The getpgrp keyword

The getpgrp function returns the current process group of the PID. For the process group of the current process, the PID should be set to 0 or should be omitted. If Perl is implemented on a machine that does not implement getpgrp(2), an exception is raised. On POSIX systems, a PID is not accepted.

  getpgrp PID
  getpgrp

   print getpgrp 0;