#!/usr/bin/perl
use strict;
use warnings;
use Date::Manip;
use feature 'say';

my $datestr = ParseDate("01/01/2016");
my $secs = UnixDate($datestr,'%s');
say ParseDateString("epoch $secs");
say UnixDate($datestr,"%J");

__END__

$ perl test.pl
2016010100:00:00
2015-W53-5