Emacs provides extensive help features accessible through a single character, C-h. C-h is a prefix key that is used only for documentation-printing commands. The characters that you can type after C-h are called help options. One help option is C-h; that is how you ask for help about using C-h. To cancel, type C-g. The function key F1 is equivalent to C-h.
C-h C-h (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 SPC or DEL to scroll through the list.
C-h or F1 means "help" in various other contexts as
well. For example, in the middle of 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 C-h, because they
define other meanings for it, but they all support F1.)
Most help buffers use a special major mode, Help mode, which lets you scroll conveniently with SPC and DEL.
Here is a summary of the defined help commands.
apropos-command).
describe-bindings).
describe-key-briefly). Here c stands for `character'. For more
extensive information on key, use C-h k.
describe-function). Since commands are Lisp functions,
a command name may be used.
info).
The complete Emacs manual is available on-line in Info.
describe-key).
view-lossage).
describe-mode).
view-emacs-news).
finder-by-keyword).
describe-syntax). See section The Syntax Table.
help-with-tutorial).
describe-variable).
where-is).
describe-coding-system).
describe-input-method).
describe-language-support).
Info-goto-emacs-command-node).
Info-goto-emacs-key-command-node).
info-lookup-symbol).
The most basic C-h options are C-h c
(describe-key-briefly) and C-h k (describe-key).
C-h c key prints in the echo area the name of the command
that key is bound to. For example, C-h c C-f prints
`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 key does.
C-h k 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.
C-h c and C-h k work for any sort of key sequences, including function keys and mouse events.
C-h f (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,
C-h f auto-fill-mode RET
displays the documentation of 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 M-x).
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 (make-vector len) and want to check that you are using
make-vector properly, type C-h f make-vector RET.
Because C-h f allows all function names, not just command names,
you may find that some of your favorite abbreviations that work in
M-x don't work in C-h f. An abbreviation may be unique
among command names yet fail to be unique when other function names are
allowed.
The function name for C-h f to describe has a default which is
used if you type RET leaving the minibuffer empty. The default is
the function called by the innermost Lisp expression in the buffer around
point, provided that is a valid, defined Lisp function name. For
example, if point is located following the text `(make-vector (car
x)', the innermost list containing point is the one that starts with
`(make-vector', so the default is to describe the function
make-vector.
C-h f is often useful just to verify that you have the right spelling for the function name. If 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 C-g to cancel the C-h f command, then go on editing.
C-h w command RET tells you what keys are bound to
command. It prints a list of the keys in the echo area. If it
says the command is not on any key, you must use M-x to run it.
C-h w runs the command where-is.
C-h v (describe-variable) is like 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. See section Variables.
A more sophisticated sort of question to ask is, "What are the
commands for working with files?" To ask this question, type C-h
a file RET, which displays a list of all command names that
contain `file', including copy-file, 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 find-file by typing
C-x C-f. The a in C-h a stands for `Apropos';
C-h a runs the command apropos-command. This command
normally checks only commands (interactive functions); if you specify a
prefix argument, it checks noninteractive functions as well.
Because 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 C-h a kill-backwards RET doesn't reveal any, don't give up. Try just kill, or just backwards, or just back. Be persistent. Also note that you can use a regular expression as the argument, for more flexibility (see section Syntax of Regular Expressions).
Here is a set of arguments to give to 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 apropos strings.
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.
To list all user variables that match a regexp, use the command 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.
To list all Lisp symbols that contain a match for a regexp, not just the ones that are defined as commands, use the command M-x apropos instead of C-h a. This command does not check key bindings by default; specify a numeric argument if you want it to check them.
The apropos-documentation command is like apropos except
that it searches documentation strings as well as symbol names for
matches for the specified regular expression.
The apropos-value command is like 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.
If the variable apropos-do-all is non-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 Mouse-2 or move there and type RET.
The 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:
abbrev -- abbreviation handling, typing shortcuts, macros.
bib -- support for the bibliography processor 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; see section Using Multiple Typefaces).
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, Unix features.
vms -- support code for VMS.
wp -- word processing.
You can use the command C-h L
(describe-language-environment) to find out the support for a
specific language environment. See section 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 C-h h (view-hello-file) displays the file
`etc/HELLO', which shows how to say "hello" in many languages.
The command C-h I (describe-input-method) describes
information about input methods--either a specified input method, or by
default the input method in use. See section Input Methods.
The command C-h C (describe-coding-system) describes
information about coding systems--either a specified coding system, or
the ones currently in use. See section Coding Systems.
Help buffers provide the commands of View mode (see section Miscellaneous File Operations), plus a few special commands of their own.
When a command name (see section Running Commands by Name) or variable name (see section Variables) appears in the documentation, it normally appears inside paired single-quotes. You can click on the name with Mouse-2, or move point there and type RET, to view the documentation of that command or variable. Use C-c C-b to retrace your steps.
There are convenient commands for moving point to cross references in
the help text. TAB (help-next-ref) moves point down to the
next cross reference. Use S-TAB to move point up to the
previous cross reference (help-previous-ref).
C-h i (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 h after entering Info to run
a tutorial on using Info.
If you specify a numeric argument, 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.
There are two special help commands for accessing Emacs documentation
through Info. C-h C-f function RET enters Info and
goes straight to the documentation of the Emacs function
function. C-h C-k key enters Info and goes straight
to the documentation of the key key. These two keys run the
commands Info-goto-emacs-command-node and
Info-goto-emacs-key-command-node.
When editing a program, if you have an Info version of the manual for the programming language, you can use the command 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.
If something surprising happens, and you are not sure what commands you
typed, use C-h l (view-lossage). C-h l prints the last
100 command characters you typed in. If you see commands that you don't
know, you can use C-h c to find out what they do.
Emacs has numerous major modes, each of which redefines a few keys and
makes a few other changes in how editing works. C-h m
(describe-mode) prints documentation on the current major mode,
which normally describes all the commands that are changed in this
mode.
C-h b (describe-bindings) and C-h s
(describe-syntax) present other information about the current
Emacs mode. C-h b displays a list of all the key bindings now in
effect; 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 (see section Customizing Key Bindings). C-h s displays the
contents of the syntax table, with explanations of each character's
syntax (see section The Syntax Table).
You can get a similar list for a particular prefix key by typing 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 C-h. One of these is ESC, because ESC C-h is actually C-M-h, which marks a defun.)
The other C-h options display various files of useful
information. C-h C-w displays the full details on the complete
absence of warranty for GNU Emacs. C-h n (view-emacs-news)
displays the file `emacs/etc/NEWS', which contains documentation on
Emacs changes arranged chronologically. C-h t
(help-with-tutorial) displays the learn-by-doing Emacs tutorial.
C-h C-c (describe-copying) displays the file
`emacs/etc/COPYING', which tells you the conditions you must obey
in distributing copies of Emacs. C-h C-d
(describe-distribution) displays the file
`emacs/etc/DISTRIB', which tells you how you can order a copy of
the latest version of Emacs. C-h C-p (describe-project)
displays general information about the GNU Project.