Re: Evaluating math without eval()

Jason Norwood-Young wrote:

On Thu, 2008-04-10 at 13:15 +0100, Richard Heyes wrote:

First post to this list! I'm trying to figure out how to evaluate a string with a mathematical expression and get a result, but without using eval() as I'm accepting user input into the string. I don't just want addition, subtraction, multiplication and division - I'd like to take advantage of other functions like ceil, floor etc. So the string "18-10" should give me 8, "ceil(1/2)*10" should be 10 (if my maths is correct) and the string "18-10;\r\nunlink('/var/www/*');" should not execute.

If you can provide your users with distinct inputs (if it's a form) go that route.

Thanks Richard Unfortunately it's not that simple. The equation sits in a DB and can be anything - eg. ((([valuation]/[purchaseprice])/100)*100)/[numyears] would be a typical field. [valuation], [purchaseprice] and [numyears] gets replaced by relevant fields from user-entered data. But the system is expandable which means I don't know what the equations, data or fields are going to be beforehand. I'm working on some kinda preg_replace function to sanitize the data at the moment and then run an eval - arg I hate regexp! Ideally eval would have some kind of sandboxing option, or you could limit the functions available in an eval. J

you might be able to leverage a call to expr on a bash sell. Just replace the variables you're expecting with preg_replace or some similar function. http://hacktux.com/bashmath http://sysblogd.wordpress.com/2007/08/26/let-bash-do-the-math-doing-calculations-using-that-bash/ I'm not sure if that's any more secure than eval though. -- Ray Hauge www.primateapplications.com