PHP

PHP is a server-side scripting language designed for web development but also used as a general-purpose programming language. As of January 2013, PHP was installed on more than 240 million websites (39% of those sampled) and 2.1 million web servers. Originally created by Rasmus Lerdorf in 1994, the reference implementation of PHP (powered by the Zend Engine) is now produced by The PHP Group. While PHP originally stood for Personal Home Page, it now stands for PHP: Hypertext Preprocessor, which is a recursive backronym.

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Anything that written outside <? or <?php and ?> are treated as output, so, if a .php file containing only a character a, that character itself would be the output.

Factoid

Some of the biggest online sites, such as Facebook, Wikipedia, and Yahoo! are powered by PHP.