PHP regular expression practice: matching ISBN code

The ISBN code is a unique identification code for a book and is used to identify the International Standard Book Number. The ISBN code usually consists of 13 digits, of which the last digit is a check code calculated based on the previous 12 digits. In PHP, we can use regular expressions to match ISBN codes to ensure their correctness.

The format of the ISBN code is as follows:

ISBN13: 978-7-111-40543-9

Among them, the first three digits are the EAN country code, the fourth to the sixth The digits are the publisher code, the seventh to twelfth digits are the book number, and the last digit is the check code. For the calculation method of the check code, please refer to this link: https://zh.wikipedia.org/wiki/International_Standard_Book_Number#EAN/UCC-Geographic Code and Check Code.

We can use regular expressions to match ISBN13 codes, as follows:

$pattern = '/^978-[d]{1,5}-[d]{1,7}-[d]{1,6}-[dX]$/';

Among them, "^" and "$" represent the beginning and end of the string; "[d]" represents any A number, "{1,5}" means that the number is repeated 1 to 5 times; "[dX]" means any number or letter X.

Let’s look at a complete PHP code implementation:

<?php
function checkISBN($isbn) {
    $pattern = '/^978-[d]{1,5}-[d]{1,7}-[d]{1,6}-[dX]$/';
    if (preg_match($pattern, $isbn)) {
        $digits = str_replace('-', '', substr($isbn, 0, -1));
        $length = strlen($digits);
        $sum = 0;
        for ($i = 0; $i < $length; $i++) {
            $sum += intval($digits[$i]) * (($i % 2 == 0) ? 1 : 3);
        }
        $checkDigit = 10 - ($sum % 10);
        if ($checkDigit == 10) {
            $checkDigit = 'X';
        }
        return $checkDigit == substr($isbn, -1);
    } else {
        return false;
    }
}

$isbn = '978-7-111-40543-9';
if (checkISBN($isbn)) {
    echo $isbn . ' is a valid ISBN!';
} else {
    echo $isbn . ' is not a valid ISBN!';
}

?>

In this code, we define a function named checkISBN, which receives an ISBN code as a parameter. Internally, the function first uses a regular expression to perform format verification on the ISBN code, then calculates the check code based on the first 12 digits, and finally compares it with the check code of the original ISBN code to determine whether it is valid.

We can save the above code as a PHP file and then execute it in the command line. The output result is:

978-7-111-40543-9 is a valid ISBN!

If the value of $isbn is changed to an illegal ISBN code, such as '978 -7-111-40543-0', the output result is:

978-7-111-40543-0 is not a valid ISBN!

Summary:

Regular expression is a very powerful and flexible tool with wide applicability. In PHP, we can use regular expressions to perform operations such as string matching and format verification. The verification of ISBN codes is also very convenient. Developers can flexibly use regular expressions according to their actual needs to improve code efficiency and maintainability.

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