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A standard UNIX tool that has been part of the Mac release for 20+ years can accomplish this task for you.
If you're "a consumer," why would you be concerned about SHA-1 (not SHA1) checksums? Try not to get entranced by everything about which you encounter some quick misinformation in a magazine.
Sorry, can't run random procedures on files stored "wherever." Files that live on your system can be subjected to checksums, whether periodically or on-demand. Does that interest you?
Be careful: assume that things that you store in "the cloud" are copied to Lord-knows-where--but certainly to major ISPs and to Uncle Sam--100% of the time.
Yes, and a solution that does this automatically would be based on a utility that has been part of the standard UNIX (hence, MacOS) release for forty years . . . but we don't build such things for the scope to which you have committed.
Actually, I built such a thing (although far more sophisticated) for a gentleman at NSA (Bernie Peters: he published in NISC Baltimore 1986) many years ago, called EXPOSE.
The idea was it reports on one's security "exposure."
All it provided--this was HIS insistence--was a single figure of merit, i.e., things match or things don't match. If they DIDN'T match, it was the NSA employee's responsibility to figure out why.
I wouldn't have done it that way, but, hey, he was paying the bill . . .
If there is, I don't know what it is, but it would clearly cost at the very least many hundreds of dollars.
Unless you want to hunt for some development kit and roll your own, and I imagine you're not a UNIX systems programmer--which I am.
I'm not proposing anything that's even remotely out of line for several hours' development plus testing effort, and a few more documenting. I don't know if you're accustomed to people just dumping code at your feet and saying, "Here it is," but I submit a professional job.
Well, that would certainly be a problem, wouldn't it?
And I wouldn't reach that conclusion.
Everyone and his brother offers seat-of-the-pants solutions for Windows: it's a paraprofessional platform that encourages that type of cowboy operation.
MacOS is a professional UNIX operating system. System programmers in that environment do not grow on trees.
I made an offer that was beyond cost-effective. I certainly cannot force you to accept it. Also, it would offer what you want, not whatever features some hastily located and downloaded program happens to offer!