crontab – – maintain crontab files for individual users  ,tables for driving cron

  crontab -e    edit your crontab entries
  crontab -l    print the entries from crontab

The first form of this command is used to install a new crontab from some named file or standard input if the pseudo-filename “-” is given.

The -l option causes the current crontab to be displayed on standard output.

The -r option causes the current crontab to be removed.

The -e option is used to edit the current crontab using the editor specified by the VISUAL orEDITOR environment variables. After you exit from the editor, the modified crontab will be installed automatically.