July 16, 2020

How to Monitor a Windows Folder for New Files and Take Action – CloudSavvy IT

Documents are in a constant state of flux on any functioning method. Sometimes they get made, at times they get deleted, sometimes they get modified, and all those are all usual issues for an functioning procedure to do. In some cases when a file gets transformed, it can trigger instability in another application that relies upon on it, this sort of as modifying a port range in a homes file, a parameter in a deployment manifest, or even fixing code in manufacturing without going via resource regulate.

As section of running these running devices, engineers need to have a way to observe what comes about to these important files and take motion when one thing does. Enter the .Internet FileSystemWatcher class and PowerShell.

In .Net and .Net Main, FileSystemWatcher is a course that life in the Procedure.IO namespace and screens information. In PowerShell, this can be quite useful, specifically when it is mixed with other PowerShell capabilities.

Instantiating the FileSystemWatcher

Instantiate this course in PowerShell by operating $watcher = New-Item Procedure.IO.FileSystemWatcher. After you do, you are going to will need to inform it which folder to observe. You do this by environment the Path parameter on the FileSystemWatcher item to the path of whichever folder you want it to enjoy. If you have a folder on Home windows known as WatchThisFolder less than C:, you would established the FileSystemWatcher to that by working $watcher.Path = 'C:WatchThisFolder'.

Since this class is also in .Web Main, you can do all this on a Linux or Mac OS technique the exact way you would on a Windows process. For case in point, if you experienced a folder on Ubuntu Linux referred to as WatchThisFolder below your existing user directory, you would run $watcher.Path = '/residence/ubuntu/WatchThisFolder'.

The relaxation of the code samples in this article perform on possibly platform without having any changes.

Triggering Events from the FileSystemWatcher

Now that you have a new FileSystemWatcher item, you can choose a look under the hood and test to figure it out. To see the precise varieties of file procedure situations that the FileSystemWatcher is viewing for, enter $watcher | Get-Member -MemberType Occasion. Get-Member shows all the things that the item passed into it consists of, and by including the MemberType filter, you can see a sure group, in this situation, functions.

People occasions are:

  • Adjusted
  • Made
  • Deleted
  • Disposed
  • Mistake
  • Renamed

When one or a lot more of these FileSystemWatcher occasions is detected at the route the item is established to observe, the watcher item raises an external occasion, for which you can define actions.

Now that the watcher item knows what to check out, and you know what situations it’s seeing for, you need to established it to raise an party when an motion is detected. Do this by running $watcher.EnableRaisingEvents = $real. Believe of this flag as an on/off swap for $watcher : If the change is off, nothing is heading to take place if any changes are designed. You can also explain to it to glance at data files and folders nested beneath the one particular set in the path by changing the IncludeSubdirectories flag to real in the identical way you did the EnableRaisingEvents flag.

Defining Steps to Just take

Once the watcher object is established up, you ought to give it an action to complete as soon as that change is detected. This can be as basic as composing to a procedure log, or as drastic as triggering a substitute of the occasion with a clean pull of the source code. To get started, you want to determine an motion block in the code. Here’s one just writes to the console:

$motion = 
    $path = $party.SourceEventArgs.FullPath
    $title = $celebration.SourceEventArgs.Title
    $changetype = $party.SourceEventArgs.ChangeType
    Produce-Host "File $identify at path $path was $changetype at $(get-date)"

You can see this code is pulling variables from the function working with the $party variable, which is created for you when the event is established by the watcher object. As quickly as the celebration terminates, the variable also terminates, indicating that it’s only going to have info pertinent to that party.

Using the Sign up-ObjectEvent

So, you’ve bought the FileSystemWatcher set up, and you’ve received steps that you want to get any time some thing transpires. Right now, these two are independent and really do not know about every other. To get them doing work with each other, you should sign up the steps with the function. PowerShell has an whole cmdlet for this—the Register-ObjectEvent cmdlet. To use Sign up-ObjectEvent, you should go it a few issues:

  • The FileSystemWatcher item
  • The occasion kind to cause the steps on
  • The steps you outlined before

If you have set up all the things the exact same way it’s detailed previously mentioned, it will search anything like this: Sign up-ObjectEvent $watcher 'Event Action' -Action $action. ‘Event Action’ can be replaced with any occasion from the FileSystemWatcher, but this will make for a good demo.

Testing It Out

Now you can take a look at it all out. In this portion, you are heading to build a new file in the specified directory, see the function motion, then disable and deregister the function.

To make a new file and trigger the celebration, run the below line in PowerShell. This is on Ubuntu Linux, but if you are pursuing alongside on Home windows, replace /household/ubuntu/ with C: and / with .

New-Item -Route "/dwelling/ubuntu/WatchThisFolder/newFile" -ItemType File

As quickly as you enter that, the celebration fires and the action triggers.

File newFile at path /house/ubuntu/WatchThisFolder/newFile was Produced at 09/26/2019 20:49:54

It fires each time you develop a new file in that listing or everything nested less than it, if you enabled the IncludeSubdirectories flag. Now that you know increasing the party works, go and change it off by running $watcher.EnableRaisingEvents = $bogus, then try developing a new file. The file should be established, but no function exhibits. This can be really valuable if you are debugging and never want to set off something while you are doing the job in the file technique.

When you are accomplished, run Get-EventSubscriber | Unregister-Celebration to unregister the celebration from the motion. Now even if the EnableRaisingEvents flag is accurate and the action comes about, the action won’t fire.

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