PHP error when input contains "/"

Question

When the input string contains a "/" symbol, I'm getting a PHP error:

Warning: preg_match() [function.preg-match]: Unknown modifier

How can I resolve it?

$token = '/<'.$tag.'[^>]*>(.*\b'.$keyword.'\b.*)<\/'.$tag.'>/siU';
if(preg_match($token, &$content, $matches))
{
    $match = 1;
}
return $match;

Answer 1

You should use preg_quote() to escape tag and keyword, like this:

$token = '/<' . preg_quote($tag, '/') . '[^>]*>(.*\b' . preg_quote($keyword, '/')
         . '\b.*)<\/' . preg_quote($tag, '/') . '>/siU';

Answer 2

preg_quote function should help you with this.