How can I find out the machine names of user variables? I'm creating a custom user profile page and I know how to print certain items attached to the user like 

$user_profile['user_picture']


but I don't know the names of any of the other fields. Is there a way that I can view a list of user profile field machine names?
All of the user variables are located in configuration-&gt;People-&gt;Account Settings-&gt;Manage Fields. So simply look at them over there.