use strict;
use Socket;

my $addr = shift || '172.17.0.1';
my ($name,$aliases) = gethostbyaddr(inet_aton($addr), AF_INET);

print "address $addr has the following names:\n";
print "\t$_\n" for ($name, split / /, $aliases);
##</code><code>##

address 172.17.0.1 has the following names:
        host1.example.com
        host2.example.com
        host3.example.com
        host4.example.com
        host5.example.com