Code Forums - View Single Post - Using regular expressions to clean HTML in user input

teknomage1 · 05-23-2006, 10:19 PM

If you want to start checking for properly balanced tags you have to build more sophisticated machinery than just regular expressions. Arbitrarily nestable expressions like (1 + (2 * (6 - 3)) and html tag trees, are not regular languages and cannot be accurately described by regular expressions.

It seems like you can get away with only replacing < or > than signs that are not next to text on your first run through. eg. 's/<([^A-Za-z])/&lt\1/g' and 's/([^A-Za-z])>/\1&gt/g' .

05-23-2006, 10:19 PM	#4 (permalink)
teknomage1 Jack of all trades Join Date: Feb 2005 Location: Los Angeles Posts: 598	If you want to start checking for properly balanced tags you have to build more sophisticated machinery than just regular expressions. Arbitrarily nestable expressions like (1 + (2 * (6 - 3)) and html tag trees, are not regular languages and cannot be accurately described by regular expressions. It seems like you can get away with only replacing < or > than signs that are not next to text on your first run through. eg. 's/<([^A-Za-z])/&lt\1/g' and 's/([^A-Za-z])>/\1&gt/g' . __________________ Stop intellectual property from infringing on me