Go Language

How to Execute Cron Job at a specific time In Go

This golang tutorial help to create schedule a jon to execute at specific time interval

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Published · Oct 21 2019

  

This golang tutorial help to create schedule a jon to execute at specific time interval.This is very helpful feature to run a process or tasks as background, that can be a job that pull data from third party server, sync data between two server, send an email notification at a specific inerval.

Getting started
To get the package, execute:
 go get gopkg.in/robfig/cron.v2

 To import this package, add the following line to your code:
 import "gopkg.in/robfig/cron.v2"

Usage
Callers may register Funcs to be invoked on a given schedule.  Cron will run them in their own goroutines. 


CRON Expression Format
 A cron expression represents a set of times, using 6 space-separated fields. 
Field name   | Mandatory? | Allowed values  | Allowed special characters
----------   | ---------- | --------------  | --------------------------
Seconds      | No         | 0-59            | * / , -
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  | * / , - ?

 Note: Month and Day-of-week field values are case insensitive.  "SUN", "Sun", and "sun" are equally accepted. 

Special Characters
Asterisk ( * ) 
- The asterisk indicates that the cron expression will match for all values of the field; e.g., using an asterisk in the 5th field (month) would indicate every month. 

Slash ( / ) 
- Slashes are used to describe increments of ranges. For example 3-59/15 in the 1st field (minutes) would indicate the 3rd minute of the hour and every 15 minutes thereafter. The form "*\/..." is equivalent to the form "first-last/...", that is, an increment over the largest possible range of the field.  The form "N/..." is accepted as meaning "N-MAX/...", that is, starting at N, use the increment until the end of that specific range.  It does not wrap around. 

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

Hyphen ( - ) 
-Hyphens are used to define ranges. For example, 9-17 would indicate every hour between 9am and 5pm inclusive. 

Question mark ( ? ) 
-Question mark may be used instead of '*' for leaving either day-of-month or day-of-week blank. 

Predefined schedules
You may use one of several pre-defined schedules in place of a cron expression. 
Entry                  | Description                                | Equivalent To
-----                  | -----------                                | -------------
@yearly (or @annually) | Run once a year, midnight, Jan. 1st        | 0 0 0 1 1 *
@monthly               | Run once a month, midnight, first of month | 0 0 0 1 * *
@weekly                | Run once a week, midnight on Sunday        | 0 0 0 * * 0
@daily (or @midnight)  | Run once a day, midnight                   | 0 0 0 * * *
@hourly                | Run once an hour, beginning of hour        | 0 0 * * * *

Intervals
You may also schedule a job to execute at fixed intervals.  This is supported by formatting the cron spec like this: 
@every <duration>

 where "duration" is a string accepted by time.ParseDuration (http://golang.org/pkg/time/#ParseDuration). 

For example, "@every 1h30m10s" would indicate a schedule that activates every 1 hour, 30 minutes, 10 seconds. 

Note: The interval does not take the job runtime into account.  For example, if a job takes 3 minutes to run, and it is scheduled to run every 5 minutes, it will have only 2 minutes of idle time between each run. 
. . .