Extract IP

This will extract the ip number (IPv4): ip -4 addr show eth0 | grep -oP '(?<=inet\s)\d+(\.\d+){3}'

Or this: ifconfig eth0 | grep -oP '(?<=inet\s)\d+(\.\d+){3}'

If you want IPv6: ip -6 addr | grep -oP '(?<=inet6\s)[\da-f:]+'

Script

!/bin/bash

OLD_IP=cat ip.txt NEW_IP=/sbin/ifconfig | awk -F "[: ]+'{ print $4}' #adapted from something I got from the internets. if [ $NEW_IP != OLD_IP ]; then nsupdate #it seems like the keys need to be in the same directory from where nsupdate was called fi echo $NEW_IP > ip.txt exit 0 #not sure if this is necessary