Ok good I think I overlooked how the printing to STDOUT is buffered by default, thanks for that. Problem solved. But I would only want the change of $| to 1 to affect that function, and when it exits I want $| back to default. Would this do that?

sub countdown {
    local $| = 1;
    my $int = $_[0];
    while ($int > 0) {
        print "$int ... ";
        sleep 1;
        $int--;
    }
    print "\n";
}
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*edit* just tried and seems to work as expected.