How to have multiple config files for a set of constants to allow for easy switching from one to another?

How to have multiple config files for a set of constants to allow for easy
switching from one to another?

References

Reference NO 1

http://stackoverflow.com/questions/15198266/how-to-have-multiple-config-files-for-a-set-of-constants-to-allow-for-easy-switc

Reference NO 2

http://codex.wordpress.org/Editing_wp-config.php

Reference NO 3

http://www.brandonsavage.net/custom-apps-some-strategies-for-easy-configuration-files/

Reference NO 4

http://digwp.com/2009/06/wordpress-configuration-tricks/

Reference NO 5

http://www.wpbeginner.com/wp-tutorials/useful-wordpress-configuration-tricks-that-you-may-not-know/

Reference NO 6

http://www.dasprids.de/blog/2009/05/08/writing-powerful-and-easy-config-files-with-php-arrays

Reference NO 7

http://wp.tutsplus.com/tutorials/security/conquering-the-wp-config-php-file-11-good-practices/

Reference NO 8

http://wordpress.stackexchange.com/questions/58391/is-moving-wp-config-outside-the-web-root-really-beneficial