DB<16> $a=join "",0..3
 
  DB<17> x $a=~/(.)(.)/g
0  0
1  1
2  2
3  3
  DB<18> x do {my @a; push @a, [$1,$2] while $a=~/(.)(.)/g; @a }
0  ARRAY(0x8ed1a18)
   0  0
   1  1
1  ARRAY(0x8ed1ce8)
   0  2
   1  3