R""(

Note: this command's interface is based heavily around installables, which you may want to read about first (nix --help).

Examples

• Evaluate a Nix expression given on the command line:

  # nix eval --expr '1 + 2'
  

• Evaluate a Nix expression to JSON using the short-form expression flag:

  # nix eval --json -E '{ x = 1; }'
  {"x":1}
  

• Evaluate a Nix expression from a file:

  # nix eval --file ./my-nixpkgs hello.name
  

• Get the current version of the nixpkgs flake:

  # nix eval --raw nixpkgs#lib.version
  

• Print the store path of the Hello package:

  # nix eval --raw nixpkgs#hello
  

• Get a list of checks in the nix flake:

  # nix eval nix#checks.x86_64-linux --apply builtins.attrNames
  

Description

This command evaluates the given Nix expression and prints the result on standard output.

Output format

nix eval can produce output in several formats:

• By default, the evaluation result is printed as a Nix expression.

• With --json, the evaluation result is printed in JSON format.

  The conversion behaviour is the same as builtins.toJSON except that paths are printed as-is without being copied to the Nix store.

• With --raw, the result must be coercible to a string, i.e., something that can be converted using ${...}.

  Integers will always generate an error when output via --raw, regardless of coerce-integers being enabled, to avoid ambiguity.

  The output is printed exactly as-is, with no quotes, escaping, or trailing newline.

)""