Asp Forum - Re: Inverting a regular expression?

Eric Mahurin

4/29/2005 12:21:00 PM

The problem with trying to do this is the length to consider a
mismatch. If you wanted the mismatch to be considered up to
the next match, you could do something like this:

/(?!#{re}).*?(?=#{re}|$)/

or

/((?!#{re}).)*/

I don't see any practical application for doing something like
this. Is this just a academic question?

--- Harry Ohlsen <Harry_Ohlsen@hyperion.com> wrote:
> A colleague of mine just asked me whether it was possible to
> invert an
> arbitrary regular expression. Ie, create a new regular
> expression that
> matches whatever the original *didn't*.
>
> It seems like quite a difficult problem to me, but maybe I'm
> just not
> looking at it the right way.
>
> Obviously simple cases are easy. Eg
>
> re = /[a-z]/
> inverse = /[^a-z]/
>
> However, I think it would be much harder for arbitrary cases.
> Eg, how
> would one automatically invert something like the following
>
> /<[^<>]*id="!?(region8-).*?>/
>
> Note that I'm not talking about finding lines that don't
> contain the
> pattern (a la "grep -v"); I'm talking about finding all the
> occurrences
> within a single line that don't match it.
>
> Inquisitively yours,
>
> Harry O.
>
>
>
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Re: Inverting a regular expression?

Eric Mahurin

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