gistfile1.php

<?php
function get_the_user_ip() {
	if ( ! empty( $_SERVER['HTTP_CLIENT_IP'] ) ) {
		//check ip from share internet
		$ip = $_SERVER['HTTP_CLIENT_IP'];
	} elseif ( ! empty( $_SERVER['HTTP_X_FORWARDED_FOR'] ) ) {
		//to check ip is pass from proxy
		$ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
	} else {
		$ip = $_SERVER['REMOTE_ADDR'];
	}
	return apply_filters( 'edd_get_ip', $ip );
}

@jamesmcinally this function simply returns the IP address. on its own it doesn't display it or store it etc. if you're just looking to log a list of IP addresses visiting your site, you should be able to do this more efficiently through your web traffic logs.