Replace shortcode with HTML multiple times on a page - php

Question

My client wants the ability to put PayPal add-to-cart buttons anywhere on a page, with potentially multiple buttons on a single page. He will use a shortcode like [price MONKEY] to have a PaylPal button replace that text, with the price and description for "monkey".
So every time we find a [price] shortcode on the page, I need to query the database to get value, insert then into the following PayPal button code, and display the button at that place on the page. Then move to the next replacement, if any.
Here's the PayPal button code:
<form target="paypal" action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" value="_cart" name="cmd" />
<input type="hidden" value="me#mydomain.com" name="business" />
<input type="hidden" value="1" name="add" />
<input type="hidden" value="MONKEY" name="item_name" />
<input type="hidden" value="" name="item_number" />
<input type="hidden" value="17.00" name="amount" />
<input type="hidden" value="2" name="no_shipping" />
<input type="hidden" value="USD" name="currency_code" />
<input border="0" type="image" name="submit" src="https://www.paypal.com/en_US/i/btn/x-click-but22.gif" alt="Make payments with PayPal - it's fast, free and secure!" />
</form>
I've been trying to do this with a preg_replace_callback() function, but having problems inserting all the HTML for the button, and then with looking for more shortcode instances on the page and replacing them.
Appreciate any help on this! It's so simple in Wordpress where all this code is already written (but where?) -- this is an application that I created from scratch and now needs some enhancement. Thanks!
Here's my regex:
$pattern = '/\[price (.*?)\]/';

Answer 1

You can just use a basic preg_replace to accomplish this task using your pattern. something like so:
<?php
function myexamplefunction($html){
$pattern = '/\[price (.*?)\]/';
$replace = '<form target="paypal" action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" value="_cart" name="cmd" />
<input type="hidden" value="me#mydomain.com" name="business" />
<input type="hidden" value="1" name="add" />
<input type="hidden" value="$1" name="item_name" />
<input type="hidden" value="" name="item_number" />
<input type="hidden" value="17.00" name="amount" />
<input type="hidden" value="2" name="no_shipping" />
<input type="hidden" value="USD" name="currency_code" />
<input border="0" type="image" name="submit" src="https://www.paypal.com/en_US/i/btn/x-click-but22.gif" alt="Make payments with PayPal - it\'s fast, free and secure!" />
</form>';
return preg_replace($pattern,$replace,$html);
}