What potential pitfalls should be considered when using regular expressions in PHP for form validation?

One potential pitfall when using regular expressions in PHP for form validation is the risk of creating overly complex or inefficient patterns that may not accurately validate user input. To mitigate this, it's important to thoroughly test regular expressions against various input scenarios to ensure they work as intended. Additionally, using built-in PHP functions like `preg_match()` can help simplify the validation process and improve code readability. 

// Example of using preg_match() for form validation
$input = $_POST['input'];

// Regular expression pattern to validate email format
$pattern = '/^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/';

if (preg_match($pattern, $input)) {
    // Valid email address
    echo "Input is a valid email address.";
} else {
    // Invalid email address
    echo "Input is not a valid email address.";
}

Keywords

regular expressions PHP form validation security vulnerabilities input sanitization

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