using System.Text.RegularExpressions;
public static void Main()
string[] lines = new string[] { "2015-03-08 10:30:00 /user841/column-width",
"2015-03-08 10:30:01 /user849/connect",
"2015-03-08 10:30:01 /user262/open-level2-price",
"2015-03-08 10:30:01 /user839/open-detailed-quotes"
string pattern = @"(.*/.*/)(.*)";
string replacement = "$2";
foreach(var line in lines)
Console.WriteLine(Regex.Replace(line, pattern, replacement));
