You’re given the job of implementing an online order form for a business in the European Union.
European tax laws stipulate that when a VAT-registered business (your customer) located in one EU country purchases from a vendor (your company) in another EU country, the vendor must not charge VAT (Value-Added Tax). If the buyer is not VAT-registered, the vendor must charge VAT and remit the VAT to the local tax office. The vendor must use the VAT registration number of the buyer as proof to the tax office that no VAT is due. This means that for the vendor, it is very important to validate the buyer’s VAT number before proceeding with the tax-exempt sale.
The most common cause of invalid VAT numbers are simple typing mistakes by the customer. To make the ordering process faster and friendlier, you should use a regular expression to validate the VAT number immediately while the customer fills out your online order form. You can do this with some client-side JavaScript or in the CGI script on your web server that receives the order form. If the number does not match the regular expression, the customer can correct the typo right away.
To keep the implementation simple, this solution is split into two parts. First we strip out spaces and punctuation. Then we validate what remains.
Retrieve the VAT number entered by the customer and store it into a variable. Before performing the check for a valid number, replace all matches of this regular expression with a blank replacement text:
[-.●]| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Recipe 3.14 shows you how to perform this initial replacement. We’ve assumed that the customer wouldn’t enter any punctuation except hyphens, dots, and spaces. Any other extraneous characters will be caught by the upcoming check.
With whitespace and punctuation stripped, this regular expression checks whether the VAT number is valid for any of the 27 EU countries:
^(
(AT)?U[0-9]{8} | # Austria
(BE)?0[0-9]{9} | # Belgium
(BG)?[0-9]{9,10} | # Bulgaria
(CY)?[0-9]{8}L | # Cyprus
(CZ)?[0-9]{8,10} | # Czech Republic
(DE)?[0-9]{9} | # Germany
(DK)?[0-9]{8} | # Denmark
(EE)?[0-9]{9} | # Estonia
(EL|GR)?[0-9]{9} | # Greece
(ES)?[0-9A-Z][0-9]{7}[0-9A-Z] | # Spain
(FI)?[0-9]{8} | # Finland
(FR)?[0-9A-Z]{2}[0-9]{9} | # France
(GB)?([0-9]{9}([0-9]{3})?|[A-Z]{2}[0-9]{3}) | # United Kingdom
(HU)?[0-9]{8} | # Hungary
(IE)?[0-9]S[0-9]{5}L | # Ireland
(IT)?[0-9]{11} | # Italy
(LT)?([0-9]{9}|[0-9]{12}) | # Lithuania
(LU)?[0-9]{8} | # Luxembourg
(LV)?[0-9]{11} | # Latvia
(MT)?[0-9]{8} | # Malta
(NL)?[0-9]{9}B[0-9]{2} | # Netherlands
(PL)?[0-9]{10} | # Poland
(PT)?[0-9]{9} | # Portugal
(RO)?[0-9]{2,10} | # Romania
(SE)?[0-9]{12} | # Sweden
(SI)?[0-9]{8} | # Slovenia
(SK)?[0-9]{10} # Slovakia
)$| Regex options: Free-spacing, case insensitive |
| Regex flavors: .NET, Java, XRegExp, PCRE, Perl, Python, Ruby |
The above regular expression uses free-spacing mode to make it easy to edit later. Every now and then, new countries join the European Union, and member countries change their rules for VAT numbers. Unfortunately, JavaScript does not support free-spacing. In this case, you’re stuck putting everything on one line:
^((AT)?U[0-9]{8}|(BE)?0[0-9]{9}|(BG)?[0-9]{9,10}|(CY)?[0-9]{8}L|↵
(CZ)?[0-9]{8,10}|(DE)?[0-9]{9}|(DK)?[0-9]{8}|(EE)?[0-9]{9}|↵
(EL|GR)?[0-9]{9}|(ES)?[0-9A-Z][0-9]{7}[0-9A-Z]|(FI)?[0-9]{8}|↵
(FR)?[0-9A-Z]{2}[0-9]{9}|(GB)?([0-9]{9}([0-9]{3})?|[A-Z]{2}[0-9]{3})|↵
(HU)?[0-9]{8}|(IE)?[0-9]S[0-9]{5}L|(IT)?[0-9]{11}|↵
(LT)?([0-9]{9}|[0-9]{12})|(LU)?[0-9]{8}|(LV)?[0-9]{11}|(MT)?[0-9]{8}|↵
(NL)?[0-9]{9}B[0-9]{2}|(PL)?[0-9]{10}|(PT)?[0-9]{9}|(RO)?[0-9]{2,10}|↵
(SE)?[0-9]{12}|(SI)?[0-9]{8}|(SK)?[0-9]{10})$| Regex options: Case insensitive |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Follow Recipe 3.6 to add this regular expression to your order form.
To make VAT numbers easier to read for humans, people often type
them in with extra punctuation to split the digits into groups. For
instance, a German customer might enter his VAT number DE123456789 as
DE
123.456.789.
A single regular expression that matches VAT numbers from 27 countries in any possible notation is an impossible job. Since the punctuation is only for readability, it is much easier to first strip all the punctuation, then validate the resulting bare VAT number.
The regular expression ‹[-.●]› matches a character that is a
hyphen, dot, or space. Replacing all matches of this regular
expression with nothing effectively deletes the punctuation characters
commonly used in VAT numbers.
The two regular expressions for validating the number are identical. The only difference is that the first one uses the free-spacing syntax to make the regular expression more readable, and to indicate the countries. JavaScript does not support free-spacing unless you use the XRegExp library. The other flavors give you the choice.
The regex uses alternation to accommodate the VAT numbers of all 27 EU countries. The essential formats are shown in Table 4-3.
Table 4-3. EU VAT number formats
Country | VAT number format |
|---|---|
Austria | U99999999 |
Belgium | 0999999999 |
Bulgaria | 999999999 or 9999999999 |
Cyprus | 99999999L |
Czech Republic | 99999999, 999999999, or 9999999999 |
Germany | 999999999 |
Denmark | 99999999 |
Estonia | 999999999 |
Greece | 999999999 |
Spain | X9999999X |
Finland | 99999999 |
France | XX999999999 |
United Kingdom | 999999999, 999999999999, or XX999 |
Hungary | 99999999 |
Ireland | 9S99999L |
Italy | 99999999999 |
Lithuania | 999999999 or 99999999999 |
Luxembourg | 99999999 |
Latvia | 99999999999 |
Malta | 99999999 |
Netherlands | 999999999B99 |
Poland | 999999999 |
Portugal | 999999999 |
Romania | 99, 999, 9999, 99999, 999999, 9999999, 99999999, 999999999, or 9999999999 |
Sweden | 99999999999 |
Slovenia | 99999999 |
Slovakia | 999999999 |
Strictly speaking, the two-letter country code is part of the VAT number. However, people often omit it, since the billing address already indicates the country. The regular expression will accept VAT numbers with and without the country code. If you want the country code to be mandatory, remove all the question marks from the regular expression. If you do, mention that you require the country code in the error message that tells the user the VAT number is invalid.
If you accept orders only from certain countries, you can leave
out the countries that don’t appear in the country selection on your
order form. When you delete an alternative, make sure to also delete
the ‹|› operator that
separates the alternative from the next or previous one. If you don’t,
you end up with ‹||› in
your regular expression. ‹||› inserts an alternative that matches the
empty string, which means your order form will accept the omission of
a VAT number as a valid VAT number.
The 27 alternatives are grouped together. The group is placed between a caret and a dollar sign, which anchor the regular expression to the beginning and ending of the string you’re validating. The whole input must validate as a VAT number.
If you’re searching for VAT numbers in a larger body of text,
replace the anchors with ‹\b› word boundaries.
The benefit of using one regular expression to check for all 27 countries is that you only need to add one regex validation to your order form. You could enhance your order form by using 27 separate regular expressions. First, check the country that the customer specified in the billing address. Then, look up the appropriate regular expression according to the country in Table 4-4.
Table 4-4. EU VAT number regular expressions
Country | VAT number regular expression |
|---|---|
Austria | ‹ |
Belgium | ‹ |
Bulgaria | ‹ |
Cyprus | ‹ |
Czech Republic | ‹ |
Germany | ‹ |
Denmark | ‹ |
Estonia | ‹ |
Greece | ‹ |
Spain | ‹ |
Finland | ‹ |
France | ‹ |
United Kingdom | ‹ |
Hungary | ‹ |
Ireland | ‹ |
Italy | ‹ |
Lithuania | ‹ |
Luxembourg | ‹ |
Latvia | ‹ |
Malta | ‹ |
Netherlands | ‹ |
Poland | ‹ |
Portugal | ‹ |
Romania | ‹ |
Sweden | ‹ |
Slovenia | ‹ |
Slovakia | ‹ |
Implement Recipe 3.6 to validate the VAT number against the selected regular expression. That will tell you if the number is valid for the country the customer claims to reside in.
The main benefit of using the separate regular expressions is that you can force the VAT number to start with the correct country code, without asking the customer to type it in. When the regular expression matches the provided number, check the contents of the first capturing group. Recipe 3.9 explains how to do this. If the first capturing group is empty, the customer did not type the country code at the start of the VAT number. You can then add the country code before storing the validated number in your order database.
Greek VAT numbers allow two country codes. EL is traditionally used for Greek VAT
numbers, but GR is the ISO country
code for Greece.
The regular expression merely checks if the number looks like a valid VAT number. This is enough to weed out honest mistakes. A regular expression obviously cannot check whether the VAT number is assigned to the business placing the order. The European Union provides a web page at http://ec.europa.eu/taxation_customs/vies/vieshome.do where you can check which business a particular VAT number belongs to, if any.
Techniques used in the regular expressions in this recipe are discussed in Chapter 2. Recipe 2.3 explains character classes. Recipe 2.5 explains anchors. Recipe 2.8 explains alternation. Recipe 2.9 explains grouping. Recipe 2.12 explains repetition.
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