Build Your Own Commands
UNIX is remarkably capable and includes hundreds of different commands, but sometimes that's not sufficient. When it becomes time to create your own unique commands, a simple shell script often suffices.
Task 15.1: Shell Variables
Programming languages usually include variables, and the shell naturally does too. Variables are just tags to identify values that may change as a program is used. In the shell, these variables can take a single value and are always interpreted as strings. Even numeric values are strings to the shell.
The C shell and Korn shell both support arrays and have means of representing numeric values. ...