Re: [PATCH v2 1/2] perl: redirect stderr to /dev/null instead of closing

From: Petr Baudis <pasky@ucw.cz>
Date: Apr 5, 2013, 23:34 UTC
Message-ID: <20130405233450.GA6137@machine.or.cz>
In-Reply-To: <7vsj34byb4.fsf@alter.siamese.dyndns.org>

On Fri, Apr 05, 2013 at 11:57:19AM -0700, Junio C Hamano wrote:

Show 15 quoted lines

> Petr Baudis <pasky@ucw.cz> writes:
> >> > -			if (defined $opts{STDERR}) {
> >> > -				close STDERR;
> >> > -			}
> >> >  			if ($opts{STDERR}) {
> >> >  				open (STDERR, '>&', $opts{STDERR})
> >
> >   I'm sorry, I don't follow. Doesn't this just break the STDERR option
> > altogether as we will try to dup2() over an already open file
> > descriptor? We do need to close STDERR if we are going to reopen it,
> > I think.
> 
> When $opts{STDERR} is 2, what the three lines the proposed patch
> removes did is actively wrong, because you dup2 the fd you just
> closed.

Indeed, though $opts{STDERR} == 2 is something weird to do, it is a case to consider.

> When $opts{STDERR} is 1, it seems to do the right thing with or
> without the "close STDERR" in front.  Isn't this because the usual
> "open($fd, <<<anything>>>) closes $fd as necessary" applies to this
> case as well?

I never actually tried that and was always happy to go with perldoc maxim

	To (re)open "STDOUT" or "STDERR" as an in-memory file, close it first:
	           close STDOUT;
	           open(STDOUT, ">", \$variable)
	               or die "Can't open STDOUT: $!";

but my assumption that this generalizes to other kinds of open was apparently invalid; an example further down the page proves me wrong completely, moreover.

  The thing is, I was confused about dup2() all along as my old UNIX
masters taught me that I must close() the original descriptor first
and since that's what's commonly done anyway, I never thought to
double-check. Now I did and I learned something new, thanks!

I guess Acked-by: Petr Baudis <pasky@ucw.cz> then. :-)

-- 
				Petr "Pasky" Baudis
	For every complex problem there is an answer that is clear,
	simple, and wrong.  -- H. L. Mencken