Gets the username under which the program is running.
GNU extension
Subroutine
CALL GETLOG(C) 
| C | Shall be of type CHARACTERand of default kind. | 
Stores the current user name in LOGIN. (On systems where POSIX functions geteuid and getpwuid are not available, and the getlogin function is not implemented either, this will return a blank string.) 
PROGRAM TEST_GETLOG CHARACTER(32) :: login CALL GETLOG(login) WRITE(*,*) login END PROGRAM
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Licensed under the GNU Free Documentation License, Version 1.3.
    https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gfortran/GETLOG.html