Why Does [System.IO.Directory]::EnumerateDirectories() Only Throw the First UnauthorizedAccessException in PowerShell?

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I use [System.IO.Directory]::EnumerateDirectories() in PowerShell instead of Get-ChildItem because it's faster.
However, I've noticed that when a System.UnauthorizedAccessException is encountered, only the first exception is thrown, and then the enumeration stops.

Issue example

Is this behavior a bug, or am I missing something in how I should be handling these exceptions?

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Answers 2

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2 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

The behavior you're seeing is by design. When you call [System.IO.Directory]::EnumerateDirectories(), the enumeration is lazy. That means the underlying API starts returning results and only throws an exception when it first encounters a directory it can't access. It doesn't aggregate multiple exceptions—it simply throws the first one it hits.

If you want to process as many entries as possible (and handle exceptions individually), you'll need to wrap your enumeration logic in a try/catch block for each directory access. For example, you could use a recursive method that catches exceptions at each level.

Here's a simple example in PowerShell to illustrate the idea:

POWERSHELL
function Get-AllDirectories {
    param (
        [string]$Root
    )

    $directories = @()

    try {
        # This is a lazy enumerable.
        $subDirs = [System.IO.Directory]::EnumerateDirectories($Root)
    }
    catch {
        Write-Warning "Access denied or error accessing $Root: $_"
        return
    }

    foreach ($dir in $subDirs) {
        $directories += $dir
        # Recursively process subdirectories
        $directories += Get-AllDirectories -Root $dir
    }
    return $directories
}

# Usage
Get-AllDirectories -Root "C:\Your\Path"

In this example, if an UnauthorizedAccessException occurs when trying to enumerate a specific directory, it is caught and a warning is issued. This way, you avoid halting the entire operation when one directory is inaccessible.

So, to summarize: you're not doing anything wrong, and it's not a bug—the method only throws the first exception encountered because of its lazy iterator design.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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Answer by JovianScientist535 • 1 month ago

Not a bug, it's the expected behavior of a .NET class method, when there is an error it throws, thus ending the enumeration.

A very easy way to demo this without needing to compile C# code:

POWERSHELL
# NOTE: If you were to use the workaround shown for PowerShell 5.1
#       using the `while` loop you could enumerate this completely.

$enumerable = [System.Linq.Enumerable]::Select(
    [System.Linq.Enumerable]::Range(0, 10),
    [System.Func[int, int]] {
        if ($args[0] -ne 5) { return $args[0] }
        throw 'woops' })

foreach ($i in $enumerable) { $i }

The concept of a non-terminating error only exists for PowerShell commands, however there are workarounds for your issue.

In PowerShell 7+, the easiest way to handle it, is to use the EnumerationOptions class:

POWERSHELL
# NOTE:
#    - Sets `IgnoreInaccessible` to `true` by default
#    - By default skips Hidden and System. To not skip those use:
#      `AttributesToSkip = [System.IO.FileAttributes]::None`  

[System.IO.Directory]::EnumerateDirectories(
    'E:\test2', '*',
    [System.IO.EnumerationOptions]@{ RecurseSubdirectories = $true })

In PowerShell 5.1, the class used above doesn't exist in .NET Framework, thus more work is needed. What you can do here is to manually enumerate your enumerable:

POWERSHELL
$enumerable = [System.IO.Directory]::EnumerateDirectories(
    'E:\test2', '*',
    [System.IO.SearchOption]::AllDirectories)

$enumerator = $enumerable.GetEnumerator()

while ($true) {
    try {
        # we're done if this is true
        if (-not $enumerator.MoveNext()) {
            break
        }

        $enumerator.Current
    }
    catch {
        # PowerShell always wraps method exceptions in `MethodInvocationException`,
        # it's safe to use `.InnerException` in this case
        Write-Error -Exception $_.Exception.InnerException
    }
}

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Why Does [System.IO.Directory]::EnumerateDirectories() Only Throw the First UnauthorizedAccessException in PowerShell?

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