Help

You get similar but much shorter output using man gem.

$ gem --help

Output

RubyGems is a sophisticated package manager for Ruby.  This is a
basic help message containing pointers to more information.

  Usage:
    gem -h/--help
    gem -v/--version
    gem command [arguments...] [options...]

  Examples:
    gem install rake
    gem list --local
    gem build package.gemspec
    gem help install

  Further help:
    gem help commands            list all 'gem' commands
    gem help examples            show some examples of usage
    gem help gem_dependencies    gem dependencies file guide
    gem help platforms           gem platforms guide
    gem help            show help on COMMAND
                                   (e.g. 'gem help install')
    gem server                   present a web page at
                                 http://localhost:8808/
                                 with info about installed gems
  Further information:
    https://guides.rubygems.org

Get help on a command.

$ gem COMMAND --help
$ gem help COMMAND