PowerShell Get-Date and DateTime

Windows PowerShell Get-Date Format

Manipulating dates is always tricky.  However, PowerShell's Get-Date cmdlet does a wonderful job of interpreting the different international formats for day / month / year.  As a result, whatever your computer's country locale, it will be easy to calculate how many days there are to Christmas.

Topics for Windows PowerShell Get-Date and DateTime

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Introduction to the Get-Date Cmdlet

On this page I am making a change to my usual running order.  I want to start by tackling the challenge presented by a real-life task.  After showing examples of Get-Date in action I will encourage you to research more methods and properties for this PowerShell cmdlet.  The result will be that you have the skills to undertake other DateTime projects.

How Many Days to Christmas? (or Thanksgiving)

Our challenge is simple enough, to knock-up a simple script that will tell us how many days there are until Christmas, Thanksgiving, or any other date you care to place in a text string.

Here in the UK, our operating systems show dates in the format: dd mmmm yyyy.  Whereas in the United States your locale is displayed as mmmm dd yyyy.  Consequently, I was amazed that PowerShell could convert both "25 December 2014" and "November 28 2014" into date values that it could understand and perform calculations.

Example 1 - Calculate Days Until Christmas Using Lots of Variables

In example one I have used several variables that are not strictly necessary, I just wanted to show my thought process in creating this very simple PowerShell script.

# PowerShell DateTime Script to display days until Christmas
Clear-Host
$DecDate = "25 December 2014"
$NovDate ="November 28 2014"
$Thanksgiving = [system.datetime]$NovDate
$Christmas = [system.datetime]$DecDate
$Today = Get-Date
$Xmas = ($Christmas.DayOfYear - $Today.DayOfYear)
$Thanks = ($Thanksgiving.DayOfYear - $Today.DayOfYear)
"There are " + $Xmas + " days until " + $DecDate
"There are " + $Thanks + " days until " + $NovDate

Note 1: You may wish to examine the values for $DecDate and $NovDate, then change the sequence of day month to suit your locale.

Note 2: It's interesting to see how PowerShell leverages .Net Framework, for example, it employs System.DateTime to convert a text string to a date format.

Note 3: I keep marvelling how PowerShell can understand both formats: dd mmmm yyyy, and mmmm dd yyyy.

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Example 2 - Production Version of 'How Many Days to Christmas'

# PowerShell DateTime Example
"There are " + (([system.datetime]"25 December 2014").DayOfYear - `
(Get-Date).DayOfYear) + " days until " + "24 December 2014"

Note 4: This is just one long command.  Observe how the backtick (`) enables the command to overspill onto the second line.  Alternatively, break the line at the open bracket symbol thus:

- (
Get-Date).DayOfYear) + " days until " + "24 December 2014"

Note 5: This command needed an extra set of round brackets to surround [system.datetime]"25 December 2014"

Note 6: It's interesting to see how PowerShell interprets a mixture of "text strings" and date calculations.  As with types of bracket, you need the correct type of "double" speech marks here.

Further Research on PowerShell's Get-Date

I'm hoping that the simple example above will give you ideas for date scripts, which will be useful in your PowerShell projects.  If so, then it's well worth examining Get-Date's properties, and in particular its methods.

a) Get-Date Methods and Properties

# Research PowerShell Get-Date Properties
Get-Date | Get-Member

Note 7: Normally it's a cmdlet's properties that I am most interested in, but with Get-Date it's the methods that intrigue me, for example .AddDays() and .IsDaylightSavingTime().

b) AddDays Method

The purpose of this script is to list all the System Error messages from the last 8 days. Incidentally, it's amazing how often we use this method with a negative number to go back in time.

# PowerShell Get-Date example
Clear-Host
$Log8d = @{
Logname = 'System'
EntryType = 'Error'
After = (Get-Date).AddDays(-8)
}

Get-EventLog @Log8d

Note 8: See more on this @{.. technique of PowerShell 'Splatting'

c) Another Job for .AddDays
Scenario: You want to list eventlog messages younger than 30 days.

# Date calculation with .AddDays()
Clear-Host
$DateCut = (Get-Date).AddDays(-20)
Get-EventLog System -EntryType Error |
Where-Object {$_.TimeWritten -ge $DateCut}

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Get-Date Parameters

# Research PowerShell's Get-Date Parameters
Clear-Host
Get-Help Get-Date -full

Thanks to PowerShell's help, I learned about the format -Uformat.

Formatting Get-Date Challenge: 
UK readers may appreciate employing this -Uformat parameter to rearrange days and months:

# PowerShell Get-Date Format Example
Clear-Host
$Now = Get-Date -Uformat "%A, %d:%m:%Y"
Write-Host "Today in the UK is $Now enjoy your day!"

Bonus Technique - DateTime and ParseExact

Once again, here is PowerShell working with the .Net Framework class DateTime.  ParseExact is a neat method which can convert a text string into its DateTime equivalent.

# ParseExact Change date and time with custom specifier.
Clear-Host
$DateString = "Sun 26 Jan 2014 12:30 AM -06:00"
$Format = "ddd dd MMM yyyy h:mm tt zzz"
$Translate = [DateTime]::ParseExact($DateString, $Format, $Provider)
Write-Host "$DateString converts to $($Translate.ToString())."

Get-Date CSV Format

Here is an example which employs another PowerShell cmdlet called ConvertTo-Csv to control the date format.

Clear-Host
$DateCsv = Get-Date
ConvertTo-Csv -Inputobject $DateCsv -NoTypeinformation

Note 9: You could change the separator from a comma to a semi-colon by appending this parameter: -Delimiter ";"

See more on ConvertTo-Csv »

Summary of PowerShell Get-Time and DateTime

Scripting dates is always tricky.  In these examples we can see how PowerShell leverages .Net Framework to convert strings into PowerShell's DateTime values, which in turn, can be use for calculations.

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See more PowerShell examples for syntax advice

PowerShell Tutorials   • Syntax   • Get-Verb   • PowerShell Nouns   • Get-Credential

PowerShell -as   • Comparison operators  • Conditional operators   • Real-time Bandwidth Monitor

Get-Date  • Quotes   • Windows PowerShell   • PowerShell Version Check   • Get-Member

Please email me if you have a better example script. Also please report any factual mistakes, grammatical errors or broken links, I will be happy to correct the fault.

 

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