What is "* * * * *" command anyway?

I was wanting to do something entirely irrelevant: Running a cron job manually and immediately

The answer suggests this:

# Create a environment file with a temporary cron entry

* * * * *  /usr/bin/env > /home/username/cron-env

and I took it literally:

~$ * * * * *  /usr/bin/env
certbot-auto: command not found

Hmm… WHAT? What is this command? What is certbot-auto anyway? How are these related? C’mon!

I will skip all the dead ends I visited here… the pain & pleasure are always in the process. Turns out, it has nothing to do with crontab, nor systemctl. It’s not linux, and it’s useless to search for 5 consequtive asterisks anyway

which *
man *

It’s bash expansion. * get expanded to a list of file names. One of the files in PWD is called certbot-auto. But to run it, you have to do ./certbot-auto, hence command not found

I’m Happy now.

Written on February 18, 2019