PHP — Regex

Basic pattern matching

<?php
$email = "alice@example.com";

// preg_match
if (preg_match("/^[\w.]+@[\w.]+\.\w+$/", $email)) {
    echo "Valid email";
}

// preg_match_all
$text = "Call 123-456-7890 or 987-654-3210";
preg_match_all("/\d{3}-\d{3}-\d{4}/", $text, $matches);
print_r($matches[0]); // [123-456-7890, 987-654-3210]
?>

Pattern syntax

<?php
// Character classes
preg_match("/[aeiou]/", "hello");    // vowel
preg_match("/[^0-9]/", "abc");       // not digit

// Quantifiers
preg_match("/a{3}/", "aaa");         // exactly 3
preg_match("/a{2,}/", "aaaa");       // 2 or more

// Anchors
preg_match("/^hello/", "hello world"); // start
preg_match("/world$/", "hello world"); // end

// Groups
preg_match("/(\d+)-(\d+)/", "123-456", $matches);
echo $matches[1]; // 123
?>

Replacing

<?php
// preg_replace
$s = "Hello, World!";
echo preg_replace("/world/i", "PHP", $s); // Hello, PHP!

// With callback
echo preg_replace_callback("/\d+/", function($matches) {
    return $matches[0] * 2;
}, "10 + 20 = 30"); // 20 + 40 = 60
?>

Splitting

<?php
// preg_split
$fields = preg_split("/\s+/", "hello   world   foo");
print_r($fields); // [hello, world, foo]
?>

Mini Practice

Write PHP code that:

1. Validates an email with regex
2. Extracts phone numbers from text
3. Replaces patterns with preg_replace
4. Splits a string with regex

Up Next

In the next lesson, you'll learn about Date Functions — working with dates.