Auto Complete User Input PowerShell 2.0

PowerShell tab completion can be extended to custom parameters and parameter values (in v3). However, this is a property of advanced functions. You can use the ValidateSetAttribute to do that.

Check the Technet help topic on advanced functions: http://technet.microsoft.com/en-us/library/hh847806.aspx

You can replace the tabexpansion (v2) and tabexpansion2 (v3) function in PowerShell to auto complete parameter values outside of advanced functions. You can get a basic definition of this in PowerShell v3 by running

 Get-Content function:TabExpansion2

Here is an example of showing custom tab expansion function.

http://www.powershellmagazine.com/2012/11/29/using-custom-argument-completers-in-powershell-3-0/

But, if you want to the user to be able to auto complete values for a Read-Host kind of input, you need to write a proxy for Read-Host to achieve that.

You can, optionally, look at PowerTab module at http://powertab.codeplex.com/

For folks who are looking for a way to do this and are fortunate enough to be using PS v3 (and my apologies for all those required to stay with V2):

The easiest way to achieve this is using the "ValidateSet" option in your input parameters.

function Show-Hello {param (    [ValidateSet("World", "Galaxy", "Universe")]    [String]$noun)$greetingString = "Hello, " + $noun + "!"Write-Host "`t=>`t" $greetingString "`t<=" }

ValidateSet throws an error if a user attempts to use any other input:

Show-Hello "Solar System"   Show-Hello : Cannot validate argument on parameter 'noun'. The argument `   "Solar System" does not belong to the set "World,Galaxy,Universe" specified `   by the ValidateSet attribute. Supply an argument that is in the set and `   then try the command again.

It also adds tab-completion to your function for that parameter. And if it is the FIRST parameter for your function, you don't even have to type in "-noun" for the tab-complete to make suggestions for its value.