Re: Negative lookbehind assertions in regexs

On Mon, Aug 29, 2005 at 14:11:37 +0100, Julian Scarfe <julian@avbrief.com> wrote:
> I'd like a regex that matches 'CD' but not 'ABCD' in any part of the regex.
> 
> Is there a workaround that allows me to do this as a single regex?
> 
> I know I could and together a ~ and !~ like this
> 
> # select ('CD' ~ 'CD') and ('CD' !~ 'ABCD');
> ?column?
> ----------
> t
> (1 row)
> 
> # select ('ABCD' ~ 'CD') and ('ABCD' !~ 'ABCD');
> ?column?
> ----------
> f
> (1 row)

The above code won't work because there could be both CD and ABCD in the
string. What you want to do is match all of the valid possibilities.
Something like:
(^.?CD)|([^B]CD)|([^A]BCD)