OK - I'm not experienced at Perl by trying to do something that should
be fairly simple for those of you who are good at it.

I need a subroutine that I can pass and IP address to. It will do a
reverse DNS lookup and get a hostname. Then lookup the hostname to
verify that one of the IP addresses it returns matched the IP that was
looked up. Return the host name if it succeeds ot an empty string if not.

How do you do that?

I'm building what will be an impressive public DNS blacklist/whitelist
which I will share when it's working.

Thanks in advance.

Oh - also.

If I have a string, what's that fastest way to count the number of
periods in the string?