PHP/File Directory/Text File Write

How to add text to the file

<?php
  $myfile = "./test.txt";
  $openfile = fopen ($myfile,"a") or die ("Couldn"t open the file");
  fwrite ($openfile,"Have a nice day! \n");
  fclose ($openfile);
  $openfile = fopen ($myfile,"r") or die ("Couldn"t open the file");
  $file_size=filesize($myfile);
  $file_contents = fread ($openfile,$file_size);
  $msg ="$file_contents";
  fclose ($openfile);
  echo $msg;
?>

Write string to text file

<?php
   $subscriberInfo = "g@wbex.ru";
   $fh = fopen("./text.txt", "at");
   fwrite($fh, $subscriberInfo);
   fclose($fh);
?>