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 is designed for use with keyboard commands because that is
29 the most efficient way to edit. You can do editing with the mouse, as
30 in other editors, and you can give commands with the menu bar and tool
31 bar, and scroll with the scroll bar. But if you keep on editing that
32 way, you won't get the benefits of Emacs. Therefore, this manual
33 documents primarily how to edit with the keyboard. You can force
34 yourself to practice using the keyboard by using the shell command
35 @samp{emacs -nw} to start Emacs, so that the mouse won't work.
37 Emacs uses an extension of the @acronym{ASCII} character set for
38 keyboard input; it also accepts non-character input events including
39 function keys and mouse button actions.
41 @acronym{ASCII} consists of 128 character codes. Some of these codes are
42 assigned graphic symbols such as @samp{a} and @samp{=}; the rest are
43 control characters, such as @kbd{Control-a} (usually written @kbd{C-a}
44 for short). @kbd{C-a} gets its name from the fact that you type it by
45 holding down the @key{CTRL} key while pressing @kbd{a}.
47 Some @acronym{ASCII} control characters have special names, and most
48 terminals have special keys you can type them with: for example,
49 @key{RET}, @key{TAB}, @key{DEL} and @key{ESC}. The space character is
50 usually known as @key{SPC}, even though strictly speaking it is a
51 graphic character that is blank.
53 Emacs extends the @acronym{ASCII} character set with thousands more printing
54 characters (@pxref{International}), additional control characters, and a
55 few more modifiers that can be combined with any character.
57 On @acronym{ASCII} terminals, there are only 32 possible control characters.
58 These are the control variants of letters and @samp{@@[]\^_}. In
59 addition, the shift key is meaningless with control characters:
60 @kbd{C-a} and @kbd{C-A} are the same character, and Emacs cannot
63 The Emacs character set has room for control variants of all
64 printing characters, and distinguishes @kbd{C-A} from @kbd{C-a}.
65 Graphical terminals make it possible to enter all these characters.
66 For example, @kbd{C--} (that's Control-Minus) and @kbd{C-5} are
67 meaningful Emacs commands on a graphical terminal.
69 Another Emacs character-set extension is additional modifier bits.
70 Only one modifier bit is commonly used; it is called Meta. Every
71 character has a Meta variant; examples include @kbd{Meta-a} (normally
72 written @kbd{M-a}, for short), @kbd{M-A} (different from @kbd{M-a},
73 but they are normally equivalent in Emacs), @kbd{M-@key{RET}}, and
74 @kbd{M-C-a}. That last means @kbd{a} with both the @key{CTRL} and
75 @key{META} modifiers. We usually write it as @kbd{C-M-a} rather than
76 @kbd{M-C-a}, for reasons of tradition.
80 @cindex @key{ESC} replacing @key{META} key
81 Some terminals have a @key{META} key, and allow you to type Meta
82 characters by holding this key down. Thus, you can type @kbd{Meta-a}
83 by holding down @key{META} and pressing @kbd{a}. The @key{META} key
84 works much like the @key{SHIFT} key. In fact, this key is more often
85 labeled @key{ALT} or @key{EDIT}, instead of @key{META}; on a Sun
86 keyboard, it may have a diamond on it.
88 If there is no @key{META} key, you can still type Meta characters
89 using two-character sequences starting with @key{ESC}. Thus, you can
90 enter @kbd{M-a} by typing @kbd{@key{ESC} a}. You can enter
91 @kbd{C-M-a} by typing @kbd{@key{ESC} C-a}. Unlike @key{META}, which
92 modifies other characters, @key{ESC} is a separate character. You
93 don't hold down @key{ESC} while typing the next character; instead,
94 you press it and release it, then you enter the next character.
95 @key{ESC} is allowed on terminals with @key{META} keys, too, in case
96 you have formed a habit of using it.
98 Emacs defines several other modifier keys that can be applied to any
99 input character. These are called @key{SUPER}, @key{HYPER} and
100 @key{ALT}. We write @samp{s-}, @samp{H-} and @samp{A-} to say that a
101 character uses these modifiers. Thus, @kbd{s-H-C-x} is short for
102 @kbd{Super-Hyper-Control-x}. Not all graphical terminals actually
103 provide keys for these modifier flags---in fact, many terminals have a
104 key labeled @key{ALT} which is really a @key{META} key. The standard
105 key bindings of Emacs do not include any characters with these
106 modifiers. But you can assign them meanings of your own by
109 If your keyboard lacks one of these modifier keys, you can enter it
110 using @kbd{C-x @@}: @kbd{C-x @@ h} adds the ``hyper'' flag to the next
111 character, @kbd{C-x @@ s} adds the ``super'' flag, and @kbd{C-x @@ a}
112 adds the ``alt'' flag. For instance, @kbd{C-x @@ h C-a} is a way to
113 enter @kbd{Hyper-Control-a}. (Unfortunately there is no way to add
114 two modifiers by using @kbd{C-x @@} twice for the same character,
115 because the first one goes to work on the @kbd{C-x}.)
117 Keyboard input includes keyboard keys that are not characters at
118 all, such as function keys and arrow keys. Mouse buttons are also not
119 characters. However, you can modify these events with the modifier
120 keys @key{CTRL}, @key{META}, @key{SUPER}, @key{HYPER} and @key{ALT},
121 just like keyboard characters.
124 Input characters and non-character inputs are collectively called
125 @dfn{input events}. @xref{Input Events,,, elisp, The Emacs Lisp
126 Reference Manual}, for the full Lisp-level details. If you are not
127 doing Lisp programming, but simply want to redefine the meaning of
128 some characters or non-character events, see @ref{Customization}.
130 @acronym{ASCII} terminals cannot really send anything to the computer except
131 @acronym{ASCII} characters. These terminals use a sequence of characters to
132 represent each function key. But that is invisible to the Emacs user,
133 because the keyboard input routines catch these special sequences
134 and convert them to function key events before any other part of Emacs
137 @node Keys, Commands, User Input, Top
142 A @dfn{key sequence} (@dfn{key}, for short) is a sequence of input
143 events that is meaningful as a unit---a ``single command.'' Some
144 Emacs command sequences are invoked by just one character or one
145 event; for example, just @kbd{C-f} moves forward one character in the
146 buffer. But Emacs also has commands that take two or more events to
151 If a sequence of events is enough to invoke a command, it is a
152 @dfn{complete key}. Examples of complete keys include @kbd{C-a},
153 @kbd{X}, @key{RET}, @key{NEXT} (a function key), @key{DOWN} (an arrow
154 key), @kbd{C-x C-f}, and @kbd{C-x 4 C-f}. If it isn't long enough to be
155 complete, we call it a @dfn{prefix key}. The above examples show that
156 @kbd{C-x} and @kbd{C-x 4} are prefix keys. Every key sequence is either
157 a complete key or a prefix key.
159 Most single characters constitute complete keys in the standard Emacs
160 command bindings. A few of them are prefix keys. A prefix key combines
161 with the following input event to make a longer key sequence, which may
162 itself be complete or a prefix. For example, @kbd{C-x} is a prefix key,
163 so @kbd{C-x} and the next input event combine to make a two-event
164 key sequence. Most of these key sequences are complete keys, including
165 @kbd{C-x C-f} and @kbd{C-x b}. A few, such as @kbd{C-x 4} and @kbd{C-x
166 r}, are themselves prefix keys that lead to three-event key
167 sequences. There's no limit to the length of a key sequence, but in
168 practice people rarely use sequences longer than four events.
170 You can't add input events onto a complete key. For example, the
171 two-event sequence @kbd{C-f C-k} is not a key, because the @kbd{C-f}
172 is a complete key in itself. It's impossible to give @kbd{C-f C-k} an
173 independent meaning as a command. @kbd{C-f C-k} is two key sequences,
176 All told, the prefix keys in Emacs are @kbd{C-c}, @kbd{C-h},
177 @kbd{C-x}, @kbd{C-x @key{RET}}, @kbd{C-x @@}, @kbd{C-x a}, @kbd{C-x
178 n}, @w{@kbd{C-x r}}, @kbd{C-x v}, @kbd{C-x 4}, @kbd{C-x 5}, @kbd{C-x
179 6}, @key{ESC}, @kbd{M-g}, and @kbd{M-o}. (@key{F1} and @key{F2} are
180 aliases for @kbd{C-h} and @kbd{C-x 6}.) This list is not cast in stone;
181 it describes the standard key bindings. If you customize Emacs, you can make
182 new prefix keys, or eliminate some of the standard ones (not
183 recommended for most users). @xref{Key Bindings}.
185 If you make or eliminate prefix keys, that changes the set of
186 possible key sequences. For example, if you redefine @kbd{C-f} as a
187 prefix, @kbd{C-f C-k} automatically becomes a key (complete, unless
188 you define that too as a prefix). Conversely, if you remove the
189 prefix definition of @kbd{C-x 4}, then @kbd{C-x 4 f} and @kbd{C-x 4
190 @var{anything}} are no longer keys.
192 Typing the help character (@kbd{C-h} or @key{F1}) after a prefix key
193 displays a list of the commands starting with that prefix. There are
194 a few prefix keys after which @kbd{C-h} does not work---for historical
195 reasons, they define other meanings for @kbd{C-h} which are painful to
196 change. @key{F1} works after all prefix keys.
198 @node Commands, Text Characters, Keys, Top
199 @section Keys and Commands
203 @cindex function definition
204 This manual is full of passages that tell you what particular keys
205 do. But Emacs does not assign meanings to keys directly. Instead,
206 Emacs assigns meanings to named @dfn{commands}, and then gives keys
207 their meanings by @dfn{binding} them to commands.
209 Every command has a name chosen by a programmer. The name is
210 usually made of a few English words separated by dashes; for example,
211 @code{next-line} or @code{forward-word}. A command also has a
212 @dfn{function definition} which is a Lisp program; this is how the
213 command does its work. In Emacs Lisp, a command is a Lisp function with
214 special options to read arguments and for interactive use. For more
215 information on commands and functions, see @ref{What Is a Function,,
216 What Is a Function, elisp, The Emacs Lisp Reference Manual}. (The
217 definition here is simplified slightly.)
219 The bindings between keys and commands are recorded in tables called
220 @dfn{keymaps}. @xref{Keymaps}.
222 When we say that ``@kbd{C-n} moves down vertically one line'' we are
223 glossing over a subtle distinction that is irrelevant in ordinary use,
224 but vital for Emacs customization. The command @code{next-line} does
225 a vertical move downward. @kbd{C-n} has this effect @emph{because} it
226 is bound to @code{next-line}. If you rebind @kbd{C-n} to the command
227 @code{forward-word}, @kbd{C-n} will move forward one word instead.
228 Rebinding keys is an important method of customization.
230 In the rest of this manual, we usually ignore this distinction to
231 keep things simple. We will often speak of keys like @kbd{C-n} as
232 commands, even though strictly speaking the key is bound to a command.
233 Usually we state the name of the command which really does the work in
234 parentheses after mentioning the key that runs it. For example, we
235 will say that ``The command @kbd{C-n} (@code{next-line}) moves point
236 vertically down,'' meaning that the command @code{next-line} moves
237 vertically down, and the key @kbd{C-n} is normally bound to it.
239 Since we are discussing customization, we should tell you about
240 @dfn{variables}. Often the description of a command will say, ``To
241 change this, set the variable @code{mumble-foo}.'' A variable is a
242 name used to store a value. Most of the variables documented in this
243 manual are meant for customization: some command or other part of
244 Emacs examines the variable and behaves differently according to the
245 value that you set. You can ignore the information about variables
246 until you are interested in customizing them. Then read the basic
247 information on variables (@pxref{Variables}) and the information about
248 specific variables will make sense.
250 @node Text Characters, Entering Emacs, Commands, Top
251 @section Character Set for Text
252 @cindex characters (in text)
254 Text in Emacs buffers is a sequence of characters. In the simplest
255 case, these are @acronym{ASCII} characters, each stored in one 8-bit
256 byte. Both @acronym{ASCII} control characters (octal codes 000
257 through 037, and 0177) and @acronym{ASCII} printing characters (codes
258 040 through 0176) are allowed. The other modifier flags used in
259 keyboard input, such as Meta, are not allowed in buffers.
261 Non-@acronym{ASCII} printing characters can also appear in buffers,
262 when multibyte characters are enabled. They have character codes
263 starting at 256, octal 0400, and each one is represented as a sequence
264 of two or more bytes. @xref{International}. Single-byte characters
265 with codes 128 through 255 can also appear in multibyte buffers.
266 However, non-@acronym{ASCII} control characters cannot appear in a
269 Some @acronym{ASCII} control characters serve special purposes in text, and have
270 special names. For example, the newline character (octal code 012) is
271 used in the buffer to end a line, and the tab character (octal code 011)
272 is used for indenting to the next tab stop column (normally every 8
273 columns). @xref{Text Display}.
275 If you disable multibyte characters, then you can use only one
276 alphabet of non-@acronym{ASCII} characters, which all fit in one byte.
277 They use octal codes 0200 through 0377. @xref{Unibyte Mode}.
284 arch-tag: 9be43eef-d1f4-4d03-a916-c741ea713a45