Example of adding a shortcode using custom fields "custom-gallery"

gistfile1.txt

function snix_childtheme_gallery() {
    global $post;

    // display this only on pages
    if (is_page()) {
    // get the correct custom field data
    $custom_gallery = get_post_meta($post->ID, 'custom-gallery', true);
        // if custom field is available, do this
        if ($custom_gallery) {
            // do_shortcode is needed
            $galleryoutput = do_shortcode( $custom_gallery ) ;
            // put it on the screen
            print $galleryoutput;
        // if no custom field, do nothing
        } else {
            // silence
        }
    }
}
// then we will hook this on "thematic_abovecontainer", but the hook can be moved anywhere.
add_action('thematic_abovecontainer', 'snix_childtheme_gallery');