write a bourne shell script cv that takes the side of a cube as a command line argument and displays the volume of the cube

#!/bin/bash
#############################################################
# Name: sy_9
#
# Usage: ./sy_9
#
# Author: Suresh Yadagiri
# Date:  August 06,2010
# Requirements:
#  write a bourne shell script cv that takes the side of a cube
#  as a command line argument and displays the volume of the
#  cube
#
##############################################################

function printusageinfo(){
echo -e "\nUsage: $0 \n"
}
function is_integer() {
    printf "%d" $1 > /dev/null 2>&1
    return $?
}

if [ $# -eq 0 ]
then
        echo "At least one argument expected"
        printusageinfo
        exit
fi

if [ $# -gt 1 ]
then
        echo "only one argument expected"
        printusageinfo
        exit
fi

if ! is_integer $1;
then
        echo -e "\nInteger argument expected"
        printusageinfo
        exit 1
fi

if [ $1 -lt 0 ]
then
        echo "Side of cube must be positive"
        printusageinfo
        exit
fi
volume=`expr $1 \* $1 \* $1`
echo "Volume of cube of side $1 is : $volume"