1 Help

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.

C-h C-h prints a list of the possible help options, and then asks you to go ahead and type the option. It prompts with this string:

a b c f i k l m n p s t v w C-c C-d C-n C-w.  Type C-h for more help:

You should then type one of those characters.

Typing a third C-h displays a description of what the options mean; it still waits for you to type an option. To cancel, type C-g.

Here is a summary of the defined help commands.

C-h a regexp <RET>

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

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

Print the name of the command that key runs (describe-key-briefly). c is 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 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 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

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

C-h s

Display current contents of the syntax table, plus an explanation of what they mean (describe-syntax). @xref{Syntax}.

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>

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

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).

1.1 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 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.

1.2 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 is known 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 default in the prompt, you have typed the name of a defined 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 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. @xref{Variables}.

1.3 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 command-apropos.

Because C-h a looks only for functions whose names contain the string which 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 (@pxref{Regexps}).

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, 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.

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 super-apropos command is like apropos except that it searches documentation strings as well as symbol names for matches for the specified regular expression.

1.4 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.

‘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}).

‘games’

Games, jokes and amusements.

‘hardware’

Support for interfacing with exotic hardware.

‘help’

Support for on-line help systems.

‘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.

‘news’

Support for netnews reading and posting.

‘non-text’

Support for editing files that are not ordinary text.

‘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.

1.5 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.

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.

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 (@pxref{Key Bindings}). C-h s displays the contents of the syntax table, with explanations of each character’s syntax (@pxref{Syntax}).

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.

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