Wrapper function in PowerShell: Pass remaining parameters

Question

I’m trying to write a wrapper function in PowerShell that basically evaluates the first parameter and based on that runs a program on the computer. All the remaining paramet

Answer 1

• Your solution works as-is for external programs (such as your C:\Program Files\some\program.exe example): you can always pass an array of values (which is what $args is) to an external program, and its elements will be passed as individual arguments (stringified, if necessary).

• You can make your solution work with any command if you change $args to @args^[1], to take advantage of a PowerShell parameter-passing technique called splatting:

function test ( [string] $option )
{
    if ( $option -eq 'A' )
    {
        Write-Host $args
    }
    elseif ( $option -eq 'B' )
    {
        # Use @args to also support passing *named* arguments
        # through to *PowerShell* commands.
        & $someCommand @args
    }
}

Caveats:

• The automatic $args variable, which collects all arguments for which no parameter was declared, is only available in simple (non-advanced) functions and scripts; advanced functions and scripts - those that use the [CmdletBinding()] attribute and/or [Parameter()] attributes - require that all potential parameters be declared.

• PowerShell has built-in magic that makes the automatic array variable $args also support passing named parameters through via splatting, which no custom array or collection supports.

  • By contrast, custom arrays and collections only support splatting positional (unnamed) arguments, which, however, covers all calls to external programs.
  • When calling PowerShell commands, this limitation is problematic, however: For instance, if you wanted to pass the named argument -Path C:\ through to the Set-Location cmdlet via splatting, using a custom collection parameter declared via ValueFromRemaining Arguments, as shown in OldFart's answer (Set-Location @Remaining), would not work; to support passing through named arguments (other than via @args, if available), you must use hashtable-based splatting.

Therefore, if your function is an advanced one and you need to support passing named arguments through to other PowerShell commands, a different approach is required: this answer shows two alternatives.

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^{[1] With external programs, there is a corner case where @args behaves differently from $args, namely if the $args array contains --%, the stop-parsing symbol: @args recognizes it, $args treats it as a literal.}