[Exim] Troubleshooting the pipe transport

Hello.

I'm pretty new to exim, but I just wrote a transport and director to work with something
I'm putting together in perl. I borrowed a lot from what someone had written
about smartlist

The problem I am having is that the command line argument that I give in
command =
is not being correctly passed as far as I can tell.

In exim.conf:

list_director:
driver = smartuser
prefix = marketing-
prefix_optional
local_parts = !.bin:!.etc
require_files=/var/list/marketing/${local_part}/listfile
transport = list_transport

list_transport:
  driver = pipe
  command = /var/list/marketing/foo.pl "${local_part_suffix}"
  current_directory = /var/list     
  user = list
  group = list
  return_fail_output

And:
/var/list/marketing/foo.pl just emails me with $ARGV[0] , which is perl's
name for the first command line argument. foo.pl works fine from the command line.

I suspect that where I've gone wrong is with suffixes and prefixes.
What I want is for the director to know that marketing-foo and foo
are the same, and, in this example, treat "foo" as the local part to care about.

Can someone give me some clue?

-dk