I have to format body of a json that gets some values substituted from user environment variables. Trying to find a way via shopt or something so the json string is substituted correctly in bash script  but preserves/puts back the double quotes to be a valid json. Tried preprocessing quotes and double quoting.

Example:
``` 
% export env_var1=val1
% export env_var2=val2
% echo {“key1”: “${env_var1}” , “key2”: “${env_var2}”}
Expected output= {“key1”: “val1”, “key2”: “val2”}
```