Page 29 - Open Soource Technologies 304.indd

Unit 2: Language Basics

Introduction Notes

PHP is a general-purpose server-side scripting language originally designed for web development
to produce dynamic web pages. For this purpose, PHP code is embedded into the HTML source
document and interpreted by a web server with a PHP processor module, which generates the
web page document. It also has evolved to include a command-line interface capability and can
be used in stand alone graphical applications. PHP can be deployed on most web servers and as a
stand alone interpreter, on almost every operating system and platform free of charge. A competitor
to Microsoft’s Active Server Pages (ASP) server-side script engine and similar languages, PHP is
installed on more than 20 million websites and 1 million web servers.
The main implementation of PHP is now produced by the PHP Group and serves as the de facto
standard for PHP as there is no formal specification. PHP is free software released under the PHP
License which is incompatible with the GNU General Public License (GPL) due to restrictions on
the usage of the term PHP.

2.1 Lexical Structure

Computer languages, like human languages, have a lexical structure. A source code of a PHP
script consists of tokens. Tokens are atomic code elements. In PHP language, we have comments,
variables, literals, operators, delimiters and keywords.
Embedding
PHP code is inserted into an HTML page between the start and end tags <? and ?>. The word
PHP follows the start tag.
html code

<?php
... PHP code goes here
?>
more html code

Case Sensitivity
• The names of user-defined classes and functions as well as built-in constructs and keywords
are case-insensitive.
• Variables are case sensitive.

Comments
Comments are used by humans to clarify the source code. All comments in PHP follow the
#character.

<?php
# comments.php
# Navneet

# ZetCode 2009
echo “This is comments.php script\n”;
?>

Everything that follows the # character is ignored by the PHP interpreter.

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