Cron工作计算

Question

I have several cron jobs and I'd like to perform some calculations on them, so I know the next time the cron jobs are executed.

For example:

30-12-2011 15:30 is the current local time, 
0 0,3,6,9,12,15,18,21 * * * is one of my cron jobs,
30-12-2011 18:00 should be the next time the cron is executed.

Doing these calculations by hand seems too hard, especially when the cron jobs become more complex. Or is there an easy way to do this?

I searched for (small) PHP libraries that can do this, but with no result. Do you know if there are any libraries available that can perform these calculations?

Answer 1

I've used the PHP Cron Expression Parser library before -- PHP 5.3+ only, but it works extremely well.