Regex for 2 letters followed by 4 digits

Question

The string should begin with \"S2\" followed by any 4 digits.

A matching string is \"S20165\".

I\'m trying with the following code, but it always echos OK ev

Answer 1

$string='S20104';
if(preg_match('/^S2[0-9]{4}$/', $string)){
    echo 'OK';
}
else{
    echo 'NOT OK';
}