Tricks on how to do bash variable indirection

bash.md

Indirection

Setting a variable

1. A "local" variable, that will be local to the function

var=foo
value="b a  r"
declare "${var}=${value}"

2. A "global" vairable, that will be set outside a function

var=foo
value="b a  r"
export -n "${var}=${value}" # Compatible with bash 3.2, use this one. Does not work on arrays prior to bash 4.2
# https://stackoverflow.com/q/10806357/4166604
# declare -g "${var}=${value}" # Not compatible with bash 3.2, only bash 4.2 or newer

3. An exported variable, that will be inherited by child processes

var=foo
value="b a  r"
export "${var}=${value}"

Setting an array

I want to conditionally set an array when it is unset, I have made a one liner for an array, using a function o replicate : ${FOO=BAR} for arrays:

function set_array_default()
{
  local default="$1"
  shift 1
  
  if ! declare -p $default &> /dev/null; then
    local IFS=''
    if [ "${BASH_VERSINFO[0]}${BASH_VERSINFO[1]}" -ge "42" ]; then
      declare -ag "${default}=()"
    else
      eval "${default}=()"
    fi
    for (( i=0; $#; i++ )); do
      read -r "${default}[$i]" <<< "${1}"
      shift 1
    done
  fi
}

set_array_default foo bar "B A  R"