Version of http://learngowith.me/gos-flag-package-creating-a-cli-tool/ using Kingpin

yes-kingpin.go

package main

import (
	"errors"
	"fmt"
	"strconv"

	"github.com/alecthomas/kingpin"
)

var (
	versionUsageText = "0.1"
	textArg          = kingpin.Arg("text", "Text to repeat (defaults to 'y').").Default("y").String()
	limitFlagCustom  = CustomFlag(kingpin.Flag("limit", "0 or greater integer value, determines times output is displayed"))
)

func main() {
	kingpin.Version(versionUsageText)
	kingpin.Parse()
	if *limitFlagCustom == 0 {
		*limitFlagCustom = -1
	}
	for i := 0; i != *limitFlagCustom; i++ {
		fmt.Println(*textArg)
	}
}

type PositiveInt int

func (p *PositiveInt) Set(s string) error {
	i, _ := strconv.Atoi(s)
	if i < 0 {
		return errors.New("flag must be >= 0")
	}
	*p = PositiveInt(i)
	return nil
}

func (p *PositiveInt) String() string {
	return strconv.Itoa(int(*p))
}

func CustomFlag(s kingpin.Settings) (target *int) {
	target = new(int)
	s.SetValue((*PositiveInt)(target))
	return
}