Grandparent Folder Name To File Name - powershell

Question

I have a script that runs when I specify the exact directory of c:\script\19\ the problem is, have other folders in the c:\script such as 18, 17, 16. The script I have is appending the 19 in front of all of the files. How do I get this to look at the grandparent of the file it's renaming and append it? An example of how it's working is files like this:
c:\script\18\00000001\Plans.txt
c:\script\19\00001234\Plans.txt
c:\script\17\00005678\App.txt
But my script is renaming the files like this
c:\script\18\00000001\19-0001 Plans.txt
c:\script\19\00001234\19-1234 Plans.txt
c:\script\17\00005678\19-5678 App.txt
My script is this:
$filepath = Get-ChildItem "C:script\" -Recurse |
ForEach-Object {
$parent = $_.Parent
$grandparent = $_.fullname | Split-Path -Parent | Split-Path -Parent | Split-Path -Leaf
}
Get-ChildItem "C:\Script\" –recurse –file |
Where-Object {$_.Name –notmatch ‘[0-9][0-9]-[0-9]’} |
rename-item -NewName {$grandparent + '-' + $_.Directory.Name.SubString($_.Directory.Name.length -4, 4) + ' ' + $_.Name}

Answer 1

The simplest solution is to combine string-splitting with the -split operator with a delay-bind script block (which you've tried to use):
Get-ChildItem C:\Script –Recurse –File -Exclude [0-9][0-9]-[0-9]* |
Rename-Item -NewName {
# Split the full path into its components.
$names = $_.FullName -split '\\'
# Compose the new file name from the relevant components and output it.
'{0}-{1} {2}' -f $names[-3], $names[-2].Substring($names[-2].Length-4), $_.Name
} -WhatIf
-WhatIf previews the renaming operation; remove it to perform actual renaming.
Note how -Exclude is used with a wildcard expression directly with Get-ChildItem to exclude files that already have the target name format.
The main reason your original didn't work is that you calculated single, static
$parent and $grandparent values, instead of deriving the input path-specific values from each input path.
Additionally, your $grandparent calculation was needlessly complicated; Gert Jan Kraaijeveld's helpful answer shows a simpler way.

Answer 2

To get the grandparent of a $file object:
$file.Directory.Parent
The parent directory of a file is the 'Directory' member of the file object.
The parent directory of a directory is the 'Parent' member of the directory object.
It is not hard, but confusing it sure is...
Edit
You asked for my solution:
Get-ChildItem C:\script -Recurse -File | ForEach-Object {
$parent = $_.Directory.Name
$grandparent = $_.Directory.Parent.Name
Rename-Item $_.FullName -NewName "$grandparent-$($parent.Substring($parent.length-4,4)) $($_.name)"
}
I used the -file parameter of Get-ChildItem to get only files from the folder structure. I'm not sure that suits in your situation