I have the following text in a file:

1 a1.html
2 b.doc
3 c.xml
4 d.tiff
5 e.jpeg
6 f.html
....

I need a regexp to match lines except those that end with ending in
".html" - iow - I want lines 2-5 above.  I believe this may require a
negative lookbehind match.  I tried the following but Ruby (1.8) gives
an undefined sequence error :

$(?<!\.html)   # <---- this seems to work with other engines

Before you jump re Ruby the version I also tested this here -
http://www.rubyxp.com/ and get invalid expression (fyi this tests with
Ruby 1.9). Any ideas/alternatives?

TIA,
BC