Minor example of ff/cli and ff/toml usage

config.toml

arr = ["gno", "land", "👍"]

main.go

package main

import (
	"context"
	"flag"
	"fmt"
	"os"

	"github.com/peterbourgon/ff/v3"
	"github.com/peterbourgon/ff/v3/ffcli"
	"github.com/peterbourgon/ff/v3/fftoml"
)

// stringArr defines the custom flag type
// that represents an array of string values.
// Example taken from:
// https://github.com/peterbourgon/ff/blob/fe611a8e5a9483e716da5c57644b8d48540d3913/fftest/vars.go#L118-L135
type stringArr []string

// String is a required output method for the flag
func (s *stringArr) String() string {
	return "whatever"
}

// Set is a required output method for the flag.
// This is where our custom type manipulation actually happens
func (s *stringArr) Set(value string) error {
	*s = append(*s, value)

	return nil
}

func main() {
	const (
		configFlagName = "config"
	)

	var (
		// Example storage for our array type
		myStrArr stringArr

		// Define a basic flag set for the command "example"
		fs = flag.NewFlagSet("example", flag.ContinueOnError)

		// Define the flag for the config path
		_ = fs.String(configFlagName, "", "the TOML config file")
	)

	// Register the flag type.
	// This array can be populated using:
	// ... --arr "value1" --arr "value2" ...
	fs.Var(&myStrArr, "arr", "array string input")

	example := &ffcli.Command{
		Name:       "example",
		ShortUsage: "example [<arg> ...]",
		ShortHelp:  "Example command that showcases arrays and TOMLs",
		FlagSet:    fs,
		Exec: func(_ context.Context, _ []string) error {
			// Print out the array arguments that were parsed.
			// For either .toml usage or explicit flag usage,
			// the FS vars should be filled
			fmt.Printf("Received an %d element string array: %v\n", len(myStrArr), myStrArr)

			return nil
		},
		Options: []ff.Option{
			ff.WithConfigFileFlag(configFlagName),
			ff.WithConfigFileParser(fftoml.Parser),
		},
	}

	if err := example.ParseAndRun(
		context.Background(),
		os.Args[1:],
	); err != nil {
		os.Exit(1)
	}
}