need to create a C# Regex similar to this perl expression
<p>I was wondering if it is possible to build equivalent C# regular expression for finding this pattern in a filename.  For example, this is the expr in perl <code>/^filer_(\d{10}).txt(.gz)?$/i</code>  Could we find or extract the <code>\d{10}</code> part so I can use it in processing?</p>
