I Can’t Protect You From Writing Bash, But I Can Protect You From Unset Bash Variables (Why Do You Need Protection From Unset Bash Variables?)

safe-vars.sh

#!/bin/bash

set -CEepuo pipefail


function cleanup() {
  trap - EXIT;
  if [ -n "${vars_in}" ]; then rm -f "${vars_in}"; fi;
  if [ -n "${vars_out}" ]; then rm -f "${vars_out}"; fi;
}
trap 'cleanup' EXIT;

readonly vars_in=$(mktemp -u); mkfifo "${vars_in}";
readonly vars_out=$(mktemp -u); mkfifo "${vars_out}";

(
  while :; do
    while read -r var; do
      echo "${!var}" > "${vars_out}";
    done < "${vars_in}";
  done;
) &

function read_var() {
  readonly var="$1";
  echo "${var}" > "${vars_in}";
  cat "${vars_out}";
}


function main() {
  echo "[l] SECONDS: ${SECONDS}";
  echo "[c] SECONDS: $(read_var SECONDS)";
  
  sleep 1;
  
  echo "[l] SECONDS: ${SECONDS}";
  echo "[c] SECONDS: $(read_var SECONDS)";
  unset SECONDS; SECONDS='unset';
  
  sleep 1;
  
  echo "[l] SECONDS: ${SECONDS}";
  echo "[c] SECONDS: $(read_var SECONDS)";
  
  sleep 1;
  
  echo "[l] SECONDS: ${SECONDS}";
  echo "[c] SECONDS: $(read_var SECONDS)";
}
main;