nix-eval

evaluates Nix expressions

Evaluate expression

$ nix eval --expr "[1 + 1]"

Evaluate from flake

$ nix eval [.#packages.x86_64-linux.default]

Evaluate and apply function

$ nix eval --apply [builtins.attrNames] --expr "{a=1; b=2;}"

Output as JSON

$ nix eval --json --expr "[{a = 1;}]"

Evaluate file

$ nix eval -f [file.nix]

Raw output

$ nix eval --raw --expr "\"hello\""

nix eval [options] [installable]

nix eval evaluates Nix expressions. It outputs the evaluated value.
The tool inspects Nix values. Useful for debugging and querying.

INSTALLABLE

Flake attribute to evaluate.

--expr EXPR

Nix expression.

--json

Output as JSON.

--raw

Raw string output.

--apply FUNC

Apply function to result.

--help

Display help information.

Part of Nix CLI. Expression syntax. Flakes or expressions.

nix eval is part of the new Nix CLI providing expression evaluation functionality.