Using Synology NAS to email you when its IP changes

Here’s a shell script I use to make my Synology email me whenever my home IP address changes.

Synology’s Task Scheduler can run a script on a schedule, with an option to email you if the task fails (exits with non-zero code).

So what this script does specifically is check my public IP using ipinfo.io/io, and if the IP is different from the last time it checked, it prints the new IP and exits with an error code, causing the Synology to send me the entire output, which includes the new IP.

If the IP hasn’t changed the program exits normally and no email is sent. Pretty handy.

set -e 
touch ip.txt

IP=$(curl -s ipinfo.io/ip)
OLD_IP=$(cat ip.txt)

if [ "$IP" = "$OLD_IP" ]; then
    echo "IP ADDRESS UNCHANGED: $IP"
else
    echo "IP ADDRESS CHANGED: $IP (Was $OLD_IP)"
    echo $IP > ip.txt
    exit 1
fi