Anyone who designs command-line interfaces for GNU/Linux should read this: https://www.gnu.org/prep/standards/html_node/Command_002dLin... and this: https://www.gnu.org/prep/standards/html_node/Option-Table.ht...

If you are using C++, Boost.Program Options is a solid choice. It is one of the relatively few command line argument parsers in the world which supports close to a full set of (GNU-like) behaviors without custom workarounds. It also enables type safety in the sense of disallowing decimals where integers were expected.