difference between Server.MapPath("."), Server.MapPath("~"), Server.MapPath(@"\") and Server.MapPath("/")?

Server.MapPath specifies the relative or virtual path to map to a physical directory.

• Server.MapPath(".") returns the current physical directory of the file (e.g. aspx) being executed
• Server.MapPath("..") returns the parent directory
• Server.MapPath("~") returns the physical path to the root of the application
• Server.MapPath("/") returns the physical path to the root of the domain name (is not necessarily the same as the root of the application)

An example:
Let's say you pointed a web site application (http://www.example.com/) to

C:\Inetpub\wwwroot

and installed your shop application (sub web as virtual directory in IIS, marked as application) in

D:\WebApps\shop

For example, if you call Server.MapPath in following request:

http://www.example.com/shop/products/GetProduct.aspx?id=2342

then:

• Server.MapPath(".") returns D:\WebApps\shop\products
• Server.MapPath("..") returns D:\WebApps\shop
• Server.MapPath("~") returns D:\WebApps\shop
• Server.MapPath("/") returns C:\Inetpub\wwwroot
• Server.MapPath("/shop") returns D:\WebApps\shop

If Path starts with either a forward (/) or backward slash (\), the MapPath method returns a path as if Path were a full, virtual path.
If Path doesn't start with a slash, the MapPath method returns a path relative to the directory of the request being processed.
Note: in C#, @ is the verbatim literal string operator meaning that the string should be used "as is" and not be processed for escape sequences.