NCrontab: Crontab for .NET

NCrontab is a library written in C# targeting .NET Standard Library 1.0 and that provides the following facilities:

• Parsing of crontab expressions
• Formatting of crontab expressions
• Calculation of occurrences of time based on a crontab schedule

This library does not provide any scheduler or is not a scheduling facility like cron from Unix platforms. What it provides is parsing, formatting and an algorithm to produce occurrences of time based on a give schedule expressed in the crontab format:

* * * * *
- - - - -
| | | | |
| | | | +----- day of week (0 - 6) (Sunday=0)
| | | +------- month (1 - 12)
| | +--------- day of month (1 - 31)
| +----------- hour (0 - 23)
+------------- min (0 - 59)

or a six-part format that allows for seconds:

* * * * * *
- - - - - -
| | | | | |
| | | | | +--- day of week (0 - 6) (Sunday=0)
| | | | +----- month (1 - 12)
| | | +------- day of month (1 - 31)
| | +--------- hour (0 - 23)
| +----------- min (0 - 59)
+------------- sec (0 - 59)

Star (*) in the value field above means all legal values as in parentheses for that column. The value column can have a * or a list of elements separated by commas. An element is either a number in the ranges shown above or two numbers in the range separated by a hyphen (meaning an inclusive range). For more, see CrontabExpression.

The default format parsed by CrontabSchedule.Parse is the five-part cron format. In order to use the six-part format that includes seconds, pass a CrontabSchedule.ParseOptions to Parse with IncludingSeconds set to true. For example:

var s = CrontabSchedule.Parse("0,30 * * * * *",
                              new CrontabSchedule.ParseOptions
                              {
                                  IncludingSeconds = true
                              });

Below is an example in IronPython of how to use CrontabSchedule class from NCrontab to generate occurrences of the schedule 0 12 * */2 Mon (meaning, 12:00 PM on Monday of every other month, starting with January) throughout the year 2000:

IronPython 1.1 (1.1) on .NET 2.0.50727.1434
Copyright (c) Microsoft Corporation. All rights reserved.
>>> import clr
>>> clr.AddReferenceToFileAndPath(r'C:\NCrontab\bin\Release\NCrontab.dll')
>>> from System import DateTime
>>> from NCrontab import CrontabSchedule
>>> s = CrontabSchedule.Parse('0 12 * */2 Mon')
>>> start = DateTime(2000, 1, 1)
>>> end = start.AddYears(1)
>>> occurrences = s.GetNextOccurrences(start, end)
>>> print '\n'.join([t.ToString('ddd, dd MMM yyyy HH:mm') for t in occurrences])
Mon, 03 Jan 2000 12:00
Mon, 10 Jan 2000 12:00
Mon, 17 Jan 2000 12:00
Mon, 24 Jan 2000 12:00
Mon, 31 Jan 2000 12:00
Mon, 06 Mar 2000 12:00
Mon, 13 Mar 2000 12:00
Mon, 20 Mar 2000 12:00
Mon, 27 Mar 2000 12:00
Mon, 01 May 2000 12:00
Mon, 08 May 2000 12:00
Mon, 15 May 2000 12:00
Mon, 22 May 2000 12:00
Mon, 29 May 2000 12:00
Mon, 03 Jul 2000 12:00
Mon, 10 Jul 2000 12:00
Mon, 17 Jul 2000 12:00
Mon, 24 Jul 2000 12:00
Mon, 31 Jul 2000 12:00
Mon, 04 Sep 2000 12:00
Mon, 11 Sep 2000 12:00
Mon, 18 Sep 2000 12:00
Mon, 25 Sep 2000 12:00
Mon, 06 Nov 2000 12:00
Mon, 13 Nov 2000 12:00
Mon, 20 Nov 2000 12:00
Mon, 27 Nov 2000 12:00

Below is the same example in F# Interactive (fsi.exe):

Microsoft (R) F# 2.0 Interactive build 4.0.40219.1
Copyright (c) Microsoft Corporation. All Rights Reserved.

For help type #help;;

> #r "NCrontab.dll"
-
- open NCrontab
- open System
-
- let schedule = CrontabSchedule.Parse("0 12 * */2 Mon")
- let startDate = DateTime(2000, 1, 1)
- let endDate = startDate.AddYears(1)
-
- let occurrences = schedule.GetNextOccurrences(startDate, endDate)
- occurrences |> Seq.map (fun t -> t.ToString("ddd, dd MMM yyy HH:mm"))
-             |> String.concat "\n"
-             |> printfn "%s";;

--> Referenced 'C:\NCrontab\bin\Release\NCrontab.dll'

Mon, 03 Jan 2000 12:00
Mon, 10 Jan 2000 12:00
Mon, 17 Jan 2000 12:00
Mon, 24 Jan 2000 12:00
Mon, 31 Jan 2000 12:00
Mon, 06 Mar 2000 12:00
Mon, 13 Mar 2000 12:00
Mon, 20 Mar 2000 12:00
Mon, 27 Mar 2000 12:00
Mon, 01 May 2000 12:00
Mon, 08 May 2000 12:00
Mon, 15 May 2000 12:00
Mon, 22 May 2000 12:00
Mon, 29 May 2000 12:00
Mon, 03 Jul 2000 12:00
Mon, 10 Jul 2000 12:00
Mon, 17 Jul 2000 12:00
Mon, 24 Jul 2000 12:00
Mon, 31 Jul 2000 12:00
Mon, 04 Sep 2000 12:00
Mon, 11 Sep 2000 12:00
Mon, 18 Sep 2000 12:00
Mon, 25 Sep 2000 12:00
Mon, 06 Nov 2000 12:00
Mon, 13 Nov 2000 12:00
Mon, 20 Nov 2000 12:00
Mon, 27 Nov 2000 12:00

Below is the same example in C# Interactive (csi.exe):

Microsoft (R) Visual C# Interactive Compiler version 1.2.0.60317
Copyright (C) Microsoft Corporation. All rights reserved.

Type "#help" for more information.
> #r "NCrontab.dll"
> using NCrontab;
> var s = CrontabSchedule.Parse("0 12 * */2 Mon");
> var start = new DateTime(2000, 1, 1);
> var end = start.AddYears(1);
> var occurrences = s.GetNextOccurrences(start, end);
> Console.WriteLine(string.Join(Environment.NewLine,
.     from t in occurrences
.     select $"{t:ddd, dd MMM yyyy HH:mm}"));
Mon, 03 Jan 2000 12:00
Mon, 10 Jan 2000 12:00
Mon, 17 Jan 2000 12:00
Mon, 24 Jan 2000 12:00
Mon, 31 Jan 2000 12:00
Mon, 06 Mar 2000 12:00
Mon, 13 Mar 2000 12:00
Mon, 20 Mar 2000 12:00
Mon, 27 Mar 2000 12:00
Mon, 01 May 2000 12:00
Mon, 08 May 2000 12:00
Mon, 15 May 2000 12:00
Mon, 22 May 2000 12:00
Mon, 29 May 2000 12:00
Mon, 03 Jul 2000 12:00
Mon, 10 Jul 2000 12:00
Mon, 17 Jul 2000 12:00
Mon, 24 Jul 2000 12:00
Mon, 31 Jul 2000 12:00
Mon, 04 Sep 2000 12:00
Mon, 11 Sep 2000 12:00
Mon, 18 Sep 2000 12:00
Mon, 25 Sep 2000 12:00
Mon, 06 Nov 2000 12:00
Mon, 13 Nov 2000 12:00
Mon, 20 Nov 2000 12:00
Mon, 27 Nov 2000 12:00

Below is the same example in C# using dotnet-script:

> #r "nuget:NCrontab"
> using NCrontab;
> var s = CrontabSchedule.Parse("0 12 * */2 Mon");
> var start = new DateTime(2000, 1, 1);
> var end = start.AddYears(1);
> var occurrences = s.GetNextOccurrences(start, end);
> Console.WriteLine(string.Join(Environment.NewLine,
*     from t in occurrences
*     select $"{t:ddd, dd MMM yyyy HH:mm}"));
Mon, 03 Jan 2000 12:00
Mon, 10 Jan 2000 12:00
Mon, 17 Jan 2000 12:00
Mon, 24 Jan 2000 12:00
Mon, 31 Jan 2000 12:00
Mon, 06 Mar 2000 12:00
Mon, 13 Mar 2000 12:00
Mon, 20 Mar 2000 12:00
Mon, 27 Mar 2000 12:00
Mon, 01 May 2000 12:00
Mon, 08 May 2000 12:00
Mon, 15 May 2000 12:00
Mon, 22 May 2000 12:00
Mon, 29 May 2000 12:00
Mon, 03 Jul 2000 12:00
Mon, 10 Jul 2000 12:00
Mon, 17 Jul 2000 12:00
Mon, 24 Jul 2000 12:00
Mon, 31 Jul 2000 12:00
Mon, 04 Sept 2000 12:00
Mon, 11 Sept 2000 12:00
Mon, 18 Sept 2000 12:00
Mon, 25 Sept 2000 12:00
Mon, 06 Nov 2000 12:00
Mon, 13 Nov 2000 12:00
Mon, 20 Nov 2000 12:00
Mon, 27 Nov 2000 12:00

Some complex schedules cannot be expressed in a single crontab expression so NCrontab can produce distinct occurrences given a sequence of CrontabSchedule instances. In the C# example below, two schedules are merged to produce a single set of occurrences over a week. The first schedule occurs every 6 hours on weekdays while the second occurs every 12 hours on weekends.

Microsoft (R) Visual C# Interactive Compiler version 1.2.0.60317
Copyright (C) Microsoft Corporation. All rights reserved.

Type "#help" for more information.
> using NCrontab;
> var s1 = CrontabSchedule.Parse("0 */6 * * Mon-Fri");
> var s2 = CrontabSchedule.Parse("0 */12 * * Sat,Sun");
> var s = new[] { s1, s2 };
> var start = new DateTime(2000, 1, 1);
> var end = start.AddDays(7);
> var occurrences = s.GetNextOccurrences(start, end);
> // `Sat, 01 Jan 2000 10:00` won't appear because `start` is exclusive
> Console.WriteLine(string.Join(Environment.NewLine,
.     from t in occurrences
.     select $"{t:ddd, dd MMM yyyy HH:mm}"));
Sat, 01 Jan 2000 12:00
Sun, 02 Jan 2000 00:00
Sun, 02 Jan 2000 12:00
Mon, 03 Jan 2000 00:00
Mon, 03 Jan 2000 06:00
Mon, 03 Jan 2000 12:00
Mon, 03 Jan 2000 18:00
Tue, 04 Jan 2000 00:00
Tue, 04 Jan 2000 06:00
Tue, 04 Jan 2000 12:00
Tue, 04 Jan 2000 18:00
Wed, 05 Jan 2000 00:00
Wed, 05 Jan 2000 06:00
Wed, 05 Jan 2000 12:00
Wed, 05 Jan 2000 18:00
Thu, 06 Jan 2000 00:00
Thu, 06 Jan 2000 06:00
Thu, 06 Jan 2000 12:00
Thu, 06 Jan 2000 18:00
Fri, 07 Jan 2000 00:00
Fri, 07 Jan 2000 06:00
Fri, 07 Jan 2000 12:00
Fri, 07 Jan 2000 18:00

If one or more schedules produce the same occurrence then only one of them if returned.

Merging Schedules

NCrontab can merge the timeline of one or more schedules. This can sometimes come handy when it's impossible to express a schedule with a single crontab expression like every 6 hours from 9 AM to 5 PM, on weekdays, but at noon on weekends. By breaking it up into two schedules:

• 0 12 * * Sat-Sun: at noon on weekends
• 0 9-17/6 * * Mon-Fri: every 6 hours from 9 AM to 5 PM on weekdays

you can merge them to produce a single timeline:

using System;
using NCrontab;

var start = new DateTime(2000, 1, 1);
var end = start.AddYears(1);
var schedules = new[]
{
    CrontabSchedule.Parse("0 12 * * Sat-Sun"),
    CrontabSchedule.Parse("0 9-17/6 * * Mon-Fri")
};
var occurrences = schedules.GetNextOccurrences(start, end);
Console.WriteLine(string.Join(Environment.NewLine,
                              from t in occurrences
                              select $"{t:ddd, dd MMM yyyy HH:mm}"));

The output from a run will:

Sat, 01 Jan 2000 12:00
Sun, 02 Jan 2000 12:00
Mon, 03 Jan 2000 09:00
Mon, 03 Jan 2000 12:00
Mon, 03 Jan 2000 15:00
Tue, 04 Jan 2000 09:00
Tue, 04 Jan 2000 12:00
Tue, 04 Jan 2000 15:00
Wed, 05 Jan 2000 09:00
Wed, 05 Jan 2000 12:00
Wed, 05 Jan 2000 15:00
Thu, 06 Jan 2000 09:00
Thu, 06 Jan 2000 12:00
Thu, 06 Jan 2000 15:00
Fri, 07 Jan 2000 09:00
Fri, 07 Jan 2000 12:00
Fri, 07 Jan 2000 15:00
Sat, 08 Jan 2000 12:00
Sun, 09 Jan 2000 12:00
...

If two or more schedules produce the same occurrence then only one of them is returned.

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This product includes software developed by the OpenSymphony Group.