DB<1> @array=qw/a b c d/

  DB<2> $stringified = join ',', @array;

  DB<3>  @permutations  = glob "{$stringified}" x 2;

  DB<4>  map {s/(.)(.)/$1-$2/} @permutations

  DB<5> x  @permutations
0  'a-a'
1  'a-b'
2  'a-c'
3  'a-d'
4  'b-a'
5  'b-b'
6  'b-c'
7  'b-d'
8  'c-a'
9  'c-b'
10  'c-c'
11  'c-d'
12  'd-a'
13  'd-b'
14  'd-c'
15  'd-d'