Checking whether a package is installed

[Andreas Gustafsson <gson%gson.org@localhost>]

Hi all,

Suppose my current directory is the pkgsrc directory of some package
(pkgsrc/category/package).  Is there a shell command I can run that
will return an exit status indicating whether or not the package in
case is already installed (regardless of version), without building 
or reinstalling it?
-- 
Andreas Gustafsson, gson%gson.org@localhost