Csharp/C Sharp by API/System.Text.RegularExpressions/RegexOptions

RegexOptions.IgnoreCase

  
using System;
using System.Text.RegularExpressions;
using System.IO;
using System.Text;
public class HTMLParser {
    public static void Main(String[] args) {
        FileInfo MyFile = new FileInfo(args[0].ToString());
        if (MyFile.Exists) {
            StreamReader sr = MyFile.OpenText();
            string text = sr.ReadToEnd();
            sr.Close();
            string pattern = @"<a\shref\S*/a>";
            MatchCollection patternMatches = Regex.Matches(text, pattern,
              RegexOptions.IgnoreCase);
            foreach (Match nextMatch in patternMatches) {
                Console.WriteLine(nextMatch.ToString());
            }
        } else
            Console.WriteLine("The input file does not exist");
    }
}

RegexOptions.Multiline

 
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Text;
using System.Text.RegularExpressions;
using System.Reflection;
public class MainClass{
   public static void Main(){
        Regex r = new Regex(@"(^\d+$\n)+", RegexOptions.Multiline);
        Console.WriteLine(r.Match("987987\n129821").Value);
   }
}