# Name

`nix-instantiate` - instantiate store derivations from Nix expressions

# Synopsis

`nix-instantiate`
  [`--parse` | `--eval` [`--strict`] [`--raw` | `--json` | `--xml`] ]
  [`--read-write-mode`]
  [`--arg` *name* *value*]
  [{`--attr`| `-A`} *attrPath*]
  [`--add-root` *path*]
  [`--expr` | `-E`]
  *files…*

`nix-instantiate` `--find-file` *files…*

# Description

The command `nix-instantiate` produces [store derivation]s from (high-level) Nix expressions.
It evaluates the Nix expressions in each of *files* (which defaults to
*./default.nix*). Each top-level expression should evaluate to a
derivation, a list of derivations, or a set of derivations. The paths
of the resulting store derivations are printed on standard output.


If *files* is the character `-`, then a Nix expression will be read from
standard input.

# Options

- `--add-root` *path*

  See the [corresponding option](nix-store.md) in `nix-store`.

- `--parse`

  Just parse the input files, and print their abstract syntax trees on
  standard output as a Nix expression.

- `--eval`

  Just parse and evaluate the input files, and print the resulting
  values on standard output.
  Store derivations are not serialized and written to the store, but instead just hashed and discarded.

  > **Warning**
  >
  > This option produces output which can be parsed as a Nix expression which
  > will produce a different result than the input expression when evaluated.
  > For example, these two Nix expressions print the same result despite
  > having different meaning:
  >
  > ```console
  > $ nix-instantiate --eval --expr '{ a = {}; }'
  > { a = <CODE>; }
  > $ nix-instantiate --eval --expr '{ a = <CODE>; }'
  > { a = <CODE>; }
  > ```
  >
  > For human-readable output, `nix eval` (experimental) is more informative:
  >
  > ```console
  > $ nix-instantiate --eval --expr 'a: a'
  > <LAMBDA>
  > $ nix eval --expr 'a: a'
  > «lambda @ «string»:1:1»
  > ```
  >
  > For machine-readable output, the `--xml` option produces unambiguous
  > output:
  >
  > ```console
  > $ nix-instantiate --eval --xml --expr '{ foo = <CODE>; }'
  > <?xml version='1.0' encoding='utf-8'?>
  > <expr>
  >   <attrs>
  >     <attr column="3" line="1" name="foo">
  >       <unevaluated />
  >     </attr>
  >   </attrs>
  > </expr>
  > ```

- `--find-file`

  Look up the given files in Nix’s search path (as specified by the
  `NIX_PATH` environment variable). If found, print the corresponding
  absolute paths on standard output. For instance, if `NIX_PATH` is
  `nixpkgs=/home/alice/nixpkgs`, then `nix-instantiate --find-file
  nixpkgs/default.nix` will print `/home/alice/nixpkgs/default.nix`.

- `--strict`

  When used with `--eval`, recursively evaluate list elements and