How do you get the ports directory for a port via a script?

[Jim Graham]

After just being told (by port install) that I couldn't build ispell
because the GNU replacement for ispell (which doesn't work like
ispell...not exactly a direct replacement) aspell was installed, and,
for some unknown reason, they're incompatible, I did some RTFM and
ran the steps, and then reconfigured it for /usr/local and installed
it.

Now, I'm building a script to force this in case I run into this again
with another port.  The one thing I'm missing is how (via a script)
to get the directory (e.g., textproc for ispell) that the port is
in.  Is there a way (that I missed while doing my RTFM), via the
'port' command or some other ports-related command, to get the
directory name (from either root or some fixed path)?

It's not absolutely necessary, but it would help avoid a manual
step or two.

Thanks,
   --jim

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