I was actually looking for something like this a few days ago. This is pretty useful as there's no crc32sum readily available on linux. Thanks for that!

I would personally change a few things, mostly small nitpicks to be fair.

1. Prefer [[ ]] over [ ] for tests. Source: https://www.shellcheck.net/wiki/SC2292
2. Use $0 instead of hardcoding crc32sum in the help messages. That way it will work even if someone names the script differently
3. You could exit 0 after the help and end the if there instead of having the whole work being done in an else.

As I said, nitpicks!

Also, I like that your example uses *.smc, that's also the reason I needed a crc32sum 🤣