Import-CSV original.csv | ForEach-Object { $data1 = 'whatever' $data2 = 'hello' $_ | Add-Member -MemberType NoteProperty -Name ColumnA -Value $data1 -PassThru | Add-Member -MemberType NoteProperty -Name ColumnB -Value $data2 -PassThru } | Export-CSV revised.csv
Something vaguely like that. You can access the current columns via $_, e.g., “$user = Get-ADUser -Identity $_.samaccountname” if the current CSV has a samaccountname column. Import-CSV brings in the CSV as objects, Add-Member adds properties to those objects, and Export-CSV writes the revised objects back to a CSV.