Question

I’m trying to replace:
*facebook.com/
with http://graph.facebook.com/

I need to be able to group anything before the facebook.com part into an optional group.

I can’t just replace facebook.com with graph.facebook.com because the incoming URL may contain https.

Here’s what I have but misses anything that doesn’t have http[s]://.

<?php
$fb_url = preg_replace('/http[s]*:\/\/[www.]*facebook.com\//', 'http://graph.facebook.com/', 'facebook.com/some/segments');
echo $fb_url;
?>

Answer 1

Addressing your question specifically:
You can make any single character (or a group of characters) optional by adding a ? after it in your regex.

A couple of tips from looking at your code:

• If you are matching strings containing / characters, simplify your life by using a different delimiter (for example #). You aren’t required to use a forward slash.
• You should escape the . dot metacharacter because it matches ANY single character, so your expression www. could conceivably match www9 or anything else along those lines
• Also, the brackets [...] are for matching a range of characters. If you want to match specifically the text www. you should use a non-captured group like (?:www\.) and make it optional by adding the ? after it like (?:www\.)?

---

So, those tips in mind, try …

<?php

$p = '#(?:https?://(?:www\.)?)?facebook\.com/#';
$r = 'http://graph.facebook.com/';
$subject = 'facebook.com/some/segments';

$fb_url = preg_replace($p, $r, $subject);
echo $fb_url; // outputs: http://graph.facebook.com/some/segments

?>