use threads;

my $fh;
my $pid;
async {
    $pid = open $fh, 
        "scp dvader@empire.gov:file1.txt dvader@deathstar.com:somedir 2>&1 |" 
        or die $!;
}->detach;

while( <$fh> ) {
    print;
}
close $fh;
kill 'quit', $pid;