Shortcode to show parent category

functions.php

<php

/**
 *
 * Shortcode to show parent category
 * 
 * [postcat]
 *
 */
function ns_post_cat_shortcode(){
	
$first_term_name = get_the_terms( $post->ID, 'category' )[0]->name;
	
return $first_term_name;
	
}	
add_shortcode( 'postcat', 'ns_post_cat_shortcode' );