#!/bin/sh
function usage()
{
      echo "need root priority"
      echo "usage:`basename $0` [exchange dns mode]"
      echo "     :`basename $0` <ip>[manual dns server ip]"
      exit -1
}

#test root priority
[ `id -u` != 0 ] && usage

function unblockresolv()
{
    chattr -i /etc/resolv.conf
    chmod 777 /etc/resolv.conf
}


function blockresolv()
{
    chmod 444 /etc/resolv.conf
    chattr +i /etc/resolv.conf
}


if [ $# == 0 ]; then
    unblockresolv
    CNT=$(cat /etc/resolv.conf|grep 127.0.0.1|wc -l)
    if [ $CNT == 1 ]; then
        echo "nameserver 8.8.8.8" > /etc/resolv.conf
    else
        echo "nameserver 127.0.0.1" > /etc/resolv.conf
    fi
    blockresolv
    exit -1
elif [ $# == 1 ]; then
    dnsip=`echo $1|grep -x -E "([0-9]{1,3}\.){3}[0-9]{1,3}"`
    if [ $? == 0 ]; then
      unblockresolv
      echo "nameserver $dnsip" > /etc/resolv.conf
      blockresolv
      exit -1
    else
      usage
    fi

else
    usage
fi