Ubuntu Unleashed 2013 Edition: Covering 12.10 and 13.04, Eighth Edition

Built-In Variables

Built-in variables are special variables provided to shell by Linux that you can use to make decisions within a shell 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 programecho "Number of parameters is $#"echo "Program name is $0"echo "Parameters as a single string is ...