changing www*.com to a clickable URL with REGEX - php

Question

I'm working on a web page and regex keeps coming up as the best way to handle string manipulation for an issue I'm trying to resolve. Unfortunately, regex is not exactly trivial and I've been having trouble. Any help is appreciated;
I would like to make strings entered from a php form into clickable links. I've received help with my first challenge; how to make strings starting with http, https or ftp into clickable links;
function make_links_clickable($message){
return preg_replace('!(((f|ht)tp(s)?://)[-a-zA-Zа-яА-Я()0-9#:%_+.~#?&;//=]+)!i', '$1', $message);
}
$message = make_links_clickable($message);
And this works well. When I look at it (and do some research), the best that I can glean from the syntax is that the first piece is matching ftp, http, and https, :, and // along with a wide range of combined patterns. I would like to know how I can;
1) Make links starting with www, or ending with .com/.net/.org/etc clickable (like google.com, or www.google.com - leaving out the http://)
2) Change youtube links like
"https://www.youtube.com/watch?v=examplevideo"
into
"<iframe width="560" height="315" src="//www.youtube.com/embed/examplevideo" frameborder="0" allowfullscreen></iframe>"
I think these two cases are basically doing the same kind of thing, but figuring out is not intuitive. Any help would be deeply appreciated.

Answer 1

The first regular expression there is made to match almost everything that follows ftp://, http://, https:// that occurs, so it might be best to implement the others as separate expressions since they'll only be matching hostnames.
For number 1, you'll need to decide how strictly you wish to match different TLDs (.com/.net/etc). For example, you can explicitly match them like this:
(www\.)?[a-z0-9\-]+\.(com|net|org)
However, that will only match URLs that end in .com, .net, or .org. If you want all top-level domains and only the valid ones, you'll need to manually write them all in to the end of that. Alternatively, you can do something like this,
(www\.)?[a-z0-9\-]+\.[a-z]{2,6}
which will accept anything that looks like a url and ends with "dot", and any combination of 2 to 6 letters (.museum and .travel). However, this will match strings like "fgs.fds". Depending on your application, you may need to add more characters to [a-z], to add support for extended character alphabets.
Edit (2 Aug 14): As pointed out in the comments below, this won't match TLDs like .co.uk. Here's one that will:
(www\.)?[a-z0-9\-]+\.([a-z]{2,3}(\.?[a-z]{2,3})?)
Instead of any string between two and six characters (following a period), this will match any two to three, then another one to three (if present), with or without a dividing period.
It'd be redundant, but you could instead remove the question mark after www on the second option, then do both tests; that way, you can match any string ending in a common TLD, or a string that begins with "www." and is followed by any characters with one period separating them, "gpspps.cobg". It would still match sites that might not actually exist, but at least it looks like a url, at it would look like one.
For the YouTube one, I went a little question mark crazy.
(?i:(?:(?:http(?:s)?://)?(?:www\.)?)?youtu(?:\.be/|be\.com/watch\?(?:[a-z0-9_\-\%\&\=]){0,}?v\=))([a-zA-Z0-9_\-]{11}){0,}?v\=))(?i)([a-zA-Z0-9_\-]{11})
EDIT: I just tried to use the above regex in one of my own projects, but I encountered some errors with it. I changed it a little and I think this version may be better:
(?i:(?:(?:http(?:s)?://)?(?:www\.)?)?youtu(?:\.be/|be\.com/watch\?(?:[a-z0-9_\-\%\&\=]){0,})?)(?:v=)?([a-zA-Z0-9_\-]{11})
For those not familiar with regular expressions, parentheses , ( ...regex... ), are stored as groups, which can be selectively picked out of matched strings. Parenthesis groups that begin with ?: as in most of the ones up there, (?:www\.) are however not captured within the groups. Because the end of that regex was left as a normal—"captured"—group, ([a-zA-Z0-9_\-]{11}), you use the $matches argument of functions like preg_match, then you can use $matches[1] to get the YouTube ID of the video, 'examplevide', then work with it however you'd like. Also note, the regex is only matching 11 characters for the ID.
This regex will match pretty much any of the current youtube url formats including incorrect cases, and out of (normal) order parameters:
http://youtu.be/dQw4w9WgXcQ
https://www.youtube.com/watch?v=dQw4w9WgXcQ
http://www.youtube.com/watch?v=dQw4w9WgXcQ&feature=featured
http://www.youtube.com/watch?feature=featured&v=dQw4w9WgXcQ
http://WWW.YouTube.Com/watch?v=dQw4w9WgXcQ
http://YouTube.Com/watch?v=dQw4w9WgXcQ
www.youtube.com/watch?v=dQw4w9WgXcQ