Run Multi Query using mysqli in PHP

mysqli__multi_query.php

if ($mysqli->multi_query("START TRANSACTION;$query--\nCOMMIT;")) {
    $idx = 0;
    $ret = 0;

    if($output = $mysqli->error) {
        echo $output, PHP_EOL;
        die(-4);
    }
    else {
        do {
            echo ++$idx;
            if($rs = $mysqli->use_result()) { $rs->free(); }
            // elseif($output = $mysqli->error) { $ret = -7; break; }

            if(!$mysqli->more_results()) break;
            if(!$mysqli->next_result()) break;

            echo '.';
        }
        while(true);

        if($ret != 0 or $output = $mysqli->error and $ret = -4) {
            echo $output, PHP_EOL;
            die($ret);
        }
        else {
            echo " done", PHP_EOL;
        }
    }
}
else {
    $output = $mysqli->error;
    echo $output, PHP_EOL;
    die(-3);
}