#! perl -slw
use strict;
use threads;

sub thread {
    my $output = '';
    open CMD, '-|', q[ perl -E"say( qq[$$:saying $_] ), warn( qq[$$:warning $_\n] ), sleep(1) for 1 .. 4" 2>&1 ] or die $!;
    $output .= $_ while <CMD>;
    close CMD;
    return $output;
}

printf "Got\n'%s'\n", $_->join for map threads->create( \&thread ), 1 .. 4;

__END__
C:\test>t-junk
Got
'33168:warning 1
33168:warning 2
33168:warning 3
33168:warning 4
33168:saying 1
33168:saying 2
33168:saying 3
33168:saying 4
'
Got
'30208:warning 1
30208:warning 2
30208:warning 3
30208:warning 4
30208:saying 1
30208:saying 2
30208:saying 3
30208:saying 4
'
Got
'15844:warning 1
15844:warning 2
15844:warning 3
15844:warning 4
15844:saying 1
15844:saying 2
15844:saying 3
15844:saying 4
'
Got
'15032:warning 1
15032:warning 2
15032:warning 3
15032:warning 4
15032:saying 1
15032:saying 2
15032:saying 3
15032:saying 4
'