What are the advantages of checking for permissible characters in a parameter rather than blocking specific characters in PHP?

Checking for permissible characters in a parameter allows for a more flexible and secure approach compared to blocking specific characters. By only allowing certain characters, you can ensure that the input is safe and conforms to your requirements without having to maintain a list of forbidden characters. This approach also simplifies validation logic and reduces the risk of overlooking certain edge cases. 

// Check for permissible characters in a parameter
function validateInput($input) {
    if (preg_match('/^[a-zA-Z0-9]+$/', $input)) {
        echo "Input is valid.";
    } else {
        echo "Invalid characters found in input.";
    }
}

$input = "abc123";
validateInput($input);

Keywords

input validation security regular expressions whitelist approach data sanitization

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