Get list of files, that exist in one folder but not another, as determined by content, not filename, on Windows

Solution 1:

The strings returned from PowerShell's Get-FileHash can be used as the keys to a hashtable to associate content with the fully-qualified path. This code creates a hashtable for each path with the following caveats.

• Empty files are ignored as the content hash of all empty files will be identical. ( You could also create a list of empty files foulnd in each directory )
• If duplicates are found within the directory we are indexing, only the first file found will be added to the $HashOut table. The $Dups table will have the list of all paths that share identical content.

PowerShell:

Function Get-DirHash ( [String]$PathIn , [PSObject]$HashOut )
{
    $HashOut.Clear()
    gci $PathIn *.txt -Recurse | ? Length -gt 0 | Get-FileHash | %{
        If ( $HashOut.Contains($_.Hash) )
        {
            If ( $Dups.Contains($_.Hash) )
            {
                $Dups[$_.Hash] += $_.Path
            }
            Else
            {
                $Dups.Add( $_.Hash , @( $HashOut[$_.Hash] , $_.Path ))
            }
        }
        Else
        {
            $HashOut.Add( $_.Hash , $_.Path )
        }
    }
}

$DirA     = 'c:\whatever'
$DirB     = 'c:\whenever'
$TableA   = @{}
$TableB   = @{}
$Dups     = @{}
$Unique2A = New-Object System.Collections.Generic.List[String]

Get-DirHash -PathIn $DirA -HashOut $TableA
Get-DirHash -PathIn $DirB -HashOut $TableB

$TableA.Keys | %{
    If ( ! ( $TableB.Contains($_) ))
    {
        $Unique2A.Add( $TableA[$_] )
    }
}

$Unique2A | Out-GridView

Not fully tested, but I believe this will do the trick of only computing the hash for files that match in size.

$DirA     = 'c:\whatever'
$DirB     = 'c:\whenever'

$TestA = [Regex]::Escape($DirA)

$MasterList = gci $DirA , $DirB -Filter *.txt -recurse | Group Length

$Unique2A_BySize = ( $MasterList | ? Count -eq 1 |
     ? { $_.Group[0].DirectoryName -match $TestA } ).Group.FullName

$Unique2A_ByHash = ( $MasterLIst | ? Count -gt 1 | %{
    $_.Group | Get-FileHash | Group Hash |
        ? Count -eq 1 |
           ? { $_.Group[0].Path -match $TestA }
} ).Group.Path

( $Unique2A = $Unique2A_BySize + $Unique2A_ByHash ) | Out-GridView

Which may be improved by the harder-to-read:

$DirA     = 'c:\whatever'
$DirB     = 'c:\whenever'

$TestA = [Regex]::Escape($DirA)

$Unique2A = ( ( $MasterList = gci $DirA , $DirB -Filter *.txt -recurse | Group Length ) |
    ? Count -eq 1 |
        ? { $_.Group[0].DirectoryName -match $TestA } ).Group.FullName +
( $MasterLIst | ? Count -gt 1 | %{
    $_.Group | Get-FileHash | Group Hash |
        ? Count -eq 1 |
           ? { $_.Group[0].Path -match $TestA }
} ).Group.Path

$Unique2A | Out-GridView