What is the use of “$” keyword in c# - web api [duplicate]

Answer 1

It's an interpolated string - the new feature of C# 6, which is basically just a syntax sugar for String.Format (compiler converts interpolated strings into the String.Format calls). Your string is equivalent to

String.Format("api/products/{0}", product.Id)

Answer 2

$"api/products/{product.Id}"

is the short version for

string.Format("api/products/{0}", product.Id);

You could have a look in the MSDN