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

my @dates = ( "2018-02-20 00:00:00",
	      "20180220",
	      "02/20/2018",
	      "02/20/18",    # interpreted as 1918-02-20
	      "2018-02-20",
	      "today");

say UnixDate( ParseDate($_), "%Y-%m-%d") for (@dates);

__END__

$ perl test.pl
2018-02-20
2018-02-20
2018-02-20
2018-02-20
2018-02-20
2018-02-20