using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
        string fileLogs = @"[08:52:18] [ERROR] Ceci doit aparaitre 
[08:52:18] [WARN] Bonjour ";
        var result = Regex.Match(fileLogs, @"\[(.+)\] \[(.+)\] (.+)");

        Console.WriteLine(result);
	}
}