From: Andrew Johnson <ajohnson@...>
Date: 2004-09-12T13:54:59+09:00
Subject: Re: look-behind in oniguruma

On 12 Sep 2004 03:44:24 GMT, Phil Tomson <ptkwt@aracnet.com> wrote:
> Apparently oniguruma supports look-behind.  Is there any documentation on how 
> to use this feature?

Essentially, they are the same as look-aheads ... zero-width assertions,
except that the look-behind expression must be a fixed width pattern (no
indeterminate quantifiers), and no captures are allowed in a negative
look-behind 

> for example, if I had the string "~ABC~DE" and I want to return a list of 
> letters in the string which are preceeded by '~' ( ['A','D'] in this case) how 
> might I use the look-behind feature in oniguruma to achieve this? or, how 
> would I get a list of letters in the string which are not preceeded by '~' 
> (['B','C', 'E'] in this example.


  str = "~ABC~DE"
  p str.scan(/(?<=~)[A-Z]/)
  p str.scan(/(?<!~)[A-Z]/)

gives:

  ["A", "D"]
  ["B", "C", "E"]

regards,
andrew

-- 
Andrew L. Johnson   http://www.siaris.net/
      There are two types of programming languages; the ones that people bitch
      about and the ones that no one uses.
          -- Bjarne Stroustrup