What is Cron Expression?

Cron expression is a string that defines a schedule for running a task or job at specified times. It consists of six fields that represent the following values, in order.

*    *    *    *    *    *
-    -    -    -    -    -
|    |    |    |    |    |
|    |    |    |    |    +----- day of the week (0 - 6) (Sunday = 0)
|    |    |    |    +---------- month (1 - 12)
|    |    |    +--------------- day of the month (1 - 31)
|    |    +-------------------- hour (0 - 23)
|    +------------------------- minute (0 - 59)
+------------------------------ second (0 - 59) [optional]

Each field can be either a specific value, a range of values, or a wildcard '*' to represent all values. For example, '0 0 * * * *' represents a schedule that runs every hour at the beginning of the hour, while '0 0 12 * * *' represents a schedule that runs every day at noon.

Cron expressions can also include special characters such as '/', '-', and ',' to specify more complex schedules. For example, '0 0 12 */2 * *' represents a schedule that runs every other day at noon.

Cron expressions are widely used in job scheduling and can be used with a variety of programming languages and platforms. In C#, libraries such as NCrontab can be used to parse and calculate cron expressions.

Example:
Sample Windows Service Job Scheduling Application that uses a Cron Expression