Finds the difference between a list of ports that you want to
have on your system and the list of ports currently installed.

When called as portdiff, it produces diff(1)-like output, when
called as portorphans it prints a list of ports that are installed
but are not in your list of wanted ports.

To create your list of wanted ports, do something like:

$ portorphans | perl -pe 's/-\d.*$//' > ~/.portdiffrc

then edit the .portdiffrc file to remove the ports you don't want.

My usual port maintenance routine goes something like:

1) portupgrade -a
2) portorphans
   a) If portorphans returns nothing, I'm done
   b) If portorphans' output contains a port I wish to keep,
      I add that to ~/.portdiffrc and goto 2.
   c) If portorphans returns some output, I run
      'portorphans | xargs pkg_delete' and goto 2.

This keeps the list of ports installed on my machine to a minimum.