flags.go

package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"log"
	"strings"
)

var (
	flDebug bool
	flFoo   string
)

func init() {
	log.SetFlags(0) // Hide timestamps

	flag.BoolVar(&flDebug, "debug", false, "run in debug mode")
	flag.StringVar(&flFoo, "foo", "", "foo")
}

func parseAndValidateFlags() {
	flag.Parse()

	if flDebug {
		log.Println("Running in debug mode")
	}

	if strings.TrimSpace(flFoo) == "" {
		log.Fatal("Error: 'foo' cannot be empty")
	}
}

func main() {
	parseAndValidateFlags()

	// ...
}