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<?php
/**
 * Wordpress: Contact form 7, Add form tag (shortcode) current url example
 */
add_action( 'wpcf7_init', 'wpcf7_add_form_tag_current_url' );
function wpcf7_add_form_tag_current_url() {
	// Add shortcode for the form [current_url]
	wpcf7_add_form_tag( 'current_url',
		'wpcf7_current_url_form_tag_handler',
		array(
			'name-attr' => true
		)
	);
}

// Parse the shortcode in the frontend
function wpcf7_current_url_form_tag_handler( $tag ) {
	global $wp;
	$url = home_url( $wp->request );
	return '<input type="hidden" name="'.$tag['name'].'" value="'.$url.'" />';
}