Returns the numerical group ID of the current process.
GNU extension
Function
RESULT = GETGID() 
The return value of GETGID is an INTEGER of the default kind. 
See GETPID for an example. 
    © Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
    https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gfortran/GETGID.html