In PHP, what best practices should be followed when validating user input to ensure that all desired characters are allowed while excluding others?

When validating user input in PHP, it is important to use regular expressions to specify the allowed characters and exclude any unwanted characters. This can help prevent security vulnerabilities such as SQL injection or cross-site scripting attacks. By defining a specific pattern for the input data, you can ensure that only valid characters are accepted. 

// Example of validating user input with regular expressions
$userInput = $_POST['user_input'];

// Define a regular expression pattern to allow only alphanumeric characters and spaces
$pattern = '/^[a-zA-Z0-9\s]+$/';

if (preg_match($pattern, $userInput)) {
    // Input is valid
    echo "Input is valid";
} else {
    // Input contains invalid characters
    echo "Invalid input";
}

Keywords

PHP validation user input character whitelist regular expressions

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