From: Tom Metge <tom@...>
Date: 2007-12-27T14:04:43+09:00
Subject: Re: Capturing error msgs from output = `cmd`


On Dec 26, 2007, at 9:30 PM, James Gray wrote:

> On Dec 26, 2007, at 9:03 PM, Tim Hunter wrote:
>
>> Victor Reyes wrote:
>>> Hello Team,
>>> I wrote the simple piece of code below which under "normal"  
>>> circumstances it
>>> works fine.
>>> If, however, the command executed generates an error msg, the  
>>> error is
>>> displayed on the screen.
>>> This is a behaviour which I don't want.
>>> I would like to capture ALL output generated by the command and  
>>> return it to
>>> the caller.
>>> I tried different tricks but nothing worked. The question is:
>>> How can I capture ALL output from line: *userCMD_output =  
>>> `#{input}`*
>>> including stderr???
>>>
>>
>> When you use backticks to capture the output from a command, what  
>> you get is whatever the command writes to stdout. If the command  
>> writes an error message to stderr you can't capture it.
>
> Well, you could fold STDERR into STDOUT.  In my Unix shell that's  
> done with:
>
>  `#{cmd} 2>&1`
>
> Hope that helps.
>
> James Edward Gray II
>

that's a great idea.  alternately, you could use open3:

http://ruby-doc.org/stdlib/libdoc/open3/rdoc/index.html

it does make it a bit easier to do error checking/handling (by  
differentiating stderr from stdout).  you can use nil for the values  
you don't want...

nil, stdout, stderr = popen3("cmd")

tom