Powershell Dynamic conditional parameters

Question

I am writing a script and I want to specify the parameters to do the following:

Parameter 1 is action (either check or kill) Parameter 2 is computername.

If neither parameter is specified I want my Usage information displayed Parameter 2 should ONLY be prompted if Parameter 1 is specified.

Param(
    [Parameter(Mandatory=$True,
    HelpMessage="Please Enter an Action. (C)heck, (K)ill, or (?) for usage")]
    [String]$Action,

    [Parameter(Mandatory = $false,
    Helpmessage="Please Enter One or More Hostnames. seperate multiple hostnames with an , EXAMPLE: Hostname1,Hostname2")]
    [ValidateNotNullorEmpty()]
    [String]$Computers 
    )

postanote · Accepted Answer · 2019-03-26 02:36:22Z

Why force users to guess at what input is expected? Just tell them up front what is expected.

For example:

Function Test-DescriptiveUserPrompt
{
    [CmdletBinding()]

    Param
    (
        [ValidateSet('C','K')]
        [string]$Action = $(
        Write-Host '
        Please Enter an Action. (C)heck, (K)ill:   ' -ForegroundColor Yellow -NoNewLine
        Read-Host 
            ),

        [ValidateNotNullorEmpty()]
        [string[]]$Computers = $(
        Write-Host '
        Please Enter One or More Hostnames. separate multiple hostnames with a comma. 
        EXAMPLE: Hostname1,Hostname2:   ' -ForegroundColor Yellow -NoNewLine
        Read-Host 
        )
    )

    Process
    {
            "You choose $Action"
            "You enter the list $Computers"
    }
}


# Results

Test-DescriptiveUserPrompt

        Please Enter an Action. (C)heck, (K)ill:   c

        Please Enter One or More Hostnames. seperate multiple hostnames with a comma. 
        EXAMPLE: Hostname1,Hostname2:   localhost,remotehost
c
localhost,remotehost


Test-DescriptiveUserPrompt -Action C -Computers localhost,remotehost

C
localhost
remotehost

HAL9256 · Accepted Answer · 2019-03-25 20:27:34Z

The quick and dirty and simpler way of doing things is to use Parameter Sets. In this case, it will default to displaying the Usage information if things aren't correct.

Function Test {
    [CmdletBinding()]
Param(
    [Parameter(Mandatory=$true, ParameterSetName = "Action",
    HelpMessage="Please Enter an Action. (C)heck, (K)ill, or (?) for usage")]
    [ValidateSet("C","K","?")]
    [Parameter(Mandatory=$false, ParameterSetName = "Usage")]
    [String]$Action,

    [Parameter(Mandatory = $true, ParameterSetName = "Action",
    Helpmessage="Please Enter One or More Hostnames. seperate multiple hostnames with an , EXAMPLE: Hostname1,Hostname2")]
    [ValidateNotNullorEmpty()]
    [String]$Computers 
    )
Process
{
    if($PSCmdlet.ParameterSetName -eq "Usage" -or $Action -eq "?")
    {
        Write-Host "Usage"
    }
    else
    {
        Write-Host "Action"
        Write-Host $Action
        Write-Host $Computers
    }
}
}

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