  In this paper, we undertake a unified study of background dynamics and
cosmological perturbations in the presence of the Chaplygin gas. This is done
by first constraining the background cosmological parameters of different
Chaplygin gas models with SNIa and $H(z)$ data for detailed statistical
analysis of the CG models. Based on the statistical criteria we followed, none
of the models has substantial observational support, but we show that the
so-called `original' and `extended/generalised' Chaplygin gas models have {\it
some observational support} and {\it less observational support}, respectively,
whereas the `modified and `modified generalised Chaplygin gas models miss out
on the category {\it less observational support}, but cannot be ruled out. The
so-called `generalised cosmic Chaplygin gas model, on the other hand, falls
under the {\it no observational support} category of the statistical criterion
and can be ruled out. The models which are statistically accepted are
considered for perturbation level in both theoretical and observational
aspects. We also apply the $1+3$ covariant formalism of perturbation theory and
derive the evolution equations of the fluctuations in the matter density
contrast of the matter-Chaplygin gas system for the models with some or less
statistical support. The solutions to these coupled systems of equations are
then computed in both short-wavelength and long-wavelength modes. Then feed
these observationally restricted parameters into the analysis of cosmological
perturbations {to address the growth of density contrast through redshift}.
Using the most recent linear growth of the data $f_{\sigma 8}$, CG models are
considered to study the linear growth of the structure.
