Reverse : Regular Expression « Regular Expression « C# / CSharp Tutorial

1. C# / CSharp Tutorial
2. Regular Expression
3. Regular Expression

using System;
using System.Text;
using System.Text.RegularExpressions;

public class MainClass
{
    static void Main( string[] args ) {
        // Create regex to search for IP address pattern.
        string pattern = @"(?<part1>[01]?\d\d?|2[0-4]\d|25[0-5])\." +
                         @"(?<part2>[01]?\d\d?|2[0-4]\d|25[0-5])\." +
                         @"(?<part3>[01]?\d\d?|2[0-4]\d|25[0-5])\." +
                         @"(?<part4>[01]?\d\d?|2[0-4]\d|25[0-5])";
        Regex regex = new Regex( pattern );
        Match match = regex.Match( "192.168.123.1" );

        string replace = @"${part4}.${part3}.${part2}.${part1}" +
                         @" (the reverse of $&)";
        Console.WriteLine( regex.Replace("192.168.123.1", replace) );
    }
}

1.123.168.192 (the reverse of 192.168.123.1)