Match URL pattern in PHP using a regular expression

Use:

preg_match("/^((https|http|ftp)\:\/\/)?([a-z0-9A-Z]+\.[a-z0-9A-Z]+\.[a-z0-9A-Z]+\.[a-zA-Z]{2,4}|[a-z0-9A-Z]+\.[a-z0-9A-Z]+\.[a-zA-Z]{2,4}|[a-z0-9A-Z]+\.[a-zA-Z]{2,4})$/i", $url)

I looked around and didn't see any that were exactly what I needed. I found this one that was close, so I modified it as follows:

^((([hH][tT][tT][pP][sS]?)\:\/\/)?([\w\\-]+(\[\w\.\&%\$\-]+)*)?((([^\s\(\)\<\>\\\"\.\   [\]\,;:]+)(\.[^\s\(\)\<\>\\\"\.\[\]\,;:]+)*(\.[a-zA-Z]{2,4}))|((([01]?\d{1,2}|2[0-4]\d|25[0-5])\.){3}([01]?\d{1,2}|2[0-4]\d|25[0-5])))(\b\:(6553[0-5]|655[0-2]\d|65[0-4]\d{2}|6[0-4]\d{3}|[1-5]\d{4}|[1-9]\d{0,3}|0)\b)?((\/[^\/][\w\.\,\?\'\\\/\+&%\$#\=~_\-]*)*[^\.\,\?\"\'\(\)\[\]!;<>{}\s\x7F-\xFF])?)$

Check it out on debuggex.

I'd use a different regex to be honest. Like this one that Gruber posted in 2009:

\b(([\w-]+://?|www[.])[^\s()<>]+(?:\([\w\d]+\)|([^[:punct:]\s]|/)))

Or this updated version that Gruber posted in 2010 (thanks, @IMSoP):

(?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`!()\[\]{};:'".,<>?«»“”‘’]))

A complete working example using Nev Stokes' given link:

public function clickableUrls($html){
    return $result = preg_replace(
        '%\b(([\w-]+://?|www[.])[^\s()<>]+(?:\([\w\d]+\)|([^[:punct:]\s]|/)))%s',
        '<a href="$1">$1</a>',
        $html
    );
}