etcdctl/ctlv2/command/update_command.go
func updateCommandFunc(c *cli.Context, ki client.KeysAPI) {
	if len(c.Args()) == 0 {
		handleError(c, ExitBadArgs, errors.New("key required"))
	}
	key := c.Args()[0]
	value, err := argOrStdin(c.Args(), os.Stdin, 1)
	if err != nil {
		handleError(c, ExitBadArgs, errors.New("value required"))
	}

	ttl := c.Int("ttl")

	ctx, cancel := contextWithTotalTimeout(c)
	resp, err := ki.Set(ctx, key, value, &client.SetOptions{TTL: time.Duration(ttl) * time.Second, PrevExist: client.PrevExist})
	cancel()
	if err != nil {
		handleError(c, ExitServerError, err)
	}

	printResponseKey(resp, c.GlobalString("output"))
}
func updateCommandFunc(c *cli.Context, ki client.KeysAPI) {
	if len(c.Args()) == 0 {
		handleError(c, ExitBadArgs, errors.New("key required"))
	}
	key := c.Args()[0]
	value, err := argOrStdin(c.Args(), os.Stdin, 1)
	if err != nil {
		handleError(c, ExitBadArgs, errors.New("value required"))
	}

	ttl := c.Int("ttl")

	ctx, cancel := contextWithTotalTimeout(c)
	resp, err := ki.Set(ctx, key, value, &client.SetOptions{TTL: time.Duration(ttl) * time.Second, PrevExist: client.PrevExist})
	cancel()
	if err != nil {
		handleError(c, ExitServerError, err)
	}

	printResponseKey(resp, c.GlobalString("output"))
}
// updateCommandFunc executes the "update" command.