#!/bin/bash
input="{
\"VariaB\": \"DONE\",
\"VariaC\": \"DONE\",
\"VariaD\": null,
\"VariaE\": true
}"
VariaA="ABCD"
VariaF="false"
printf "{
\"VariaA\": \"$VariaA\",
%s
\"VariaF\": $VariaF
}" "$(grep -v '[{}]' <<< "$input")"
IyEvYmluL2Jhc2gKCmlucHV0PSJ7CiAgXCJWYXJpYUJcIjogXCJET05FXCIsCiAgXCJWYXJpYUNcIjogXCJET05FXCIsCiAgXCJWYXJpYURcIjogbnVsbCwKICBcIlZhcmlhRVwiOiB0cnVlCn0iCgpWYXJpYUE9IkFCQ0QiClZhcmlhRj0iZmFsc2UiCgpwcmludGYgInsKICBcIlZhcmlhQVwiOiBcIiRWYXJpYUFcIiwKJXMKICBcIlZhcmlhRlwiOiAkVmFyaWFGCn0iICIkKGdyZXAgLXYgJ1t7fV0nIDw8PCAiJGlucHV0IikiCg==