From: Craig Jolicoeur <cpjolicoeur@...>
Date: 2009-04-29T11:03:49+09:00
Subject: Issue with regexp pattern matcher withing String#gsub

I'm having a strange issue I can't wrap my head around.  I've posted the
full details as a gist here: http://gist.github.com/103523 but I will
also paste the same contents here for everyones benefit.

## The pattern matcher in both the following will match either the
single or double quote
## at the start of the src= attribute (this is what is available in $1

## this regexp replacement works fine and will convert
## src="/foo/bar.png"
## to
## src="/RAILS_ROOT/public/foo/bar.png"

html_string.gsub!( /src=(["'])[\.\/]/ ) { |m| 'src=' + $1 +
"#{RAILS_ROOT}/public/" }

## this regexp errors with the following error message
## TypeError: can't convert nil into String
##  from (irb):84:in `+'
##  from (irb):84
##  from (irb):84:in `gsub'
##  from (irb):84

html_string.gsub!( /src=(["'])\S+\?\d*\1/ ) { |s| s.split('?').first +
$1 }

## the question is why can I do string concat with + $1 in the first
regexp and
## why am I unable to do it in the second regexp where doing str + $1
throws the error??
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