The shells provide facilities for storing useful information and
transferring it between programs. Among these is the ability to
handle variables (named pieces of text or numbers, that can be used
in a variety of ways).
Variables have many uses. For example, if you frequently need to
cd to /u/work/systems/Admin, you could define
the variable ADMIN to be /u/work/systems/Admin,
then type cd $ADMIN to change to that directory.
Variables consist of a name (or label) and an associated value. In
the example above, the variable is named ADMIN; its value
is /u/work/systems/Admin. You refer to the value of a
variable by prefixing its name with a ``$'' symbol. When the
shell reads the ``$'' symbol it checks the subsequent text to
see if it is a variable name (such as NAME), and replaces
the input text $NAME with the value of NAME.
There are two types of variable available to you:
The sections below explain how to create and refer to shell variables
and environment variables.
These are created within a shell and are used to temporarily store
information and to control the execution of shell scripts.
Shell variables are not visible to any other program, and are lost
when the shell terminates.
All programs running on the system have a special memory area called
an environment. When a program is run, it inherits a copy of its
parent program's environment, complete with any variables stored in
it. Environment variables are used to pass configuration information
to child processes executed by the shell. They are created by
exporting a shell variable into the shell's environment,
which makes them visible to all programs subsequently executed under
that shell (see
``Exporting variables to the environment'').
However, it is not possible for a child to alter its parent shell's
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UnixWare 7 Release 7.1.4 - 22 April 2004