Select Code to Download

use strict;
use warnings;
...
   my $filename = <$FN[$k]>;
   print("$filename\n");
}

a
Use of uninitialized value in concatenation (.) or string at 689777.pl
+ line 6.

for (@FN) {
   while (defined(my $filename = glob($_))) {
      ...
   }
}

for my $filename (@FN) {
   ...
}

for (0..18, 20..28, 30..38) {
   my $filename = sprintf('out-02-%02d.txt', $_);
   ...
}