A useful script to manage GFS retention in multiple folders which contain backup files such as "backup_ddMMyyy.7z". It looks for backups done within a predefined year, then group them into Monthly, Weekly & Daily

Managing Backup GFS Retention.ps1

# Created by beancurd1 (please distribute the code with this session, thanks)
# https://gist.github.com/beancurd1
# A useful script to manage GFS retention in a single folder which contains backup files 
# such as "backup_ddMMyyy.7z". It looks for backups done within a year, then put them 
# into Monthly, Weekly & Daily.groups

Clear
# Create a String array to store end of month dates for X months (e.g. 31DEC15 to 31JAN15)
# define how many years of data to retain (it will search files created in that year, split them into Monthly, Weekly and Daily)
$year=1
for($i=0; $i -ge (-11*$year); $i--) {
    $date = (Get-Date).AddMonths($i)           
    $startofmonth = Get-Date $date -Day 1 -hour 0 -minute 0 -second 0
    $endofmonth = (($startofmonth).AddMonths(1).AddSeconds(-1))
    [array]$eomArray += @($endofmonth.ToString("dd MMM yyyy"))
}

# Find Monthly (bakups done on the last day of a month for the last 12 months), 
#      Weekly (bakups done on Sat & Sun in last 12 months), 
#      Daily (backups done in last 12 months except above)
# It loops through the folders (e.g. Databases, Reports, Invoices, etc) in Bakcup folder and identify files as M/W/D backups
# Note: It groups backups by creation date, you need to include you actions (e.g. move, del, rename, etc.)
$backupPath = "X:\Backup\*"
$dirs = Get-Item -Path "$backupPath" | ?{$_.PSIsContainer}
ForEach ($dir in $dirs){
    Get-ChildItem "$($dir.FullName)\*" -include @("*.7z","*.zip","*.bak") |
        Where-Object { $_.CreationTime -ge (Get-Date).AddYears(-1*$year) -and $_.CreationTime -le (Get-Date) }|
        Sort-Object CreationTime -Descending |
        Foreach-Object{
			if ($eomArray -contains $_.CreationTime.ToString("dd MMM yyyy")) {
				# Write-Host  $_ $_.CreationTime $_.CreationTime.DayOfWeek "Monthly"
				# Your Action HERE
			} elseif ($_.CreationTime.DayOfWeek -eq 'Saturday' -or $_.CreationTime.DayOfWeek -eq 'Sunday') {
				# Write-Host $_ $_.CreationTime $_.CreationTime.DayOfWeek ”Weekly"
				# Your Action HERE
			} else {
				# Write-Host $_ $_.CreationTime $_.CreationTime.DayOfWeek "Daily"
				# Your Action HERE
			}
        }
}