add_isbn.php

<?
//This is terribly insecure.  We don't even pretend that we're authenticating here.  
//We take parameters straight from _GET.  
//Don't actually use this as is, please.

//Simple UPC -> ISBN code
function parseUPC($upc) {
        if(false !== strstr($upc,'978')){
                $isbn = substr($upc,3,9);
                $xsum=0;
                $add=0;
                for ($i=0; $i< 9; $i++) {
                        $add = substr($isbn,$i,1);
                        $xsum += (10 - $i ) * $add;
                }
                $xsum = $xsum % 11;
                $xsum = 11 - $xsum;
                if ($xsum == 10) { $xsum = "X"; }
                if ($xsum == 11) { $xsum = "0"; }
                $isbn .= $xsum;
                return $isbn;
        }
        else
            return $upc;
}

if($_GET['isbn']) {
        $fp = fopen('isbns.txt','a');
        $isbn = parseUPC($_GET['isbn']);
        $isbn .= "\r\n";
        fwrite($fp, $isbn);
        fclose($fp);
        echo "added " . $isbn;
        exit;
}
?>
Not Added