$ ack --version
Running under Perl 5.8.8 at ***
Copyright 2005-2009 Andy Lester.
This program is free software; you can redistribute it and/or modify
it under the terms of either: the GNU General Public License as
published by the Free Software Foundation; or the Artistic License.
$ echo foo|ack
Use of uninitialized value in string eq at ***/ack line 1578.
Use of uninitialized value in regexp compilation at ***/ack line 1959.
This is fixed as of ack2.