To call a user-defined function in PHP using a string variable, you can use the call_user_func() or call_user_func_array() functions. These functions allow you to invoke a callback function specified by a string name. The other mentioned options (execute_function(), execute_user_func(), invoke_function(), invoke_user_func(), run_function(), run_user_func()) are not valid PHP functions. For further information, consult the PHP documentation on call_user_func(): http://php.net/manual/en/function.call-user-func.php and call_user_func_array(): http://php.net/manual/en/function.call-user-func-array.php

PHP constants are case-sensitive. It means that constant names are treated as case-sensitive identifiers. For example, if a constant is defined as "CONSTANT_NAME", you cannot access it as "constant_name" or "CoNsTaNt_NaMe". The constant name must match exactly with its defined case. This behavior ensures that constants are accessed consistently based on their exact names. Learn more: https://www.php.net/manual/en/language.constants.php

Exception::getMessage returns the error message associated with the exception, while Exception::getLine returns the line number where the exception occurred. They provide different information about the exception. Learn more: http://php.net/manual/en/class.exception.php

The unlink() function in PHP is used to delete a file from the server. It takes a single argument, which is the path to the file you want to delete. For example, you can use unlink('path/to/file.txt') to delete the file "file.txt" located in the "path/to" directory. It's important to note that the unlink() function permanently deletes the file, and there is no way to undo this operation. Therefore, caution should be exercised when using this function. It's also worth mentioning that the unlink() function requires appropriate file system permissions to delete the file.

The statement is correct. In a PHP do...while loop, the code block is executed at least once, even if the condition is false. After the first execution, the condition is checked. If the condition is true, the loop continues executing the block of code. If the condition is false, the loop terminates. This behavior ensures that the code block is executed at least once, regardless of the condition. Learn more: https://www.php.net/manual/en/control-structures.do.while.php

The main purpose of a destructor in a PHP class is to perform cleanup tasks before the object is destroyed. The correct option is "tasks." The destructor is automatically called when an object is no longer referenced or explicitly destroyed, allowing you to release resources, close connections, or perform other necessary cleanup operations. For more information, consult the PHP documentation on destructors: https://www.php.net/manual/en/language.oop5.decon.php#language.oop5.decon.destruct

To destroy a session in PHP, you can use the session_destroy() function. This function is called as a statement to remove all session data and end the current session. It effectively destroys the session. It's important to note that session_destroy() alone may not unset all session variables, so you may also need to call session_unset() to unset all session variables before calling session_destroy(). Learn more: http://php.net/manual/en/function.session-destroy.php

To sanitize a string in PHP, you can use the filter_var() function with the FILTER_SANITIZE_STRING filter. This filter specifically sanitizes the string by removing HTML tags and encoding special characters, making the string safe for output. The filter_var() function provides a convenient and reliable way to sanitize strings in PHP. For more information, see: http://php.net/manual/en/function.filter-var.php

This statement is false. The PHP interpreter completely ignores comments during the script's execution. Comments are purely for the developers' benefit and do not have any impact on the functioning of the code. They are not executed as part of the script and are not sent to the client's browser. It's important to remember that comments are solely used for documentation purposes and have no effect on the actual program logic. Learn more: https://www.php.net/manual/en/language.basic-syntax.comments.php

Common actions performed on files in PHP include opening files to read or write data, and performing various file operations like copying, moving, or deleting files. Other actions like searching, sorting, calculating, and comparing are not exclusive to files and can be performed on various data structures.