How can I redefine a function that was exported by a powershell module

Question

Is there a way that I can re-define a function that was exported by a module and is used by another? Given the following folder structure: ``` C:. │ MyScript.ps1 │ └───MyModules ├───Deployment │ Deployment.psm1 │ └───Logging Logging.psm1 ``` And the following content for each file: MyScript.ps1: ``` #Add MyModules to the module path $cleanedModulePath = @() $env:PSModulePath -split ";" | %{ if( !( $_ -Match "MyModules") ){ $cleanedModulePath += $_ } } $thisDir = (Split-Path -parent $script:MyInvocation.MyCommand.Definition) $moduleDir = Join-Path $thisDir "MyModules" $cleanedModulePath += $moduleDir $env:PSModulePath = ($cleanedModulePath -Join ";") Import-Module Deployment -DisableNameChecking #Neither of these manage to redefine Log-Debug - even if put before the Import function Log-Debug{} Set-Item -Path function:Log-Debug -Value {} -Option "AllScope,ReadOnly" -Force Do-Something ``` Deployment.psm1: ``` Import-Module Logging -DisableNameChecking function Do-Something { Log-Debug "…

Accepted Answer

I would've guessed that simply defining an empty function with the same name should suffice. And it actually does, when both modules are imported directly in PowerShell:

```
PS C:\> $modules = "$env:USERPROFILE\Documents\WindowsPowerShell\Modules"
PS C:\> Get-Content "$modules\Logging\Logging.psm1"
function Log-Debug($msg) {
  Write-Host "DEBUG: $msg"
}
Export-ModuleMember -Function Log-Debug
PS C:\> Get-Content "$modules\Deployment\Deployment.psm1"
function Foo($msg) {
  Write-Output 'FOO: something'
  Log-Debug $msg
}
Export-ModuleMember Foo
PS C:\> Import-Module Logging -DisableNameChecking
PS C:\> Import-Module Deployment
PS C:\> Foo 'bar'
FOO: something
DEBUG: bar
PS C:\> function Log-Debug {}
PS C:\> Foo 'bar'
FOO: something
PS C:\> _
```

But for some reason you cannot re-define or remove a function that was imported from a module by another module (or at least I didn't find a way to do so).

However, you should be able to override the function by making use of command precedence. Since aliases are evaluated first, you can define an alias `Log-Debug` to a custom logging function:

```
PS C:\> $modules = "$env:USERPROFILE\Documents\WindowsPowerShell\Modules"
PS C:\> Get-Content "$modules\Logging\Logging.psm1"
function Log-Debug($msg) {
  Write-Host "DEBUG: $msg"
}
Export-ModuleMember -Function Log-Debug
PS C:\> Get-Content "$modules\Deployment\Deployment.psm1"
Import-Module Logging -DisableNameChecking
function Foo($msg) {
  Write-Output 'FOO: something'
  Log-Debug $msg
}
Export-ModuleMember Foo
PS C:\> Import-Module Deployment
PS C:\> Foo 'bar'
FOO: something
DEBUG: bar
PS C:\> function Log-DebugSuperseded {}
PS C:\> Set-Alias -Name Log-Debug -Value Log-DebugSuperseded
PS C:\> Foo 'bar'
FOO: something
PS C:\> _
```

That way you can even change the logging implementation on the fly, or switch back and forth between original and custom logging function:

```
PS C:\> Foo 'bar'
FOO: something
DEBUG: bar
PS C:\> function Log-DebugSuperseded {}
PS C:\> Set-Alias -Name Log-Debug -Value Log-DebugSuperseded
PS C:\> Foo 'bar'
FOO: something
PS C:\> function Log-DebugSuperseded {'baz'}
PS C:\> Foo 'bar'
FOO: something
baz
PS C:\> Remove-Item Alias:\Log-Debug
PS C:\> Foo 'bar'
FOO: something
DEBUG: bar
PS C:\> _
```

Edit:

To make this work in a script you need to define both function and alias as global objects:

```
PS C:\> Get-Content .	est.ps1
Import-Module Deployment
Write-Host '--- without alias ---'
Foo 'bar'
function global:Log-DebugSuperseded {}
Set-Alias -Name Log-Debug -Value Log-DebugSuperseded -Scope global
Write-Host '--- with alias ---'
Foo 'bar'
PS C:\> ./test.ps1
--- without alias ---
FOO: something
DEBUG: bar
--- with alias ---
FOO: something
PS C:\> _
```

How can I redefine a function that was exported by a powershell module

Solution

Problem