From: Eric Hodel <drbrain@...7.net>
Date: 2009-05-21T04:01:25+09:00
Subject: Re: I want to redirect stderr to StringIO.

On May 19, 2009, at 23:14, Robert Klemme wrote:
> 2009/5/20 Eric Hodel <drbrain@segment7.net>:
>> On May 19, 2009, at 21:30, ErMaker wrote:
>>
>>>>> IO.new(2).reopen(StringIO.new)
>>>
>>> TypeError: can't convert StringIO into String
>>>       from (irb):1:in `reopen'
>>>       from (irb):1
>>>>>
>>>>> IO.new(2).reopen(IO.new(1))
>>>
>>> => #<IO:0x2a81630>
>>>
>>> StringIO also do as IO, but IO#reopen fails.
>>>
>>> I want to redirect stderr to StringIO, but it doesn't work.
>>
>> Always use reopen as a last resort.
>>
>> http://blog.segment7.net/articles/2006/08/17/stdout-vs-stdout
>
> I am not sure I agree.  Actually, if you want the redirection to be
> permanent for sub processes you have to use $stdout.reopen.  And this
> is not a "last resort" but the proper solution.

Most of the time people capture IO from sub processes via Kernel#` or  
IO::popen instead of handling the sub process themselves.  Ruby's nice  
features make use of #reopen an exceptional circumstance, but there  
are times where it's appropriate.

> Btw, in 1.8 there is also $defout - I believe _that- is the stream
> used by Kernel#puts and the like in those versions:
>
> 08:13:00 ~$ ruby -r stringio -e 'puts 1; $defout=StringIO.new; puts 2'
> 1
> -e:1: warning: $defout is obsolete; use $stdout instead

This warning says otherwise.  They happen to be the same object though:

$ ruby -e 'p $stdout.object_id, $defout.object_id'
97260
97260