Hash-based Diff for Directories

Recently I was working on a project where I needed to quickly and reliably detect changes to the contents of a directory, and when a change was detected run a series of commands. There are any number of file differential tools, the venerable [diff][1] chief among them, and I think they would certainly do the job. They would certainly do a very complete job allowing for a comparison of every line of every file and be able to show exactly what changed where. But for what I needed to do, this seemed overkill. Ultimately what I needed to know was ***if*** something had changed, not specifically ***what*** had changed. To that end, I realized what I needed was a view of the directory, not a view of the files themselves.…
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