<?php
  $fh = fopen("testfile.txt", 'r+') or die("Failed to open file");
  $text = fgets($fh);

  if (flock($fh, LOCK_EX))
  {
    fseek($fh, 0, SEEK_END);
    fwrite($fh, "$text") or die("Could not write to file");
    flock($fh, LOCK_UN);
  }

  fclose($fh);
  echo "File 'testfile.txt' successfully updated";
?>