class Gem::CommandManager

def find_command(cmd_name)
  possibilities = find_command_possibilities cmd_name
  if possibilities.size > 1 then
    raise Gem::CommandLineError,
          "Ambiguous command #{cmd_name} matches [#{possibilities.join(', ')}]"
  elsif possibilities.empty? then
    raise Gem::CommandLineError, "Unknown command #{cmd_name}"
  end
  self[possibilities.first]
end