Restoring a PowerShell alias when a module is unloaded

Question

How do I restore a PowerShell alias when my module has been unloaded.

The code I have so far does not work although executing the Set-Alias command by itself does. It stores the definition in a local variable, which is available when the OnRemove event is fired.

$orig_cd = (Get-Alias -Name 'cd').Definition
$MyInvocation.MyCommand.ScriptBlock.Module.OnRemove = {
    Set-Alias -Name 'cd' -Value $orig_cd -Force -Option AllScope -Scope Global
}

I should also mention that I am overriding the existing cd command alias like so

Set-Alias -Name cd -Value cdX -Force -Option AllScope -Scope Global

Here is the source code to the module https://github.com/vincpa/z/blob/master/z.psm1

Update

Adding a Write-Host command within the OnRemove handler shows that the value of $orig_cd is indeed Set-Location.

Answer 1

I tried this, and it works:

$orig_cd = (Get-Alias -Name 'cd').Definition
$MyInvocation.MyCommand.ScriptBlock.Module.OnRemove = {
    set-item alias:cd -value $orig_cd
}

Set-item alias:cd -Value 'cdX'

Also, a suggestion - you are writing a module which people will use in their terminals. I don't expect a use case where some one would want to remove your module. These steps maybe overkill for the module you are writing.

Answer 2

Although about_scopes is a bit confusing, the Alias Provider looks like it has the key.

The alias is already scoped with AllScope which means children scope have copies/access. All you have to do is change the value.

Look at the switch -Options in Set-Alias - http://technet.microsoft.com/en-us/library/hh849938.aspx

-- AllScope: The alias is copied to any new scopes that are created.

#Override the existing CD command with the wrapper in order to log 'cd' commands.
Set-Item alias:cd -Value 'cdx'
Set-Alias -Name pushd -Value pushdX -Force -Option AllScope -Scope Global

$orig_cd = (Get-Alias -Name 'cd')
$MyInvocation.MyCommand.ScriptBlock.Module.OnRemove = {
    set-item alias:cd -value 'set-content'
}

Export-ModuleMember -Function z, cdX, pushdX -alias ''