The overall challenge is _my_ code takes sshutle as input parameter, so I can't have any guesses on what the external program could be ( any ), I don't try to get any workarounds ( like catch/ignore signals ) either.

That's just not good. You might not have the source code of the program, but you do need to know how it behaves regarding IPC. A good example (if memory serves me well) in the bc program from UNIX. I think Perl documentation mentions that this kind of program is not reliable at all for IPC.

Worst, some part of the program might be changed in the next release, and due buffering/signals handling it may broke down your IPC handling.

But wait, you do have access to sshutle code... are you sure CPAN doesn't have something that implements the same you're looking for?

If not, maybe you would be willing to implement a version in Perl as well. Or even fork the project and make the program behave well through IPC... or even use sockets instead!