foreach (@ARGV) { $Y{$y}++,next if $y eq $_;  }
[download]

• next is not needed here as there's nothing happening after it, anyway.
• Once we removed next, we can see it basically counts how many times $y appears in @ARGV, so a bit more readable way might be

      $Y{$y} += grep $y eq $_, @ARGV;
  [download]

• This automatically does anything only when @ARGV is not empty (as otherwise, grep returns 0). What can we do to get rid off the if? Well, if @ARGV is empty, we want to increase $Y{$y} by one, which could be achieved by

      $Y{$y} += (grep $y eq $_, @ARGV) || 1;
  [download]

  This can replace the whole if/else.

It's unclear what happens in the ellipses. Note that if 0 is in @ARGV, it won't be counted in %Y because of next unless $y.