Regex to match www.example.com only if http:// not present

Question

I have the following regex that isn't working. I want to match the string 'www.example.com' but not the string 'http://www.example.com' (or 'anythingwww.example.com' for that matter):

/\bwww\.\w.\w/ig

This is used in JavaScript like this:

text = text.replace(/\bwww\.\w.\w/ig, 'http://$&');

I know the second part of the regex doesn't work correctly either, but it is the http:// part that is confusing me. It will currently match 'http://www.example.com' resulting in output of 'http://htpp://www.example.com'.

Answer 1

Does this do what you want? The anchor ensures the text starts with www. But obviously this will fail with other subdomains.

text = text.replace(/^www\.\w+\.\w+$/ig, "http://$&");

EDIT: Fixed thanks to Chris Lutz's comment. I did test earlier, but a strange combo of bugs (missing anchor, unescaped dot, etc.) made it seemingly work. I should reiterate that this is fragile anyway.

Answer 2

You can use the ^ indicator (anchor) to require the text to match to start with www:

echo -e "http://www.example.com\nanythingwww.example.com\nwww.example.com" | grep "^www.example.com"
www.example.com

Answer 3

Are you searching for the occurrence of www.example.com in a larger string? Maybe you can be more specific about what you want to match exactly, but something like this may work for you:

text = text.replace(/(\s)(www\.\w+\.\w+)/ig, "$1http://$2");

The problem with \b (which matches word boundaries) is that it also matches between http:// and www, because / is not a word character.

Answer 4

Perhaps something like this?

text = text.replace(/(^|\s)(www(?:\.\w+){2,})/ig, "$1http://$2");

This will match the URLs in:

• "www.example.com" -> "http://www.example.com"
• "Visit www.example.com" -> "Visit http://www.exmaple.com"
• "Visit www.example.co.uk" -> "Visit http://www.example.co.uk"

But not:

• "http://www.example.com"
• "ftp.example.com"
• "www.com"