osx man page for getgid

GETGID(2)						      BSD System Calls Manual							 GETGID(2)

NAME
     getegid, getgid -- get group process identification

SYNOPSIS
     #include <unistd.h>

     gid_t
     getegid(void);

     gid_t
     getgid(void);

DESCRIPTION
     The getgid() function returns the real group ID of the calling process, getegid() returns the effective group ID of the calling process.

     The real group ID is specified at login time.

     The real group ID is the group of the user who invoked the program.  As the effective group ID gives the process additional permissions dur-
     ing the execution of ``set-group-ID'' mode processes, getgid() is used to determine the real-user-id of the calling process.

ERRORS
     The getgid() and getegid() functions are always successful; no return value is reserved to indicate an error.

LEGACY SYNOPSIS
     #include <sys/types.h>
     #include <unistd.h>

     The include file <sys/types.h> is necessary.

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

STANDARDS
     Getgid() and getegid() conform to IEEE Std 1003.1-1988 (``POSIX.1'').

4.2 Berkeley Distribution					   June 4, 1993 					 4.2 Berkeley Distribution