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Lightweight, fast and dependency-free Cron expression parser (due checker, next/prev due date finder), task runner, job scheduler and/or daemon for Golang (tested on v1.13+) and standalone usage. If you are bold, use it to replace crontab entirely.

License

adhocore/gronx

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adhocore/gronx

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gronx is Golang cron expression parser ported from adhocore/cron-expr with task runner and daemon that supports crontab like task list file. Use it programatically in Golang or as standalone binary instead of crond. If that's not enough, you can use gronx to find the next (NextTick()) or previous (PrevTick()) run time of an expression from any arbitrary point of time.

  • Zero dependency.
  • Very fast because it bails early in case a segment doesn't match.
  • Built in crontab like daemon.
  • Supports time granularity of Seconds.

Find gronx in pkg.go.dev.

Installation

go get -u github.com/adhocore/gronx

Usage

import (
	"time"

	"github.com/adhocore/gronx"
)

gron := gronx.New()
expr := "* * * * *"

// check if expr is even valid, returns bool
gron.IsValid(expr) // true

// check if expr is due for current time, returns bool and error
gron.IsDue(expr) // true|false, nil

// check if expr is due for given time
gron.IsDue(expr, time.Date(2021, time.April, 1, 1, 1, 0, 0, time.UTC)) // true|false, nil

Batch Due Check

If you have multiple cron expressions to check due on same reference time use BatchDue():

gron := gronx.New()
exprs := []string{"* * * * *", "0 */5 * * * *"}

// gives []gronx.Expr{} array, each item has Due flag and Err enountered.
dues := gron.BatchDue(exprs)

for _, expr := range dues {
    if expr.Err != nil {
        // Handle err
    } else if expr.Due {
        // Handle due
    }
}

// Or with given time
ref := time.Now()
gron.BatchDue(exprs, ref)

Next Tick

To find out when is the cron due next (in near future):

allowCurrent = true // includes current time as well
nextTime, err := gronx.NextTick(expr, allowCurrent) // gives time.Time, error

// OR, next tick after certain reference time
refTime = time.Date(2022, time.November, 1, 1, 1, 0, 0, time.UTC)
allowCurrent = false // excludes the ref time
nextTime, err := gronx.NextTickAfter(expr, refTime, allowCurrent) // gives time.Time, error

Prev Tick

To find out when was the cron due previously (in near past):

allowCurrent = true // includes current time as well
prevTime, err := gronx.PrevTick(expr, allowCurrent) // gives time.Time, error

// OR, prev tick before certain reference time
refTime = time.Date(2022, time.November, 1, 1, 1, 0, 0, time.UTC)
allowCurrent = false // excludes the ref time
nextTime, err := gronx.PrevTickBefore(expr, refTime, allowCurrent) // gives time.Time, error

The working of PrevTick*() and NextTick*() are mostly the same except the direction. They differ in lookback or lookahead.

Standalone Daemon

In a more practical level, you would use this tool to manage and invoke jobs in app itself and not mess around with crontab for each and every new tasks/jobs.

In crontab just put one entry with * * * * * which points to your Go entry point that uses this tool. Then in that entry point you would invoke different tasks if the corresponding Cron expr is due. Simple map structure would work for this.

Check the section below for more sophisticated way of managing tasks automatically using gronx daemon called tasker.


Go Tasker

Tasker is a task manager that can be programatically used in Golang applications. It runs as a daemon and invokes tasks scheduled with cron expression:

package main

import (
	"context"
	"time"

	"github.com/adhocore/gronx/pkg/tasker"
)

func main() {
	taskr := tasker.New(tasker.Option{
		Verbose: true,
		// optional: defaults to local
		Tz:      "Asia/Bangkok",
		// optional: defaults to stderr log stream
		Out:     "/full/path/to/output-file",
	})

	// add task to run every minute
	taskr.Task("* * * * *", func(ctx context.Context) (int, error) {
		// do something ...

		// then return exit code and error, for eg: if everything okay
		return 0, nil
	}).Task("*/5 * * * *", func(ctx context.Context) (int, error) { // every 5 minutes
		// you can also log the output to Out file as configured in Option above:
		taskr.Log.Printf("done something in %d s", 2)

		return 0, nil
	})

	// run task without overlap, set concurrent flag to false:
	concurrent := false
	taskr.Task("* * * * * *", , tasker.Taskify("sleep 2", tasker.Option{}), concurrent)

	// every 10 minute with arbitrary command
	taskr.Task("@10minutes", taskr.Taskify("command --option val -- args", tasker.Option{Shell: "/bin/sh -c"}))

	// ... add more tasks

	// optionally if you want tasker to stop after 2 hour, pass the duration with Until():
	taskr.Until(2 * time.Hour)

	// finally run the tasker, it ticks sharply on every minute and runs all the tasks due on that time!
	// it exits gracefully when ctrl+c is received making sure pending tasks are completed.
	taskr.Run()
}

Concurrency

By default the tasks can run concurrently i.e if previous run is still not finished but it is now due again, it will run again. If you want to run only one instance of a task at a time, set concurrent flag to false:

taskr := tasker.New(tasker.Option{})

concurrent := false
expr, task := "* * * * * *", tasker.Taskify("php -r 'sleep(2);'")
taskr.Task(expr, task, concurrent)

Task Daemon

It can also be used as standalone task daemon instead of programmatic usage for Golang application.

First, just install tasker command:

go install github.com/adhocore/gronx/cmd/tasker@latest

Or you can also download latest prebuilt binary from release for platform of your choice.

Then prepare a taskfile (example) in crontab format (or can even point to existing crontab).

user is not supported: it is just cron expr followed by the command.

Finally run the task daemon like so

tasker -file path/to/taskfile

You can pass more options to control the behavior of task daemon, see below.

Tasker command options:

-file string <required>
    The task file in crontab format
-out string
    The fullpath to file where output from tasks are sent to
-shell string
    The shell to use for running tasks (default "/usr/bin/bash")
-tz string
    The timezone to use for tasks (default "Local")
-until int
    The timeout for task daemon in minutes
-verbose
    The verbose mode outputs as much as possible

Examples:

tasker -verbose -file path/to/taskfile -until 120 # run until next 120min (i.e 2hour) with all feedbacks echoed back
tasker -verbose -file path/to/taskfile -out path/to/output # with all feedbacks echoed to the output file
tasker -tz America/New_York -file path/to/taskfile -shell zsh # run all tasks using zsh shell based on NY timezone

File extension of taskfile for (-file option) does not matter: can be any or none. The directory for outfile (-out option) must exist, file is created by task daemon.

Same timezone applies for all tasks currently and it might support overriding timezone per task in future release.

Notes on Windows

In Windows if it doesn't find bash.exe or git-bash.exe it will use powershell. powershell may not be compatible with Unix flavored commands. Also to note: you can't do chaining with cmd1 && cmd2 but rather cmd1 ; cmd2.


Cron Expression

A complete cron expression consists of 7 segments viz:

<second> <minute> <hour> <day> <month> <weekday> <year>

However only 5 will do and this is most commonly used. 5 segments are interpreted as:

<minute> <hour> <day> <month> <weekday>

in which case a default value of 0 is prepended for <second> position.

In a 6 segments expression, if 6th segment matches <year> (i.e 4 digits at least) it will be interpreted as:

<minute> <hour> <day> <month> <weekday> <year>

and a default value of 0 is prepended for <second> position.

For each segments you can have multiple choices separated by comma:

Eg: 0 0,30 * * * * means either 0th or 30th minute.

To specify range of values you can use dash:

Eg: 0 10-15 * * * * means 10th, 11th, 12th, 13th, 14th and 15th minute.

To specify range of step you can combine a dash and slash:

Eg: 0 10-15/2 * * * * means every 2 minutes between 10 and 15 i.e 10th, 12th and 14th minute.

For the <day> and <weekday> segment, there are additional modifiers (optional).

And if you want, you can mix the multiple choices, ranges and steps in a single expression:

0 5,12-20/4,55 * * * * matches if any one of 5 or 12-20/4 or 55 matches the minute.

Real Abbreviations

You can use real abbreviations (3 chars) for month and week days. eg: JAN, dec, fri, SUN

Tags

Following tags are available and they are converted to real cron expressions before parsing:

  • @yearly or @annually - every year
  • @monthly - every month
  • @daily - every day
  • @weekly - every week
  • @hourly - every hour
  • @5minutes - every 5 minutes
  • @10minutes - every 10 minutes
  • @15minutes - every 15 minutes
  • @30minutes - every 30 minutes
  • @always - every minute
  • @everysecond - every second

For BC reasons, @always still means every minute for now, in future release it may mean every seconds instead.

// Use tags like so:
gron.IsDue("@hourly")
gron.IsDue("@5minutes")

Modifiers

Following modifiers supported

  • Day of Month / 3rd of 5 segments / 4th of 6+ segments:
    • L stands for last day of month (eg: L could mean 29th for February in leap year)
    • W stands for closest week day (eg: 10W is closest week days (MON-FRI) to 10th date)
  • Day of Week / 5th of 5 segments / 6th of 6+ segments:
    • L stands for last weekday of month (eg: 2L is last tuesday)
    • # stands for nth day of week in the month (eg: 1#2 is second monday)

License

© MIT | 2021-2099, Jitendra Adhikari

Credits

This project is ported from adhocore/cron-expr and release managed by please.


Other projects

My other golang projects you might find interesting and useful:

  • urlsh - URL shortener and bookmarker service with UI, API, Cache, Hits Counter and forwarder using postgres and redis in backend, bulma in frontend; has web and cli client
  • fast - Check your internet speed with ease and comfort right from the terminal
  • goic - Go Open ID Connect, is OpenID connect client library for Golang, supports the Authorization Code Flow of OpenID Connect specification.
  • chin - A Go lang command line tool to show a spinner as user waits for some long running jobs to finish.