SharePoint Online: Find Duplicate Files using PowerShell

Requirement: Find Duplicate Documents in SharePoint Online.

When multiple people from different teams work together, there is a huge possibility for duplicate content in SharePoint. People may have uploaded a same document to different libraries or even different folders in document libraries. So, How to find duplicate documents in SharePoint Online?

SharePoint Online: Find Duplicate Documents using PowerShell - File Hash Method
How to find duplicate files in SharePoint Online? Lets find duplicate files in a SharePoint Online document library by comparing file hash:

#Load SharePoint CSOM Assemblies
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.dll"
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.Runtime.dll"

#Parameters
$SiteURL = "https://crescenttech.sharepoint.com"
$ListName ="Documents"

#Array to Results Data
$DataCollection = @() 

#Get credentials to connect
$Cred = Get-Credential

Try {
    #Setup the Context
    $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
    $Ctx.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.UserName, $Cred.Password)

    #Get the Web
    $Web = $Ctx.Web
    $Ctx.Load($Web)

    #Get all List items from the library - Exclude "Folder" objects
    $List = $Ctx.Web.Lists.GetByTitle($ListName)
    $Query = New-Object Microsoft.SharePoint.Client.CamlQuery
    $Query.ViewXml="<View Scope='RecursiveAll'><Query><Where><Eq><FieldRef Name='FSObjType'/><Value Type='Integer'>0</Value></Eq></Where></Query></View>"
    $ListItems = $List.GetItems($Query)
    $Ctx.Load($ListItems)
    $Ctx.ExecuteQuery()
    
    $Count=1
    ForEach($Item in $ListItems)
    {
        #Get the File from Item
        $File = $Item.File
        $Ctx.Load($File)
        $Ctx.ExecuteQuery()
        Write-Progress -PercentComplete ($Count / $ListItems.Count * 100) -Activity "Processing File $count of $($ListItems.Count)" -Status "Scanning File '$($File.Name)'" 

        #Get The File Hash
        $Bytes = $Item.file.OpenBinaryStream()
        $Ctx.ExecuteQuery()
        $MD5 = New-Object -TypeName System.Security.Cryptography.MD5CryptoServiceProvider 
        $HashCode = [System.BitConverter]::ToString($MD5.ComputeHash($Bytes.Value)) 

        #Collect data        
        $Data = New-Object PSObject 
        $Data | Add-Member -MemberType NoteProperty -name "File Name" -value $File.Name
        $Data | Add-Member -MemberType NoteProperty -Name "HashCode" -value $HashCode
        $Data | Add-Member -MemberType NoteProperty -Name "URL" -value $File.ServerRelativeUrl
        $DataCollection += $Data

        $Count++
    }
    #$DataCollection
    #Get Duplicate Files
    $Duplicates = $DataCollection | Group-Object -Property HashCode | Where {$_.Count -gt 1}  | Select -ExpandProperty Group
    If($Duplicates.Count -gt 1)
    {
        $Duplicates | Out-GridView
    }
    Else
    {
        Write-host -f Yellow "No Duplicates Found!"
    }
}
Catch {
    write-host -f Red "Error:" $_.Exception.Message
}

However, this method does not work for Office documents like .docx, .pptx, .xlsx, etc. because the metadata for Office documents in SharePoint is stored within the document itself whereas for other document types the metadata is stored in the SharePoint content database. So, when you upload a same Office document twice, their metadata like "Created On" differs!

PowerShell to Find All Duplicate Files in a Site (Compare Hash, File Name and File Size)
This PowerShell script scans all files from all document libraries in a site and extracts the File Name, File Hash and Size parameters for comparison, Outputs a CSV report with all data.

#Load SharePoint CSOM Assemblies
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.dll"
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.Runtime.dll"

#Parameters
$SiteURL = "https://crescenttech.sharepoint.com"
$CSVPath = "C:\Temp\FilesInventory.csv"
#Array for Result Data
$DataCollection = @() 

#Get credentials to connect
$Cred = Get-Credential

Try {
    #Setup the Context
    $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
    $Ctx.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.UserName, $Cred.Password)

    #Get the Web
    $Web = $Ctx.Web
    $Lists = $Web.Lists
    $Ctx.Load($Web)
    $Ctx.Load($Lists)
    $Ctx.ExecuteQuery()

    #Iterate through Each List on the web
    ForEach($List in $Lists)
    {
        #Filter Lists
        If($List.BaseType -eq "DocumentLibrary" -and $List.Hidden -eq $False  -and $List.Title -ne "Site Pages")
        {
            #Get all List items from the library - Exclude "Folder" objects
            $Query = New-Object Microsoft.SharePoint.Client.CamlQuery
            $Query.ViewXml="<View Scope='RecursiveAll'><Query><Where><Eq><FieldRef Name='FSObjType'/><Value Type='Integer'>0</Value></Eq></Where></Query></View>"
            $ListItems = $List.GetItems($Query)
            $Ctx.Load($ListItems)
            $Ctx.ExecuteQuery()
    
            $Count=1
            ForEach($Item in $ListItems)
            {
                #Get the File from Item
                $File = $Item.File
                $Ctx.Load($File)
                $Ctx.ExecuteQuery()
                Write-Progress -PercentComplete ($Count / $ListItems.Count * 100) -Activity "Processing File $count of $($ListItems.Count) in $($List.Title) of $($Web.URL)" -Status "Scanning File '$($File.Name)'" 

                #Get The File Hash
                $Bytes = $Item.file.OpenBinaryStream()
                $Ctx.ExecuteQuery()
                $MD5 = New-Object -TypeName System.Security.Cryptography.MD5CryptoServiceProvider 
                $HashCode = [System.BitConverter]::ToString($MD5.ComputeHash($Bytes.Value)) 

                #Collect data        
                $Data = New-Object PSObject 
                $Data | Add-Member -MemberType NoteProperty -name "FileName" -value $File.Name
                $Data | Add-Member -MemberType NoteProperty -Name "HashCode" -value $HashCode
                $Data | Add-Member -MemberType NoteProperty -Name "URL" -value $File.ServerRelativeUrl
                $Data | Add-Member -MemberType NoteProperty -Name "FileSize" -value $File.Length        
                $DataCollection += $Data
                $Count++
            }
        }
    }    
    #Export All Data to CSV
    $DataCollection | Export-Csv -Path $CSVPath -NoTypeInformation
    Write-host -f Green "Files Inventory has been Exported to $CSVPath"

    #Get Duplicate Files by Grouping Hash code
    $Duplicates = $DataCollection | Group-Object -Property HashCode | Where {$_.Count -gt 1}  | Select -ExpandProperty Group
    Write-host "Duplicate Files Based on File Hashcode:"
    $Duplicates | Format-table -AutoSize

    #Group Based on File Name
    $FileNameDuplicates = $DataCollection | Group-Object -Property FileName | Where {$_.Count -gt 1}  | Select -ExpandProperty Group
    Write-host "Potential Duplicate Based on File Name:"
    $FileNameDuplicates| Format-table -AutoSize

    #Group Based on File Size
    $FileSizeDuplicates = $DataCollection | Group-Object -Property FileSize | Where {$_.Count -gt 1}  | Select -ExpandProperty Group
    Write-host "Potential Duplicates Based on File Size:"
    $FileSizeDuplicates| Format-table -AutoSize
}
Catch {
    write-host -f Red "Error:" $_.Exception.Message
}