foreach my $file (@filenames) {
   my $h = \%files;
   my @parts = split(/[-_.]/,$file);
   my $last = pop(@parts);

   foreach (@parts) {
      $h->{$_} ||= {};
      $h = $h->{$_};
   }

   $h->{$last} = 1;
}

##</code><code>##

foreach my $file (@filenames) {
   my $p = \\%files;
   my @parts = split(/[-_.]/,$file);
   $p = \(${$p}->{$_}) foreach @parts;
   ${$p} = 1;
}

##</code><code>##

foreach (@filenames) {
   my $p = \\%files;
   $p = \(${$p}->{$_}) foreach split /[-_.]/;
   ${$p} = 1;
}