Watch file for changes and run command with powershell

Here is an example I have found in my snippets. Hopefully it is a little bit more comprehensive.

First you need to create a file system watcher and subsequently you subscribe to an event that the watcher is generating. This example listens for “Create” events, but could easily be modified to watch out for “Change”.

$folder = "C:\Users\LOCAL_~1\AppData\Local\Temp\3"
$filter = "*.LOG"
$Watcher = New-Object IO.FileSystemWatcher $folder, $filter -Property @{ 
    IncludeSubdirectories = $false
    NotifyFilter = [IO.NotifyFilters]'FileName, LastWrite'
}
$onCreated = Register-ObjectEvent $Watcher -EventName Created -SourceIdentifier FileCreated -Action {
   $path = $Event.SourceEventArgs.FullPath
   $name = $Event.SourceEventArgs.Name
   $changeType = $Event.SourceEventArgs.ChangeType
   $timeStamp = $Event.TimeGenerated
   Write-Host "The file '$name' was $changeType at $timeStamp"
   Write-Host $path
   #Move-Item $path -Destination $destination -Force -Verbose
}

I will try to narrow this down to your requirements.

If you run this as part of your “profile.ps1” script you should read The Power of Profiles which explains the different profile scripts available and more.

Also, you should understand that waiting for a change in a folder can’t be run as a function in the script. The profile script has to be finished, for your PowerShell session to start. You can, however use a function to register an event.

What this does, is register a piece of code, to be executed every time an event is triggered. This code will be executed in the context of your current PowerShell host (or shell) while the session remains open. It can interact with the host session, but has no knowledge of the original script that registered the code. The original script has probably finished already, by the time your code is triggered.

Here is the code:

Function Register-Watcher {
    param ($folder)
    $filter = "*.*" #all files
    $watcher = New-Object IO.FileSystemWatcher $folder, $filter -Property @{ 
        IncludeSubdirectories = $false
        EnableRaisingEvents = $true
    }

    $changeAction = [scriptblock]::Create('
        # This is the code which will be executed every time a file change is detected
        $path = $Event.SourceEventArgs.FullPath
        $name = $Event.SourceEventArgs.Name
        $changeType = $Event.SourceEventArgs.ChangeType
        $timeStamp = $Event.TimeGenerated
        Write-Host "The file $name was $changeType at $timeStamp"
    ')

    Register-ObjectEvent $Watcher -EventName "Changed" -Action $changeAction
}

 Register-Watcher "c:\temp"

After running this code, change any file in the “C:\temp” directory (or any other directory you specify). You will see an event triggering execution of your code.

Also, valid FileSystemWatcher events you can register are “Changed”, “Created”, “Deleted” and “Renamed”.