Both JavaFan and suhailck solutions work correctly.

The quotemata or \Q is what I need in my code. The $in / $out were just to show a sample of the problem. Sorry, I didn't noticed the reversing of pattern at the time, since I got the same error message.

The actual code has only 1 variable, but without the backslash of '+' my solution didn't work in all case.

Thank you.