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Wednesday, May 30, 2012

rbenv - quick start

rbenv is a way to handle multiple versions of Ruby on a single machine and is an alternative to rvm.

I have been using rvm for some time and it works fine, but rbenv seems to have a slight edge in terms of simplicity and, perhaps, transparency in the way it handles version specific gems.

I installed it on a new machine with Mac OS X Lion using homebrew
$ brew update
$ brew install rbenv
$ brew install ruby-build
The only wrinkle was that it requires a regular installation of the gcc compiler, whereas Xcode installs llvn-gcc. You can find the good version at https://github.com/kennethreitz/osx-gcc-installer

You can see which versions of ruby are available using
$ rbenv versions
You can install them like this
$ rbenv install 1.9.3-p0
$ rbenv install 1.8.7-p302
$ rbenv install jruby-1.6.7
Not surprisingly, Jruby required that Java be installed but it was smart enough to trigger the download automatically.

You need to add two lines to your .bashrc, .bash_profile or whatever config file is appropriate for your preferred shell. Then create a new shell to pick up the definitions.

export PATH="$HOME/.rbenv/bin:$PATH"
eval "$(rbenv init -)"
The documentation is pretty straightforward in terms of setting different versions of Ruby in different projects.

Things get a bit confusing when it comes time to set up gems. rvm places copies of each gem in directories that are linked to each ruby version. By and large, rbenv doesn't mess with them.

With rbenv you install specific gems into a single system wide directory, as you would with a single Ruby version. For a given project you specify the required gems in a Gemfile in the project directory and you run

$ bundle exec

to make sure that you have correct versions of all the gems for that given project.
If you have installed a specific gem but find that it does not work or does not appear to exist then run this to, hopefully, fix the issue.

$ rbenv rehash

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