1 @c This is part of the Emacs manual.
2 @c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 2002, 2003,
3 @c 2004, 2005, 2006 Free Software Foundation, Inc.
4 @c See file emacs.texi for copying conditions.
6 @chapter Characters, Keys and Commands
8 This chapter explains the character sets used by Emacs for input
9 commands and for the contents of files, and the fundamental concepts of
10 @dfn{keys} and @dfn{commands}, whereby Emacs interprets your keyboard
18 @node User Input, Keys, Screen, Top
19 @section Kinds of User Input
20 @cindex input with the keyboard
21 @cindex keyboard input
22 @cindex character set (keyboard)
23 @cindex @acronym{ASCII}
26 @cindex control characters
28 GNU Emacs uses an extension of the @acronym{ASCII} character set for keyboard
29 input; it also accepts non-character input events including function
30 keys and mouse button actions.
32 @acronym{ASCII} consists of 128 character codes. Some of these codes are
33 assigned graphic symbols such as @samp{a} and @samp{=}; the rest are
34 control characters, such as @kbd{Control-a} (usually written @kbd{C-a}
35 for short). @kbd{C-a} gets its name from the fact that you type it by
36 holding down the @key{CTRL} key while pressing @kbd{a}.
38 Some @acronym{ASCII} control characters have special names, and most
39 terminals have special keys you can type them with: for example,
40 @key{RET}, @key{TAB}, @key{DEL} and @key{ESC}. The space character is
41 usually known as @key{SPC}, even though strictly speaking it is a
42 graphic character that is blank.
44 Emacs extends the @acronym{ASCII} character set with thousands more printing
45 characters (@pxref{International}), additional control characters, and a
46 few more modifiers that can be combined with any character.
48 On @acronym{ASCII} terminals, there are only 32 possible control characters.
49 These are the control variants of letters and @samp{@@[]\^_}. In
50 addition, the shift key is meaningless with control characters:
51 @kbd{C-a} and @kbd{C-A} are the same character, and Emacs cannot
54 The Emacs character set has room for control variants of all
55 printing characters, and distinguishes @kbd{C-A} from @kbd{C-a}.
56 Graphical terminals make it possible to enter all these characters.
57 For example, @kbd{C--} (that's Control-Minus) and @kbd{C-5} are
58 meaningful Emacs commands on a graphical terminal.
60 Another Emacs character-set extension is additional modifier bits.
61 Only one modifier bit is commonly used; it is called Meta. Every
62 character has a Meta variant; examples include @kbd{Meta-a} (normally
63 written @kbd{M-a}, for short), @kbd{M-A} (different from @kbd{M-a},
64 but they are normally equivalent in Emacs), @kbd{M-@key{RET}}, and
65 @kbd{M-C-a}. That last means @kbd{a} with both the @key{CTRL} and
66 @key{META} modifiers. We usually write it as @kbd{C-M-a} rather than
67 @kbd{M-C-a}, for reasons of tradition.
71 @cindex @key{ESC} replacing @key{META} key
72 Some terminals have a @key{META} key, and allow you to type Meta
73 characters by holding this key down. Thus, you can type @kbd{Meta-a}
74 by holding down @key{META} and pressing @kbd{a}. The @key{META} key
75 works much like the @key{SHIFT} key. In fact, this key is more often
76 labeled @key{ALT} or @key{EDIT}, instead of @key{META}; on a Sun
77 keyboard, it may have a diamond on it.
79 If there is no @key{META} key, you can still type Meta characters
80 using two-character sequences starting with @key{ESC}. Thus, you can
81 enter @kbd{M-a} by typing @kbd{@key{ESC} a}. You can enter
82 @kbd{C-M-a} by typing @kbd{@key{ESC} C-a}. Unlike @key{META}, which
83 modifies other characters, @key{ESC} is a separate character. You
84 don't hold down @key{ESC} while typing the next character; instead,
85 you press it and release it, then you enter the next character.
86 @key{ESC} is allowed on terminals with @key{META} keys, too, in case
87 you have formed a habit of using it.
89 Emacs defines several other modifier keys that can be applied to any
90 input character. These are called @key{SUPER}, @key{HYPER} and
91 @key{ALT}. We write @samp{s-}, @samp{H-} and @samp{A-} to say that a
92 character uses these modifiers. Thus, @kbd{s-H-C-x} is short for
93 @kbd{Super-Hyper-Control-x}. Not all graphical terminals actually
94 provide keys for these modifier flags---in fact, many terminals have a
95 key labeled @key{ALT} which is really a @key{META} key. The standard
96 key bindings of Emacs do not include any characters with these
97 modifiers. But you can assign them meanings of your own by
100 If your keyboard lacks one of these modifier keys, you can enter it
101 using @kbd{C-x @@}: @kbd{C-x @@ h} adds the ``hyper'' flag to the next
102 character, @kbd{C-x @@ s} adds the ``super'' flag, and @kbd{C-x @@ a}
103 adds the ``alt'' flag. For instance, @kbd{C-x @@ h C-a} is a way to
104 enter @kbd{Hyper-Control-a}. (Unfortunately there is no way to add
105 two modifiers by using @kbd{C-x @@} twice for the same character,
106 because the first one goes to work on the @kbd{C-x}.)
108 Keyboard input includes keyboard keys that are not characters at
109 all, such as function keys and arrow keys. Mouse buttons are also not
110 characters. However, you can modify these events with the modifier
111 keys @key{CTRL}, @key{META}, @key{SUPER}, @key{HYPER} and @key{ALT},
112 just like keyboard characters.
115 Input characters and non-character inputs are collectively called
116 @dfn{input events}. @xref{Input Events,,, elisp, The Emacs Lisp
117 Reference Manual}, for the full Lisp-level details. If you are not
118 doing Lisp programming, but simply want to redefine the meaning of
119 some characters or non-character events, see @ref{Customization}.
121 @acronym{ASCII} terminals cannot really send anything to the computer except
122 @acronym{ASCII} characters. These terminals use a sequence of characters to
123 represent each function key. But that is invisible to the Emacs user,
124 because the keyboard input routines catch these special sequences
125 and convert them to function key events before any other part of Emacs
128 @node Keys, Commands, User Input, Top
133 A @dfn{key sequence} (@dfn{key}, for short) is a sequence of input
134 events that is meaningful as a unit---a ``single command.'' Some
135 Emacs command sequences are invoked by just one character or one
136 event; for example, just @kbd{C-f} moves forward one character in the
137 buffer. But Emacs also has commands that take two or more events to
142 If a sequence of events is enough to invoke a command, it is a
143 @dfn{complete key}. Examples of complete keys include @kbd{C-a},
144 @kbd{X}, @key{RET}, @key{NEXT} (a function key), @key{DOWN} (an arrow
145 key), @kbd{C-x C-f}, and @kbd{C-x 4 C-f}. If it isn't long enough to be
146 complete, we call it a @dfn{prefix key}. The above examples show that
147 @kbd{C-x} and @kbd{C-x 4} are prefix keys. Every key sequence is either
148 a complete key or a prefix key.
150 Most single characters constitute complete keys in the standard Emacs
151 command bindings. A few of them are prefix keys. A prefix key combines
152 with the following input event to make a longer key sequence, which may
153 itself be complete or a prefix. For example, @kbd{C-x} is a prefix key,
154 so @kbd{C-x} and the next input event combine to make a two-event
155 key sequence. Most of these key sequences are complete keys, including
156 @kbd{C-x C-f} and @kbd{C-x b}. A few, such as @kbd{C-x 4} and @kbd{C-x
157 r}, are themselves prefix keys that lead to three-event key
158 sequences. There's no limit to the length of a key sequence, but in
159 practice people rarely use sequences longer than four events.
161 You can't add input events onto a complete key. For example, the
162 two-event sequence @kbd{C-f C-k} is not a key, because the @kbd{C-f}
163 is a complete key in itself. It's impossible to give @kbd{C-f C-k} an
164 independent meaning as a command. @kbd{C-f C-k} is two key sequences,
167 All told, the prefix keys in Emacs are @kbd{C-c}, @kbd{C-h},
168 @kbd{C-x}, @kbd{C-x @key{RET}}, @kbd{C-x @@}, @kbd{C-x a}, @kbd{C-x
169 n}, @w{@kbd{C-x r}}, @kbd{C-x v}, @kbd{C-x 4}, @kbd{C-x 5}, @kbd{C-x
170 6}, @key{ESC}, @kbd{M-g}, and @kbd{M-o}. (@key{F1} and @key{F2} are
171 aliases for @kbd{C-h} and @kbd{C-x 6}.) This list is not cast in stone;
172 it describes the standard key bindings. If you customize Emacs, you can make
173 new prefix keys, or eliminate some of the standard ones (not
174 recommended for most users). @xref{Key Bindings}.
176 If you make or eliminate prefix keys, that changes the set of
177 possible key sequences. For example, if you redefine @kbd{C-f} as a
178 prefix, @kbd{C-f C-k} automatically becomes a key (complete, unless
179 you define that too as a prefix). Conversely, if you remove the
180 prefix definition of @kbd{C-x 4}, then @kbd{C-x 4 f} and @kbd{C-x 4
181 @var{anything}} are no longer keys.
183 Typing the help character (@kbd{C-h} or @key{F1}) after a prefix key
184 displays a list of the commands starting with that prefix. There are
185 a few prefix keys after which @kbd{C-h} does not work---for historical
186 reasons, they define other meanings for @kbd{C-h} which are painful to
187 change. @key{F1} works after all prefix keys.
189 @node Commands, Text Characters, Keys, Top
190 @section Keys and Commands
194 @cindex function definition
195 This manual is full of passages that tell you what particular keys
196 do. But Emacs does not assign meanings to keys directly. Instead,
197 Emacs assigns meanings to named @dfn{commands}, and then gives keys
198 their meanings by @dfn{binding} them to commands.
200 Every command has a name chosen by a programmer. The name is
201 usually made of a few English words separated by dashes; for example,
202 @code{next-line} or @code{forward-word}. A command also has a
203 @dfn{function definition} which is a Lisp program; this is how the
204 command does its work. In Emacs Lisp, a command is a Lisp function with
205 special options to read arguments and for interactive use. For more
206 information on commands and functions, see @ref{What Is a Function,,
207 What Is a Function, elisp, The Emacs Lisp Reference Manual}. (The
208 definition here is simplified slightly.)
210 The bindings between keys and commands are recorded in tables called
211 @dfn{keymaps}. @xref{Keymaps}.
213 When we say that ``@kbd{C-n} moves down vertically one line'' we are
214 glossing over a subtle distinction that is irrelevant in ordinary use,
215 but vital for Emacs customization. The command @code{next-line} does
216 a vertical move downward. @kbd{C-n} has this effect @emph{because} it
217 is bound to @code{next-line}. If you rebind @kbd{C-n} to the command
218 @code{forward-word}, @kbd{C-n} will move forward one word instead.
219 Rebinding keys is an important method of customization.
221 In the rest of this manual, we usually ignore this distinction to
222 keep things simple. We will often speak of keys like @kbd{C-n} as
223 commands, even though strictly speaking the key is bound to a command.
224 Usually we state the name of the command which really does the work in
225 parentheses after mentioning the key that runs it. For example, we
226 will say that ``The command @kbd{C-n} (@code{next-line}) moves point
227 vertically down,'' meaning that the command @code{next-line} moves
228 vertically down, and the key @kbd{C-n} is normally bound to it.
230 Since we are discussing customization, we should tell you about
231 @dfn{variables}. Often the description of a command will say, ``To
232 change this, set the variable @code{mumble-foo}.'' A variable is a
233 name used to store a value. Most of the variables documented in this
234 manual are meant for customization: some command or other part of
235 Emacs examines the variable and behaves differently according to the
236 value that you set. You can ignore the information about variables
237 until you are interested in customizing them. Then read the basic
238 information on variables (@pxref{Variables}) and the information about
239 specific variables will make sense.
241 @node Text Characters, Entering Emacs, Commands, Top
242 @section Character Set for Text
243 @cindex characters (in text)
245 Text in Emacs buffers is a sequence of characters. In the simplest
246 case, these are @acronym{ASCII} characters, each stored in one 8-bit
247 byte. Both @acronym{ASCII} control characters (octal codes 000
248 through 037, and 0177) and @acronym{ASCII} printing characters (codes
249 040 through 0176) are allowed. The other modifier flags used in
250 keyboard input, such as Meta, are not allowed in buffers.
252 Non-@acronym{ASCII} printing characters can also appear in buffers,
253 when multibyte characters are enabled. They have character codes
254 starting at 256, octal 0400, and each one is represented as a sequence
255 of two or more bytes. @xref{International}. Single-byte characters
256 with codes 128 through 255 can also appear in multibyte buffers.
257 However, non-@acronym{ASCII} control characters cannot appear in a
260 Some @acronym{ASCII} control characters serve special purposes in text, and have
261 special names. For example, the newline character (octal code 012) is
262 used in the buffer to end a line, and the tab character (octal code 011)
263 is used for indenting to the next tab stop column (normally every 8
264 columns). @xref{Text Display}.
266 If you disable multibyte characters, then you can use only one
267 alphabet of non-@acronym{ASCII} characters, which all fit in one byte.
268 They use octal codes 0200 through 0377. @xref{Unibyte Mode}.
275 arch-tag: 9be43eef-d1f4-4d03-a916-c741ea713a45