SharePoint Online: Rename Files in Document Library using PowerShell

Requirement: Rename files in SharePoint document library using PowerShell
How to Rename a Document in SharePoint Online?
Renaming a file in the SharePoint Online document library is pretty straight forward. The quickest way to rename a document is:

• Right-click on your desired File and select Choose the Rename option.
  
• You can also rename a document in SharePoint by selecting the file >> Click on three little dots in the toolbar and then click on the "Rename" button. Provide a new name to the file in the Rename pop-up and click Save.
  

SharePoint Online also provides rename options through properties pane and by opening the file in Office web apps!

PowerShell CSOM Script to rename a file in SharePoint Online:

#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"
  
#Set Variables for Site URL, Old File Name and New File Name
$SiteURL= "https://crescent.sharepoint.com/sites/sales/"
$OldFileURL="/sites/Sales/Documents/Legal.docx"
$NewFileURL="/sites/Sales/Documents/LegalTemplate.docx"

#Setup Credentials to connect
$Cred = Get-Credential
$Cred = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.UserName,$Cred.Password)

Try {
    #Setup the context
    $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
    $Ctx.Credentials = $Cred

    #Rename the File
    $File = $Ctx.Web.GetFileByServerRelativeUrl($OldFileURL) 
    $File.MoveTo($NewFileURL, [Microsoft.SharePoint.Client.MoveOperations]::Overwrite) 
    $Ctx.ExecuteQuery()

    write-host -f Green "File Renamed successfully!"
}
Catch {
    write-host -f Red "Error Renaming File!" $_.Exception.Message
}

This script renames the given document to new name. How about renaming all files from a SharePoint online document library?

SharePoint online rename files in bulk using PowerShell:
Say in SharePoint online, you want to rename all documents which has a specific string in their names. 

#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"
  
#Set Variables for Site URL, Library Name and Item ID
$SiteURL= "https://crescent.sharepoint.com/sites/sales/"
$LibraryName="Documents"
$OldString="National"
$NewString="Crescent"

#Setup Credentials to connect
$Cred = Get-Credential
$Cred = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.UserName,$Cred.Password)

Try {
    #Setup the context
    $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
    $Ctx.Credentials = $Cred

    #Get the web and Library
    $Web=$Ctx.Web
    $List=$web.Lists.GetByTitle($LibraryName)

    #Get all items
    $Query = [Microsoft.SharePoint.Client.CamlQuery]::CreateAllItemsQuery()
    $ListItems = $List.GetItems($Query)
    $Ctx.Load($ListItems)
    $Ctx.ExecuteQuery()

    #Rename each file matching given old string
    Foreach($Item in $ListItems)
    {
        #Replace string in the File Name
        if($Item["FileRef"].ToString().Contains($OldString))
        {
            $CurrentURL=$Item["FileRef"].ToString()
            $NewURL = $CurrentURL.Replace($OldString,$NewString) 
            $Item.File.MoveTo($NewURL, [Microsoft.SharePoint.Client.MoveOperations]::Overwrite) 
            $ctx.ExecuteQuery()
            Write-host -f Green "Renamed: "$CurrentURL
        }
    }
}
Catch {
    write-host -f Red "Error Renaming File!" $_.Exception.Message
} 

SharePoint Online: Rename a File using PnP PowerShell

#Config Variables
$SiteURL = "https://crescenttech.sharepoint.com/sites/marketing"
$FileURL= "Shared Documents/Active/Office 365 Proposal.pdf"
$NewFileName ="Office 365 Proposal V2.pdf"

#Connect to PnP Online
Connect-PnPOnline -Url $SiteURL -Credentials (Get-Credential)

#Rename the File
Rename-PnPFile -SiteRelativeUrl $FileURL -TargetFileName $NewFileName -Force

Use "-OverwriteIfAlreadyExists" switch to perform rename and replace the original file, if exists! Also, you can use "-ServerRelativeUrl" parameter to provide a server relative URL of the source file.

Similarly, we can rename all files in a document library  using PnP PowerShell, as:

#Config Variables
$SiteURL = "https://crescent.sharepoint.com/sites/marketing"
$LibraryName = "Documents"
 
#Connect to PnP Online
Connect-PnPOnline -Url $SiteURL -Credentials (Get-Credential)

#Get All Files from the document library
$Files = Get-PnPListItem -List $LibraryName -PageSize 1000 | Where {$_["FileLeafRef"] -like "*.*"}
 
#Loop through each File
Write-host -f Green "Number of Files Found:"$Files.Count
ForEach($File in $Files)
{  
    Write-Host ("Renaming File '{0}' at {1}" -f $File["FileLeafRef"], $File["FileRef"])
    #Rename File
    Rename-PnPFile -ServerRelativeUrl $File["FileRef"] -TargetFileName "Old_$($File['FileLeafRef'])" -OverwriteIfAlreadyExists -Force
}