POSTS

Get-PreviousWeekdayDate

July 14, 2009

I am fleshing out my automated monitoring/reporting system and I wanted to include some performance data exports. As part of this I always wanted my weekly exports to start on a certain day of the week no matter when the script was run. I also needed to make sure that I received a weeks worth of data.

To help out I wrote this function:

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# Find the date of a previous weekday.  Originally conceived to export performance
# from a give day of the week no matter when it was called.
function Get-PreviousWeekdayDate
{
    param
    (
        [DateTime]$date = $(Get-Date),
        [System.DayOfWeek]$weekDay = $([System.DayOfWeek]::Sunday),  # Full weekday names work here.
        [switch]$fullWeek # The return date must be a full week ago.
    )

  Set-Variable -Name DAYS_IN_WEEK -Value 7 -Option Constant
  $dayDelta = 0 # The difference in days between $date and the target day.
  # If we are further in the week then we just go back x days.
  if ([Int32]$date.DayOfWeek -ge [Int32]$weekDay)
  {
      $dayDelta = [Int32]$date.DayOfWeek &#8211; [Int32]$weekDay
  }
  # Otherwise we need wrap around the week
  else
  {
      $dayDelta = $DAYS_IN_WEEK + [Int32]$date.DayOfWeek &#8211; [Int32]$weekDay
  }

  $date = $date.AddDays(-$dayDelta)

  # Go back 7 days
  if ($fullWeek)
  {
      $date = $date.AddDays(-$DAYS_IN_WEEK)
  }
  
  $date
}