use Bit::Vector; my $joins = 2; my $splits = 3; my $length = $joins+$splits; my $start = '0'x$joins . '1'x$splits; my $vector = Bit::Vector->new_Bin($length, $start); my @combinations = (); for my $pos ($joins-1..$length-1) { # 0-based, right? for my $bit ($splits-1..0) { $vector->bit_flip($pos+$bit); $vector->bit_flip($pos+$bit-1); push @combinations, $vector->to_Bin(); } }