PowerShell to compare files in folder B to a lookup for new names and then new name to files in folder A

I have two folders on my hard drive A and B. I want to compare all files in B to A. Any file thats in B and not in A, shall be copied into a third folder C. All this to be done in the PowerShell 2.0. I want to keep A , B and C as variables so set A=C:/A for example.

One little twist is that I can not compare all of B/*.* to A/*.* using the filenames as is. For that I need a lookup file.

So, under B, a file called 1.doc is the same as myfile1.doc in A.
B/1.doc = A/myfile1.doc
The lookup file has this information in the following format:

"Z:\B\1.doc","myfile1.doc",<some string>,<some string>

How can I do this? Part of the code is placed below but needs to be augmented for the lookup file and correct picking of filename in A.
Who is Participating?
oBdAConnect With a Mentor Commented:
Try this:
$SourceA = "D:\Temp\A"
$SourceB = "D:\Temp\B"
$Target = "D:\Temp\C"
$LookupFile = "D:\Temp\lookup.csv"
## Set this to $True if the file names in the target folder should have the name from the lookup file (folder A) rather than folder B.
$CopyUsingLookupName = $False
$Lookup = @{}
## Read the lookup file and create the lookup hash table:
ForEach ($Line In (Get-Content -Path $LookupFile)) {
	$FileB = $Line.Split(",")[0].Trim('"')
	$FileB = Split-Path $FileB -Leaf
	$FileA = $Line.Split(",")[1].Trim('"')
	$Lookup[$FileB] = $FileA
## Get all files in B
ForEach ($FileItem In (Get-ChildItem -Path $SourceB -Filter "*.*" | Where {-Not $_.PSIsContainer})) {
	## Check if the file is in the lookup table, and set the name to search for accordingly
	If ($Lookup.ContainsKey($FileItem.Name)) {
		$LookFor = $Lookup[$FileItem.Name]
		"Processing '$($FileItem.Name)' (--> $($LookFor)) ..." | Write-Host -NoNewLine
	} Else {
		$LookFor = $FileItem.Name
		"Processing '$($FileItem.Name)' ..." | Write-Host -NoNewLine
	## Check if the file is in folder A, and if not, copy it to C
	If (Get-Item -Path (Join-Path -Path $SourceA -ChildPath $LookFor) -ErrorAction SilentlyContinue) {
		" found in '$SourceA'." | Write-Host
	} Else {
		" copying to '$Target'." | Write-Host
		If ($CopyUsingLookupName) {
			$TargetFile = $LookFor
		} Else {
			$TargetFile = $FileItem.Name
		Copy-Item -Path $FileItem.FullName -Destination (Join-Path -Path $Target -ChildPath $TargetFile) -Force
"Done." | Write-Host

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Joe KlimisConnect With a Mentor Commented:

I think this is a good starting point , please can you clarify if the  file from b is onlu in the corresponding folder in A or anywhere on drive A

Also when copying the files to C into 1 folder or copy structure  , and also the name structure for the file copied to c  eg 1.doc or myfile1.doc ?

$folderA = "c:\temp\1\a"
$Folderb = "c:\temp\1\b"
$folderc = "c:\temp\1\c"
# define the lookup prefix
$lookup  = "myfile"
# get a list of all the filenames for both folders
$a = get-childitem $foldera -recurse
$b = get-childitem $folderb -recurse

#Compare them and copy  files that dont match
foreach ($item in $b)
	if ( -not ($A.name.contains( "$lookup$($item.BaseName)$($item.Extension)")))
	copy-item $item.fullname $folderc -verbose

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