mourjo / chronic

Cron parser

chronic

Parse cron strings to show the possible values for minute, hour, day, month, day-of-week.

For */15 0 1,15 * 1-5 /usr/bin/find, the expected output is

Minute: 0,15,30,45
Hour: 0
Day of Month: 1,15
Month: 1,2,3,4,5,6,7,8,9,10,11,12
Day of Week: 1,2,3,4,5
Command: /usr/bin/find

For an invalid cron string */15 0 1,15 * 1-5000 /usr/bin/find abcd, the output is

Invalid cron: */15 0 1,15 * 1-5000 /usr/bin/find abcd
Unexpected atom: Out of range: 5000

Usage

Pre-requisites:

• Apache Maven 3.8.6+
• Java: 18.0.1.1+

Compile using:

mvn clean package

Run using:

java -jar target/chronic.jar "*/15 0 1,15 * 1-5 /usr/bin/find abcd"

The output for the above:

Minute: 0,15,30,45
Hour: 0
Day of Month: 1,15
Month: 1,2,3,4,5,6,7,8,9,10,11,12
Day of Week: 1,2,3,4,5
Command: /usr/bin/find abcd

Code structure

• A cron expression is contained in the Expression which contains a sequence of Feilds.
• A Field is responsible for understanding how to parse a cron string.
• Subclasses like CommandField and HourField are responsible for parsing the command portion and the hour portion respectively.
• A Field that is numeric, like HourField uses the NumericParser to convert the cron for that field into a sequence of numbers.
• NumericParser checks syntax of a cron string for a field and generates a sequence of numbers according to the field's bounds.

Notes

• Only minute, hour, day of month, month, and day of week are supported
• ? is not supported
• Special time strings like @yearly are not supported
• , is given the highest priority, so / when applied to a comma-separated string, the / applies only to the last item in the list, example: 1-5,11-15/5 will choose 1,2,3,4,5,15

License

This program and the accompanying materials are made available under the terms of the Eclipse Public License 2.0 which is available at http://www.eclipse.org/legal/epl-2.0.

This Source Code may also be made available under the following Secondary Licenses when the conditions for such availability set forth in the Eclipse Public License, v. 2.0 are satisfied: GNU General Public License as published by the Free Software Foundation, either version 2 of the License, or (at your option) any later version, with the GNU Classpath Exception which is available at https://www.gnu.org/software/classpath/license.html.