PHP preg_match yyyy-mm-dd

Question

I need some help with a regular expressions. I'm trying to validate if a string looks like 'yyyy-mm-dd', this is my code so far:

case "date":
                if (preg_match("/^[0-9\-]/i",$value)){
                    $date = explode("-",$value);
                    $year = $date[0];
                    $month = $date[1];
                    $day = $date[2];
                    if (!checkdate($month,$day,$year))
                    {
                        $this->errors[] = "Ogiltigt datum.";
                    }
                } else {
                    $this->errors[] = "Ogiltigt datum angivet.";
                }
            break;

I am very new to regular expressions, thanks.

Are you sure? Will you allow 9999-99-99 as well? Or are you looking to see if a date is valid or not? — Madara's Ghost, Jan 11 '14 at 16:40
Yes, I'm just making sure it looks like a correct date, then I explode it and validate it using checkdate(), which take everything in consideration, leap years etc. — Petter Pettersson, Jan 11 '14 at 16:40
possible duplicate of [PHP Regex to check date is in YYYY-MM-DD format](http://stackoverflow.com/questions/13194322/php-regex-to-check-date-is-in-yyyy-mm-dd-format) — Matt Johnson-Pint, Jun 18 '14 at 04:23

Casimir et Hippolyte · Accepted Answer · 2017-05-16T10:14:07.787

10

You can use this:

if ( preg_match('/^[0-9]{4}-[0-9]{2}-[0-9]{2}\z/', $value) ) { ...

however this kind of pattern can validate something like 0000-40-99

pattern details:

/         # pattern delimiter
^         # anchor: start of the string
[0-9]{4}  # four digits
-         # literal: -
[0-9]{2}
-
[0-9]{2}
\z        # anchor: end of the string
/         # pattern delimiter

edited May 16 '17 at 10:14

answered Jan 11 '14 at 16:38

Casimir et Hippolyte

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Thanks that works great, but could anyone explain why? I'd like to know why and how it works, thanks. – Petter Pettersson Jan 11 '14 at 16:41
@PetterPettersson: `[0-9]` = any character between 0 to 9. `{4}` previous character class (0 to 9) 4 times. `-` dash, and so on. See https://www.debuggex.com/r/iDL-oQxvjyTC2AhF – Madara's Ghost Jan 11 '14 at 16:42
@PetterPettersson: I added a description of the pattern, however keep in mind that this use only very basic regex notions. I suggest you to read a tutorial about regex, for example: http://regular-expressions.info – Casimir et Hippolyte Jan 11 '14 at 16:46
Thanks, I will check this out. I will use your answer as best answer. – Petter Pettersson Jan 11 '14 at 16:47

falsetru · Answer 2 · 2014-01-11T16:49:15.050

2

Using capturing group, you don't need call explode.

if (preg_match('/^(\d{4})-(\d{2})-(\d{2})$/', $value, $matches)) {
    $year = $matches[1];
    $month = $matches[2];
    $day = $matches[3];
    ...
}

\d matches any digit characters.
{n} is quantifier: to match previous pattern exactly 4 times.
You can access the matched group using $matches[1], $matches[2], ...
- $matches[0] contains entire matched string.

edited Jan 11 '14 at 16:49

answered Jan 11 '14 at 16:40

falsetru

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Thanks, that worked, I never thought about the $matches thing, it worked great as well. – Petter Pettersson Jan 11 '14 at 16:50

score 0 · Answer 3 · edited May 23 '17 at 12:26

0

While you can use regex one can also use a simple function to validate the date according to the Swedish format (yyyy-mm-dd) or any other format for that matter.

function validateDate($date, $format = 'Y-m-d H:i:s') {
    $d = DateTime::createFromFormat($format, $date);
    return $d && $d->format($format) == $date;
}

var_dump(validateDate('2014-01-11', 'Y-m-d')); // true
var_dump(validateDate('2014-1-11', 'Y-m-d')); // false

^{function was copied from this answer or php.net}

edited May 23 '17 at 12:26

Community

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answered Jan 11 '14 at 16:54

user555

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Yes, but this is the function I'm building to use for validating dates. – Petter Pettersson Jan 11 '14 at 17:02
@PetterPettersson I'm just saying that you can validate the format and the date using only one function. – user555 Jan 11 '14 at 17:08

PHP preg_match yyyy-mm-dd

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