Extract URL from string

I'm trying to find a reliable solution to extract a url from a string of characters. I have a site where users answer questions and in the source box, where they enter their source of information, I allow them to enter a url. I want to extract that url and make it a hyperlink. Similar to how Yahoo Answers does it.

Does anyone know a reliable solution that can do this?

All the solutions I have found work for some URL's but not for others.

Thanks

Solution 1:

John Gruber has spent a fair amount of time perfecting the "one regex to rule them all" for link detection. Using preg_replace() as mentioned in the other answers, using the following regex should be one of the most accurate, if not the most accurate, method for detecting a link:

(?i)\b((?:[a-z][\w-]+:(?:/{1,3}|[a-z0-9%])|www\d{0,3}[.]|[a-z0-9.\-]+[.][a-z]{2,4}/)(?:[^\s()<>]+|\(([^\s()<>]+|(\([^\s()<>]+\)))*\))+(?:\(([^\s()<>]+|(\([^\s()<>]+\)))*\)|[^\s`!()\[\]{};:'".,<>?«»“”‘’]))

If you only wanted to match HTTP/HTTPS:

(?i)\b((?:https?://|www\d{0,3}[.]|[a-z0-9.\-]+[.][a-z]{2,4}/)(?:[^\s()<>]+|\(([^\s()<>]+|(\([^\s()<>]+\)))*\))+(?:\(([^\s()<>]+|(\([^\s()<>]+\)))*\)|[^\s`!()\[\]{};:'".,<>?«»“”‘’]))

Solution 2:

$string = preg_replace('/https?:\/\/[^\s"<>]+/', '<a href="$0" target="_blank">$0</a>', $string);

It only matches http/https, but that's really the only protocol you want to turn into a link. If you want others, you can change it like this:

$string = preg_replace('/(https?|ssh|ftp):\/\/[^\s"]+/', '<a href="$0" target="_blank">$0</a>', $string);