Bash function calling another function that requires passing user-defined options

Question

I have a function plist that is able to call head and tail commands. But for processing regions I call a different function pregion.

# --- plist ---

  ("-H"|"--head")
    local -r hn="$2" ; shift 2 ;;
  ("-T"|"--tail")
    local -r tm="$2" ; shift 2 ;;

  ("--FS")                           # field separator
    local fs="$2" ; shift 2 ;;
  ("--incl")
    local incl+=("$2") ; shift 2 ;;  # file type suffix
  ("--excl")
    local excl+=("$2") ; shift 2 ;;  # file type suffix

  ("--RP")
    local pn=$2 ; shift 2 ;;
  ("--RQ")
    local qn=$2 ; shift 2 ;;

  ("--dyn"|"--dynamic")
    local dyn="1" ; shift 1 ;;
  ("-C"|"--context")
    local ctx=$2 ; shift 2 ;;

  ("-d"|"--directory")
    local fdir=$2 ; shift 2 ;;

  (--)
    shift;  break  ;;

  ...

  if [[ -v hn ]]; then

     head -v -hn "$n"
    
  elif [[ -v tm ]]; then

    tail -v -n "$tm"

  elif [[ -v dyn ]]; then

    pregion "$@"  # requires original options here

  fi

With head and tail, I only use options -H, -T', --FS, and --incl. Because I am using shift when processing options, I need to have a copy ef the original plist input arguments, because I cannot simply pass "$@" to pregion.

This will call head or tail

  plist -H 8 ./01cuneus

  plist -T 13 ./01cuneus

Examples of calling pregion

plist --dyn -C 8 "Martin" ./01cuneus

plist --incl .texi --incl .org --RP 8 --RQ 13 ./01cuneus

plist --incl .texi --incl .org --dyn -C 8 "Martin" ./01cuneus

Answer 1

Copy the orginal args to an array, and use that with pregion. e.g.

plist() {
  local -a origargs=("$@")
  ...
  case
    ...
  esac
  ...

  if
    ...
  elif [[ -v dyn ]]; then
    pregion "${origargs[@]}"
  fi

Answer 2

You could indeed save the contents of $@ to an array

plist() {
    local args
    args=("$@")
    case $1 in ...
        # some shifting etc.
    esac
    if something; then
        pregion "${args[@]}"
    fi
}

But, that would mean that pregion would need to do the whole option processing again. In effect, you'd implement the same process in two places. And what about returning errors for invalid options from plist? You couldn't do that before figuring out if you're going to call pregion, since it might accept some options plist doesn't.

Instead, I'd suggest doing the option parsing only once, and then calling pregion with the appropriate values already parsed to individual arguments:

plist() {
    local args
    args=("$@")
    local this=default that=otherdefault
    local call_pregion=
    case $1 in ...
        this) this=$2; shift; shift;;
        that) that=$2; shift; shift;;
        dyn) call_pregion=1
    esac
    if [ "$call_pregion" ]; then
        pregion "$this" "$that"
    fi
}

that way pregion can just take the values from static positions in the list, e.g. $1 for $this and $2 for $that.

Also, btw, using shift 2 there is risky. Depending on the shell it may silently fail there aren't enough arguments to shift. E.g. set a b c; shift 4; echo $1 will exit with an error in Dash, but in Bash, it'll happily just print a. That may leave your option parsing stuck in a loop if the user gives an option without the corresponding option-argument.