    # File lib/rubygems/command_manager.rb, line 109
        def find_command(cmd_name)
          possibilities = find_command_possibilities(cmd_name)
          if possibilities.size > 1
            raise "Ambiguous command #{cmd_name} matches [#{possibilities.join(', ')}]"
          end
          if possibilities.size < 1
            raise "Unknown command #{cmd_name}"
          end

          self[possibilities.first]
        end