How have you used regular expressions in your…

Used regular expressions for data validation, substring search and replacement, parsing, and working with URIs.

Examples:

Email validation:

<?php
$email = "test@example.com";
if (preg_match("/^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/", $email)) {
    echo "Email is valid.";
} else {
    echo "Email is invalid.";
}

Finding URLs in text:

<?php
$text = "Visit our website https://example.com or contact us at mailto:info@example.com";
preg_match_all("/\b(?:https?|ftp):\/\/[-A-Z0-9+&@#\/%?=~_|!:,.;]*[-A-Z0-9+&@#\/%=~_|]/i", $text, $matches);
print_r($matches[0]);

Replacing characters:

<?php
$string = "This_is_a_string_with_underscores.";
$cleaned_string = preg_replace("/[_]/", " ", $string);
echo $cleaned_string; // Output: This is a string with underscores.

Parsing logs:

<?php
$log_line = '192.168.1.1 - - [10/Oct/2000:13:55:36 -0700] "GET /apache_pb.gif HTTP/1.0" 200 2326';
preg_match('/^(\S+) (\S+) (\S+) \[([^\]]+)\] "([^"]+)" (\d+) (\d+)$/', $log_line, $matches);
print_r($matches);
/*
Array
(
    [0] => 192.168.1.1 - - [10/Oct/2000:13:55:36 -0700] "GET /apache_pb.gif HTTP/1.0" 200 2326
    [1] => 192.168.1.1  // IP address
    [2] => -            // User
    [3] => -            // Group
    [4] => 10/Oct/2000:13:55:36 -0700 // Date and time
    [5] => GET /apache_pb.gif HTTP/1.0 // Request
    [6] => 200           // Status code
    [7] => 2326          // Size
)
*/

Routing (in frameworks): Although I didn't directly write regexes for routing in ready frameworks (Symfony, Laravel), I understood how they are used to match URIs with controllers and actions.
```
// Example (simplified, how it might work internally in a router)
// Route: /users/{id}
// Regex: #^/users/(\d+)$#
// Matching /users/123 -> Extracting 123 as ID
```

Overall, I used preg_match, preg_match_all, preg_replace, and preg_split, choosing the function depending on the task.

How have you used regular expressions in your projects?