In computing, regular expressions allows programmers to match complex patterns within text. I was fortunate to learn how to work with regular expressions when I was 20, in 2001 through the help of a perl programmer named Larry back in the day when I was working for qode.com.

A friend of mine asked me how he could match different parts of a url. He wanted the:
[1] the entire url
[2] the entire domain
[3] only the domain & tld.

This is what I came up with in PHP.

$string = 'http://www.thinkleandro.com/labels/politics.html';

$regExp =	"/";
$regExp.=	"(";	// Start of [1] Entire Url
$regExp.=	".*?://";	// Match Protocol (http://)
$regExp.=	"(";	// Start of [2] Entire Domain
$regExp.=	".*?";	// Match all subdomains (if any)
$regExp.=	"(";	// Start of [3]
$regExp.=	"[^.]*?";	// Match everything except for a period (domain name without sub domain)
$regExp.=	"..{3,6}?";	// Match (period) and 3-6 characters (domain tld
$regExp.=	")";	// End of [3]
$regExp.=	")";	// End of [2]
$regExp.=	"/.*";	// Match Everything after the domain (/...)
$regExp.=	")";	// End of [1]
$regExp.=	"/";

preg_match($regExp,$string,$matches);

print_r($matches);

Result:
Array
(
[0] => http://www.thinkleandro.com/labels/politics.html
[1] => http://www.thinkleandro.com/labels/politics.html
[2] => www.thinkleandro.com
[3] => thinkleandro.com
)

Labels: php, programming