#Open the output file for saving the results;  
  open my $fh_out, '>', $write_dir.'/'.$filename
      or die "failed to open '$filename' for write";

##</code><code>##

 #Open the output file for saving the results;  
  open my $fh_out, '>', "$write_dir/$filename"
      or die "failed to open \'$filename\' for write $!";