use List::MoreUtils qw/uniq/;

if (scalar (uniq @serials) == 1) {
  say $resultsfh join (',', 'MATCH', $fqdn, @serials);
} else {
  say $resultsfh join (',', 'MISMATCH', $fqdn, @serials);
  push @errors, join (',', 'MISMATCH', $fqdn, @serials);
}