它比绳子更方便。格式，你也可以在这里使用智能感知。

下面是我的测试方法:

[TestMethod]
public void StringMethodsTest_DollarSign()
{
    string name = "Forrest";
    string surname = "Gump";
    int year = 3; 
    string sDollarSign = $"My name is {name} {surname} and once I run more than {year} years."; 
    string expectedResult = "My name is Forrest Gump and once I run more than 3 years."; 
    Assert.AreEqual(expectedResult, sDollarSign);
}

$是字符串的简写。格式和字符串插值一起使用，这是c# 6的一个新特性。正如在您的例子中使用的那样，它什么也不做，就像string.Format()一样。

当使用它来构建引用其他值的字符串时，它就发挥了作用。以前必须写成:

var anInt = 1;
var aBool = true;
var aString = "3";
var formated = string.Format("{0},{1},{2}", anInt, aBool, aString);

现在就变成:

var anInt = 1;
var aBool = true;
var aString = "3";
var formated = $"{anInt},{aBool},{aString}";

还有一种不太为人所知的字符串插值形式，使用$@(两个符号的顺序很重要)。它允许@""字符串的特性与$""混合，以支持字符串插值，而不需要在整个字符串中使用\\。下面这两行:

var someDir = "a";
Console.WriteLine($@"c:\{someDir}\b\c");

将输出:

c:\a\b\c

注意，你也可以将两者结合起来，这很酷(尽管看起来有点奇怪):

// simple interpolated verbatim string
WriteLine($@"Path ""C:\Windows\{file}"" not found.");

$语法很好，但有一个缺点。

如果你需要一个字符串模板，在类级别上声明为field…它本该在一个地方。

然后你必须在同一层次上声明变量…这一点都不酷。

使用字符串要好得多。这类事情的格式语法

class Example1_StringFormat {
 string template = $"{0} - {1}";

 public string FormatExample1() {
   string some1 = "someone";
   return string.Format(template, some1, "inplacesomethingelse");
 }

 public string FormatExample2() {
   string some2 = "someoneelse";
   string thing2 = "somethingelse";
   return string.Format(template, some2, thing2);
 }
}

全局变量的使用并不是很好，除此之外，它也不适用于全局变量

 static class Example2_Format {
 //must have declaration in same scope
 static string some = "";
 static string thing = "";
 static string template = $"{some} - {thing}";

//This returns " - " and not "someone - something" as you would maybe 
//expect
 public static string FormatExample1() {
   some = "someone";
   thing = "something";
   return template;
 }

//This returns " - " and not "someoneelse- somethingelse" as you would 
//maybe expect
 public static string FormatExample2() {
   some = "someoneelse";
   thing = "somethingelse";
   return template;
 }
}

下面的示例强调了使用插值字符串相对于string.Format()在简洁和可读性方面的各种优点。它还显示{}内的代码像任何其他函数参数一样被求值，就像调用string.Format()一样。

using System;

public class Example
{
   public static void Main()
   {
      var name = "Horace";
      var age = 34;
      // replaces {name} with the value of name, "Horace"
      var s1 = $"He asked, \"Is your name {name}?\", but didn't wait for a reply.";
      Console.WriteLine(s1);

      // as age is an integer, we can use ":D3" to denote that
      // it should have leading zeroes and be 3 characters long
      // see https://learn.microsoft.com/en-us/dotnet/standard/base-types/how-to-pad-a-number-with-leading-zeros
      //
      // (age == 1 ? "" : "s") uses the ternary operator to 
      // decide the value used in the placeholder, the same 
      // as if it had been placed as an argument of string.Format
      //
      // finally, it shows that you can actually have quoted strings within strings
      // e.g. $"outer { "inner" } string"
      var s2 = $"{name} is {age:D3} year{(age == 1 ? "" : "s")} old.";
      Console.WriteLine(s2); 
   }
}
// The example displays the following output:
//       He asked, "Is your name Horace?", but didn't wait for a reply.
//       Horace is 034 years old.

示例代码

public class Person {
    public String firstName { get; set; }
    public String lastName { get; set; }
}

// Instantiate Person
var person = new Person { firstName = "Albert", lastName = "Einstein" };

// We can print fullname of the above person as follows
Console.WriteLine("Full-Name - " + person.firstName + " " + person.lastName);
Console.WriteLine("Full-Name - {0} {1}", person.firstName, person.lastName);
Console.WriteLine($"Full-Name - {person.firstName} {person.lastName}");

输出

Full-Name - Albert Einstein
Full-Name - Albert Einstein
Full-Name - Albert Einstein

它是插值字符串。可以在任何可以使用字符串字面量的地方使用插值字符串。当运行您的程序将使用插值字符串文字执行代码时，代码将通过计算插值表达式计算一个新的字符串文字。每次执行带有插值字符串的代码时都会进行此计算。

以下示例生成一个字符串值，其中所有字符串插值值都已计算完毕。它是最终结果，类型为string。所有出现的双大括号(“{{”和“}}”)都被转换为单个大括号。

string text = "World";
var message = $"Hello, {text}";

执行以上2行后，变量message包含“Hello, World”。

Console.WriteLine(message); // Prints Hello, World

参考资料- MSDN