Invoke method on ScriptBlock truncating array - powershell

Question

I have the following ScriptBlock defined:
[ScriptBlock]$strSb = {
param(
[Parameter(Mandatory=$false,Position=0)]
[String[]]$Modules = #('String3','String4')
)
Write-Host "Passed in params:"
foreach($m in $Modules){
Write-Host $m
}
$defaultModules = #('String3','String4')
# Add Default Modules back if not present #
foreach($module in $defaultModules){
if($Modules -notcontains $module){
$Modules += $module
}
}
Write-Host "Final set:"
# Load Dependencies #
foreach($m in $Modules){
Write-Host $m
}
}
As the parameter states in the ScriptBlock, I want to be able to pass in an array of strings. When I call $strSb.Invoke(#('String11','String12')) I receive the following:
Passed in params:
String11
Final set:
String11
String3
String4
What I expect is:
Passed in params:
String11
String12
Final set:
String11
String12
String3
String4
Why is the invoke method truncating my array to the first item entered? And how would I go about fixing it so I can pass in an array of strings?
FWIW: I'm working in v2 and v3.

Answer 1

The problem is that the Invoke method takes an array of arguments (kind of like commands that have an -ArgumentList parameter), so each element in your array is parsed as a separate argument. The first argument, 'String11', is assigned to the first postitional parameter, $Modules, and any subsequent arguments are discarded, since there are no more positional parameters. It doesn't matter that $Modules is declared as a string array; since each element of the argument list is a separate argument, you're setting $Modules to an array of one element.
If you use the , operator to indicate that you're passing in a single array argument, it works as intended:
$strSb.Invoke((,#('String11','String12')))
BTW, you don't really need the #, because a comma-separated list of strings is interpreted as an array by default. Not just in this particular context, but in general. So just use this:
$strSb.Invoke((,('String11','String12')))
To prove out the explanation above, try this scriptblock, which is the same except that a second parameter (creatively named $SecondParameter) is declared, and then displayed after the loop that displays the value of the first parameter:
[ScriptBlock]$strSb = {
param(
[Parameter(Mandatory=$false,Position=0)]
[String[]]$Modules = #('String3','String4'),
[String]$SecondParameter
)
Write-Host "Passed in params:"
foreach($m in $Modules){
Write-Host $m
}
Write-Host "`nSecondParameter: $SecondParameter`n"
$defaultModules = #('String3','String4')
# Add Default Modules back if not present #
foreach($module in $defaultModules){
if($Modules -notcontains $module){
$Modules += $module
}
}
Write-Host "Final set:"
# Load Dependencies #
foreach($m in $Modules){
Write-Host $m
}
}
If you then pass in the arguments as you were, $strSb.Invoke(#('String11','String12')), you get these results:
11-26-13 19:02:12.55 D:\Scratch\soscratch» $strSb.Invoke(#('String11','String12'))
Passed in params:
String11
SecondParameter: String12
Final set:
String11
String3
String4
11-26-13 19:02:29.34 D:\Scratch\soscratch»
One last tip, not directly related to the question, is that you can compact the foreach loops by using a pipelines, which is are not only more succinct but generally more efficient. Here's a compacted version of your code:
[ScriptBlock]$strSb = {
param(
[Parameter(Mandatory=$false,Position=0)]
[String[]]$Modules = ('String3','String4')
)
Write-Host "Passed in params:"
$Modules | Write-Host
$defaultModules = 'String3','String4'
# Add Default Modules back if not present #
$defaultModules | ?{$Modules -notcontains $_} | %{$Modules += $_}
Write-Host "Final set:"
# Load Dependencies #
$Modules | Write-Host
}

Answer 2

If I understand what you're doing, you want to take 2 arrays, concatenate them, and ensure uniqueness...
First, Since you have a [Parameter...] on your parameter, you magically get [CmdletBinding()] on the method. This means that you are automatically going to get $Modules split into multiple calls.
Second, ScriptBlock.Invoke() takes a params style array and puts them into the method as separate arguments.
The first thing I would try is to add the attribute to gather all values:
[Parameter(ValueFromRemainingArguments=$true, Position=0, Mandatory=$true)]
[String[]]$Modules
However, for the Join, you can much more easily do something like:
($modules + $defaultModules) | Select -Unique

Answer 3

Not sure exactly why, but it doesn't seem to like that named parameter. Seems to like $args, tho :
[ScriptBlock]$strSb = {
$Modules = $args
Write-Host "Passed in params:"
foreach($m in $modules){
Write-Host $m
}
$defaultModules = #('String3','String4')
# Add Default Modules back if not present #
foreach($module in $defaultModules){
if($Modules -notcontains $module){
$Modules += $module
}
}
Write-Host "Final set:"
# Load Dependencies #
foreach($m in $Modules){
Write-Host $m
}
}
$strSb.Invoke('String11','String12')
Passed in params:
String11
String12
Final set:
String11
String12
String3
String4