use ChangeExtension for robustness

Public/ConvertTo-ExcelXlsx.ps1

@@ -3,60 +3,76 @@ function ConvertTo-ExcelXlsx {
     param
     (
         [parameter(Mandatory = $true, ValueFromPipeline)]
-        [string]$Path,
+        [string[]]$Path,
         [parameter(Mandatory = $false)]
         [switch]$Force
     )
     process {
-        if (-Not ($Path | Test-Path) ) {
+        try {
-            throw "File not found"
+            foreach ($singlePath in $Path) {
-        }
+                if (-Not ($singlePath | Test-Path) ) {
-        if (-Not ($Path | Test-Path -PathType Leaf) ) {
+                    throw "File not found"
-            throw "Folder paths are not allowed"
+                }
-        }
+                if (-Not ($singlePath | Test-Path -PathType Leaf) ) {
+                    throw "Folder paths are not allowed"
+                }
 
-        $xlFixedFormat = 51 #Constant for XLSX Workbook
+                $xlFixedFormat = 51 #Constant for XLSX Workbook
-        $xlsFile = Get-Item -Path $Path
+                $xlsFile = Get-Item -Path $singlePath
-        $xlsxPath = "{0}x" -f $xlsFile.FullName
+                $xlsxPath = [System.IO.Path]::ChangeExtension($xlsFile.FullName, ".xlsx")
 
-        if ($xlsFile.Extension -ne ".xls") {
+                if ($xlsFile.Extension -ne ".xls") {
-            throw "Expected .xls extension"
+                    throw "Expected .xls extension"
-        }
+                }
+
+                if (Test-Path -Path $xlsxPath) {
+                    if ($Force) {
+                        try {
+                            Remove-Item $xlsxPath -Force
+                        }
+                        catch {
+                            throw "{0} already exists and cannot be removed. The file may be locked by another application." -f $xlsxPath
+                        }
+                        Write-Verbose $("Removed {0}" -f $xlsxPath)
+                    }
+                    else {
+                        throw "{0} already exists!" -f $xlsxPath
+                    }
+                }
+
+                if ($null -eq $Excel)
+                {
+                    try {
+                        $Excel = New-Object -ComObject "Excel.Application"
+                    }
+                    catch {
+                        throw "Could not create Excel.Application ComObject. Please verify that Excel is installed."
+                    }
+                }
 
-        if (Test-Path -Path $xlsxPath) {
-            if ($Force) {
                 try {  
-                    Remove-Item $xlsxPath -Force
+                    $Excel.Visible = $false
+                    $workbook = $Excel.Workbooks.Open($xlsFile.FullName, $null, $true)
+                    if ($null -eq $workbook) {
+                        Write-Host "Failed to open workbook"
+                    } else {
+                        $workbook.SaveAs($xlsxPath, $xlFixedFormat)
+                    }
                 }
                 catch {
-                    throw "{0} already exists and cannot be removed. The file may be locked by another application." -f $xlsxPath
+                    Write-Error ("Failed to convert {0} to XLSX." -f $xlsFile.FullName)
+                    throw
+                }
+                finally {
+                    if ($null -ne $workbook) {
+                        $workbook.Close()
+                    }
                 }
-                Write-Verbose $("Removed {0}" -f $xlsxPath)
             }
-            else {
-                throw "{0} already exists!" -f $xlsxPath
-            }
-        }
-
-        try {
-            $Excel = New-Object -ComObject "Excel.Application"
-        }
-        catch {
-            throw "Could not create Excel.Application ComObject. Please verify that Excel is installed."
-        }
-
-        try {  
-            $Excel.Visible = $false
-            $null = $Excel.Workbooks.Open($xlsFile.FullName, $null, $true)
-            $Excel.ActiveWorkbook.SaveAs($xlsxPath, $xlFixedFormat)
         }
         finally {
-            if ($null -ne $Excel.ActiveWorkbook) {
-                $Excel.ActiveWorkbook.Close()
-            }
-            
             $Excel.Quit()
+            $Excel = $null
         }
     }
 }
-