demo_set_environment_variable Program

     program demo_set_environment_variable
     use M_system, only : set_environment_variable
     use iso_c_binding
     implicit none
     integer :: ierr
        !x!
        write(*,'(a)')'no environment variables containing "GRU":'
        call execute_command_line('env|grep GRU')
        !x!
        call set_environment_variable('GRU','this is the value',ierr)
        write(*,'(a,i0)')'now "GRU" should be defined, status=',ierr
        call execute_command_line('env|grep GRU')
        !x!
        call set_environment_variable('GRU2','this is the second value',ierr)
        write(*,'(a,i0)')'now "GRU" and "GRU2" should be defined, status =',ierr
        !x!
        call execute_command_line('env|grep GRU')
     end program demo_set_environment_variable