Quoting from macports-users 20 Feb 2007:
That said, it still remains second to the first idea of mel who started this thread, to implement a dry run feature. Maybe, dry run would just be half of the implementation of prefetch.
Due to the reason above, I'd prefer the the dry run feature to be implemented first, because I think in the long run it will help to improve port's variants feature.
I have submitted a patch (dry.3.patch attached to http://trac.macports.org/projects/macports/ticket/11892) against the current svn version (r24893) which adds a -y option for dry run. (I chose -y since it's the only letter left from "dry" which was not already an option.) It turns out to be a pretty simple patch, only touching one tcl source file except for documentation and parsing the switch. I now use it all the time for checking out recursive dependencies and the behavior of different variants. Perhaps it will catch the eye of someone who can incorporate it into the development version of MacPorts. Hope this is helpful, Glen Whitney