I'd thought i do a regex replace 

```
Regex r = new Regex("[0-9]"); 
return r.Replace(sz, "#");

```

on a file named aa514a3a.4s5 . It works exactly as i expect. It replaces all the numbers including the numbers in the ext. How do i make it NOT replace the numbers in the ext. I tried numerous regex strings but i am beginning to think that its a all or nothing pattern so i cant do this? do i need to separate the ext from the string or can i use regex?