shell script to get cpu usage

####################################################
#  Author  : Saurabh Gupta                         #
#  Created : 9:30 AM 9/5/2011                      #
#  shell script to calculate the cpu usage         #
#  It will display the idle % of the cpu           #
####################################################

#!/bin/bash

id=0; tot=0; p_id=0; p_tot=0;

for ((i=0; $i < 100; ++i )) ; do

    p_id=$id; p_tot=$tot;

    x=`cat /proc/stat | grep -w cpu`;

    id=`echo $x | cut -d " " -f 5`;

    tot=0;

    for f in `echo $x`; do

        tot=$(($tot + $f));

    done;

    echo "idle cpu usage% = "$((($id - $p_id)*100/($tot - $p_tot)));

    sleep 3;

done