Neither STDERR nor STDOUT will be buffered (they'll be "hot") after these lines:

select(STDERR);
$|=1;            # Autoflush STDERR.
select(STDOUT);  # This doesn't undo STDERR's autoflushing.
$|=1;            # Autoflush STDOUT.
# STDOUT will be the default print handle
# because it was the last select()ed handle.
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