Fastest way to find strings in a file

Question

I have a log file that is not more than 10KB (File size can go up to 2 MB max) and I want to find if atleast one group of these strings occurs in the files. These strings w

Answer 1

This code sample searches for strings in a large text file. The words are contained in a HashSet. It writes the found lines in a temp file.

        if (File.Exists(@"temp.txt")) File.Delete(@"temp.txt");

        String line;
        String oldLine = "";
        using (var fs = File.OpenRead(largeFileName))
        using (var sr = new StreamReader(fs, Encoding.UTF8, true))
        {
            HashSet hash = new HashSet();
            hash.Add("house");
            using (var sw = new StreamWriter(@"temp.txt"))
            {
                while ((line = sr.ReadLine()) != null)
                {
                    foreach (String str in hash)
                    {
                        if (oldLine.Contains(str))
                        {
                            sw.WriteLine(oldLine); 
                            // write the next line as well (optional)
                            sw.WriteLine(line + "\r\n");                                    
                        }
                    }
                    oldLine = line;
                }
            }
        }