Shell script to post to Slack every time the Raspberry Pi changes its IP Address via DHCP. Should be in the folder /lib/dhcpcd/dhcpcd-hooks/

90-notify_ip_to_slack.sh

#!/bin/bash
if [ "$interface" = wlan0 ]; then
  if [ "$if_up" = true ]; then
        IP=`ip add show wlan0|grep global |awk '{print $2}'`
        PREVIOUS_IP=`cat /tmp/notify_output`
        if [ "$PREVIOUS_IP" != "$IP" ]; then
          echo 'Notifying ip: '$IP' to Slack Channel..'
          echo $IP > /tmp/notify_output
          curl -X POST -H 'Content-type: application/json' --data '{"text":"RaspBerry TV IP is now: '${IP}'","icon_emoji":":tv:", "username":"RaspBerry"}' https://hooks.slack.com/services/XXXX
        fi
  fi
fi