Question

So basicly, when a form is submitted on a comment and in the comment it contains @username or @ then someone’s username, I want to do something, e.g. send a notification to the username.

So, if it contains an @ and a word (with letters or numbers) afterwards, I want to get the value and do something with it.

e.g.

if (contains an @ symbol, get the value of it)  {
// do something
}

Answer 1

$str = 'hello @user';
preg_match('/@([a-z0-9]+)/i', $str, $matches);

// $matches[0] = '@user';
// $matches[1] = 'user';