Prev: master perl calling slave perl
Next: FAQ 4.17 How do I find yesterday's date?
From: Ben Morrow on 6 May 2008 18:59

Quoth ddunham(a)taos.com (Darren Dunham):
> xhoster(a)gmail.com wrote:
> > ddunham(a)taos.com (Darren Dunham) wrote:
> >> Ben Morrow <ben(a)morrow.me.uk> wrote:
> >> > I would normally say 'Use lexical filehandles!' at this point;
> >> > unfortunately, IPC::Open3 was written before they existed and the
> >> > obvious way
> >> >
> >> > my $pid = open3(my $CMD_IN, my $CMD_OUT, my $CMD_ERR, @cmd)...
> >> >
> >> > doesn't work (and can't be made to since undef is already meaningful).
> >>
> >> What's wrong with the above?
> >
> > It causes cmd's stderr to go to $CMD_OUT rather than the obviously
> > intended $CMD_ERR.
>
> I don't know that it's obviously intended. It took me quite a while to
> realize that I even had an option to return output and error on a single
> filehandle. I mention that explicitly because the OP might have been
> having issues with selecting between the two, when reading them combined
> may have been preferable.
>
> However, if you do want them separated, then the other choices offered
> seem quite verbose. Instead of them, I would pass in a (defined)
> filehandle. That takes one more line of code (two if you count bringing
> in the FileHandle module.
>
> my $CMD_ERR = FileHandle->new();
> my $pid = open3(my $CMD_IN, my $CMD_OUT, $CMD_ERR, @cmd)...

....which is essentially the same as what I proposed, except that I
prefer to avoid FileHandle (and IO::Handle) and use Symbol::gensym
directly. That's just a matter of taste, of course.

Ben

From: Ilya Zakharevich on 6 May 2008 20:04
[A complimentary Cc of this posting was NOT [per weedlist] sent to
Ben Morrow
<ben(a)morrow.me.uk>], who wrote in article <jtb6f5-qg1.ln1(a)osiris.mauzo.dyndns.org>:
> > sub open3 ($$$$@) {
> > $_[0] = IO::Handle->new unless defined $_[0]; # Or whatever is THE
> > initializer
> > ...
> > }

> Yeah, in general you can do that; however, for the specific case of
> open3, the docs say
>
> If CHLD_ERR is false, or the same file descriptor as CHLD_OUT, then
> STDOUT and STDERR of the child are on the same filehandle.

Thanks, I forgot about this semantic. Which does not mean that one
could not write ALSO open3_autovivify... ;-)

Yours,
Ilya
 | 
Pages: 1
Prev: master perl calling slave perl
Next: FAQ 4.17 How do I find yesterday's date?