Question

In my code behind in C# I have the following code. How do I change the replace so that only
the first occurance of www is replaced?
For example if the User enters http://www.testwww.com then I should be saving it as testwww.com.
Currently as per the below code it saves as http://www.com (guess due to substr code).
Please help. Thanks in advance.

private string FilterUrl(string url)
    {
        string lowerCaseUrl = url.ToLower();
        lowerCaseUrl = lowerCaseUrl.Replace("http://", string.Empty).Replace("https://", string.Empty).Replace("ftp://", string.Empty);
        lowerCaseUrl = lowerCaseUrl.Replace("www.", string.Empty);

        string lCaseUrl = url.Substring(url.Length - lowerCaseUrl.Length, lowerCaseUrl.Length);
        return lCaseUrl; 
    }

Answer 1

As Ally suggested. You are much better off using System.Uri. This also replaces the leading www as you wish.

private string FilterUrl(string url)
{
    Uri uri = new UriBuilder(url).Uri; // defaults to http:// if missing
    return Regex.Replace(uri.Host, "^www.", "") + uri.PathAndQuery;
}

Edit: The trailing slash is because of the PathAndQuery property. If there was no path you are left with the slash only. Just add another regex replace or string replace. Here’s the regex way.

return Regex.Replace(uri.Host, "^www.", "") + Regex.Replace(uri.PathAndQuery, "/$", "");