From: Robert Klemme <shortcutter@...>
Date: 2006-11-21T04:55:09+09:00
Subject: Re: File descriptors

On 20.11.2006 20:24, Antonio Moreno wrote:
> I'm trying to code a script for replacing an application which takes 
> it's input from file descriptors 0 (stdin) and 1 (stdout).

This is not possible.  You can only read from stdin and not stdout.

 > It must also
> be able to open another application which in turn also reads from the 
> above mentioned file descriptors.

This is not clear to me: does the other app read from the same fd's 
(i.e. reading continues in the sub process) or do you want to connect 
them via a pipe?  (The latter is done with IO.popen() or Kernel open as 
you discovered already).

> I've managed to take stdin and put it into stdin of the second app, 
> though couldn't find the way of opening stdout for reading.
> 
> In http://www.rubycentral.com/book/ref_m_kernel.html#Kernel.open, for 
> example, states pretty clear that "...The returned IO object may be used 
> to write to the standard input and read from the standard output of this 
> subprocess..."
> 
> Does anybody have a clue about this? I'm not very skilled in Ruby, so 
> any help will be very appreciated.

What exactly is your problem?  Did you try it and it did not work? 
Here's a simply sample that works for me

irb(main):010:0> open("|cat", "r+") {|io| Thread.new {5.times {|i| 
io.puts i}; io.flush; io.close_write}; p io.readlines}
["0\n", "1\n", "2\n", "3\n", "4\n"]
=> nil

Note the mode flag.

Kind regards

	robert