G. Help

Emacs provides extensive help features accessible through a single character, C-h. C-h is a prefix key that is used for commands that display documentation. 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. It also offers hyperlinks to further help regarding cross-referenced names, Info nodes, customization buffers and the like. See section G.7 Help Mode Commands.

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.

C-h a topic RET

This searches for commands whose names match topic, which should be a regular expression (see section K.5 Syntax of Regular Expressions). Browse the buffer that this command displays to find what you are looking for. See section G.4 Apropos.

M-x apropos RET topic RET

This works like 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. See section G.4 Apropos.

M-x apropos-documentation RET topic RET

This searches the documentation strings (the built-in short descriptions) of all variables and functions (not their names) for a match for topic, a regular expression. See section G.4 Apropos.

C-h i d m emacs RET i topic RET

This looks up topic in the indices of the Emacs on-line manual. If there are several matches, Emacs displays the first one. You can then press , to move to other matches, until you find what you are looking for.

C-h i d m emacs RET s topic RET

Similar, but searches for topic (which can be a regular expression) in the text of the manual rather than in its indices.

C-h F

This brings up the Emacs FAQ, where you can use the usual search commands (see section K. Searching and Replacement) to find the information.

C-h p

Finally, you can try looking up a suitable package using keywords pertinent to the feature you need. See section G.5 Keyword Search for Lisp Libraries.

To find the documentation of a key sequence or a menu item, type 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 C-h C-f for reading documentation of a command.

G.1 Help Summary

Here is a summary of the defined help commands.

C-h a regexp RET

Display a list of commands whose names match regexp (apropos-command).

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 (describe-bindings).

C-h c key

Show the name of the command that key runs (describe-key-briefly). Here c stands for "character." For more extensive information on key, use C-h k.

C-h f function RET

Display documentation on the Lisp function named function (describe-function). Since commands are Lisp functions, a command name may be used.

C-h h

Display the `HELLO' file, which shows examples of various character sets.

C-h i

Run Info, the program for browsing documentation files (info). The complete Emacs manual is available on-line in Info.

C-h k key

Display the name and documentation of the command that key runs (describe-key).

C-h l

Display a description of the last 100 characters you typed (view-lossage).

C-h m

Display documentation of the current major mode (describe-mode).

C-h n

Display documentation of Emacs changes, most recent first (view-emacs-news).

C-h P

Display info on known problems with Emacs and possible workarounds (view-emacs-problems).

C-h p

Find packages by topic keyword (finder-by-keyword).

C-h s

Display the current contents of the syntax table, plus an explanation of what they mean (describe-syntax). See section AD.6 The Syntax Table.

C-h t

Enter the Emacs interactive tutorial (help-with-tutorial).

C-h v var RET

Display the documentation of the Lisp variable var (describe-variable).

C-h w command RET

Show which keys run the command named command (where-is).

C-h C coding RET

Describe coding system coding (describe-coding-system).

C-h C RET

Describe the coding systems currently in use.

C-h I method RET

Describe an input method (describe-input-method).

C-h L language-env RET

Display information on the character sets, coding systems, and input methods used for language environment language-env (describe-language-environment).

C-h C-c

Display the copying conditions for GNU Emacs.

C-h C-d

Display information about getting new versions of GNU Emacs.

C-h C-f function RET

Enter Info and go to the node documenting the Emacs function function (Info-goto-emacs-command-node).

C-h C-k key

Enter Info and go to the node where the key sequence key is documented (Info-goto-emacs-key-command-node).

C-h C-p

Display information about the GNU Project.

C-h TAB symbol RET

Display the Info documentation on symbol symbol according to the programming language you are editing (info-lookup-symbol).

G.2 Documentation for a Key

The most basic C-h options are C-h c (describe-key-briefly) and C-h k (describe-key). C-h c key displays in the echo area the name of the command that key is bound to. For example, C-h c C-f displays `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.

G.3 Help by Command or Variable Name

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 default function name for C-h f to describe, if you type just RET, is the name of 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 displays 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 AD.2 Variables.

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 using Emacs. For real intimacy with Emacs, you must read the source code.

G.4 Apropos

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 K.5 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.

G.5 Keyword Search for Lisp Libraries

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 J.1 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, system features.
vms --- support code for VMS.
wp --- word processing.

G.6 Help for International Language Support

You can use the command C-h L (describe-language-environment) to find out information about the support for a specific language environment. See section Q.3 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 Q.4 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 Q.7 Coding Systems.

G.7 Help Mode Commands

Help buffers provide the same commands as View mode (see section M.10 Miscellaneous File Operations), plus a few special commands of their own.

SPC

Scroll forward.

DEL

BS

Scroll backward. On some keyboards, this key is known as BS or backspace.

RET

Follow a cross reference at point.

TAB

Move point forward to the next cross reference.

S-TAB

Move point back to the previous cross reference.

Mouse-2

Follow a cross reference that you click on.

When a command name (see section Running Commands by Name) or variable name (see section AD.2 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).

G.8 Other Help Commands

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. You can use C-h C-k to find the documentation of a menu item: just select that menu item when C-h C-k prompts for a key.

C-h C-f and 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 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 displays 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) displays 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, 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 (see section AD.4 Customizing Key Bindings). C-h s displays the contents of the syntax table, with explanations of each character's syntax (see section AD.6 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 containing 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 F (view-emacs-FAQ) displays the Emacs frequently-answered-questions list. 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. C-h P (view-emacs-problems) displays the file `emacs/etc/PROBLEMS', which lists known problems with Emacs in various situations with solutions or workarounds in many cases.

G.9 Help on Active Text and Tooltips

When a region of text is "active," so that you can select it with the mouse or a key like 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"). See section P.18 Tooltips (or "Balloon Help").