1。在正则表达式中定义变量并调用：
using System;
using System.Text.RegularExpressions;
public class Test
{
public static void Main ()
{
// Define a regular expression for repeated words.
Regex rx = new Regex(@"\b(?<word>\w+)\s+(\k<word>)\b",
RegexOptions.Compiled | RegexOptions.IgnoreCase);
// Define a test string.
string text = "The the quick brown fox fox jumped over the lazy dog dog.";
// Find matches.
MatchCollection matches = rx.Matches(text);
// Report the number of matches found.
Console.WriteLine("{0} matches found.", matches.Count);
// Report on each match.
foreach (Match match in matches)
{
string word = match.Groups["word"].Value;
int index = match.Index;
Console.WriteLine("{0} repeated at position {1}", word, index);
}
}
}
其中?<word>定义了一个变量，之后的\k<word>调用自身定义的变量word。
2。好用的Regex.Replace 和Match.Result
这个例子实现输入的日期更改格式的功能，用正则表达式自动搜索字符串并替换，注意正则表达式中变量的使用。
public string MDYToDMY(string input)
{
return Regex.Replace(input,
"\\b(?<month>\\d{1,2})/(?<day>\\d{1,2})/(?<year>\\d{2,4})\\b",
"${day}-${month}-${year}");
}
Match.Result是返回一个可以带正则表达式中变量值的字符串。
public string Extension(string url)
{
Regex r = new Regex(@"^(?<proto>\w+)://[^/]+?(?<port>:\d+)?/",
RegexOptions.Compiled);
return r.Match(url).Result("${proto}${port}");
}
