Replace QueryString value using regular expressions

Question

In C#, I'm trying to use regular expressions to replace values in a querystring. So, if I have:

http://www.url.com/page.aspx?id=1

I'd like to write a function where I pass in the url, the querystring value and the value to replace. Something along the lines of:

string url = "http://www.url.com/page.aspx?id=1";
string newURL = ReplaceQueryStringValue(url, "id", "2");

private string ReplaceQueryStringValue(string url, string replaceWhat, string replaceWith)
{
    return Regex.Replace(url, "[^?]+(?:\?"+replaceWhat+"=([^&]+).*)?",replaceWith);
}

Answer 1

It might be easier to use String.Split to initially cut the URL into page and query string parts, and then use Split.String again to cut the query string into distinct parts.

var urlSplit = url.Split('?');
var originalURL = urlSplit[0];

var urlRedefined = url;   
if(urlSplit.Length == 2)
{
  var queryString = urlSplit[1].Split('&');

  //your code here

  var urlRedefined = String.Format("{0}?{1}", 
    originalURL, 
    String.Join("&", queryString);
}

A regular expression may be overkill for your needs. Also, the System.Uri class might be a better fit. Its use is covered in http://stackoverflow.com/questions/1029909/url-split-in-c.

Answer 2

Here is a function that would do the job:

static string replace(string url, string key, string value)
{
    return Regex.Replace(
     url, 
     @"([?&]" + key + ")=[^?&]+", 
     "$1=" + value);
}