Using script scope modifier on PowerShell functions in modules has no effect? - powershell

Question

I assumed that using the script scope modifier on a function in a PowerShell module would prevent the function from being exported. Sample:
function script:Get-One { 1 }
When I import the module the Get-One function is exported.
Questions
Is it supposed to work to use the script scope modifier to make module functions private?
If not: Why? Any other scope modifiers that I can use?
I know I can use Export-ModuleMember to control which functions to export, but I only have a few functions that should not be exported. I would rather specify which functions to ignore.

Answer 1

script scope in a module is redundant because the default scope is the script/module in which it's defined. It is the equivalent of an instance variable. global in a module is akin to a static variable. Posh-Git for example uses a Global preferences variable for consistency between shells.
I used an in-memory module but the idea is the same when using a psd1 to define the arguments to New-Module
# remove module from namespace for repeated testing
if(Get-Module -Name 'SOTest') { Remove-Module -Name 'SOTest' }
new-Module -Function:'*' -Name:'SOTest' -ScriptBlock {
$global:helpers = [PSCustomObject]#{}
Add-Member -InputObject:$global:helpers -MemberType:ScriptMethod -Name:'HiddenFoo' -Value { return "Private Foo!" }
Add-Member -InputObject:$global:helpers -MemberType:ScriptMethod -Name:'HiddenFooWithArgs' -Value { return "Private " + $args -join ',' + '!' }
Add-Member -InputObject:$global:helpers -MemberType:ScriptMethod -Name:'HiddenFooWithParams' -Value { param ([string]$str, [int]$num); return "Private Str = $str + num; $num!" }
## script: scope refers to module scope, which makes it redundant
function WriteFoo {
Write-Output "PublicFoo!"
}
function WritePrivate {
#This fails, because the private now refers to the function scoped $private:helpers
$private:helpers.HiddenFoo | Write-Verbose -Verbose
}
function WritePrivateShort {
# This works because the helpers object is static across instances
$helpers.HiddenFoo() | Write-Verbose -Verbose
$helpers.HiddenFooWithArgs("Cow", "Moo") | Write-Verbose -Verbose
$helpers.HiddenFooWithParams("Four", 4) | Write-Verbose -Verbose
# This errors due to argument type mismatch
$helpers.HiddenFooWithParams("Five", "Five") | Write-Verbose -Verbose
}
} | Import-Module
# Prefer short errors for this demo
$ErrorView = "CategoryView"
Get-Module -Name 'SOTest'
'WF-----------------'
WriteFoo
'WP-----------------'
WritePrivate
'WPS----------------'
WritePrivateShort
'-------------------'
And the output:
ModuleType Version Name ExportedCommands
---------- ------- ---- ----------------
Script 0.0 SOTest {WriteFoo, WritePrivate, WritePrivateShort}
WF-----------------
PublicFoo!
WP-----------------
InvalidData: (:) [Write-Verbose], ParameterBindingValidationException
WPS----------------
VERBOSE: Private Foo!
VERBOSE: Private Cow Moo
VERBOSE: Private Str = Four + num = 4!
InvalidArgument: (:) [], RuntimeException
-------------------

Answer 2

For a Powershell module, Export-ModuleMember is the preferred way to do that.
As an alternative, you can define the function that you don't want exported from inside the function(s) which uses it (in the Begin block, for example).
This makes the function only visible by the "parent" function, making it effectively private.
Also, you could try using the Private scope , instead of the Script scope.