PowerShell to Delete All Files in SharePoint Document Library

Requirement: Delete All Files in SharePoint Document Library using PowerShell

SharePoint PowerShell to Delete All Documents
To delete all documents in SharePoint library, use this PowerShell:

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

#Function to Delete all files in a Folder    
Function Delete-AllFilesFromLibrary([Microsoft.SharePoint.SPFolder]$Folder)
{
    #Delete All Files in the Folder
    Foreach ($File in @($Folder.Files))  
    {
        #Delete the file
        $File.Recycle() | Out-Null

        Write-host -f Green "Deleted File '$($File.Name)' from '$($File.ServerRelativeURL)'"
    }

    #Delete files in Sub-folders
    Foreach ($SubFolder in $Folder.SubFolders | where {$_.Name -ne "Forms"})
    {
        #Call the function recursively
        Delete-AllFilesFromLibrary($SubFolder)
    }
}

#Get the Web and Library
$Web = Get-SPWeb "http://intranet.crescent.com/sales"
$Library = $Web.Lists.TryGetList("Documents")

#Call the function to Delete all files in the Library
Delete-AllFilesFromLibrary $Library.RootFolder

Please note, this script sends all files from all folders-sub folders in a library to recycle bin. If you want to permanently delete files use: $File.Delete() method instead of $File.Recycle().

PowerShell to Delete All Items from SharePoint Library
The above script deletes all files - without deleting folders and sub-folders. What if you want to remove all files and folders?

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

#Function to Delete all files in a Folder    
Function Delete-AllFilesFromLibrary([Microsoft.SharePoint.SPFolder]$Folder)
{
    #Delete All Files in the Folder
    Foreach ($File in @($Folder.Files))  
    {
        #Delete the file
        $File.Delete() | Out-Null

        Write-host -f Green "Deleted File '$($File.Name)' from '$($File.ServerRelativeURL)'"
    }

    #Delete files in Sub-folders
    Foreach ($SubFolder in $Folder.SubFolders | where {$_.Name -ne "Forms"})
    {
        #Call the function recursively
        Delete-AllFilesFromLibrary($SubFolder)
    }

    #Delete folders
    ForEach ($SubFolder in @($Folder.SubFolders))
    {
        #Exclude "Forms" and Hidden folders
        If(($SubFolder.Name -ne "Forms") -and (-Not($SubFolder.Name.StartsWith("_"))))
        {
            #Delete the Sub-Folder
            $SubFolder.Delete() | Out-Null
            Write-host -f Green "Deleted Folder '$($SubFolder.Name)' from '$($SubFolder.ServerRelativeUrl)'"
        }
    }
}

#Get the Web and Library
$Web = Get-SPWeb "http://intranet.crescent.com/sales"
$Library = $Web.Lists.TryGetList("Documents")

#Call the function to Delete all files in the Library
Delete-AllFilesFromLibrary $Library.RootFolder 

To delete all files in SharePoint Online, refer: PowerShell to Bulk Delete Files in SharePoint Online