use strict;
use warnings;

use Test::More;

my @good = (
    '1234',
    '5566foo bar',
    'baz9980'
);

my @bad = (
    'a',
    '12',
    '12.4',
    '-124baz',
    '2018-01-01'
);

my $re = qr/\d{4}(?!-)/a;

plan tests => @good + @bad;

for my $str (@good) {
    like ($str, $re, "$str matched");
}
for my $str (@bad) {
    unlike ($str, $re, "$str not matched");
}