Convert Dup Files to hardlinks

PRISM.psm1

function Add-Hash ($file)
{
    $hasher = [System.Security.Cryptography.SHA1]::Create()
    $inputStream = New-Object IO.StreamReader $file.FullName 
    $hashBytes = $hasher.ComputeHash($inputStream.BaseStream)
    $inputStream.Close()
    $builder = New-Object System.Text.StringBuilder
    $hashBytes | Foreach-Object { 
        [void] $builder.Append( $PSItem.ToString("X2") ) 
    }
    $hash = [string] $builder.ToString()
    $FullName=$file.FullNAme
    $file | Add-Member -type NoteProperty -name hash -value $hash        
    return $file
}


<#
.Synopsis
   Converts duplicated files to hardlinks
.DESCRIPTION
   Long description
.EXAMPLE
   Example of how to use this cmdlet
.EXAMPLE
   Another example of how to use this cmdlet
.INPUTS
   Inputs to this cmdlet (if any)
.OUTPUTS
   Output from this cmdlet (if any)
.NOTES
   General notes
.COMPONENT
   The component this cmdlet belongs to
.ROLE
   The role this cmdlet belongs to
.FUNCTIONALITY
   The functionality that best describes this cmdlet
#>
function ConvertTo-HardLink
{
    [CmdletBinding(DefaultParameterSetName='Parameter Set 1', 
                  SupportsShouldProcess=$true, 
                  ConfirmImpact='High')]
    Param
    (
        # File mask to process
        [Parameter(Mandatory=$true, 
                   ValueFromPipeline=$true,
                   ValueFromPipelineByPropertyName=$true, 
                   ValueFromRemainingArguments=$false, 
                   Position=0,
                   ParameterSetName='Parameter Set 1')]
        [ValidateNotNull()]
        [ValidateNotNullOrEmpty()]
        [string] $FileMask,

        # Min file size to process
        [Parameter(ParameterSetName='Parameter Set 1')]
        [AllowNull()]
        [AllowEmptyCollection()]
        [AllowEmptyString()]
        [int]
        $MinFileSize = 0
    )

    Begin
    {
        $saved = 0
    }
    Process
    {
        if ($pscmdlet.ShouldProcess("Target", "Operation"))
        {
            $prev=$null
            $c=1

            Get-ChildItem -File -include $fileMask -Recurse | Select-Object FullName, Length | where $PSItem.Length -gt $MinFileSize | ForEach-Object {
                Add-Hash $PSItem
            } | Sort-Object -Property hash | ForEach-Object {
                Write-Verbose $PSItem.FullName $PSItem.Length
                if ($prev.hash -eq $PSItem.hash)
                {
                    if($c -eq 1) { Write-Host $c $prev.FullName $prev.hash }     
                    $c += 1
                    Write-Verbose $c $PSItem.FullName $PSItem.hash 
                    $pname = [string] $prev.FullName
                    $fname = [string] $PSItem.FullName
                    Remove-Item -Path $fname -Force 
                    & cmd /c mklink /h $fname $pname
                    $saved += $PSItem.Length
                } else 
                {  
                    $c=1
                    $prev = $PSItem 
                }
            }

        }
    }
    End
    {
        Write-Host "Saved: $saved"
    }
}

Export-ModuleMember ConvertTo-HardLink
Export-ModuleMember Add-Hash

test.ps1

Import-Module 'D:\Work - Copy\ps_examples\savespace\PRISM.psm1' -Force
ConvertTo-HardLink -FileMask '*.pdf'