What problem are you trying to solve?

Are you trying to add IPv6 connectivity to an application that only speaks IPv4? Are you trying to add IPv4 connectivity to an application that only speaks IPv6?

Are you trying to find the IPv4 address of a user that connects to your application using IPv6? Are you trying to find the IPv6 address of a user that connects to your application via IPv4?

If you can show us a short, self-contained example (in Perl) of what you have and what you need, then we can likely give you much better advice.