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6bf7aab6 | 1 | @c This is part of the Emacs manual. |
b65d8176 | 2 | @c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 2002, 2003, |
8d99e09d | 3 | @c 2004, 2005, 2006 Free Software Foundation, Inc. |
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4 | @c See file emacs.texi for copying conditions. |
5 | @iftex | |
6 | @chapter Characters, Keys and Commands | |
7 | ||
8 | This chapter explains the character sets used by Emacs for input | |
9 | commands and for the contents of files, and also explains the concepts | |
10 | of @dfn{keys} and @dfn{commands}, which are fundamental for understanding | |
11 | how Emacs interprets your keyboard and mouse input. | |
12 | @end iftex | |
13 | ||
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14 | @ifnottex |
15 | @raisesections | |
16 | @end ifnottex | |
17 | ||
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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) | |
76dd3692 | 23 | @cindex @acronym{ASCII} |
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24 | @cindex C- |
25 | @cindex Control | |
26 | @cindex control characters | |
27 | ||
76dd3692 | 28 | GNU Emacs uses an extension of the @acronym{ASCII} character set for keyboard |
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29 | input; it also accepts non-character input events including function |
30 | keys and mouse button actions. | |
31 | ||
76dd3692 | 32 | @acronym{ASCII} consists of 128 character codes. Some of these codes are |
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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}. | |
37 | ||
76dd3692 | 38 | Some @acronym{ASCII} control characters have special names, and most terminals |
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39 | have special keys you can type them with: for example, @key{RET}, |
40 | @key{TAB}, @key{DEL} and @key{ESC}. The space character is usually | |
41 | referred to below as @key{SPC}, even though strictly speaking it is a | |
a85cdd1f | 42 | graphic character whose graphic happens to be blank. |
6bf7aab6 | 43 | |
76dd3692 | 44 | Emacs extends the @acronym{ASCII} character set with thousands more printing |
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45 | characters (@pxref{International}), additional control characters, and a |
46 | few more modifiers that can be combined with any character. | |
47 | ||
76dd3692 | 48 | On @acronym{ASCII} terminals, there are only 32 possible control characters. |
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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 | |
52 | distinguish them. | |
53 | ||
54 | But the Emacs character set has room for control variants of all | |
55 | printing characters, and for distinguishing between @kbd{C-a} and | |
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56 | @kbd{C-A}. Graphical terminals make it possible to enter all these |
57 | characters. For example, @kbd{C--} (that's Control-Minus) and | |
58 | @kbd{C-5} are meaningful Emacs commands on a graphical terminal. | |
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59 | |
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 | |
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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. | |
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68 | |
69 | @cindex Meta | |
70 | @cindex M- | |
71 | @cindex @key{ESC} replacing @key{META} key | |
72 | Some terminals have a @key{META} key, and allow you to type Meta | |
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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. | |
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78 | |
79 | If there is no @key{META} key, you can still type Meta characters | |
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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. | |
177c0ea7 | 88 | |
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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 | |
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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 | |
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97 | modifiers. But you can assign them meanings of your own by |
98 | customizing Emacs. | |
6bf7aab6 | 99 | |
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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}.) | |
107 | ||
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108 | Keyboard input includes keyboard keys that are not characters at |
109 | all: for example function keys and arrow keys. Mouse buttons are also | |
110 | outside the gamut of characters. However, you can modify these events | |
111 | with the modifier keys @key{CTRL}, @key{META}, @key{SUPER}, | |
112 | @key{HYPER} and @key{ALT}, just as you can modify keyboard characters. | |
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113 | |
114 | @cindex input event | |
115 | Input characters and non-character inputs are collectively called | |
116 | @dfn{input events}. @xref{Input Events,,, elisp, The Emacs Lisp | |
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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}. | |
6bf7aab6 | 120 | |
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121 | @acronym{ASCII} terminals cannot really send anything to the computer except |
122 | @acronym{ASCII} characters. These terminals use a sequence of characters to | |
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123 | represent each function key. But that is invisible to the Emacs user, |
124 | because the keyboard input routines recognize these special sequences | |
125 | and convert them to function key events before any other part of Emacs | |
126 | gets to see them. | |
127 | ||
128 | @node Keys, Commands, User Input, Top | |
129 | @section Keys | |
130 | ||
131 | @cindex key sequence | |
132 | @cindex key | |
133 | A @dfn{key sequence} (@dfn{key}, for short) is a sequence of input | |
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134 | events that are meaningful as a unit---as ``a single command.'' Some |
135 | Emacs command sequences are just one character or one event; for | |
136 | example, just @kbd{C-f} is enough to move forward one character in the | |
137 | buffer. But Emacs also has commands that take two or more events to | |
138 | invoke. | |
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139 | |
140 | @cindex complete key | |
141 | @cindex prefix key | |
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. | |
149 | ||
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, | |
8e7692a9 | 154 | so @kbd{C-x} and the next input event combine to make a two-event |
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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 | |
8e7692a9 | 157 | r}, are themselves prefix keys that lead to three-event key |
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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. | |
160 | ||
161 | By contrast, you can't add more events onto a complete key. For | |
8e7692a9 | 162 | example, the two-event sequence @kbd{C-f C-k} is not a key, because |
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163 | the @kbd{C-f} is a complete key in itself. It's impossible to give |
164 | @kbd{C-f C-k} an independent meaning as a command. @kbd{C-f C-k} is two | |
165 | key sequences, not one.@refill | |
166 | ||
167 | All told, the prefix keys in Emacs are @kbd{C-c}, @kbd{C-h}, | |
35ea7c7c | 168 | @kbd{C-x}, @kbd{C-x @key{RET}}, @kbd{C-x @@}, @kbd{C-x a}, @kbd{C-x |
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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}.) But this list is not cast in | |
172 | concrete; it is just a matter of Emacs's standard key bindings. If | |
173 | you customize Emacs, you can make new prefix keys, or eliminate some | |
174 | of the standard ones. @xref{Key Bindings}. | |
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175 | |
176 | If you do 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 you | |
cd30a00e | 179 | define that too as a prefix). Conversely, if you remove the prefix |
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180 | definition of @kbd{C-x 4}, then @kbd{C-x 4 f} (or @kbd{C-x 4 |
181 | @var{anything}}) is no longer a key. | |
182 | ||
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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 for 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. But @key{F1} should work for all prefix keys. | |
177c0ea7 | 188 | |
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189 | @node Commands, Text Characters, Keys, Top |
190 | @section Keys and Commands | |
191 | ||
192 | @cindex binding | |
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193 | @cindex command |
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. | |
199 | ||
200 | Every command has a name chosen by a programmer. The name is usually | |
201 | 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 what makes | |
204 | the command do what it does. In Emacs Lisp, a command is actually a | |
205 | special kind of Lisp function; one which specifies how to read arguments | |
206 | for it and call it interactively. For more information on commands and | |
207 | functions, see @ref{What Is a Function,, What Is a Function, elisp, The | |
208 | Emacs Lisp Reference Manual}. (The definition we use in this manual is | |
209 | simplified slightly.) | |
210 | ||
211 | The bindings between keys and commands are recorded in various tables | |
212 | called @dfn{keymaps}. @xref{Keymaps}. | |
213 | ||
214 | When we say that ``@kbd{C-n} moves down vertically one line'' we are | |
215 | glossing over a distinction that is irrelevant in ordinary use but is vital | |
216 | in understanding how to customize Emacs. It is the command | |
217 | @code{next-line} that is programmed to move down vertically. @kbd{C-n} has | |
218 | this effect @emph{because} it is bound to that command. If you rebind | |
219 | @kbd{C-n} to the command @code{forward-word} then @kbd{C-n} will move | |
220 | forward by words instead. Rebinding keys is a common method of | |
221 | customization.@refill | |
222 | ||
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223 | In the rest of this manual, we usually ignore this distinction to |
224 | keep things simple. We will often speak of keys like @kbd{C-n} as | |
225 | commands, even though strictly speaking a key is bound to some | |
226 | command. To give the information needed for customization, we state | |
227 | the name of the command which really does the work in parentheses | |
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228 | after mentioning the key that runs it. For example, we will say that |
229 | ``The command @kbd{C-n} (@code{next-line}) moves point vertically | |
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230 | down,'' meaning that @code{next-line} is a command that moves |
231 | vertically down, and @kbd{C-n} is a key that is normally bound to it. | |
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232 | |
233 | While we are on the subject of information for customization only, | |
234 | it's a good time to tell you about @dfn{variables}. Often the | |
235 | description of a command will say, ``To change this, set the variable | |
236 | @code{mumble-foo}.'' A variable is a name used to remember a value. | |
237 | Most of the variables documented in this manual exist just to facilitate | |
238 | customization: some command or other part of Emacs examines the variable | |
239 | and behaves differently according to the value that you set. Until you | |
240 | are interested in customizing, you can ignore the information about | |
241 | variables. When you are ready to be interested, read the basic | |
242 | information on variables, and then the information on individual | |
243 | variables will make sense. @xref{Variables}. | |
244 | ||
245 | @node Text Characters, Entering Emacs, Commands, Top | |
246 | @section Character Set for Text | |
247 | @cindex characters (in text) | |
248 | ||
249 | Text in Emacs buffers is a sequence of 8-bit bytes. Each byte can | |
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250 | hold a single @acronym{ASCII} character. Both @acronym{ASCII} control characters (octal |
251 | codes 000 through 037, and 0177) and @acronym{ASCII} printing characters (codes | |
252 | 040 through 0176) are allowed; however, non-@acronym{ASCII} control characters | |
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253 | cannot appear in a buffer. The other modifier flags used in keyboard |
254 | input, such as Meta, are not allowed in buffers either. | |
255 | ||
76dd3692 | 256 | Some @acronym{ASCII} control characters serve special purposes in text, and have |
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257 | special names. For example, the newline character (octal code 012) is |
258 | used in the buffer to end a line, and the tab character (octal code 011) | |
259 | is used for indenting to the next tab stop column (normally every 8 | |
260 | columns). @xref{Text Display}. | |
261 | ||
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262 | Non-@acronym{ASCII} printing characters can also appear in buffers. When |
263 | multibyte characters are enabled, you can use any of the non-@acronym{ASCII} | |
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264 | printing characters that Emacs supports. They have character codes |
265 | starting at 256, octal 0400, and each one is represented as a sequence | |
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266 | of two or more bytes. @xref{International}. Single-byte characters |
267 | with codes 128 through 255 can also appear in multibyte buffers. | |
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268 | |
269 | If you disable multibyte characters, then you can use only one | |
76dd3692 | 270 | alphabet of non-@acronym{ASCII} characters, but they all fit in one byte. They |
854c6911 | 271 | use codes 0200 through 0377. @xref{Unibyte Mode}. |
ab5796a9 | 272 | |
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273 | @ifnottex |
274 | @lowersections | |
275 | @end ifnottex | |
276 | ||
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277 | @ignore |
278 | arch-tag: 9be43eef-d1f4-4d03-a916-c741ea713a45 | |
279 | @end ignore |