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
}

##</code><code>##

@down=<$ifh>;
foreach my $line(@down)
{
push @down{$addy}, $_ ;
}
or
@down{$addy}=<$ifh>;

##</code><code>##

    $down{$addy} = 1 unless ! $down{$addy};
    delete $down{$addy} if exists $down{$addy} and ! $down{$addy};
}

##</code><code>##

print $ifh sort keys %down;