The include_once statement includes and evaluates the specified file during the execution of the script. This is a behavior similar to the include statement, with the only difference being that if the code from a file has already been included, it will not be included again.
|include_once filename;||includes the specified file into current script
filename can be referenced by a variable
filename is case-sensitive
<?php echo "Hello\r\n"; ?>
<?php include "test.php"; // include test.php include "test.php"; // include test.php again include_once "test.php"; // not include test.php ?>
[result] Hello Hello