<?php
 
$vat = "ATU12345678";
 $pattern = '/^(
                        (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
                        )$/x';
 
 
        $match = preg_match($pattern,$vat);
        echo $match;

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