How to find out if a package is installed?

[Steve Greenland <stevegr@Starbase.NeoSoft.COM>]

I'm trying to work out how to upgrade an existing installation
of cern-httpd to use the new names. Before I blow away the existing
/usr/sbin/httpd, I need to determine if it's cern's, apache's, or
(possibly), somebody else's. Since cern and apache conflict, it
should be one or the other's. What's the best way to do this?

1) apache has /etc/httpd as a directory, while with cern (rev 4),
   it's a file. This seems to work, but doesn't solve the
   general case.

2) make dpkg tell me. I can grep the output from dpkg --status,
   but that seems cludgy.

3) Look for /var/lib/dpkg/info/{pkg}.list. I have no idea if
   this is reliable, but I really hate to muck around in other
   packages property.

Better ideas?

Thanks,
Steve Greenland

-- 
The Mole - I think, therefore I scream 

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