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nix-shell: how to load environment variables from env file?

Related to this question: nix-shell: how to specify a custom environment variable?

With this derivation:

stdenv.mkDerivation rec {
  FOO = "bar";
}

FOO will be available in the nix shell as an environment variable, but is it possible to load environment variables from an env file?

Solution

  • You could use nix-shell's shellHook to load environment variables from a file by sourcing them as shell code. For example:

    stdenv.mkDerivation {
  name = "my-shell";
  shellHook = ''
    # Mark variables which are modified or created for export.
    set -a
    source env.sh
    # or to make it relative to the directory of this shell.nix file
    # source ${toString ./env.sh}
    set +a
  '';
}

    You could switch from stdenv.mkDerivation to mkShell if your shell isn't also a package.