using System;
using System.Text.RegularExpressions;
 
public class Test
{
    public static void Main()
    {
        string pattern = @"(?m)\r?\n^(?!""2018)";
        string substitution = @"";
        string input = @"""2018-02-22 10:06:10,857"",""[7]"","" ERROR"",""MyApp.Web.Infrastructure.ErrorResponseCommand"",""ErrorResponseCMD logs Controller: webinar | Action: Index"",""""
""2018-02-22 10:06:37,742"",""[11]"","" INFO "",""MyApp.Web.MvcApplication"",""Anon Session Starts with: {""""FirstPage"""": """"https://w...content-available-to-author-only...s.com/wp-login.php"""", """"QueryString"""": """""""", """"SessionId"""": """"uhnev2dnds33dastwrdgftvm"""", """"FirstCookies"""": {""""CookieName"""": """"ASP.NET_SessionId"""", """"Value"""": """"uhnev2dnds33dastwrdgftvm""""}}"",""""
""2018-02-22 10:06:48,053"",""[11]"","" INFO "",""MyApp.Web.Controllers.CartController"",""SessionInfo{
  """"FirstPage"""": null,
  """"RemoteAddress"""": """"207.46.13.159"""",
  """"RemoteHost"""": """"207.46.13.159"""",
  """"RemoteUser"""": """""""",
RelativeConfirmPasswordResetUrl:Account/PasswordResetConfirm
//and other non-predictable BOL patterns.
},""""
""2018-02-22 10:06:10,857"",""[7]"","" ERROR"",""MyApp.Web.Infrastructure.ErrorResponseCommand"",""ErrorResponseCMD logs Controller: webinar | Action: Index"",""""
";
        Regex regex = new Regex(pattern);
        string result = regex.Replace(input, substitution);
        Console.WriteLine(result);
    }
}