index.php

<?php 
// this file lives in the site's theme directory
if( defined( 'EMA_ENVIRONMENT' ) !== true || constant( 'EMA_ENVIRONMENT' ) === 'prod' ) { {
  // do stuff
} ?>

wp-config.php

<?php
// this file lives in the web root directory

if( file_exists( dirname(__FILE__) . '/../' . basename(__DIR__) . '-env-config.php' ) ){
	require_once( dirname(__FILE__) . '/../' . basename(__DIR__) . '-env-config.php' );
} else {
	define( 'EMA_ENVIROMENT', 'prod' );
}

	
// ** MySQL settings ** //
/** The name of the database for WordPress */
define('DB_NAME', 'wordpress_database_name');

/** MySQL database username */
define('DB_USER', 'the_db_user');

/** MySQL database password */
define('DB_PASSWORD', 'the_db_password');

/** MySQL hostname */
define('DB_HOST', 'localhost_or_whatever_it_is');

/** Database Charset to use in creating database tables. */
define('DB_CHARSET', 'utf8');

/** The Database Collate type. Don't change this if in doubt. */
define('DB_COLLATE', '');

/** Blah, blah, blah. Rest of the file goes below ...

{basename}-env-config.php

 <?php
 
 // This file lives one level up from the directory containing wp-config.php
 // and is not in version control. This file is completely omitted from production
 // deployments.
 
 define( 'EMA_ENVIRONMENT', 'stage' );