Heroku has defaulted to Ruby 2.0 for all applications, so its probably time you updated that crufty old version you have been running. Unfortunately the process is less than straightforward, especially when using a version manager. Assuming you are running rbenv with a Homebrew version of ruby-build, this guide will get you running the latest version of Ruby:
To begin, check which versions of Ruby Rbenv knows about. Rbenv delegates this work to ruby-build:
rbenv install --list
Best case scenario you have a recent version of ruby-build and you see the version of Ruby you want in this listing. At the time of this writing, version 2.0.0-p247 is the most current. If your desired version is present, skip the following steps and just install the Ruby version via:
rbenv install 2.0.0-p247
If your version is not present in the list, you will need to upgrade ruby-build so rbenv knows about the more recent versions of Ruby. Assuming you installed ruby-build via Homebrew, you can update it by issuing:
sudo brew update
Issuing this command complained about having untracked files within the Homebrew directory (which is actually just a git clone of the homebrew project). This may not be the correct way to fix this problem, but I issued the following command to stash these untracked files, and uncommited changes so they don’t interfere with the upgrade process:
cd /usr/local && git add . && git stash
This should now be a clean directory, and you can issue the brew update command again.
Now that brew is updated, you should have the latest “formula” for ruby-build. You can then issue the command to update ruby-build itself:
brew upgrade ruby-build
Once this completes, we can list versions of Ruby via rbenv again to ensure our desired Ruby version is now in the list. Once you see this, you can issue the following command to install a known version of Ruby:
rbenv install 2.0.0-p247
To use your shiny new version of Ruby, you can set this to be the default version:
rbenv global 2.0.0-p247
You can also set this per project, or by setting an environmental variable to override, so don’t worry if not all your projects are Ruby 2.0 ready. You can easily switch between versions – and that’s the point of version management right?
You can confirm you are running the latest Ruby version by issuing:
Note that you will need to re-bundle any gems from your Gemfile against the new Ruby version, as well as rehash any rbenv shims for these gem executables:
gem install bundler && bundle install && rbenv rehash
For more information, check out the rbenv, and ruby-build documentation. To discover the latest stable version of Ruby you can peek at the official Ruby download page to find out the latest version and patch number. Finally, check out the Homebrew docs if you are still stuck.