A crontab file consists of commands, one command per line, that execute automatically at the time specified by the first five fields of each command line, which are separated by spaces.
The following are the acceptable numerical values for crontab time entry:
0-59
0-23
1-31
1-12
0-6 (0 = Sunday)
The following special characters are used in crontab time fields:
Space separates each field
Comma separates multiple values
Hyphen designates a range of values
Asterisk (*) is a wildcard to include all possible values
Comment mark (#) at the beginning of a line indicates a comment or a blank line
For example, the following crontab command entry displays a reminder in the user's console window at 4 pm on the first and fifteenth days of every month.
0 16 1,15 * * echo Timesheets Due > /dev/console
Each command within a crontab file must consist of one line, even if that line is very long. The crontab file does not recognize extra carriage returns. For more detailed information about crontab entries and command options, refer to the crontab(1) man page.