From: Jeremy Tregunna <jtregunna@...>
Date: 2006-08-26T06:53:00+09:00
Subject: Re: Can you temporarily turn off STDERR ??


On 06-08-25, at 15:30, bradjpeek wrote:

> Inside a ruby script I want to:
>
> 1)  redirect STDERR to /dev/null
> 2)  Issue a system call (e.g. system(tar xf tarfile file) )
> 3)  revert to normal STDERR output
>
> I have a script that issues 3-4 system calls that are returning the
> following message to STDERR:
>
> warning: Insecure world writable dir /opt, mode 040777
>
> I'd like to suppress these messages (Let's assume that I can't change
> the permissions on /opt).
>
> An example of one of the lines that is throwing the error is:
>
> x = `tar tf mytar.tar`   #  envoke the unix tar command
> print x
>
> I can suppress the messages by:
>
> $stderr.reopen('/dev/null', 'w')            # send STDERR to /dev/null
> STDERR.puts "can you see me?"    #  message is suppressed
>
> But I haven't been able to figure out how to revert STDERR back to
> before the the reopen.  I only want to suppress this particular
> message, but not others that may prove to be useful such as error
> messages from the ruby interpreter.
>
> I've tried variations of:
>
> stderr = $stderr                 # save current STDERR IO instance
> $stderr.reopen('/dev/null', 'w') # send STDERR to /dev/null
> STDERR.puts "can you see me?"    #  message is suppressed
> $stderr.reopen(stderr)           # revert to default behavior   
> (doesn't
> work)
> STDERR.puts "what about me?      #  I want to see this but I don't
>
> Any suggestions?

Modify that slightly:

$stderr_backup = $stderr.dup
$stderr.reopen("/dev/null", "w")
STDERR.puts "should not see this"
$stderr = $stderr_backup.dup
STDERR = $stderr # can safely ignore the warning
STDERR.puts "foo" # will print foo to the screen

I make no guarantees that this is the best way to do it, infact I can  
safely say it's probably not.

--
Jeremy Tregunna
jtregunna@blurgle.ca