MADD/monitor.sh

#!/usr/bin/env bash

interface="${MADD_INTERFACE:-"eth0"}"
interface="wlp0s20f3"  
client_script="${MADD_CLIENT_SCRIPT:-"./client.sh"}"

ip -4 monitor address label dev "$interface" | while read event; do
    if [[ $event == \[ADDR\]* ]]; then
        ipv4=$(ip -4 addr show dev "$interface" | grep -Po 'inet \K[\d.]+')
        if [ -n "$ipv4" ]; then
            export MADD_IP="$ipv4"
            $client_script
        fi
    fi
done