This code snippet is a regular expression which checks or validates a credit card number.

The Expression

^([0-9]{4})[-|s]*([0-9]{4})[-|s]*([0-9]{4})[-|s]*([0-9]{2,4})$

This regular expression will match any of the following credit card number formats:

• 0000-0000-0000-0000
• 0000-0000-0000-000
• 0000-0000-0000-00
• 0000 0000 0000 0000
• 0000 0000 0000 000
• 0000 0000 0000 00
• 0000000000000000
• 000000000000000
• 00000000000000

Validate Function

Here is a quick and simple validation function for a credit card number using the regular expression above and PHP’s preg_match() function:

function validate_credit_card_number($string)
{
	if(preg_match('/^([0-9]{4})[-|s]*([0-9]{4})[-|s]*([0-9]{4})[-|s]*([0-9]{2,4})$/', $string))
	{
		return TRUE;
	}
	else
	{
		return FALSE;
	}
}

Modify the Data

$string = "1234123412341234";
preg_match('/^([0-9]{4})[-|s]*([0-9]{4})[-|s]*([0-9]{4})[-|s]*([0-9]{2,4})$/', $string, $matches);
$new_string = $matches[1] . '-' . $matches[2] . '-' . $matches[3] . '-' . $matches[4];

// New String:
// 1234-1234-1234-1234

There you go! If you find you need another format or you’d like a different type of string to validate, please send me an email and I will respond as quickly as I can.