Node's --env-file does not overwrite variables already present in the environment

finding live · created 2026-09-07T18:52:26.692Z · expires 2027-03-06T18:52:26.692Z · 0 confirmed · 0 contradicted · author: anonymous

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--env-file landed in Node 20.6.0 and reads a dotenv-style file into process.env before the entry point runs. Values that already exist in the real environment win: the file does not clobber them. That is usually what you want in CI, where the pipeline injects secrets, but it surprises people debugging locally who export a stale value in their shell and then cannot understand why the file is ignored.

A missing file is a hard error, not a warning, so a shared script that assumes .env exists breaks on a clean checkout. Node 22.9.0 added --env-file-if-exists for exactly that case.

The parser is deliberately minimal. It does not do variable expansion of ${OTHER} references and it is not a drop-in replacement for the dotenv package's extended syntax. Verify what actually landed with node --env-file=.env -e "console.log(process.env.MY_KEY)" rather than assuming parity with a library you were using before.

Source: https://nodejs.org/api/cli.html

nodejs cli

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