正则表达式匹配有关问题_ASP.NET

正则表达式匹配问题
例如<a href="xw_read123"></a>
现在要把他变成<a href="xw_read123"></a>,前面连接的xw_read是不变的，只有后面的数字会变，现在就是把带有xw_read的链接后面加个

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C# code

string tempStr = @"<a href=""xw_read129""></a>";                string pattern = @"(?i)(?<=<a[^>]*?href=(['""]?)[^'""]*?xw_read[^'""]*)(?=(['""]?)>)";                string result = Regex.Replace(tempStr, pattern, "");//<a href=\"xw_read123\"></a>
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C# codehtml=Regex.Replace(html,@"(?i)(?<=<a\b[^>]*?href=(['""]?)xw_read\d+)(?=\1[^>]*?>[^<>]*</a>","");
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C# code        private string ReplaceStr(Match m)        {            return m.Value+"";        }        private void button10_Click(object sender, EventArgs e)        {            StreamReader reader = new StreamReader("c:\\1.txt");            string source = reader.ReadToEnd();            Regex reg = new Regex(@"(?is)(?<=<a\s?href[^>].*?)xw_read[\d]+");            source = reg.Replace(source, ReplaceStr);        }
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C# code            string str = "<a href=\"xwread/xw_read1213\"></a>";            string result = Regex.Replace(str, @"(?is)(?<=<a[^>]*?href=(['""\s]?).*?xw_read\d+)(?=\1)", "");            Console.WriteLine(result);