Cron expression parser

Given a cron expression, you can get the previous timestamp or the next timestamp that satisfies the cron expression.

I have used cron expression syntax to implement a new feature called deploy freeze window in Gitploy.

Install

go get github.com/gitploy-io/cronexpr

Usage

Import the package, first:

import "time"
import "github.com/gitploy-io/cronexpr"

prevTime := cronexpr.MustParse("0 0 29 * *").Prev(time.Now())
nextTime := cronexpr.MustParse("0 0 29 * *").Next(time.Now())

You can check the detail in the _example directory.

Implementation

Field name     Mandatory?   Allowed values    Allowed special characters
----------     ----------   --------------    --------------------------
Minutes        Yes          0-59              * / , -
Hours          Yes          0-23              * / , -
Day of month   Yes          1-31              * / , - 
Month          Yes          1-12 or JAN-DEC   * / , -
Day of week    Yes          0-6 or SUN-SAT    * / , - 

Asterisk ( * )

The asterisk indicates that the cron expression matches for all values of the field. E.g., using an asterisk in the 4th field (month) indicates every month.

Slash ( / )

Slashes describe increments of ranges. For example 3-59/15 in the minute field indicate the third minute of the hour and every 15 minutes thereafter (i.e. 3, 18, 33, and 48). The form */... is equivalent to the form "first-last/...", that is, an increment over the largest possible range of the field.

Comma ( , )

Commas are used to separate items of a list. For example, using MON,WED,FRI in the 5th field (day of week) means Mondays, Wednesdays and Fridays.

Hyphen ( - )

Hyphens define ranges. For example, 0-6 indicates every hours between 0 and 6 AM, inclusive.

Details

• The return value of Next and Prev is zero if the pattern doesn't match in five years.