[SOLVED] PowerShell array param with optional values

PowerShell array param with optional values

I'd like my PS script to have an interface like this:

tool.ps1 -Update item1, item2, item3 # Update individual items
tool.ps1 -Update # Update all items

I've tried all known attribute combinations (AllowEmptyCollection etc), and still can't get the second example to work: PS asks to provide a param value.

Any ideas?

Solution

You can achieve the described behavior by separating the -Update parameter from the optional arguments:

[CmdletBinding(DefaultParameterSetName = 'Default')]
param(
  [Parameter(Mandatory = $true, ParameterSetName = 'Update')]
  [switch]$Update,

  [Parameter(ValueFromRemainingArguments = $true, DontShow = $true)]
  [string[]]$Values
)

if ($PSCmdlet.ParameterSetName -eq 'Update') {
  # update requested
  if ($Values.Count) {
    Write-Host "Updating items: $($Values -join ', ')"
  }
  else {
    Write-Host "Updating all items!"
  }
}
else {
  Write-Host "No update requested"
}

Now, if present, the additional arguments will be bound to the hidden -Values parameter instead (thanks to the ValuesFromRemainingArguments flag), which should give you the behavior you want:

PS ~> .\tool.ps1 -Update
Updating all items!
PS ~> .\tool.ps1 -Update item1, item2, item3
Updating items: item1, item2, item3
PS ~> .\tool.ps1
No update requested