Recursively download all files from a SharePoint Document Library folder using the Microsoft Graph PowerShell SDK.

Start-MgSPOLibraryDownload.ps1

<#
    .SYNOPSIS
        This script will download all files from a specified SharePoint Document Library path.
    .EXAMPLE
        $ScriptParams = @{
            SharePointTenant            = 'mycompany.sharepoint.com'
            SiteName                    = 'mysite/my subsite'
            DocumentLibraryName         = 'Documents'
            DocumentLibraryPath         = 'my directory/my subdirectory'
            LastModifiedDate            = (Get-Date '2024-01-01')
        }
        Start-MgSPOLibraryDownload @ScriptParams
#>
[CmdletBinding()]
param (
    [Parameter(Mandatory)]
    [string]$SharePointTenant,

    [Parameter(Mandatory)]
    [string]$SiteName,

    [Parameter(Mandatory)]
    [string]$DocumentLibraryName,

    [Parameter(Mandatory)]
    [string]$DocumentLibraryPath,
    
    # Only process files modified after this date
    [Parameter()]
    [datetime]$LastModifiedDate
)
#region Init
$ErrorActionPreference = 'Stop'

# Define the base URL for Microsoft Graph API
$GraphEndpoint = 'https://graph.microsoft.com/v1.0'

# Define SharePoint details
$DocumentLibraryFullPath = "$SiteName/$DocumentLibraryName/$DocumentLibraryPath"
#endregion Init

#region Login
try {
    # Connect to Microsoft Graph with the required API Scope
    Write-Output 'Connect to Microsoft Graph'
    Connect-MgGraph -Scopes 'Sites.Read.All' -NoWelcome
} catch {
    Write-Error "Failed to connect to Microsoft Graph: $_"
}
#endregion Login

# region Functions
function Get-SPODriveItemsRecursively {
    param(
        [Parameter(Mandatory)]
        [string] $GraphEndpoint,

        [Parameter(Mandatory)]
        [string]$FolderId,

        [Parameter(Mandatory)]
        [string]$DriveId
    )

    try {
        # Get the child items of the specified folder
        Write-Verbose "Getting child items of folder [$FolderId]"
        $DriveItems = Invoke-MgGraphRequest -Method GET -Uri "$GraphEndpoint/drives/$DriveId/items/$FolderId/children"
    } catch {
        Write-Error "Failed to get child items in folder [$FolderId]: $_"
    }

    foreach ($Item in $DriveItems.value) {
        if ($Item.folder) {
            # Recursively get the children of the folder
            Get-SPODriveItemsRecursively -GraphEndpoint $GraphEndpoint -FolderId $Item.id -DriveId $DriveId
        } else {
            $Item
        }
    }
}
#endregion Functions

#region GetDriveId
try {
    # Get SharePoint site details
    Write-Output "Get SharePoint site [$SharePointTenant/$SiteName] details"
    $Site = Invoke-MgGraphRequest -Method GET -Uri "$GraphEndpoint/sites/$SharePointTenant`:/sites/$SiteName"
} catch {
    Write-Error "Failed to get SharePoint site [$SharePointTenant/$SiteName] details using Microsoft Graph: $_"
}

# Extract the Site ID and SubSite ID from the Site details
$SiteId = $Site.id.Split(',')[1]
$SubSiteId = $Site.id.Split(',')[2]

try {
    # Get the Drives (Document Libraries) in the Site
    Write-Output "Get a list of Document Libraries in SharePoint site [$SiteName]"
    $SiteDrives = Invoke-MgGraphRequest -Method GET -Uri "$GraphEndpoint/sites/$SiteId/sites/$SubSiteId/drives"
} catch {
    Write-Error "Failed to get a list of Document Libraries in SharePoint site [$SiteName]: $_"
}

# Find the Drive ID of the specified Document Library
$DriveId = $SiteDrives.value | Where-Object { $_.name -eq $DocumentLibraryName } | Select-Object -ExpandProperty Id
#endregion GetDriveId

#region GetSharePointItems
try {
    # Get the details of the specified path in the Document Library
    Write-Output "Get the Item ID of the Document Library path [$DocumentLibraryFullPath]"
    $DocumentLibraryPathId = Invoke-MgGraphRequest -Method GET -Uri "$GraphEndpoint/drives/$DriveId/root:/$DocumentLibraryPath" | Select-Object -ExpandProperty Id
} catch {
    Write-Error "Failed to get the Item ID of the Document Library path [$DocumentLibraryFullPath]: $_"
}

# Recursively get all items in the specified Document Library path
Write-Output "Recursively retrieve all items in the SharePoint Document Library path [$DocumentLibraryFullPath]"
$DocumentLibraryPathItems = Get-SPODriveItemsRecursively -GraphEndpoint $GraphEndpoint -FolderId $DocumentLibraryPathId -DriveId $DriveId

# Filter folders out of the list of items to process
$DocumentLibraryFiles = $DocumentLibraryPathItems | Where-Object { $_.file }

# Filter files based on LastModifiedDateTime if a cutoff date is provided
if ($LastModifiedDate) {
    $DocumentLibraryFiles = $DocumentLibraryFiles | Where-Object { $_.lastModifiedDateTime -gt $LastModifiedDate }
}
Write-Output "Processing [$($DocumentLibraryFiles.Count)] files in the SharePoint Document Library path [$DocumentLibraryFullPath]"
#endregion GetSharePointItems

#region DownloadFiles
$CompletedFiles = 0
foreach ($DocumentLibraryFile in $DocumentLibraryFiles) {
    # Parse SharePoint Document Library path
    $SharePointFilePath = $DocumentLibraryFile.parentReference.path.split('/root:/')[1]

    # Define local path for the file
    $LocalPath = "$($env:TEMP)\$($DocumentLibraryFile.id)_$($DocumentLibraryFile.name)"

    Write-Output "Processing [$([math]::Round($DocumentLibraryFile.Size / 1kb, 2)) KB] file [$($DocumentLibraryFile.name) ($($DocumentLibraryFile.id))]"
    try {
        # Download file from SharePoint
        Invoke-RestMethod -Uri $DocumentLibraryFile.'@microsoft.graph.downloadUrl' -OutFile $LocalPath -ProgressAction SilentlyContinue
        $CompletedFiles++
    } catch {
        Write-Warning "Failed to download file [$SharePointFilePath/$($DocumentLibraryFile.name) ($($DocumentLibraryFile.id))] from SharePoint Online: $_"
    }
}
#endregion DownloadFiles

Write-Output "Complete. Downloaded [$CompletedFiles] files from SharePoint Online."