Tutorial :How do I install the Ruby ri documentation?


I've recently installed Ruby 1.9.1 on Windows 7, and apparently it doesn't come with the standard ri documentation. So when I do 'ri Array', I get:

C:\>ri Array    Nothing known about Array  

Is there a way I can install this documentation so that the above works?


Seems you have installer Ruby 1.9.1 distributed by the RubyInstaller project.

You can use the Windows Help Files (CHM) that came with the installer instead of the ri documentation.

The problem of the RI documentation is that some versions of RDoc have problems generating it and also generated more than 10 thousands files which slowed down the installers considerably.


In case people on other platforms need to install their ri docs (like I did). This article gives the why and the how:


The command is:

gem rdoc --all --ri --no-rdoc  


If you are using rvm you should rvm docs generate (or just rvm docs generate-ri)

See this info (2011August) about rvm and ri


None of the proposed solutions worked for me. In the end the solution I found was super simple, so I'll leave it here. (I'm running ruby 2.2.4 on win7 x64 in case that's relevant)

(captain obvious alert: ruby must be installed and in your PATH)

-open cmd

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

And you're set! test that it worked by running:

-$ ri Array It should give you all the lovely documentation for the class!

Hope this helps!

ps. I just noticed that this is the solution that Luis Lavena proposed in a comment, but his comment wasn't clear to me so I had continued searching. Basically this is the same solution but explained more clearly so that that doesn't happen to anyone else :)



RVM does not automatically generate and install each Ruby's ri / rdoc documentation. You can generate using the following command: rvm docs generate


Things are still largely the same with Ruby Installer (year 2017). If I run ri Array, it shows Array < Object and nothing else. If I run ri "Array#each", I get the familiar "Nothing known..." message. In short, the ri-format documentation on Ruby core and standard libraries are missing.

Here's how I got my copy of core/stdlib ri-documentation. Of course, Ruby must be installed prior to this.

  1. Get ruby's source code that most closely matches my version from their Github releases page.
  2. Extract the .zip or .tar.gz archive to some folder
  3. Open cmd.exe/Powershell, cd to that folder and run rdoc --all --ri
    • This command parses .c files, .rb files, and a few other file types in the current directory recursively and generates ri-documentation to ~/.rdoc directory.
    • Took about 5 minutes on my laptop with i7-3520M processor to complete, with no errors.
  4. Delete the archive and the directory containing the source code because we don't need them anymore.

Now if you try running ri Array or ri "Array#each" you'll get the documentation in all its glory.


Run rdoc --all --ri on directory containing source code for same ruby version as your installed version.

Appendix Z: Comments on other answers

  1. The rvm docs generate-ri could work, but you have to use Cygwin or Ubuntu on Windows (if on Windows 10) to use rvm.
  2. gem rdoc --all --ri --no-rdoc installs ri-documentation for all your gems. It doesn't install the core/stdlib documentations.
  3. gem install rdoc-data followed by rdoc-data --install only works for Ruby versions up to 2.3.0.


All the Ruby Docs are at http://www.ruby-doc.org

So the array documentation is at:


Never tried it on windows but because its saying Nothing Known about X its not that its not installed just not got anything there.

Try installing a gem as you can then ri GEM_CLASS as that should provide defentions, should let us see if its missing documentation or if ri's not looking in the right place

Note:If u also have question or solution just comment us below or mail us on toontricks1994@gmail.com
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