Fellow Monks,
it has already been hard enough to find a good title for this question and even harder for me to find the solution to this problem (which -I am sure- must be very plain and simple, because I am looking for it so long(*))

I am building a regexp dynamically, say

$re = qr(/($<!$a)$b/);
[download]

(using a look behind just to make it a little more spicy) where $a and $b will always contain exactly one char, but that char might be special in regexps. For example $a can be "?" or "-" depending on the current situation.

The question is: is there any way (a module at CPAN which I have overlooked or an operator I didn't fully understand or ...) to dynamically escape those w/o me going through a list of special chars and checking them?

Footnotes:
(*) A simple rule of programming: the longer you search (for an error, for a solution, for the correct way, ...) the plainer is the answer (read as: the more stupid was the error, the simpler is the solution, the cleaner is the correct way ...) ;-)