PHP regex pattern modification needed

Question

I'm sure this has been asked before and I did read through a lot of posts but nothing helped me. Since my regex knowledge is limited I thought I would ask for help.

I need to validate some user input (zip code format). Only certain characters are allowed: A , N , CC , ? , space ( ) and hyphen ( - ).

Sample Input Data

$input = "CC-XNNNNN", "ANNNNAAA", "AAAA NAA", "ANN ????"

Regex Pattern

$pattern = "(?:C{2})*|A*|N*|\?*|\-*|\ *"

PHP Code

if(preg_match('/' . $pattern . '/', $input))
{
 echo("pass<br>" . PHP_EOL);
}
else
{
 echo("fail<br>" . PHP_EOL);
}

I don't think I need to use anchors, because the allowed characters can be in any position. With the above code I get 'pass' but I should get 'fail' (X not allowed). I've looked this over so much I can't see the forest for the trees anymore.

Can anyone see what I've done wrong? OR is regex the wrong tool for this?

Answer 1

Could you please try following regex, written and tested with shown samples. Online demo of regex is: Regex online demo

^(?:[aA]|[nN]|[cC]{2}|\?|\s+|-)+$

Explanation: Adding detailed explanation for above.

^(?:       ##Starting a non capturing group from starting of value here.
[aA]       ##Checking if its either small a or capital A here.
|[nN]      ##OR if its N or n here.
|[cC]{2}   ##OR its c or C here with 2 occurrences.
|\?        ##Or its ? as a literal character.
|\s+       ##OR its one or more occurrences of spaces.
|-         ##OR its a dash
)+         ##Closing non capturing group and + will make sure only these characters follow
$          ##till end of the value.

Also I have matched characters with their small letter form also in case you don't need that we could change above to: ^(?:A|N|C{2}|\?|\s+|-)+$ then.

Answer 2

You could also use a character class instead of alternating between the single characters.

To also match the lowercase variant, you can use the /i flag

^(?:[AN? -]|CC)+$

The pattern matches:

• ^ Start of string
• (?: Non capture group
  • [AN? -] [AN? -] Match one of the listed characters
  • | Or
  • CC Match CC
• )+ Close the group and repeat it 1+ times
• $ End of string

Regex demo