PHP Regular Expressions (Regex) Tutorial with Examples | Learn Pattern Matching in PHP

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PHP Regular Expressions (Regex) – Complete Tutorial with Examples

Welcome to phponline.in – your one-stop hub for mastering PHP programming.

In this detailed course page, we will cover PHP Regular Expressions (Regex) step by step.

Regular Expressions (often called Regex) are powerful tools used to search, match, validate, and manipulate strings. Whether you are building a form validation system, email checker, or search engine, mastering regex in PHP is a must.

By the end of this guide, you will:

Understand what regular expressions are
Learn about Regex syntax and metacharacters
Work with preg_match, preg_match_all, preg_replace, preg_split
Validate inputs like email, phone, and passwords
Build real-world projects using regex
Discover advanced regex techniques for complex matching

What You will Learn

What are Regular Expressions?
Why Use Regex in PHP?
Regex Support in PHP
Regex Syntax Basics
Regex Metacharacters Explained
Regex Quantifiers
Regex Character Classes
Anchors in Regex
Groups and Alternation
Escaping Special Characters
PHP Regex Functions Overview
Using preg_match()
Using preg_match_all()
Using preg_replace()
Using preg_split()
Validating Email with Regex
Validating Phone Numbers with Regex
Validating Passwords with Regex
Extracting Data from Strings
Regex with $_POST Form Data
Real-World Example: Login Form Validation
Real-World Example: URL Matching
Real-World Example: Extracting Hashtags
Real-World Example: Validating Dates
Regex and Performance Considerations
Regex vs. String Functions in PHP
Best Practices for Regex in PHP
Common Mistakes with Regex
Advanced Regex Techniques (Lookaheads, Lookbehinds)
Tools for Testing Regex
Regex in Security Applications
Regex in Data Scraping
Regex in File Handling
Regex in PHP Arrays
Regex in Loops and Conditions
PHP Regex and Global Variables
Real-Life Mini Project: Regex-Based Contact Form Validator
Real-Life Mini Project: PHP Regex URL Extractor
Regex in Object-Oriented PHP
Summary & Conclusion

1. What are Regular Expressions?

Regular Expressions are patterns used to match text. They help in:

Searching strings
Replacing parts of text
Validating input fields
Extracting data

Example:

$pattern = "/php/i";
$text = "I love PHP programming!";
if (preg_match($pattern, $text)) {
    echo "Match found!";
}

Output:

Match found!

2. Why Use Regex in PHP?

Regex is used for:

Form validation (email, phone, password)
Data scraping from text
Replacing unwanted words
Extracting structured data

3. Regex Support in PHP

PHP provides regex support via PCRE (Perl Compatible Regular Expressions).

Main functions:

preg_match() – find pattern in string
preg_match_all() – find all matches
preg_replace() – replace text
preg_split() – split string

4. Regex Syntax Basics

Patterns are enclosed between forward slashes /.../
Case-insensitive search uses i modifier

Example:

preg_match("/hello/i", "Hello World!");

5. Regex Metacharacters Explained

Some special regex symbols:

. – any character
^ – start of string
$ – end of string
* – zero or more
+ – one or more
? – zero or one
[] – character class
| – OR

6. Regex Quantifiers

{n} – exact n times
{n,} – n or more times
{n,m} – between n and m times

Example:

preg_match("/[0-9]{3}/", "My number is 123");

7. Regex Character Classes

[0-9] – digits
[a-z] – lowercase letters
[A-Z] – uppercase letters
\d – digits
\w – word characters
\s – whitespace

8. Anchors in Regex

^word – match at start
word$ – match at end

9. Groups and Alternation

(abc) – group
a|b – OR

10. Escaping Special Characters

Use \ before special characters.

preg_match("/\$100/", "Price is $100");

11. PHP Regex Functions Overview

preg_match()
preg_match_all()
preg_replace()
preg_split()

12. Using preg_match()

if (preg_match("/php/i", "I love PHP")) {
    echo "Match!";
}

13. Using preg_match_all()

preg_match_all("/\d+/", "My numbers are 12 and 34", $matches);
print_r($matches);

14. Using preg_replace()

$text = "Hello World!";
echo preg_replace("/World/", "PHP", $text);

15. Using preg_split()

$str = "apple,banana,orange";
$fruits = preg_split("/,/", $str);
print_r($fruits);

16. Validating Email with Regex

$email = "test@example.com";
if (preg_match("/^[\w.-]+@[\w.-]+\.[a-z]{2,}$/i", $email)) {
    echo "Valid Email";
}

17. Validating Phone Numbers with Regex

$phone = "9876543210";
if (preg_match("/^[0-9]{10}$/", $phone)) {
    echo "Valid Phone";
}

18. Validating Passwords with Regex

Strong password: at least 8 chars, 1 uppercase, 1 number.

$password = "Test1234";
if (preg_match("/^(?=.*[A-Z])(?=.*[0-9]).{8,}$/", $password)) {
    echo "Strong Password";
}

19. Extracting Data from Strings

preg_match_all("/\d+/", "Order IDs: 123, 456, 789", $matches);
print_r($matches);

20. Regex with $_POST Form Data

Form validation example:

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    if (preg_match("/^[a-zA-Z ]+$/", $_POST['name'])) {
        echo "Valid Name";
    } else {
        echo "Invalid Name";
    }
}

21. Real-World Example: Login Form Validation

Validate username and password.

22. Real-World Example: URL Matching

$url = "https://phponline.in";
if (preg_match("/^https?:\/\/[a-z0-9.-]+\.[a-z]{2,}$/i", $url)) {
    echo "Valid URL";
}

23. Real-World Example: Extracting Hashtags

$text = "Learning #PHP and #Regex";
preg_match_all("/#(\w+)/", $text, $matches);
print_r($matches[1]);

24. Real-World Example: Validating Dates

$date = "2025-08-18";
if (preg_match("/^\d{4}-\d{2}-\d{2}$/", $date)) {
    echo "Valid Date";
}

25. Regex and Performance Considerations

Complex regex may slow execution
Use specific patterns for efficiency

26. Regex vs. String Functions in PHP

Regex = flexible and powerful
String functions = faster for simple tasks

27. Best Practices for Regex in PHP

Use anchors ^ and $
Test regex with tools
Keep patterns readable

28. Common Mistakes with Regex

Forgetting escape characters
Overusing greedy quantifiers

29. Advanced Regex Techniques

Lookahead: (?=...)
Lookbehind: (?<=...)
Non-capturing groups: (?:...)

30. Tools for Testing Regex

regex101.com
phpliveregex

31. Regex in Security Applications

Prevent SQL injection
Validate inputs before DB insert

32. Regex in Data Scraping

Extract emails, phone numbers from text files.

33. Regex in File Handling

Rename files based on patterns.

34. Regex in PHP Arrays

Filter array values with regex.

35. Regex in Loops and Conditions

Use regex inside loops for filtering datasets.

36. PHP Regex and Global Variables

Regex with $_GET, $_POST, and $_SERVER.

37. Mini Project: Regex-Based Contact Form Validator

Validate name, email, and phone.

38. Mini Project: PHP Regex URL Extractor

Extract all URLs from a web page.

39. Regex in Object-Oriented PHP

Encapsulate regex logic inside classes.

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Summary & Conclusion

Regex is essential for validation and text processing
PHP provides preg_ functions for regex operations
Real-world apps: validation, scraping, security

Frequently Asked Questions (FAQ)

Q1: What is regex in PHP?
A: Regex is a pattern-matching technique used for string validation and manipulation.

Q2: Which PHP functions use regex?
A: preg_match, preg_match_all, preg_replace, preg_split.

Q3: Is regex faster than string functions?
A: For simple tasks, string functions are faster. Regex is better for complex patterns.

Q4: How to validate email in PHP using regex?
A: Use preg_match("/^[\w.-]+@[\w.-]+\.[a-z]{2,}$/i", $email).

Q5: Can regex prevent security attacks?
A: Regex helps sanitize input, reducing XSS and SQL injection risks.