From: Sean O'Halpin <sean.ohalpin@...>
Date: 2012-06-30T07:03:17+09:00
Subject: Re: Asynchronous IO

Hi,

> Currently I'm using OI.popen to open a new pipe to another process, and
> I feed commands to it; but sometimes the other process could run for
> multiple minutes before closing the pipe; and only at that stage can I
> then see the output. Now, what I really need is to see the output of the
> process as it writes to stdout already and not only when closing the
> pipe?

I just so happen to have been mucking about with the PTY
(pseudoterminal) library under ruby 1.9.3.
A pseudoterminal might be what you need if you can't change the
buffering of the programs you're trying to manage.

I've put my current test script here: https://gist.github.com/3020873

You'll need to play with the options to get the result you want -
there's no really generic way to automatically manage interactive
programs that expect to interact with a person.

I've found it useful to run the test script in one terminal with the
--debug option and in another use

  tail -F dbg.log

to see exactly what is passing between the parent and the child process.

As an example you could look at the differences between:

  ./pty-test.rb --debug irb --simple-prompt
  ./pty-test.rb --debug --raw irb --simple-prompt
  ./pty-test.rb --debug --errpipe --raw irb --simple-prompt

Another one to try is

  ./pty-test.rb --debug --errpipe --raw vi

Regards,
Sean