In Perl, how can I watch a directory for changes?

Question

use Text::Diff;
for($count = 0; $count <= 1000; $count++){
   my $data_dir=\"archive/oswiostat/oracleapps.*dat\";
   my $data_file= `ls -t $data_dir | head -1`;
          


        

Answer 1

Note that I'm answering your original question, why the stat() seemed to fail, rather than the newly edited question title, which asks something different.

This is the fix:

my $data_file= `ls -t $data_dir | head -1`;
chomp($data_file);

The reason this is the fix is a little murky. Without that chomp(), $data_file contains a trailing newline: "some_filename\n". The two argument form of open() ignores trailing newlines in filenames and I don't know why because two-arg open mimics shell behavior. Your call to stat(), however, does not ignore the newline in the filename, so it is stat()ing a non-existent file and thus $stats1 is undef.

Answer 2

The real fix is File::ChangeNotify or File::Monitor or something similar (e.g., on Windows, Win32::ChangeNotify).

use File::ChangeNotify;

my $watcher = File::ChangeNotify->instantiate_watcher(
    directories => [ 'archive/oswiostat' ],
    filter => qr/\Aoracleapps[.].*dat\z/,
);

while (my @events = $watcher->wait_for_events) {
    # ...
}