Well, ignoring shell solutions, you could use the Filter module.

Something like this at the beginning of your script.

use Filter::Handle qw/subs/;

open (*FH, ">OUTPUT_PATH/filename.txt") or die "Could open filename.tx
+t:$!";
my $output_file = *FH;    

Filter \*STDOUT, sub { 
            print $output_file $_;
            
        };
[download]

This code is untested. I hacked it from an internal program I wrote a while back that does what your asking. Let me know if you have problems.
Update: Left out comma, duh. Fixed it.

-Lee

"To be civilized is to deny one's nature."