11. Help

Emacs provides extensive help features, all accessible through the help character, C-h. This is a prefix key that is used for commands that display documentation; the next character you type should be a help options, to ask for a particular kind of help. You can cancel the C-h command with C-g. The function key F1 is equivalent to C-h.

C-h itself is one of the help options; C-h C-h displays a list of help options, with a brief description of each one (help-for-help). You can scroll the list with SPC and DEL, then type the help option you want. To cancel, type C-g.

C-h or F1 means "help" in various other contexts as well. For instance, you can type them after a prefix key to display list of the keys that can follow the prefix key. (A few prefix keys don't support C-h in this way, because they define other meanings for it, but they all support F1 for help.)

Most help buffers use a special major mode, Help mode, which lets you scroll conveniently with SPC and DEL. You can also follow hyperlinks to URLs, and to other facilities including Info nodes and customization buffers. See section Help Mode Commands.

If you are looking for a certain feature, but don't know what it is called or where to look, we recommend three methods. First, try an apropos command, then try searching the manual index, then look in the FAQ and the package keywords.

C-h a topics RET

This searches for commands whose names match the argument topics. The argument can be a keyword, a list of keywords, or a regular expression (see section Syntax of Regular Expressions). This command displays all the matches in a new buffer. See section Apropos.

C-h i d m emacs RET i topic RET

This searches for topic in the indices of the on-line Emacs manual, and displays the first match found. Press , to see subsequent matches. You can use a regular expression as topic.

C-h i d m emacs RET s topic RET

Similar, but searches the text of the manual rather than the indices.

C-h C-f

This displays the Emacs FAQ. You can use the Info commands to browse it.

C-h p

This displays the available Emacs packages based on keywords. See section Keyword Search for Lisp Libraries.

11.1 Help Summary

Here is a summary of the Emacs interactive help commands. (The character that follows C-h is the "help option.") See section Help Files, for other help commands that display fixed files of information.

C-h a topics RET

Display a list of commands whose names match topics (apropos-command; see section Apropos).

C-h b

Display all active key bindings; minor mode bindings first, then those of the major mode, then global bindings (describe-bindings).

C-h c key

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

C-h d topics RET

Display the commands and variables whose documentation matches topics (apropos-documentation).

C-h e

Display the *Messages* buffer (view-echo-area-messages).

C-h f function RET

Display documentation on the Lisp function named function (describe-function). Since commands are Lisp functions, this works for commands too.

C-h h

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

C-h i

Run Info, the GNU documentation browser (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 p

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

C-h s

Display the current contents of the syntax table, with an explanation of what they mean (describe-syntax). See section 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 the coding system coding (describe-coding-system).

C-h C RET

Describe the coding systems currently in use.

C-h I method RET

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

C-h L language-env RET

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

C-h F function RET

Enter Info and goes to the node that documents the Emacs function function (Info-goto-emacs-command-node).

C-h K key

Enter Info and goes to the node that documents the key sequence key (Info-goto-emacs-key-command-node).

C-h S symbol RET

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

C-h .

Display the help message for a special text area, if point is in one (display-local-help). (These include, for example, links in `*Help*' buffers.)

11.2 Documentation for a Key

The help commands to get information about a key sequence are C-h c and C-h k. 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 gives you 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. It displays this information in a window, since it may not fit in the echo area.

To find the documentation of a key sequence key, type C-h K key. This displays the appropriate manual section which contains the documentation of key.

C-h c, C-h k and C-h K work for any sort of key sequences, including function keys, menus, and mouse events. For instance, after C-h k you can select a menu item from the menu bar, to view the documentation string of the command it runs.

C-h w command RET lists the keys that are bound to command. It displays the list in the echo area. If it says the command is not on any key, that means you must use M-x to run it. C-h w runs the command where-is.

11.3 Help by Command or Variable Name

C-h f function RET (describe-function) displays the documentation of Lisp function function, in a window. Since commands are Lisp functions, you can use this method to view the documentation of any command whose name you know. 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 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 completion abbreviations that work in M-x don't work in C-h f. An abbreviation that is unique among command names may not be unique among all function names.

If you type C-h f RET, it describes the function called by the innermost Lisp expression in the buffer around point, provided that function name is a valid, defined Lisp function. (That name appears as the default while you enter the argument.) 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 C-h f RET will describe the function make-vector.

C-h f is also useful just to verify that you spelled a function name correctly. If the minibuffer prompt for C-h f shows the function name from the buffer as the default, it means that name is defined as a Lisp function. Type C-g to cancel the C-h f command if you don't really want to view the documentation.

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, if that is the name of a defined Lisp variable. See section Variables.

Help buffers that describe Emacs variables and functions normally have hyperlinks to the corresponding source definition, if you have the source files installed. (See section Hyperlinking and Navigation Features.) If you know Lisp (or C), this provides the ultimate documentation. If you don't know Lisp, you should learn it. (The Introduction to Emacs Lisp Programming, available from the FSF through fsf.org, is a good way to get started.) If Emacs feels you are just using it, treating it as an object program, its feelings may be hurt. For real intimacy, read the Emacs source code.

To find a function's documentation in a manual, use C-h F (Info-goto-emacs-command-node). This knows about various manuals, not just the Emacs manual, and finds the right one.

11.4 Apropos

The apropos commands answer questions like, "What are the commands for working with files?" More precisely, you specify an apropos pattern, which means either a word, a list of words, or a regular expression. Each apropos command displays a list of items that match the pattern, in a separate buffer.

C-h a pattern RET

Search for commands whose names match pattern.

M-x apropos RET pattern RET

Search for functions and variables whose names match pattern. Both interactive functions (commands) and noninteractive functions can be found by this command.

M-x apropos-variable RET pattern RET

Search for user-option variables whose names match pattern.

M-x apropos-value RET pattern RET

Search for functions whose definitions pattern, and variables whose values match pattern.

C-h d pattern RET

Search for functions and variables whose documentation strings match pattern.

The simplest kind of apropos pattern is one word. Anything which contains that word matches the pattern. Thus, to find the commands that work on files, type C-h a file RET. This displays a list of all command names that contain `file', including copy-file, find-file, and so on. Each command name comes with a brief description and a list of keys you can currently invoke it with. In our 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.

For more information about a function definition, variable or symbol property listed in the apropos buffer, you can click on it with Mouse-1 or Mouse-2, or move there and type RET.

When you specify more than one word in the apropos pattern, a name must contain at least two of the words in order to match. Thus, if you are looking for commands to kill a chunk of text before point, you could try C-h a kill back backward behind before RET. The real command name kill-backward will match that; if there were a command kill-text-before, it would also match, since it contains two of the specified words.

For even greater flexibility, you can specify a regular expression (see section Syntax of Regular Expressions). An apropos pattern is interpreted as a regular expression if it contains any of the regular expression special characters, `^$*+?.\['.

Following the conventions for naming Emacs commands, here are some words that you'll find useful in apropos patterns. By using them in C-h a, you will also get a feel for the naming conventions.

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.

Use M-x apropos instead of C-h a to list all the Lisp symbols that match an apropos pattern, not just the symbols that are commands. This command does not list key bindings by default; specify a numeric argument if you want it to list them.

Use M-x apropos-variable to list user-customizable variables that match an apropos pattern. If you specify a prefix argument, it lists all matching variables.

The apropos-documentation command is like apropos except that it searches documentation strings instead of symbol names for matches.

The apropos-value command is like apropos except that it searches variables' values for matches for the apropos pattern. With a prefix argument, it also checks symbols' function definitions and property lists.

If the variable apropos-do-all is non-nil, the apropos commands always behave as if they had been given a prefix argument.

By default, apropos lists the search results in alphabetical order. If the variable apropos-sort-by-scores is non-nil, the apropos commands try to guess the relevance of each result, and display the most relevant ones first.

By default, apropos lists the search results for apropos-documentation in order of relevance of the match. If the variable apropos-documentation-sort-by-scores is nil, apropos lists the symbols found in alphabetical order.

11.5 Help Mode Commands

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

SPC

Scroll forward.

DEL

Scroll backward.

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-1

Mouse-2

Follow a cross reference that you click on.

C-c C-c

Show all documentation about the symbol at point.

When a function name (see section Running Commands by Name), variable name (see section Variables), or face name (see section Using Multiple Typefaces) appears in the documentation, it normally appears inside paired single-quotes. To view the documentation of that command, variable or face, you can click on the name with Mouse-1 or Mouse-2, or move point there and type RET. Use C-c C-b to retrace your steps.

You can follow cross references to URLs (web pages) also. This uses the browse-url command to view the page in the browser you choose. See section Following URLs.

There are convenient commands to move point to cross references in the help text. TAB (help-next-ref) moves point down to the next cross reference. S-TAB moves up to the previous cross reference (help-previous-ref).

To view all documentation about any symbol name that appears in the text, move point to the symbol name and type C-c C-c (help-follow-symbol). This shows all available documentation about the symbol as a variable, function and/or face. As above, use C-c C-b to retrace your steps.

11.6 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:

11.7 Help for International Language Support

You can use the command C-h L (describe-language-environment) to get information about a specific language environment. See section Language Environments. This tells you which languages this language environment supports. It also lists the character sets, coding systems, and input methods that work with this language environment, and finally 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 an input method--either a specified input method, or by default the input method currently in use. See section Input Methods.

The command C-h C (describe-coding-system) describes coding systems--either a specified coding system, or the ones currently in use. See section Coding Systems.

11.8 Other Help Commands

C-h i (info) runs the Info program, which browses structured documentation files. The entire Emacs manual is available within Info, along with many other manuals for the GNU system. Type h after entering Info to run a tutorial on using Info.

With a numeric argument n, C-h i selects the Info buffer `*info*<n>'. This is useful if you want to browse multiple Info manuals simultaneously. If you specify just C-u as the prefix argument, C-h i prompts for the name of a documentation file, so you can browse a file which doesn't have an entry in the top-level Info menu.

The help commands C-h F function RET and C-h K key, described above, enter Info and go straight to the documentation of function or key.

When editing a program, if you have an Info version of the manual for the programming language, you can use C-h S (info-lookup-symbol) to find symbol (keyword, function or variable) in the proper manual. The details of how this command works depend on the major mode.

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

To review recent echo area messages, use C-h e (view-echo-area-messages). This displays the buffer *Messages*, where those messages are kept.

Each Emacs major mode typically redefines a few keys and makes other changes in how editing works. C-h m (describe-mode) displays documentation on the current major mode, which normally describes the commands and features that are changed in this mode.

C-h b (describe-bindings) and C-h s (describe-syntax) show other information about the current environment within Emacs. C-h b displays a list of all the key bindings now in effect: first the local bindings of the current minor modes, 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 list of subcommands 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.)

11.9 Help Files

The Emacs help commands described above display dynamic help based on the current state within Emacs, or refer to manuals. Other help commands display pre-written, static help files. These commands all have the form C-h C-char; that is, C-h followed by a control character.

C-h C-c

Display the Emacs copying conditions (describe-copying). These are the rules under which you can copy and redistribute Emacs.

C-h C-d

Display how to download or order the latest version of Emacs and other GNU software (describe-distribution).

C-h C-e

Display the list of known Emacs problems, sometimes with suggested workarounds (view-emacs-problems).

C-h C-f

Display the Emacs frequently-answered-questions list (view-emacs-FAQ).

C-h C-n

Display the Emacs "news" file, which lists new features in the most recent version of Emacs (view-emacs-news).

C-h C-p

Display general information about the GNU Project (describe-project).

C-h C-t

Display the Emacs to-do list (view-todo).

C-h C-w

Display the full details on the complete absence of warranty for GNU Emacs (describe-no-warranty).

11.10 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. For instance, most parts of the mode line have help text. On graphical displays, the help text is displayed as a "tooltip" (sometimes known as "balloon help"), when you move the mouse over the active text. See section Tooltips. On some systems, it is shown in the echo area. On text-only terminals, if Emacs cannot follow the mouse, it cannot show the help text on mouse-over.

You can also access text region help info using the keyboard. The command C-h . (display-local-help) displays any help text associated with the text at point, using the echo area. If you want help text to be displayed automatically whenever it is available at point, set the variable help-at-pt-display-when-idle to t.

This document was generated by Mark Kaminski on July, 3 2008 using texi2html 1.70.