PowerShellでFileSystemWatcherを使ってファイル変更を検知する方法

Id     Name            PSJobTypeName   State         HasMoreData     Location             Command
--     ----            -------------   -----         -----------     --------             -------
1      Watcher_Created                 NotStarted    False                                …
2      Watcher_Changed                 NotStarted    False                                …
3      Watcher_Deleted                 NotStarted    False                                …
4      Watcher_Renamed                 NotStarted    False                                …
5      Watcher_Error                   NotStarted    False                                …

モニタリング開始：C:\Logs
Ctrl+C で停止できます。停止時はイベント解除と Dispose() が実行されます。
[実際の日時] Created : C:\Logs\新規 テキスト ドキュメント.txt
[実際の日時] Renamed : C:\Logs\新規 テキスト ドキュメント.txt -> C:\Logs\test.txt
[実際の日時] Changed : C:\Logs\test.txt
[実際の日時] Deleted : C:\Logs\test.txt
モニタリング終了

$watchFolder = "C:\Logs"
$logFile = "C:\Temp\watch_log.txt"

# 監視対象フォルダーが存在するか確認
if (-not (Test-Path -LiteralPath $watchFolder -PathType Container)) {
    throw "監視対象フォルダーが存在しません: $watchFolder"
}

# ログの出力先フォルダーがなければ作成
$logDirectory = Split-Path -Path $logFile -Parent

if (-not (Test-Path -LiteralPath $logDirectory -PathType Container)) {
    New-Item -ItemType Directory -Path $logDirectory -Force -ErrorAction Stop | Out-Null
}

$watcher                       = New-Object System.IO.FileSystemWatcher
$watcher.Path                  = $watchFolder
$watcher.Filter                = "*.log"
$watcher.IncludeSubdirectories = $false
$watcher.NotifyFilter          = [System.IO.NotifyFilters]::LastWrite -bor [System.IO.NotifyFilters]::FileName

$action = {
    $info          = $Event.SourceEventArgs
    $targetLogFile = [string]$Event.MessageData
    $path          = $info.FullPath
    $type          = $info.ChangeType
    $time          = (Get-Date).ToString("yyyy-MM-dd HH:mm:ss")
    $entry         = "[$time] $type : $path"

    try {
        Add-Content -LiteralPath $targetLogFile -Value $entry -ErrorAction Stop
        Write-Host $entry
    }
    catch {
        Write-Warning "ログの書き込みに失敗しました: $($_.Exception.Message)"
    }
}

Register-ObjectEvent -InputObject $watcher -EventName "Created" -SourceIdentifier "WL_Created" -MessageData $logFile -Action $action | Out-Null
Register-ObjectEvent -InputObject $watcher -EventName "Changed" -SourceIdentifier "WL_Changed" -MessageData $logFile -Action $action | Out-Null
Register-ObjectEvent -InputObject $watcher -EventName "Deleted" -SourceIdentifier "WL_Deleted" -MessageData $logFile -Action $action | Out-Null

$watcher.EnableRaisingEvents = $true
Write-Host "監視中。ログ出力先: $logFile"
Write-Host "Ctrl+Cで停止します。"

try {
    while ($true) {
        Start-Sleep -Seconds 1
    }
}
finally {
    Unregister-Event -SourceIdentifier "WL_Created" -ErrorAction SilentlyContinue
    Unregister-Event -SourceIdentifier "WL_Changed" -ErrorAction SilentlyContinue
    Unregister-Event -SourceIdentifier "WL_Deleted" -ErrorAction SilentlyContinue

    $watcher.EnableRaisingEvents = $false
    $watcher.Dispose() 

    Write-Host "監視を終了しました。"
}

$srcFolder = "C:\Drop"
$dstFolder = "C:\Processed"

# サンプルをそのまま実行できるようにフォルダーを作成
foreach ($folder in @($srcFolder, $dstFolder)) {
    if (-not (Test-Path -LiteralPath $folder -PathType Container)) {
        New-Item -ItemType Directory -Path $folder -Force -ErrorAction Stop | Out-Null
    }
}

$watcher                       = New-Object System.IO.FileSystemWatcher
$watcher.Path                  = $srcFolder
$watcher.Filter                = "*.*"
$watcher.IncludeSubdirectories = $false
$watcher.NotifyFilter          = [System.IO.NotifyFilters]::FileName

$action = {
    $info        = $Event.SourceEventArgs
    $srcPath     = $info.FullPath
    $name        = $info.Name
    $destination = [string]$Event.MessageData
    $dstPath     = Join-Path -Path $destination -ChildPath $name

    # Created発生直後は書き込み中の場合があるため少し待つ
    Start-Sleep -Milliseconds 500

    try {
        Copy-Item -LiteralPath $srcPath -Destination $dstPath -Force -ErrorAction Stop
        Write-Host "コピー完了: $name"
    }
    catch {
        Write-Warning "コピー失敗: $name - $($_.Exception.Message)"
    }
}

Register-ObjectEvent -InputObject $watcher -EventName "Created" -SourceIdentifier "AC_Created" -MessageData $dstFolder -Action $action | Out-Null

$watcher.EnableRaisingEvents = $true

Write-Host "自動コピー監視中: $srcFolder -> $dstFolder"
Write-Host "Ctrl+Cで停止します。"

try {
    while ($true) {
        Start-Sleep -Seconds 1
    }
}
finally {
    Unregister-Event -SourceIdentifier "AC_Created" -ErrorAction SilentlyContinue
    $watcher.EnableRaisingEvents = $false
    $watcher.Dispose()
    Write-Host "自動コピー監視を終了しました。"
}

Start-Sleep -Milliseconds 500

function Wait-FileReady {
    param(
        [Parameter(Mandatory)]
        [string]$LiteralPath,

        [int]$RetryCount = 20,

        [int]$IntervalMilliseconds = 500
    )

    $lastSignature = $null

    for ($attempt = 1; $attempt -le $RetryCount; $attempt++) {
        # フォルダーの場合は処理しない
        if ([System.IO.Directory]::Exists($LiteralPath)) {
            return $false
        }

        # ファイルがまだ存在しない場合は次の確認まで待つ
        if (-not [System.IO.File]::Exists($LiteralPath)) {
            if ($attempt -lt $RetryCount) {
                Start-Sleep -Milliseconds $IntervalMilliseconds
            }

            continue
        }

        $stream    = $null
        $signature = $null

        try {
            # 他のプロセスが使用していないか確認
            $stream = [System.IO.File]::Open(
                $LiteralPath,
                [System.IO.FileMode]::Open,
                [System.IO.FileAccess]::Read,
                [System.IO.FileShare]::None
            )

            $lastWriteTime = [System.IO.File]::GetLastWriteTimeUtc(
                $LiteralPath
            ).Ticks

            # ファイルサイズと最終更新日時を組み合わせて比較
            $signature = "{0}:{1}" -f $stream.Length, $lastWriteTime
        }
        catch [System.UnauthorizedAccessException] {
            throw "ファイルを読み取る権限がありません: $LiteralPath"
        }
        catch [System.IO.IOException] {
            # 書き込み中や他プロセスによる使用中の場合
            $lastSignature = $null
        }
        finally {
            if ($null -ne $stream) {
                $stream.Dispose()
            }
        }

        if ($null -ne $signature) {
            # 2回続けて状態が変わっていなければ処理可能と判断
            if ($signature -eq $lastSignature) {
                return $true
            }

            $lastSignature = $signature
        }

        if ($attempt -lt $RetryCount) {
            Start-Sleep -Milliseconds $IntervalMilliseconds
        }
    }

    return $false
}

$settings = @{
    Destination          = $dstFolder
    RetryCount           = 20
    IntervalMilliseconds = 500
}

$action = {
    function Wait-FileReady {
        param(
            [Parameter(Mandatory)]
            [string]$LiteralPath,

            [int]$RetryCount = 20,

            [int]$IntervalMilliseconds = 500
        )

        $lastSignature = $null

        for ($attempt = 1; $attempt -le $RetryCount; $attempt++) {
            if ([System.IO.Directory]::Exists($LiteralPath)) {
                return $false
            }

            if (-not [System.IO.File]::Exists($LiteralPath)) {
                if ($attempt -lt $RetryCount) {
                    Start-Sleep -Milliseconds $IntervalMilliseconds
                }

                continue
            }

            $stream    = $null
            $signature = $null

            try {
                $stream = [System.IO.File]::Open(
                    $LiteralPath,
                    [System.IO.FileMode]::Open,
                    [System.IO.FileAccess]::Read,
                    [System.IO.FileShare]::None
                )

                $lastWriteTime = [System.IO.File]::GetLastWriteTimeUtc(
                    $LiteralPath
                ).Ticks

                $signature = "{0}:{1}" -f $stream.Length, $lastWriteTime
            }
            catch [System.UnauthorizedAccessException] {
                throw "ファイルを読み取る権限がありません: $LiteralPath"
            }
            catch [System.IO.IOException] {
                $lastSignature = $null
            }
            finally {
                if ($null -ne $stream) {
                    $stream.Dispose()
                }
            }

            if ($null -ne $signature) {
                if ($signature -eq $lastSignature) {
                    return $true
                }

                $lastSignature = $signature
            }

            if ($attempt -lt $RetryCount) {
                Start-Sleep -Milliseconds $IntervalMilliseconds
            }
        }

        return $false
    }

    $info     = $Event.SourceEventArgs
    $settings = $Event.MessageData
    $srcPath  = $info.FullPath
    $name     = $info.Name

    # フォルダー作成イベントは対象外
    if ([System.IO.Directory]::Exists($srcPath)) {
        return
    }

    try {
        $ready = Wait-FileReady `
            -LiteralPath $srcPath `
            -RetryCount $settings.RetryCount `
            -IntervalMilliseconds $settings.IntervalMilliseconds

        if (-not $ready) {
            Write-Warning "ファイルの書き込み完了を確認できませんでした: $srcPath"
            return
        }

        $dstPath = Join-Path `
            -Path $settings.Destination `
            -ChildPath $name

        Copy-Item `
            -LiteralPath $srcPath `
            -Destination $dstPath `
            -Force `
            -ErrorAction Stop

        Write-Host "コピー完了: $name"
    }
    catch {
        Write-Warning "コピー失敗: $name - $($_.Exception.Message)"
    }
}

Register-ObjectEvent `
    -InputObject $watcher `
    -EventName "Created" `
    -SourceIdentifier "AC_Created" `
    -MessageData $settings `
    -Action $action |
    Out-Null

$watcher.Filter                = "*.log"
$watcher.IncludeSubdirectories = $false
$watcher.NotifyFilter          = [System.IO.NotifyFilters]::FileName `
    -bor [System.IO.NotifyFilters]::LastWrite

# 例：内部バッファを16KBに設定
$watcher.InternalBufferSize = 16384

Register-ObjectEvent `
    -InputObject $watcher `
    -EventName "Error" `
    -SourceIdentifier "Watcher_Error" `
    -Action {
        $exception = $Event.SourceEventArgs.GetException()

        Write-Warning "監視エラーが発生しました: $($exception.Message)"
    } |
    Out-Null

Unregister-Event `
    -SourceIdentifier "Watcher_Error" `
    -ErrorAction SilentlyContinue

$watchFolder = "C:\Drop"
$dstFolder   = "C:\Processed"

if (-not (Test-Path -LiteralPath $watchFolder -PathType Container)) {
    throw "監視対象フォルダーが存在しません: $watchFolder"
}

if (-not (Test-Path -LiteralPath $dstFolder -PathType Container)) {
    New-Item `
        -ItemType Directory `
        -Path $dstFolder `
        -Force `
        -ErrorAction Stop |
        Out-Null
}

$testFile = Join-Path `
    -Path $dstFolder `
    -ChildPath ".filesystemwatcher_write_test_$PID.tmp"

try {
    Set-Content `
        -LiteralPath $testFile `
        -Value "write test" `
        -ErrorAction Stop

    Remove-Item `
        -LiteralPath $testFile `
        -Force `
        -ErrorAction Stop
}
catch {
    throw "コピー先へ書き込めません: $($_.Exception.Message)"
}

while ($true) {
    Start-Sleep -Seconds 1
}

try {
    while ($true) {
        Start-Sleep -Seconds 1
    }
}
finally {
    Unregister-Event `
        -SourceIdentifier "Watcher_Created" `
        -ErrorAction SilentlyContinue

    Unregister-Event `
        -SourceIdentifier "Watcher_Changed" `
        -ErrorAction SilentlyContinue

    Unregister-Event `
        -SourceIdentifier "Watcher_Deleted" `
        -ErrorAction SilentlyContinue

    Unregister-Event `
        -SourceIdentifier "Watcher_Renamed" `
        -ErrorAction SilentlyContinue

    Unregister-Event `
        -SourceIdentifier "Watcher_Error" `
        -ErrorAction SilentlyContinue

    $watcher.EnableRaisingEvents = $false
    $watcher.Dispose()

    Write-Host "モニタリング終了"
}