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Re: [Gnu-arch-users] Preventing matches in regular expressions
From: |
Tom Lord |
Subject: |
Re: [Gnu-arch-users] Preventing matches in regular expressions |
Date: |
Wed, 11 Aug 2004 00:22:52 -0700 (PDT) |
> From: Jan Hudec <address@hidden>
> On Mon, Aug 09, 2004 at 15:29:53 -0400, Aaron Bentley wrote:
[regexp foo]
> A general solution would be to use a negative lookahead
> assertion. But I don't know whether they are implemented in
> hackerlab. Hackerlab has something called a "cut" operator. I
> can't find it's documentation so I am not sure whether it can be
> used, but I think it can.
You're right that `cut' can be used.
"Negative lookahead operators" (or more generally, just boolean logic
over regexps) can, in theory, be implemented -- but `not' and `and'
are fairly expensive.
`cut' plays a trick to optimize just a few special cases of what you
could do with "negative lookahead operators", one of which is the case
abentley wants to have (essentially the same case optimized by
`lex(1)').
-t
Re: [Gnu-arch-users] Preventing matches in regular expressions, Tom Lord, 2004/08/11