How to subtract Excel cells using Powershell - excel

Question

I am trying to perform arithmetic on an existing excel sheet that has figures in it. My code:
$Excel = New-Object -ComObject Excel.Application
$ExcelWorkBook = $Excel.Workbooks.Open($temp)
$ExcelWorkSheet = $Excel.WorkSheets.item(1)
$ExcelWorkSheet.activate()
$Prehit = $ExcelWorkSheet.Cells.Item(2,1)
$Hit1 = $ExcelWorkSheet.Cells.Item(2,2)
$Hit2 = $ExcelWorkSheet.Cells.Item(2,3)
$Hit3 = $ExcelWorkSheet.Cells.Item(2,4)
$Remain = 0
If ($hit -eq 1) {
$Remain = $Prehit - $Hit1
}
If ($hit -eq 2) {
$Remain = $Prehit - $Hit1- $Hit2
}
Yields the following error:
Method invocation failed because [System.__ComObject] does not contain a method named 'op_Subtraction'.
At C:\path_to_ps1_file.ps1:40 char:3
+ $Remain = $Prehit - $Hit1- $Hit2
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (op_Subtraction:String) [], RuntimeException
+ FullyQualifiedErrorId : MethodNotFound
I have tried casting all the variables as ints yet that yields the same error. I even casted the numbers as ints in the powershell modules used to create this excel file. What am I missing?

Answer 1

I realize now I was referencing the cell values incorrectly. The correct way is to do:
$Prehit = $ExcelWorkSheet.Cells.Item(2,1).Text
$Hit1 = $ExcelWorkSheet.Cells.Item(2,2).Text
$Hit2 = $ExcelWorkSheet.Cells.Item(2,3).Text
$Hit3 = $ExcelWorkSheet.Cells.Item(2,4).Text

Answer 2

Whenever I've run into this sort of thing, I just the 'Excel Marco Recorder' and review the VBA code it produces and then convert that to PowerShell for later automation use cases.
Yet at no point in the code you posted are you making the XLS visible for you to act on it.
For example:
# Instantiate Excel instnace
$excel_test = New-Object -ComObject Excel.Application
# Make the instance visiable to work with it
$excel_test.visible = $true
# Catch alerts
$excel_test.DisplayAlerts = $true
# Add in the file source
$excel_test.Workbooks.Add('D:\Temp\Test.xlsx')
# Choose a sheet in the workbook
$Sheet = $excel_test.Worksheets.Item(1)
# Assign a formula to the target variable
$strFormula = '=(SUM(A1:C3)/3) - 1'
# Assign the formula to the target variable
$Sheet.Cells.Item(4,4) = $strFormula
$SourcecellCell = ($Sheet.Cells.Item(4,4)).Value2
$NewCell = 3
$sheet.Cells.Item(5,5) = $SourcecellCell - $NewCell
# Exit the XLS without saving
$excel_test.Quit()

Answer 3

Whenever I've run into this sort of thing, I just the 'Excel Marco Recorder' and review the VBA code it produces and then convert that to PowerShell for later automation use cases.
Yet at no point in the code you posted are you making the XLS visible for you to act on it. Since it is not visible, you cannot perform UI actions on it.
Secondly, this...
$excel_test.Worksheets.Item(2).Cells.Item(2,2).Formula() = $strFormula
... is where your issues begin. If you step through this one step at a time, you'll immediately see the aforementioned will simply fail.
For example:
# Instantiate Excel instance
$excel_test = New-Object -ComObject Excel.Application
# Make the instance visible to work with it
$excel_test.visible = $true
# Catch alerts
$excel_test.DisplayAlerts = $true
# Add in the file source
$excel_test.Workbooks.Add('D:\Temp\Test.xlsx')
# Results
<#
Application : Microsoft.Office.Interop.Excel.ApplicationClass
Creator : 1480803660
Parent : Microsoft.Office.Interop.Excel.ApplicationClass
...
#>
# Assign a formula to the target variable
$strFormula = "=((A1:C4/10000)-1)"
# Assign the formula to the target variable
$excel_test.Worksheets.Item(2).Cells.Item(2,2).Formula() = $strFormula
<#
Invalid index. (Exception from HRESULT: 0x8002000B (DISP_E_BADINDEX))
At line:1 char:1
+ $excel_test.Worksheets.Item(2).Cells.Item(2,2).Formula() = $strFormul ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : OperationStopped: (:) [], COMException
+ FullyQualifiedErrorId : System.Runtime.InteropServices.COMException
#>
$Error | Format-List -Force
<#
Exception : System.Management.Automation.RuntimeException: The variable '$command' cannot be retrieved because it has not been set.
at System.Management.Automation.VariableOps.GetVariableValue(VariablePath variablePath, ExecutionContext executionContext,
VariableExpressionAst varAst)
at Prompt(Closure , FunctionContext )
TargetObject : command
CategoryInfo : InvalidOperation: (command:String) [], RuntimeException
FullyQualifiedErrorId : VariableIsUndefined
ErrorDetails :
InvocationInfo : System.Management.Automation.InvocationInfo
ScriptStackTrace : at Prompt, C:\Users\Daniel\Documents\WindowsPowerShell\Microsoft.PowerShellISE_profile.ps1: line 55
at <ScriptBlock>, <No file>: line 1
PipelineIterationInfo : {}
PSMessageDetails :
...
#>