Windows: File Monitoring Script (Batch/VBS)

I'm currently in 开发者_开发技巧working on a script to create a custom backup script, the only piece I'm missing is a file monitor. I need some form of a script that will monitor a folder for file changes, and then run a command with the file that's changed.

So, for example, if the file changes, it'll execute "c:/syncbatch.bat %Location_Of_File%"

In VBScript, you can monitor a folder for file changes by subscribing to the WMI __InstanceModificationEvent event. These articles contain sample code that you can learn from and adapt to your specific needs:

• WMI and File System Monitoring
• How Can I Monitor for Different Types of Events With Just One Script?

Calling WMI is fairly cryptic and it causes the WMI service to start running which can contribute to bloat since its fairly large and you really can't cancel the file change notifications you've requested from it without rebooting. Some people experimenting with remote printing from a Dropbox folder found that a simple VBScript program that ran an endless loop with a 10 second WScript.Sleep call in the loop used far less resource. Of course to stop it you have to task kill that script or program into it some exit trigger it can find like a specifically named empty file in the watch folder, but that is still easier to do than messing with WMI.

The Folder Spy http://venussoftcorporation.blogspot.com/2010/05/thefolderspy.html is a free lightweight DOT.NET based file/folder watching GUI application I'ved used before to run scripts based on file changes. It looks like the new version can pass the event filename to the launched command. The old version I had didn't yet support file event info so when launched, my script had to instance a File System Object and scan the watched folder to locate the new files based on criteria like datestamps and sizes.

This newer version appears to let you pass the file name to the script if you say myscript.vbs "*f" on the optional script call entry. Quotes can be important when passing file paths that have spaces in folder names. Just remember if you are watching change events you will get a lot of them as a file grows or is edited, usually you just want notification of file adds or deletes.

Another trick your script can do is put the file size in a variable, sleep for a few seconds, and check the file again to see if its changed. if it hasn't changed in a few seconds you can usually assume whatever created it is done writing it to disk. if it keeps changing just loop until its stable.