Why not cycle through the top-level array, shifting off the bottom element in each sub-array? Something like

@array = ([1,2,3],[4,5,6],[7,8,9]);
while (grep scalar @{ $_ }, @array) {
  for $i (@array) {
    print shift @{ $i };
    }
  }
[download]

This has the merit that not only do you not need to code (or even initialise, or know) the number and length of sub-arrays, but they can also be of different lengths.

§ George Sherston