#!/usr/bin/perl
use warnings;
use strict;

open  (IN, '-|', 'perl PrintStdoutStdErr.pl') or die "$!";
while (<IN>)
{ 
    print;
}

__END__ 
prints:
this went to STDERR
this went to STDOUT

##</code><code>##

#!/usr/bin/perl
use warnings;
use strict;

$|=1;

print STDOUT "this went to STDOUT\n";
print STDERR "this went to STDERR\n";