Special Variables

In the last tutorial about shell functions, you used $1 to represent the first argument passed to function_A. Moreover, here are some special variables in shell:

• $0 - The filename of the current script.
• $n - The Nth argument passed to the script was invoked or function was called.
• $# - The number of arguments passed to the script or function.
• $@ - All arguments passed to the script or function.
• $* - All arguments passed to the script or function.
• $? - The exit status of the last command executed.
• $$ - The process ID of the current shell. For shell scripts, this is the process ID under which they are executing.
• $! - The process number of the last background command.

Example:

#!/bin/bash
echo "Script Name: $0"
function func {
    for var in $*
    do
        let i=i+1
        echo "The \$${i} argument is: ${var}"
    done
    echo "Total count of arguments: $#"
}
func We are argument

$@ and $* have different behavior when they are enclosed in double quotes:

#!/bin/bash
function func {
    echo "--- \"\$*\""
    for ARG in "$*"
    do
        echo $ARG
    done

    echo "--- \"\$@\""
    for ARG in "$@"
    do
        echo $ARG
    done
}
func We are argument

Exercise

A function func prints the total count of arguments it receives. Call func below with the three arguments We, are, and argument so that the output reads Total count of arguments: 3.