[PROJ] cs2cs in a pipe

[Schmitz, Uwe]

Roger,

You didn't post sample code, so I only can guess some things.
In addition, you haven't written what you have tried so far,
so maybe the following is not unknown to you.

First, I suppose that you set up a pipe to cs2cs like:

set fid [open "|cs2cs" r+]

Second, to send line by line to the pipe you should do

chan configure $fid –buffering line

Finally, you have to make sure that the output is not buffered.
I assume that cs2cs buffers its output. That seems to be your problem,
I guess. You can verify this by sending say 10000 or more transformation 
lines to the pipe. At some point cs2cs may flush its output and you will see
it by reading the pipe.
IMHO, there is no way to prevent cs2cs from buffering.
But... under Linux you can try unbuffer:
https://linux.die.net/man/1/unbuffer

E.g.:
set fid [open "|unbuffer cs2cs" r+]

If you really consider using the bare C-Api, I recommend 
using the great Ffidl package:

https://wiki.tcl-lang.org/page/Ffidl

Hope this helps a bit.
-- 
Uwe Schmitz