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Re: [Gnu-arch-users] Preventing matches in regular expressions

From: Aaron Bentley
Subject: Re: [Gnu-arch-users] Preventing matches in regular expressions
Date: Tue, 10 Aug 2004 08:47:04 -0400
User-agent: Mozilla Thunderbird 0.5 (X11/20040309)

Jan Hudec wrote:
Does anyone know a better general solution?

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.

The cut operator is documented here:

And here:

The state label of the final DFA state for most regexps is 1 . If a pattern contains the cut operator [[:cut <n>:]] its DFAs will contain a final state with label n at that point in the regexp. This is useful for detecting which of several possible alternatives actually occured in a match, as in this example:

     pattern: if[[:cut 1:]]\\|while[[:cut 2:]]

       pmatch[0].final_tag is 1 after matching "if"
       pmatch[0].final_tag is 2 after matching "while"

We were going to use it to optimize inventory operations by combining all the regexes into one. But it turned out that libhackerlab needed to be fixed, because the cut operator was disabling important regex optimizations.


Aaron Bentley
Director of Technology
Panometrics, Inc.

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