>perl -wMstrict -le
"my $s = 'abcxyzdef';
 my $exclude = qr{ xyz }xms;
 my $all_not_xyz = qr{ (?! $exclude) . }xms;
 my @matches = $s =~ m{ ($all_not_xyz+) }xmsg;
 print qq{@matches};
"
abc yzdef