Batch real time wait for a file

Question

I have some batch scripts which wait for files. The wait loop is done with the typical IF EXISTS loop:

:waitloop
IF EXISTS file.zip GOTO waitloopend
sleep.exe 60
goto waitloop
: waitloopend

I am looking for a more efficient way of waiting for files. Something like a waitfile.exe command which will block and wait until the file appears. Internally, it should use the FileSystemWatcher class to be able to exit as soon as the file appears.

In Linux I have my own Perl script which internally uses Inotify.

Do you know if there exists a tool like this?

Answer 1

Your method is preferable and perfectly acceptable. FileSystemWatcher wastes resources, even more than your loop.

Even if you make your loop as tight as with one second delay, you'll still be totally unnoticeable in any process monitor that measures CPU or hard disk load.

BTW, you can use timeout command instead of sleep.exe.

Also, you have some typos in your code:

:waitloop
IF EXIST "scanning.done" GOTO waitloopend
timeout /t 1
goto waitloop
:waitloopend

Some info on 'wasting resources' can be found here: https://stackoverflow.com/questions/239988/filesystemwatcher-vs-polling-to-watch-for-file-changes; the main point being that it could be unreliable. But I have to admit, my answer goes mainly from the years of practice and experience.

Answer 2

A typical file system monitor detects file creations and if the file will be created while the tool is active you will receive the event, but if you will start the tool with an already existing file, there will be no subsequent creation events and the tool will wait forever.

It looks like you need to implement a custom tool, which will first check if the file already exists and if not start monitoring for the file.

Answer 3

Use PowerShell to access the FileSystemWatcher API.

#By BigTeddy 05 September 2011 

#This script uses the .NET FileSystemWatcher class to monitor file events in folder(s). 
#The advantage of this method over using WMI eventing is that this can monitor sub-folders. 
#The -Action parameter can contain any valid Powershell commands.  I have just included two for example. 
#The script can be set to a wildcard filter, and IncludeSubdirectories can be changed to $true. 
#You need not subscribe to all three types of event.  All three are shown for example. 
# Version 1.1 

$folder = 'c:\scripts\test' # Enter the root path you want to monitor. 
$filter = '*.*'  # You can enter a wildcard filter here. 

# In the following line, you can change 'IncludeSubdirectories to $true if required.                           
$fsw = New-Object IO.FileSystemWatcher $folder, $filter -Property @{IncludeSubdirectories = $false;NotifyFilter = [IO.NotifyFilters]'FileName, LastWrite'} 

# Here, all three events are registerd.  You need only subscribe to events that you need: 

Register-ObjectEvent $fsw Created -SourceIdentifier FileCreated -Action { 
$name = $Event.SourceEventArgs.Name 
$changeType = $Event.SourceEventArgs.ChangeType 
$timeStamp = $Event.TimeGenerated 
Write-Host "The file '$name' was $changeType at $timeStamp" -fore green 
Out-File -FilePath c:\scripts\filechange\outlog.txt -Append -InputObject "The file '$name' was $changeType at $timeStamp"} 

Register-ObjectEvent $fsw Deleted -SourceIdentifier FileDeleted -Action { 
$name = $Event.SourceEventArgs.Name 
$changeType = $Event.SourceEventArgs.ChangeType 
$timeStamp = $Event.TimeGenerated 
Write-Host "The file '$name' was $changeType at $timeStamp" -fore red 
Out-File -FilePath c:\scripts\filechange\outlog.txt -Append -InputObject "The file '$name' was $changeType at $timeStamp"} 

Register-ObjectEvent $fsw Changed -SourceIdentifier FileChanged -Action { 
$name = $Event.SourceEventArgs.Name 
$changeType = $Event.SourceEventArgs.ChangeType 
$timeStamp = $Event.TimeGenerated 
Write-Host "The file '$name' was $changeType at $timeStamp" -fore white 
Out-File -FilePath c:\scripts\filechange\outlog.txt -Append -InputObject "The file '$name' was $changeType at $timeStamp"} 

# To stop the monitoring, run the following commands: 
# Unregister-Event FileDeleted 
# Unregister-Event FileCreated 
# Unregister-Event FileChanged

Found here: https://gallery.technet.microsoft.com/scriptcenter/Powershell-FileSystemWatche-dfd7084b