google-analytics-tracking-code.php

<?php
/*
Plugin Name: Google Analytics Tracking Code MU-Plugin
Description: A must-use plugin that adds immutable Google Analytics tracking code.
*/

/* This plugin is used to ensure that Google Analytics is always present on the site (thus the use of a mu-plugin)
and to maintain the relationship between WordPress themes (design) and WordPress plugins (functionality) by keeping this
code out of the theme and in a plugin. */


/* If HTTP host URL contains either the strings "staging" or "local", do nothing.
In all other cases, add Google Analytics tracking code */
if ((strpos($_SERVER['HTTP_HOST'], 'staging') !== false) || (strpos($_SERVER['HTTP_HOST'], 'local') !== false)) {
  // do nothing
} else {
  // add Google Analytics tracking code
  add_action( 'wp_head', 'google_analytics_tracking', 1 );
}

function google_analytics_tracking( $priority ) {
    ?>

    <!-- Global site tag (gtag.js) - Google Analytics -->
    <script async src="https://www.googletagmanager.com/gtag/js?id=UA-XXXXXXX-X"></script>
    <script>
      window.dataLayer = window.dataLayer || [];
      function gtag(){dataLayer.push(arguments);}
      gtag('js', new Date());

      gtag('config', 'UA-XXXXXXX-X');
    </script>


		<?php
};

?>

// REMEMBER TO UPDATE UA CODE "UA-XXXXXXX-X" IN BOTH PLACES IN GIST ABOVE