PowerShell cmdlet parameter value tab completion - powershell

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

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 2

Check the TabExpansionPlusPlus module on github, written by a former PowerShell team magician.
https://github.com/lzybkr/TabExpansionPlusPlus#readme

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
...
}