Converting URLs Into Links With Regex

4.5 (14 votes)

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.

 

You might also like...

Date Posted:
Last Updated:
Posted by:
Total Views to date: 14669

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.

Recent Comments

Gfw 03/02/2017 09:48
In response to Free SSL Certificates On IIS With LetsEncrypt
I have used WinSimple for about the last 9 months - works great. One thing that you want to make of...

Ted Driver 02/02/2017 13:24
In response to Free SSL Certificates On IIS With LetsEncrypt
This looks great is you have command line access to your web server - what about those of us on Is...

Carl T. 06/11/2016 05:43
In response to Server.MapPath Equivalent in ASP.NET Core
Very succinct and easy to follow. Worked perfectly the first time for me. Thanks!!...

Manoj Kulkarni 04/11/2016 05:47
In response to Entity Framework Core DbContext Updated
Great post....

Sivu 19/10/2016 08:21
In response to Entity Framework Core TrackGraph For Disconnected Data
Oh that's very very very nice ! Thanks for the write up Mike, much appreciated for the taking the to...

Mark 12/10/2016 16:42
In response to ASP.NET Web Pages vNext or Razor Pages
Although "Web Pages" was removed from the roadmap, has it just been renamed to "Razor Pages"?...

Satyabrata 12/10/2016 09:20
In response to Entity Framework Core TrackGraph For Disconnected Data
Nice article. Please write more articles featuring ASP.Net web pages. Thank you...

Julian 26/09/2016 14:27
In response to Loading ASP.NET Core MVC Views From A Database Or Other Location
Fantastic, many thanks Mike! Had got half way down this road before finding your article - saved...

Abolfazl Roshanzamir 14/09/2016 05:36
In response to Loading ASP.NET Core MVC Views From A Database Or Other Location
Nice article. Thanke you so much ....

cyrus 02/09/2016 15:12
In response to ASP.NET Web Pages vNext or Razor Pages
I've got some news. As Damian stated in this link: https://github.com/aspnet/Mvc/issues/5208 “We...