I don't know if the following code is the correct solution for your problem because it does not handle any (interactive) user input (besides it's just a quick hack -- without error handling).

Short Description:
------------------
- open a pipe to each given process (@ARGV) 8|
- poll each pipe for new data (optionally print data)
- finished if each filehandle returns eof

#!/usr/local/bin/perl -w

use strict;
use IO::File;

my $count = 0;
my @fdesc = ();
my %fdname;

# create pipes
foreach my $prog (@ARGV) {
  my $fh = IO::File->new("$prog |");
  push(@fdesc, $fh);
  $fdname{$fh} = $prog;
}

# listen
my $notDone=0;
do {
  $notDone=0;
  foreach my $fh (@fdesc) {
    if (!$fh->eof()) {
      $notDone=1;
      print "<",$fdname{$fh},">: ",$fh->getline();
    }
  }
} while ($notDone);
[download]

example usage: combineLog.pl ls "ps auxw" "du -sk ~*" > comb.log 2>&1

MP