Cronfab

Cronfab is a crontab time-and-date specification parser and processor with a configurable calendar.

For projects that need extensibility beyond standard cron libraries like robfig/cron, cronfab exposes a configurable field system: define custom calendar fields (e.g. week-of-month, moon phase) with named ranges and arbitrary units — no forking required.

All the standard crontab features are supported:

• units may be specified by number or name (with prefix matching — jan, mon, etc.)
• lists and ranges are supported
• step values are supported
• aliases: @yearly, @annually, @monthly, @weekly, @daily, @midnight, @hourly

Cronfab does not support shell command execution.

Built-in Configs

• DefaultCrontabConfig — classic 5-field: minute, hour, day-of-month, month, day-of-week
• SecondCrontabConfig — 7-field: second, minute, hour, day-of-month, week-of-month, month, day-of-week

Both configs include aliases (@daily, @hourly, etc.) that expand to their corresponding expressions.

Example

markers, err := cronfab.DefaultCrontabConfig.ParseCronTab("*/5 * * * *")
if err != nil {
	log.Fatal(err)
}

next, err := cronfab.DefaultCrontabConfig.Next(markers, time.Now())
if err != nil {
	log.Fatal(err)
}
fmt.Println(next)

Aliases work the same way:

markers, err := cronfab.DefaultCrontabConfig.ParseCronTab("@daily")

Custom Calendars

FieldConfig fields are exported, so any package can construct its own calendar by implementing the Unit interface and calling NewCrontabConfig:

config, err := cronfab.NewCrontabConfig([]cronfab.FieldConfig{
	{
		Unit:     cronfab.HourUnit{},
		Name:     "hour",
		Min:      0,
		Max:      23,
		GetIndex: func(t time.Time) int { return t.Hour() },
	},
	{
		Unit:       MoonPhaseUnit{},
		Name:       "moon phase",
		RangeNames: []string{"new", "waxingcrescent", "firstquarter", "waxinggibbous", "full", "waninggibbous", "thirdquarter", "waningcrescent"},
		Min:        0,
		Max:        7,
		GetIndex:   moonPhaseIndex,
	},
})

Custom configs can also define their own aliases by setting the Aliases map on the returned *CrontabConfig.

A full working example is in examples/lunar.