Correct Regular expressions to match a date

What i开发者_C百科s the correct regular expression to use to validate a date like. 2009-10-22 or 2009-01-01 etc. Platform PHP

This (from regexplib.com) will match what you want, and perform checks for leap years, days-per-month etc. It's a little more tolerant of separators than you want, but that can be easily fixed. As you can see, it's rather hideous.

Alternatively (and preferably in my opinion) you may want to simply check for figures in the correct places, and then perform leap year and days-per-month checks in code. Sometimes one regexp isn't so understandable and there's greater clarity in performing the checks in code explicitly (since you can report precisely what's wrong - "only 30 days in November", rather than a "doesn't match pattern" message, which is next to useless)

If you want something simple that does a little more than just validates format, but doesn't go as far as validating how many days is in the month that is entered, or leap years, you can use this:

^(19|20)[0-9]{2}-(0[1-9]|1[0-2])-(0[1-9]|[12][0-9]|3[01])$

This example allows years 19xx and 20xx

As you have to deal with accepting 2009-02-28 but not 2009-02-29 but accept 2008-02-28 you need more logic that 1 think a regex can give. (But if someone can show it I would be impressed)

I would try to convert it to a date and report if the conversion failed or if you you language has a check date function use that.

\d{4}-\d{2}-\d{2} would match string in that form, but to check if date is valid, you'd had to break that string to year, month and date (you can use this regexp for that) parts and check each of them.

You can additionally, make sure that year must start with 1 or 2: [12]\d{3}-\d{2}-\d{2}, and you can also do the same for month and day: [12]\d{3}-[01]\d-[0123]\d (but I would go with the first regexp and compare parts "manually")

found this on the web tested it with a few dates and looks stable, for dates between 1900 and 2000:

(19|20)\d\d[- /.](0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])

OK, a regex that will validate month and day ranges could be

[0-9]{4}-(?:1[0-2]|[1-9])-(?:3[01]|[12][0-9]|[1-9])

If you want to restrict the years, say, from 1900 to 2050, you could end up with

(?:2050|20[0-4][0-9]|19[0-9]{2})-(?:1[0-2]|[1-9])-(?:3[01]|[12][0-9]|[1-9])

They will not catch "subtly wrong" dates like February 31st, so it's really quite clear that a sanity check needs to be performed outside of the regex.

In .NET Regex:

\d{4}\-\d{2}\-\d{2}

[0-9]{4}-[0-9]{2}-[0-9]{2}

or

\d\d\d\d-\d\d-\d\d

or

...

simply read first regex tutorial

 ^\d{4}-\d{2}-\d{2}$

but no regular expression can prevent someone to enter "9867-39-56"

For a complete validation (which would include verifying that the day, month and year parts are valid) a Regex is not the tool of choice. Apart from month issues you'd get into trouble with leap years...

So, if you just want to check if the rough format is correct, or isolate the different parts (year-month-day), a regex is fine.

([0-9]{1,4})-(1[012]|0?[1-9])-([12][0-9]|3[01]|0?[1-9])

This is already pretty exact and captures the year (0..9999), month and day into capture groups, ready for parsing...

If you can rely on more than a regular expression, an hybrid solution by using Posix functions date() and time() delivered with PHP could look like this:

<?php
date_default_timezone_set("GMT");

function validateDate($date)
{
    if (preg_match("^[0-9]{4}-[0-9]{2}-[0-9]{2}^", $date))
    {
        return date('Y-m-d', strtotime($date)) === $date;
    }
    return false;
}

// Some tests
$dates = array(
    '2009-09-09', '2009-09-32', '2009-31-00', '2035-01-02',
);
foreach($dates AS $date)
{
    echo $date .': '. (validateDate($date) ? 'OK' : 'FAILS') ."\n";
}
?>

It's not elegant plus you'll be limited by Unix Epoch time (from January 1 1970 00:00:00 GMT to January 19 2038 03:14:07 GMT), but it's reliable and it's well supported in PHP.