Shell Programming and Scripting

host $ipaddr  >> iptohostname.txt

4.68.16.172.in-addr.arpa domain name pointer g-4.xxx.yyyy.zz.
3.68.16.172.in-addr.arpa domain name pointer g-3.xxx.yyyy.zz.

    hostname=$(grep -e $ipaddr "iptohostname.txt" | awk '{ print $1; }')
    echo "here"
    echo $hostname

4.68.16.172.in-addr.arpa

cat iptohostname.txt | grep "$ipaddr" | awk '{ print $1}'

host 72.21.206.6 | awk '{print $NF}'

host 72.21.206.6 | awk '{print $NF}'
206-6.amazon.com.

host 72.21.206.6 | awk '{print substr($NF,1,length($NF)-1)}'

    hostname=$(host $ipaddr | awk '{print substr($NF,1,length($NF)-1)}')
    echo $hostname
    $h= get the current hostname
    if [ $hostname -ne $h ]
    then
    //instructions
    fi