Your description sounds very suspicious to me. How are you going to access the variable in the parent process?

fork

Does a fork(2) system call to create a new process running the same program at the same point. It returns the child pid to the parent process, 0 to the child process, or undef if the fork is unsuccessful. File descriptors (and sometimes locks on those descriptors) are shared, while everything else is copied.
-- http://perldoc.perl.org/functions/fork.html

Or am I misunderstanding and you do not want to access a child's variable from the parent?