Looping are a powerful programming tool that are used to execute a set of commands repeatedly. The various looping statement are:
The while statement has the general form is:
While command-list 1
The command in command-list are executed; and if the exit status of the last command in that list is 0 (zero). The command in command-list 2 are executed. The sequence is repeated as long as the exit status of command-list 1 is 0 (zero).
The For loop notation has the general form is:
for var in list-if-words
Commands is a sequence of one or more commands separated by a newline or; (semicolon). The reserved words do and done must be preceded by a newline or ; (semicolon).
Small loops can be written in a single line e.g. for var in list; do commands; done.
The Until statement has the general forms is:
Until command-list 1
This is identical in function to the while command except that the loop is executed as long as the exit status of command-list is no-zero.
The exit status of a While/Until command is the exit status of the list command executed in command-list 2. If on such command list is executed, a While/ Until has an exit status of 0 (zero).