PHP Introduction

What You Should Already Know

Before you continue you should have a basic understanding of the following:

HTML
CSS
JavaScript

What is PHP?

PHP is an acronym for "PHP Hypertext Preprocessor"
PHP is a widely-used, open source scripting language
PHP scripts are executed on the server
PHP costs nothing, it is free to download and use

What is a PHP File?

PHP files can contain text, HTML, CSS, JavaScript, and PHP code
PHP code are executed on the server, and the result is returned to the browser as plain HTML
PHP files have extension ".php"

What Can PHP Do?

PHP can generate dynamic page content
PHP can create, open, read, write, and close files on the server
PHP can collect form data
PHP can send and receive cookies
PHP can add, delete, modify data in your database
PHP can restrict users to access some pages on your website
PHP can encrypt data

With PHP you are not limited to output HTML. You can output images, PDF files, and even Flash movies. You can also output any text, such as XHTML and XML.

Why PHP?

PHP runs on various platforms (Windows, Linux, Unix, Mac OS X, etc.)
PHP is compatible with almost all servers used today (Apache, IIS, etc.)
PHP supports a wide range of databases
PHP is free. Download it from the official PHP resource: www.php.net
PHP is easy to learn and runs efficiently on the server side

Basic PHP Syntax

A PHP script can be placed anywhere in the document.

A PHP script starts with <?php and ends with ?>:

<?php
// PHP code goes here
?>

The default file extension for PHP files is ".php".

A PHP file normally contains HTML tags, and some PHP scripting code.

Below, we have an example of a simple PHP file, with a PHP script that uses a built-in PHP function "echo" to output the text "Hello World!" on a web page:

Example

<html>
<body>

<h1>My first PHP page</h1>

<?php
echo "Hello World!";
?>

</body>
</html>

Comments in PHP

A comment in PHP code is a line that is not read/executed as part of the program. Its only purpose is to be read by someone who is editing the code!

Comments are useful for:

To let others understand what you are doing - Comments let other programmers understand what you were doing in each step (if you work in a group)
To remind yourself what you did - Most programmers have experienced coming back to their own work a year or two later and having to re-figure out what they did. Comments can remind you of what you were thinking when you wrote the code.

Example

PHP Case Sensitivity

In PHP, all user-defined functions, classes, and keywords (e.g. if, else, while, echo, etc.) are NOT case-sensitive.

In the example below, all three echo statements below are legal (and equal):

Example

<html>
<body>

<?php
ECHO "Hello World!<br>";
echo "Hello World!<br>";
EcHo "Hello World!<br>";
?>

</body>
</html>