“RVM is not a function” error

So, you just installed rvm and various ruby versions. Now, you are trying to run 'rvm use  ... '

But it throws an error:

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

What do you do? 

1. In terminal, Go to Edit > Profile Preferences

2. Select the "Title and Command" Tab

3. Check the "Run command as a login shell" checkbox 

4. Restart the terminal and use 'rvm use ...'. It works...! 

Some details on what login shell is: https://rvm.io/support/faq/#shell_login

Cheers.