title: How to detect changing directory size in Perl
body: <p>I am trying to find a way of monitoring directories in Perl, in particular the size of a directory, and upon detecting a change in directory size, perform a particular action.<br>
  The issue I have is with large files that require a noticeable amount of time to copy into this directory, i.e. > 100MB.  What happens (in Windows, not Unix) is the system reserves enough disk space for the entire file, even though the file is still copying in progress.  This causes problems for me, because my script will try to perform an action on this file that has not finished copying over.  I can easily detect directory size changes in Unix via 'du', but 'du' in Windows does not behave the same way.</p>
  
  <p>Are there any accurate methods of detecting directory size changes in Perl?</p>
  
  <p>Edit:  Some points to clarify:
  - My Perl script is only monitoring a particular directory, and upon detecting a new file or a new directory, perform an action on this new file or directory.  It is not copying any files; users on the network will be copying files into the directory I am monitoring.
  - The problem occurs when a new file or directory appears (copied, not moved) that is significantly large (> 100MB, but usually a couple GB) and <strong>my program fires before this copy completes</strong>
       - In Unix I can easily 'du' to see that the file/directory in question is growing in size, and take the appropriate action
       - In Windows the size is static, so I cannot detect this change
  - opendir/readdir/closedir is not feasible, as some of the directories that appear may contain thousands of files, and I want to avoid the overhead of </p>
  
  <p>Ideally I would like my program to be triggered on change, but I am not sure how to do this.  As of right now it busy waits until it detects a change.  The change in file/directory size is not in my control.</p>