How to validate an UK (United Kingdom) Post Code

I had a client, David, from UK and he asked me to build him a user management script so I accepted the job.
When it came to validation I was, at first, intrigued by their post code system (here,in my country, it is very simple : 6 digits, ex : 505200 ) but after I read some documents the UK system was also very simple .
The accepted formats are :

Besides this table there is an exception : GIR 0AA, a Postcode that was issued historically.
So, a function to do this validation will need to take in consideration that the user may or may not insert the space/s so the first thing needed to be done is to strip the spaces from the input parameter. The next step is to see if we have a match using the preg_match function and then return the result (true or false).

(If you want to copy it use the (Show Plain Code link))

function IsPostcode($postcode)
{
$postcode = strtoupper(str_replace(' ','',$postcode));
if(preg_match("/^[A-Z]{1,2}[0-9]{2,3}[A-Z]{2}$/",$postcode) || preg_match("/^[A-Z]{1,2}[0-9]{1}[A-Z]{1}[0-9]{1}[A-Z]{2}$/",$postcode) || preg_match("/^GIR0[A-Z]{2}$/",$postcode))
return true;
else
return false;
}

How to use it? Just like a normal PHP function ….

$e = "AB235RB";
if (IsPostcode($e))
print "Valid Post Code";
else
print "Invalid Post Code";

Bibliography :

• http://php.net/preg_match – The preg_match function documentation + examples
• http://www.govtalk.gov.uk/gdsc/html/frames/PostCode.htm – UK Government Data Standards Catalogue : Postcode