Cron Format

Cron format is a simple, yet powerful and flexible way to define time and frequency of various actions. nnCron make active use of cron format in both classic and extended modes.

Traditional (inherited from Unix) cron format consists of five fields separated by white spaces:

<Minute> <Hour> <Day_of_the_Month> <Month_of_the_Year> <Day_of_the_Week>

nnCron can use both traditional and "enhanced" version of cron format, which has an additional (6th) field: <Year>:

<Minute> <Hour> <Day_of_the_Month> <Month_of_the_Year> <Day_of_the_Week> <Year>

A user can select the format he would like to use by selecting or unselecting the Year field checkbox on General tab in Options dialog (which can be opened by doublecliking the nnCron icon in system tray). By default, nnCron uses the enhanced format.

The following graph shows what it consists of:

* * * * * *
| | | | | |
| | | | | +-- Year              (range: 1900-3000)
| | | | +---- Day of the Week   (range: 1-7, 1 standing for Monday)
| | | +------ Month of the Year (range: 1-12)
| | +-------- Day of the Month  (range: 1-31)
| +---------- Hour              (range: 0-23)
+------------ Minute            (range: 0-59)

Any of these 6 fields may be an asterisk (*). This would mean the entire range of possible values, i.e. each minute, each hour, etc. In the first four fields, nnCron users can also use "nonstandard" character ? (question mark), described here.

Any field may contain a list of values separated by commas, (e.g. 1,3,7) or a range of values (two integers separated by a hyphen, e.g. 1-5).

After an asterisk (*) or a range of values, you can use character / to specify that values are repeated over and over with a certain interval between them. For example, you can write "0-23/2" in Hour field to specify that some action should be performed every two hours (it will have the same effect as "0,2,4,6,8,10,12,14,16,18,20,22"); value "*/4" in Minute field means that the action should be performed every 4 minutes, "1-30/3" means the same as "1,4,7,10,13,16,19,22,25,28".

In Month and Day of Week fields, you can use names of months or days of weeks abbreviated to first three letters ("Jan,Feb,...,Dec" or "Mon,Tue,...,Sun") instead of their numeric values.

Examples:

* * * * * *                         Each minute

59 23 31 12 5 *                     One minute  before the end of year if the last day of the year is Friday

59 23 31 DEC Fri *                  Same as above (different notation)

45 17 7 6 * *                       Every  year, on June 7th at 17:45

45 17 7 6 * 2001,2002               Once a   year, on June 7th at 17:45, if the year is 2001 or  2002

0,15,30,45 0,6,12,18 1,15,31 * 1-5 *  At 00:00, 00:15, 00:30, 00:45, 06:00, 06:15, 06:30,
06:45, 12:00, 12:15, 12:30, 12:45, 18:00, 18:15,
18:30, 18:45, on 1st, 15th or  31st of each  month, but not on weekends

*/15 */6 1,15,31 * 1-5 *            Same as above (different notation)

0 12 * * 1-5 * (0 12 * * Mon-Fri *) At midday on weekdays

* * * 1,3,5,7,9,11 * *              Each minute in January,  March,  May, July, September, and November

1,2,3,5,20-25,30-35,59 23 31 12 * * On the  last day of year, at 23:01, 23:02, 23:03, 23:05,
23:20, 23:21, 23:22, 23:23, 23:24, 23:25, 23:30,
23:31, 23:32, 23:33, 23:34, 23:35, 23:59

0 9 1-7 * 1 *                       First Monday of each month, at 9 a.m.

0 0 1 * * *                         At midnight, on the first day of each month

* 0-11 * * *                        Each minute before midday

* * * 1,2,3 * *                     Each minute in January, February or March

* * * Jan,Feb,Mar * *               Same as above (different notation)

0 0 * * * *                         Daily at midnight

0 0 * * 3 *                         Each Wednesday at midnight

In extended mode, crontab notation may be abridged by omitting the rightmost asterisks.

Examples: (only for extended mode)

Full notation                         Abridged notation

* * * * * *

59 23 31 12 5 2003                    59 23 31 12 5 2003

59 23 31 12 5 *                       59 23 31 12 5

45 17 7 6 * *                         45 17 7 6

0,15,30,45 0,6,12,18 1,15,31 * * *    0,15,30,45 0,6,12,18 1,15,31

0 12 * * 1-5 *                        0 12 * * 1-5

* * * 1,3,5,7,9,11 * *                * * * 1,3,5,7,9,11

1,2,3,5,20-25,30-35,59 23 31 12 * *   1,2,3,5,20-25,30-35,59 23 31 12

0 9 1-7 * 1 *                         0 9 1-7 * 1

0 0 1 * * *                           0 0 1

* 0-11 * * * *                        * 0-11

* * * 1,2,3 * *                       * * * 1,2,3

0 0 * * * *                           0 0

0 0 * * 3 *                           0 0 * * 3

Both in classic and extended modes, nnCron users can use a "nonstandard" character "?" in the first four fields of cron format. It stands for time of nnCron startup, i. e. when a field is processed, startup time will be substituted for the question mark: minutes for Minute field, hour for Hour field, day of the month for Day of month field and month for Month field.

For example, if you write the following:

Time: ? ? * * * *

the task will be executed on nnCron startup and then will be executed daily at the same time (unless the user doesn't restart nnCron, of course): question marks will be "replaced" by nnCron startup time. For example, if nnCron was started at 8:25, question marks will be substituted this way:

Time: 25 8 * * * *

Some more examples:

\ task will be executed only on nnCron startup
\ (this has the sane effect  as "Time: START-TIME")
Time: ? ? ? ? * *

\ task will be executed on nnCron startup (e.g. at 10:15)
\ and then will be executed again each hour:
\ at 11:15, 12:15, 13:15 etc.
Time: ? * * * * *

\ task will be started each minute after nnCron startup until the next hour starts.
\ The next day, if nnCron has not been restarted in the meanwhile,
\it will be executed again each minute during the same hour.
Time: * ? * * * *

\ task will be executed daily,  every five minutes,
\ during the hour when nnCron was started.
Time: */5 ? * * * *