> What is the correct way, or convention, to specify and parse command line arguments, for example?

I often use variations of this pattern:

  version=1.0.0

  usage() {
    cat << EOF
  USAGE: $0 {{-f|--file} <filename>}

  Some description.

  OPTIONS
    -h, --help
      Display this help.

    -v, --version
      Display version.

    -f <filepath>, --file <filepath>
      Specify input file.
  EOF
  }

  while (( $# )); do
    case "$1" in
      -h|--help)
        usage
        exit
      ;;

      -v|--version)
        printf "%s\n" "$version"
        exit
      ;;

      -f|--file)
        input_file="$2"
        shift
      ;;

      *)
        >&2 printf "Unknown option: %s\n" "$1"
        >&2 usage
        exit 1
      ;;
    esac
    shift
  done

[1] https://www.gnu.org/prep/standards/standards.html#Command_00...

[2] https://cli-guide.readthedocs.io/en/latest/design/guidelines...

https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1...

http://catb.org/~esr/writings/taoup/html/ch10s05.html