I like it dirt - instead of

   {
       local $" = "\n";
       open my $fh, '>', "$ENV{HOME}/number_list.txt"
           or die $!;
       print $fh "@list\n";
   }
[download]

use

   my $prefix = "something";
   {
       local $" = "\n$prefix";
       open my $fh, '>', "$ENV{HOME}/number_list.txt"
           or die $!;
       print $fh "$prefix@list\n";
   }
[download]

Of course it's just to show you that you can put whatever separator inside $"; if you want a clean solution, use Zaxo's.