Get last business day factoring in holidays in Powershell - powershell

Question

I have the following Powershell script that works fine to get the last business/working days, however I am trying to factor in (US) holidays. Can that be done by improving the following script?
$DateOffset = If ((get-date).dayofweek.value__ -eq 1) {-3} Else {-1}

Answer 1

You could do something like this:
function Get-LastBusinessDay {
[CmdletBinding()]
param (
[Parameter(Position = 1)]
[System.DateTime]$Date = [System.DateTime]::Today,
[Parameter(Position = 2)]
[System.DateTime[]]$Holidays
);
$Weekends = #([System.DayOfWeek]::Saturday, [System.DayOfWeek]::Sunday);
$LastBusinessDay = $Date.AddDays(-1);
while (($LastBusinessDay.DayOfWeek -in $Weekends) -or ($LastBusinessDay.Date -in $Holidays)) {
$LastBusinessDay = $LastBusinessDay.AddDays(-1);
}
return $LastBusinessDay;
}
$HolidayTable = #(
# 2018 US Federal Holidays
'January 1, 2018',
'January 15, 2018',
'February 19, 2018',
'May 28, 2018',
'July 4, 2018',
'September 3, 2018',
'October 8, 2018',
'November 12, 2018',
'November 22, 2018',
'December 25, 2018'
);
Get-LastBusinessDay -Date '2018-12-26' -Holidays $HolidayTable
# Returns December 24
Get-LastBusinessDay -Date '2018-09-04' -Holidays $HolidayTable
# Returns Aug 31
The list of holidays can come from anywhere.

Answer 2

Holidays can be difficult to work with when calculating workdays. I use a script from Alan Kaplan that pulls holidays from TimeAndDate.com for any year and any country as PowerShell object.
With that, it should be easy to adjust the calculation as needed.
#Example. Get US National Holidays for 2015, display in two columns with Holiday and Date with day.
$holidays =Get-Holidays 2015
#$holidays now is an object with the holidays for 2015, which you can manipulate
$holidays | where {$_.type -like "National Holiday"} |
select #{Name="Holiday"; Expression = {$_.holidayName}}, #{Name="Date"; Expression = {Get-Date($_.date) -format D}} |
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