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https://github.com/tsikov/clerk

A cron-like scheduler with sane DSL
https://github.com/tsikov/clerk

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A cron-like scheduler with sane DSL

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# Clerk



A cron-like scheduler with sane DSL



## Example usage



### Job MACRO



```

(job "Say 'Hi' all the time" every 5.seconds (print "Hi"))



(job "Compose and send monthly report"

     every 1.month (send-report (compose-monthly-report)))

```



If you want to see it with your eyes, make sure to load the following code:



```

(defun write-to-file (msg file)

  (with-open-file (log file

                       :direction :output

                       :if-exists :append

                       :if-does-not-exist :create)

    (format log "~A~%" msg)))



(job "Print farbe" every 3.seconds (write-to-file "Farbe" "log.txt"))

(job "Print colour" every 2.seconds (write-to-file "Colour" "log.txt"))

(job "Print @@@@ 1 min @@@@@" every 1.minute

       (write-to-file "@@@@@@ 1 min @@@@@@" "log.txt"))

```

Now, after `(clerk:start)`, tailing `log.txt` should give you something like this:



```

Colour

Farbe

Colour

Colour

Farbe

Colour

Farbe

Colour

Colour

Farbe

Colour

/one minute later.../

@@@@@@ 1 min @@@@@@

/etc.../

```



### Job FUNCTION



The original idea was for users to use the library to execute some sort of execution of a configuration file. However you can use the job creation process programatically with the underlying function `job-fn`. E.g.:



```

(defparameter *query-interval* 5)

(job-fn (format nil "Query the API every ~A seconds" *query-interval*)

        'every

        `(,*query-interval* seconds)

        #'query-api-fn)

```



As you can see, you have to provide a function (either anonimous function or a function symbol) as the last argument.



## Instalation and usage



Clone the repo inside `quicklisp/local-projects` and do `(ql:quicklisp :clerk)` in your REPL.



Make sure your jobs are loaded before executing `(clerk:start)`. The jobs reside inside `clerk:*jobs*`, but you can also type `(clerk:calendar)` to see a list of all scheduled and running jobs. 



### Job types



There are two types of jobs - `continuous` and `one-time`. If a job has the keyword `every` after the job description - the job will be countinuous. This means that when an event is fired, a new event will be pushed in the event queue for firing exactly `interval` time from now. The jobs above are an example for `continuous` jobs.



A `one-time` job is fired once and then it is removed from the jobs' queue. An example for a one-time job can be:



```

(job "Extraordinary event" in 5.days (send-mail "Don't forget X"))

```



You can use any word instead of `in`.



### Intervals



Right now (more are coming soon) there are 2 type of intervals:



1) **Numbered intervals**



```

[number].[interval-type]

```



where the number is a positive integer and the `interval-type` if one of the following: `second`, `minute`, `hour`, `day`, `week`, `month`, `year`. Also you can use the plural form of all these words. For example `1.second` and `2.seconds` are both valid.



2) **Days of the week**



```

(job "Weekly report" every monday (create-report))

```



Pretty self-explanatory. The idea is that if you type the day of the week, clerk will calculate when it is and add an event to the queue.



## Issues / Contribution



If you have issues - open a github issue or contact me at `(reverse "moc.liamg@vokist")`. If you want to contribute - open an issue or make a PR. Thanks!