From: Jilles Tjoelker <jilles@stack.nl>
To: Parke <parke.nexus@gmail.com>
Cc: "dash@vger.kernel.org" <dash@vger.kernel.org>
Subject: Re: why does dash save, dup, and restore redirected descriptor in the parent, rather than redirect in the child?
Date: Fri, 3 Feb 2017 23:37:55 +0100 [thread overview]
Message-ID: <20170203223755.GA69960@stack.nl> (raw)
In-Reply-To: <CAPxz1+au53RAak7Goisz7QKrzUSvtZidLFZ4b7sgV1QR_JeK5Q@mail.gmail.com>
On Tue, Jan 31, 2017 at 06:27:00PM -0800, Parke wrote:
> On Tue, Jan 31, 2017 at 12:00 PM, Mark Galeck <mark_galeck@pacbell.net> wrote:
> > This is strange. Why save, dup and dup again to restore, descriptors
> > in the parent, when it would be much simpler to just dup in the
> > child, and not have to save and restore. This is simpler and I
> > checked it works the same:
> > I am sure there must be a good reason and I am not understanding
> > something deeper. What is it?
> I am not a dash developer, but one reason to make system calls in the
> parent is that it is much simpler to handle errors in the parent.
> In your example:
> > if (!fork()) {
> > fd = open64("foobar.txt", O_WRONLY|O_CREAT);
> > dup2(fd, 1);
> > execl("/bin/date", "date", (char *)NULL);
> > }
> What happens if open64 fails? How should the child inform the parent
> of this specific error?
In general, you are right, but in the shell's case there is no
difficulty. The error is reported via an error message to stderr and a
non-zero exit status of the command, and the child process can easily do
those things.
--
Jilles Tjoelker
next prev parent reply other threads:[~2017-02-03 22:45 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <2132582962.805179.1485892834849.ref@mail.yahoo.com>
2017-01-31 20:00 ` why does dash save, dup, and restore redirected descriptor in the parent, rather than redirect in the child? Mark Galeck
2017-01-31 20:30 ` Harald van Dijk
2017-02-01 2:27 ` Parke
2017-02-03 22:37 ` Jilles Tjoelker [this message]
2017-02-02 18:17 ` Mark Galeck
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