PHP – Validate a UK postcode

Returns a true/false against a UK postcode, as well as attempting to format it correctly.

There are a million versions of this code on the internet, but being true to my FluffedVision roots and treating this as my notebook, rather than a traditional blog, I’m noting this snippet down here.

function isValidPostcode($originalPostcode)
{
    $alpha1 = "[abcdefghijklmnoprstuwyz]";
    $alpha2 = "[abcdefghklmnopqrstuvwxy]";
    $alpha3 = "[abcdefghjkpmnrstuvwxy]";
    $alpha4 = "[abehmnprvwxy]";
    $alpha5 = "[abdefghjlnpqrstuwxyz]";

    $pcexp[0] = '/^('.$alpha1.'{1}'.$alpha2.'{0,1}[0-9]{1,2})([[:space:]]{0,})([0-9]{1}'.$alpha5.'{2})$/';
    $pcexp[1] = '/^('.$alpha1.'{1}[0-9]{1}'.$alpha3.'{1})([[:space:]]{0,})([0-9]{1}'.$alpha5.'{2})$/';
    $pcexp[2] = '/^('.$alpha1.'{1}'.$alpha2.'{1}[0-9]{1}'.$alpha4.')([[:space:]]{0,})([0-9]{1}'.$alpha5.'{2})$/';
    $pcexp[3] = '/^(gir)([[:space:]]{0,})(0aa)$/';
    $pcexp[4] = '/^(bfpo)([[:space:]]{0,})([0-9]{1,4})$/';
    $pcexp[5] = '/^(bfpo)([[:space:]]{0,})(c/o([[:space:]]{0,})[0-9]{1,3})$/';
    $pcexp[6] = '/^([a-z]{4})([[:space:]]{0,})(1zz)$/';
    $pcexp[7] = '/^ai-2640$/';
    $postcode = strtolower($originalPostcode);

    $valid = FALSE;

    foreach ($pcexp as $regexp)
    {
        if (preg_match($regexp, $postcode, $matches))
        {
            $postcode = strtoupper ($matches[1] . ' ' . $matches [3]);
            $postcode = preg_replace ('/C/O([[:space:]]{0,})/', 'c/o ', $postcode);
            preg_match($pcexp[7], strtolower($originalPostcode), $matches) AND $postcode = 'AI-2640';
            $valid = TRUE;
            break;
        }
    }

    return $valid ? $postcode : FALSE;
}

Usage:

if(isValidPostcode("thePostcodeToCheck"))
{
  // postcode is valid
}
else
{
  // postcode is not valid
}