sort unique all files in golang

uniqueFiles.go

import (
	"errors"
	"io/ioutil"
	"os"
	"os/exec"
)

func UniqueFiles(files ...string) (err error) {
	if len(files) == 0 {
		return errors.New("no files provided")
	}

	for _, name := range files {
		if err = createIfNotExists(name); err != nil {
			return
		}
	}

	var args = []string{"-u"}
	args = append(args, files...)
	cmd := exec.Command("sort", args...)

	// open the out file for writing
	outfile, err := ioutil.TempFile("", "")
	if err != nil {
		return
	}
	defer outfile.Close()
	cmd.Stdout = outfile

	if err = cmd.Start(); err != nil {
		return
	}
	cmd.Wait()

	return os.Rename(outfile.Name(), files[0])
}

func createIfNotExists(name string) error {
	f, err := os.OpenFile(name, os.O_CREATE|os.O_EXCL, 666)
	if err != nil {
		if !os.IsExist(err) {
			return err
		} else {
			return nil
		}
	}

	return f.Close()
}