local *STDOUT = new IO::Tee(\*STDOUT, '>file.txt');

##</code><code>##

open STDOUT, '>&', new IO::Tee(\*STDOUT, '>file.txt');

##</code><code>##

# Append
open STDOUT, '>>&', new IO::Tee(\*STDOUT, '>file.txt');

# Save the extra file descriptor
open STDOUT, '>&=', new IO::Tee(\*STDOUT, '>file.txt');
open STDOUT, '>>&=', new IO::Tee(\*STDOUT, '>file.txt');