Detect New File in a Directory

Hi All,

Last time when I google this question, I actually found a function that does what I need, but I couldn't find it this time.

Basically what I need is to monitor a directory for any new files. If there are new files, I will read the files in and continue to monitor for new files.

Any help will be greatly appreciated!

Thank you,

Lynniz

[Walter Roberson]

The mechanisms for doing this are operating-system specific. Please indicate which OS you are using.

[lynniz]

I have Windows 7. Another question is do OS always return files in an alphabetical order?

Thanks,

Lynniz

Answer 1

[Honglei Chen]

Hi lynniz,

You can use dir to list all the files under a certain directory, cache it and constantly query the folder and use setdiff to see whether a new file showed up. The following example shows a brief example. Note that I'm assuming everything underneath the directory is a regular file. If you have subdirectories, you can filter them out using the isdir field in the result of dir.

dir_content = dir;
filenames = {dir_content.name};
current_files = filenames;
while true
  dir_content = dir;
  filenames = {dir_content.name};
  new_files = setdiff(filenames,current_files);
  if ~isempty(new_files)
    % deal with the new files
    current_files = filenames;
  else
    fprintf('no new files\n')
  end
end

Of course you may want to define an exit flag to get you out of the loop easily.

HTH

[Walter Roberson]

Sadly, without operating system support, you cannot tell whether a new file is ready for reading. It is not easy to probe a file to determine whether there are any processes that are writing to it.

[Fangjun Jiang]

What if file name keeps the same but it is newly updated? You might need to check the time stamp of the file, compare it to the last time that the checking is done, to see if it is "new".

[lynniz]

Thanks for the inputs. I will monitor the time stamp as well.

Answer 2

[Dimitrios Patikas]

To avoid looping over and over again, you may use a timer function and keep it working on the background unless younstom the timer. An example to get always the newest file:

t = timer;
t.TimerFcn = @timerFunc;
t.Period = 0.6; % how often you want to check
t.ExecutionMode = 'fixedRate';
t.start % use t.stop to stop the timer

function timerFunc(~,~)
persistent CurrentNewest
Path = 'A/path/you/want/to/keep/track';
CurrentNewest = 'NewestFilename.new'
ListFiles = dir(Path);
ListFiles = ListFiles(~[ListFiles.isdir]);
[~, idx] = sort([ListFiles.datenum]);
newest = ListFiles(idx(end));
if ~strcmp(newest.name, CurrentNewest)
    disp(['The newest file is now: ', newest.name])
    CurrentNewest = newest.name;
end
end

Answer 3

[Walter Roberson]

For Windows see https://www.mathworks.com/matlabcentral/answers/99277-how-do-i-programmatically-detect-a-change-in-a-directory

For a Java based monitor see https://www.mathworks.com/matlabcentral/answers/398152-listening-to-the-creation-deletion-of-a-file-with-specific-name#answer_317920