UNIX® Shells by Example, Third Edition

11.3. Variables

Types of Variables. There are two types of variables: local and environment. Local variables are known only to the shell in which they were created. Environment variables are available to any child processes spawned from the shell from which they were created. Some variables are created by the user and others are special shell variables.

Naming Conventions. Variable names must begin with an alphabetic or underscore character. The remaining characters can be alphabetic, decimal digits (0 to 9), or an underscore character. Any other characters mark the termination of the variable name. Names are case-sensitive. When assigning a value to a variable, do not include any whitespace surrounding the equal sign. To set the variable to ...