Sets the current process group for the specified PID, 0
 for the current
process.  Raises an exception when used on a machine that doesn't
implement POSIX setpgid(2) or BSD setpgrp(2).  If the arguments are omitted,
it defaults to 0,0
.  Note that the BSD 4.2 version of setpgrp does not
accept any arguments, so only setpgrp(0,0) is portable.  See also
POSIX::setsid()
.
Portability issues: setpgrp in perlport.