From: Carlos <angus@...>
Date: 2006-12-21T08:02:53+09:00
Subject: Re: Regex question: this should be easy but doesn't work as I expect.

[Sam Kong <sam.s.kong@gmail.com>, 2006-12-20 20.10 CET]
> What I want is
> 
> "one two three four five" #=> [["one", "three", "five']]
> "one two four five" #=> [["one", nil, "five']]
> 
> In short, in the string, "three" might or might not exist.
> What regex can match for both?

Hi. The problem is that you can very easily NOT match "three" even if it's
there. I mean, if you have
   /1.*3?.*5/ =~ '12345'

the engine can succeed matching the 1 at the beginning, the 5 at the end,
and trying to match the 3 where the 4 is... and failing, but since it's
optional, the overall match succeeds.

I think you should try it in two steps: first, try to match with the 3; if
that fails, without the "3". Something like:

 /(?:(1).*(3)|(1)).*(5)/

(The '1' will come either on the first or third array position, you'll have
to take care of that.)

Maybe there is a simpler solution, but it doesn't come to my mind.

Good luck.
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