How to tell if a PowerShell variable has not been Declared

November 10, 2015 powershell

In most situations in PowerShell, I am really only interested if a variable has a value or not (e.g. not null). Checking for this is easy:

if ($myvariable -eq $null) {
    Write-Host -Message '$MyVariable is null'
} else {
    Write-Host -Message '$MyVariable has a non-null and non-blank value'
}

But what if I want to know if a variable is not declared at all? The method of doing that is not so obvious and being PowerShell there are many ways of doing it. By far the clearest I think is to use the Test-Path cmdlet using the Variable provider:

if (Test-Path -Path Variable:\MyVariable) {
    Write-Host -Message '$MyVariable is declared'
} else {
    Write-Host -Message '$MyVariable is not declared'
}

If there is a cleaner or officially recommended way of doing this I’d be most keen to hear about it.