LU decomposition: backsubstitution available?

[Thomas Hoffmann]

It is a known procedure for the solution of a sequence of
systems of linear equations Ax=b with only varying rhs to
make once a LU decompostion of A (function lu() of octave)
and then backsubstitute for the several b's, e.g.
  x=backsubs(l,u,b)
As e.g. RLaB has such an mechanism, I thought of similar
functionality in Octave, but did not find any.

Can anybody shed some light on this?

Thomas.