Keep case with regex find and replace

Question

My question is pretty straightforward, using only a regular expression find and replace, is it possible to keep the case of the original words.

So if I have the string: "Pretty pretty is so pretty" How can I turn it into: "Lovely lovely is so lovely"

All I have so far is find /(P|p)retty/g and replace with $1ovely but I dont know how to replace caplital P with L and lowercase p with l.

I am not interested in accomplishing this in any particular language, I want to know if it is possible to do with pure regex.

Answer 1

It can't be possible to replace captured uppercase or lowercase letter with the letter according to the type of letter captured through regex alone. But it can be possible through language built-in functions + regex.

In php, i would do like.

$str = "Pretty pretty is so pretty";
echo preg_replace_callback('~([pP])retty~', function ($m)
        { 
            if($m[1] == "P") {
            return "Lovely"; }
            else { return "lovely"; }
        }, $str);

Output:

Lovely lovely is so lovely