Do you already know all the possible categories/subcategories? Is there a tree structure, or is it more free-form? Basically, we need to know how we can tell the end of the name of a category and the beginning of the name of a subcategory. If we knew, for example, that there were just categories, clocks, birds, and eels, and subcategories for each include vert and mood, we might have something like:

while(readdir(DIRHANDLE))
  {
  if(s/^clocks//)
    {
    $thisline{category} = 'clocks';
    }
  if(s/^birds//)
    {
    $thisline{category} = 'birds';
    }
  ...
  if(! defined($thisline{category}))
    {
    die "No category defined!\n";
    }
  if(s/^vert//)
    {
    $thisline{category} = 'vert';
    }
  ... # And so on, for 2nd level subcategories.
  }
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On the other hand, depending on how your categories and subcategories are, another approach might be better. If you can clarify your question, I can probably give you a better answer.