PHP function that receive a cron string and return the next run timestamp

Question

I need to develop a task system that should be able to work on servers that doesn't support crontab.

I'm asking if there is any existing code that can take a cron string (e.g. '0 0,12 1 */2 *' and return the timestamp of the next scheduled run.

If such a code couldn't be found then how should I start with that?

Solution 1

You could use this class PHP-Parse-cron-strings-and-compute-schedules

It'll also compute the last scheduled run

Solution 2

Use this function:

function parse_crontab($time, $crontab)
         {$time=explode(' ', date('i G j n w', strtotime($time)));
          $crontab=explode(' ', $crontab);
          foreach ($crontab as $k=>&$v)
                  {$time[$k]=intval($time[$k]);
                   $v=explode(',', $v);
                   foreach ($v as &$v1)
                           {$v1=preg_replace(array('/^\*$/', '/^\d+$/', '/^(\d+)\-(\d+)$/', '/^\*\/(\d+)$/'),
                                             array('true', $time[$k].'===\0', '(\1<='.$time[$k].' and '.$time[$k].'<=\2)', $time[$k].'%\1===0'),
                                             $v1
                                            );
                           }
                   $v='('.implode(' or ', $v).')';
                  }
          $crontab=implode(' and ', $crontab);
          return eval('return '.$crontab.';');
         }
var_export(parse_crontab('2011-05-04 02:08:03', '*/2,3-5,9 2 3-5 */2 *'));
var_export(parse_crontab('2011-05-04 02:08:03', '*/8 */2 */4 */5 *'));

Solution 3

You can try this: http://mtdowling.com/blog/2012/06/03/cron-expressions-in-php/ which use PHP Cron-Expression parser library, a php class https://github.com/mtdowling/cron-expression

Solution 4

I found diyism had a great answer, but found a crucial bug.

If you enter a cron time such as 0 * * * *, it'll run at 0 minute, 8th, minute and 9th minute. The code gives a conditional 08===0, which returns true, because PHP interprets numbers starting with 0 as octal, and 08 and 09 are not valid octal numbers so they're interpreted as 0. More information here.

How to prevent PHP from doing octal math in conditionals? (why does 08 === 0)

Here's a fixed and well commented version of diyism's code.

// Parse CRON frequency
function parse_crontab($time, $crontab) {
    // Get current minute, hour, day, month, weekday
    $time = explode(' ', date('i G j n w', strtotime($time)));
    // Split crontab by space
    $crontab = explode(' ', $crontab);
    // Foreach part of crontab
    foreach ($crontab as $k => &$v) {
        // Remove leading zeros to prevent octal comparison, but not if number is already 1 digit
        $time[$k] = preg_replace('/^0+(?=\d)/', '', $time[$k]);
        // 5,10,15 each treated as seperate parts
        $v = explode(',', $v);
        // Foreach part we now have
        foreach ($v as &$v1) {
            // Do preg_replace with regular expression to create evaluations from crontab
            $v1 = preg_replace(
                // Regex
                array(
                    // *
                    '/^\*$/',
                    // 5
                    '/^\d+$/',
                    // 5-10
                    '/^(\d+)\-(\d+)$/',
                    // */5
                    '/^\*\/(\d+)$/'
                ),
                // Evaluations
                // trim leading 0 to prevent octal comparison
                array(
                    // * is always true
                    'true',
                    // Check if it is currently that time, 
                    $time[$k] . '===\0',
                    // Find if more than or equal lowest and lower or equal than highest
                    '(\1<=' . $time[$k] . ' and ' . $time[$k] . '<=\2)',
                    // Use modulus to find if true
                    $time[$k] . '%\1===0'
                ),
                // Subject we are working with
                $v1
            );
        }
        // Join 5,10,15 with `or` conditional
        $v = '(' . implode(' or ', $v) . ')';
    }
    // Require each part is true with `and` conditional
    $crontab = implode(' and ', $crontab);
    // Evaluate total condition to find if true
    return eval('return ' . $crontab . ';');
}

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