title: Inserting something at a particular line in a text file using PHP
body: <p>I have a file called config.php, I want it to remain exactly as is, however on Line # 4 there is a line saying:</p>
  
  <pre><code>$config['url'] = '...could be anything here';
  </code></pre>
  
  <p>I'd like to only replace the contents of line # 4 with my own url provided for <code>$config['ur']</code>, is there a way to do this in PHP?</p>