from NetAddr::IP tutorial...

Optimising the address space

This is one of the reason for writing NetAddr::IP in the first place. Let's say you have a few chunks of IP space and you want to find the optimum CIDR representation for them. By optimum, I mean the least amount of CIDR subnets that exactly represent the given IP address space. The code below is an example of this:

use NetAddr::IP;

push @addresses, NetAddr::IP->new($_) for <DATA>;
print join(", ", NetAddr::IP::compact(@addresses)), "\n";
__DATA__
10.0.0.0/18
10.0.64.0/18
10.0.192.0/18
10.0.160.0/19

Which will, of course, output 10.0.0.0/17, 10.0.160.0/19, 10.0.192.0/18.

and also in the tutorial is enough to print those combined ranges in just about any format you can come up with.