Simple regex for Canadian postal codes in PHP

valid-canadian-postal-code.php

<?php

// test with: `php valid-canadian-postal-code.php`

$expression = '/^([a-zA-Z]\d[a-zA-Z])\ {0,1}(\d[a-zA-Z]\d)$/';

// lower, no space
$valid = (bool)preg_match($expression, 'k0a3m0');

var_dump($valid);

// lower, with space
$valid2 = (bool)preg_match($expression, 'k0a 3m0');

var_dump($valid2);

// mixed case, with space
$valid3 = (bool)preg_match($expression, 'K0a 3M0');

var_dump($valid3);

// all upper case, with space
$valid4 = (bool)preg_match($expression, 'K0A 3M0');

var_dump($valid4);

// all upper case, with no space
$valid5 = (bool)preg_match($expression, 'K0A3M0');

var_dump($valid5);

// all upper case, with too many spaces
$invalid = (bool)preg_match($expression, 'K0A  3M0');

var_dump($invalid);

// with leading digit
$invalid2 = (bool)preg_match($expression, '00A 3M0');

var_dump($invalid2);