在进程打开时获取进程的PID

How do I get the pid of a process as soon as it opens. Like lets say we run ./file.pl and then ./file2.pl As both these files will create a pid in /proc/ folder. How do I instantly know if the process has been created when the executable is run. I have a file with all the commands ready to be run as soon as it gets the green signal that there is a new process in the /proc/ folder. How do I do that? EDIT: Please don't answer with a shell command. I don't need to know the pid. I need to develop a script which can know right away that we have a guest in the proc departmentHow do I get the pid of a process as soon as it