When you fork each program (parent and child) has its own copy of the STDOUT and STDERR handles. You capture the output in the usual way:

my @cmds = qw ( cmd1 cmd2 );
my $pid = fork();
defined $pid or die "fork $!\n";
if ( $pid ) {
    $parent_captures = `$cmds[0] 2>&1`;
}
else {
    $kid_captures = `$cmds[1] 2>&1`;
}
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You can probably open STDERR onto STDOUT before the fork and then just capture STDOUT as well but I don't do it that way.

cheers

tachyon

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#!/usr/bin/perl -wT
use strict;

my $pid1=fork();
unless($pid1) {
  # First child
  my $stdout_file = 'child1_stdout.log';
  my $stderr_file = 'child1_stderr.log';

  local(*STDERR);
  local(*STDOUT);
  open(STDOUT1, '>'.$stdout_file)
    or die $stdout_file . ': ' . $!;
  open(STDERR1, '>'.$stderr_file)
    or die $stderr_file . ': ' . $!;

  open(STDOUT, ">&STDOUT1")
    or die "Couldn't redir stdout: $!";
  open(STDERR, ">&STDERR1")
    or die "Couldn't redir stderr: $!";

  system('cmd1');

  close(STDOUT1);
  close(STDERR1);
  exit();
}

my $pid2=fork();
unless($pid2) {
  # Same thing but call cmd2 instead of cmd1

  exit();
}


# Don't forget to wait for each child
wait();
wait();
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exec "cmd1 >/tmp/cmdone.log 2>&1"; #combine stdout/stdin
exec "cmd2 >/tmp/cmdtwo.out 2>/tmp/cmdtwo.err";# split them up
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Various ways of accomplishing the effect that you are looking for:

1. Use ">/tmp/command.out 2>/tmp/command.err" in the shell command string. Read the files after the command completes, and remove the files.
2. Use IPC::Open3() and select() to monitor all pipes, reading data from pipes that have data ready.
3. Spawn a thread off to read data from each sub process pipe. The thread would update a shared variable as data arrived on the pipe. The thread would exit when the pipe was closed.

In order to decide which method would work best, many factors need to be analyzed, including the acceptable level of complexity of the final product, the efficiency of the product, the purpose for capturing stdout/stderr, and the host environment (UNIX vs WIN32).

 open OUT1, "echo world |";
 open OUT2, "echo hello, |"
 print "output is ...\n", <OUT2>, <OUT1>;
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