Test to determine which Parts of a Script to execute
Executed only if test evaluates to TRUE
Executed only if test evaluates to FALSE
Executed regardless of the value of test
Bourne Shell Scripts
As known, Bourne shell is not only a command interpreter but also a programming language (Bach 2006; Bourne 1978; Bourne 1983; Miller et al 2000; Mohay et al 1997; Quarterman et al 1985; Ritchie et al 1974; Sarwar et al 2006).
It can be used by UNIX users to write shell scripts in order to perform various tasks that cannot be done by any single UNIX command.
A shell script is a program that can be stored in disk as a file, which can contain any of UNIX commands that can be typed in on a command line and be executed like an external command (Bourne 1978; Joy 1980; Korn 1983; Rosenblatt et al 2002).
Like any language program, shell scripts have a basic structure. Before learning how to program in Bourne shell, it is helpful to get a whole picture that a shell script looks like. In this way, the readers know at least what their scripts have in order to make the shells execute them properly.