DSC Script resource does not read environement variable - powershell

Question

I have a DSC configuration which install nodejs, adds npm to environment Path variable and then installs a npm module.
xPackage InstallNodeJs {
Name = 'Node.js'
Path = "$env:SystemDrive\temp\node-v4.4.7-x64.msi"
ProductId = '8434AEA1-1294-47E3-9137-848F546CD824'
Arguments = "/quiet"
}
Environment AddEnvironmentPaths
{
Name = "Path"
Ensure = "Present"
Path = $true
Value = "$env:SystemDrive\ProgramData\npm"
}
Script UpgradeNpm {
SetScript = {
& npm install --global --production npm-windows-upgrade
& npm-windows-upgrade --npm-version 3.10.6
}
TestScript = {
$npmVersion = & npm -v
return $npmVersion -eq "3.10.6"
}
GetScript = {
return {#{Result = "UpgradeNpm"}}
}
}
Installing nodejs and adding npm to Path variable seems to be successful. Both nodejs and npm location are added to Path and I can use them both in powershell and cmd.
However, Script resource returns that 'npm' is not recognized as internal or external command ...
the same is for node which is used inside npm-windows-upgrade script file.
Do you know why Script resource cannot read newly added Path entires?

Answer 1

The Environment DSC resource implementation makes the change by updating the values stored in the registry (with the exception of variables targeting Process). Changes made to environment variables stored in the registry are not reflected in the current session (read once, on session start).
You can affect values stored in the current session by:
Using System.Environment.SetEnvironmentVariable ([System.Environment]::SetEnvironmentVariable)
Modifying $env:<VariableName>
Of those, only the first allows you to write a persistent change. The latter can be considered a volatile change.
It's an odd limitation of the resource, I've looked at this before and felt it a little lacking.

Answer 2

There's no dependency information in there, so you can't count on the Environment resource running before the Script resource. There's not enough information in your post to tell if that's the case for sure, but you should consider controlling it anyway:
xPackage InstallNodeJs {
Name = 'Node.js'
Path = "$env:SystemDrive\temp\node-v4.4.7-x64.msi"
ProductId = '8434AEA1-1294-47E3-9137-848F546CD824'
Arguments = "/quiet"
}
Environment AddEnvironmentPaths
{
Name = "Path"
Ensure = "Present"
Path = $true
Value = "$env:SystemDrive\ProgramData\npm"
DependsOn = '[xPackage]InstallNodeJs'
}
Script UpgradeNpm {
SetScript = {
& npm install --global --production npm-windows-upgrade
& npm-windows-upgrade --npm-version 3.10.6
}
TestScript = {
$npmVersion = & npm -v
return $npmVersion -eq "3.10.6"
}
GetScript = {
return {#{Result = "UpgradeNpm"}}
}
DependsOn = '[Environment]AddEnvironmentPaths'
}

Answer 3

Can you share which version of DSC you are using? You can get this by doing a $PSVersionTable on the PowerShell console. I am able to add to the PATH variable and use it in a script resource.
configuration NPMTest
{
Environment AddEnvironmentPaths
{
Name = 'Path'
Ensure = 'Present'
Path = $true
Value = "$env:SystemDrive\ProgramData\npm"
}
Script p
{
GetScript = {#{}}
TestScript = {return $false}
SetScript = {$a = & a.ps1 ; Write-Verbose $a -Verbose}
}
}
The script a.ps1 was executed fine even though I am not specifying the full path to the script.