i know that through child process I cant modify parents' variables. But just asking if there is a way

Fortunately not. I would feel very uneasy as a programmer if I had to worry whether my child processes secretly change my environment without me noticing. This is already pretty nasty in Windoze batch programming where this "feature" is possible.

IMHO, values should passed back to the parent in a way which is clearly visible (i.e. the caller has to ask for the values). How this is done, depends on the application being called. For instance, you might pass a filename to the application, and it writes any output parameters into the file. Or, the application uses stdout to pass data back, and you use qx() instead of system() to catch it.