How to know Which character was replaced while using regex

Question

String string = "Tĥïŝ ĩš â fůňķŷ Šťŕĭńġs not cool \"oops" ;    
    string = string.replaceAll("[^a-zA-Z0-9 ]+", ... );

The problem is that I want to append to non alphanumeric non whitespace characters an escape character. ie

" -> \" 
' -> \'.

So what exactly should be a second argument in the replaceAll method? Or is there any other cool way (I don't want to hardcode)

Answer 1

If this is Java (I added the relevant tag), then you could do

String resultString = subjectString.replaceAll("[\\W\\S]", "\\\\$0");

which will replace any non-alnum/non-space character with its escaped counterpart.

Note that the regex is making no attempt to detect whether a character is already escaped. You should also be aware that \W in Java is not locale-aware, so it will match Unicode letters, too.