Use PowerShell session variables as default values for parameters

Question

Can values that are stored in a PowerShell session variable be used to populate a parameter's default value?

In this example, the session variables are populate the first time the script is run, but aren't used in subsequent executions:

function Get-Authetication
{

    [cmdletbinding()]
    param(
        [parameter(Mandatory=$true)]
        [string]$Server = { if ($PSCmdlet.SessionState.PSVariable.Get('Server').Value) { $PSCmdlet.SessionState.PSVariable.Get('Server').Value } },

        [parameter(Mandatory=$true)]
        [pscredential]$Credential = (Get-Credential)

    )

    # store
    $PSCmdlet.SessionState.PSVariable.Set('Server',$Server)
    $PSCmdlet.SessionState.PSVariable.Set('Credential',$Credential)

    # return for testing
    [PsCustomObject]@{
        Server=$PSCmdlet.SessionState.PSVariable.Get('Server').Value;
        Username=($PSCmdlet.SessionState.PSVariable.Get('Credential').Value).Username
    }
}

Get-Authetication

briantist · Accepted Answer · 2016-10-05 13:59:36Z

2

This should be done by the caller using $PSDefaultParameterValues.

Or, do it in the function instead of using a default value:

function Get-Authetication
{

    [cmdletbinding()]
    param(
        [parameter()]
        [string]$Server,

        [parameter()]
        [pscredential]$Credential = (Get-Credential)

    )
    if (!$PSCmdlet.SessionState.PSVariable.Get('Server').Value -and !$Server) {
        $Server = Read-Host 'Enter server'
        # Alternatively
        # throw [System.ArgumentException]'You must supply a Server value'
    }
    if ($Server) {
        $PSCmdlet.SessionState.PSVariable.Set('Server',$Server)
    }
    $myServer = $PSCmdlet.SessionState.PSVariable.Get('Server').Value

    # return for testing
    [PsCustomObject]@{
        Server=$myServer;
    }
}

(abbreviated example)

edited Oct 5, 2016 at 13:59

answered Oct 5, 2016 at 13:25

briantist

48.3k6 gold badges94 silver badges139 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

craig Over a year ago

this prompts me to supply a value for both variables initially (as expected) and subsequently (hoping to avoid). What am I not understanding?

briantist Over a year ago

@craig I meant to take away the Mandatory=$true part. See updated code.

craig Over a year ago

As I mentioned in the question, I want it to prompt the first time (if a value) isn't supplied, but not prompt subsequent times. I tried setting the $PSDefaultParameterValues in code, but that didn't have the desired effect either.

briantist Over a year ago

@craig my example should work for $Server, I didn't do it for $Credential in my answer, but if $Server works as expected you can apply the same logic.

craig Over a year ago

$Server isn't working as expected. I'll ignore $Credential to simplify matters.

|

adamt8 · Accepted Answer · 2022-12-03 21:59:21Z

This looks like the question you're asking is:

I am always going to run this script/function as the same person. But after I run it the first time, I want it to remember that one credential.

If that is in fact your question, then it's not clear that this approach won't do that. You're trying to persist a value to use later, and it happens to be a credential. There are several ways to accomplish this, and this is a great article that includes all your options:

https://purple.telstra.com.au/blog/using-saved-credentials-securely-in-powershell-scripts#:~:text=From%20that%20perspective%20your%20process%20to%20have%20a,and%20store%20that%20in%20a%20file%20More%20items

Basically, you're going to need to save an encrypted value in a file the first time, then access that file in subsequent runs.

HOWEVER, if you are intending for multiple people to be able to do this, or YOU want to run this on more than one server, you'll have many additional things to contend with, like using a network share to store the file, or keeping track of different users.

Good luck researching.

Collectives™ on Stack Overflow

Use PowerShell session variables as default values for parameters

2 Answers 2

7 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

7 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related