How to Clean Up PowerShell Script Variables without Restarting PowerShell ISE

Many times while authoring PowerShell scripts, the expected output will be incorrect because PowerShell ISE does not automatically cleanup it’s variable between manual runs of a script.  In my experience this poses two practical issue which lead to incorrect script results:

1) If the variable is not explicitly re-initialized in the script (very common practice), the script will be initialized with a value from the previous run, and,

2) If a script is changed so that a variable is not properly assigned a value, PowerShell ISE will still show the value from the previous run because it has not been assigned a new value since

This all leads to confusion.  I’ve been trying to find the best way to clear all the variables a script has set a value for without restarting PowerShell ISE.

I am not particular happy with what I’ve come up with, but suffice to say, so far, this seems to be the easiest and quickest method:

Remove-Variable * -ErrorAction SilentlyContinue; Remove-Module *; $error.Clear(); Clear-Host

Here is a shorter version using aliases:

rv * -ea SilentlyContinue; rmo *; $error.Clear(); cls

** Note:  this will indiscriminately remove ANY variables set during your PowerShell ISE session – not just the ones specific to the script you are working on.

Microsoft MVP Pat Richards has a similar approach which analyses the actual .ps script file to identify and remove only the variables used in the script.  He wraps this in a function which can be invoked at anytime: https://www.ucunleashed.com/247.

function Remove-ScriptVariables($path) {
$result = Get-Content $path |
ForEach  {

if ( $_ -match ‘(\$.*?)\s*=’) {
$matches[1]  | ? { $_ -notlike ‘*.*’ -and $_ -notmatch ‘result’ -and $_ -notmatch ‘env:’}
}

}

ForEach ($v in ($result | Sort-Object | Get-Unique))  {
Write-Host “Removing” $v.replace(“$”,””)
Remove-Variable ($v.replace(“$”,””)) -ErrorAction SilentlyContinue
}

}
# end function Get-ScriptVariables

For reasons I cannot figure out, Remove-Variable does not always remove all the variables for me using this function; but I like the approach.

So here is another method that works well:

1. At the start of your script, include this line which gets the state of the variables before the script is run:
   • $DefaultVariables = $(Get-Variable).Name
2. Then at the end of your script, do a comparison and remove all of the variables added:
   • ((Compare-Object -ReferenceObject (Get-Variable).Name -DifferenceObject $DefaultVariables).InputObject).foreach{Remove-Variable -Name $_}

This seems to work consistently the best.