Question

I need a working Regex code in C# that detects plain text urls (http/https/ftp/ftps) in a string and make them clickable by putting an anchor tag around it with same url. I have already made a Regex pattern and the code is attached below.

However, if there is already any clickable url is present in the input string then the above code puts another anchor tag over it. For example the existing substring in the below code: string sContent: “ftp://www.abc.com’>ftp://www.abc.com” has another anchor tag over it when the code below is run. Is there any way to fix it?

        string sContent = "ttt <a href='ftp://www.abc.com'>ftp://www.abc.com</a> abc ftp://www.abc.com abbbbb http://www.abc2.com";

        Regex regx = new Regex("(http|https|ftp|ftps)://([\\w+?\\.\\w+])+([a-zA-Z0-9\\~\\!\\@\\#\\$\\%\\^\\&amp;\\*\\(\\)_\\-\\=\\+\\\\\\/\\?\\.\\:\\;\\'\\,]*)?", RegexOptions.IgnoreCase);

        MatchCollection mactches = regx.Matches(sContent);

        foreach (Match match in mactches)
        {
            sContent = sContent.Replace(match.Value, "<a href='" + match.Value + "'>" + match.Value + "</a>");
        }

Also, I want a Regex code to make emails as clickable with “mailto” tag. I can do it myself but the above mentioned issue of double anchor tag will also appear in it.

Answer 1

I noticed in your example test string that if a duplicate link e.g. ftp://www.abc.com is in the string and is already linked then the result will be to double anchor that link. The Regular Expression that you already have and that @stema has supplied will work, but you need to approach how you replace the matches in the sContent variable differently.

The following code example should give you what you want:

string sContent = "ttt <a href='ftp://www.abc.com'>ftp://www.abc.com</a> abc ftp://www.abc.com abbbbb http://www.abc2.com";

Regex regx = new Regex("(?<!(?:href='|<a[^>]*>))(http|https|ftp|ftps)://([\\w+?\\.\\w+])+([a-zA-Z0-9\\~\\!\\@\\#\\$\\%\\^\\&amp;\\*\\(\\)_\\-\\=\\+\\\\\\/\\?\\.\\:\\;\\'\\,]*)?", RegexOptions.IgnoreCase);

MatchCollection matches = regx.Matches(sContent);

for (int i = matches.Count - 1; i >= 0 ; i--)
{
    string newURL = "<a href='" + matches[i].Value + "'>" + matches[i].Value + "</a>";

   sContent = sContent.Remove(matches[i].Index, matches[i].Length).Insert(matches[i].Index, newURL);
}