preg_replace allow space

[admin]

$pattern = "/[^\d\w\s]/";
$replacement = "*";
$subject = "1 Main str, #5";

echo preg_replace($pattern, $replacement, $subject);

The ^ symbol negate a class. Right after this symbol we put the classes:

\d - digits
\w - words
\s - space

So, it reads as: "replace with * all the symbols from $subject, which are not digits, words and spaces".