Escaping regular expressions in PHP

Question

I am trying to escape a PCRE in PHP for use in a script. For some reason I can't get it to function when it has been escaped, I've only managed to get it working when the REGEX is given as a form input.

The Regex I'm using is:

$pattern = '£((http|ftp|https):\/\/)?([\w\-_]+(?:(?:\.[\w\-_]+)+))([\w\-\.,@?^=%&:/~\+#]*[\w\-\@?^=%&/~\+#])?£';

So far I have tried:

preg_quote(): converts the Regex to the following and throws an error: £((http\\|ftp\\|https):\\/\\/)\\?([\\w\\-_]+(\\?:(\\?:\\.[\\w\\-_]+)+))([\\w\\-\\.,@\\?\\^\\=%&:/~\\+#]*[\\w\\-\\@\\?\\^\\=%&/~\\+#])\\?£

htmlentities(): gives error: Warning: preg_match(): Unknown modifier 'a'

addslashes(): same as above

mixture of the 3: same as above

Does anyone have an idea of what I'm doing wrong?

Answer 1

The pound symbol was the issue here, replacing it to an exclamation mark solved the problem. Working expression:

$pattern = '!((http|ftp|https):\/\/)?([\w\-_]+(?:(?:\.[\w\-_]+)+))([\w\-\.,@?^=%&:/~\+#]*[\w\-\@?^=%&/~\+#])?!';

For some reason this is working fine with no escape functions.