#!/usr/bin/env perl
use strict;
use warnings;
use Net::DNS;
use 5.010;

my @nameservers = qw(8.8.8.8 4.2.2.2);
my @errors;

open(my $resultsfh, '>', "results-serials.csv")
	or die "cannot open > results-serials.csv: $!";

print $resultsfh "Result,Zone";
foreach (@nameservers) {
	print $resultsfh ",Serial for: $_";
}
print $resultsfh "\n";

while (<DATA>) {
	my $fqdn = $_;
	chomp $fqdn;

	my @serials;

	my $res = Net::DNS::Resolver->new;
	$res->tcp_timeout(2);
	$res->udp_timeout(2);

	foreach my $ns (@nameservers) {
		$res->nameservers($ns);
		my $reply = $res->query("$fqdn", "SOA");
		if ($reply) {
				push(@serials, ($reply->answer)[0]->serial);
		} else {
				push(@serials, $res->errorstring);
	 	}
 	}
	# Compare Serials
	no warnings 'numeric';
	if ($serials[0] == $serials[1]) {
      	say $resultsfh "MATCH,$fqdn,$serials[0],$serials[1]";
    } else {
      	say $resultsfh "MISMATCH,$fqdn,$serials[0],$serials[1]";
      	push @errors,  "MISMATCH.$fqdn,$serials[0],$serials[1]";
    }
}

if (@errors) {
	say "ERRORS:";
	foreach (@errors) {
	  say "$_";
	}
}

__DATA__
google.com
apple.com