Chapter 4. The ABLE shell

Table of Contents

4.1. Conditional execution
4.2. Shell variables
4.2.1. Simple variables
4.2.2. Non volatile variables
4.2.3. Positional variables
4.2.4. Special variables
4.2.5. Accessing variables
4.2.6. Variables with special meanings
4.3. Functions
4.4. Command substitution
4.5. Shell script

The ABLE shell is a very basic UNIX® bourne shell and should be familiar to anyone experienced with that environment.

The shell executes a series of commands one after another provided from either the command line (see Chapter 3, Command Line Interface) or from a file (see Section 4.5, “Shell script”.

Each command completes with an exit code which is a simple integer number. Command execution can be made conditional on the exit code values of previous commands. The test(1) command may be used to perform a variety of logical tests which allows for script execution control.

Commands may be grouped together using curly brackets ({}) the commands within these groups must be separated by conditionals and the list must be terminated by a semicolon. One notable difference to standard bourne shell is that command groups may not use newlines as separators.

A command group may be used as a function which allows for simple procedural programming.

variables may be set to store information and control program execution. In addition these user variables access is available to the non volatile settings of ABLE.