Profanity filter to replace each letter of bad words with asterisks

Question

I had a working function that was getting an array of bad words then replacing the bad words with asterisks.

When I upgraded to PHP7, I had to use preg_replace_callback since the use of preg_replace with the e modifier was deprecated.

This is how I was using it:

function filterwords($text){
    $filterWords = array("dummy");
    $filterCount = sizeof($filterWords);

    for ($i = 0; $i < $filterCount; $i++) {
        $text = preg_replace('/\b' . $filterWords[$i] . '\b/ie', "str_repeat('*', strlen('$0'))", $text);
    }

    return $text;
}

Here is my new code:

echo filterwords("I am a dummy");

function filterwords($text) {
    $filterWords = array("dummy");
    $filterCount = sizeof($filterWords);

    for ($i = 0; $i < $filterCount; $i++) {
        $text = preg_replace_callback('/\b' . $filterWords[$i] . '\b/i',
            function ($matches) {
                return str_repeat('*', strlen('$0'));
            },
            $text
        );  
    }

   return $text;
}

This outputs I am a **, but my desired output is I am a ***** (with 5 asterisks instead of 2).

Answer 1

The backreferences used in preg_replace like $0 have no meaning in preg_replace_callback. You are passing the matches into the function as $matches but you are checking strlen('$0') which is just a 2 character string $0 so you get 2 *.

Use $matches and the number of the backreference. Just like you are used to, 0 is the full match:

return str_repeat('*', strlen($matches[0]));