Common behavior of dotenv packages is not overriding existing environment variables. .env by default. env should not write over existing variables or at least provide an option to avoid overriding:

Examples of the common behavior
Go: https://github.com/joho/godotenv/blob/master/godotenv_test.go#L122
Ruby: https://github.com/bkeepers/dotenv/blob/master/spec/dotenv/environment_spec.rb#L25
Haskell: https://github.com/stackbuilders/dotenv-hs/blob/master/spec/Configuration/DotenvSpec.hs#L21
Clojure: https://github.com/tpope/lein-dotenv/blob/master/test/lein_dotenv/plugin_test.clj#L11

Why does this implementation work differently?