  V5579 Sgr was a fast nova discovered in 2008 April 18.784 UT. We present the
optical spectroscopic observations of the nova observed from the Castanet
Tolosan, SMARTS and CTIO observatories spanning over 2008 April 23 to 2015 May
11. The spectra are dominated by hydrogen Balmer, Fe II and O I lines with
P-Cygni profiles in the early phase, typical of an Fe II class nova. The
spectra show He I and He II lines along with forbidden lines from N, Ar, S, and
O in the nebular phase. The nova showed a pronounced dust formation episode
that began about 20 days after the outburst. The dust temperature and mass were
estimated using the WISE data from spectral energy distribution (SED) fits. The
PAH-like features are also seen in the nova ejecta in the mid-IR Gemini spectra
taken 522 d after the discovery. Analysis of the light curve indicates values
of t$_2$ and t$_3$ about 9 and 13 days, respectively, placing the nova in the
category of fast nova. The best fit cloudy model of the early decline phase JHK
spectra obtained on 2008 May 3 and the nebular optical spectrum obtained on
2011 June 2 shows a hot white dwarf source with T$_{BB}$ $\sim$ 2.6 $\times$
10$^5$ K having a luminosity of 9.8 $\times$ 10$^{36}$ ergs s$^{-1}$. Our
abundance analysis shows that the ejecta is significantly enhanced relative to
solar, O/H = 32.2, C/H = 15.5 and N/H = 40.0 in the early decline phase and O/H
= 5.8, He/H = 1.5 and N/H = 22.0 in the nebular phase.
