date format validation: Validate a date in "YYYY-MM-DD" format. - From http://snippetlib.com/php/date_format_validation

validation_date.php

<?php

/**
 * check for date-format
 *
 * @param string $date valid is only "YYYY-MM-DD"
 *
 * @return bool
 */
function checkDateFormat($date)
{
  // match the format of the date
  if (preg_match ("/^([0-9]{4})-([0-9]{2})-([0-9]{2})$/", $date, $parts))
  {

    // check whether the date is valid or not
    if (checkdate($parts[2],$parts[3],$parts[1])) {
      return true;
    } else {
      return false;
    }

  } else {
    return false;
  }
}