program list_files
! An example of a subroutine procedure call
! JWP 22/10/98

implicit none

! The following says what the subroutine looks like..
interface
 subroutine system (arg)
  character*(*),  intent(in) :: arg
 end subroutine
end interface
! .. in most cases the above can be omitted!
!
! This instruction makes it work:
call system ('ls')
!
end program list_files