Renaming Files in Go using a rename function

main.go

package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"strings"
)

func main() {
	files, err := ioutil.ReadDir(".")
	if err != nil {
		log.Fatal(err)
	}

	for _, file := range files {
		newName, ok := rename(file.Name())

		if ok {
			err := os.Rename(file.Name(), newName)
			if err != nil {
				log.Println(err)
			} else {
				log.Printf("Renamed %s to %s \n", file.Name(), newName)
			}
		} else {
			log.Printf("Skipping %s as no need to rename \n", file.Name())
		}

	}
}

func rename(oldName string) (newName string, shouldRename bool) {
	s := strings.Split(oldName, ".")
	if len(s) != 3 {
		//this is not named in our current way so we get out
		return
	}
	//if file is named .down then add a U to start
	switch s[1] {
	case "up":
		s[0] = fmt.Sprintf("V%s", s[0])
	case "down":
		s[0] = fmt.Sprintf("U%s", s[0])
	default:
		return
	}

	//replace all instance of _ with -
	s[0] = strings.Replace(s[0], "_", "-", -1)
	//replace first _ with __
	s[0] = strings.Replace(s[0], "-", "__", 1)

	//join the bits removing the up/down
	newName = fmt.Sprintf("%s.%s", s[0], s[2])
	shouldRename = true
	return
}