I think the subject line is surprisingly self explanatory but here is
the longer version:

I call an application via a pipe command and process its output via
fconfig. The handler is a rather big, old, inherited chunk of code. It
works fine, though.

Now I have written a new proc that does some parts of that external
command and I need to interface the new proc with the old handler. But
I would rather avoid getting into the inner-workings of the handler
code. I think I can, if I figure out a way to do an fconfig on the proc
or its output. Then I can simply forward it onto the old handler and
all will be fine.

I am a little out of shape in terms of Tcl at the moment so I would
appreciate any tips.

PS. As I wrote this, it occurred to me that I could call the new proc,
save its output to a file, open that file, somehow pipe it and continue
from there. I think this would work but I hope there is a way to avoid
this intermediate file solution.