From: Brian Candler <b.candler@...>
Date: 2009-01-06T17:55:58+09:00
Subject: Re: Question about run external program in Ruby

Zhao Yi wrote:
> How can I get stderr in this method?

You are already combining stderr with stdout (2>&1)

To get them separately, see open3.rb in the standard library.

# Open3 grants you access to stdin, stdout, and stderr when running 
another
# program. Example:
#
#   require "open3"
#   include Open3
#
#   stdin, stdout, stderr = popen3('nroff -man')
#
# Open3.popen3 can also take a block which will receive stdin, stdout 
and
# stderr as parameters.  This ensures stdin, stdout and stderr are 
closed
# once the block exits. Example:
#
#   require "open3"
#
#   Open3.popen3('nroff -man') { |stdin, stdout, stderr| ... }

However, since it forks twice, I believe you lose the exit status from 
the (grand)child. You also need to be careful not to block on reading 
from stdout when the child has written a large amount of data to stderr, 
or vice versa. (For example, you could use select, or you could have two 
separate threads reading from stdout and stderr)
-- 
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