Crontab: 2- file

Crontab syntax :
A crontab file has five fields for specifying day , date and time followed by the command to be run at that interval.

*     *     *   *    *        command to be executed

|     |     |   |    +----- day of week (0 - 6) (Sunday=0) 

|     |     |   +------- month (1 - 12) 

|     |     +--------- day of        month (1 - 31)

|     +----------- hour (0 - 23)

+------------- min (0 - 59) 

Example:

30     18     *     *     *         rm /home/someuser/tmp/*