Introduction to PHP

So you want to learn PHP? You may already know HTML or XHTML or a scripting language such as Javascript and you want to move on to something more interactive, or you may have heard about PHP and are curious about it, or one of many other reasons. Whatever your reason(s) may be, PHP is a great language to learn!

This lesson focuses on:

What you should already know
What is PHP?
PHP file extensions
What can be done with PHP?

What you should already know

Before beginning your studies of PHP, you should already have at least a basic understanding of:

HTML/XHTML
PHP scripts are placed on webpages with HTML/XHTML tags and without knowing these tags, you will not know where and how to place PHP scripts on a webpage. If you need to study HTML, you can do so at our HTML section. If you need to study XHTML, you can do so at our XHTML section.
a scripting language such as Javascript
PHP is an advanced scripting language. If you already know another scripting language such as Javascript, learning PHP will be easier. You can read more about Javascript at our Javascript section.

What is PHP?

PHP stands for Hypertext Preprocessor (it is a recursive acronym). PHP is a language used to develop interactive and dynamic content on the web and it is often used together with the Apache web server. It can also be used with Microsoft's IIS web server.

PHP is a scripting language
PHP is a scripting language. This means that code written in PHP is not executed but interpreted by another program at runtime instead of being compiled by a computers processor. Other scripting languages include Javascript and VBScript.
PHP is a web language
PHP is a web language. It is used to create content on webpages.
PHP is a server-side language
PHP is a server-side language. Unlike some other web languages, PHP is server-side as opposed to client-side. If you try to view the source code of a web page, you will see that it may have been written in various language including HTML and Javascript. The source code you will be seeing however, is client-side code - the code of those languages that execute on the browser. If a webpage is written using PHP, you will not see the PHP source code used to create the page if you try to view the source code of the page. While PHP executes on the server, and not the browser, PHP files will be returned to the browser as plain HTML.
PHP is an object-oriented language
PHP is an object-oriented language. This means that in PHP you can define your own reusable data structures called objects as well as define their attributes (properties) and things they can do(methods). You can also create relationships between various objects and data structures.
PHP is an open source language
PHP is an open source language. This means that PHP's source code (the source code used to create PHP) is freely available to the general public.

PHP file extensions

PHP files have an extension of .php, .php3, or .phtml. The .php extension is the one that is used most often.

What can be done with PHP?

There is alot you can do with PHP:

Get data from forms
You can get data from forms submitted by users. For example, you can have users submit their e-mail addresses to be added to a mailing list.
Read and write cookies
A cookie is a small text file stored by a website on a users hard drive. With PHP, you can create cookies to store on a users hard drive and later read them. For example, you can store a users preference for the background color of a webpage in a cookie, and every time the user visits your website again you can read the cookie that stores this value and set the background color to the users preference accordingly.
Read from and write to files
You can read from and write to files. For example, you can create a guestbook on your website that is stored in a text file, and you can let users sign or view the guestbook.
Detect the user's browser
Detect what web browser a user is using. For example, you can find out if a user is using Netscape or Firefox.
Communicate with databases
Read data stored in a database or write new data to a database. For example, you can store a users name and e-mail address in a database, and allow them to retrieve this information and view it or change it, and the change will be reflected in the database.