Regular Expressions Cookbook, 2nd Edition

4.13. Validate ISBNs

Problem

You need to check the validity of an International Standard Book Number (ISBN), which can be in either the older ISBN-10 or the current ISBN-13 format. You want to allow a leading “ISBN” identifier, and ISBN parts can optionally be separated by hyphens or spaces. All of the following are examples of valid input:

• ISBN 978-0-596-52068-7

• ISBN-13: 978-0-596-52068-7

• 978 0 596 52068 7

• 9780596520687

• ISBN-10 0-596-52068-9

• 0-596-52068-9

Solution

You cannot validate an ISBN using a regex alone, because the last digit is computed using a checksum algorithm. The regular expressions in this section validate the format of an ISBN, whereas the subsequent code examples include a validity check for the final digit.

Regular expressions

Three regex solutions follow that allow you to match ISBN-10s and ISBN-13s, either exclusively or together. Each of the solutions is shown with and without free-spacing and comments. JavaScript doesn’t support free-spacing, but with other programming languages you can choose whichever suits you best.

In the free-spaced regexes, literal space characters have been escaped with backslashes. Java’s free-spacing mode requires that even spaces within character classes be escaped.

ISBN-10:

^(?:ISBN(?:-10)?:?●)?(?=[0-9X]{10}$|(?=(?:[0-9]+[-●]){3})[-●0-9X]{13}$)↵
[0-9]{1,5}[-●]?[0-9]+[-●]?[0-9]+[-●]?[0-9X]$

Regex options: None

Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

^ (?:ISBN(?:-10)?:?\ )? # Optional ISBN/ISBN-10 identifier. (?= # Basic format ...