cron job syntax: past the basics

Cron jobs are awesome, but I often forget the syntax. In the process of learning to write one of my first cron jobs, I found this diagram in a blog post about scheduling Netlify Deploys with Github Actions quite useful and reference it frequently:

 ┏━━━━━━━━━━━━ minute (0 - 59)
 ┃ ┏━━━━━━━━━━ hour (0 - 23)
 ┃ ┃ ┏━━━━━━━━ day of month (1 - 31)
 ┃ ┃ ┃ ┏━━━━━━ month (1-12)
 ┃ ┃ ┃ ┃ ┏━━━━ day of week (0 - 6) or use names;
 ┃ ┃ ┃ ┃ ┃       0 and 7 are Sunday, 1 is Monday,
 ┃ ┃ ┃ ┃ ┃       2 is Tuesday, etc.
 ┃ ┃ ┃ ┃ ┃
 * * * * * <command to execute>

Even still, there are some things that it glosses over.

Like how to run something every 15 minutes:

*/15 * * * *

Or how to run a cron job twice a day at 8am and 6pm:

* 8,18 * * *

Or how about every month from the 1st through the 5th:

* * 1-5 * *

Each section of the cron syntax has different accepted values, but they all share the four operators demonstrated above:

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

Crontab.guru’s simple tool for validating a cron job syntax is awesome and I learned a lot just by clicking the “random” button and seeing what came up. If nothing else, I now understand that the syntax is much more versatile than was immediately obvious to me.