In my original code (which does not work for the test data :() I detected the end of the looping by testing to see if any of the arrays where still defined (had contents). Since I needed to pull the next number off the list to display it, I just combined a few operations from

      if ($a[0]==$i) {
           printf "%5s",$a[0];
           shift @a;
      }
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into the code you see. Oh, and I used scalar probably without need, but I wanted to make sure that the shift statement didn't pull off more than one element.