PHP partial postcode match

Question

I am trying to create a simple postcode form where a users enters a postcode and if the postcode exists, the user is redirected to a link.

So, I have this html form:

<form method="get" action="index.php">
    <input type="text" class="form-control input-lg" name="postcode" id="postcode" placeholder="Postcode">
    <span class="input-group-btn">
    <input class="btn btn-default btn-lg find" name="did_submit" id="submithome" type="submit" value="Find My Matchmaker" class="searchbutton">
    </span>
</form>

And the PHP script:

<?php
  if(isset($_GET['postcode'])){
      $valid_prefixes = array(
          2 => array('NH', 'AQ'),
          3 => array('NZ2', 'GT5'),
          4 => array('NG89', 'NG76')
      );

  foreach($valid_prefixes as $length => $prefixes) {
      if (in_array(substr($_GET['postcode'], 0, $length), $prefixes)) {
          header("Location: http://www.google.com/");
      } else {
          echo "<script> $('#myModal').modal('show') </script>";
      }
      exit;
  }}
?>

So, if the entered postcode is CV or NG, the script will redirect the user to google and if not, a modal would be launched.

Now the question. Obviously, the users would enter CV12DB (full postcode) and they would get the modal as if the postcode doesn't exist. What I am trying to do with the PHP script is to search what the user has entered and if his postcode contains CV or NG or SH, redirect him to google.

I have tried using "preg_match" or using keys instead of the array, but with no luck.. I can't seem to figure out how to make it work.

UPDATE After replacing the code, for some reason, it only recognizes the two-letter array. For example if NG76PL is entered, it doesn't recognize it so it goes to "else"

Answer 1

Should it start with one of those two-letter combinations? Then use:

if (in_array(substr($_GET['postcode'], 0, 2), $validatepostcode) {
    // redirect
}

If you have multiple length prefixes you can use:

for ($i = $min_prefix_length; $i <= $max_prefix_length; $i++) {
    if (in_array(substr($_GET['postcode'], 0, $i), $validatepostcode) {
        // redirect
    }
}

Or (more efficient):

$valid_prefixes = array(
    2 => array('NH', 'AQ'),
    3 => array('NZ2', 'GT5'),
);
foreach($valid_prefixes as $length => $prefixes) {
    if (in_array(substr($_GET['postcode'], 0, $length), $prefixes) {
        // redirect
    }
}

You can use regular expressions like ^(NH|AQ|NZ2|GT5) but I don't think that would be a good solution if you have a lot of options.