my $match = qr[([ab]+)([ab]+)]; my $str = 'aba'; $str =~ /^ $match $ (?{ print "1: $1-$2\n" }) a /x; $str =~ /^ $match $ (?{ print "2: $1-$2\n" }) b /x; $str =~ /^ $match $ (?{ print "3: $1-$2\n" }) (*F) b /x; $str =~ /^ $match $ (?{ print "4: $1-$2\n" }) (*F) .. /x; __END__ 1: ab-a 1: a-ba 3: ab-a 3: a-ba