DataTables/examples/resources/examples.php

<?php

if ( isset( $_POST['src'] ) && (
	preg_match( '/^scripts\/[a-zA-Z_\-_]+\.php$/', $_POST['src'] ) !== 0 ||
	preg_match( '/^\.\.\/server_side\/scripts\/[a-zA-Z_\-_]+\.php$/', $_POST['src'] ) !== 0
) ) {
	echo htmlspecialchars( file_get_contents( '../server_side/'.$_POST['src'] ) );
}

else {
	echo '';
}