Anyone know of any generic implementation of a pipeline in ruby?  That
is, one which takes a bunch of GoF Command objects, and strings them
together in the classical pipeline configuration.

Any advice on that?

I have a process with a lot of sequential processing, and think that a
pipeline of Command objects (not just Proc's) might be the way to do
it.

The downsides of pipelines:
1) You can't do selections (if) or sequences (loops).  If you can
handle this, though, this becomes a virtue, as it keeps everything
crystal clear and simple.  Witness the ever useful Unix command line
pipelines.

2) They don't encapsulate very well, as each stage totally overwrites
the previous ones.  I'm not sure if I should just accept this, or try
to use some modification (append only pipeline, etc.).

Any experience or ideas on this appreciated.