Don't know which part of Bangalore you live in. But where I'm right now I still see shops using plastic bags. And I haven't seen Bangalore become any cleaner after the supposed ban.
The ban has limitations on the thickness of the plastic bags used. Garbage bags etc are still allowed.Over the last few months the plastic cups/plates etc have almost disappeared from the city.
Himachal has such a ban for over 10 years now and has had really positive effects.