shopify-buy-button-and-wordpress-shortcode.php

function shopify_shortcode ($atts) {
  $a = shortcode_atts(array(
    'id' => ''
  ), $atts);

  return '<div data-shopify-product="' . $a['id'] . '"></div>';
}

add_shortcode( 'shopify_product', 'shopify_shortcode' );