$extKey = 'my_extension'; $extPath = \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::extPath($extKey); // Returns something like /var/www/html/typo3conf/ext/my_extension/
$extKey = 'my_extension'; require_once(\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::extPath($extKey) . 'Classes/MyClass.php'); // Loads the MyClass.php file from the my_extension extensionIn this example, we are using the extPath function to require a class file from the "my_extension" extension. Package library for t3lib_extMgm is TYPO3 CMS itself.