Code to parse user agent string?
The get_browser() function has been available in PHP for quite a long a time.
The PHP manual is free, can be downloaded in various formats and viewed online (with comments)
https://github.com/browscap/browscap-php - this is a standalone library that aims to replace get_browser function. For shared hostings it seems to be a better option.
Works on: PHP 5
You can try to use: https://github.com/tobie/ua-parser. This is multi-language tool to parsing user agent string. For PHP is here: https://github.com/tobie/ua-parser/tree/master/php