remove invalid characters from filenames regex valid filename I'm not 100% happy with the method as that whole "remove invalid characters" block is repetetive and I know it's creating a new string object with each call. Microsoft Apps How to filter a string for invalid filename characters using regex ]*” with ‘_’ would be a better first step. I was using sp_OACreate and sp_OAMethod and didn't pay attention to the filenames -- now I have files and folders I cannot delete because Windows cannot find the file. … character, and they cannot be an empty string. html input field using regex to get rid of invalid characters for … This will match any special character from € (hex code 80) to ÿ (hex code FF).