Regular Expression application: Analyze and query strings

As an analysis technology, regular expressions can be used in many places, and most basic expressions may be used by everyone. Here, we will explain the regular expression through a series of simple examples. How to analyze the required data for a given address, for example, the following URL, the basic idea of analyzing each query string is: 1 first get it? The following part, 2, then split according to & and =, and get first? The following part matches the regular expression of the query string :\? (? <Querystring> ([^ &] + &?) +), The regular expression for removing the naming part is :\? ([^ &] + &?) + Matched '? Word = test & tn = sitehao123 & ie = UTF-8 \? ([^ &] + &?) + Description :\? Indicates already? Because? The regular expression has special meanings, so a slash \ escape is required. [^ &] + Indicates that the matching is not any or multiple characters &? Indicates that & appears once or does not appear \? ([^ &] + &?) + The overall meaning is that 1 matches? The first 2 2.1 matches are not & multiple characters 2.2 matches & one or no 2.3 repeats 2.1, 2.2 times or multiple times 3 ([^ &] + &?) +) If some matched characters are named querystring, the regular expression is changed :\? (? <Querystring> ([^ &] + &?) +) 2. Then, the regular expression of the query string based on & and = is :((? <Key> [^ & =] +) = (? <Value> [^ & =] +) +, removes the regular expression of the naming part as :( ([^ & =] +) = ([^ & =] + )) + [^ & =] + indicates that the match is not any or multiple characters ([^ & =] +) = ([^ & =] + )) + The overall meaning is that 1 matching is not any or multiple characters, 2 matching equal signs = 3 matching is not any or multiple characters, 4 repeating more than 1, 2, 3. Name the matching character 1 as the key, and the matching character 3 as the value. Then, the regular expression is changed ((? <Key> [^ & =] +) = (? <Value> [^ & =] +) + the test code is as follows:

private static void Test()         {            string url = "http://www.baidu.com/s?word=test&tn=sitehao123&ie=utf-8";              Regex reg = new Regex(@"\?(?<querystring>([^&]+&?)+)");                        Match m =  reg.Match(url);              string querystring = m.Groups["querystring"].Value;              Regex reg2 = new Regex(@"((?<key>[^&=]+)=(?<value>[^&=]+))+");              Dictionary<string, string> querystringKeyValue = new Dictionary<string, string>();              foreach (Match item in reg2.Matches(querystring))            {                           querystringKeyValue.Add(item.Groups["key"].Value, item.Groups["value"].Value);                         }                }