Converting URLs Into Links With Regex

Following on from the recent spate of extensions methods I've posted, here's another I use to convert URLs and email addresses into links within HTML. You may want to restrict users from submitting HTML tags via forms in your application, which means that URLs and email addresses that they submit appear as plain text unless they are subjected to some kind of processing.


/// <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.

 

Date Posted:
Last Updated:
Posted by:
Total Views to date: 11223

1 Comment

- Tvrtko

Hello Mike,
this works great, however, part with email link will duplicate anchor tag. For http urls you did ignore existing html anchors from match correctly , but for email they get matched even if they have html anchor around already.
Add your comment

If you have any comments to make about this article, please use this form to do so. Make sure that your comment relates specifically to the article above. More general comments can be posted through the form on the Contact page.

Please note, all comments are moderated, and I end up deleting quite a lot. The kind of things that will ensure your comment is deleted without ever seeing the light of day are as follows:

  • Requests to fix your code (post a question to forums.asp.net instead, please)
  • Gratuitous links to your own site or product
  • Anything abusive or libellous
  • Spam

I do not pass email addresses on to spammers, so a valid one will assist me in responding to you personally if required.

Recent Comments

Lorenzo 3/26/2015 8:21 AM
In response to iTextSharp - Introducing Tables
Hi Mike How can I add padding to all cells in the table? Kind Regards Lorenzo...

Satyabrata Mohapatra 3/25/2015 8:11 AM
In response to How To Send Email In ASP.NET MVC
Great article. Simple and up to the point....

Afzaal Ahmad Zeeshan 3/24/2015 8:17 PM
In response to How To Send Email In ASP.NET MVC
A great way to teach the MVC framework for sending the emails... Also, what I found helpful was the...

Jim H 3/24/2015 2:32 PM
In response to Migrating From Razor Web Pages To ASP.NET MVC 5 - Model Binding And Forms
Thank you. This helps....

wazz 3/22/2015 5:48 AM
In response to Posting Data With jQuery AJAX In ASP.NET Razor Web Pages
great info!!...

rael 3/21/2015 8:53 PM
In response to Getting the identity of the most recently added record
I spent hours trying to figure how to achieve this in C#. This article helped me. Thanks a lot...

Stephen 3/21/2015 8:48 PM
In response to Ajax with Classic ASP using jQuery
This was very helpful, thanks:)...

patrick voes 3/19/2015 10:19 AM
In response to iTextSharp - Introducing Tables
Thank you! very helpfull....

Bigmachini 3/19/2015 6:13 AM
In response to ASP.NET MVC DropDownLists - Multiple Selection and Enum Support
This just made my day, afternoon, evening, night... was looking for a way of doing this without to a...

Bobbyg 3/19/2015 4:14 AM
In response to HTML Helpers For Forms In Razor Web Pages
Nice article. There are bugs in MVC 5 with dropdowns retaining values from other screens and them. I...