Validate UK Postcode - both short and long version

Question

I have tried the one on the .gov website, as stated on many questions here, but it doesnt seem to work for short postcodes.

My regex:

preg_match('^(([gG][iI][rR] {0,}0[aA]{2})|((([a-pr-uwyzA-PR-UWYZ][a-hk-yA-HK-Y]?[0-9][0-9]?)|(([a-pr-uwyzA-PR-UWYZ][0-9][a-hjkstuwA-HJKSTUW])|([a-pr-uwyzA-PR-UWYZ][a-hk-yA-HK-Y][0-9][abehmnprv-yABEHMNPRV-Y]))) {0,}[0-9][abd-hjlnp-uw-zABD-HJLNP-UW-Z]{2}))^', $this->post['location'], $matches)

When I use a long postcode of format: AA9 9ZZ it works, but one of format AA9 doesnt. I need the following formats to work:

• AA9
• AA99
• AA9 9ZZ
• AA99 9ZZ

Answer 1

According to the pattern you have given and making the second part optional, I obtain:

~^(?:gir(?: *0aa)?|[a-pr-uwyz](?:[a-hk-y]?[0-9]+|[0-9][a-hjkstuw]|[a-hk-y][0-9][abehmnprv-y])(?: *[0-9][abd-hjlnp-uw-z]{2})?)$~i

demo

or to make it more readable:

~ # pattern delimiter
^ # start of the string anchor
(?: # branch 1
    gir
    (?:[ ]*0aa)? # second part optional (branch 1)
  | # branch 2
    [a-pr-uwyz] # I put it in factor to shorten the pattern
    (?:
        [a-hk-y]?[0-9]+
      |
        [0-9][a-hjkstuw]
      |
        [a-hk-y][0-9][abehmnprv-y]
    )
    (?:[ ]*[0-9][abd-hjlnp-uw-z]{2})? # second part optional (branch 2)
)
$ # end of the string anchor
~ix