my $haystack = "abcdefghijklmnopqrstuvwxyz";
$haystack =~ /(abc)|(cde)|(fgh)|(ghi)|(ijk)|(pqr)|(rst)|(xyz)/g;
print map {defined($_) ? " $_" : " undef"} @-;
print " is \@-",$/;
print map {defined($_) ? " $_" : " undef"} @+;
print " is \@+",$/;
__END__
 0 0 is @-
 3 3 undef undef undef undef undef undef undef is @+