This section covers variables and assignment statements and how to write a simple shell script and make it executable.
The Bourne Again, TC, and Z Shells allow you to create and use variables. The rules for naming and referring to variables are similar in all three shells (page 566). You assign values to variables in the Bourne Again and Z Shells with the following syntax:
There can be no whitespace on either side of the equal (=) sign. If you want to include SPACEs in the value of the variable, put quotation marks around the value or quote the SPACEs.
In all three shells you reference the value of a variable by preceding the variable name with a dollar sign and enclosing it in braces, as in ...