These I’ve added as my following rules:
'search/do'=>'search/do',
'search/do/<town:.*?>'=>'search/do',
'search/do/<town:.*?>/<cat:.*?>'=>'search/do',
'search/do/<town:.*?>/<cat:.*?>/<scat:.*?>'=>'search/do',
the url search/do & search/do/chicago working fine. But search/do/chicago/restaurants gives an error for $_GET[‘cat’] (undefined index cat)