Piping into a ScriptBlock - powershell

Question

I'm trying to find some way of flexibly altering/substituting pipeline elements in PowerShell:
Function Where-DirectlyReportsTo {
Param (
[Parameter(
ValueFromPipeline = $true,
HelpMessage = "The ADUser object to be tested"
)]
[Microsoft.ActiveDirectory.Management.ADUser] $ADUser,
[Parameter(
Mandatory = $true,
ValueFromPipeline = $false,
Position = 0
)]
[String] $mgrDN
)
Process {
If ($ADUser) {
If ($ADUser.Manager -eq $mgrDN) { Return $ADUser }
}
}
}
$Properties = #("Manager")
$users = Get-ADUser -Filter * -SearchBase $OU -Properties $Properties
[ScriptBlock] $sb = {Where-DirectlyReportsTo "CN=Colonel Foobar,$OU"}
$DNs = $users | $sb | %{$_.DistinguishedName}
Which I want to return the DNs of all the users that report to Colonel Foobar, but it gives me the error Expressions are only allowed as the first element of a pipeline.
This is a trivial example, but I'd ultimately like to be able to put the pipeline step inside a loop and pass it different ScriptBlocks to get different sets of users, or use more complicated ScriptBlocks (e.g.: {Where-IsEmployee | Where-IsInDepartment "Finance" | Where-LikesIceCream}).
I realize that I may be going about this all wrong, and I would very much appreciate being pointed in the right direction.
EDIT: To clarify, here's a rough outline of what I'd like to accomplish:
[ScriptBlock[]] $arrBlocks = #( # lots of different cases
)
ForEach ($sb In $arrBlocks) {
$DNs = $users | $sb | %{$_.DistinguishedName}
# Then do something with the DNs
}
Realistically, this will probably involve a hash table instead of an array, so that I know what to do with each set of results.

Answer 1

The syntax error is simple:
# Wrong:
$DNs = $users | $sb | %{$_.DistinguishedName}
# Correct; note the call operator in front of $sb:
$DNs = $users | &$sb | %{$_.DistinguishedName}
This still leaves the matter of your pipeline hitting a dead end. You don't need to get fancy here; just pipe $Input along to the next function:
[ScriptBlock] $sb = {$Input | Where-DirectlyReportsTo "CN=Colonel Foobar,$OU"}
You shouldn't have $sb itself enumerate the input. That's extra overhead, and if you use param(), bumps the script block up to a cmdlet. You really don't need that.
In fact, you could simplify this whole thing down to four lines, or even one really long line:
$properties = #("Manager")
$managers = #(
"CN=Colonel Foobar,$OU"
"CN=Sergeant Foobar,$OU"
"CN=Random Manager,$OU"
)
$users = Get-ADUser -Filter * -SearchBase $OU -Properties $properties
$DNs = $users | ?{ $managers -contains $_.Manager } | %{ $_.DistinguishedName }
I tested that with this code:
$OU = 'OU=test'
$users = #(
#{
Manager = "CN=Colonel Foobar,$OU";
DistinguishedName = "Show me!"
}
#{
Manager = "CN=Anon Y Mous,$OU";
DistinguishedName = "Don't show me!"
}
'rabbit'
42
$null
#{
DistinguishedName = "Don't show me, either!"
}
#{
Manager = "CN=Random Manager,$OU";
DistinguishedName = "Show me, too!"
}
)
$managers = #(
"CN=Colonel Foobar,$OU"
"CN=Sergeant Foobar,$OU"
"CN=Random Manager,$OU"
)
$DNs = $users | ?{ $managers -contains $_.Manager } | %{ $_.DistinguishedName }
$DNs | Write-Host
You could make it a bit more verbose, if you wanted to:
$properties = #("Manager")
$managers = #(
"CN=Colonel Foobar,$OU"
"CN=Sergeant Foobar,$OU"
"CN=Random Manager,$OU"
)
$filter = { $managers -eq $_.Manager }
$selector = { $_.DistinguishedName }
$users = Get-ADUser -Filter * -SearchBase $OU -Properties $properties
$DNs = $users | ?{ &$filter } | %{ &$selector }
You sound like you want to eventually have multiple filters. This is pretty easy, too:
$properties = #("Manager")
$managers = #(
"CN=Colonel Foobar,$OU"
"CN=Sergeant Foobar,$OU"
"CN=Random Manager,$OU"
)
$filters = #(
{ $managers -contains $_.Manager }
{ ![string]::IsNullOrWhiteSpace($_.DistinguishedName) }
)
$selector = { $_.DistinguishedName }
$users = Get-ADUser -Filter * -SearchBase $OU -Properties $properties
$DNs = $users | ?{ $filters.Invoke() -notcontains $false } | %{ &$selector }

Answer 2

There needs to be something at the head of the pipeline in your scriptblock and you have to define your scriptblock as taking pipeline input.g.:
[scriptBlock]$sb = {[CmdletBinding()]param([Parameter(ValueFromPipeline=$true)]$obj) `
process {
foreach ($o in $obj) {
$o | Where-DirectlyReportsTo "CN=Colonel Foobar,$OU"}}}
You also can't throw $sb into the pipeline quite like that, try this:
$users | &$sb | %{$_.DistinguishedName}

Answer 3

In PS 2.0 this somewhat more concise (readable?) syntax works. (doesn't work in PS 3.0, where setting isFilter throws an exception)
$filterSet =
{$_.property -eq "desired value"},
{$_.method() -eq "I like the return value"},
{$_.gettype() -eq [special.type.I.like]},
{arbritraryBoolPSfunction $_}
$filterSet | % {$_.isFilter = $true} # make 'em all filters
ForEach ($filter In $filterSet) {
$DNs = $users | & $filter | %{$_.DistinguishedName}
# Then do something with the DNs
}