how check the value of variables

hello all
               i want to apply rule through php script,but plz tell me first 
about value passing to recipe.
$LOGNAME, i read it from manpages,how its value can be set.
or how can i check which user login and who's recipe is call 
i can't understand that thing. plz guide me for passing variable.how a recipe 
get the variable.
r it is just like file handling in which u write anything.
plz guide me a little
thanks (any response)