Enter Info and go to the node where the key sequence @var{key} is
documented (@code{Info-goto-emacs-key-command-node}).
@item C-h C-p
Display information about the GNU Project.
@item C-h @key{TAB} @var{symbol} @key{RET}
Display the Info documentation on symbol @var{symbol} according to the
programming language you are editing (@code{info-lookup-symbol}).
@end table

@node Key Help
@section Documentation for a Key

@kindex C-h c
@findex describe-key-briefly
  The most basic @kbd{C-h} options are @kbd{C-h c}
(@code{describe-key-briefly}) and @w{@kbd{C-h k}} (@code{describe-key}).
@kbd{C-h c @var{key}} displays in the echo area the name of the command
that @var{key} is bound to.  For example, @kbd{C-h c C-f} displays
@samp{forward-char}.  Since command names are chosen to describe what
the commands do, this is a good way to get a very brief description of
what @var{key} does.

@kindex C-h k
@findex describe-key
  @kbd{C-h k @var{key}} is similar but gives more information: it
displays the documentation string of the command as well as its name.
This is too big for the echo area, so a window is used for the display.

  @kbd{C-h c} and @kbd{C-h k} work for any sort of key sequences,
including function keys and mouse events.

@node Name Help
@section Help by Command or Variable Name

@kindex C-h f
@findex describe-function
  @kbd{C-h f} (@code{describe-function}) reads the name of a Lisp function
using the minibuffer, then displays that function's documentation string
in a window.  Since commands are Lisp functions, you can use this to get
the documentation of a command that you know by name.  For example,

@example
C-h f auto-fill-mode @key{RET}
@end example

@noindent
displays the documentation of @code{auto-fill-mode}.  This is the only
way to get the documentation of a command that is not bound to any key
(one which you would normally run using @kbd{M-x}).

  @kbd{C-h f} is also useful for Lisp functions that you are planning to
use in a Lisp program.  For example, if you have just written the
expression @code{(make-vector len)} and want to check that you are using
@code{make-vector} properly, type @kbd{C-h f make-vector @key{RET}}.
Because @kbd{C-h f} allows all function names, not just command names,
you may find that some of your favorite abbreviations that work in
@kbd{M-x} don't work in @kbd{C-h f}.  An abbreviation may be unique
among command names yet fail to be unique when other function names are
allowed.

  The default function name for @kbd{C-h f} to describe, if you type
just @key{RET}, is the name of the function called by the innermost Lisp
expression in the buffer around point, @emph{provided} that is a valid,
defined Lisp function name.  For example, if point is located following
the text @samp{(make-vector (car x)}, the innermost list containing
point is the one that starts with @samp{(make-vector}, so the default is
to describe the function @code{make-vector}.

  @kbd{C-h f} is often useful just to verify that you have the right
spelling for the function name.  If @kbd{C-h f} mentions a name from the
buffer as the default, that name must be defined as a Lisp function.  If
that is all you want to know, just type @kbd{C-g} to cancel the @kbd{C-h
f} command, then go on editing.

@kindex C-h w
@findex where-is
  @kbd{C-h w @var{command} @key{RET}} tells you what keys are bound to
@var{command}.  It displays a list of the keys in the echo area.  If it
says the command is not on any key, you must use @kbd{M-x} to run it.
@kbd{C-h w} runs the command @code{where-is}.

  @kbd{C-h v} (@code{describe-variable}) is like @kbd{C-h f} but describes
Lisp variables instead of Lisp functions.  Its default is the Lisp symbol
around or before point, but only if that is the name of a known Lisp
variable.  @xref{Variables}.@refill

  Help buffers describing variables or functions defined in Lisp
normally have hyperlinks to the Lisp definition, if you have the Lisp
source files installed.  If you know Lisp, this provides the ultimate
documentation.  If you don't know Lisp, you should learn it.  If you
are treating Emacs as an object file, then you are just @emph{using}
Emacs.  For real intimacy with Emacs, you must read the source code.

@node Apropos
@section Apropos

@kindex C-h a
@findex apropos-command
@cindex apropos
  A more sophisticated sort of question to ask is, ``What are the
commands for working with files?''  To ask this question, type @kbd{C-h
a file @key{RET}}, which displays a list of all command names that
contain @samp{file}, including @code{copy-file}, @code{find-file}, and
so on.  With each command name appears a brief description of how to use
the command, and what keys you can currently invoke it with.  For
example, it would say that you can invoke @code{find-file} by typing
@kbd{C-x C-f}.  The @kbd{a} in @kbd{C-h a} stands for ``Apropos'';
@kbd{C-h a} runs the command @code{apropos-command}.  This command
normally checks only commands (interactive functions); if you specify a
prefix argument, it checks noninteractive functions as well.

  Because @kbd{C-h a} looks only for functions whose names contain the
string you specify, you must use ingenuity in choosing the
string.  If you are looking for commands for killing backwards and
@kbd{C-h a kill-backwards @key{RET}} doesn't reveal any, don't give up.
Try just @kbd{kill}, or just @kbd{backwards}, or just @kbd{back}.  Be
persistent.  Also note that you can use a regular expression as the
argument, for more flexibility (@pxref{Regexps}).

  Here is a set of arguments to give to @kbd{C-h a} that covers many
classes of Emacs commands, since there are strong conventions for naming
the standard Emacs commands.  By giving you a feel for the naming
conventions, this set should also serve to aid you in developing a
technique for picking @code{apropos} strings.

@quotation
char, line, word, sentence, paragraph, region, page, sexp, list, defun,
rect, buffer, frame, window, face, file, dir, register, mode, beginning, end,
forward, backward, next, previous, up, down, search, goto, kill, delete,
mark, insert, yank, fill, indent, case, change, set, what, list, find,
view, describe, default.
@end quotation

@findex apropos-variable
  To list all user variables that match a regexp, use the command
@kbd{M-x apropos-variable}. This command shows only user variables and
customization options by default; if you specify a prefix argument, it
checks all variables.

@findex apropos
  To list all Lisp symbols that contain a match for a regexp, not just
the ones that are defined as commands, use the command @kbd{M-x apropos}
instead of @kbd{C-h a}.  This command does not check key bindings by
default; specify a numeric argument if you want it to check them.

@findex apropos-documentation
  The @code{apropos-documentation} command is like @code{apropos} except
that it searches documentation strings as well as symbol names for
matches for the specified regular expression.

@findex apropos-value
  The @code{apropos-value} command is like @code{apropos} except that it
searches symbols' values for matches for the specified regular
expression.  This command does not check function definitions or
property lists by default; specify a numeric argument if you want it to
check them.

@vindex apropos-do-all
  If the variable @code{apropos-do-all} is non-@code{nil}, the commands
above all behave as if they had been given a prefix argument.

  If you want more information about a function definition, variable or
symbol property listed in the Apropos buffer, you can click on it with
@kbd{Mouse-2} or move there and type @key{RET}.

@node Library Keywords
@section Keyword Search for Lisp Libraries

@kindex C-h p
@findex finder-by-keyword
The @kbd{C-h p} command lets you search the standard Emacs Lisp
libraries by topic keywords.  Here is a partial list of keywords you can
use:

@display
abbrev --- abbreviation handling, typing shortcuts, macros.
bib --- support for the bibliography processor @code{bib}.
c --- C and C++ language support.
calendar --- calendar and time management support.
comm --- communications, networking, remote access to files.
data --- support for editing files of data.
docs --- support for Emacs documentation.
emulations --- emulations of other editors.
extensions --- Emacs Lisp language extensions.
faces --- support for using faces (fonts and colors; @pxref{Faces}).
frames --- support for Emacs frames and window systems.
games --- games, jokes and amusements.
hardware --- support for interfacing with exotic hardware.
help --- support for on-line help systems.
hypermedia --- support for links within text, or other media types.
i18n --- internationalization and alternate character-set support.
internal --- code for Emacs internals, build process, defaults.
languages --- specialized modes for editing programming languages.
lisp --- support for using Lisp (including Emacs Lisp).
local --- libraries local to your site.
maint --- maintenance aids for the Emacs development group.
mail --- modes for electronic-mail handling.
matching --- searching and matching.
news --- support for netnews reading and posting.
non-text --- support for editing files that are not ordinary text.
oop --- support for object-oriented programming.
outlines --- hierarchical outlining.
processes --- process, subshell, compilation, and job control support.
terminals --- support for terminal types.
tex --- support for the @TeX{} formatter.
tools --- programming tools.
unix --- front-ends/assistants for, or emulators of, system features.
vms --- support code for VMS.
wp --- word processing.
@end display

@node Language Help
@section Help for International Language Support

  You can use the command @kbd{C-h L}
(@code{describe-language-environment}) to find out information about
the support for a specific language environment.  @xref{Language
Environments}.  This tells you which languages this language
environment is useful for, and lists the character sets, coding
systems, and input methods that go with it.  It also shows some sample
text to illustrate scripts.

  The command @kbd{C-h h} (@code{view-hello-file}) displays the file
@file{etc/HELLO}, which shows how to say ``hello'' in many languages.

  The command @kbd{C-h I} (@code{describe-input-method}) describes
information about input methods---either a specified input method, or by
default the input method in use.  @xref{Input Methods}.

  The command @kbd{C-h C} (@code{describe-coding-system}) describes
information about coding systems---either a specified coding system, or
the ones currently in use.  @xref{Coding Systems}.

@node Help Mode
@section Help Mode Commands

  Help buffers provide the same commands as View mode (@pxref{Misc File
Ops}), plus a few special commands of their own.

@table @kbd
@item @key{SPC}
Scroll forward.
@item @key{DEL}
@itemx @key{BS}
Scroll backward.  On some keyboards, this key is known as @key{BS} or
@key{backspace}.
@item @key{RET}
Follow a cross reference at point.
@item @key{TAB}
Move point forward to the next cross reference.
@item S-@key{TAB}
Move point back to the previous cross reference.
@item Mouse-2
Follow a cross reference that you click on.
@end table

  When a command name (@pxref{M-x,, Running Commands by Name}) or
variable name (@pxref{Variables}) appears in the documentation, it
normally appears inside paired single-quotes.  You can click on the name
with @kbd{Mouse-2}, or move point there and type @key{RET}, to view the
documentation of that command or variable.  Use @kbd{C-c C-b} to retrace
your steps.

@kindex @key{TAB} @r{(Help mode)}
@findex help-next-ref
@kindex S-@key{TAB} @r{(Help mode)}
@findex help-previous-ref
  There are convenient commands for moving point to cross references in
the help text.  @key{TAB} (@code{help-next-ref}) moves point down to the
next cross reference.  Use @kbd{S-@key{TAB}} to move point up to the
previous cross reference (@code{help-previous-ref}).

@node Misc Help
@section Other Help Commands

@kindex C-h i
@findex info
@cindex Info
@cindex manuals, on-line
@cindex on-line manuals
  @kbd{C-h i} (@code{info}) runs the Info program, which is used for
browsing through structured documentation files.  The entire Emacs manual
is available within Info.  Eventually all the documentation of the GNU
system will be available.  Type @kbd{h} after entering Info to run
a tutorial on using Info.

  If you specify a numeric argument, @kbd{C-h i} prompts for the name of
a documentation file.  This way, you can browse a file which doesn't
have an entry in the top-level Info menu.  It is also handy when you
need to get to the documentation quickly, and you know the exact name of
the file.

@kindex C-h C-f
@kindex C-h C-k
@findex Info-goto-emacs-key-command-node
@findex Info-goto-emacs-command-node
  There are two special help commands for accessing Emacs documentation
through Info.  @kbd{C-h C-f @var{function} @key{RET}} enters Info and
goes straight to the documentation of the Emacs function
@var{function}.  @kbd{C-h C-k @var{key}} enters Info and goes straight
to the documentation of the key @var{key}.  These two keys run the
commands @code{Info-goto-emacs-command-node} and
@code{Info-goto-emacs-key-command-node}.  You can use @kbd{C-h C-k} to
find the documentation of a menu item: just select that menu item when
@kbd{C-h C-k} prompts for a key.

  @kbd{C-h C-f} and @kbd{C-h C-k} know about commands and keys
described in manuals other than the Emacs manual.  Thus, they make it
easier to find the documentation of commands and keys when you are not
sure which manual describes them, like when using some specialized
mode.

  When editing a program, if you have an Info version of the manual for
the programming language, you can use the command @kbd{C-h C-i} to refer
to the manual documentation for a symbol (keyword, function or
variable).  The details of how this command works depend on the major
mode.

@kindex C-h l
@findex view-lossage
  If something surprising happens, and you are not sure what commands you
typed, use @kbd{C-h l} (@code{view-lossage}).  @kbd{C-h l} displays the last
100 command characters you typed in.  If you see commands that you don't
know, you can use @kbd{C-h c} to find out what they do.

@kindex C-h m
@findex describe-mode
  Emacs has numerous major modes, each of which redefines a few keys and
makes a few other changes in how editing works.  @kbd{C-h m}
(@code{describe-mode}) displays documentation on the current major mode,
which normally describes all the commands that are changed in this
mode.

@kindex C-h b
@findex describe-bindings
  @kbd{C-h b} (@code{describe-bindings}) and @kbd{C-h s}
(@code{describe-syntax}) present other information about the current
Emacs mode.  @kbd{C-h b} displays a list of all the key bindings now in
effect, showing the local bindings defined by the current minor modes first,
then the local bindings defined by the current major mode, and finally
the global bindings (@pxref{Key Bindings}).  @kbd{C-h s} displays the
contents of the syntax table, with explanations of each character's
syntax (@pxref{Syntax}).

  You can get a similar list for a particular prefix key by typing
@kbd{C-h} after the prefix key.  (There are a few prefix keys for which
this does not work---those that provide their own bindings for
@kbd{C-h}.  One of these is @key{ESC}, because @kbd{@key{ESC} C-h} is
actually @kbd{C-M-h}, which marks a defun.)

@kindex C-h F
@findex view-emacs-FAQ
@kindex C-h n
@findex view-emacs-news
@kindex C-h C-c
@findex describe-copying
@kindex C-h C-d
@findex describe-distribution
@kindex C-h C-w
@findex describe-no-warranty
@kindex C-h C-p
@findex describe-project
@kindex C-h P
@findex view-emacs-problems
  The other @kbd{C-h} options display various files containing useful
information.  @kbd{C-h C-w} displays the full details on the complete
absence of warranty for GNU Emacs.  @kbd{C-h n} (@code{view-emacs-news})
displays the file @file{emacs/etc/NEWS}, which contains documentation on
Emacs changes arranged chronologically.  @kbd{C-h F}
(@code{view-emacs-FAQ}) displays the Emacs frequently-answered-questions
list.  @kbd{C-h t} (@code{help-with-tutorial}) displays the
learn-by-doing Emacs tutorial.  @kbd{C-h C-c} (@code{describe-copying})
displays the file @file{emacs/etc/COPYING}, which tells you the
conditions you must obey in distributing copies of Emacs.  @kbd{C-h C-d}
(@code{describe-distribution}) displays the file
@file{emacs/etc/DISTRIB}, which tells you how you can order a copy of
the latest version of Emacs.  @kbd{C-h C-p} (@code{describe-project})
displays general information about the GNU Project.  @kbd{C-h P}
(@code{view-emacs-problems}) displays the file
@file{emacs/etc/PROBLEMS}, which lists known problems with Emacs in
various situations with solutions or workarounds in many cases.

@node Help Echo
@section Help on Active Text and Tooltips

@cindex tooltips
@cindex balloon help
  When a region of text is ``active,'' so that you can select it with
the mouse or a key like @kbd{RET}, it often has associated help text.
Areas of the mode line are examples.  This help will normally be
shown in the echo area when you move point into the active text.  In
a window system you can display the help text as a ``tooltip''
(sometimes known as ``balloon help'').  @xref{Tooltips}.