Aeonic is a command line date/time wrapper for Chronic, which allows natural language parsing of times and dates.
gem install aeonic
This will install globally, and insert the aeonic executable into your path.
Give aeonic a time or date, and the date, time and unix timestamp are returned.
Time.now #=> 2012-09-30 20:52:33 +0100
$ aeonic
2012-09-30 20:52:33 +0100 : 1349034753
$ aeonic "now"
2012-09-30 20:52:33 +0100 : 1349034753
$ aeonic "2012-09-30 20:52:33"
2012-09-30 20:52:33 +0100 : 1349034753
$ aeonic 1349034753
2012-09-30 20:52:33 +0100 : 1349034753
$ aeonic "tuesday 5pm"
2012-10-02 17:00:00 +0100 : 1349193600