using regex to find invalid postcode - php

Question

I'm new to php and I'm trying to write a function to find an invalid postcode. This is an option, however I've been told this isnt the ideal format:
function postcode_valid($postcode) {
return preg_match('/\w{2,3} \d\w{2}/', $postcode);
}
//more accurate
//[A-Z]{1,2}[0-9]{1,2}[A-Z]? [0-9][A-Z]{2}
I understand the first function, but I don't know how to write the 'ideal' solution as a function, please can you advise?

Answer 1

If the regular expression you provided in the comment field is the correct one and you don't know how to use it in PHP, here is the solution:
function postcode_valid($postcode) {
return preg_match('/^[A-Z]{1,2}[0-9]{1,2}[A-Z]? [0-9][A-Z]{2}$/', $postcode);
}
You need to add two slashes (one in front, one at the end) of the regular expression and pack it in a string in PHP. I would also highly recommend you to use ^ and $ at the beginning resp. at the end of the regular expression to indicate the beginning and the end of the string (otherwise, it is valid, if only a part of the string contains the correct pattern i.e. a longer string with a valid part would be accepted.) Here is a live example.
If you are looking for the validation of a UK post code, you should be using the following regex instead (source):
(GIR 0AA)|((([A-Z-[QVX]][0-9][0-9]?)|(([A-Z-[QVX]][A-Z-[IJZ]][0-9][0-9]?)|(([A-Z-[QVX]][0-9][A-HJKPSTUW])|([A-Z-[QVX]][A-Z-[IJZ]][0-9][ABEHMNPRVWXY])))) [0-9][A-Z-[CIKMOV]]{2})
If you are looking for something else, please provide a comment below.