How to replace the last octet in an IP adress using Bash?

Question

I have a variable that contains an IP address.

ip=192.165.12.30 

How can I replace the last octet with 0 so that it becomes as below?

ip=192.168.12.0

Answer 1

You can use a parameter expansion:

$ ip=${ip%.*}.0
$ echo "$ip"
192.165.12.0