$re = '~[\s,]*[-*/+\d]+~m';
$str = 'quanity*price/2+tax
quanity*price/2
quanity , *price/2+tax
quanity - *price,/2
quanity -, -- , *price,/2
quantity - 3 //,,/price';
$subst = "\n";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php