powershell

How to clear all variables defined in the current loop

An operation which assigns something to a variable might fail. We might want to continue despite the failure, but now we have data from the last loop iteration in the variable, leading to unexpected results.

For example in the following code $z will not be assigned when $RAND happens to be a 0, because division by 0 will throw an error. This causes the Write-Host to output the value from last iteration.

foreach ($i in 1..10) {
    $RAND = Get-Random -Minimum 0 -Maximum 11
    $z = $i / $RAND
    Write-Host "Value: $z" -ForegroundColor Green
    Remove-Variable -Name z -ErrorAction SilentlyContinue
}

I want to clear all variables defined in the current loop iteration. I could type them all out manually in the Remove-Variable section, which is how I do it right now. But is there a way to determine all variables defined in the current loop iteration?

Solution

  • The solution indicated by @zett42 in the comments (wrapping the whole loop iteration in a scriptblock) aka wrapping your code in an (anonymous) function, might be an easy solution as it creates a complete new scope for every variable (as indeed questioned) but is rather expensive, see: What is the best way to reuse static code.

    Besides, from a coding perspective, it might be better to be specific on the part that might fail and the specific variable that you would (re)set in case of an error. You might do this by using a Try/Catch block and leaving the assignment outside. Meaning $z = Try { $i / $RAND } Catch { Write-Error $_ } and not: Try { $z = $i / $RAND } Catch { Write-Error $_ }.

    foreach ($i in 1..10) {
    $RAND = Get-Random -Minimum 0 -Maximum 11
    $z = Try { $i / $RAND } Catch { Write-Error $_ }
    Write-Host "Value: $z" -ForegroundColor Green
}