Native bash method for pulling a substring out from between two markers

carve

# TODO: Make this more robust, build in validation etc
# This might wind up being a script in its own right rather than a function
carve() {
  read -r count1 delim1 _ count2 delim2 <<< "${@}"
  case "${count1}" in
    ([0-9]*) count1="${count1//[!0-9]/}" ;;
    (first)  count1="1" ;;
    (last)   count1="last" ;;
    (''|*)
      printf -- '%s\n' \
        "Usage: carve SHORT_ORDINAL DELIM1 to SHORT_ORDINAL DELIM2" \
        "Example: carve 2nd '/' to 3rd ':'" \
        "'first' or 'last' can also be used in the short ordinal fields" >&2
    ;;
  esac
  case "${count2}" in
    ([0-9]*) count2="${count1//[!0-9]/}" ;;
    (first)  count2="1" ;;
    (last)   count2="last" ;;
  esac
  while IFS= read -r; do
    case "${count1}" in
      (first) line="${REPLY#*${delim1}}" ;;
      (last)  line="${REPLY##*${delim1}}" ;;
      (*)
        for (( i=0;i<count1;i++ )); do
          (( i == 0 )) && line="${REPLY#*${delim1}}"
          (( i >= 1 )) && line="${line#*${delim1}}"
        done
      ;;
    esac
    case "${count2}" in
      (first) line="${line%%${delim2}*}" ;;
      (last)  line="${line%${delim2}*}" ;;
      (*)
        for (( i=0;i<count2;i++ )); do
          line="${line%%${delim2}*}"
        done
      ;;
    esac
    printf -- '%s\n' "${line}"
  done
}