Enable/Disable tasks in Crontab by Bash/Shell

Question

Is there a way to enable and disable Crontab tasks using Bash/Shell?

So when the user starts Server 1, it will enable the Server 1 Crontab line and so on. And when the user stops Server 1, the Server 1 Crontab line get disabled (#). Is this possible and how?

Thanks in advance

*/1 * * * * Server 1 check
*/1 * * * * Server 2 check
*/1 * * * * Server 3 check

Answer 1

SERVERNUM=$1

To enable:

crontab -l | sed "/^#.*Server $SERVERNUM check/s/^#//" | crontab -

To disable:

crontab -l | sed "/^[^#].*Server $SERVERNUM check/s/^/#/" | crontab -

Transcript:

barmar@dev$ crontab -l
*/1 * * * * Server 1 check
*/1 * * * * Server 2 check
*/1 * * * * Server 3 check
barmar@dev$ crontab -l | sed '/^[^#].*Server 1 check/s/^/#/' | crontab -
barmar@dev$ crontab -l
#*/1 * * * * Server 1 check
*/1 * * * * Server 2 check
*/1 * * * * Server 3 check
barmar@dev$ crontab -l | sed '/^#.*Server 1 check/s/^#//' | crontab -
barmar@dev$ crontab -l
*/1 * * * * Server 1 check
*/1 * * * * Server 2 check
*/1 * * * * Server 3 check

Answer 2

I suggest you add your cron jobs to /etc/cron.d for every server one script. Then let the cron script scan for some marker file if the cron job should be executed.