Array of variables in PowerShell has null members - arrays

Question

I have a PowerShell script, where I want to make sure certain variables have value before proceeding.
So I have the following:
$dataRow = $sheet.Cells.Find($country).Row
$serverCol = $sheet.Cells.Find($serverString).Column
$databaseCol = $sheet.Cells.Find($databaseString).Column
$userCol = $sheet.Cells.Find($userString).Column
$passwordCol = $sheet.Cells.Find($passString).Column
$partnerCol = $sheet.Cells.Find($partnerString).Column
#All variables in this array are required. If one is empty - the script cannot continue
$requiredVars = #($dataRow, $serverCol, $databaseCol, $userCol, $passwordCol, $partnerCol)
But when I foreach over the array like so:
foreach ($var in $requiredVars)
{
Write-Host DataRow = ($dataRow -eq $var)
Write-Host ServerCol = ($serverCol -eq $var)
Write-Host DatabaseCol = ($databaseCol -eq $var)
Write-Host UserCol = ($userCol -eq $var)
Write-Host PasswordCol = ($passwordCol -eq $var)
Write-Host PartnerCol = ($partnerCol -eq $var)
if ($var -eq $null)
{
[System.Windows.Forms.MessageBox]::Show("No data found for given string!")
$excel.Quit()
return
}
}
I always get the MessageBox. I added the "Write-Host" part to see the value of each variable, then changed it to see which variable was null but all variables have values in them and all the checks you see here return "False".
I'd like to know what I'm doing wrong and if the $requiredVars array only copies values, not references or something.

Answer 1

Instead of using separate variables, you may consider using a Hashtable to store them all.
This makes checking the individual items a lot simpler:
# get the data from Excel and store everything in a Hashtable
# to use any of the items, use syntax like $excelData.passwordCol or $excelData['passwordCol']
$excelData = #{
'dataRow' = $sheet.Cells.Find($country).Row
'serverCol' = $sheet.Cells.Find($serverString).Column
'databaseCol' = $sheet.Cells.Find($databaseString).Column
'userCol' = $sheet.Cells.Find($userString).Column
'passwordCol' = $sheet.Cells.Find($passString).Column
'partnerCol' = $sheet.Cells.Find($partnerString).Column
}
# check all items in the hash. If any item is $null then exit
foreach ($item in $excelData.Keys) {
# or use: if ($null -eq $excelData[$item])
if (-not $excelData[$item]) {
[System.Windows.Forms.MessageBox]::Show("No data found for item $item!")
$excel.Quit()
# IMPORTANT: clean-up used COM objects from memory when done with them
[System.Runtime.Interopservices.Marshal]::ReleaseComObject($sheet) | Out-Null
# Your code doesn't show this, but you'll have a $workbook object in there too
# [System.Runtime.Interopservices.Marshal]::ReleaseComObject($workbook) | Out-Null
[System.Runtime.Interopservices.Marshal]::ReleaseComObject($excel) | Out-Null
[System.GC]::Collect()
[System.GC]::WaitForPendingFinalizers()
return
}
}

Answer 2

One way to directly solve your question is this:
$a = "foo"
$b = "bar"
$c = $null
$requiredVariables = $a, $b, $c
# How many total entries in array?
($requiredVariables).Count
# How many of them have a value?
($requiredVariables | Where-Object {$_}).Count
# So one option for a single check would be:
if (($requiredVariables.Count) -ne ($requiredVariables | Where-Object {$_}).Count) {
Write-Warning "Not all values provided"
}
However an alternative [and better] approach is to make your code in to a function that includes parameter validation
function YourCustomFunction {
Param (
[ValidateNotNullOrEmpty()]
$a
,
[ValidateNotNullOrEmpty()]
$b
,
[ValidateNotNullOrEmpty()]
$c
)
Process {
Write-Output "Your function code goes here..."
}
}
# Call your function with the params
YourCustomFunction -a $a -b $b -c $c
Example output:
Test-YourCustomFunction: Cannot validate argument on parameter 'c'. The argument is null or empty. Provide an argument that is not null or empty, and
then try the command again.
At line:39 char:48