From: ara.t.howard@...
Date: 2006-09-09T13:01:57+09:00
Subject: Re: Capturing stderr from Kernel.exec

On Sat, 9 Sep 2006, Carl Lerche wrote:

> Hello,
>
> I'm trying to run some simple commands using Kernel.exec but need to capture
> the stderr for them. Is there an (easy) way to do it with just ruby and the
> standard library or should I get open4?
>
> Thanks,
> -carl

open4 adds quite a bit to open3, which is in the stdlib.  so depending on your
exact needs you may or may not need it.

however, by capture i assume you are on unix, since otherwise you cannot fork
and exec just replaces the calling process so theres nothing to capture.  that
being the case you can just

   out_err = ''

   IO.popen("#{ cmd } 2>&1") do |pipe|
     while((line = pipe.gets))
       out_err << line
     end
   end

if you need to separate them you can do

   require 'open3'

   stdout, stderr = '', ''

   Open3.popen3(cmd) do |i,o,e|
     i.close

     while((line = o.gets))
       stdout << line
     end

     while((line = e.gets))
       stderr << line
     end
   end

open4, as mentioned, does a whole lot more - check out the docs/samples.

regards.

-a
-- 
what science finds to be nonexistent, we must accept as nonexistent; but what
science merely does not find is a completely different matter... it is quite
clear that there are many, many mysterious things.
- h.h. the 14th dalai lama