#!/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", # current date
	      "now" # current date with also time
    );

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

__END__

$ perl test.pl in.txt
2018-02-20 00:00:00 CET
2018-02-20 00:00:00 CET
2018-02-20 00:00:00 CET
2018-02-20 00:00:00 CET
2018-02-20 00:00:00 CET
2018-02-20 00:00:00 CET
2018-02-20 18:03:16 CET