This one is fine. But I prefer less keystrokes to make copy-paste more easy.

use vars qw($Bin $Script);
BEGIN { ($Bin, $Script) = split /([^\/\\]+)$/, $0 }
use lib $Bin . 'lib';
[download]

It works for Win, Unix/Linux. I don't care about Mac

UPDATE: It works on Mac too. see Re: Paths in Perl