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I run this script:

if (Copy-Item .\test.ps1 $env:SystemRoot\System32)
{
    Write-Host "Done."
    exit 0
}
else
{
    Write-Host "Not done."
    Write-Host "You must be root."
    exit 1
}

When I run this script as a normal user I got the message in else statement, because I am not root. And this is okay.

But I run this script as root I also got the message in else statement! But file copy operation is succeded. I can't get the message in if statement. Why?

I also check the error code and its always False.

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  • 1
    As an alternative to checking for success or failure, you can check for administrator before attempting to run the other code. I use if (!([Security.Principal.WindowsPrincipal][Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole([Security.Principal.WindowsBuiltInRole]::Administrator) { Write-Error 'Please run as administrator'; exit }
    – Richard Robertson
    Mar 12, 2020 at 19:16
  • @RichardRobertson another alternative to this would be to add #Requires -RunAsAdministrator at the start of your script, then the whole script would only run if you are admin
    – SimonS
    Mar 13, 2020 at 7:59

1 Answer 1

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82

An if statement does not evaluate whether the command inside its condition ran successfully. It will only check the value (in your case the return of your command) and cast it to a bool.

Copy-Item does not return anything by default, and that's why your if statement is always false, because [bool]$null is $false.

You have three options here:

Add the -PassThru parameter to get some form of return:

if (Copy-Item .\test.ps1 $env:SystemRoot\System32 -PassThru)

Use the $? variable to see if your previous command was successful:

Copy-Item .\test.ps1 $env:SystemRoot\System32
if ($?) {
    Write-Host "Done."
    exit 0
}
else {
    Write-Host "Not done."
    Write-Host "You must be root."
    exit 1
}

However, the most reliable way would be to wrap it in Try {} Catch {} and add -ErrorAction Stop

Try {
    Copy-Item .\test.ps1 $env:SystemRoot\System32 -ErrorAction Stop
    Write-Host "Done."
    exit 0
}
Catch {
    Write-Host "Not done."
    Write-Host "You must be root."
    exit 1
}
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