using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @" (?(DEFINE)
(?<unreserved>[a-z0-9_~\-]) # . is missing as it is used to separate labels
(?<sub_delims>[!$&'()*+,;=])
(?<encoded>%[A-F0-9]{2})
(?<reg_name>(?:(?&unreserved)|(?&sub_delims)|(?&encoded))*)
)
^(?:(?®_name)\.)*(?®_name)\.?$";
string input = @"_example.com";
RegexOptions options = RegexOptions.IgnoreCase | RegexOptions.IgnorePatternWhitespace;
Match m = Regex.Match(input, pattern, options);
Console.WriteLine("'{0}' found at index {1}", m.Value, m.Index);
}
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx