  Sliding ferroelectricity was originally proposed to elucidate the
out-of-plane polarization generated by a specific stacking arrangement of
non-polar van der Waals layers. However, the concept of sliding
ferroelectricity can be generalized to more geometries. Here, the NbI$_4$ bulk
is theoretical demonstrated as a quasi-one-dimensional sliding ferroelectric
material, which exhibits a polarization of $0.11$ $\mu$C/cm$^2$ perpendicular
to the Nb's chains. The most possible ferroelectric switching path is found to
be via the interchain sliding along the chain direction, while other paths like
Peierls-dimerization of Nb pairs may also work. Moreover, its polarization can
be augmented for $82\%$ by hydrostatic pressure up to $10$ GPa, beyond which
NbI$_4$ becomes a polar metal. In addition, the negative longitudinal
piezoelectricity is also predicted.
