Update request - how can I get yesterday's date

[doctordns]

Summary of the update request

How can I get yesterday's date?

https://devblogs.microsoft.com/scripting/how-can-i-get-yesterdays-date/

I see a lot of questions like this

Needs to be re-written for PowerShell

The article should explain the DateTime class plus show how to use the methods.

[Szeraax]

Seems like it would be nice to sync this up with a new PSKoans foundations learning block on datetime and datetimeoffset along with datetime math ($_.LastWriteTime -gt (Get-Date).AddDays(-1))

[Szeraax]

Should also definitely link to the docs on those classes.

[doctordns]

Thanks for trhe comments. It is my intention that each post should contain a bit of background to the question. So in this case, this article should talk about system.datetime class (and properties, as well as the Get-Date cmdlet.

[doctordns]

@Szeraax I am not personally familiar with PSKoans - feel free to suggest how to integrate it. Seems a great idea.

[Szeraax]

I think that we would need to create a new PSKoan script module and then ask Vexx to add it to the module. I like that Hashtable is in the foundations area and think datetime would fit too. Maybe DateTimeOffset and TimeSpan aren't as important and should be cut out.

I just spent a few minutes creating a really quick partial sample of what it could be. Someone completing this module would need to edit all the instances of $__ to something else that makes the unit tests not fail:

using module PSKoans
[Koan(Position = 122)]
param()
<#
    Dates

    In this module, you will test your understanding of DateTimes,
    TimeSpans, DateTimeOffset's, and date/time math.

    A date/time is called a datetime and points to a local time. Each
    datetime object points to a specific time, but each DateTimeOffset
    object points to a specific global moment in time.

    You will need to understand the ramifications of both to complete
    these challenges.
#>
Describe 'Datetimes' {

    It 'allows you to point to a time' {
        <#
            A DateTime object can be created many ways

            Refer to MS Docs for more help:
            https://docs.microsoft.com/en-us/dotnet/api/system.datetime.-ctor
        #>
        [datetime]"$__" | Should -Be (Get-date 2000-01-01).Date
        [datetime]::new($__) | Should -Be (Get-Date 2001-02-03).Date
    }

    It 'can be compared and operated on' {
        # Which one, which one
        # Does it really matter?
    $One = [datetime]"2020-01-01"
    $Two = [datetime]"2020-01-02"
    $__ -gt $__ | Should -Be $true
    $__.AddDays(-7) -lt $__ | Should -Be $true
    }

}

Describe 'TimeSpans' {

    It 'is a length of time' {
        [timespan]"$__" | Should -Be [timespan]::New(2, 15, 3)
    }
    # Add more
}

Describe 'DateTimeOffsets' {
    It 'is always the same instant' {
        # Add more
    }
    # Add more
}

[doctordns]

As this article is now up on the blog, I will close this PR.

I don't want to lose the comment regarding PSKoans. Can I suggest that @Szeraax post the issue and suggestion to their issue page