code: func cmdBuild() *subcommands.Command {
  	return &subcommands.Command{
  		Advanced:  true,
  		UsageLine: "pkg-build [options]",
  		ShortDesc: "builds a package instance file",
  		LongDesc:  "Builds a package instance producing *.cipd file.",
  		CommandRun: func() subcommands.CommandRun {
  			c := &buildRun{}
  			c.registerBaseFlags()
  			c.inputOptions.registerFlags(&c.Flags)
  			c.hashOptions.registerFlags(&c.Flags)
  			c.Flags.StringVar(&c.outputFile, "out", "<path>", "Path to a file to write the final package to.")
  			return c
  		},
  	}
  }
docs: ////////////////////////////////////////////////////////////////////////////////
  // 'pkg-build' subcommand.