Powershell not returning correct value - function

Question

As some background, this should take an excel file, and convert it to PDF (and place the PDF into a temporary folder).
E.g. 'C:\Users\gjacobs\Desktop\test\stock.xlsx'
becomes
'C:\Users\gjacobs\Desktop\test\pdf_merge_tmp\stock.pdf'
However, the new file path does not return correctly.
If I echo the string $export_name from within the function, I can see that it has the correct value: "C:\Users\gjacobs\Desktop\test\pdf_merge_tmp\stock.pdf".
But once $export_name is returned, it has a different (incorrect value): "C:\Users\gjacobs\Desktop\test\pdf_merge_tmp C:\Users\gjacobs\Desktop\test\pdf_merge_tmp\stock.pdf".
function excel_topdf{
param(
$file
)
#Get the parent path
$parent = Split-Path -Path $file
#Get the filename (no ext)
$leaf = (Get-Item $file).Basename
#Add them together.
$export_name = $parent + "\pdf_merge_tmp\" + $leaf + ".pdf"
echo ($export_name) #prints without issue.
#Create tmp dir
New-Item -Path $parent -Name "pdf_merge_tmp" -ItemType "Directory" -Force
$objExcel = New-Object -ComObject excel.application
$objExcel.visible = $false
$workbook = $objExcel.workbooks.open($file, 3)
$workbook.Saved = $true
$xlFixedFormat = “Microsoft.Office.Interop.Excel.xlFixedFormatType” -as [type]
$workbook.ExportAsFixedFormat($xlFixedFormat::xlTypePDF, $export_name)
$objExcel.Workbooks.close()
$objExcel.Quit()
return $export_name
}
$a = excel_topdf -file 'C:\Users\gjacobs\Desktop\test\stock.xlsx'
echo ($a)

Answer 1

The issue you're experiencing is caused by the way how PowerShell returns from functions. It's not something limited to New-Item cmdlet. Every cmdlet which returns anything would cause function output being altered with the value from that cmdlet.
As an example, let's take function with one cmdlet, which returns an object:
function a {
Get-Item -Path .
}
$outputA = a
$outputA
#### RESULT ####
Directory:
Mode LastWriteTime Length Name
---- ------------- ------ ----
d--hs- 12/01/2021 10:47 C:\
If you want to avoid that, these are most popular options (as pointed out by Lasse V. Karlsen in comments):
# Assignment to $null (or any other variable)
$null = Get-Item -Path .
# Piping to Out-Null
Get-Item -Path . | Out-Null
NOTE: The behavior described above doesn't apply to Write-Host:
function b {
Write-Host "bbbbbb"
}
$outputB = b
$outputB
# Nothing displayed
Interesting thread to check if you want to learn more.