Do you *know* that only one process (instance of your program, for example) will be used at a time?

You don't want two instances to try to do the same thing.

Two ideas come to mind here.

1. Use a daemon (google for it)
2. Instead of naming the directories (in essence using the filename as metadata (one of my pet projects, hehe))- name the directory something constant, and use a config file (YAML) or Storable.
   Or even cooler.. maybe Cache::File

   If you do something like store meta in config files..
   If your dir is
   /stuff/JohnSmith_jhon99

   Then your meta is
   /stuff/JohnSmith_jhon99/.meta