// server-side programming

What Is PHP?

PHP is a programming language widely used for server-side web development. It can generate web pages, process forms, communicate with databases, manage sessions and build dynamic websites and applications.

// definition

PHP is a server-side scripting language

PHP is a general-purpose programming language particularly suited to web development.

PHP code commonly runs on a web server rather than directly inside the user's browser.

The server executes the PHP code and sends the resulting output, often HTML, back to the browser.

// name

What does PHP stand for?

PHP is officially described using the recursive acronym:

PHP: Hypertext Preprocessor

The name reflects PHP's long association with generating and processing web content.

// example

What does PHP look like?

<?php echo "Hello, world!"; ?>

The echo statement sends text to the output.

In a web application, that output can become part of the HTML returned to the browser.

// server

PHP usually runs before the page reaches the browser

Browser requests page ↓ Web server receives request ↓ PHP code executes ↓ PHP generates output ↓ Server sends response ↓ Browser displays page

The browser usually receives the output generated by PHP rather than the original PHP source code.

// php + html

PHP can be embedded inside HTML

<h1>Welcome</h1> <p> Today is <?php echo date("d F Y"); ?> </p>

PHP executes on the server and inserts the generated value into the document before it is sent to the user.

// variables

PHP can store information in variables

<?php $name = "Alice"; $orders = 4; echo $name; echo $orders; ?>

PHP variable names normally begin with a $ symbol.

// data types

PHP supports different kinds of data

Type	Example
String	"Freelance Coder"
Integer	42
Float	19.99
Boolean	true
Array	["HTML", "CSS", "PHP"]
Null	null
Object	new Customer()

// arrays

PHP arrays can store collections of data

<?php $skills = [ "HTML", "CSS", "JavaScript", "PHP" ]; echo $skills[0]; ?>

This outputs:

HTML

// associative arrays

PHP arrays can also use named keys

<?php $customer = [ "name" => "Alice", "orders" => 4, "active" => true ]; echo $customer["name"]; ?>

Associative arrays are useful for representing structured information using named keys and values.

// conditions

PHP can make decisions

<?php $loggedIn = true; if ($loggedIn) { echo "Welcome back."; } else { echo "Please sign in."; } ?>

Conditional statements allow different code to run depending on the state of the application.

// functions

PHP functions package reusable logic

<?php function greet($name) { return "Hello, " . $name; } echo greet("Alice"); ?>

The full stop operator joins strings together in PHP.

// loops

PHP can repeat tasks

<?php for ($i = 1; $i <= 5; $i++) { echo $i; } ?>

Loops are useful when the same operation must be repeated several times.

// foreach

foreach is useful for collections

<?php $skills = [ "HTML", "CSS", "PHP" ]; foreach ($skills as $skill) { echo $skill; } ?>

The loop processes each item in the array one at a time.

// forms

PHP can process form submissions

A website might contain a form:

<form method="post"> <input type="text" name="name" > <button type="submit"> Send </button> </form>

PHP can receive the submitted data:

<?php if ($_SERVER["REQUEST_METHOD"] === "POST") { $name = $_POST["name"] ?? ""; } ?>

User input should be validated and handled safely. Real applications should never assume that submitted information is automatically trustworthy.

// databases

PHP can communicate with databases

PHP is commonly used with relational databases such as MySQL and PostgreSQL.

An application might use a database to store:

Users Products Orders Blog Posts Settings Transactions

// database connection

PHP provides database interfaces

One common approach is PHP Data Objects, or PDO.

<?php $pdo = new PDO( "mysql:host=localhost;dbname=shop;charset=utf8mb4", $username, $password ); ?>

Applications can then execute database queries through the connection.

// sql safety

Prepared statements are important

<?php $stmt = $pdo->prepare( "SELECT * FROM users WHERE email = ?" ); $stmt->execute([$email]); $user = $stmt->fetch(); ?>

Prepared statements allow values to be supplied separately from the SQL structure and are an important defence against SQL injection.

// sessions

PHP can maintain session data

<?php session_start(); $_SESSION["user_id"] = 123; ?>

Sessions allow a server to associate information with a user across multiple requests.

They are commonly used for login systems and other stateful website features.

// cookies

PHP can also work with cookies

<?php setcookie( "theme", "light", time() + 3600 ); ?>

Cookies are stored by the browser and can later be sent back to the server with requests.

// json

PHP works with JSON

PHP can convert arrays and objects into JSON:

<?php $data = [ "name" => "Alice", "orders" => 4 ]; echo json_encode($data); ?>

It can also convert JSON into PHP data:

<?php $data = json_decode( $json, true ); ?>

This makes PHP useful for building and consuming APIs.

// APIs

PHP can power APIs

Instead of returning an HTML page, a PHP application can return structured data.

<?php header( "Content-Type: application/json" ); echo json_encode([ "status" => "success", "message" => "Data received" ]); ?>

Another application can then consume the JSON response.

// php vs javascript

PHP and JavaScript often work together

PHP

Commonly runs on the server and handles server-side application logic.

JavaScript

Commonly runs in the browser and handles interactive client-side behaviour.

PHP Output

Can generate HTML or JSON that is sent to the browser.

JavaScript Requests

Can send requests to PHP-powered APIs and process their responses.

// web application

A PHP web application might work like this

User ↓ Browser ↓ HTTP request ↓ Web server ↓ PHP application ↓ Database ↓ PHP generates response ↓ HTML or JSON ↓ Browser

PHP often acts as the server-side layer connecting users, application logic and stored data.

// wordpress

WordPress is built with PHP

PHP has played a major role in the development of content management systems.

WordPress uses PHP extensively for themes, plugins, templates, database interaction and server-side logic.

<?php the_title(); the_content(); ?>

WordPress-specific PHP functions can dynamically retrieve and display website content.

// .php files

PHP code is commonly stored in .php files

index.php contact.php login.php api.php functions.php

A web server configured for PHP can execute the PHP code when one of these files is requested.

// security

Server-side code must handle data carefully

PHP applications often process passwords, form inputs, database queries, cookies and uploaded files.

Secure applications therefore need appropriate validation, escaping, authentication and database practices.

Never trust input simply because it came from your own website. Server-side code should validate data and apply the correct security controls for how that data will be used.

// frameworks

PHP has a large software ecosystem

Developers can use frameworks and content management systems rather than building every component from scratch.

Laravel Symfony WordPress Composer PHPUnit

// uses

What is PHP used for?

Dynamic Websites WordPress APIs Databases Forms Authentication E-commerce Web Applications Server-Side Logic Automation

// summary

The server does the work.

PHP is a programming language widely used for server-side web development. It can generate HTML, process forms, manage sessions, communicate with databases, work with JSON and APIs, and power dynamic websites and applications such as WordPress.