module lmdz_new_unit

  IMPLICIT NONE

contains

  ! Returns an existing unit id that isn't already opened
  SUBROUTINE new_unit(unit)
    INTEGER, INTENT(OUT):: unit

    LOGICAL opened, exist

    unit = 0
    DO
       INQUIRE(unit=unit, opened=opened, exist=exist)
       IF (exist .AND. .NOT. opened) RETURN
       unit = unit + 1
    END DO

  END SUBROUTINE  new_unit

end module lmdz_new_unit