DSC Script Resource

Applies To: Windows PowerShell 4.0, Windows PowerShell 5.x

The Script resource in Windows PowerShell Desired State Configuration (DSC) provides a mechanism to run Windows PowerShell script blocks on target nodes. The Script resource uses GetScript, SetScript, and TestScript properties that contain script blocks you define to perform the corresponding DSC state operations.

Syntax

Script [string] #ResourceName
{
    GetScript = [string]
    SetScript = [string]
    TestScript = [string]
    [ Credential = [PSCredential] ]
    [ DependsOn = [string[]] ]
}

Note

The GetScript, TestScript, and SetScript blocks are stored as strings.

Properties

Property Description
GetScript A script block that returns the current state of the Node.
SetScript A script block that DSC uses to enforce compliance when the Node is not in the desired state.
TestScript A script block that determines if the Node is in the desired state.
Credential Indicates the credentials to use for running this script, if credentials are required.
DependsOn Indicates that the configuration of another resource must run before this resource is configured. For example, if the ID of the resource configuration script block that you want to run first is ResourceName and its type is ResourceType, the syntax for using this property is DependsOn = "[ResourceType]ResourceName".

GetScript

DSC does not use the output from GetScript. The Get-DscConfiguration cmdlet executes the GetScript to retrieve a node's current state. A return value is not required from GetScript. If you specify a return value, it must be a hashtable containing a Result key whose value is a String.

TestScript

The TestScript is executed by DSC to determine if the SetScript should be run. If the TestScript returns $false, DSC executes the SetScript to bring the node back to the desired state. It must return a boolean value. A result of $true indicates that the node is compliant and SetScript should not executed.

The Test-DscConfiguration cmdlet, executes the TestScript to retrieve the nodes compliance with the Script resources. However, in this case, the SetScript does not run, no matter what the TestScript block returns.

Note

All output from your TestScript is part of its return value. PowerShell interprets unsuppressed output as non-zero, which means that your TestScript will return $true regardless of your node's state. This results in unpredictable results, false positives, and causes difficulty during troubleshooting.

SetScript

The SetScript modifies the node to enfore the desired state. It is called by DSC if the TestScript script block returns $false. The SetScript should have no return value.

Examples

Example 1: Write sample text using a Script resource

This example tests for the existence of C:\TempFolder\TestFile.txt on each node. If it does not exist, it creates it using the SetScript. The GetScript returns the contents of the file, and its return value is not used.

Configuration ScriptTest
{
    Import-DscResource –ModuleName 'PSDesiredStateConfiguration'

    Node localhost
    {
        Script ScriptExample
        {
            SetScript = {
                $sw = New-Object System.IO.StreamWriter("C:\TempFolder\TestFile.txt")
                $sw.WriteLine("Some sample string")
                $sw.Close()
            }
            TestScript = { Test-Path "C:\TempFolder\TestFile.txt" }
            GetScript = { @{ Result = (Get-Content C:\TempFolder\TestFile.txt) } }
        }
    }
}

Example 2: Compare version information using a Script resource

This example retrieves the compliant version information from a text file on the authoring computer and stores it in the $version variable. When generating the node's MOF file, DSC replaces the $using:version variables in each script block with the value of the $version variable. During execution, the compliant version is stored in a text file on each Node and compared and updated on subsequent executions.

$version = Get-Content 'version.txt'

Configuration ScriptTest
{
    Import-DscResource –ModuleName 'PSDesiredStateConfiguration'

    Node localhost
    {
        Script UpdateConfigurationVersion
        {
            GetScript = {
                $currentVersion = Get-Content (Join-Path -Path $env:SYSTEMDRIVE -ChildPath 'version.txt')
                return @{ 'Result' = "$currentVersion" }
            }
            TestScript = {
                # Create and invoke a scriptblock using the $GetScript automatic variable, which contains a string representation of the GetScript.
                $state = [scriptblock]::Create($GetScript).Invoke()

                if( $state['Result'] -eq $using:version )
                {
                    Write-Verbose -Message ('{0} -eq {1}' -f $state['Result'],$using:version)
                    return $true
                }
                Write-Verbose -Message ('Version up-to-date: {0}' -f $using:version)
                return $false
            }
            SetScript = {
                $using:version | Set-Content -Path (Join-Path -Path $env:SYSTEMDRIVE -ChildPath 'version.txt')
            }
        }
    }
}