uses sysinternals handle.exe to find/list the current open handles

Find-OpenHandle.ps1

function Find-OpenHandle([string]$Filter = '') {
    # handle.exe returns all the open files grouped by process as:
    #       ------------------------------------------------------------------------------
    #       System pid: 4 \<unable to open process>
    #         720: Section       \Win32kCrossSessionGlobals
    #       ------------------------------------------------------------------------------
    #       svchost.exe pid: 1208 NT AUTHORITY\SYSTEM
    #         198: File  (R-D)   C:\Windows\System32\en-US\svchost.exe.mui
    # the first line has the following fields:
    #       svchost.exe pid: 1208 NT AUTHORITY\SYSTEM
    #       ^^^^^^^^^^^      ^^^^ ^^^^^^^^^^^^^^^^^^^
    #       process name     |    process user
    #                        process id
    # the other lines have the following fields:
    #       198: File  (R-D)   C:\Windows\System32\en-US\svchost.exe.mui
    #       ^^^  ^^^^   ^^^    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    #    handle  type   |      path
    #                   attributes
    (
        (
            handle.exe -nobanner $Filter `
                | ForEach-Object {$_.Trim()} `
                | Where-Object {$_} `
                | Select-Object -Skip 1
        ) -join "`n" -split '-{10,}\n'
    ) `
    | ForEach-Object {
        $processLine, $handlesLines = $_ -split "`n"
        if ($processLine -notmatch '^(?<processName>.+?) pid: (?<processId>\d+) (?<processUser>.+)$') {
            throw "unable to parse process line $processLine"
        }
        $processName = $Matches['processName']
        $processId = $Matches['processId']
        $processUser = $Matches['processUser']
        @($handlesLines) | Where-Object {$_} | ForEach-Object {
            if ($_ -notmatch '^(?<handle>.+?): (?<type>.+?)(\s+\((?<attributes>.+?)\))?\s+(?<path>.+)$') {
                throw "unable to parse handle line $_"
            }
            New-Object PSObject -Property @{
                ProcessName = $processName
                ProcessId = $processId
                ProcessUser = $processUser
                Handle = $Matches['handle']
                Type = $Matches['type']
                Attributes = $Matches['attributes']
                Path = $Matches['path']
            }
        }
    }
}