my $dat = IO::File->new($filename, 'w')
or die(...);

$dat->autoflush(1);
print $dat ...;          # Auto-flushed.
$dat->print(...);        # Auto-flushed.

$dat->autoflush(0);
print $dat ...;          # Not flushed.
$dat->print(...);        # Not flushed.
$dat->flush();           # Flushed.

$dat->printflush(...);   # Flushed.