PowerShell Filtering between pipelines

Question

I'm writing a script to archive files in folders, which works fine. But now I want to implement an extra filter called $OlderThan and that's where I'm struggling now.

The script:

[CmdletBinding(SupportsShouldProcess=$True)]
Param (
    [parameter(Mandatory=$true,Position=0)]
    [ValidateNotNullOrEmpty()]
    [ValidateScript({Test-Path $_ -PathType Container})]
    [String]$Source,
    [parameter(Mandatory=$false,Position=1)]
    [ValidateNotNullOrEmpty()]
    [ValidateScript({Test-Path $_ -PathType Container})]
    [String]$Destination = $Source,
    [parameter(Mandatory=$false)]
    [ValidateSet('Year','Year\Month','Year-Month')]
    [String]$Structure = 'Year\Month',
    [parameter(Mandatory=$false)]
    [ValidateSet('Day','Month','Year')]
    [String]$OlderThan = 'Day',
    [parameter(Mandatory=$false)]
    [Int]$Quantity = '1'
)
Begin {
    $Today = Get-Date
    $When = ($Today.AddDays(-"$Quantity")).Date
}
Process {
    Get-ChildItem $Source -File | ForEach-Object {
        $File = $_
        # Get folder name
        $ChildPath = Switch ($Structure) {
            'Year'       { [String]$File.CreationTime.Year }
            'Year\Month' { [String]$File.CreationTime.Year+"\"+$File.CreationTime.ToString("MM") }
            'Year-Month' { [String]$File.CreationTime.Year+"-"+$File.CreationTime.ToString("MM") }
        }
        $Target = Join-Path -Path $Destination -ChildPath $ChildPath

        # Move the file
        if (Test-Path $Target -PathType Container) { 
            Move-Item -Path $File.FullName -Destination $Target -ErrorAction SilentlyContinue
        } 
        else {
            New-Item $Target -Type Directory | Out-Null
            Move-Item -Path $File.FullName -Destination $Target -ErrorAction SilentlyContinue
        }
    }
}

The extra filter:

Switch ($OlderThan) {
    'Day'    { where ($File.CreationTime -le $(($Today.AddDays(-"$Quantity")).Date))}
    'Month'  { where {$File.CreationTime.Month -lt $Today.Month }}
    'Year'   { where {$File.CreationTime.Year -lt $Today.Year }}
}

How can I implement this the best way? The purpose is that when Day, Month or Year is chosen, this filter is applied after Get-ChildItem based on the file's CreationTime. So only those files are moved that comply with the filter.

For the moment I created a workaround for this, by creating a function like below. But is it really needed to create a function just to have these 3 filters between the pipeline? It feels like I'm over complicating things.

Current workaround:

Function Select-Stuff {
    Param(
        [Parameter(ValueFromPipeline=$True)]
        $File
    )
    Process {
        Switch ($OlderThan) {
            'Day'    { if ($File.CreationTime -le $When) {Write-Output $File} }
            'Month'  { if ($File.CreationTime.Month -lt $Today.Month) {Write-Output $File} }
            'Year'   { if ($File.CreationTime.Year -lt $Today.Year) {Write-Output $File} }
        }
    }
}

Get-ChildItem $Source -File | Select-Stuff | ForEach-Object {

Thank you for your help.

I can off course always make a script block out of it and call it from within the Switch. But I would like to be able to use the pipeline if possible. — DarkLite1
– DarkLite1, Commented Sep 16, 2014 at 11:15

mjolinor · Accepted Answer · 2014-09-16 12:09:12Z

1

I think the easiest way to create that filter would be to (literally) create that filter:

 Begin {
    $Today = Get-Date
    $When = ($Today.AddDays(-"$Quantity")).Date

    Switch ($OlderThan) {
    'Day'    { filter Get-OlderThan  { if ($_.CreationTime -le $(($Today.AddDays(-"$Quantity").Date))) {$_} } }
    'Month'  { filter Get-OlderThan { if ( $_.CreationTime.Month -lt $Today.Month) {$_} } }
    'Year'   { filter Get-OlderThan { if ($_.CreationTime.Year -lt $Today.Year) {$_} } }
    Default  { filter Get-OlderThan {$_ } }
  }
}
Process {
    Get-ChildItem $Source -File | 
    Get-OlderThan | ForEach-Object {
    ...
    }

edited Sep 16, 2014 at 12:09

answered Sep 16, 2014 at 11:59

mjolinor

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3 Comments

DarkLite1 Over a year ago

Awesome, awesome, awesome! I didn't know about the existence of Filter in PowerShell. And writing a function specifically for this with parameters and everything seemed like overkill. Thank you very much mjolinor, appreciate it!

mjolinor Over a year ago

Welcome! Filters are basically just a function that implicitly have only a Process block. You don't see them used much, but they can be handy things on occasion :)

DarkLite1 Over a year ago

I fully agree! They make things a lot cleaner/easier to read when it's only about filtering stuff :)

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