Red Hat Linux 7 Unleashed

Red Hat Linux 7 Unleashed

By William Ball

Built-In Variables

Built-in variables are special variables that Linux provides to you that can be used to make decisions within a program. You cannot modify the values of these variables within the shell program.

Some of these variables are

$# Number of positional parameters passed to the shell program
$? Completion code of the last command or shell program executed within the shell program (returned value)
$0 The name of the shell program
$* A single string of all arguments passed at the time of invocation of the shell program

To show these built-in variables in use, here is a sample program called mypgm2:

#!/bin/sh
#my test program
echo "Number of parameters is "$#
echo "Program name is "$0
echo "Parameters as a single string is "$*

If you execute mypgm2 from the command line in pdksh and bash as follows


   # . mypgm2 Sanjiv Guha

you get the following result:

Number of parameters is 2
Program name is mypgm2
Parameters as a single string is Sanjiv Guha

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