heroku gem readline error

This is a quick one for all the Ruby types out there. I installed the heroku gem onto a fresh Amazon Linux box today, and then this happened:


[ec2-user@newbox ~]$ heroku
:29:in `require': no such file to load -- readline (LoadError)
from :29:in `require'
from /usr/local/lib/ruby/gems/1.9.1/gems/heroku-2.9.0/lib/heroku/command/run.rb:1:in `'
from :29:in `require'
from :29:in `require'
from /usr/local/lib/ruby/gems/1.9.1/gems/heroku-2.9.0/lib/heroku/command.rb:17:in `block in load'
from /usr/local/lib/ruby/gems/1.9.1/gems/heroku-2.9.0/lib/heroku/command.rb:16:in `each'
from /usr/local/lib/ruby/gems/1.9.1/gems/heroku-2.9.0/lib/heroku/command.rb:16:in `load'
from /usr/local/lib/ruby/gems/1.9.1/gems/heroku-2.9.0/bin/heroku:13:in `'
from /usr/local/bin/heroku:19:in `load'
from /usr/local/bin/heroku:19:in `

'

Ooops.

The gem install missed a dependency. This fixes it:

gem install rb-readline

That was easy, but took a good 10 minutes to figure out. Here's hoping you don't stumble over the same thing!