Unbenownst to many Ruby developers, Ruby has a wonderful CUI (Composite User Interface) for referencing the API of the language and all available libraries: ri. ri stands for “Ruby Interactive”, which is an odd name for a tool to navigate documentation, and one which inevitably gets confused with irb (Interactive RuBy). Seriously, try Googling “Ruby Interactive”.

Perhaps it is due to the popularity of editors such as TextMate or Sublime, or perhaps because it is the ease of finding documentation through Google, but it seems that most developers either don’t know about, or don’t use ri. I do, but I’m a command-line junkie and I’ve not found another tool which is as simple or as accessible as plain old ri.

Getting Started

If you have Ruby installed, you should have all that’s necessary to play around with ri. If you are have troubles, look at “Troubleshooting” below.

To try it out, at the command-line type ri followed by the class or method you want documentation about. Typing ri Array should show you the docs for the Array class. If you type ri Array.min, ri will provide the documentation for Array’s min instance method. To be very specific about things, use a :: or # for class and instance methods rather than the generic ..


ri Array::wrap # class method lookup
ri Array#min # instance method lookup

One really useful feature of the tool is the suggestions ri provides when you enter only part of what you are looking for. Try it out:

$ ri Enumerable.each
Enumerable.each not found, maybe you meant:


Neat. I didn’t know about #each_with_object.

In Technicolor

You may have noticed that all the documentation is in black and white - or at least you would have if you were using my color scheme. If you want to add a little color to your output, use the “ansi” format.

ri -f ansi Array.sort

If you like this, you can set up an alias in your .bashrc or .zshrc.

alias ri='ri -f ansi'

Make sure not to use a direct path to ri since RVM projects will have ri located somewhere else. You want to use your project’s instance of ri.

It’s All About the Interactive

It might surprise you to learn that “Ruby Interactive” actually has an “interactive” mode. You can start ri in interactive mode by passing the -i flag.

Here’s what that looks like:

 $ ri -i

Enter the method name you want to look up.
You can use tab to autocomplete.
Enter a blank line to exit.


At the prompt, just type in what methods, classes, or what-have-you and hit return. To exit, just hit return again, or the ever available ctrl-d.

Unlike calling ri with a specific parameter, interactive mode will, like an inquisitive child, keep prompting you to search again.

VIM and ri

It’s not always convenient to drop down to the command-line just to look up documentation. Wouldn’t it be cool if you could search the docs from your favorite editor? Daniel Choi thought so and created the excellent ri_vim plugin. It’s easy to install, but you will need to install it in each RVM project you want to use it in.

ri isn’t for everybody and that’s cool, but for those of us who are more at home at the command-line than in our own house, it’s indispensible. Try it out for yourself, you may very well find it’s more accessible and useful than you realized.


If you are not in an RVM project and you are unable to find ri documentation, try this:

gem install rdoc rdoc-data
rdoc-data --install

If you are in an RVM project, this should clear things up.

rvm docs generate-ri

Further Reading