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You are reading about GNU Emacs, the GNU incarnation of the advanced,
self-documenting, customizable, extensible real-time display editor
Emacs. (The `G' in `GNU' is not silent.)
We say that Emacs is a "display" editor because normally the text
being edited is visible on the screen and is updated automatically as
you type your commands. Note: Display.
We call it a "real-time" editor because the display is updated very
frequently, usually after each character or pair of characters you
type. This minimizes the amount of information you must keep in your
head as you edit. Note: Real-time.
We call Emacs advanced because it provides facilities that go beyond
simple insertion and deletion: filling of text; automatic indentation of
programs; viewing two or more files at once; and dealing in terms of
characters, words, lines, sentences, paragraphs, and pages, as well as
expressions and comments in several different programming languages.
"Self-documenting" means that at any time you can type a special
character, `Control-h', to find out what your options are. You can
also use it to find out what any command does, or to find all the
commands that pertain to a topic. Note: Help.
"Customizable" means that you can change the definitions of Emacs
commands in little ways. For example, if you use a programming
language in which comments start with `<**' and end with `**>', you can
tell the Emacs comment manipulation commands to use those strings
(Note: Comments.). Another sort of customization is rearrangement of
the command set. For example, if you prefer the four basic cursor
motion commands (up, down, left and right) on keys in a diamond pattern
on the keyboard, you can have it. Note: Customization.
"Extensible" means that you can go beyond simple customization and
write entirely new commands, programs in the Lisp language to be run by
Emacs's own Lisp interpreter. Emacs is an "on-line extensible" system,
which means that it is divided into many functions that call each other,
any of which can be redefined in the middle of an editing session. Any
part of Emacs can be replaced without making a separate copy of all of
Emacs. Most of the editing commands of Emacs are written in Lisp
already; the few exceptions could have been written in Lisp but are
written in C for efficiency. Although only a programmer can write an
extension, anybody can use it afterward.
When run under the X Window System, Emacs provides its own menus and
convenient bindings to mouse buttons. But Emacs can provide many of the
benefits of a window system on a text-only terminal. For instance, you
can look at or edit several files at once, move text between them, and
edit files at the same time as you run shell commands.
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