#PSTip Find variables in a script

Note: This tip requires PowerShell 3.0 or later.

I had recently completed writing a PowerShell module for an internal project. Within this module, I ended up using variables in the Script scope to share data between different parts of the module. Now, as the module grew into multi-hundred line script, I had a tough time finding all variables that were declared or used in the Script scope. It was important for me to ensure that these are used and disposed correctly.

PowerShell AST to the rescue! The VariableExpressionAst gives us a peek into the variables in a script.

1
2
3

$AbstractSyntaxTree = [System.Management.Automation.Language.Parser]::ParseInput($psISE.CurrentFile.Editor.Text, [ref]$null, [ref]$null)
$Variables = $AbstractSyntaxTree.FindAll({$args[0] -is [System.Management.Automation.Language.VariableExpressionAst ]}, $true)
$variables | Where-object { $_.VariablePath.IsScript } | Select -Unique

In the last line of code, by replacing $.VariablePath.IsScript_ with $.VariablePath.IsGlobal_, we can find all variables in the Global scope.

Also, in my scenario, I was using PowerShell ISE for script editing and it was easy for me to use the ISE object model to grab the script content. If you have a file on the disk, you can use the Get-Content cmdlet to read the script content instead of $psISE.CurrentFile.Editor.Text.