Optional option argument with getopts

Question

while getopts \"hd:R:\" arg; do
  case $arg in
    h)
      echo \"usgae\" 
      ;;
    d)
      dir=$OPTARG
      ;;
    R)
      if [[ $OPTARG =~ ^[0-9]+$ ]];then         


        

Answer 1

Inspired in @calandoa's answer (the only one that actually works!), I've made a simple function that can make it easy to be used multiple times.

getopts_get_optional_argument() {
  eval next_token=\${$OPTIND}
  if [[ -n $next_token && $next_token != -* ]]; then
    OPTIND=$((OPTIND + 1))
    OPTARG=$next_token
  else
    OPTARG=""
  fi
}

An example usage:

while getopts "hdR" option; do
  case $option in
  d)
    getopts_get_optional_argument $@
    dir=${OPTARG}
    ;;
  R)
    getopts_get_optional_argument $@
    level=${OPTARG:-1}
    ;;
  h)
    show_usage && exit 0
    ;;
  \?)
    show_usage && exit 1
    ;;
  esac
done

This gives us a practical way to get "that missing feature" in getopts :)

NOTE that nevertheless command-line options with optional args seems to be discouraged explicitly

Guideline 7: Option-arguments should not be optional.

but I have no intuitive way to implement my case without this: I have 2 modes that are activated by either using one flag or other, and those have both an argument with a clear default. Introducing a third flag just to disambiguate makes it look a bad CLI style.

I've tested this with many combinations, including all in @aaron-sua's answer and works well.