From: 7stud -- <bbxx789_05ss@...>
Date: 2009-02-09T21:26:29+09:00
Subject: Re: assignment to $stdout deprecated?

Brian Candler wrote:
>

Thanks for the detailed response.

> If you reassign $stdout to point to a completely different Ruby object, 
> then any code you write which does $stdout.puts will write to this 
> object - but FD 1 still remains connected to the original stdout.
>

Ok.

> Therefore, STDOUT.puts will still write to the original destination, as 
> will any child process.
> 

Ok.

>   $stdout = File.open("/tmp/stdout.txt","w")
> 
>   puts "Hello"            # uses $stdout, goes to the file
>   STDOUT.puts "World"     # goes to the terminal (FD 1)
>   system("echo Wheee")    # goes to the terminal (FD 1)
> 

AFAIK, all child processes receive a copy of their environment including 
copies of all the variables in the parent.  So echo doesn't write to 
$stdout because echo doesn't understand ruby and therefore ignores 
variables like $stdout?


> If you need to redirect to a StringIO object, then you have little 
> choice but to use $stdout, because a StringIO is not a Unix file, i.e. 
> it doesn't have an entry in the file descriptor table.
> 

Ok.

> (If you wanted to get very fancy, you could perhaps set up a pipe, 
> connect stdout to the writer end, and have a Ruby thread reading from 
> the reader end and appending to a StringIO object. But you'd only jump 
> through those hoops if you wanted the stdout from spawned child 
> processes to write to the StringIO too, and in that case you'd be better 
> off using IO.popen anyway)

Thanks for taking the time to write such an informative post.

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