Maybe Escape in Dynamic RegExps

[stefan k]

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/);

(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 ...) ;-)

[saintmike]

Just escape them via the quotemeta() function or, better yet, using \Q and \E:

    $re = qr(/($<!\Q$a\E)\Q$b\E/);

[gellyfish]

The simplest way would be to use the \Q and \E in the expression:

     $re= qr(/($<!\Q$a\E)\Q$b/);

and it will do the right thing.

/J\

[Zaxo]

This does what you want. my $re = qr/(?<!\Q$c\E)\Q$d\E/; The \Q . . \E pair is like quotemeta. I've changed the names to protect sort. Extra ( . . ) delimiter pair is cut.

[stefan k]

Thanks to all that replied. It works just fine :-) I knew that it had to be that simple and I do feel kinda stupid right now.

[halley]

The \Q and \E is the correct answer; the quotemeta() function is the equivalent function.

However, for perl5 anyway, a useful rule of thumb is that alphanumeric characters need escapes to be special, and everything else need escapes to be normal. There are a lot of non-alphanumeric characters that the escaping would be redundant but not harmful (such as \=).