getpgrp

getpgrp 
pid

Returns the current process group for the specified process ID ( pid ). Use a pid of 0 for the current process. Invoking getpgrp will produce a fatal error if used on a machine that doesn't implement the getpgrp system call. If pid is omitted, the function returns the process group of the current process (the same as using a pid of 0 ). On systems implementing this operator with the POSIX getpgrp(2) system call, pid must be omitted or, if supplied, must be 0 .