use strict;
use warnings;
use File::Temp;

my $temp_stdout = File::Temp->new;

local *OLDOUT;
local *OLDERR;

open( OLDOUT, ">&STDOUT" );
open( OLDERR, ">&STDERR" );
open( STDOUT, ">$temp_stdout" );
open( STDERR, ">&STDOUT" );

# Funky quoting for Windows.  Sigh.
system('perl -e "print q{to stdout}; warn q{to stderr}; print q{more to stdout}');
 
close(STDOUT); 
open(STDOUT, ">&OLDOUT");
open(STDERR, ">&OLDERR");

open CAPTURED, "<$temp_stdout";
my $capture = do { local $/; <CAPTURED> };
close CAPTURED;

print "Got this:\n$capture";