Title: Matching Royal Mail Postal Codes
Submitter: Ken Simpson (other recipes)
Last Updated: 2001/06/20
Version no: 1.0
Category: Miscellaneous

Description:

This regular expression matches valid postal codes as defined by the Royal Mail
(the UK's postal company).

Usage: Text Source

#!/usr/bin/perl -w
# postcode - validate British post codes (demo for clpm)
# Craig Berry (20010614)

use strict;

my @patterns = ('AN NAA', 'ANN NAA', 'AAN NAA', 'AANN NAA',
                'ANA NAA', 'AANA NAA', 'AAA NAA');

foreach (@patterns) {
  s/A/[A-Z]/g;
  s/N/\\d/g;
  s/ /\\s?/g;
}

my $re = join '|', @patterns;

while (<>) {
  print /^(?:$re)$/o ? "valid\n" : "invalid\n";
}

The license for this recipe is available here.

Discussion:

This regular expression comes to us from Craig Berry from a posting
in the comp.lang.perl.misc newsgroup (article 30293132).
The regular expression is built by grokking the @patterns array, replacing A's
with [A-Z], N's with \d, and spaces with \s? and combining the elements of
the array with branch operators (i.e., the pipe character, '|').