From: Antonio Moreno <ejsglobal@...>
Date: 2006-11-21T05:42:41+09:00
Subject: Re: File descriptors

Robert Klemme wrote:
> 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.
> 
(snif)

>  > 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
> 
I'll tell you exactly what am I trying to do. I have qmail and I want to 
replace qmail-queue 
(http://www.qmail.org/qmail-manual-html/man8/qmail-queue.html) with my 
ruby script in order to make some mangling of the email, and then call 
qmail-queue to let the email go on.

> 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

Thanks, Robert,

Regards.

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