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

open my $olderror, ">&STDERR" or die "Can't dup STDERR: $!";
open STDERR, ">&STDOUT" or die "Can't dup STDOUT: $!";

warn "This is sent on STDOUT\n";

open STDERR, ">&", $olderror or die "Can't dup \$olderror: $!";

warn "This is sent on STDERR\n";