STDOUT->autoflush(1); makes STDOUT autoflush, not FH. $| = 1 make the currently selected file handle autoflush, which isn't FH in your snippet.

my $text = "Printing test...\n";
open FH, ">LPT1:";
select(*FH);
$| = 1; # Turn on autoflush for FH
select(*STDOUT);
print FH "$text\n";
[download]