using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

​

        var pattern = @"\b" +"开99889aaa";

        var existing = "开99889aaa银行开曼分行";

        var match = Regex.Match(existing, pattern);

        Console.WriteLine(match.Success);

         pattern = @"\b" +"99889aaa";

         existing = "开99889aaa银行开曼分行";

         match = Regex.Match(existing, pattern);

        Console.WriteLine(match.Success);

         pattern = @"\b" +"开99889aaa";

         existing = "...开99889aaa银行开曼分行";

         match = Regex.Match(existing, pattern);

        Console.WriteLine(match.Success);

                 pattern = @"\b" +"开99889aaa";

         existing = "שדגע...开99889aaa银行开曼分行";

         match = Regex.Match(existing, pattern);

        Console.WriteLine(match.Success);

    }

}