Convert list of parameters to a string that can be invoked

Question

My PowerShell scripting skills are pretty poor, but I've managed to hobble together got this script:

function Create-Process() {
    param([string] $fileName, [string] $arguments)

    $pinfo = New-Object System.Diagnostics.ProcessStartInfo
    $pinfo.RedirectStandardError = $true
    $pinfo.RedirectStandardOutput = $true
    $pinfo.UseShellExecute = $false
    $pinfo.FileName = $fileName
    $pinfo.Arguments = $arguments

    $p = New-Object System.Diagnostics.Process
    $p.StartInfo = $pinfo

    return $p
}

function Pack {
    param(
        [string] $nuspec,

        [string] $OutputDirectory,

        [string] $BasePath,

        [ValidateSet("normal", "quiet", "detailed", IgnoreCase = $true)]
        [string] $Verbosity,

        [switch] $Symbols
    )
    # format parameters for NuGet.exe
    If ($BasePath) {
        $basePathParam = "-BasePath ""$BasePath"""
    } 
    If ($OutputDirectory) {
        $outputDirParam = "-OutputDirectory ""$BasePath"""
    }
    If ($Verbosity) {
        $verbosityParam = "-Verbosity $Verbosity"
    }
    If ($Symbols) {
        $symbolsParam = "-Symbols"
    }

    Write-Log "Creating package..." -ForegroundColor Green
    $packageTask = Create-Process .\NuGet.exe ("pack $nuspec $basePathParam $outputDirParam $verbosityParam $symbolsParam")
    $packageTask.Start() | Out-Null
    $packageTask.WaitForExit()

    $output = ($packageTask.StandardOutput.ReadToEnd() -Split '[\r\n]') |? {$_}
    $error = (($packageTask.StandardError.ReadToEnd() -Split '[\r\n]') |? {$_}) 
    Write-Log $output
    Write-Log $error Error

    $global:ExitCode = $packageTask.ExitCode
}

So that I can call it elsewhere like this:

Pack .\Package.nuspec -BasePath $TargetDir -OutputDirectory $TargetDir -Verbosity Detailed

How can I clean up the process for formatting the arguments string? It seems pretty ugly at the moment, and if I have to add any more parameters, it's just going to get uglier. Is there an easy way to convert a list of parameters to a string that's suitable for invoking another function?

^{Note: Simply passing in the parameters as a single string (e.g. Pack .\Package.nuspec "-Verbosity Detailed") doesn't really solve my issue, it just moves it back one step. I'd like to create the string within Pack itself.}

Answer 1

Here's what I've been able to come up with so far. It could probably be improved further.

function Pack {
    param(
        [Parameter(Mandatory=$true)]
        [string] $nuspec,

        [string] $OutputDirectory,

        [string] $BasePath,

        [ValidateSet("normal", "quiet", "detailed", IgnoreCase = $true)]
        [string] $Verbosity,

        [switch] $Symbols 
    )

    # these parameters are passed as name - value pairs
    $named = @('OutputDirectory', 'BasePath', 'Verbosity') 

    # these parameters are passed as switches
    $keyed = @('Symbols')

    $p = $PSBoundParameters
    Write-Log "Creating package..." -ForegroundColor Green
    $output = Invoke-Command {
            .\NuGet.exe "pack" $nuspec ($p.Keys | foreach { 
                If ($named -contains $_) { "-$_", $p[$_] } 
                ElseIf ($keyed -contains $_) { "-$_" } 
            })
        } -ErrorVariable error

    Write-Log $output
    Write-Log $error Error
    Write-Log " "

    $global:ExitCode = $LastExitCode
}