You can solve this if you use use a progressbar that works like your browser progress bar. It displays how many searched directories out of the total number of directories seen (in the browser it displays number of link/pics gotten out of how many links there have been seen on the current page).
But for that to work, you do need to calculate your own progress, but it should be as simple as $prog->value( 100 * $numdirssearched / $numdirsseen );
And then you have to use a bread-first search, which is NOT what finddepth does...

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