calc

<?php
$string = $argv[1];
$string = preg_replace('/(([-+\/*])|^)-/', '\\1|', $string);
$svals = array();
foreach(explode('+', $string) as $ppart){
    $mvals = array();
    $i = 0;
    foreach(explode('-', $ppart) as $spart){
        $prod = 1;
        foreach(explode('*', $spart) as $fac){
            $prod *= (int)str_replace('|', '-', $fac);
        }
        if (0 != $i++){
            $mvals[] = -1 * $prod;
        } else {
            $mvals[] = (int)$prod;
        }
    }
    $svals[] = array_sum($mvals);
}
echo array_sum($svals);