Removing commas from number

Thanks to the suggestions, I use number_format($my_number, 2) to format the number in an edit field. Now I need to reenter it into MySQL. How should I use preg_replace to remove the commas? This removes the commas *and* the decimal point: preg_replace('/\D/', '', $str) In reviewing patterns, I cannot find the purpose of the "/" character in the above. Many thanks.... Todd