Shortcode for retrieving URL variables within WordPress

functions.php

<?php

/** 
 * Insert this code inside your functions.php file. Do not have the opening <?php tag, as this should
 * already exist at the top of your functions file.
 * 
 * USAGE: If you have firstname as a variable in your page's URL (e.g. http://mydomain.com?firstname=Martyn)
 * then putting [get var=firstname] into a WordPress post type or widget would print "Martyn" to the screen.
 * After using exec PHP plugins for months (i.e. <?php echo $_GET['firstname']; ?>) I'm moving away from 
 * executing PHP directly in posts/pages and widegets. This is the whole reason shortcodes were invented in the 
 * first place. Enjoy!
 **/
 
function get( $var ) 
{
	extract( shortcode_atts( array(
		'var' => ''
	), $var ) );

	// referring to the Product Class
	return $_GET[$var];
}
add_shortcode( 'get', 'get' );