Syntax

PHP primarily acts as a filter. The PHP program takes input from a file or stream containing text and special PHP instructions and outputs another stream of data for display. From PHP 4, the PHP parser compiles input to produce bytecode for processing by the Zend Engine, giving improved performance over its interpreter predecessor. The Zend Engine II is at the heart of PHP 5.

The usual Hello World code example for PHP is:

echo 'Hello, World!';

?>

PHP only parses code within its delimiters, such as . Anything outside its delimiters is sent directly to the output and not parsed by PHP. The example above is equivalent to the following text (and indeed is converted into this form):

Hello, World!

Variables are prefixed with a dollar symbol and a type does not need to be specified in advance. Unlike function and class names, variable names are case sensitive. Both double-quoted ("") and heredoc strings allow the ability to embed the variable's value into the string.

PHP treats new lines as whitespace, in the manner of a free-form language (except when inside string quotes). Statements are terminated by a semicolon, except in a few special cases.

PHP has three types of comment syntax: /* */ which serves as block comments, and // as well as # which is used for inline comments.