[Evolution] shell command mail filter syntax

[Monte Ohrt <monte ispi net>]

Hi,

What is the proper syntax for a shell command filter?

I tried:
/usr/bin/foo

and guessed, maybe netscape style?
/usr/bin/foo < %s

Neither seem to get the message content to the shell command stdin. I
couldn't find any instructions or examples in the manual either.

Thanks
Monte