is there a way to eject all external hard drives from the command line? (OS X)

Question

Is there a way to eject all the mounted hard drive volumes on an OS X computer from the command line? Applescript is OK if I can wrap that in a shell script.

Answer 1

I do it like this:

df | grep Volumes | awk '{ print $1 }' | while read disk; do diskutil unmount "$disk"; done