From: Tom Pollard <tomp@...>
Date: 2006-11-01T11:37:29+09:00
Subject: Re: Nonblocking IO read


On Oct 31, 2006, at 7:20 PM, srobertjames@gmail.com wrote:
> In the interests of promoting creativity, I'll ask the question  
> without
> any prior assumptions:
>
> I'm using popen4 (great gem, btw) to run an external command and
> capture stdout and stderr.  If one (or both) of those is empty, I  
> don't
> want to hang.  Just keep on moving.  In fact, stderr will normally be
> empty.
>
> How could I do this?

Have you tried simply reading from them?  When the command  
terminates, that should close those pipes on the command's end.  At  
that point, a simple read on the stdout handle, for instance, will  
return whatever output there was and then eof.  If there's no output,  
the read should return immediately.  Did you try that yet?  Did you  
try the (Windows-oriented) example from the 'ri Open4' page?  If  
you're working in Unix you could try

   status = POpen4::poen4('cat -') do |stdout, stderr, stdin|
     stdin.puts 'hello world'
     stdin.close
     puts "stdout: #{stdout.read.strip}"
     puts "stderr: #{stderr.read.strip}"
   end

Anyway, you would only need nonblocking IO if you wanted to read bits  
of the stderr stream before the command exited, but that doesn't  
sound like what you're want.

Tom