UK Postcode Regex

Most UK postcode regexes seem to be strict validators. For London Cinema I am more interested in what the user meant than I am in making sure they have entered an exactly legal postcode.

The Google geocoding stuff that I use in my geocoder is surprisingly unliberal in what it accepts (for example it won’t accept a postcode with a missing space), probably because it is using a strict validator like those you can find all over the web. I wrote this disambiguation function that tries to turn possibly-funky user input into a canonical postcode. The test uses genuine inputs to London Cinema from the last few days.

function disambiguate_uk_postcode($s) {
    $target = str_replace(' ', '', mb_strtoupper($s));
    $postcode_finder = '/^([A-Z][A-Z]?)([O0-9][O0-9]?)([A-Z]?)([O0-9])([A-Z][A-Z])$/';
    if (preg_match($postcode_finder, $target, $matches)) {
        return $matches[1] . str_replace('O', '0', $matches[2]) . $matches[3]
            . " " . str_replace('O', '0', $matches[4]) . $matches[5];
    } else {
        return $s;
    }
}

function test_disambiguate_uk_postcode() {
    assert(disambiguate_uk_postcode('se 15 5 ed') === 'SE15 5ED');
    assert(disambiguate_uk_postcode('se229ef') === 'SE22 9EF');
    assert(disambiguate_uk_postcode('wc1n1as') === 'WC1N 1AS');
    assert(disambiguate_uk_postcode('w111pg') === 'W11 1PG');
    assert(disambiguate_uk_postcode('e113bz') === 'E11 3BZ');
    assert(disambiguate_uk_postcode('cro 5al') === 'CR0 5AL');
    assert(disambiguate_uk_postcode('E15JA') === 'E1 5JA');
    assert(disambiguate_uk_postcode('ha80hb') === 'HA8 0HB');
    assert(disambiguate_uk_postcode('E4 7 DT') === 'E4 7DT');
    assert(disambiguate_uk_postcode('SW179HN') === 'SW17 9HN');
    assert(disambiguate_uk_postcode('south woodford') === 'south woodford');
}

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