Select Code to Download

my %down;

...
    $down{$addy} = system qq{nc -w 1 $addy 22 > /dev/null 2>&1}; # 0 =
+ up, not 0 = down
}

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

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

print $ifh sort keys %down;