sub nextmask { if ($_[0] =~ s/0(0*)$/1$1/) {1;} elsif ($_[0] =~ s/1(0*)1$/01$1/) {2;} else {0;} } my @factors = qw(2 3 5 7); my $mask = '0' x scalar(@factors); while (my $transtype = nextmask($mask)) { print "BREAK\n" if ($transtype > 1); # do stuff print join " ", map { substr($mask, $_, 1) ? $factors[$_] : ' ' } 0 .. $#factors; print "\n"; }