Diffing compressed tarballs

[Ryan Schmidt]

Part of my workflow when updating ports used to be as follows:

install current version of port
modify port in some way and increase revision
install new version of port
cd to /opt/local/var/macports/software/portname
run "diff -ru oldversion newversion" and ensure the change I wanted made has been made

Now that MacPorts installs compressed tarballs of ports in /opt/local/var/macports/software instead of the actual files, this doesn't work.

So I think what I want is a utility I could run like "somediff oldversion.tbz2 newversion.tbz2", which would decompress both archives to a temporary location, diff them with "diff -ru", and then clean up the temporary files. Anyone know of a utility that already does that? I could write it but if it already exists I'd rather use that.

Or any other ideas about how to do this task now?