IPC::Open3 does not auto-create an error handle #9372

p5pRT · 2008-06-10T13:44:36Z

Migrated from rt.perl.org#55570 (status was 'resolved')

Searchable as RT55570$

p5pRT · 2008-06-10T13:44:37Z

From fiji@ayup.limey.net

Created by fiji@ayup.limey.net

The POD for IPC::Open3 says:
my($wtr, $rdr, $err);
$pid = open3($wtr, $rdr, $err, 'some cmd and args', 'optarg', ...);

However, that always results in an undef $err.

Looking at the source of the module I see (in the sub _open3):
unless (eval {
$dad_wtr = $_[1] = gensym unless defined $dad_wtr && length $dad_wtr;
$dad_rdr = $_[2] = gensym unless defined $dad_rdr && length $dad_rdr;
1; })

It clearly is not doing the magic to autogenerate the $err handle.

Either the POD or the code needs to be fixed... the current behavior
ends up with the STDERR being sent to STDOUT.

Perl Info


Flags:
    category=core
    severity=medium

This perlbug was built using Perl v5.8.8 in the Red Hat build system.
It is being executed now by Perl v5.8.8 - Mon Nov 26 14:23:46 EST 2007.

Site configuration information for perl v5.8.8:

Configured by Red Hat, Inc. at Mon Nov 26 14:23:46 EST 2007.

Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
  Platform:
    osname=linux, osvers=2.6.20-1.3001.fc6xen, archname=i386-linux-thread-multi
    uname='linux xenbuilder4.fedora.phx.redhat.com 2.6.20-1.3001.fc6xen #1 smp thu aug 9 16:18:42 edt 2007 i686 i686 i386 gnulinux '
    config_args='-des -Doptimize=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables -Dversion=5.8.8 -Dmyhostname=localhost -Dperladmin=root@localhost -Dcc=gcc -Dcf_by=Red Hat, Inc. -Dinstallprefix=/usr -Dprefix=/usr -Darchname=i386-linux -Dvendorprefix=/usr -Dsiteprefix=/usr -Duseshrplib -Dusethreads -Duseithreads -Duselargefiles -Dd_dosuid -Dd_semctl_semun -Di_db -Ui_ndbm -Di_gdbm -Di_shadow -Di_syslog -Dman3ext=3pm -Duseperlio -Dinstallusrbinperl=n -Ubincompat5005 -Uversiononly -Dpager=/usr/bin/less -isr -Dd_gethostent_r_proto -Ud_endhostent_r_proto -Ud_sethostent_r_proto -Ud_endprotoent_r_proto -Ud_setprotoent_r_proto -Ud_endservent_r_proto -Ud_setservent_r_proto -Dinc_version_list=5.8.7 5.8.6 5.8.5 -Dscriptdir=/usr/bin'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=define use5005threads=undef useithreads=define usemultiplicity=define
    useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
    use64bitint=undef use64bitall=undef uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -Wdeclaration-after-statement -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -I/usr/include/gdbm',
    optimize='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -Wdeclaration-after-statement -I/usr/local/include -I/usr/include/gdbm'
    ccversion='', gccversion='4.1.2 20070925 (Red Hat 4.1.2-27)', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='gcc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lresolv -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lpthread -lc
    perllibs=-lresolv -lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    libc=/lib/libc-2.6.so, so=so, useshrplib=true, libperl=libperl.so
    gnulibc_version='2.6'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E -Wl,-rpath,/usr/lib/perl5/5.8.8/i386-linux-thread-multi/CORE'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables -L/usr/local/lib'

Locally applied patches:
    


@INC for perl v5.8.8:
    /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.8
    /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.8
    /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.7/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.6/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.5/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.8
    /usr/lib/perl5/site_perl/5.8.7
    /usr/lib/perl5/site_perl/5.8.6
    /usr/lib/perl5/site_perl/5.8.5
    /usr/lib/perl5/site_perl
    /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.7/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.6/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.5/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.8
    /usr/lib/perl5/vendor_perl/5.8.7
    /usr/lib/perl5/vendor_perl/5.8.6
    /usr/lib/perl5/vendor_perl/5.8.5
    /usr/lib/perl5/vendor_perl
    /usr/lib/perl5/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/5.8.8
    .


Environment for perl v5.8.8:
    HOME=/home/fiji
    LANG=en_US
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/usr/lib/qt-3.3/bin:/usr/kerberos/bin:/usr/local/bin:/bin:/usr/bin:/usr/lib/jre/bin:/sbin:/usr/sbin/:/usr/local/sbin:.:/home/fiji/bin
    PERL5LIB=/usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi:/usr/lib/perl5/site_perl/5.8.8:/usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi:/usr/lib/perl5/vendor_perl/5.8.8
    PERL_BADLANG (unset)
    SHELL=/bin/bash

p5pRT · 2008-06-11T10:24:35Z

From renee.baecker@smart-websolutions.de

This is a small patch that solves the problem:

rbaecker@www-devel-rbaecker ~/perl510/perl-5.10.0 $ ./perl -Ilib
../bugs/open.pl
test at /home/rbaecker/perl510/bugs/test.pl line 6.
rbaecker@www-devel-rbaecker ~/perl510/perl-5.10.0 $ cd ../test/perl-5.10.0
rbaecker@www-devel-rbaecker ~/perl510/test/perl-5.10.0 $ ./perl -Ilib
../../bugs/open.pl
Use of uninitialized value $err in <HANDLE> at ../../bugs/open.pl line 11.
readline() on unopened filehandle at ../../bugs/open.pl line 11.
rbaecker@www-devel-rbaecker ~/perl510/perl-5.10.0 $ cat ../bugs/open.pl
#!/usr/bin/perl

use strict;
use warnings;
use IPC::Open3;

my ($wtr,$rdr,$err);

my $pid = open3($wtr,$rdr,$err,'perl /home/rbaecker/perl510/bugs/test.pl');

print <$err>;

rbaecker@www-devel-rbaecker ~/perl510/perl-5.10.0 $ cat ../bugs/test.pl
#!/usr/bin/perl

use strict;
use warnings;

warn "test";

rbaecker@www-devel-rbaecker ~/perl510/perl-5.10.0 $

Another related bug report is #31738
(http://rt.perl.org/rt3/Ticket/Display.html?id=31738)

--
Renée Bäcker
renee.baecker@smart-websolutions.de

XING: http://www.xing.com/profile/Renee_Baecker
Foo-Magazin: http://foo-magazin.de

p5pRT · 2008-06-11T10:24:35Z

From renee.baecker@smart-websolutions.de

open3.patch

--- ../test/perl-5.10.0/lib/IPC/Open3.pm	2007-12-18 11:47:07.000000000 +0100
+++ lib/IPC/Open3.pm	2008-06-11 12:20:30.000000000 +0200
@@ -194,7 +194,7 @@
     unless (eval  {
 	$dad_wtr = $_[1] = gensym unless defined $dad_wtr && length $dad_wtr;
 	$dad_rdr = $_[2] = gensym unless defined $dad_rdr && length $dad_rdr;
-	1; }) 
+	$dad_err = $_[3] = gensym unless defined $dad_err && length $dad_err; }) 
     {
 	# must strip crud for croak to add back, or looks ugly
 	$@ =~ s/(?<=value attempted) at .*//s;

p5pRT · 2008-06-11T10:24:37Z

The RT System itself - Status changed from 'new' to 'open'

p5pRT · 2008-06-11T10:37:36Z

From p5p@perl.wizbit.be

Citeren "fiji@ayup.limey.net (via RT)" <perlbug-followup@perl.org>:

-----------------------------------------------------------------
[Please enter your report here]

The POD for IPC::Open3 says:
my($wtr, $rdr, $err);
$pid = open3($wtr, $rdr, $err, 'some cmd and args', 'optarg', ...);

However, that always results in an undef $err.

[...]

It clearly is not doing the magic to autogenerate the $err handle.

Either the POD or the code needs to be fixed... the current behavior
ends up with the STDERR being sent to STDOUT.

-----------------------------------------------------------------

If you read further in the POD it says:

'If either reader or writer is the null string, this will be replaced
by an autogenerated filehandle.'

Which doesn't talk about $err.

But what has to change?

Changing the code might break a program that relies on $err being the
same as $wtr when undef is passed...

Kind regards,

Bram

p5pRT · 2008-06-11T10:41:34Z

From renee.baecker@smart-websolutions.de

Sorry, the doc says:

"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."

So the behaviour is documented. But it is really confusing to define a
variable for the error filehandle and then it is never used...

Renée Bäcker wrote:

This is a small patch that solves the problem:
...

--

Renée Bäcker
renee.baecker@smart-websolutions.de

XING: http://www.xing.com/profile/Renee_Baecker
Foo-Magazin: http://foo-magazin.de

p5pRT · 2008-06-11T14:48:33Z

From ben@morrow.me.uk

Quoth p5p@perl.wizbit.be (Bram):

Citeren "fiji@ayup.limey.net (via RT)" <perlbug-followup@perl.org>:

The POD for IPC::Open3 says:
my($wtr, $rdr, $err);
$pid = open3($wtr, $rdr, $err, 'some cmd and args', 'optarg', ...);

However, that always results in an undef $err.

[...]

It clearly is not doing the magic to autogenerate the $err handle.

Either the POD or the code needs to be fixed... the current behavior
ends up with the STDERR being sent to STDOUT.

-----------------------------------------------------------------

If you read further in the POD it says:

'If either reader or writer is the null string, this will be replaced
by an autogenerated filehandle.'

Which doesn't talk about $err.

But what has to change?

The pod. Something like

use Symbol qw/gensym/;
my ($rdr, $wtr, $err);
open3($rdr, $wtr, $err = gensym, ...);

Changing the code might break a program that relies on $err being the
same as $wtr when undef is passed...

Yes. This (unfortunate) API decision is why Open3 couldn't be updated to
auto-viv filehandles when that idea was invented.

Ben

--
The cosmos, at best, is like a rubbish heap scattered at random.
Heraclitus
ben@morrow.me.uk

p5pRT · 2008-06-11T22:41:23Z

From @ikegami

--- ../test/perl-5.10.0/lib/IPC/Open3.pm 2007-12-18
11:47:07.000000000 +0100
+++ lib/IPC/Open3.pm 2008-06-11 12:20:30.000000000 +0200
@@ -194,7 +194,7 @@
unless (eval {
$dad_wtr = $_[1] = gensym unless defined $dad_wtr && length $dad_wtr;
$dad_rdr = $_[2] = gensym unless defined $dad_rdr && length $dad_rdr;
- 1; })
+ $dad_err = $_[3] = gensym unless defined $dad_err && length
$dad_err; })
{
# must strip crud for croak to add back, or looks ugly
$@ =~ s/(?<=value attempted) at .*//s;

That patch would break compatibility with the documented behaviour.
One solution is to use gensym.

use IPC::Open3 qw( open3 );
use Symbol qw( gensym );

my $pid = open3(
my $to_chld = gensym(),
my $fr_chld = gensym(),
my $fr_chld_err = gensym(),
'command', 'with', 'args'
);

p5pRT · 2008-06-13T07:18:43Z

From @rgs

2008/6/11 Ben Morrow <ben@morrow.me.uk>:

If you read further in the POD it says:

'If either reader or writer is the null string, this will be replaced
by an autogenerated filehandle.'

Which doesn't talk about $err.

But what has to change?

The pod. Something like

use Symbol qw/gensym/;
my ($rdr, $wtr, $err);
open3($rdr, $wtr, $err = gensym, ...);

Changing the code might break a program that relies on $err being the
same as $wtr when undef is passed...

Yes. This (unfortunate) API decision is why Open3 couldn't be updated to
auto-viv filehandles when that idea was invented.

I tend to agree with that. But such an API modification would go with
a dual-lifing.

p5pRT · 2009-01-07T16:06:40Z

From mark.zealey@pipex.net

Hi all, could we get a doc change for this as was suggested:

use Symbol qw/gensym/;
my ($rdr, $wtr, $err);
open3($rdr, $wtr, $err = gensym, ...);

It's misleading at the moment as the example given in the docs doesn't
do what you expect.

Thanks,

Mark

p5pRT · 2009-01-12T09:29:12Z

From module@renee-baecker.de

On Mi. 07. Jan. 2009, 08:06:40, mzealey wrote:

Hi all, could we get a doc change for this as was suggested:

use Symbol qw/gensym/;
my ($rdr, $wtr, $err);
open3($rdr, $wtr, $err = gensym, ...);

It's misleading at the moment as the example given in the docs doesn't
do what you expect.

Thanks,

Mark

Hi Mark,

can you provide a small patch and send it to Perl 5 Porters
(perl5-porters@perl.org)?

Cheers,
Renee

p5pRT · 2012-09-14T12:20:22Z

From bitcard@profvince.com

Thanks for your report. Looks like this issue was a duplicate of RT
#31738, which has been fixed in december 2011.

Vincent

p5pRT · 2012-09-14T12:20:23Z

bitcard@profvince.com - Status changed from 'open' to 'resolved'

p5pRT closed this as completed Sep 14, 2012

p5pRT added Severity Medium distro-Linux documentation type-library labels Oct 18, 2019

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IPC::Open3 does not auto-create an error handle #9372

IPC::Open3 does not auto-create an error handle #9372

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p5pRT commented Sep 14, 2012

IPC::Open3 does not auto-create an error handle #9372

IPC::Open3 does not auto-create an error handle #9372

Comments

p5pRT commented Jun 10, 2008

p5pRT commented Jun 10, 2008

From fiji@ayup.limey.net

Created by fiji@ayup.limey.net

p5pRT commented Jun 11, 2008

From renee.baecker@smart-websolutions.de

p5pRT commented Jun 11, 2008

From renee.baecker@smart-websolutions.de

p5pRT commented Jun 11, 2008

p5pRT commented Jun 11, 2008

From p5p@perl.wizbit.be

p5pRT commented Jun 11, 2008

From renee.baecker@smart-websolutions.de

p5pRT commented Jun 11, 2008

From ben@morrow.me.uk

p5pRT commented Jun 11, 2008

From @ikegami

p5pRT commented Jun 13, 2008

From @rgs

p5pRT commented Jan 7, 2009

From mark.zealey@pipex.net

p5pRT commented Jan 12, 2009

From module@renee-baecker.de

p5pRT commented Sep 14, 2012

From bitcard@profvince.com

p5pRT commented Sep 14, 2012