my $bar = 'asdf  asdf  asdf-rdf';
my $mor = () = $bar =~ /asdf(?:-rdf)?/;
my $gor = () = $bar =~ /asdf(?:-rdf)?/g;
my @gor = $bar =~ /asdf(?:-rdf)?/g;

warn scalar @gor;
die "$mor and $gor = @gor";
__END__
3 at - line 6.
1 and 3 = asdf asdf asdf-rdf at - line 7.