PHP - replace http with https in URL

Question

I am trying to figure out how to add s after HTTP once a user checks a box in the html form.

I have in my PHP,

$url = 'http://google.com';  if(!isset($_POST['https'])) {    //something here } 

So basically, when the user checks a box with the name="https" i want to add s to $url's http making it https://google.com.

I have little knowledge on PHP and if someone can explain to me how to go about doing this, this would be really helpful! thanks.

Answer 1

$url = preg_replace("/^http:/i", "https:", $url);