Adapted from cronexpr

Cron

A cron expression parser and next occurrence calculator

Usage

import "time"
import "github.com/amasanelli/cron"

next := cron.MustParse("0 0 1 * 1", time.UTC).Next(time.Now())

Parse(cronExpression, timezone)

Parses the cron expression and sets it's timezone. The cron expression must be written for the desired timezone; e.g., if the cron should run every day at 00:00 in Melbourne the cron expression should be "0 0 * * *" and the

timezone, _ = time.LoadLocation("Australia/Melbourne")

It throws an error in case of failure.

MustParse(cronExpression, timezone)

Does the same as Parse, but it panics in case of failure

Next(referenceTime)

Calculares the next occurence for the cron expression and the given time. It converts the input to the timezone setted in the Parse/MustParse function to perform the calulation

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              * / , -
Day of week    Yes          0-6               * / , - 

Asterisk (*)

Asterisks indicate that the field matches all the allowed values; e.g., using an asterisk in the 4th field (months) means every month.

Slash (/)

Slashes are used to indicate steps; e.g., */15 in the 1st field (minutes) means that the cron will run every 15 minutes

Comma (,)

Commas are used to separate items of a list; e.g., 5-6,0-1 in the 5th field (dow) could be used to indicate a cron that runs from Friday to Monday

Hyphen (-)

Hyphens define ranges of values; e.g., 0-6 in the 2nd field (hours) indicates the range of hours from 0 to 6, inclusive