In that case (and assuming you have no control over the format) you have a problem of a whole different order of complexity. What you need to achieve in that case is to map the input syntax to Perl's regex syntax and that is likely not a trivial task.

At the very least you will require a formal description of the input syntax and, from that, you will have to work out how to achieve the same results using Perl's regex facilities. Watch out along the way for security issues. For example if the user can introduce (?{die}) (for example) into the search string and that gets passed through to the regex, unfortunate things may happen :).