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

From: Thomas Rast <trast@inf.ethz.ch>
Date: Apr 6, 2013, 08:07 UTC
Message-ID: <878v4wrsj7.fsf@linux-k42r.v.cablecom.net>
In-Reply-To: <20130405233450.GA6137@machine.or.cz>

Petr Baudis <pasky@ucw.cz> writes:

Show 5 quoted lines

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

Indeed, that's the crucial point here. dup2() is defined to close the original FD first if needed.

It's much saner this way for the case of stderr, as there is no time when we have no stderr available to report errors: the FD is replace atomically from the POV of the program.

The manpage for dup2 does, however, say

   If newfd was open, any errors  that  would  have  been  reported  at
   close(2) time are lost.  A careful programmer will not use dup2() or
   dup3() without closing newfd first.

which is probably what you were referring to.

-- 
Thomas Rast
trast@{inf,student}.ethz.ch