http://www.perlmonks.org?node_id=526667

keiusui has asked for the wisdom of the Perl Monks concerning the following question:

I know that $ENV{REMOTE_ADDR} returns the IP address of a visitor. How do I get the hostname of a visitor?

For example, this website tells you your hostname:
whatismyipaddress.com/staticpages/index.php/whatismyhostname