Regex/Php: Cannot match question mark in live site - php

Question

I would like to remove the $_GET parameter of the first "page" item on a website.
The following works perfectly in a test script on my local server:
$urls = array(
'http://www.foo.com/bar.html?p=1', //should match
'http://www.foo.com/bar.html?p=23',
'http://www.foo.com/bar.html?p=120',
'http://www.foo.com/bar.html?baz=123&p=1' //should match
);
foreach ($urls as $url) {
echo $url . '<br>';
echo preg_replace('/([\?&]p=1)(?!\d)/', '', $url) . '<p>';
}
This produces:
http://www.foo.com/bar.html?p=1
http://www.foo.com/bar.html
http://www.foo.com/bar.html?p=23
http://www.foo.com/bar.html?p=23
http://www.foo.com/bar.html?p=120
http://www.foo.com/bar.html?p=120
http://www.foo.com/bar.html?baz=123&p=1
http://www.foo.com/bar.html?baz=123
However on the live site, it never matches.
To make matters worse,
str_replace('?p=1','',$url);
will not work as well. What am I missing? I can match a single question mark, but as soon as something follows it, I'm out of luck. This is the case for both str_replace and preg_replace. I feel like I'm missing something obvious, but I cannot figure it out. Thank you for your help.
Solution:
In my specific case, it turned out that the underlying Magento shop system was already giving out html_encoded characters. This, plus the fact the first parameter is always a session ID which is later removed from the URL string, made my task as easy as
$url = str_replace('&p=1', '', $url);

Answer 1

try \\\? instead of \? ; if that doesn't work, you might run a regex engine version which doesnt support negative lookahead.
In that case you could reform your preg_replace to
preg_replace('/([\?&]p=1)([^\d])/', '$2', $url) . '<p>';
which would consume the non-digit, but put it back in again. There might be edge cases where this differs from your regex, but I don't think you'd be able to encounter those with urls (and I can't think of any from the top of my head)
of course, there are other non-regex solutions to this, but as regex is a very powerful tool, it's always good to learn something about it ;)