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
Portability issues: "setpgrp" in perlport.