Because there are characters in $b that are interpreted differently when used in a regex. The ".", "(", and ")" are such characters. You'd have to do $a =~ /\Q$b\E/ to get it work, or else use quotemeta(). If you want to see if they're equal, though, use 'eq'. If you want to see if one contains the other, use index(). If you want to match a pattern, THEN use a regex.

Can I ask why you're quoting $a and $b?

Jeff japhy Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and perl hacker
How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart

In reply to Re: Matching quoted variables. Cant make it work.. by japhy
in thread Matching quoted variables. Cant make it work.. by johntweed

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