isValidPostCode

In this final installment of the postal code trilogy, we turn our attention to the United Kingdom. Postal codes in the UK are called postcodes. They are similar to postal codes in Canada in that they contain both letters and numbers, but unlike Canadian postal codes, they are variable in length.

A postcode can have any of the following formats:

• A9 9AA
• A99 9AA
• A9A 9AA
• AA9 9AA
• AA99 9AA
• AA9A 9AA

To match all of these formats, we'll use the following regular expression: [A-PR-UWYZ]([0-9]{1,2}|([A-HK-Y][0-9]|[A-HK-Y][0-9]([0-9]|[ABEHMNPRV-Y]))|[0-9][A-HJKS-UW])\ [0-9][ABD-HJLNP-UW-Z]{2}. You may notice that, like Canadian postal codes, certain letters are only allowed in certain positions, or not at all.

There are also a few special cases that are valid postcodes but deviate from the regular format:

• Girobank - (GIR\ 0AA)
• Father Christmas - (SAN\ TA1)
• British Forces Post Office - (BFPO\ (C\/O\ )?[0-9]{1,4})
• Overseas territories - ((ASCN|BBND|[BFS]IQQ|PCRN|STHL|TDCU|TKCA)\ 1ZZ)

ASP

1. function isValidPostCode(postCode)
2.     dim regEx
4.     set regEx = new RegExp
6.     with regEx
7.         .IgnoreCase = true
8.         .Global = true
9.         .Pattern = "^([A-PR-UWYZ]([0-9]{1,2}|([A-HK-Y][0-9]|[A-HK-Y][0-9]([0-9]|[ABEHMNPRV-Y]))|[0-9][A-HJKS-UW])\ [0-9][ABD-HJLNP-UW-Z]{2}|(GIR\ 0AA)|(SAN\ TA1)|(BFPO\ (C\/O\ )?[0-9]{1,4})|((ASCN|BBND|[BFS]IQQ|PCRN|STHL|TDCU|TKCA)\ 1ZZ))$"
10.     end with
12.     if regEx.Test(trim(CStr(postCode))) then
13.         isValidPostCode = true
14.     else
15.         isValidPostCode = false
16.     end if
18.     set regEx = nothing
19. end function

PHP

1. function isValidPostCode($postCode)
2. {
3.     $pattern = "/^([A-PR-UWYZ]([0-9]{1,2}|([A-HK-Y][0-9]|[A-HK-Y][0-9]([0-9]|[ABEHMNPRV-Y]))|[0-9][A-HJKS-UW])\ [0-9][ABD-HJLNP-UW-Z]{2}|(GIR\ 0AA)|(SAN\ TA1)|(BFPO\ (C\/O\ )?[0-9]{1,4})|((ASCN|BBND|[BFS]IQQ|PCRN|STHL|TDCU|TKCA)\ 1ZZ))$/i";
4.     return (preg_match($pattern, trim($postCode)) > 0) ? true : false;
5. }

• View ASP implementation on Snipplr
• View PHP implementation on Snipplr