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Access the current environment variables with process.env or Bun.env.
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Bun.env.API_TOKEN; // => "secret"
process.env.API_TOKEN; // => "secret"

Set these variables in a .env file. Bun reads the following files automatically (listed in order of increasing precedence).
  • .env
  • .env.production, .env.development, .env.test (depending on value of NODE_ENV)
  • .env.local (not loaded when NODE_ENV=test)
.env
FOO=hello
BAR=world

You can also set variables on the command line.
FOO=helloworld bun run dev
# Using CMD
set FOO=helloworld && bun run dev

# Using PowerShell
$env:FOO="helloworld"; bun run dev

See Environment variables.