Question

I am trying to write a RegEx rule to find all a href HTML links on my webpage and add a ‘rel=”nofollow”‘ to them.

However, I have a list of URLs that must be excluded (for exmaple, ANY (wildcards) internal link (eg. pokerdiy.com) – so that any internal link that has my domain name in is excluded from this. I want to be able to specify exact URLs in the exclude list too – for example – http://www.example.com/link.aspx)

Here is what I have so far which is not working:

(]+)(href=”http://.*?(?!(pokerdiy))[^>]+>)

If you need more background/info you can see the full thread and requirements here (skip the top part to get to the meat):
http://www.snapsis.com/Support/tabid/601/aff/9/aft/13117/afv/topic/afpgj/1/Default.aspx#14737

Answer 1

(<a href="https?://)((?:(?!\b(pokerdiy.com|www\.example\.com/link\.aspx)\b)[^"])+)"

would match the first part of any link that starts with http:// or https:// and doesn’t contain pokerdiy.com or www.example.com/link.aspx anywhere in the href attribute. Replace that by

\1\2" rel="nofollow"

If a rel="nofollow" is already present, you’ll end up with two of these. And of course, relative links or other protocols like ftp:// etc. won’t be matched at all.

Explanation:

(?!\b(foo|bar)\b)[^"] matches any non-" character unless it it possible to match foo or bar at the current location. The \bs are there to make sure we don’t accidentally trigger on rebar or foonly.

This whole contruct is repeated ((?: ... )+), and whatever is matched is preserved in backreference \2.

Since the next token to be matched is a ", the entire regex fails if the attribute contains foo or bar anywhere.