Gnome Version – How to Find the Current Version

Modify the following line(71) at win7-setup.sh:

if [ $DESKTOP_SESSION = "gnome" -o $DESKTOP_SESSION = "classic-gnome" ] ; then

to

if [ $DESKTOP_SESSION = "gnome" -o $DESKTOP_SESSION = "gnome-classic" ] ; then

(This answer was tested with Ubuntu 14.04. It is probably not useful for newer Ubuntu editions)

I do not know about ligthDM (@muru confirm that lightDM behave the same), but if you use gdm as display manager the default session is simply the last one you choose (at least, it was --- I hope they didn't change this; can't test now because I removed all desktops minus the gnome-shell one).

To install gdm (which, by the way, is the best thing to do if you want gnome-shell --- I had problems with gnome-shell + lightDM), simply

sudo apt-get install gdm

If you have it already installed, just

sudo dpkg-reconfigure gdm 

will ask you which display manager to use.

Then when you login, you choose Gnome as the desktop you want, and the subsequent login that will be the default.