C# code to linkify urls in a string

Question

Hello,

Does anyone have any good c# code that will parse a string and "linkify" any urls that may be in the string?

Answer 1

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#

Answer 2

It's not that easy as you can read in this blog post by Jeff Atwood. It's especially hard to detect where an URL ends.

For example, is the trailing parenthesis part of the URL or not:

• http://en.wikipedia.org/wiki/PCTools(CentralPointSoftware)
• an URL in parentheses (http://en.wikipedia.org) more text

In the first case, the parentheses are part of the URL. In the second case they are not!

Answer 3

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;
}

Answer 4

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;
    }