integer function GetLun ()
! by Steve Lionel, Ron Shepherd, William Clodius, Cleve Page,
! Jeff Drummond. and others as posed at comp.lang.fortran on
! 9 September 1997
      implicit none
      logical :: exs, opn
      integer :: i
      getlun = -1  ! returned if no units are available.
      do i=7,99
        inquire (unit=i,exist=exs,opened=opn)
          if (exs .and. .not. opn) then
            getlun = i
            return
          end if
      end do
      write (*,*) "There are no free Fortran logical units available."
      return
 end function getlun

 program TestLun
   implicit none
   integer :: GetLun, gL
   open(unit=7,status="scratch")
   gL = GetLun()
   if (gL > 0) then
     write(*,*) "Free Fortran Logical Unit= ",gL
   endif
 end program TestLun