In PowerShell, how do I test whether or not a specific variable exists in global scope?

Question

I\'m using PowerShell scripts for some UI automation of a WPF application. Normally, the scripts are run as a group, based on the value of a global variable. It\'s a littl

Answer 1

Personal preference is to use Ignore over SilentlyContinue here because it's not an error at all. Since we're expecting it to potentially be $false let's prevent it (with Ignore) from being put (albeit silently) in the $Error stack.

You can use:

if (Get-Variable 'foo' -Scope 'Global' -ErrorAction 'Ignore') {
    $true
} else {
    $false
}

More tersely:

[bool](gv foo -s global -ea ig)

Output of either:

False

Alternatively

You can trap the error that is raised when the variable doesn't exist.

try {
    Get-Variable foo -Scope Global -ErrorAction 'Stop'
} catch [System.Management.Automation.ItemNotFoundException] {
    Write-Warning $_
}

Outputs:

WARNING: Cannot find a variable with the name 'foo'.

Answer 2

So far, it looks like the answer that works is this one.

To break it out further, what worked for me was this:

Get-Variable -Name foo -Scope Global -ea SilentlyContinue | out-null

$? returns either true or false.

Answer 3

$myvar = if ($env:variable) { $env:variable } else { "default_value" }