PHP can be used in three primary ways:
In this book, we'll concentrate on the first item, using PHP to develop dynamic web content.
PHP runs on all major operating systems, from Unix variants including Linux, FreeBSD, and Solaris to such diverse platforms as Windows and Mac OS X. It can be used with all leading web servers, including Apache, Microsoft IIS, and the Netscape/iPlanet servers.
The language is very flexible. For example, you aren't limited to outputting just HTML or other text files any document format can be generated. PHP has built-in support for generating PDF files, GIF, JPG, and PNG images, and Flash movies.
One of PHP's most significant features is its wide-ranging support for databases. PHP supports all major databases (including MySQL, PostgreSQL, Oracle, Sybase, and ODBC-compliant databases), and even many obscure ones. With PHP, creating web pages with dynamic content from a database is remarkably simple.
Finally, PHP provides a library of PHP code to perform common tasks, such as database abstraction, error handling, and so on, with the PHP Extension and Application Repository (PEAR). PEAR is a framework and distribution system for reusable PHP components. You can find out more about it at http://pear.php.net.