add crontab list with command

Add a command

crontab -l | { /bin/echo "* 3 * * * aplay /home/ubuntu/321.wav;" } | crontab -

Multiple commands

crontab -l | { /bin/cat; /bin/echo "* 3 * * * aplay /home/ubuntu/321.wav; ls -alh"; } | crontab -

Add more commands

crontab -l | { crontab -l; /bin/echo "* 3 * * * aplay /home/ubuntu/321.wav ;"} | crontab -

Add more commands with index

crontab -l | { crontab -l; /bin/echo "* 3 * * * aplay /home/ubuntu/321.wav #index_1;"} | crontab -

Remove specific command

crontab -u mobman -l | grep -v 'index_1'  | crontab -u mobman -

Remove all

crontab -r

ref:
stackoverflow
stackoverflow