While I agree that output buffering is the problem, setting autoflush is the less-preferred solution in this case.

I would recommend terminating each line with a "\n", as in

print "Hello World\n";
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The newline will cause the buffer to flush without any fussing with autoflush. This is why you see most perl scripts terminate "print" lines with "\n" (It also makes the output lines separate, which , in most cases , is desirable.