bsd man page for getpgrp

GETPGRP(2)							System Calls Manual							GETPGRP(2)

NAME
       getpgrp - get process group

SYNOPSIS
       pgrp = getpgrp(pid)
       int pgrp;
       int pid;

DESCRIPTION
       The process group of the specified process is returned by getpgrp.  If pid is zero, then the call applies to the current process.

       Process	groups	are used for distribution of signals, and by terminals to arbitrate requests for their input: processes that have the same
       process group as the terminal are foreground and may read, while others will block with a signal if they attempt to read.

       This call is thus used by programs such as csh(1) to create process groups in implementing job control.	The TIOCGPGRP and TIOCSPGRP  calls
       described in tty(4) are used to get/set the process group of the control terminal.

SEE ALSO
       setpgrp(2), getuid(2), tty(4)

4.2 Berkeley Distribution					  August 26, 1985							GETPGRP(2)