sub printtolog
{
	my $txt = shift;
	my $logf;

    $txt = getdirdatetag() . ': ' . $txt . "\n";
    # see https://perldoc.perl.org/functions/open
	open($logf, ">>:utf8", $logging_logfile)
		|| die "$0: can't open $logging_logfile for appending: $!";

	# see https://perldoc.perl.org/functions/select
	# this does not work
# 	my $oldfh = select $logf;
# 	$| = 1;
# 	select($oldfh);
	# this also does not work
# 	$logf->autoflush(1);
	print $logf $txt;
	# this does not work
# 	$logf->flush;
# 	$logf->sync;
	# this also does not work
# 	$select()->flush();
# 	$select()->sync();
	close $logf;
}