Possible Duplicate:
ruby 1.9 ri problem
When I try to use Ruby's ri tool in a command prompt window to get help about classes, methods, etc. it seems to always fail. For example if I type:
ri Array
I get a message saying:
Updating class cache with 0 classes... Nothing known about Array
I am using Vista 64 with Ruby 1.9.1p243 (2009-07-16 revision 24175) [i386-mingw32] installed.
What should I do to configure ri to work?
Although this question is old, nobody has yet provided a proper solution. I just ran into the same issue, and found the solution:
If you are using RVM:
rvm docs generate-ri # <- Just the ri docs, much faster
rvm docs generate # <- Everything (rdoc + ri)
More info on managing RVM docs here:
https://rvm.io/rubies/docs
If not using RVM:
gem install rdoc-data
# Regenerate system docs
rdoc-data --install
# Regenerate all gem docs (rdoc + ri)
gem rdoc --all --overwrite
# Regenerate all gem docs (ri only)
gem rdoc --all --overwrite --ri --no-rdoc
# Regenerate specific gem doc with specific version
gem rdoc gemname -v 1.2.3 --overwrite
来源：https://stackoverflow.com/questions/1575373/why-does-my-ruby-ri-tool-not-return-results-in-command-prompt