Regex Tutorial (PHPRegex Edition)

This tutorial takes you from your first pattern to PCRE features used in production. It uses the PHPRegex CLI and API throughout, so you learn regex and the parser at the same time.

What You’ll Learn

Before You Start

Every chapter mixes two things: regex concepts you can use with preg_match() today, and the PHPRegex tools that explain and validate them. Install the library once — the regex CLI and the Regex facade used throughout both come with it.

composer require --dev php-regex/php-regex:2.x-dev

Prerequisites

• PHP 8.2 or newer
• the mbstring extension
• nothing else: the regex engine (PCRE2) ships inside PHP itself

Under the pre-release monorepo install, the vendor/bin/regex binary is available immediately; in the split layout it ships as the php-regex/regex-cli package.

The Tools You Will Use

The regex CLI

Every chapter asks you to run the CLI to see what a pattern does:

vendor/bin/regex explain '/^cat.*dog$/'

PHPRegex 2.0.0-DEV by Younes ENNAJI

Runtime : PHP 8.4.26
Command : explain
Format  : text

  [1/2] Pattern
  Pattern
      → /^cat.*dog$/

  [2/2] Explanation
Regex matches
  Anchor: the beginning of a line
  'c'
  'a'
  't'
    Wildcard: any character (may or may not match line terminators) (zero or more times)
  'd'
  'o'
  'g'
  Anchor: the end of a line

vendor/bin/regex diagram '/^cat.*dog$/'

PHPRegex 2.0.0-DEV by Younes ENNAJI

Runtime : PHP 8.4.26
Command : diagram
Format  : text

  [1/1] Rendering diagram
  Pattern
      → /^cat.*dog$/

Regex
\-- Sequence
    |-- Anchor (^)
    |-- Literal ('c')
    |-- Literal ('a')
    |-- Literal ('t')
    |-- Quantifier (*, greedy)
    |   \-- Dot (.)
    |-- Literal ('d')
    |-- Literal ('o')
    |-- Literal ('g')
    \-- Anchor ($)

Two more commands show up later in the track — highlight for colorized output, and analyze for ReDoS risk checks:

vendor/bin/regex analyze '/(a+)+$/'

The PHP API

use PHPRegex\Toolkit\Regex;

$regex = Regex::create();

// Validate what you wrote
$result = $regex->validate('/your-pattern/');

// Get explanations
echo $regex->explain('/your-pattern/');

// Generate test data
$sample = $regex->generate('/your-pattern/');

What Is a Regular Expression?

A regular expression (regex) is a pattern that describes text. Think of it like a recipe for matching strings:

Recipe: "Start with 'cat', then any characters, end with 'dog'"
Regex:  /^cat.*dog$/

Recipe: "An '@' symbol between two words"
Regex:  /\w+@\w+/

Analogy: Finding a Book

Imagine you’re in a library looking for a specific book:

Real-World Examples

How to Use This Tutorial

For Absolute Beginners

1. Read each chapter in order
2. Try every example in a PHP REPL or script
3. Use vendor/bin/regex explain to see what your pattern does
4. Work through the exercises at the end of each chapter

For Those Who Know Regex

1. Skim chapters to find what you need
2. Focus on the “Good vs Bad” sections
3. Learn how PHPRegex can validate and explain patterns
4. Pay special attention to the Performance chapter

For a compact list of everyday patterns and the special characters that need escaping, see Chapter 1 and the diagnostics cheatsheet.

Start Here

Chapter 1: Regex Basics

If You Get Stuck

1. Use the explain command: vendor/bin/regex explain '/your-pattern/'
2. Visualize it: vendor/bin/regex diagram '/your-pattern/'
3. Check for errors: vendor/bin/regex validate '/your-pattern/'
4. Read the FAQ: FAQ & glossary
5. Ask questions: GitHub Issues

Other Resources

• Regex in PHP Guide - PHP-specific regex details
• Cookbook - Ready-to-use patterns
• ReDoS Guide - Security and performance
• Regex101 - Interactive regex tester

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