my $regex = qr{
	^\[
	\S+\s+
	(\S+)\s+
	([0-9]+)\s+([0-9:]+)\s+([0-9]+) # Datum
	\]
	\s+
	\[
	([^\]]+) # Fehler
	\]
	\s+
	(?>\[\S+\s([^\]]+)\]\s+)? # falls [client ...] Lookahead 
	(.+)
	$
}sx;