# Simple Resolver Function 
# with some error checking: 
# (invalid ips, host starts with a number)

use Socket;

# wrapper -- feed it from STDIN
while (<>) {
    &resolve ($_);
}

# the actual SUB

sub resolve($) {
    my $target = $_;
    chomp $target; # kill newline ARGH! I wasted hours on this!!
    if ($target =~ /^(\d+)\.(\d+)\.(\d+)\.(\d+)$/&&((1|$1|$2|$3|$4)<256)) { # if $target is a valid IP address
        my $hostname = gethostbyaddr(inet_aton($target), AF_INET); # attempt to resolve
        if (! $hostname) { # gethostbyaddr returned undef
            print "Couldn't resolve ($target)\n";
        }
        else {
            print "$hostname\n";
        }
    }
    elsif ($target =~ /^\d/ ){ # $target starts with a number and of course wasn't caught by above loop
        print "Invalid Host $target\n";
    }
    else { # resolve an actual validish hostname
        my $ip = gethostbyname($target);
        if ($ip) { # gethostbyname actually returned something other than undef
            $ip = inet_ntoa($ip);
            print "$ip\n";
        } else {
            print "Couldn't resolve ($target)\n";
        }
    }
}