nix-instantiate

TLDR

Instantiate expression

$ nix-instantiate [expression.nix]

Evaluate and print

$ nix-instantiate --eval [expression.nix]

Evaluate to JSON

$ nix-instantiate --eval --json [expression.nix]

Parse only (check syntax)

$ nix-instantiate --parse [expression.nix]

Use expression from command line

$ nix-instantiate --eval -E '1 + 2'

SYNOPSIS

nix-instantiate [options] files...

DESCRIPTION

nix-instantiate instantiates Nix expressions, producing store derivations. With --eval, it evaluates expressions and prints results.
This is useful for debugging and testing Nix expressions.

PARAMETERS

--eval

Evaluate and print result.

--json

Output as JSON.

--strict

Evaluate strictly.

--parse

Parse only.

-E expr

Evaluate expression.

--arg name value

Pass argument.

-A attr

Select attribute.

EXAMPLES

$ # Evaluate expression
nix-instantiate --eval -E 'let x = 1; in x + 1'
# Output: 2

# Get derivation
nix-instantiate '<nixpkgs>' -A hello
# Output: /nix/store/...-hello.drv

CAVEATS

Newer nix commands (nix eval) supersede some uses. Strict evaluation required for full values. Part of legacy Nix CLI.

HISTORY

nix-instantiate is one of the original Nix commands, part of the core tooling since Nix was first released in 2003.