Regular expression to find URLs not inside a hyperlink

Question

There's many regex's out there to match a URL. However, I'm trying to match URLs that do not appear anywhere within a <a> hyperlink tag (HREF, inner value, etc.). So NONE of the URLs in these should match:

<a href="http://www.example.com/">something</a>
<a href="http://www.example.com/">http://www.example2.com</a>
<a href="http://www.example.com/"><b>something</b>http://www.example.com/<span>test</span></a>

Any URL outside of <a></a> should be matched.

One approach I tried was to use a negative lookahead to see if the first <a> tag after the URL was an opening <a> or a closing </a>. If it is a closing </a> then the URL must be inside a hyperlink. I think this idea was okay, but the negative lookahead regex didn't work (or more accurately, the regex wasn't written correctly). Any tips are very appreciated.

Answer 1

I was looking for this answer as well and because nothing out there really worked like I wanted it too this is the regex that I created. Obviously since its a regex be aware that this is not a perfect solution.

/(?!<a[^>]*>[^<])(((([A-Za-z]{3,9}:(?:\/\/)?)(?:[-;:&=\+\$,\w]+@)?[A-Za-z0-9.-]+|(?:www.|[-;:&=\+\$,\w]+@)[A-Za-z0-9.-]+)((?:\/[\+~%\/.\w-_]*)?\??(?:[-\+=&;%@.\w_]*)#?(?:[\w]*))?))(?![^<]*<\/a>)/gi

And the whole function to update html is:

function linkifyWithRegex(input) {
  let html = input;
  let regx = /(?!<a[^>]*>[^<])(((([A-Za-z]{3,9}:(?:\/\/)?)(?:[-;:&=\+\$,\w]+@)?[A-Za-z0-9.-]+|(?:www.|[-;:&=\+\$,\w]+@)[A-Za-z0-9.-]+)((?:\/[\+~%\/.\w-_]*)?\??(?:[-\+=&;%@.\w_]*)#?(?:[\w]*))?))(?![^<]*<\/a>)/gi;
  html = html.replace(
    regx,
    function (match) {
      return '<a href="' + match + '">' + match + "</a>";
    }
  );
  return html;
}

Answer 2

You can do it in two steps instead of trying to come up with a single regular expression:

1. Blend out (replace with nothing) the HTML anchor part (the entire anchor tag: opening tag, content and closing tag).

2. Match the URL

In Perl it could be:

my $curLine = $_; #Do not change $_ if it is needed for something else.
$curLine =~ /<a[^<]+<\/a>//g; #Remove all of HTML anchor tag, "<a", "</a>" and everything in between.
if ( $curLine =~ /http:\/\//)
{
  print "Matched an URL outside a HTML anchor !: $_\n";
}