So the thing to remember is that in POSIX shell (and BASH, etc.) all for loops are for-each loops. If you wanted to loop over integers, you might write `for i in $(seq 10); do echo $i; done`, but that just turns into `for i in 1 2 3 4 5 6 7 8 9 10; do echo $i; done` when it runs. So this one just iterates over "s", "u", and "b" instead.