go语言学习笔记----模拟实现文件拷贝函数

//main
package main

import (
	"bufio"
	"flag"
	"fmt"
	"io"
	"os"
	"strings"
)

func fileExists(filename string) bool {
	_, err := os.Stat(filename)
	return err == nil || os.IsExist(err)
}

func copyFile(src, dst string) (w int64, err error) {
	srcFile, err := os.Open(src)
	if err != nil {
		fmt.Println(err.Error())
		return
	}

	defer srcFile.Close()
	dstFile, err := os.Create(dst)

	if err != nil {
		fmt.Println(err.Error())
		return
	}

	defer dstFile.Close()

	return io.Copy(dstFile, srcFile)

}
func copyFileAction(src, dst string, showProgress, force bool) {
	if !force {
		if fileExists(dst) {
			fmt.Printf("%s exists override? y/n
", dst)
			reader := bufio.NewReader(os.Stdin)
			data, _, _ := reader.ReadLine()

			if strings.TrimSpace(string(data)) != "y" {
				return
			}

		}

	}
	copyFile(src, dst)
	if showProgress {
		fmt.Printf("'%s'->'%s'
", src, dst)
	}
}

func main() {
	var showProgress, force bool
　　　　//定义命令行参数
	flag.BoolVar(&force, "f", false, "force copy when existing")
	flag.BoolVar(&showProgress, "v", false, "explain what is being done")

	flag.Parse()
　　　　//非法命令行数量检测
	if flag.NArg() < 2 {
		flag.Usage()
		return
	}
       //取第0个参数与第一个参数作为源文件名跟目标文件名
	copyFileAction(flag.Arg(0), flag.Arg(1), showProgress, force)
}