scriptcs -repl
#r "System.Xml.Linq"
using System.Xml.Linq;
XDocument doc = XDocument.Load("app.config");
var result = doc.Element("configuration")
  .Element("connectionStrings")
  .Elements("add")
  .Single(el => el.Attribute("name").Value == "MongoDB");
result.SetAttributeValue("connectionString", "mongodb://%deploy.DatabaseHost%:%deploy.DatabasePort%/%deploy.DatabaseName%");
doc.Save("app.config");
Environment.Exit(0);
echo.