How to match exact word anywhere in string with PHP regexp

Question

I want to find out if user has used the words admin or username anywhere in their possible username string.

So if user wants to use admin

Answer 1

Just look for words using word boundaries:

/\b(?:admin|username)\b/i

and if there is a match return error e.g.

if (preg_match('/\b(?:admin|username)\b/i', $input)) {
    die("Invalid Input");
}