Dynamically creating aliases in PowerShell

Question

I'd like to create some aliases dynamically but I can't get my code to work. Here's the code:

# Drives
$drives = ("a","b","c","d","e")
foreach ($drive in $drives) {
    New-Item -Path alias:\ -Name $drive -Value GoToDrive($drive) #.GetNewClosure()
}

function GoToDrive($drive) {
    $formatted = "$($drive):\"
    if (Test-Path $formatted) {
        Set-Location $formatted
    } else {
        Write-Host "`"$formatted`" does not exist."
    }
}

When I type "a", or "b", or any of the letters in $drives, it should change my working directory to that drive's letter (e.g.: A:).

The error I'm getting now is this:

New-Item : A positional parameter cannot be found that accepts argument 'a'.
At C:\Users\prubi\OneDrive\Documentos\WindowsPowerShell\Microsoft.PowerShell_profile.ps1:17 char:5
+     New-Item -Path alias:\ -Name $drive -Value GoToDrive($drive) #.Ge ...
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [New-Item], ParameterBindingException
    + FullyQualifiedErrorId : PositionalParameterNotFound,Microsoft.PowerShell.Commands.NewItemCommand

New-Item : A positional parameter cannot be found that accepts argument 'b'.
At C:\Users\prubi\OneDrive\Documentos\WindowsPowerShell\Microsoft.PowerShell_profile.ps1:17 char:5
+     New-Item -Path alias:\ -Name $drive -Value GoToDrive($drive) #.Ge ...
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [New-Item], ParameterBindingException
    + FullyQualifiedErrorId : PositionalParameterNotFound,Microsoft.PowerShell.Commands.NewItemCommand

New-Item : A positional parameter cannot be found that accepts argument 'c'.
At C:\Users\prubi\OneDrive\Documentos\WindowsPowerShell\Microsoft.PowerShell_profile.ps1:17 char:5
+     New-Item -Path alias:\ -Name $drive -Value GoToDrive($drive) #.Ge ...
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [New-Item], ParameterBindingException
    + FullyQualifiedErrorId : PositionalParameterNotFound,Microsoft.PowerShell.Commands.NewItemCommand

New-Item : A positional parameter cannot be found that accepts argument 'd'.
At C:\Users\prubi\OneDrive\Documentos\WindowsPowerShell\Microsoft.PowerShell_profile.ps1:17 char:5
+     New-Item -Path alias:\ -Name $drive -Value GoToDrive($drive) #.Ge ...
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [New-Item], ParameterBindingException
    + FullyQualifiedErrorId : PositionalParameterNotFound,Microsoft.PowerShell.Commands.NewItemCommand

New-Item : A positional parameter cannot be found that accepts argument 'e'.
At C:\Users\prubi\OneDrive\Documentos\WindowsPowerShell\Microsoft.PowerShell_profile.ps1:17 char:5
+     New-Item -Path alias:\ -Name $drive -Value GoToDrive($drive) #.Ge ...
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [New-Item], ParameterBindingException
    + FullyQualifiedErrorId : PositionalParameterNotFound,Microsoft.PowerShell.Commands.NewItemCommand

Can anybody help me get this to work, please?

Answer 1

The immediate problem is that PowerShell is interpreting -Value GoToDrive($drive) as specifying the switch -Value 'GoToDrive' and also a positional parameter $drive. (This is bizarre and unintuitive, yes.) Enclosing GoToDrive($drive) in parentheses would try to call the as-yet-nonexistent GoToDrive function and then use the results as the argument for -Value, which is not what you're after even if GoToDrive had been defined previously. Another problem is that aliases cannot supply arguments to the command they call; they are only alternate names for commands.

You need to dynamically execute commands that create the shortcut functions:

# This is the exact same GoToDrive function you've been using
function GoToDrive($drive) {
    $formatted = "$($drive):\"
    if (Test-Path $formatted) {
        Set-Location $formatted
    } else {
        Write-Host "`"$formatted`" does not exist."
    }
}

# This does the magic
'a', 'b', 'c', 'd', 'e' | % {iex "function $_ {GoToDrive '$_'}"}

Invoke-Expression, or iex for short, runs its determined-at-runtime argument as if you had typed it on the command line yourself. So that last line executes function a {GoToDrive 'a'}, then function b {GoToDrive 'b'}, and so on.