my $hostfile = "/ansible/awsLists";
my $deadfile = "/ansible/awsGone";
my $newdeadfile = $deadfile.'-tmp';

my %down;

open my $ifh, '<', $hostfile or die "Can't read '$hostfile: $!\n";

while(my $addy = <$ifh>) {
    chomp $addy;
    $down{$addy} = system qq{nc -w 1 $addy 22 > /dev/null 2>&1}; # 0 = up, not 0 = down
}

open $ifh, '<', $deadfile or die "Can't read '$deadfile: $!\n";

while(my $addy = <$ifh>) {
    chomp $addy;
    $down{$addy} = 1 unless ! $down{$addy};
    delete $down{$addy} if exists $down{$addy} and ! $down{$addy};
}

# only the down ones remain in %down now

open my $ofh, '>', $newdeadfile or die "Can't write '$newdeadfile': $!\n";
print $ofh $down{$_},"\n" for sort keys %down;
close $ofh;

rename $newdeadfile, $deadfile;