Unix shell script to get cpu usage

Unix shell script to get CPU usage

#!/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 is % = "$((($id - $p_id)*100/($tot - $p_tot)));

    sleep 3;
done