Bash function for parsing script arguments for passing to sub command and sub-sub-command

bash_arg_parsing.sh

# Flexible argument parsing
#
# Example:
#   Command:
#   ```
#   ./docker/script --env=APP_ENV=development -v $(pwd)/foo:/foo docker.househappy.org/datafeed ./bin/run "puts 'hello'"
#   ```
#
#   Script:
#   ```
#   subcommand_parse_args "$@"
#
#   docker run \
#     --rm \
#     "${OUTER_ARGS[@]}" \
#     docker.househappy.org/datafeed \
#     "${SUB_COMMAND[@]}"
#   ```
#
#   Translates to:
#   ```
#   ./show_args run \
#     --rm \
#     --env=APP_ENV=development -v $(pwd)/foo:/foo \
#     docker.househappy.org/datafeed \
#     ./bin/run "puts 'hello'"
#   ```
function subcommand_parse_args {
  OUTER_ARGS=()
  SUB_COMMAND=()

  in_sub_command=
  short_flag=

  for arg in "$@"; do
    if [ "$in_sub_command" ]; then
      SUB_COMMAND+=("$arg")
    elif [ "$short_flag" ]; then
      OUTER_ARGS+=("$arg")
      short_flag=
    elif [ ${arg:0} == '--' ]; then
      in_sub_command=1
    elif [ ${arg:0:2} == '--' ]; then
      OUTER_ARGS+=("$arg")
    elif [ ${arg:0:1} == '-' ]; then
      OUTER_ARGS+=("$arg")
      short_flag=1
    else
      in_sub_command=1
      SUB_COMMAND+=("$arg")
    fi
  done
}