Crontab expression for every first tuesday of every month

[Hein Pauwelyn]

How could I create an timer trigger with Azure Functions (version 3 and .NET Core) that must be executed every first Tuesday from every month at 8 AM. Starting from now (05/08/2020) this must be the next five occurrences:

1. 2020/06/02 Tue 08:00:00
2. 2020/07/07 Tue 08:00:00
3. 2020/08/04 Tue 08:00:00
4. 2020/09/01 Tue 08:00:00
5. 2020/10/06 Tue 08:00:00

By using www.cronmaker.com, I've next NCRONTAB:

0 0 8 ? 1/1 TUE#1 *

But then I've next exception:

The schedule expression 0 0 8 ? 1/1 Tue#1 * was not recognized as a valid CRON expression or TimeSpan string.

Then I've start changing the CRON expression to next varations:

CORN	Result
0 0 8 ? 1/1 Tue#1	Error from above
0 0 8 * 1/1 Tue#1	Error from above
0 0 8 1/1 Tue#1 *	Error from above
0 0 8 * 1/1 Tue 1	Error from above
0 0 8 ? 1/1 Tue 1	Error from above
0 0 8 * 1/1 Tue/1	2020/05/29 08:00:00 - 2020/05/30 08:00:00
0 0 8 * * Tue/2	2020/05/30 08:00:00 - 2020/06/02 08:00:00
0 0 8 * 1/1 Tue/2	2020/05/30 08:00:00 - 2020/06/02 08:00:00
0 0 8 ? 1/1 Tue/2	Error from above

So every expression I've made, would not work as expected. My question is now: What's the correct expression?

[Atif Aziz]

This library only supports the original contrab expression. The #1 modifier is an extension, which is why you get an error. CronMaker specifically states that “Generated expressions are based on Quartz cron format.”

A first Tueday of a month can only occur on days 1-7, so you could use the 0 8 1-7 * Tue expression to effectively get 8 AM on first seven days of any month that's a Tuesday.

[Atif Aziz]

@HeinPauwelyn Consider closing this issue if the question's been answered.