sub parse_fqdn {
    my $fqdn = shift;
    my @tlds = (
        [qw(com net org)],    # common
        [qw(gov edu co\.uk)], # not-so-common
        [qw(la li it po)]     # downright odd (long list)
    );

    foreach my $level (@tlds) {
        #warn "pass ". ++$pass;
        for(@{$level}) {
            return $1 if $fqdn =~ /\.(\w+?\.$_)$/;
        }
    }

    warn "unable to find domain from $fqdn\n";
    return $fqdn;
}

my $domain = parse_fqdn('www.cs.niu.edu'); 
print "www.cs.niu.edu => $domain\n"; # niu.edu