First you should use strict and use warnings. That would tell you that you missed parens in this declaration:

    my (@less, @equal, @greater, @answer);
[download]

It would also inform you that you misspelled @equal in:

    unshift(@answer, @equal); # was @equals
[download]

Fixing those two problems and adding a print statement at the end yields:

My pivot is 5
My pivot is 3
My pivot is 6
answer: 9 6 5 4 3 1
[download]

Btw, I don't know why you feel you have to use (shift @copy) in your pushes. You can achieve the same thing with the much simpler:

  if ($_ < $pivot) {
    push(@less, $_);
  }
  if ($_ == $pivot) {
    push(@equal, $_);
  }
  # etc...
[download]