Add a calculated field to an imported csv based on datetime - powershell

Question

Could someone please assist with this one.
My current code imports a csv file which has three columns, so far it will update the column names to be more readable. I need to add a fourth column which is a calculated field based on a datetime field.
So need to check the datetime field then display a number of days before it is 90 days old.
e.g. "Today's date" - "03/03/2020 8:00:00 AM" = 31 days
90 days - 31 days = 59 days (the 59 days is to go into the calculated field column
Bit of a newb with powershell and have all other functions working, but this is what I'm left with and need to add it into the below call, when the csv is imported, header columns updated then exported to a new file.
$input = "C:\Data\test\unchanged101.csv"
$output = "C:\Data\test\unchanged101conv.csv"
$checkDate = (Get-Date).AddDays(-90)
$data = Import-Csv $input |
Where-Object {
($_."pwdlastset" -as [DateTime]) -lt $CheckDate
}
$headerConversion = #(
#{ Name = 'User account'; Expression = { $_.'cn' } }
#{ Name = 'Last modified date'; Expression = { $_.'pwdlastset' } }
#{ Name = 'Email address'; Expression = { $_.'mail' } }
)
(Import-Csv -Path $input) |
Select-Object -Property $headerConversion | Select-Object *,"Days Left" |
Export-Csv -Path $output -NoTypeInformation
The new column is the "Days Left" where I need to display the number of days left until it is 90 days old. How to I get the result from the code here, into that column for each row?
$checkDate = (Get-Date).AddDays(-90)
$data = Import-Csv $input |
Where-Object {
($_."pwdlastset" -as [DateTime]) -lt $CheckDate
}
Been working on this one for the past few days and just cant figure the last part out.

Answer 1

First of all, you should not use variable name $input as this is an Automatic variable
If you subtract one datetime object from another, the result is a TimeSpan object which has a property called Days you could use
$inputFile = "C:\Data\test\unchanged101.csv"
$outputFile = "C:\Data\test\unchanged101conv.csv"
$checkDate = (Get-Date).AddDays(-90).Date # .Date sets this to midnight
$result = Import-Csv $inputFile |
Where-Object { [DateTime]$_.pwdlastset -lt $CheckDate } |
Select-Object #{ Name = 'User account'; Expression = { $_.cn } },
#{ Name = 'Last modified date'; Expression = { $_.pwdlastset } },
#{ Name = 'Email address'; Expression = { $_.mail } },
#{ Name = 'Days Left'; Expression = { ($checkDate - [DateTime]$_.pwdlastset).Days } }
# output on screen
$result | Format-Table -AutoSize
# output to csv
$result | Export-Csv -Path $outputFile -NoTypeInformation

Answer 2

I would first add the new column and then go trough all the lines (with a foreach loop) check the remaining days and write them to the new "Days Left" column.
Note: I omitted your header conversion here. You need to run it first and then the "Days Left" code...
$data = Import-Csv $input #import everything
foreach($line in $data){
$daysLeft = 0
$daysSinceLastSet = ((Get-Date) - [DateTime]$line.pwdlastset).Days
if ($daysSinceLastSet -lt 90){
$daysLeft = 90-$daysSinceLastSet
}
$line."Days Left" = $daysLeft
}
$data | Export-Csv -Path $output -NoTypeInformation