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

[Aaron Bentley]

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:
tla-1.2/src/docs-hackerlab/html/introduction-to-regexps.html#The_cut_Operator

And here:
tla-1.2/src/docs-hackerlab/html/posix-regexps.html#Posix_Regexp_Functions

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

--
Aaron Bentley
Director of Technology
Panometrics, Inc.