PowerShell cmdlet parameter value tab completion

Question

How do you implement the parameter tab completion for PowerShell functions or cmdlets like Get-Service and Get-Process in PowerShell 3.0?

I realise ValidateSet works for a known list, but I want to generate the list on demand.

Adam Driscoll hints that it is possible for cmdlets but unfortunately hasn't elaborated.

Trevor Sullivan shows a technique for functions, but as I understand it, his code only generates the list at the time the function is defined.

Answer 1

Check the TabExpansionPlusPlus module on github, written by a former PowerShell team magician.

https://github.com/lzybkr/TabExpansionPlusPlus#readme

Answer 2

I puzzled over this for a while, because I wanted to do the same thing. I put together something that I'm really happy with.

You can add ValidateSet attributes from a DynamicParam. Here's an example of where I've generated my ValidateSet on-the-fly from an xml file. See the "ValidateSetAttribute" in the following code:

function Foo() {
    [CmdletBinding()]
    Param ()
    DynamicParam {
        #
        # The "modules" param
        #
        $modulesAttributeCollection = new-object -Type System.Collections.ObjectModel.Collection[System.Attribute]

        # [parameter(mandatory=...,
        #     ...
        # )]
        $modulesParameterAttribute = new-object System.Management.Automation.ParameterAttribute
        $modulesParameterAttribute.Mandatory = $true
        $modulesParameterAttribute.HelpMessage = "Enter one or more module names, separated by commas"
        $modulesAttributeCollection.Add($modulesParameterAttribute)    

        # [ValidateSet[(...)]
        $moduleNames = @()
        foreach($moduleXmlInfo in Select-Xml -Path "C:\Path\to\my\xmlFile.xml" -XPath "//enlistment[@name=""wp""]/module") {
            $moduleNames += $moduleXmlInfo.Node.Attributes["name"].Value
        }
        $modulesValidateSetAttribute = New-Object -type System.Management.Automation.ValidateSetAttribute($moduleNames)
        $modulesAttributeCollection.Add($modulesValidateSetAttribute)

        # Remaining boilerplate
        $modulesRuntimeDefinedParam = new-object -Type System.Management.Automation.RuntimeDefinedParameter("modules", [String[]], $modulesAttributeCollection)

        $paramDictionary = new-object -Type System.Management.Automation.RuntimeDefinedParameterDictionary
        $paramDictionary.Add("modules", $modulesRuntimeDefinedParam)
        return $paramDictionary
    }
    process {
        # Do stuff
    }
}

With that, I can type

Foo -modules M<press tab>

and it will tab-complete "MarcusModule" if that module was in the XML file. Furthermore, I can edit the XML file and the tab-completion behavior will immediately change; you don't have to re-import the function.

Answer 3

Classically, I used regex.

for example,

function TabExpansion {

    param($line, $lastWord) 

    if ( $line -match '(-(\w+))\s+([^-]*$)' )
    {
    ### Resolve Command name & parameter name
        $_param = $matches[2] + '*'
        $_opt = $Matches[3].Split(" ,")[-1] + '*'
        $_base = $Matches[3].Substring(0,$Matches[3].Length-$Matches[3].Split(" ,")[-1].length)

        $_cmdlet = [regex]::Split($line, '[|;=]')[-1]

        if ($_cmdlet -match '\{([^\{\}]*)$')
        {
            $_cmdlet = $matches[1]
        }

        if ($_cmdlet -match '\(([^()]*)$')
        {
            $_cmdlet = $matches[1]
        }

        $_cmdlet = $_cmdlet.Trim().Split()[0]

        $_cmdlet = @(Get-Command -type 'Cmdlet,Alias,Function,Filter,ExternalScript' $_cmdlet)[0]

        while ($_cmdlet.CommandType -eq 'alias')
        {
            $_cmdlet = @(Get-Command -type 'Cmdlet,Alias,Function,Filter,ExternalScript' $_cmdlet.Definition)[0]
        }

    ### Currently target is Get-Alias & "-Name" parameter

        if ( "Get-Alias" -eq $_cmdlet.Name -and "Name" -like $_param )
        {
           Get-Alias -Name $_opt | % { $_.Name } | sort | % { $_base + ($_ -replace '\s','` ') }
           break;
        }
    }
}

Reference http://gallery.technet.microsoft.com/scriptcenter/005d8bc7-5163-4a25-ad0d-25cffa90faf5

---

Posh-git renames TabExpansion to TabExpansionBackup in GitTabExpansion.ps1.
And posh-git's redifined TabExpansion calls original TabExpansion(TabExpansionBackup) when completions don't match with git commands.
So all you have to do is redefine TabExpansionBackup.

(cat .\GitTabExpansion.ps1 | select -last 18)
============================== GitTabExpansion.ps1 ==============================

if (Test-Path Function:\TabExpansion) {
    Rename-Item Function:\TabExpansion TabExpansionBackup
}

function TabExpansion($line, $lastWord) {
    $lastBlock = [regex]::Split($line, '[|;]')[-1].TrimStart()

    switch -regex ($lastBlock) {
        # Execute git tab completion for all git-related commands
        "^$(Get-AliasPattern git) (.*)" { GitTabExpansion $lastBlock }
        "^$(Get-AliasPattern tgit) (.*)" { GitTabExpansion $lastBlock }

        # Fall back on existing tab expansion
        default { if (Test-Path Function:\TabExpansionBackup) { TabExpansionBackup $line $lastWord } }
    }
}

===============================================================================

Redefine TabExpansionBackup(original TabExpansion)

function TabExpansionBackup {
    ...

    ### Resolve Command name & parameter name

    ...

    ### Currently target is Get-Alias & "-Name" parameter

    ...
}