PHP can be used in three primary ways:
PHP was originally designed to create dynamic web content, and it is still best suited for that task. To generate HTML, you need the PHP parser and a web server to send the documents. Lately, PHP has also become popular for generating XML documents, graphics, Flash animations, PDF files, and more.
PHP can run scripts from the command line, much like Perl, awk, or the Unix shell. You might use the command-line scripts for system administration tasks, such as backup and log parsing.
Client-side GUI applications
Using PHP-GTK (http://gtk.php.net), you can write full-blown, cross-platform GUI applications in PHP.
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 filesany 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.