json

configFiles := []altsrc.Sourcer{
	altsrc.StringSourcer(filepath.Join(testdataDir, "config.json")),
	altsrc.StringSourcer(filepath.Join(testdataDir, "alt-config.json")),
}

app := &cli.Command{
	Name: "greet",
	Flags: []cli.Flag{
		&cli.StringFlag{
			Name:    "name",
			Aliases: []string{"n"},
			Sources: cli.NewValueSourceChain(JSON("greet.name", configFiles[0]), JSON("greet.name", configFiles[1])),
		},
		&cli.IntFlag{
			Name:    "enthusiasm",
			Aliases: []string{"!"},
			Sources: cli.NewValueSourceChain(JSON("greet.enthusiasm", configFiles[0]), JSON("greet.enthusiasm", configFiles[1])),
		},
	},
	Action: func(ctx context.Context, cmd *cli.Command) error {
		punct := ""
		if cmd.Int("enthusiasm") > 9000 {
			punct = "!"
		}

		fmt.Fprintf(os.Stdout, "Hello, %[1]v%[2]v\n", cmd.String("name"), punct)

		return nil
	},
}

// Simulating os.Args
os.Args = []string{"greet"}

if err := app.Run(context.Background(), os.Args); err != nil {
	fmt.Fprintf(os.Stdout, "OH NO: %[1]v\n", err)
}

Output:

Hello, Berry!