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   A "variable" is a Lisp symbol which has a value.  The symbol's name
is also called the name of the variable.  A variable name can contain
any characters that can appear in a file, but conventionally variable
names consist of words separated by hyphens.  A variable can have a
documentation string which describes what kind of value it should have
and how the value will be used.

   Lisp allows any variable to have any kind of value, but most
variables that Emacs uses require a value of a certain type.  Often the
value should always be a string, or should always be a number.
Sometimes we say that a certain feature is turned on if a variable is
"non-`nil'," meaning that if the variable's value is `nil', the feature
is off, but the feature is on for *any* other value.  The conventional
value to use to turn on the feature--since you have to pick one
particular value when you set the variable--is `t'.

   Emacs uses many Lisp variables for internal recordkeeping, as any
Lisp program must, but the most interesting variables for you are the
ones that exist for the sake of customization.  Emacs does not
(usually) change the values of these variables; instead, you set the
values, and thereby alter and control the behavior of certain Emacs
commands.  These variables are called "options".  Most options are
documented in this manual, and appear in the Variable Index (*note
Variable Index::.).

   One example of a variable which is an option is `fill-column', which
specifies the position of the right margin (as a number of characters
from the left margin) to be used by the fill commands (*note

* Examining
Examining or setting one variable's value.
* Edit Options
Examining or editing list of all variables' values.
* Hooks
Hook variables let you specify programs for parts of Emacs to run on particular occasions.
* Locals
Per-buffer values of variables.
* File Variables
How files can specify variable values.

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