From: Phlip <phlip2005@...>
Date: 2007-08-17T23:29:58+09:00
Subject: Regexp riddle; escaping escapes

Rubies:

Someone didn't escape their & in their HTML correctly. Let's fix it.

This regexp correctly does not escape &dude, because we only want to escape
raw & markers:

  p "yo &dude".gsub(/&([^a-z])/i, '&amp;\1')

That passed "yo &dude" thru unchanged. (I am aware "dude" has no ; on the
end; we are leaving that optional, for whatever reason...)

Now escape & followed by a non-alphabetic character:

  p "yo & dude".gsub(/&([^a-z])/i, '&amp;\1')

That correctly provides: "yo &amp; dude"

Now how to escape "yo && dude"? Note that the ([^a-z]) consumes the second
&, leading to this incorrect output:

  "yo &amp;& dude"

The only workaround I can think of is to run the Regexp twice:

  x = "yo && dude"
  2.times{ x.gsub!(/&([^a-z])/i, '&amp;\1') }
  p x

Can someone help my feeb Regexp skills and get a "yo &amp;&amp; dude" in one
line?

-- 
 Phlip
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