Golang. Append string to a file. If the file didn't exist, created it.

append.go

package main

import (
	"log"
	"os"
)

func appendFile(fileName, content string) {
	file, err := os.OpenFile(fileName, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0644)
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()

	if _, err = file.WriteString(content); err != nil {
		log.Fatal(err)
	}
}

func main() {
	appendFile("test.txt", "Hello")
	appendFile("test.txt", " World\n")
}