Question

Hello How can I can I allow only digit [^0-9] and a minus sign in front the digit. Example :
Valid = -1…-9, Invalid = –1-…

Answer 1

Just remove every invalid character and check if the remaining has a valid format:

$cleaned = preg_replace('/[^-0-9]+/', '', $str);
if (preg_match('/^-?[0-9]+$/', $cleaned)) {
    // now valid
}

Ok, here’s another suggestion:

preg_replace('/.*?(-?\d+).*/', '$1', $str)