Focus Keyword: PHP

include(), require(), include_once(), and require_once() are all PHP functions used to include and evaluate external files in a PHP script. The main difference between them lies in how they handle file inclusions:

• include(): The include() function includes and evaluates the specified file, but if the file is not found or there is an error, a warning will be issued, and the script will continue executing.
• require(): The require() function works similarly to include(), but if the specified file is not found or there is an error, a fatal error will occur, and the script execution will stop.
• include_once(): The include_once() function includes and evaluates the specified file, but it will only do so once even if it is called multiple times in the script.
• require_once(): The require_once() function is similar to include_once(), but if the same file is being included multiple times, it will only include it once to avoid redeclaration errors.

It is important to choose the appropriate function based on the requirements of your PHP script to handle file inclusions efficiently and handle errors effectively.