\Q interpretation is not done by the regex engine, but by string interpolation. Except you add the \Q in a single quote string, so the interpolation does not happen, and the \Q and \E are still there for the regex engine to read, though they don't have meaning in a regex. If you want to pre-process a string so that its special chars are excaped, you can use quotemeta, which is what \Q does implicitly. my $pref = "^".quotemeta($1);