<pre>
LINKS
==============================================
https://help.ubuntu.com/community/CronHowto
https://unixhelp.ed.ac.uk.CGI/man-cgi?crontab+5
https://unixgeeks.org/security/newbie/unix/cron-1.html
https://en.wikipedia.org/wiki/Cron
https://ratholeradio.org/

SCRIPT
==============================================
username@computer:~$ vi /home/username/bin/hello.bash

username@computer:~$ cat /home/username/bin/hello.bash
#!/bin/bash
echo "hello world"

username@computer:~$ /home/username/bin/hello.bash
bash: /home/username/bin/hello.bash: Permission denied

username@computer:~$ chmod +x /home/username/bin/hello.bash

username@computer:~$ /home/username/bin/hello.bash
hello world

username@computer:~$ export |grep EDITOR
declare -x EDITOR="vim"

username@computer:~$ crontab -l
no crontab for username

username@computer:~$ crontab -e
no crontab for username - using an empty one
No modification made

username@computer:~$ crontab -e
no crontab for username - using an empty one
crontab: installing new crontab

username@computer:~$ crontab -l
# m h  dom mon dow   command
* * * * * /home/username/bin/hello.bash > /home/username/hello.output 2>&1

username@computer:~$ cat /home/username/hello.output
hello world
</pre>