This

     if ($str =~ /nbk[A-z0-9]{4}/ or /nbd[A-z0-9]{4}/ or /root/){
[download]

is the same as

     if ($str =~ /nbk[A-z0-9]{4}/ or $_ =~ /nbd[A-z0-9]{4}/ or $_ =~ /
+root/){
[download]

which not what I think you're after. Perhaps you meant

     if ($str =~ /nbk[A-z0-9]{4}/ or $str =~ /nbd[A-z0-9]{4}/ or $str 
+=~ /root/){
[download]