PowerShell Remove-Item not waiting

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不知归路
不知归路 2021-01-13 05:20

If have this piece of code

if(Test-Path -Path $OUT) 
{ 
    Remove-Item $OUT -Recurse 
}
New-Item -ItemType directory -Path $OUT

Sometimes

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4条回答
  • 2021-01-13 05:49

    The Remove-Item command has a known issue.

    Try this instead:

    if (Test-Path $OUT) 
    { 
        # if exists: empty contents and reuse the directory itself
        Get-ChildItem $OUT -Recurse | Remove-Item -Recurse
    }
    else
    {
        # else: create
        New-Item -ItemType Directory -Path $OUT
    }
    

    Note:

    • The Get-ChildItem command only finds non-hidden files and subdirectories, so emptying out the target directory may not be complete; to include hidden items too, add -Force.

    • Similarly, add -Force to -RemoveItem to force removal of files that have the read-only attribute set.

      • Without -Force, emptying may again be incomplete, but you'll get non-terminating errors in this case; if you want to treat them as terminating errors, add -ErrorAction Stop too.
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  • 2021-01-13 05:53

    Update: Starting with Windows 10 version 1909, (at least) build 18363.657 (I don't know that Windows Server version and build that corresponds to; run winver.exe to check your version and build), the DeleteFile Windows API function now exhibits synchronous behavior, which implicitly solves the problems with PowerShell's Remove-Item and .NET's System.IO.File.Delete / System.IO.Directory.Delete (but, curiously, not with cmd.exe's rd /s).


    Remove-Item -Recurse is unexpectedly asynchronous, ultimately because the Windows API methods for file and directory removal are inherently asynchronous and Remove-Item doesn't account for that.

    This intermittently, unpredictably manifests in one of two ways:

    • Your case: recreating a removed directory immediately after removal can fail, because the removal may not have completed yet by the time re-creation is attempted.

    • More typically: Removing a nonempty directory itself can fail, if removal of a subdirectory or file hasn't completed yet by the time an attempt is made to remove the parent directory - this is demonstrated in the ServerFault answer marsze links to.

    A potential workaround is to reuse an existing directory by emptying it - instead of deleting and recreating it.

    However, emptying the directory with Get-ChildItem $OUT -Recurse | Remove-Item -Recurse is also susceptible to intermittent failures, though likely less often.

    The problem not only affects PowerShell's Remove-Item, but also cmd.exe's rd /s as well as .NET's [System.IO.Directory]::Delete():

    As of Windows PowerShell v5.1 / PowerShell Core 6.2.0-preview.1 / cmd.exe 10.0.17134.407 / .NET Framework 4.7.03056, .NET Core 2.1, neither Remove-Item, nor rd /s, nor [System.IO.Directory]::Delete() work reliably, because they fail to account for the asynchronous behavior of the Windows API file/directory-removal functions:

    • PowerShell Core bug report
    • cmd.exe bug report
    • .NET Core bug report

    For a custom PowerShell function that provides a reliably synchronous workaround, see this answer.

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  • 2021-01-13 05:54

    For completeness' sake: You can also use the safe and fast .NET methods:

    if ([System.IO.Directory]::Exists($OUT)) {
        [System.IO.Directory]::Delete($OUT, $true)
    }
    [System.IO.Directory]::CreateDirectory($OUT)
    

    Note:

    Depending on where you get the value of $OUT you might want to convert it to a full path first to make sure the .NET methods remove the correct directory (see @mklement0`s comment):

    $fullPath = Convert-Path $OUT
    
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  • 2021-01-13 05:55

    If you type Get-Help Remove-Item -Detailed you'll see:

    Example 4: Delete files in subfolders recursively
    PS C:\>Get-ChildItem * -Include *.csv -Recurse | Remove-Item
    
    This command deletes all of the CSV files in the current folder and all subfolder recursively.
    

    Because the Recurse parameter in Remove-Item has a known issue, the command in this example uses Get-ChildItem to get the desired files, and then uses the pipeline operator to pass them to Remove-Item .

    Do what specification recommends:

    if(Test-Path -Path $OUT) 
    { 
        Get-ChildItem $OUT -Recurse | Remove-Item
    }
    New-Item -ItemType directory -Path $OUT
    
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