# ri displays information about Ruby classes, modules, and methods

# show help for the File class
ri File

# show help for the File class on the stdout stream
# do not start a pager for it
ri --no-pager File

# show help for the File.directory? method
ri File.directory?

# start an interactive Ruby documentation repl
ri -i

# Generate the missing ri docs for all your installed gems
gem rdoc --all --ri --no-rdoc