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Built-in Constants

Here are the constants built into the Nix expression evaluator:

  • builtins\ The set builtins contains all the built-in functions and values. You can use builtins to test for the availability of features in the Nix installation, e.g.,

    if builtins ? getEnv then builtins.getEnv "PATH" else ""
    

    This allows a Nix expression to fall back gracefully on older Nix installations that don’t have the desired built-in function.

  • builtins.currentSystem\ The built-in value currentSystem evaluates to the Nix platform identifier for the Nix installation on which the expression is being evaluated, such as "i686-linux" or "x86_64-darwin".


Last update: November 4, 2021
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