From: Peter Hickman <peterhickman386@...>
Date: 2012-04-06T00:53:08+09:00
Subject: Re: Want to get exact match from sentence

The you could use a.index(b) to find at what position b starts as a
substring of a and use that to look backwards two characters and check
them if they are acceptable.

def is_match(a, b)
  pos = a.index(b)
  if pos == nil
    return false
  elsif pos < 2
    # we matched within the first 2 characters of the string
    # there is not enough room for special charaters
    return true
  elsif a[pos-2,2] == '@@'
    return false
  else
    return true
  end
end

Warning! Untested code, just written in the email.