Write multiple line into external files

i have input like this:

<input type='hidden' name='col12[]'><input type='hidden' name='col13[]'><input type='hidden' name='col14[]'><input type='hidden' name='col15[]'>

i want to write multiple record from these fields into external file, i use php code to execute like this:

<?php    if (isset($_POST["buttonSave"])) {        $colFile = fopen("estimasi.txt", "w") or die();        $colItems = $_POST['col12'];        $colQty = $_POST['col13'];        $colUnit = $_POST['col14'];        $colPrice = $_POST['col15'];        for($i=0;$i<sizeof($colPrice);$i++) {            ?><?php            echo $colItems[$i];            echo $colQty[$i];            echo $colUnit[$i];            echo $colPrice[$i];            ?><?php        fwrite($colFile, $colItems[$i], $colQty[$i], $colUnit[$i], $colPrice[$i]);        echo '<meta http-equiv="refresh" content="0;url='.dirname($_SERVER['SCRIPT_NAME']).'" />';        }    }    ?>

but that is not working, is it wrong?