The extraneous commas are no problem. That is one of the many improvements of Perl versus C. These extra commas allow easier additions to the hash with any of Emacs, Vi, Notepad, Wordpad, Ultra-edit, or even ed.

Another possible style, which I prefer, consists in writing the comma at the beginning of the next line, not the end of the previous one. Example:

my %switch_hash =
  (
   chrdex   => 
   {
    DEX   => 
    {
        '01-AUG-02'  => 1
      , '03-AUG-02'  => 3
    }
   }
    
 , uslcgb5e2sm => 
   {
    Greensboro  => 
    {
        '4-AUG-02'   => 1
      , '6-AUG-02'   => 2
    }
   },
    
 , uslecat25e1       => 
   {
    'Atlanta II' =>  # quotation marks are required here
    {
        '1-AUG-02'   => 1
      , '2-AUG-02'   => 3
      , '3-AUG-02'   => 1
      , '4-AUG-02'   => .25
    }
   }
  );

This style also allows easier editing of the hash.