Usually when I need documentation for a RubyGem I’m working with, I go to RubyDoc.info. Today, however, it was not responding. After catching up on Twitter it occurred to me that I could read the documentation locally since I already had the gem installed.

Running gem rdoc prawn1 generates documentation for the prawn gem. Then gem server will start a server on localhost:8808 hosting the generated RDoc.

This worked fine, but it occurred to me that starting and stopping the gem server whenever I want to see the documentation is annoying. OS X has the concept of launch agents which can be kept alive by the operating system whenever you are logged in. I thought I would make a launch agent to run a gem server so that I could open it whenever I wanted.

Unfortunately, running gem server in a default shell uses the version of Ruby that ships with OS X. I have gems installed in different versions of Ruby using chruby, and I might want to see any of them depending on what project I’m working on. So I decided to run a server for each version of Ruby I have installed (except the system Ruby). Each server runs on a different port chosen based on the Ruby version it supports. Ruby 2.0.0 is available at localhost:8200, 2.1.4 is available at localhost:8214, and 2.2.1 is at localhost:8221.

I wrote a script and an accompanying launch agent plist to run it and posted them in a gist.


  1. There was one catch to generating the documentation. I keep my ~/.gemrc with gem: --no-ri --no-rdoc so that bundle installs go quickly, but in this case it was causing the gem rdoc command to fail. I had to remove that option to successfully generate the documentation.