From: Edwin Fine <efine145-nospam01@...>
Date: 2007-06-03T14:02:16+09:00
Subject: Re: No way of looking for a regrexp match starting from a pa

Kenneth McDonald wrote:
> I'm probably just missing something obvious, but I haven't found a way
> to match a regular expression against only part of a string, in
> particular only past a certain point of a string, as a way of finding
> successive matches. Of course, one could do a match against a string,
> take the substring past that match and do a match against the substring,
> and so on, to find all of the matches for the string, but that could be
> very expensive for very large strings.
> 
> I'm aware of the String.scan method, but that doesn't work for me
> because it doesn't return MatchData instances.
> 
> What I want is just something like regexp.match(string, n), where the
> regexp starts looking for a match at or after position n in the string.
> 
> 
> Thanks,
> Ken

How about this?

def match(s, re, n)
  /(?:.{#{n}})(#{re})/.match(s)
end

irb(main):043:0> p s
"abdefgh abdefgh abdefgh abdefgh abdefgh abdefgh abdefgh abdefgh abdefgh 
abdefgh "
irb(main):044:0> p match(s, /abd/, 10).begin(1)
16
irb(main):045:0> p match(s, /abd/, 20).begin(1)
24

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