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

my $DEFAULT_TIME_ZONE = "GMT";

my @dates = (
    "0618-01-01 00:00:00",    # intpreted as 2518-01-01
    "1066-10-14 00:00:00",
    "1899-06-24 09:44:00",
    "1900-12-31 23:59:59",
    "1901-01-01 00:00:00",
    "1960-12-31 23:59:59",
    "1968-12-31 23:59:59",
    "1969-01-01 00:00:00",
    "1969-12-31 23:59:59",
    "1970-01-01 00:00:01",
    "2000-01-01 00:00:00",
    "2018-02-20 00:00:00",
    "20180220",
    "02/20/2018",
    "02/20/18",    # interpreted as 1918-02-20
    "2018-02-20",
    "2238-02-20 09:44:00"
);

# define format for printf statements
say "Well formatted date  Variable input date";
say UnixDate( ParseDate($_), '%Y-%m-%d %T' ) . qq{  $_} for (@dates);

exit 0;

__END__

$ format_date.pl
Well formatted date  Variable input date
0618-01-01 00:00:00  0618-01-01 00:00:00
1066-10-14 00:00:00  1066-10-14 00:00:00
1899-06-24 09:44:00  1899-06-24 09:44:00
1900-12-31 23:59:59  1900-12-31 23:59:59
1901-01-01 00:00:00  1901-01-01 00:00:00
1960-12-31 23:59:59  1960-12-31 23:59:59
1968-12-31 23:59:59  1968-12-31 23:59:59
1969-01-01 00:00:00  1969-01-01 00:00:00
1969-12-31 23:59:59  1969-12-31 23:59:59
1970-01-01 00:00:01  1970-01-01 00:00:01
2000-01-01 00:00:00  2000-01-01 00:00:00
2018-02-20 00:00:00  2018-02-20 00:00:00
2018-02-20 00:00:00  20180220
2018-02-20 00:00:00  02/20/2018
2018-02-20 00:00:00  02/20/18
2018-02-20 00:00:00  2018-02-20
2238-02-20 09:44:00  2238-02-20 09:44:00