Powershell: Why would Move-Item on a file result in the target file being 0 bytes?

Question

I notice that this code:

Move-Item $path -Destination $destination -Force -Verbose

Often results in the destination file being 0 bytes (where the source file is say 90K). I can see the file size is 0 a couple of ways:

• In interactive File Explorer, it shows as 0 bytes
• When I run a file converter on the file, it throws an error (because the file is 0 bytes)

Historically, my code did not check for file size. I just started noticing the problem intermittently. Now I have checks, but that isn't perfect. Would prefer for it to be reliable!

The code works %99 of the time. Permissions are not the issue. (It is 100% local operations, on simple directories. Single file operations. Zero remote anything. This is c:\foo\bar.txt to c:\foo2\bar.txt)

How to chase/resolve?

Answer 1

The issue is that the file was being downloaded by a web browser, and in some cases there is a delay for the file to be written out.

At least with firefox, there is an interesting behavior, downloading foo.wav:

gooked-123132asdfas.wav.part // appears first on file system foo.wav // appears, with file size either correct or 0 foo.wav // shows up with contents (if it started as zero

There can be 150+ msec between each of those steps. Even 350+.

The solution was:

       $i = 1 
       while (((Get-Item $path).length -eq 0kb) -and  ([System.IO.File]::Exists($path))) 
            {
            # This loop is actually constructive, because it forces the process to wait until the 
            # the file has been written out....
            Write-Host "file size of $path is " (Get-Item $path).length
            Start-Sleep -Seconds .1 
            
            $i++
                # If the file stays at 0 bytes, get out of the loop and forget this file...
                # means there is a download issue. Exit the whole larger block.
            if ($i=11) {continue processingLoop}
         }

This is done prior to the Move-Item call, and the whole thing gets a lot more reliable. (Well, perfectly reliable so far.)