RVM is not a function, selecting rubies with 'rvm use …' will not work

I got above error while upgrading rails and start using it. Most probably this is because of the rvm upgrading. Easiest solution is

open the terminal.

got to edit -> "Profile-Preferences"

choose "title and command" tab from the window

check on "Run command as a login shell"

and then close and restart the terminal. boom.. you will be able to choose correct ruby version and continue.

Happy Coding!!!!