C# code to linkify urls in a string

It's a pretty simple task you can acheive it with Regex and a ready-to-go regular expression from:

• http://regexlib.com/

Something like:

var html = Regex.Replace(html, @"^(http|https|ftp)\://[a-zA-Z0-9\-\.]+" +                         "\.[a-zA-Z]{2,3}(:[a-zA-Z0-9]*)?/?" +                         "([a-zA-Z0-9\-\._\?\,\'/\\\+&%\$#\=~])*$",                         "<a href=\"$1\">$1</a>");

You may also be interested not only in creating links but in shortening URLs. Here is a good article on this subject:

• Resolve and shorten URLs in C#

See also:

• Regular Expression Workbench at MSDN
• Converting a URL into a Link in C# Using Regular Expressions
• Regex to find URL within text and make them as link
• Regex.Replace Method at MSDN
• The Problem With URLs by Jeff Atwood
• Parsing URLs with Regular Expressions and the Regex Object
• Format URLs in string to HTML Links in C#
• Automatically hyperlink URL and Email in ASP.NET Pages with C#

well, after a lot of research on this, and several attempts to fix times when

1. people enter in http://www.sitename.com and www.sitename.com in the same post
2. fixes to parenthisis like (http://www.sitename.com) and http://msdn.microsoft.com/en-us/library/aa752574(vs.85).aspx
3. long urls like: http://www.amazon.com/gp/product/b000ads62g/ref=s9_simz_gw_s3_p74_t1?pf_rd_m=atvpdkikx0der&pf_rd_s=center-2&pf_rd_r=04eezfszazqzs8xfm9yd&pf_rd_t=101&pf_rd_p=470938631&pf_rd_i=507846

we are now using this HtmlHelper extension... thought I would share and get any comments:

    private static Regex regExHttpLinks = new Regex(@"(?<=\()\b(https?://|www\.)[-A-Za-z0-9+&@#/%?=~_()|!:,.;]*[-A-Za-z0-9+&@#/%=~_()|](?=\))|(?<=(?<wrap>[=~|_#]))\b(https?://|www\.)[-A-Za-z0-9+&@#/%?=~_()|!:,.;]*[-A-Za-z0-9+&@#/%=~_()|](?=\k<wrap>)|\b(https?://|www\.)[-A-Za-z0-9+&@#/%?=~_()|!:,.;]*[-A-Za-z0-9+&@#/%=~_()|]", RegexOptions.Compiled | RegexOptions.IgnoreCase);    public static string Format(this HtmlHelper htmlHelper, string html)    {        if (string.IsNullOrEmpty(html))        {            return html;        }        html = htmlHelper.Encode(html);        html = html.Replace(Environment.NewLine, "<br />");        // replace periods on numeric values that appear to be valid domain names        var periodReplacement = "[[[replace:period]]]";        html = Regex.Replace(html, @"(?<=\d)\.(?=\d)", periodReplacement);        // create links for matches        var linkMatches = regExHttpLinks.Matches(html);        for (int i = 0; i < linkMatches.Count; i++)        {            var temp = linkMatches[i].ToString();            if (!temp.Contains("://"))            {                temp = "http://" + temp;            }            html = html.Replace(linkMatches[i].ToString(), String.Format("<a href=\"{0}\" title=\"{0}\">{1}</a>", temp.Replace(".", periodReplacement).ToLower(), linkMatches[i].ToString().Replace(".", periodReplacement)));        }        // Clear out period replacement        html = html.Replace(periodReplacement, ".");        return html;    }

protected string Linkify( string SearchText ) {    // this will find links like:    // http://www.mysite.com    // as well as any links with other characters directly in front of it like:    // href="http://www.mysite.com"    // you can then use your own logic to determine which links to linkify    Regex regx = new Regex( @"\b(((\S+)?)(@|mailto\:|(news|(ht|f)tp(s?))\://)\S+)\b", RegexOptions.IgnoreCase );    SearchText = SearchText.Replace( " ", " " );    MatchCollection matches = regx.Matches( SearchText );    foreach ( Match match in matches ) {        if ( match.Value.StartsWith( "http" ) ) { // if it starts with anything else then dont linkify -- may already be linked!            SearchText = SearchText.Replace( match.Value, "<a href='" + match.Value + "'>" + match.Value + "</a>" );        }    }    return SearchText;}