Farhad Rahimi Klie

Posted on Dec 6 • Edited on Dec 21

PHP in 2025: A Practical Guide for Beginners and Intermediate Developers

#php #programming #development #farhadrahimiklie

PHP (Hypertext Preprocessor) is a widely-used open-source server-side scripting language primarily designed for web development. It powers millions of websites, including WordPress, Facebook, and Wikipedia. This article dives deep into PHP, covering everything from architecture to syntax, internals, and key features.

1. PHP Architecture

PHP has a modular and layered architecture designed for flexibility, efficiency, and ease of embedding within HTML.

Key Components:

Zend Engine The core of PHP, responsible for parsing and executing PHP code. It includes:

Lexer: Converts PHP code into tokens.
Parser: Converts tokens into an Abstract Syntax Tree (AST).
Compiler: Translates AST to opcodes.
Executor: Runs opcodes to produce output.

PHP SAPI (Server API) PHP can run in different environments through SAPIs:

Apache Module (mod_php): Embedded in Apache.
CGI / FastCGI: Interface for web servers.
CLI (Command Line Interface): Run PHP scripts from the terminal.

Extensions and Libraries PHP is extendable using C-based extensions:

MySQL, PostgreSQL, SQLite, MongoDB
cURL, GD (graphics), OpenSSL
Custom extensions

Configuration (php.ini) Central configuration file controlling PHP behavior:

Error reporting
Memory limits
Upload size
Extensions

Architecture Flow:

PHP Script → Lexer → Parser → AST → Compiler → Opcodes → Executor → Output

2. PHP Internals

Understanding PHP internals helps optimize performance and debug issues.

2.1 Memory Management

PHP uses a reference counting mechanism for garbage collection.
Memory is allocated for variables dynamically.
Circular references are handled by a cyclic garbage collector.

2.2 Variable Handling

Variables in PHP are loosely typed.
Stored as zval structures internally:

struct _zval_struct {
    zend_value value;
    zend_uint refcount__gc;
    zend_uchar type;
    zend_uchar is_ref__gc;
};

2.3 Execution Model

PHP is interpreted, though Opcache can compile code to bytecode for performance.
Each request starts a new execution environment.

3. PHP Syntax

PHP syntax is C-like and designed for easy embedding into HTML.

3.1 Basic Structure

<?php
// Single-line comment
# Another single-line comment
/*
  Multi-line comment
*/
echo "Hello, World!";
?>

3.2 Variables

Prefix with $.

$name = "Klie";
$age = 25;
$price = 99.99;
$isActive = true;

3.3 Data Types

PHP supports scalar, compound, and special types.

Type	Example
Integer	`$i = 100;`
Float	`$f = 10.5;`
Boolean	`$b = true;`
String	`$s = "PHP";`
Array	`$arr = [1,2,3];`
Object	`$obj = new MyClass();`
NULL	`$n = null;`
Resource	`$res = fopen("file.txt");`

3.4 Operators

Arithmetic: + - * / % **
Assignment: = += -= *= /= %= .=
Comparison: == === != !== < > <= >= <=>
Logical: && || ! and or xor
String: . .=

3.5 Control Structures

Conditional Statements

if ($age > 18) {
    echo "Adult";
} elseif ($age > 12) {
    echo "Teenager";
} else {
    echo "Child";
}

Switch Statement

switch($color) {
    case "red":
        echo "Red color";
        break;
    case "blue":
        echo "Blue color";
        break;
    default:
        echo "Unknown color";
}

Loops

// while loop
$i = 0;
while ($i < 5) {
    echo $i;
    $i++;
}

// for loop
for ($i=0; $i<5; $i++) {
    echo $i;
}

// foreach loop
$arr = [1,2,3];
foreach($arr as $value) {
    echo $value;
}

3.6 Functions

function add($a, $b): int {
    return $a + $b;
}
echo add(5, 10);

Variable functions

function hello() { echo "Hello!"; }
$func = "hello";
$func(); // Calls hello()

3.7 Classes and Objects

class Person {
    public $name;
    private $age;

    public function __construct($name, $age) {
        $this->name = $name;
        $this->age = $age;
    }

    public function greet() {
        return "Hello, I'm " . $this->name;
    }
}

$p = new Person("Klie", 25);
echo $p->greet();

Visibility Keywords

public, protected, private
static properties and methods

Inheritance

class Employee extends Person {
    public $salary;
}

Interfaces & Abstract Classes

interface Workable {
    public function work();
}

abstract class Staff {
    abstract public function report();
}

3.8 Namespaces

namespace MyApp\Utils;
class Helper {}

3.9 Traits

trait Logger {
    public function log($msg) { echo $msg; }
}
class User { use Logger; }

3.10 Error Handling

try {
    $result = 10 / 0;
} catch (DivisionByZeroError $e) {
    echo "Error: " . $e->getMessage();
} finally {
    echo "Always executed";
}

3.11 File Handling

$file = fopen("test.txt", "w");
fwrite($file, "Hello PHP");
fclose($file);

3.12 Superglobals

$_GET, $_POST, $_REQUEST
$_SESSION, $_COOKIE, $_FILES, $_SERVER

3.13 Regular Expressions

preg_match("/php/i", "PHP is great", $matches);
print_r($matches);

3.14 Advanced Features

Anonymous functions & Closures

$sum = function($a, $b) { return $a + $b; };
echo $sum(5,10);

Generators

function genNumbers() {
    for ($i=0;$i<5;$i++) yield $i;
}
foreach(genNumbers() as $n) echo $n;

Type Declarations

function greet(string $name): string {
    return "Hello, $name";
}

Error & Exception Handling
Attributes (PHP 8+) for metadata

4. PHP Extensions

Popular extensions include:

Extension	Purpose
PDO	Database abstraction
cURL	HTTP requests
GD	Image manipulation
OpenSSL	Encryption
mbstring	Multibyte string functions
JSON	JSON encode/decode

5. PHP Best Practices

Always use prepared statements for SQL.
Enable strict typing (declare(strict_types=1);).
Use namespaces to avoid collisions.
Follow PSR standards (PSR-1, PSR-4).
Keep error reporting enabled in development.

6. PHP Evolution

PHP 1.0 (1995) – Personal Home Page tools
PHP 3.0 (1997) – Standardized scripting language
PHP 4.0 (2000) – Zend Engine 1
PHP 5.0 (2004) – OOP support, PDO
PHP 7.0 (2015) – Performance boost, scalar types
PHP 8.0 (2020) – JIT compiler, attributes, union types

7. Conclusion

PHP is a versatile, mature, and continually evolving language. Understanding its architecture, internals, syntax, and features empowers developers to write efficient, secure, and maintainable web applications. With its massive ecosystem and modern features, PHP remains a top choice for web development today.

DEV Community