Why does my Ruby 'ri' tool not return results in command prompt? [duplicate]

Question

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