Ars Technica

Run a command when the IP changes

I would think one of dynamic DNS client utilities might do this... Check through the list here and see if any allow running an external command on detection ...
Network World

Use bash to change an IP address from dynamic to static on Linux

The bash script described here can change Linux systems' IP addresses from dynamic to static with much less manual work. Changing the IP address of a Linux system from dynamic to static is not ...
MUO on MSN

5 Windows Terminal commands I run first when the internet breaks

Feel smarter than your router in 60 seconds.