PHP, which stands for "Hypertext Preprocessor", is a server-side, HTML embedded scripting language used to create dynamic Web pages. Much of its syntax is borrowed from C, Java and Perl with some unique features thrown in. The goal of the language is to allow Web developers to write dynamically generated pages quickly. In an HTML page, PHP code is enclosed within special PHP tags. When a visitor opens the page, the server processes the PHP code and then sends the output (not the PHP code itself) to the visitor's browser. It means that, unlike Java Script, you don't have to worry that someone can steal your PHP script. PHP offers excellent connectivity to many databases including MySQL, Informix, Oracle, Sybase, Solid, PostgreSQL, and Generic ODBC. The popular PHP-MySQL combination (both are open-source products) is available on almost every UNIX host. Being web-oriented, PHP also contains all the functions to do things on the Internet - connecting to remote servers, checking email via POP3 or IMAP, url encoding, setting cookies, redirecting, etc.

• HTTP authentication with PHP : The HTTP Authentication hooks in PHP are only available when it is running as an Apache module and is hence not available in the CGI version. In an Apache module PHP script, it is possible to use the header() function to send an "Authentication Required" message to the client browser causing it to pop up a Username/Password input window. Once the user has filled in a username and a password, the URL containing the PHP script will be called again with the predefined variables PHP_AUTH_USER, PHP_AUTH_PW, and AUTH_TYPE set to the user name, password and authentication type respectively. These predefined variables are found in the $_SERVER and $HTTP_SERVER_VARS arrays.
• Cookies : PHP transparently supports HTTP cookies. Cookies are a mechanism for storing data in the remote browser and thus tracking or identifying return users. You can set cookies using the set cookie() or setrawcookie() function. Cookies are part of the HTTP header, so setcookie() must be called before any output is sent to the browser. This is the same limitation that header() has. You can use the output buffering functions to delay the script output until you have decided whether or not to set any cookies or send any headers. Any cookies sent to you from the client will automatically be included into a $_COOKIE auto-global array if variables_order contains "C". If you wish to assign multiple values to a single cookie, just add [] to the cookie name.
• Sessions : Session support in PHP consists of a way to preserve certain data across subsequent accesses. This enables you to build more customized applications and increase the appeal of your web site.
• Dealing with XForms : XForms defines a variation on traditional webforms which allows them to be used on a wider variety of platforms and browsers or even non-traditional media such as PDF documents. The first key difference in XForms is how the form is sent to the client.XForms for HTML Authors contains a detailed description of how to create XForms
• Handling file uploads : POST method uploads This feature lets people upload both text and binary files. With PHP's authentication and file manipulation functions, you have full control over who is allowed to upload and what is to be done with the file once it has been uploaded. PHP is capable of receiving file uploads from any RFC-1867 compliant browser (which includes Netscape Navigator 3 or later, Microsoft Internet Explorer 3 with a patch from Microsoft, or later without a patch).
• Using remote files : With the help of "allow_url_fopen" when enabled in php.ini, you can use HTTP and FTP URLs with most of the functions that take a filename as a parameter. In addition, URLs can be used with the include(), include_once(), require() and require_once() statements.
• Connection handling : Internally in PHP a connection status is maintained. There are 3 possible states:
  
  0 - NORMAL
  1 - ABORTED
  2 - TIMEOUT
  
  When a PHP script is running normally the NORMAL state, is active. If the remote client disconnects the ABORTED state flag is turned on. A remote client disconnect is usually caused by the user hitting his STOP button. If the PHP-imposed time limit (see set_time_limit()) is hit, the TIMEOUT state flag is turned on.
• Persistent Database Connections: Persistent connections are links that do not close when the execution of your script ends. When a persistent connection is requested, PHP checks if there's already an identical persistent connection (that remained open from earlier) - and if it exists, it uses it. If it does not exist, it creates the link. An 'identical' connection is a connection that was opened to the same host, with the same username and the same password (where applicable).
• Safe Mode : The PHP safe mode is an attempt to solve the shared-server security problem. It is architecturally incorrect to try to solve this problem at the PHP level, but since the alternatives at the web server and OS levels aren't very realistic, many people, especially ISP's, use safe mode for now.

Connectivity for many databases like:

• MSSQL
• Informix
• Oracle
• Sybase
• Solid
• PostgreSQL