include, include_once, require or require_once?

Question

I have PHP file where I have defined the server access variables as well as the mysql_connect and mysql_select_db, as this functions are regularly

Answer 1

Functional Work : All functions perform similar work. All functions will include and evaluates the specific file while executing the code.

Functional Difference :

include vs include_once : There is only one difference between include() and include_once(). If the code from a file has been already included then it will not be included again if we use include_once(). Means include_once() include the file only once at a time.

include vs require : if include() is not able to find a specified file on location at that time it will throw a warning however, it will not stop script execution. For the same scenario, require() will throw a fatal error and it will stop the script execution.

require vs require_once : There is only one difference between require() and require_once(). If the code from a file has been already included then it will not be included again if we use require_once(). Means require_once() include the file only once at a time.

To get the detailed knowledge with example please review these amazing articles
(1) http://www.readmyviews.com/include-vs-include-once/
(2) http://www.readmyviews.com/include-vs-require/