Overview
By the end of this chapter, you will be able to work with PHP's built-in templating engine; write simple HTML files; run a PHP script from the command line; create and assign variables to print simple messages on the web browser; and run PHP's built-in web server on your machine.
Introduction
Welcome to the world of Hypertext Preprocessor (PHP). PHP is a popular programming language that's used all over the internet to create web pages/websites and applications. A web page is a single page, while multiple web pages together are commonly referred to as a website or web application. PHP powers sites such as Facebook, Wikipedia, and WordPress.
PHP was created as a scripting language to allow rich dynamic content (content can come from other PHP pages or can be dynamic in nature and come from external sources such as a database). PHP is an interpreted language, which means you do not have to compile it and create an executable file. Instead, PHP files are interpreted line by line by the web server running PHP.
Compiled languages cannot run directly after each change. Instead, they require an interpreter to compile the code into a program that can be executed. Interpreted languages, on the other hand, can be reloaded as soon as there is a change in the code, allowing for changes to be seen quickly.
PHP is used along with HTML, JavaScript, and CSS to create dynamic web applications. Since PHP is easy to learn, it has a huge developer community around the world. This has led to more and more developers releasing open source projects, frameworks, and resources. For instance, PHP Framework Interop Group, otherwise known as PHP-FIG, (https://packt.live/2oJ0FvY) has created a series of standard recommendations that most developers use to write their code. GitHub houses many open source projects for others to use, and sites such as https://packt.live/2oaK3gt have many videos on web development.
Getting Started with PHP Web Development
PHP is a server-side scripting language. Server-side scripting is a way that web servers can respond to client requests via HTTP. The way this works is that a client (a browser) requests a URL. This request is then sent by a web server to a script. The script then reads this request and, depending on the code in the script, returns the contents of a page.
This process happens every time a web page is visited. When working with forms, data is sent from the client to the server. The data is processed and a response is returned. A common example is that on Facebook, you enter a status update and press Enter. The text is sent via a POST request to the server, checked by the scripts on the server, and then saved to a database. The web page is then updated with the new post. PHP sites can also be API services, which may be called either from JavaScript scripts (as AJAX calls, for instance) or from other services. In those and similar cases, there is no browser request involved.
The following tools are needed for web development:
- A browser such as Google Chrome, Firefox, or Microsoft Edge.
- A text editor such as Microsoft Visual Studio Code, or an Integrated Development Environment (IDE) such as PHP Storm.
- A server to run PHP Apache or NGINX can be used, as well as PHP's built-in server.
Built-in Templating Engine
PHP was created to write applications for the web. It can be written alongside HTML to create dynamic pages. We will see examples of this in a moment.
A PHP templating engine is a way to allow PHP code to output its content alongside HTML content. This gives flexibility to pages. Any page intended to use PHP code has a .php extension instead of an .html extension. This informs the web server to expect PHP content.
A PHP file has a .php extension, and it can contain HTML, JavaScript, and CSS, along with PHP. Since the PHP interpreter needs to know where the code is placed in a PHP file, PHP code is written between two special tags (<?php...?>). These tags are called opening and closing tags. A typical PHP file looks like this:
Example1.01.php
1 <!DOCTYPE html>
2 <html lang="en">
3 <head>
4 <meta charset="UTF-8">
5 <meta name="viewport" content="width=device-width, initial-scale=1.0">
6 <meta http-equiv="X-UA-Compatible" content="ie=edge">
7 <title>My First PHP Page</title>
8 </head>
9 <body>
10 <div>
11 <h1>The Heading</h1>
12 <p>
13 <?php
14 // your php code goes here
15 ?>
https://packt.live/326OLKU
This page starts off with HTML declaring the doctype, which tells the browser to expect HTML content, followed by meta tags that inform the browser to expect UTF-8 content and a meta tag to use the latest rendering engine and zooming levels.
Note
HTML is covered in detail later in the chapter.
Alternatively, short open tags are also available in PHP, but they are turned off by default. This can be changed by editing a .phpini configuration file when using Apache (this goes beyond the scope of this introduction). Short codes look like this:
<?
// php code here
?>
In short, opening and closing tags inform the PHP interpreter when to start and stop interpreting the PHP code line by line.
Since PHP is a useful web development tool, you will often be working in the browser. However, you will also need to be familiar with the interactive shell.
PHP in the Interactive Shell
Interactive shells are known by a few different names. On Windows, they are referred to as Command Prompt. On Linux/Mac, Terminal is the name given to the computer application that allows commands to be issued and understood by the shell and picked up by PHP.
The interactive shell allows a PHP script to run without a browser. This is how scripts are commonly executed on a server.
Exercise 1.1: Printing Hello World to the Standard Output
In this exercise, we will print a simple statement using the interactive shell. The interactive shell can be used to execute PHP code and/or scripts. Before we begin, ensure that you have followed the installation steps in the preface. Follow these steps to complete the exercise:
- Open a Terminal/Command Prompt on your machine.
- Write the following command to start PHP's interactive shell and hit Enter:
php -a
You will obtain ...
