Surely unsigned (aka modulo) arithmetic and arrays are expressible in shell script? edit: For reference, someone's take on building out better bash-like array

Surely unsigned (aka modulo) arithmetic and arrays are expressible in shell script? edit: For reference, someone's take on building out better bash-like array functionality in posix shell: https://github.com/friendly-bits/POSIX-arrays https://github.com/friendly-bits/POSIX-arrays (there's only very rudimentary array support built-in to posix sh, basically working with stuff in $@ using set -- arg1 arg2..)