how to edit HTML in the textarea and update it in PHP

The coding for Edit and Update the HTML content of the text area is given below

                       

       

  <?php       $file="./file name which you want to edit in text area";      $READ = file_get_contents($file);      if(isset($_POST['txt'])){      $data=$_POST['txt'];      file_put_contents($file,$data);  }                         ?>         <form action="file name.php" method="POST">          <textarea name="txt"><?php echo $READ?> </textarea>          <input type="submit" value="submit">         </form>