From: Heesob Park <phasis@...>
Date: 2009-04-29T12:24:50+09:00
Subject: Re: Issue with regexp pattern matcher withing String#gsub

2009/4/29 Craig Jolicoeur <cpjolicoeur@gmail.com>:
> 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??
The side effect of String#split is changing the value of $1.

You can work acound like this:
html_string.gsub!( /src=(["'])\S+\?\d*\1/ ) {|s| t=$1;s.split('?').first + t }

Regards,

Park Heesob