using (StreamReader sr = new StreamReader(@"D:\1.txt"))            {                string s = sr.ReadToEnd();                //开始字符串                 string s1 = textBox1.Text;                //结束字符串                 string s2 = textBox2.Text;               // Regex rg = new Regex("(?<=(" + s1 + "))[.\\s\\S]*?(?=(" + s2 + "))", RegexOptions.Multiline | RegexOptions.Singleline);                                  Regex rg = new Regex("(?<=(" + s1 + "))[^("+s1+")]*?(?=(" + s2 + "))", RegexOptions.Multiline | RegexOptions.Singleline);                // 避免s1xxxs1xxxs2这类bug                 foreach (var m in rg.Matches(s))                {                    StreamWriter sw = new StreamWriter(@"D:\2.txt", true);                    sw.WriteLine(m.ToString());                    sw.Close();                }