Need proper query to search for zip code with regex

[StevenHu]

I just heard that the proper way to search via ZIP code in the U.S. is by the first three digits. I'm trying to use regular expressions to do this, but can't get the syntax right. Here's what I have. It comes up blank with no error messages:

if(isset($_POST['postalcode'])) 
{
    $postalcode = $_POST['postalcode'];
    $postalcode = strip_tags($postalcode);
    $postalcode = trim($postalcode);
    $postalcode = htmlspecialchars($postalcode);

    // Grab first three digits of the zip code.
    $first3 = substr('$postalcode', 0, 3);

$searchsql = mysql_query 
    ("SELECT ID, Shop, Track, Country, Name, Street1, Street2, City, State, Zipcode, Phone, Fax, Email, WebSite, TrackInfo
    FROM shopdirectory
    WHERE Zipcode LIKE '%$first3%' ORDER BY Zipcode ASC
    ");
if (!$searchsql) {
    die('Invalid query: ' . mysql_error()); } 

Is my regular expression wrong or the query?

Thanks!

[r937]

WHERE Zipcode LIKE '$first3%'

notice no leading wildcard character

and by the way, LIKE and REGEXP are completely different

[StevenHu]

I could put '92708' in the search box for the old code and it would return one result. This change in the code did not return anything.

I guess substr() is not a regex but a function. Faux pas!