[NEW:2021-03-26] CLI/commandline to add a CRON within a script

echo "* * * * * \$HOME/path/to/scriptOrApp.sh" >> /var/spool/cron/USERNAME;

#!/bin/bash
cronUserName="usernameToAddCronjobFOR";
cronToAddDesc="#Description of the task (optional and for convenience)";  #[OPTIONAL] description of the task (MUST start with # to become a comment)
cronToAdd="* * * * * \$HOME/path/to/scriptOrApp.sh";                      #Task or app (MUST escape $HOME if used)

[[ -n $cronToAddDesc ]] && (crontab -u $cronUserName -l; printf "\n$cronToAddDesc\n" ) | crontab -u $cronUserName -;  #add the description above the task
[[ -n $cronToAdd ]]     && (crontab -u $cronUserName -l; echo "$cronToAdd" ) | crontab -u $cronUserName -;      #add the task itself

crontab -u $cronUserName -l;  #Check this user’s crontab #4DBG#