For a cmdlet parameter provide a list of common options, but still let them enter anything they want

Question

Using ValidateSet for a parameter on a cmdlet, will give a list of possible parameters. But will not let the user of that cmdlet enter other values. Example the below

[ValidateSet('A','B')

Would let the users enter A or B, but nothing else.

I would like to provide a list that give the most common option, but also allow them to enter anything else.

For example, a parameter that takes a path to a build. Build A and B are shipped and stable builds. But there are many other builds. So, I want to provide a list of A and B build so they do not need to know the path to them but then also let them enter any other path to any other build.

Is this possible?

Answer 1

Use an ArgumentCompleter attribute, which specifies what values should be offered via tab-completion, while not limiting what values may be passed (by entering them manually / pasting them); e.g.:

function Get-Foo {
  param(
    # Suggest 'A' and 'B' as tab-completions, but allow any
    # other value to be passed as well.
    [ArgumentCompleter({ 
      param($cmd, $param, $wordToComplete) 
      'A', 'B' -like "$wordToComplete*" 
    })]
    [string] $MyParam
  )
 
  "[$MyParam]" # sample output
}

Typing Get-Foo <tab> then offers A and B as completions, while still allowing any other value to be passed too.

With single-character completion values such as A and B it isn't obvious, but the solution above allows you type a prefix of the completion values to narrow down the completions.