file writing and file appending || file handling in php

<?php
/*
 *file reading and file appending
 * */
$pointer = fopen('hello.txt', 'w');//mode is w means file open for writing purpose
fwrite($pointer, "Hello world\n"); //that will replace all existing sentence or word and write hello world in hello.txt file
fclose($pointer);

$pointer = fopen('hello.txt', 'a');//mode is a means file open for appending some line / word
fwrite($pointer, 'Hello world in another line');