For use with multiple sub-folder WordPress installations. This allows you to store all wp-config.php in any folder on your server. WP config files are renamed to correspond with the server name. This approach helps you protect your wp-config files when you have multiple docroots in one folder.

wp-config-switcher.php

<?php
# ------------------
#   no shenanigans
# ------------------
if ( __FILE__ == $_SERVER['SCRIPT_FILENAME'] ) { die(); }

# ---------------
#   server name
# ---------------
$server = $_SERVER['SERVER_NAME'];

# -----------------------
#   wp-config directory
# -----------------------
$configs_dir = dirname( __FILE__ );

# ----------------------------
#   config file name
#   example: dev_mydomain_com
# -----------------------------
$file_name = str_replace( '.', '_', $server );

# --------------------
#   config file path
# --------------------
$config_path = "$config_path/$server.php";


# ------------------------------
#   set ABSPATH to proper path
# ------------------------------
if( !defined( 'ABSPATH' ) )
    define( 'ABSPATH', dirname( __FILE__ ) . '/' );

# -------------------------------
#   load domain-specific config
# -------------------------------
if( file_exists( $config_path ) )
	require_once( $config_path );
else
	throw new Exception( "No config file could be found at: $config_path" );