Powershell Compare-Objects returns wrong results

Question

I'm trying to compare the contents of 2 folders using this command:

Compare-Object (Get-ChildItem C:\\compare -recurse) (Get-ChildItem J:\\compare -recurse) -Property FullName

This is the result that I should get:

FullName                       SideIndicator
--------                       -------------         
J:\compare\test1.txt           =>                     
C:\compare\install.msi         <=           
C:\compare\setup.exe           <=                    
C:\compare\subfolder\test3.txt <=     

This is what I actually get (I've noted where objects exist in both folders and should be excluded from the comparison):

FullName                       SideIndicator
--------                       -------------
J:\compare\subfolder           => (exists in both folders)          
J:\compare\doc1.pdf            => (exists in both folders)           
J:\compare\doc2.pdf            => (exists in both folders)           
J:\compare\test1.txt           =>           
J:\compare\subfolder\test2.txt => (exists in both folders)           
C:\compare\subfolder           <= (exists in both folders)           
C:\compare\doc1.pdf            <= (exists in both folders)           
C:\compare\doc2.pdf            <= (exists in both folders)           
C:\compare\install.msi         <=           
C:\compare\setup.exe           <=           
C:\compare\subfolder\test2.txt <= (exists in both folders)           
C:\compare\subfolder\test3.txt <=  

Why is Powershell flagging objects that exist in both folders as not existing in either folder? It's as if I'm using -IncludeEqual with Compare-Object (which I'm not), but instead of the == side indicators I'm getting <= and => instead.

Answer 1

Your comparison should be

Compare-Object `
  (Get-ChildItem C:\Compare -Recurse | Select-Object -ExpandProperty FullName | Split-Path -NoQualifier) `
  (Get-ChildItem J:\Compare -Recurse | Select-Object -ExpandProperty FullName | Split-Path -NoQualifier)

This is because, as @TessellatingHeckler noted, the drive letters (qualifiers) are always different between the two paths, and you want to ignore that part.