How to set current date in input type=date in php code example

Example 1: get current date from year input php

$date_input = '2003';
$date_output= date( "Y-m-d", mktime( 0, 0, 0, 1, 1, $date_input ));
//date_output = 2003-01-01

Example 2: current date time in php for input

<input type="datetime-local" name="followupon" value=<?php echo date('Y-m-d\TH:i:s'); ?>">