my @y = glob('{a,b,c}'x6);
my $y = '(?:(?!\1)a()|(?!\2)a()|(?!\3)b()|(?!\4)b()|(?!\5)c()|(?!\6)c()){6}\1\2\3\4\5\6';

for my $j (@y)
{
    $j =~ $y and say $j;
}