I'm trying to set up a folder action that triggers only when a new file is less than a certain size. With my limited understanding I haven't been able to figure out a way to do this. Can anyone help?

Here's a run-down of my problem and my current approach: I'm doing some 3D rendering in Blender through the command line in Terminal, but having a persistent error. Blender renders each frame's image, but after usually 3 or 4 frames of animation rendering, the GPU bombs out and all the subsequent frames render black with a size of 28kB.

My brute force method of remedying this so I can render unattended:

  1. Blender is set to not overwrite existing files as it creates new frame renders
  2. Automator Folder Action whenever a new frame is saved:

    on run {input, parameters}

    -- ignoring application responses
    tell application "Keyboard Maestro Engine"
        do script "BA8776AB-5030-4753-85FB-0032D396B9B1"
        -- or: do script "renderhack"
    end tell
    -- end ignoring
    return input

    end run

  3. This triggers a Keyboard Maestro macro which does the following:

3a. Activates Terminal Window

3b. Types Ctrl-C keystroke to kill Blender process (it's already started rendering next frame)

3c. Executes a shell script to delete any small files i.e. find -name "*.png" -size -1M -delete (this is unnecessary for now but would be if I could solve my problem)

3d. Reactivates Terminal Window

3e. Types Up-arrow key, Return to relaunch blender in the Terminal.

So this does work, but I would love to find a more elegant solution, which would save a few more seconds every frame. If the folder action could work conditionally somehow, to only trigger the next script/macro if the most recent file is a certain size.

I hope this makes sense. Unfortunately just moving small files out of the folder doesn't work, since Blender will keep rendering black frames. I need to trigger the above steps (or something like it that also includes killing Blender) when a small file appears in the folder.

  • 1
    Please show us the research already done and add your brute force action as a hint what you want to do.
    – klanomath
    Commented Oct 8, 2016 at 10:55
  • Ok I'll add more description in the OP Commented Oct 8, 2016 at 13:16
  • OK, that's almost a different question ;-) though my answer is correct in regard to the original question...
    – klanomath
    Commented Oct 8, 2016 at 13:54

1 Answer 1


You can use Automator to create a folder action which filters Finder items like this:

Choose "Folder Action" in the start screen of Automator and create a workflow similar to this one:


Save it. The folder action will move all files smaller than 100 KB received in the folder "sort" to the Desktop folder.

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