From: Sarah Allen <sarah@...>
Date: 2009-05-11T21:38:05+09:00
Subject: Re: gsub pattern substitution and ${...}

Robert Klemme wrote:
> even with proper escaping this won't work as the string interpolation
> takes place *before* gsub is invoked and hence URI.escape will insert
> something but not the matched portion.  In your tests it has probably
> worked because $2 was properly set from the previous match.

really? so the ${...} gets evaluated before the param is passed to gsub, 
but the block is passed as code, so then it is evaluated after.

Using the previous attempt, with a fresh irb session, I can see the 
issue:
>> $1
=> nil
>> $2
=> nil
>> $3
=> nil
>> require 'URI'
=> true
>> s.gsub(/href=(['"])([^']*)/, "href=\\1#{URI.escape($2)}\\3")
NoMethodError: private method `gsub' called for nil:NilClass
  from 
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/uri/common.rb:289:in 
`escape'
  from (irb):8

>> $1
=> nil
>> $2
=> nil
>> $3
=> nil
>> s = "<a href='http://foo.com/one=>two'/>"
=> "<a href='http://foo.com/one=>two'/>"
>> require 'URI'
=> true
>> s.gsub(/href=(["'])([^'"]+)\1/) {
?> "href=#$1#{URI.escape($2)}#$1" }
=> "<a href='http://foo.com/one=%3Etwo'/>"

Nice!

> Note that my regexp has another weakness: the quote character not used
> to quote the URI should be allowed as part of the URI.  I did not want
> to complicate things too much but if you want to deal with this the
> regular expression must be made a bit more complex.

Wow, interesting. That would be incorrect HTML that the browser doesn't 
deal with well, so I'll not worry about it for this case, but I would be 
curious how it might be handled.

Thanks so much,
Sarah
-- 
Posted via http://www.ruby-forum.com/.