chang the encoding of a file

UTF8_BOM.go

package main

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

func checkBOM(filepath string) bool {
	file, err := os.Open(filepath)
	if err != nil {
		fmt.Println("Error:", err)
		os.Exit(1)
	}
	defer file.Close()

	buffer := make([]byte, 3)
	_, err = file.Read(buffer)
	if err != nil {
		fmt.Println("Error:", err)
		os.Exit(1)
	}

	correct := []byte{0xEF, 0xBB, 0xBF}
	for i := range buffer {
		if buffer[i] != correct[i] {
			return false
		}
	}
	return true
}

func UTF8_TO_BOM(filepath string) {
	// Add the BOM at the beginning of the file
	b, err := ioutil.ReadFile(filepath)
	if err != nil {
		fmt.Println("Error:", err)
		os.Exit(1)
	}
	b = append([]byte{0xEF, 0xBB, 0xBF}, b...)
	err = ioutil.WriteFile(filepath, b, 0644)
	if err != nil {
		fmt.Println("Error:", err)
		os.Exit(1)
	}
}

func BOM_TO_UTF8(filepath string) {
	// Remove the first three bytes
	b, err := ioutil.ReadFile(filepath)
	if err != nil {
		fmt.Println("Error:", err)
		os.Exit(1)
	}
	b = b[3:]
	err = ioutil.WriteFile(filepath, b, 0644)
	if err != nil {
		fmt.Println("Error:", err)
		os.Exit(1)
	}
}

// 0xEF, 0xBB, 0xBF
func main() {
	if len(os.Args) != 3 {
		fmt.Println("command not enough arguments")
		os.Exit(1)
	}
	cmd := os.Args[1]
	filepath := os.Args[2]
	
	if cmd == "check" {
		fmt.Println(checkBOM(filepath))
		return
	} else if cmd == "transform" {
		if checkBOM(filepath) {
			fmt.Println("current is BOM")
			BOM_TO_UTF8(filepath)
		} else {
			fmt.Println("current is UTF-8")
			UTF8_TO_BOM(filepath)
		}
	} else {
		fmt.Println("command not support")
		os.Exit(1)
	}
}