It's probably clearer if you just say what you mean:

$sentence =
  @array <= 0 ? "" :
  @array <= 1 ? $array[0] :
  @array <= 2 ? join(" and ", @array) :
  join(", ", @array[0..$#array-1], "and $array[-1]");
[download]

That's clearer to me, and safe in case you delete or add a case.

-- Randal L. Schwartz, Perl hacker