Gem::Command#get_one_gem_name

# File tmp/rubies/ruby-3.3.0/lib/rubygems/command.rb, line 219
def get_one_gem_name
  args = options[:args]

  if args.nil? || args.empty?
    raise Gem::CommandLineError,
          "Please specify a gem name on the command line (e.g. gem build GEMNAME)"
  end

  if args.size > 1
    raise Gem::CommandLineError,
          "Too many gem names (#{args.join(", ")}); please specify only one"
  end

  args.first
end