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Algorithm::CheckDigits::M23_002(3pm) User Contributed Perl Documentation Algorithm::CheckDigits::M23_002(3pm)


CheckDigits::M23_002 - compute check digits for Tax Identification Number (IE)


  use Algorithm::CheckDigits;
  $dni = CheckDigits('tin_ie');
  if ($dni->is_valid('8473625E')) {
        # do something
  $cn = $dni->complete('1234567.W');
  # $cn = '1234567TW'
  $cd = $dni->checkdigit('1234577IA');
  # $cd = 'I'
  $bn = $dni->basenumber('1234577WW');
  # $bn = '1234577.W'



The irish TIN (Tax Identification Number) or VAT Regstration Number consists of 7 digits, a letter in the range from 'A' - 'W' as checksum, and an optionally letter in the range from 'A' - 'I' or the letter 'W'.

In reverse order, each digit is multiplied by a weight started at 2. (i.e. the number left from the check digit is multiplied with 2, the next with 3 and so on).
If there is an optional letter following the checksum letter (position 9), this letter is mapped to a numeric value based on the following mapping: "A" = 1, "B" = 2, ... "H" = 8, "I" = 9. "W" or absence of this letter means a value of 0. This numeric value is multiplied with 9.
All products from step 1 and 2 are added.
The check digit is the sum from step 3 modulo 23. This number is expressed as the corresponding letter from the alphabet where A-V correspond to 1-22 and W stands for check digit 0.


Returns true only if $number complies with the rules given above and there is a valid check digit at position eight.

Returns false otherwise,

The check digit for $number is computed and inserted at position eight of $number.

Returns the complete number with check digit or '' if $number does not consist solely of digits and an optional letter at position nine.

Returns the basenumber of $number if $number has a valid check digit. As a placeholder for the checksum a point ('.') is inserted at position eight when the checksum contains the optional letter at position nine.

Return '' otherwise.

Returns the checkdigit of $number if $number has a valid check digit.

Return '' otherwise.


None by default.


Mathias Weidner, "<>"


perl, CheckDigits,

2021-11-17 perl v5.40.0