| 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. |
| 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 the fundamental concepts of |
| 10 | @dfn{keys} and @dfn{commands}, whereby Emacs interprets your keyboard |
| 11 | and mouse input. |
| 12 | @end iftex |
| 13 | |
| 14 | @ifnottex |
| 15 | @raisesections |
| 16 | @end ifnottex |
| 17 | |
| 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} |
| 24 | @cindex C- |
| 25 | @cindex Control |
| 26 | @cindex control characters |
| 27 | |
| 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. |
| 36 | |
| 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. |
| 40 | |
| 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}. |
| 46 | |
| 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. |
| 52 | |
| 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. |
| 56 | |
| 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 |
| 61 | distinguish them. |
| 62 | |
| 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. |
| 68 | |
| 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. |
| 77 | |
| 78 | @cindex Meta |
| 79 | @cindex M- |
| 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. |
| 87 | |
| 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. |
| 97 | |
| 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 |
| 107 | customizing Emacs. |
| 108 | |
| 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}.) |
| 116 | |
| 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. |
| 122 | |
| 123 | @cindex input event |
| 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}. |
| 129 | |
| 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 |
| 135 | gets to see them. |
| 136 | |
| 137 | @node Keys, Commands, User Input, Top |
| 138 | @section Keys |
| 139 | |
| 140 | @cindex key sequence |
| 141 | @cindex key |
| 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 |
| 147 | invoke. |
| 148 | |
| 149 | @cindex complete key |
| 150 | @cindex prefix key |
| 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. |
| 158 | |
| 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. |
| 169 | |
| 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, |
| 174 | not one.@refill |
| 175 | |
| 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}. |
| 184 | |
| 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. |
| 191 | |
| 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. |
| 197 | |
| 198 | @node Commands, Text Characters, Keys, Top |
| 199 | @section Keys and Commands |
| 200 | |
| 201 | @cindex binding |
| 202 | @cindex command |
| 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. |
| 208 | |
| 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.) |
| 218 | |
| 219 | The bindings between keys and commands are recorded in tables called |
| 220 | @dfn{keymaps}. @xref{Keymaps}. |
| 221 | |
| 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. |
| 229 | |
| 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. |
| 238 | |
| 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. |
| 249 | |
| 250 | @node Text Characters, Entering Emacs, Commands, Top |
| 251 | @section Character Set for Text |
| 252 | @cindex characters (in text) |
| 253 | |
| 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. |
| 260 | |
| 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 |
| 267 | buffer. |
| 268 | |
| 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}. |
| 274 | |
| 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}. |
| 278 | |
| 279 | @ifnottex |
| 280 | @lowersections |
| 281 | @end ifnottex |
| 282 | |
| 283 | @ignore |
| 284 | arch-tag: 9be43eef-d1f4-4d03-a916-c741ea713a45 |
| 285 | @end ignore |