in reply to Process ID of qx

From within the same program? No, not really. qx/backticks works much like system, in that the execution of your program stops while the command in qx() is executed. When your program resumes execution, the qx() subprocess is gone. See perlop for greater detail on how it works. If you want to spawn child processes in a more flexible, asynchronous way, start by reading fork. Threads, Multi-Processing, and Inter-Process Communication (in Tutorials) provides some interesting research material.