#!/bin/sh
clear
printf "IP Address?: "
read u_ip

ipchk=`ifconfig | grep "$u_ip"`

while [ "x$ipchk" == "x" ]
  do
        echo "Invalid Ip"
        printf "IP Address?: "
        read ip

  done

if [ "x$ipchk" != "x" ] ; then

        ip="$u_ip"

        echo "IP: $ip"
fi


### results ###

# get-test
IP Address?: 45
[: x    inet 208.74.173.145 netmask 0xffffff80 broadcast 208.74.173.255: unexpected operator
IP: 45