clintonm9 has asked for the wisdom of the Perl Monks concerning the following question:

I need to split up stdout and stderr from a shell process i am executing in perl. I went down the path of using CaptureOutput perl module to accomplish my objective. I am now having problems with the Success flag if I am in a child process with $SIG{CHLD} = 'IGNORE'; set. Please see my sample below and let me know if there is anything that I could do to make this process return success like it should. If not is there another way to handle getting stdout and stderr into different scalars that would be 100% reliable? 
#!/usr/bin/perl
use Data::Dumper;
use IO::CaptureOutput qw/capture_exec/;

# The first test shows the Success = 1
&runCommand();

# Now the same thing in a child process shows Success = 1 
unless ( $pid = fork ) {
    &runCommand();
    exit;
}

# Now child process with IGNORE set, shows Success = 0
$SIG{CHLD} = 'IGNORE'; 
unless ( $pid = fork ) {
    &runCommand();
    exit;
}

sub runCommand
{
    ($stdout, $stderr, $success, $exit_code) = capture_exec('perl', '-
+e', 'print "Test"');
    print "stdout: $stdout\n";
    print "stderr: $stderr\n";
    print "Success: $success\n";
    print "exit code: $exit_code\n";    
}

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Re: Using IO::CaptureOutput in a child process to caputre STDOUT and STDERR
by Khen1950fx (Canon) on Apr 10, 2011 at 08:57 UTC
    I think that you were missing a few things, primarily a reaper subroutine---without that, it'll always return -1. Here's how I would do it: 
    !/usr/bin/perl

use strict;
use warnings;
use IO::CaptureOutput qw(capture capture_exec);
use Proc::Killall;
use POSIX qw(:signal_h :errno_h :sys_wait_h);

&runCommand();

my $pid;
unless ( $pid = fork ) {
    &runCommand();
    exit;
}

$SIG{'CHLD'} = \&Reaper;
unless ( $pid = fork ) {
    &runCommand();
    exit;
}


sub runCommand
{
    my ($stdout, $stderr, $success, $exit_code) = 
        capture_exec('perl', '-e', 'print "Test"');
    print "stdout: $stdout\n";
    print "stderr: $stderr\n";
    print "Success: $success\n";
    print "exit code: $exit_code\n";    
}

sub Reaper {
    my $pid;
    waitpid(-1, &WNOHANG);
}

killall('HUP', -$$);

    [download]
    Update: added a kill.
[reply]
[d/l]
      small comment: there is no "&" in front of WNOHANG. 
      sub reaper
{
   my $kid;
   while ( ( $kid = waitpid(-1, WNOHANG) >0 ) ){};
}

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[reply]
[d/l]
        small comment: there is no "&" in front of WNOHANG.

        Because you removed it! :) 

        $ perl -Mstrict -Mwarnings -e " print WNOHANG "
Name "main::WNOHANG" used only once: possible typo at -e line 1.
print() on unopened filehandle WNOHANG at -e line 1.

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[reply]
[d/l]

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