Safer use of crontab. Add this function to the user's ~/.profile or ~/.bashrc

crontab_wrapper

crontab() {
  crontab_usage() {
    echo 'Usage:' >&2
    echo '  $ crontab -[elr]' >&2
    echo '  $ crontab ~/crons    # to update your crons' >&2
  }

  if [ $# -eq 1 ]; then
    if [ "$*" = '-' ]; then  # worse than crontab -e
      crontab_usage
    elif [[ ! "$*" =~ ^-[a-zA-Z]$ ]]; then
      /usr/bin/crontab $*
    else
      OPTIND=1
      while getopts 'elr' cronopt; do
        case "$cronopt" in
          e)
           (echo "'crontab -e' is disabled for $USER"
            echo 'To update your crons, please edit ~/crons, then load the'
            echo 'updated file:'
            echo
            echo '  $ crontab ~/crons'
            echo
            echo 'If this file does not yet exist (or to ensure it is up to date!)'
            echo 'you can create it as follows:'
            echo
            echo '  $ crontab -l >~/crons') >&2
          ;;
          r)
           (echo 'You may not delete the crontab.  To make changes, edit'
            echo '~/crons (which may be empty) and load the updated file:'
            echo
            echo '  $ crontab ~/crons') >&2
          ;;
          l)
            /usr/bin/crontab -l
          ;;
          *)
            crontab_usage
          ;;
        esac
      done
      OPTIND=1
    fi
  else
    crontab_usage
  fi
  unset -f crontab_usage
}