for i in a b c d do for j in 1 2 3 4 do echo "$i $j" done done
a 1 a 2 a 3 a 4 b 1 b 2 b 3 b 4 c 1 c 2 c 3 c 4 d 1 d 2 d 3 d 4
a 1 b 2 c 3 d 4