Built-in Constants

These constants are built into the Nix language evaluator:

  • builtins (attribute set)

    Contains all the built-in functions and values, in order to avoid polluting the global scope.

    Since built-in functions were added over time, testing for attributes in builtins can be used for graceful fallback on older Nix installations:

    if builtins ? getEnv then builtins.getEnv "PATH" else ""
    
  • builtins.currentSystem (string)

    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".