Thank you very much, I resolved this in my next reply, let me know if we had the same idea,but for now 
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
}

[download]
For the above could I have said the following to put the dead ips into the hash ? Is there a difference? 
@down=<$ifh>;
foreach my $line(@down)
{
push @down{$addy}, $_ ;
}
or
@down{$addy}=<$ifh>;

[download]
Also I am not understanding your logic on this line, all ips dead and alive are now in keys %down, you are assigning the value of 1 unless the ip is not apart of keys %down? 
    $down{$addy} = 1 unless ! $down{$addy};
    delete $down{$addy} if exists $down{$addy} and ! $down{$addy};
}

[download]
then lastly, couldn't I just have said below, or you had to go through the hash to get \n formatting? 
print $ifh sort keys %down;

[download]

In reply to Re^2: Writing to File based on condition by cbtshare
in thread Writing to File based on condition by cbtshare

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