open2() returns the process ID of the child process. It doesn't return on
failure: it just raises an exception matching
Additionally, this is very dangerous as you may block forever. It assumes it's going to talk to something like bc, both writing to it and reading from it. This is presumably safe because you ``know'' that commands like bc will read a line at a time and output a line at a time. Programs like sort that read their entire input stream first, however, are quite apt to cause deadlock.
The big problem with this approach is that if you don't have control
over source code being run in the the child process, you can't control what it does
with pipe buffering. Thus you can't just open a pipe to
cat -v and continually
read and write a line from it.