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datepowershelliso8601

Calculate date from calendar week, weekday and year in powershell

How to calculate a date from ISO 8601 calendar week, weekday and year in powershell?

Example: calendar week 3, weekday 4, year 2017 should return a date object 1/19/2017

Solution

  • Using the module IsoDates.psm1 by Joel Bennett
    It's as easy as:

    ## Q:\Test\2017\01\19\SO_41743960.ps1
Import-Module 'Q:\test\posh\IsoDates.psm1'

"IsoDayofWeek for {0:D} is {1} vs {2}" -f `
      (Get-Date "01/15/2017"),
      (Get-ISODayOfWeek "01/15/2017"),
      ((Get-Date "01/15/2017").DayOfweek.value__)
"ISODateString for today is {0}" -F (Get-ISODateString)
"ConvertFrom-ISODateString {0} is {1:D}" -f "2017-W01-1",
      (ConvertFrom-ISODateString("2017-W01-1"))

    Returning this output (on my German locale pc):

    IsoDayofWeek for Sonntag, 15. Januar 2017 is 7 vs 0
ISODateString for today is 2017-W03-4
ConvertFrom-ISODateString 2017-W01-1 is Montag, 2. Januar 2017