[Plugin: HookPress] Regex the post content?

First off, what an amazing plugin. WordPress and it’s community of developers never fail to amaze me with the things it can do.

I’m trying to run some Regex on my post’s content. The goal is to strip out all of the plain text, and only show any hyperlinks contained within the post. So I was looking for an answer on two things:

Number one, when you a run a webhook on postcontent, your webhook “sees” that postcontent as raw HTML, correct?

And secondly, here’s the code for my webhook, currently it blanks out everything in the post. I’m looking to see if I’m even remotely close to having the correct code. I have confirmed that the Regex works, as an expression, it’s a matter of getting it to work in the webhook’s PHP!

<?php
$text_to_strip = 'content';
$pattern = '/\S+:\/\/\S+/';
preg_match_all($pattern,$text_to_strip,$matches);
$stripped_text = implode("\n", $matches[0]);
print($stripped_text);
?>

Here is the actual regular expression:
Search pattern: (.|\s)*?(\S+:\/\/\S+)
Replace with: \2\n

Thank you!