powershell delete some files older than 90 days, with exceptions - powershell

Question

$timeLimit1 = Get-Date.AddDays(-90)
Get-ChildItem <path> | ? {$_.LastWriteTime -le $timeLimit1 } | Remove-Item
So I have the easier part, but I am trying to figure out how to do something a little more complex.
I am setting up a backup deletion routine. The requirement is to keep the last 90 days of backups, then the final day of each month prior to that for the current year and finally a backup from December 31st for the prior 2 years.
I couldn't find any examples other than just a single check; is it possible to do several checks to automate that.

Answer 1

I suggest writing a custom filter to apply the logic e.g.
filter MyCustomFilter{
$File = $_
$FileDate = $File.LastWriteTime
$Now = (Get-Date)
$FileAgeDays = ($Now - $FileDate).TotalDays
if (
# Keep files for at least 90 days
( $FileAgeDays -lt 91
) -or
# Keep files from last day of the month this year
( $FileDate.Year -eq $Now.Year -and
$FileDate.Month -ne $FileDate.AddDays(1).Month
) -or
# Keep files from 31 Dec for up to 2 years
( $FileAgeDays -lt ( 2 * 365 ) -and
$FileDate.Month -eq 12 -and
$FileDate.Day -eq 31
)
) {
# File should be kept, so nothing is returned by the filter
} else {
# File should be deleted, so pass the file down the pipeline
write-output $File
}
}
Now your overall code would look something like this:
get-childItem -path <path> |
where-object { -not $_.PSIsContainer } |
MyCustomFilter |
Remove-Item
It goes without saying, that proper testing is required before letting this loose on production systems.
EDIT: A Simpler test for last day of month
I thought of a neater 'last day of the month' test, which is simply to compare the month property of the date under test, with the month property of the following day e.g.
$FileDate.Month -ne $FileDate.AddDays(1).Month
will return $true if $FileDate is last day of the month.

Answer 2

Just create an array of your "special" dates and add them to your filter.
$timeLimit1 = Get-Date
$timeLimit1.AddDays(-90)
$specialDates = (Get-Date "31-12-2014"), (Get-Date "31-05-2017") # continue the list
Get-ChildItem <path> | ? {$_.LastWriteTime -le $timeLimit1 -and $specialDates -notcontains $_.LastAccessTime.Date } | Remove-Item
I would also make a function to find the "special" dates.