Filtering by specific cookie

[Mikkel =?unknown-8bit?B?SMO4Z2g=?=]

Hi there,

I'm trying to throw together a workaround for a tricky caching issue
with the CMS/CMF I'm using, Drupal, and for that purpose, I need to take
decisions about whether to serve cached content on the basis of the
client not sending a particular cookie.

In http://varnish.projects.linpro.no/wiki/VCLExampleRemovingSomeCookies,
the example shows removing cookies with regular expressions via the
regsub function which I can't seem to find documentation on.
Is there a similar function just for checking whether there's a match,
or even better, a way to check this that doesn't involve regular
expressions?

Kind regards,

      Mikkel Høgh