PHP 5.4 Will Have a Built-in Web Server
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Yet another new feature to look forward to in PHP 5.4.0 - the CLI SAPI will now provide a built-in web server which is geared toward developmental purposes. It shouldn't be used in production right now.
According to the page on this feature, which was updated today:
"URI requests are served from the current working directory where PHP was started, unless the -t option is used to specify an explicit document root.
If a URI request does not specify a file, then either index.php or index.html in the given directory are returned. If neither file exists, then a 404 response code is returned.
If a PHP file is given on the command line when the web server is
started it is treated as a "router" script for the web server.
The script is run at the start of each HTTP request. If this
script returns FALSE, then the requested resource is returned
as-is. Otherwise the script's output is returned to the browser." --php.net
Go check out the examples over on docs.php.net: