How do I most efficiently move, rename files and log this action?

Question

I have the following CSV list (in reality 1000s of lines):

needle,code
123456,AB
121212,BB
33333333,CVV

And I have a directory (C:\\old_files) c

Answer 1

You need to actually check if you have a match before copying the matching file.

Get-ChildItem "C:\old_files" | ForEach-Object {
  $n = ($_.Name -split '.')[1]
  if ($pair[$n]) {
    $oldname = $_.FullName
    $newname = Join-Path 'C:\new_files' ($pair[$n] + $_.Name)
    Copy-Item $oldname $newname
  }
}

Do the logging after the copy operation:

Copy-Item $oldname $newname
if ($?) {
  # log success information here
} else {
  # log error information here
}