Simple Shortcode for Display Post Date

date_shortcode.php

function get_post_date( $atts ) {
	$a = shortcode_atts( array(
		'format' => $atts['format']
	), $atts );
	
	if ( array_key_exists("format",$a) ) {
		return get_the_date($a['format']);
	} else {
		return get_the_date('m dd, y');
	}
}
add_shortcode( 'post_date', 'get_post_date' );