t.sh

function error() {
  echo "foo: $1"
  exit 1
}

# loop over arguments
while [ $# -gt 0 ]; do
  case "$1" in
    # flag with value
    -c | -r | -i | -o)
      if [ -z "$2" ]; then
        error "option $1 expects a value"
      fi
      echo "$1: $2"
      shift
      ;;
    # flag without value
    -o)
      echo "$1: true"
      ;;
    # value without flag
    *)
      # exit if the value starts with '-'
      if [[ "$1" == -* ]] ; then
        error "option $1 is invalid"
      fi
      # concatenate the current value to $vals
      vals="$vals $1"
      ;;
  esac
  shift
done

# set arguments to $vals
set -- $vals