初识正则表达式

 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();

                }