append.go

import (
  "log"
  "os"
)
/*
append.txt initally:
An existing line

append.txt after calling appendToFile:
An existing line
Adding a new line
*/
func appendToFile(){
	content := "\nAdding a new line";
	file, err := os.OpenFile("append.txt", os.O_APPEND | os.O_WRONLY, 0644);
  	defer file.Close();
	if err != nil {
		log.Fatal(err);
	}
	file.Write([]byte(content));
}