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Built-in Constants
Here are the constants built into the Nix expression evaluator:
-
builtins
The setbuiltins
contains all the built-in functions and values. You can usebuiltins
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
]{#builtins-currentSystem}
The built-in valuecurrentSystem
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"
.