setpgrp
See the current Perl documentation for setpgrp.
Here is our local, out-dated (pre-5.6) version:
setpgrp - set the process group of a process
setpgrp PID,PGRP
Sets the current process group for the specified
PID, 0 for the current process. Will produce a fatal error if used on a machine that doesn't implement
setpgrp(2). If the arguments are omitted, it defaults to
0,0. Note that the
POSIX version of setpgrp() does not accept any arguments, so only setpgrp 0,0 is portable.