Parse/evaluate/generate CrontabExpressions outside of linux?

Question

I\'m building some software that needs a scheduling input, and I\'d really like to re-use the design of crontab because it simply works.

CrontabExpressions can be re

Answer 1

To output the next 25 timestamps that match the crontab you could use crontab Python module:

from datetime import datetime, timedelta
import crontab

tab = crontab.CronTab('2-59/3 1,9,22 11-26 1-6 ? 2012')

dt = datetime.now()
for _ in xrange(25):
    delay = tab.next(dt) # seconds before this crontab entry can be executed.
    dt += timedelta(seconds=delay)
    print(dt)

Output

2012-01-11 22:41:00
2012-01-11 22:44:00
2012-01-11 22:47:00
2012-01-11 22:50:00
2012-01-11 22:53:00
2012-01-11 22:56:00
2012-01-11 22:59:00
2012-01-12 01:02:00
2012-01-12 01:05:00
2012-01-12 01:08:00
2012-01-12 01:11:00
2012-01-12 01:14:00
2012-01-12 01:17:00
2012-01-12 01:20:00
2012-01-12 01:23:00
2012-01-12 01:26:00
2012-01-12 01:29:00
2012-01-12 01:32:00
2012-01-12 01:35:00
2012-01-12 01:38:00
2012-01-12 01:41:00
2012-01-12 01:44:00
2012-01-12 01:47:00
2012-01-12 01:50:00
2012-01-12 01:53:00

There is also python-crontab that provides crontab module but with richer functionality (parse/generate).

Answer 2

There is a Java library as part of the Quartz Scheduler which can be used to evaluate cron expressions quite easily.

The class CronExpression yields methods like isSatisfiedBy(Date date) or getNextValidTimeAfter(Date date) which is very useful.

The library is freely available.