How to handle config files

[Martin Kropfinger]

Hi there!

The porters handbook describes a way to handle config files:

http://www.freebsd.org/doc/en/books/porters-handbook/plist-config.html

It is recommended to do it this way for keeping changed files after
deinstallation on the system. But the example is not really clear to me.

What does this line do:
@exec if [ ! -f %D/etc/orbit.conf ] ; then cp -p %D/%F %B/orbit.conf; fi

Nothing is said about those variables... %D (which seems to be
%%PREFIX%%) and %F or %B.

Can anyone give me some help?

Thanx a lot!