So, you’re writing a Ruby Gem with a command-line program or two, and you want to support a --version option. When that option is displayed, obviously, your program will just emit the version and exit. Ideally, you want to use the version number that’s in the Gem Specification file, so you don’t have put the version string in multiple places. So, you have to find your gem’s specification file at runtime and pull the data you want from it.

I had a surprisingly difficult time searching for the canonical way to accomplish that task. I finally resorted to UTSL, at which point, all became clear.

The solution is to use a Gem::GemPathSearcher class, an instance of which is available via Gem::searcher:

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    PROGRAM_NAME = 'coolness'
    THIS_GEM_PATH = 'coolness' # What you'd require to pull this thing in

    def show_version_only
      gem_spec = Gem.searcher.find(THIS_GEM_PATH)
      if not gem_spec
        raise StandardError.new("Can't find Gem specification for path \"#{THIS_GEM_PATH}\".")
      end
      puts("#{PROGRAM_NAME}, version #{gem_spec.version}. #{gem_spec.homepage}")
    end

The GemPathSearcher class is documented here. Or, you can just use the source, Luke.