gistfile1.php

<?php

// DISPLAY USER'S FIRST NAME

function user_first_name() {
	global $current_user;
	get_currentuserinfo();
	$first_name = esc_attr( $current_user->user_firstname );
	return $first_name;
}

add_shortcode( 'user_first_name', 'user_first_name' );