URL handling is one of the tasks you have to do from time to time in PHP. Sometimes you have to do it because you want to record the referral sites, other times because you want to write your own spider or just because you want to retrieve your current URL.
PHP is a language developed around web for web developers and it contains all the functions you might need in your quests. There is a section in php documentation which groups the URL functions. Along with a few functions used to encode/decode which are rarely used the package contains the functions you can not live without: