Very basic URL parsing with regular expressions and named capture groups.

Parse URL

Regex ParseUrl = new Regex(@"(?:^\w*:?//)?       # Protocol
                             (?<domain> [\.\w]+) # Domain
                             (?::\d)?            # Port
                             (?:/.*)?            # Path",
                           RegexOptions.IgnoreCase |
                           RegexOptions.IgnorePatternWhitespace);

// Example usage
var domain = ParseUrl.Replace(url, @"${domain}");