  We present a detailed temporal and spectral study of the blazar 3C\,279 using
multi-wavelength observations from Swift-XRT, Swift-UVOT and Fermi-LAT during a
flare in 2018 January. The temporal analysis of $\gamma$-ray light curve
indicates a lag of $\sim 1$ d between the 0.1--3 GeV and 3--500 GeV emission.
Additionally, the $\gamma$-ray light curve shows asymmetry with slow rise--fast
decay in energy band 0.1--3 GeV and fast rise--slow decay in the 3--500 GeV
band. We interpret this asymmetry as a result of shift in the Compton spectral
peak. This inference is further supported by the correlation studies between
the flux and the parameters of the log-parabola fit to the source spectra in
the energy range 0.1--500 GeV. We found that the flux correlates well with the
peak spectral energy and the log-parabola fit parameters show a hard index with
large curvature at high flux states. Interestingly, the hardest index with
large curvature was synchronous with a very high energy flare detected by
H.E.S.S. Our study of the spectral behavior of the source suggests that
$\gamma$-ray emission is most likely to be associated with the Compton
up-scattering of IR photons from the dusty environment. Moreover, the fit
parameters indicate the increase in bulk Lorentz factor of emission region to
be a dominant cause for the flux enhancement.
