#!/bin/bash
read -p "Give me an IP : " IP
while [ 1 ]
do echo "$IP" | egrep -q '^([0-9]{1,3}\.){3}[0-9]{1,3}$'
 if [ $? -eq 0 ]
 then valid=1
 for number in ${IP//./ }
 do if [ $number -gt 255 ]
 then valid=0
 break
 fi
 done
 if [ $valid -eq 1 ]
 then break
 fi
 fi
 read -p "Incorrect format, please input again : " IP
done
echo "IP=$IP"