The rvm sudo gem install gotcha

The title of the post says it all.  Ruby Version Manager (RVM) is handy for quickly switching between different versions of ruby, but if you have been using a system installation, your muscle memory may have you typing this to install a gem:

sudo gem install

It doesn't work as you might expect with rvm. It installs the gem in the gem repository of the system ruby.

I got caught out by this, and I hope others can learn from my mistakes.

So if you have done:

rvm use 1.9.2

Then to install a gem, you should go

gem install