UNIX® Shells by Example, Third Edition

13.7. Variables

Tcsh variables hold only strings or a set of strings. Some variables are built into the shell and can be set either by turning them on or off, such as the noclobber or filec variable. Others are assigned a string value, such as the path variable. You can create your own variables and assign them to strings or the output of commands. Variable names are case-sensitive and may contain up to 20 characters consisting of numbers, letters, and the underscore.

There are two types of variables: local and environment. The scope of a variable is its visibility. A local variable is visible to the shell where it is defined. The scope of environment variables is often called global. Their scope is for this shell and all processes spawned (started) ...