Problems with regex - removing currency symbols - regex

Question

I'm working on a module which passes data to an online accounting site, and one thing I need to do in order for it to parse correctly is remove a currency symbol from the price of a product.
My regex pattern is as follows:
$regex = '/^\D?([\d\.,]*)\D?$/is';
I've tested this on the https://regex101.com/ website and it works correctly, but when I do the preg_replace as follows:
$price_no_curr = preg_replace($regex,"$1",$product_price);
where $product_price is, for example £123.45, $price_no_curr just returns as £123.45 as it was originally. So, when I cast it to a float it returns nothing.
Where am I going wrong with this regex?

Answer 1

Simplest solution, use /u modifier to make it support UTF-8 characters.
$regex = '/^[^\d\.,]?([\d\.,]*)[^\d\.,]?$/u';
$price_no_curr = preg_replace($regex,"$1",$product_price);

Answer 2

£ is outside of the ASCII range and needs several bytes to be encoded in UTF-8:
$a="£";
echo implode(' ', array_map(function ($i) {
return dechex(ord($i));
}, str_split($a)));
// c2 a3
By default the regex engine works byte by byte (one byte = one character). That is why \D can't match the two bytes of £.
To make it works with multibyte strings, you need to switch on the u modifier. This way the regex engine will read the string character by character whatever the number of bytes used to encode it.
Your pattern can be written like this:
$regex = '/^\D?([\d.,]*)\D?$/u';
but you can also do it without the u modifier if you change your quantifiers:
$regex = '/^\D*([\d.,]*)\D*$/';
A more simple and flexible way consists to remove all that is a currency and eventually white-spaces without taking account of their position:
$str = preg_replace('~[\p{Sc}\s]+~u', '', $str);
\p{Sc} is a unicode character class that contains all currency symbols.
or more radically:
$str = preg_replace('~[^\d.,]+~u', '', $str);
or without regex:
$str = '£1823.45';
$allowed_chars = [0,1,2,3,4,5,6,7,8,9,'.',','];
echo implode('', array_intersect(str_split($str), $allowed_chars));