How can a PHP programmer ensure that a file is not double included in a script to avoid redeclaration errors?

To prevent a file from being double included in a PHP script and avoid redeclaration errors, a programmer can use the `include_once` or `require_once` functions instead of `include` or `require`. These functions ensure that the file is only included once, even if the script tries to include it multiple times. 

<?php
// Include the file only once
require_once 'file.php';
?>

Keywords

PHP include_once require_once redeclaration errors file inclusion

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