PHP Regular Expressions (Regex) – Complete Course for Beginners

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

Why PHP Regular Expressions Are Powerful

Regex allows you to perform complex text operations with minimal code.

Key Benefits of PHP Regex

• Validates user input efficiently
• Searches text patterns quickly
• Replaces content dynamically
• Enhances application security
• Saves development time

Understanding preg_match Function in PHP Regex

The preg_match() function checks if a pattern exists in a string.

Example: Check If a Word Exists in a String

$text = "Welcome to PHP Online";
$pattern = "/PHP/";

if (preg_match($pattern, $text)) {
    echo "Match found";
} else {
    echo "Match not found";
}

Output

Match found

PHP Regex Case Insensitive Matching Example

Regex can ignore case sensitivity using modifiers.

Example: Case Insensitive Match

$text = "Learning php regex";
$pattern = "/PHP/i";

preg_match($pattern, $text, $matches);
echo "Matched successfully";

Output

Matched successfully

Using preg_match_all in PHP Regular Expressions

The preg_match_all() function finds all matches in a string.

Example: Find All Numbers in a String

$text = "Order IDs: 45, 67, 89";
$pattern = "/\d+/";

preg_match_all($pattern, $text, $matches);
print_r($matches[0]);

Output

Array
(
    [0] => 45
    [1] => 67
    [2] => 89
)

PHP Regex for Replacing Text Using preg_replace

The preg_replace() function replaces matched patterns.

Example: Replace Word in String

$text = "I love PHP";
$pattern = "/PHP/";
$replace = "Programming";

echo preg_replace($pattern, $replace, $text);

Output

I love Programming

PHP Regex Special Characters Explained with Example

Some commonly used regex symbols:

Example: Validate Digits Only

$value = "12345";
$pattern = "/^\d+$/";

echo preg_match($pattern, $value) ? "Valid" : "Invalid";

Output

Valid

PHP Regex for Email Validation Example

Regex is commonly used to validate emails.

Example: Email Validation

$email = "user@example.com";
$pattern = "/^[\w\-\.]+@([\w\-]+\.)+[\w\-]{2,4}$/";

echo preg_match($pattern, $email) ? "Valid Email" : "Invalid Email";

Output

Valid Email

PHP Regex Modifiers Explained Simply

Regex modifiers change how patterns behave.

Using preg_split with PHP Regular Expressions

The preg_split() function splits a string using regex.

Example: Split String by Comma or Space

$text = "PHP, JavaScript HTML";
$result = preg_split("/[\s,]+/", $text);
print_r($result);

Output

Array
(
    [0] => PHP
    [1] => JavaScript
    [2] => HTML
)

Real World Use Cases of PHP Regular Expressions

Regex is widely used in PHP applications.

Practical Applications

• Form input validation
• Password strength checking
• URL rewriting
• Search filters
• Data sanitization

Best Practices for Using PHP Regex

Follow these professional tips:

• Keep regex patterns simple
• Add comments for complex patterns
• Test regex before deployment
• Avoid overly complex expressions
• Use regex only when necessary

Common Mistakes While Using PHP Regex

Avoid These Errors

• Writing overly complex patterns
• Forgetting delimiters
• Ignoring regex modifiers
• Using regex instead of simple string functions
• Not validating user input properly

What You will Learn

1. What are Regular Expressions?
2. Why Use Regex in PHP?
3. Regex Support in PHP
4. Regex Syntax Basics
5. Regex Metacharacters Explained
6. Regex Quantifiers
7. Regex Character Classes
8. Anchors in Regex
9. Groups and Alternation
10. Escaping Special Characters
11. PHP Regex Functions Overview
12. Using preg_match()
13. Using preg_match_all()
14. Using preg_replace()
15. Using preg_split()
16. Validating Email with Regex
17. Validating Phone Numbers with Regex
18. Validating Passwords with Regex
19. Extracting Data from Strings
20. Regex with $_POST Form Data
21. Real-World Example: Login Form Validation
22. Real-World Example: URL Matching
23. Real-World Example: Extracting Hashtags
24. Real-World Example: Validating Dates
25. Regex and Performance Considerations
26. Regex vs. String Functions in PHP
27. Best Practices for Regex in PHP
28. Common Mistakes with Regex
29. Advanced Regex Techniques (Lookaheads, Lookbehinds)
30. Tools for Testing Regex
31. Regex in Security Applications
32. Regex in Data Scraping
33. Regex in File Handling
34. Regex in PHP Arrays
35. Regex in Loops and Conditions
36. PHP Regex and Global Variables
37. Real-Life Mini Project: Regex-Based Contact Form Validator
38. Real-Life Mini Project: PHP Regex URL Extractor
39. Regex in Object-Oriented PHP

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

1. preg_match()
2. preg_match_all()
3. preg_replace()
4. 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.