fn load_shell_name(shell: &str) -> Result<Shell, ShellErr> {
    shell
        .split('/')
        .last()
        .map(|shell| {
            Shell::from_str(shell).map_err(|unknown_shell| ShellErr::UnknownShell {
                shell: unknown_shell,
            })
        })
        .unwrap_or_else(|| Err(ShellErr::MissingArg))
}
Either provided as a path with `/` as separator or directly.
src/config/args.rs