do.c was my first attempt based on the unix 'script' command.
this is more powerful but it separates the I/O to and from the app into multiple forks
which is not what we want

fifo.c was a rewrite once I realised a simpler way of doing it with a combination of popen and a named pipe.
however this way requires line at a time IO and no prompts or echoing
Note I had to use popen rather than system("... &") because I think the calls to system have no job control


the final product may be a hybrid of these two mechanisms - not entirely unlike the 'expect' program
(in fact invoking expect from within C might be an easier solution)