bsd man page for getgid

GETGID(2)							System Calls Manual							 GETGID(2)

NAME
       getgid, getegid - get group identity

SYNOPSIS
       #include <sys/types.h>

       gid = getgid()
       gid_t gid;

       egid = getegid()
       gid_t egid;

DESCRIPTION
       Getgid returns the real group ID of the current process, getegid the effective group ID.

       The real group ID is specified at login time.

       The  effective  group ID is more transient, and determines additional access permission during execution of a ``set-group-ID'' process, and
       it is for such processes that getgid is most useful.

SEE ALSO
       getuid(2), setregid(2), setgid(3)

4.2 Berkeley Distribution					  January 7, 1986							 GETGID(2)