Runar Ovesen Hjerpbakk

Programmer. Software Architect. Technical Manager.

cron

Simplify your crontab entries with crontab.guru

As you’ve seen from my previous posts, I’ve used cron a lot lately to schedule periodic tasks on my RaspberryPi. cron is driven by crontab, cron table files, configuration files that specifies shell commands to run periodically on a given schedule.

# ┌───────────── minute (0 - 59)
# │ ┌───────────── hour (0 - 23)
# │ │ ┌───────────── day of month (1 - 31)
# │ │ │ ┌───────────── month (1 - 12)
# │ │ │ │ ┌───────────── day of week (0 - 6) (Sunday to Saturday; 
# │ │ │ │ │              7 is also Sunday on Raspbian)
# │ │ │ │ │
# │ │ │ │ │
# * * * * *  command to execute

The timing syntax is understandable enough. In addition to numbers, we can use special operators:

*	any value
,	value list separator
-	range of values
/	step values

An expression to achieve At 22:00 on every day-of-week from Monday through Friday looks like this:

0 22 * * 1-5

My problem is that I get the elements confused. Without reading the explanation, is 22 in the expression above minute or hour? You have to read the spec to find out.

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