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Converting URLs Into Links With Regex

/// <summary>
/// Finds web and email addresses in a string and surrounds then with the appropriate HTML anchor tags 
/// </summary>
/// <param name="s"></param>
/// <returns>String</returns>
public static string WithActiveLinks(this string s)
{
  //Finds URLs with no protocol
  var urlregex = new Regex(@"\b\({0,1}(?<url>(www|ftp)\.[^ ,""\s<)]*)\b", 
    RegexOptions.IgnoreCase | RegexOptions.Compiled);
  //Finds URLs with a protocol
  var httpurlregex = new Regex(@"\b\({0,1}(?<url>[^>](http://www\.|http://|https://|ftp://)[^,""\s<)]*)\b", 
    RegexOptions.IgnoreCase | RegexOptions.Compiled);
  //Finds email addresses
  var emailregex = new Regex(@"\b(?<mail>[a-zA-Z_0-9.-]+\@[a-zA-Z_0-9.-]+\.\w+)\b", 
    RegexOptions.IgnoreCase | RegexOptions.Compiled);
  s = urlregex.Replace(s, " <a href=\"http://${url}\" target=\"_blank\">${url}</a>");
  s = httpurlregex.Replace(s, " <a href=\"${url}\" target=\"_blank\">${url}</a>");
  s = emailregex.Replace(s, "<a href=\"mailto:${mail}\">${mail}</a>");
  return s;
}

This will convert most URLs, but not all. Parsing URLs is not the easiest thing to do so you need to make a judgement on what type of URLs your users/visitors are most likely to provide and alter the regex patterns accordingly. One thing to point out is that the second pattern (the one that matches URLs with a protocol - http, https etc) also checks to make sure that it isn't already a hyperlink. By the time the second Replace() operations takes place, URLs without protocols will already be fitted with them, and have HTML surrounding them.

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Date Posted: 22 May 2010 22:56
Last Updated:
Posted by: Mikesdotnetting
Total Views to date: 2926