#!/usr/bin/env bash

normal_v="O"; null_v=""; unset unset_v
echo -e "Pre-define: normal_v="O"; null_v=""; unset unset_v\n"

printf "\${var:+X} normal_v:%1s  null_v:%1s  unset_v:%1s\n"   "${normal_v:+X}" "${null_v:+X}" "${unset_v:+X}"
printf "\${var+X}  normal_v:%1s  null_v:%1s  unset_v:%1s\n\n" "${normal_v+X}"  "${null_v+X}"  "${unset_v+X}"

printf "\${var:-X} normal_v:%1s  null_v:%1s  unset_v:%1s\n"   "${normal_v:-X}" "${null_v:-X}" "${unset_v:-X}"
printf "\${var-X}  normal_v:%1s  null_v:%1s  unset_v:%1s\n\n" "${normal_v-X}"  "${null_v-X}"  "${unset_v-X}"

printf "\${var:=X} normal_v:%1s  null_v:%1s  unset_v:%1s\n"   "${normal_v:=X}" "${null_v:=X}" "${unset_v:=X}"
printf  "  After   normal_v=%1s  null_v=%1s  unset_v=%1s\n"   "${normal_v}"    "${null_v}"    "${unset_v}"
normal_v="O"; null_v=""; unset unset_v      # reset variables

printf "\${var=X}  normal_v:%1s  null_v:%1s  unset_v:%1s\n"   "${normal_v=X}"  "${null_v=X}"  "${unset_v=X}"
printf  "  After   normal_v=%1s  null_v=%1s  unset_v=%1s\n\n" "${normal_v}"    "${null_v}"    "${unset_v}"
normal_v="O"; null_v=""; unset unset_v      # reset variables

printf "\${var:?X} ---\n"
printf "    normal_v : ${normal_v:?X}\n"
printf "    null_v   : \${null_v:?X}  # skip, or the script will be interrupted\n"
printf "    unset_v  : \${unset_v:?X} # skip, or the script will be interrupted\n"

printf "\${var?X}  ---\n"
printf "    normal_v : ${normal_v?X}\n"
printf "    null_v   : ${null_v?X}\n"
printf "    unset_v  : \${unset_v?X}  # skip, or the script will be interrupted\n"