Cron commands to plain English | Hacker News Reader

Cron commands to plain English

cronchecker.net

85 pointsspncr226 comments

> the arcane syntax

Arcane, seriously? What kind of syntax would be modern and clear in your opinion? YAML? JSON? XML probably, with a nice 150-page XTBJSPCOSDF (Extensible Time-Based Job Scheduling for POSIX-Compatible Operating Systems Description Framework) spec? ;)

Personally, I think this is pretty straightforward:

  #minute hour    mday    month   wday    command
  30      1       *       *       *       /bin/sh /etc/daily
  30      3       *       *       6       /bin/sh /etc/weekly
  30      5       1       *       *       /bin/sh /etc/monthly

I'd dig something going in the opposite direction! Especially packed in a shell script, e.g. `cronglish "echo testing" every half hour >> ~/.crontab`

OK, so I gave it this:

    8-59/30 * * * * do_something

It replied:

    The command do_something will execute
    the 8th through 59/30th minutes of
    every hour every day.

That's a pretty poor description of something that will run at 8 and 38 minutes past the hour, every hour of every day.

Not impressed - seems overly simplistic.

> Not impressed - seems overly simplistic.

Agreed that it's not impressive, beings that the explanation is simply wrong. It's an edge case I'm definitely not handling properly. I've got [an open issue](https://github.com/pbyrne/cron-checker/issues/7) about combining ranges and modulo, but haven't gotten around to implementing it yet. Displaying an incorrect explanation is probably worse than no explanation, though, in retrospect.

The challenge is to decide what you would want it to say in the case of, say, "14-59/15". Do you want it to list all the possibilities? That becomes tedious if you have something like 2-57/2. Do you want to try to create a more direct plain English parse?

    14-59/15 - Every 15th minute starting with the 14th
               up to and including the 59th.

     2-57/2  - Every 2nd minutes starting with the 2nd
               up to and including the 56th.

A choice needs to be made - the direct plain English parse is quite long, and not always easy to read.

I built the opposite version of this, convert plain English to cron commands: http://thomseddon.github.io/cronstring

Awesome, now you have a test suite

    assert(cronchecker(cronstring(input)) == input)

You can also use DuckDuckGo to do this: https://duckduckgo.com/?q=cron+0+0+*+*+*+some_report.sh&t=lm

>Cron will schedule the job at this frequency: 0:00:00 on 2 Aug, 2014 0:00:00 on 3 Aug, 2014 0:00:00 on 4 Aug, 2014

Results are a little harder to read. This other site gives more natural sentences.

Does not understand this syntax: "1-56/5 * * * * foo"

Sorry about that. It's a [known issue](https://github.com/pbyrne/cron-checker/issues/7).

What does that do?

CronWTF doesn't understand it either and that one even has a cat!

> 1-56/5 * * * * foo

The first minute of the hour, then every 5 minutes until the 56th minute, inclusive

Every 5 starting at 1 instead of 0

Just played a bit with it. http://goo.gl/q8lT9B

Looks like they're the chaps behind https://deadmanssnitch.com which looks like a simple and useful service.

Hi there. Popping in to clarify that the (excellent) folks behind Dead Man's Snitch are advertising on the site, but that otherwise I'm not affiliated with them and they haven't contributed to the project beyond the ad.

That said, it's a pretty great product and you should check them out!

It would be great to also list the next few datetimes that this would occur on as examples.

It would also be great to support the seconds field.

I believe cron does not have a seconds field:

From "man 5 crontab":

    cron(8) examines cron entries once every minute.
    The time and date fields are:

              field          allowed values
              -----          --------------
              minute         0-59
              hour           0-23
              day of month   1-31
              month          1-12 (or names, see below)
              day of week    0-7 (0 or 7 is Sun, or use names)

    A field may be an asterisk (*), which always stands
    for "first-last".

    Ranges  of  numbers  are allowed.  Ranges are two
    numbers separated with a hyphen.  The specified
    range is inclusive.

    For example, 8-11 for an "hours" entry specifies
    execution at hours 8, 9, 10 and 11.

    Lists are allowed.  A list is a set of numbers (or
    ranges) separated by commas.  Examples: "1,2,5,9",
    "0-4,8-12".

In some uses of the CRON format there is also a seconds field at the beginning of the pattern. In that case, the CRON expression is a string comprising 6 or 7 fields.

http://en.wikipedia.org/wiki/Cron#Format

For visualizing a large quantity of crons, I'd recommend something akin to https://github.com/federatedmedia/cronviz which will graphically show when jobs are scheduled to run.

@reboot cd ~/bin/some_daemon

is not a very good example. It will launch a shell which will change to the specified directory and then terminate. (It might produce an error message if the directory doesn't exist.)

This is nice.

I also turn to http://cronwtf.github.io when I need to sanity-check my crontab, which is a little more verbose and includes JSSpec tests.

Also see crontab2english: http://interglacial.com/pub/crontab2english.html

I've been using http://cronwtf.github.io/ for years to double-check cron expressions.

Not bad, each line in my cron has somthing lke that next to it :)

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