nix flake metadata - Lix Reference Manual

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> Warning
> This program is experimental and its interface is subject to change.

# Name

`nix flake metadata` - show flake metadata

# Synopsis

`nix flake metadata` [option...] flake-url

# Examples

- Show what `nixpkgs` resolves to:

      # nix flake metadata nixpkgs
      Resolved URL:  github:edolstra/dwarffs
      Locked URL:    github:edolstra/dwarffs/f691e2c991e75edb22836f1dbe632c40324215c5
      Description:   A filesystem that fetches DWARF debug info from the Internet on demand
      Path:          /nix/store/769s05vjydmc2lcf6b02az28wsa9ixh1-source
      Revision:      f691e2c991e75edb22836f1dbe632c40324215c5
      Last modified: 2021-01-21 15:41:26
      Inputs:
      ├───nix: github:NixOS/nix/6254b1f5d298ff73127d7b0f0da48f142bdc753c
      │   ├───lowdown-src: github:kristapsdz/lowdown/1705b4a26fbf065d9574dce47a94e8c7c79e052f
      │   └───nixpkgs: github:NixOS/nixpkgs/ad0d20345219790533ebe06571f82ed6b034db31
      └───nixpkgs follows input 'nix/nixpkgs'

- Show information about `dwarffs` in JSON format:

      # nix flake metadata dwarffs --json | jq .
      {
        "description": "A filesystem that fetches DWARF debug info from the Internet on demand",
        "lastModified": 1597153508,
        "locked": {
          "lastModified": 1597153508,
          "narHash": "sha256-VHg3MYVgQ12LeRSU2PSoDeKlSPD8PYYEFxxwkVVDRd0=",
          "owner": "edolstra",
          "repo": "dwarffs",
          "rev": "d181d714fd36eb06f4992a1997cd5601e26db8f5",
          "type": "github"
        },
        "locks": { ... },
        "original": {
          "id": "dwarffs",
          "type": "indirect"
        },
        "originalUrl": "flake:dwarffs",
        "path": "/nix/store/hang3792qwdmm2n0d9nsrs5n6bsws6kv-source",
        "resolved": {
          "owner": "edolstra",
          "repo": "dwarffs",
          "type": "github"
        },
        "resolvedUrl": "github:edolstra/dwarffs",
        "revision": "d181d714fd36eb06f4992a1997cd5601e26db8f5",
        "url": "github:edolstra/dwarffs/d181d714fd36eb06f4992a1997cd5601e26db8f5"
      }

# Description

This command shows information about the flake specified by the flake reference flake-url. It resolves the flake reference using the flake registry, fetches it, and prints some meta data. This includes:

- `Resolved URL`: If flake-url is a flake identifier, then this is the flake reference that specifies its actual location, looked up in the flake registry.

- `Locked URL`: A flake reference that contains a commit or content hash and thus uniquely identifies a specific flake version.

- `Description`: A one-line description of the flake, taken from the `description` field in `flake.nix`.

- `Path`: The store path containing the source code of the flake.

- `Revision`: The Git or Mercurial commit hash of the locked flake.

- `Revisions`: The number of ancestors of the Git or Mercurial commit of the locked flake. Note that this is not available for `github` flakes.

- `Last modified`: For Git or Mercurial flakes, this is the commit time of the commit of the locked flake; for tarball flakes, it's the most recent timestamp of any file inside the tarball.

- `Inputs`: The flake inputs with their corresponding lock file entries.

With `--json`, the output is a JSON object with the following fields:

- `original` and `originalUrl`: The flake reference specified by the user (flake-url) in attribute set and URL representation.

- `resolved` and `resolvedUrl`: The resolved flake reference (see above) in attribute set and URL representation.

- `locked` and `lockedUrl`: The locked flake reference (see above) in attribute set and URL representation.

- `description`: See `Description` above.

- `path`: See `Path` above.

- `revision`: See `Revision` above.

- `revCount`: See `Revisions` above.

- `lastModified`: See `Last modified` above.

- `locks`: The contents of `flake.lock`.

# Options

- `--json` Produce output in JSON format, suitable for consumption by another program.

Common evaluation options:

- `--arg` name expr Pass the value expr as the argument name to Nix functions.

- `--argstr` name string Pass the string string as the argument name to Nix functions.

- `--debugger` Start an interactive environment if evaluation fails.

- `--eval-store` store-url The URL of the Nix store to use for evaluation, i.e. to store derivations (`.drv` files) and inputs referenced by them.

- `--impure` Allow access to mutable paths and repositories.

- `--include` / `-I` path Add path to the Nix search path. The Nix search path is initialized from the colon-separated `NIX_PATH` environment variable, and is used to look up the location of Nix expressions using paths enclosed in angle brackets (i.e., `<nixpkgs>`).

  For instance, passing

      -I /home/eelco/Dev
      -I /etc/nixos

  will cause Lix to look for paths relative to `/home/eelco/Dev` and `/etc/nixos`, in that order. This is equivalent to setting the `NIX_PATH` environment variable to

      /home/eelco/Dev:/etc/nixos

  It is also possible to match paths against a prefix. For example, passing

      -I nixpkgs=/home/eelco/Dev/nixpkgs-branch
      -I /etc/nixos

  will cause Lix to search for `<nixpkgs/path>` in `/home/eelco/Dev/nixpkgs-branch/path` and `/etc/nixos/nixpkgs/path`.

  If a path in the Nix search path starts with `http://` or `https://`, it is interpreted as the URL of a tarball that will be downloaded and unpacked to a temporary location. The tarball must consist of a single top-level directory. For example, passing

      -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/master.tar.gz

  tells Lix to download and use the current contents of the `master` branch in the `nixpkgs` repository.

  The URLs of the tarballs from the official `nixos.org` channels (see the manual page for `nix-channel`) can be abbreviated as `channel:<channel-name>`. For instance, the following two flags are equivalent:

      -I nixpkgs=channel:nixos-21.05
      -I nixpkgs=https://channels.nixos.org/nixos-21.05/nixexprs.tar.xz

  You can also fetch source trees using flake URLs and add them to the search path. For instance,

      -I nixpkgs=flake:nixpkgs

  specifies that the prefix `nixpkgs` shall refer to the source tree downloaded from the `nixpkgs` entry in the flake registry. Similarly,

      -I nixpkgs=flake:github:NixOS/nixpkgs/nixos-22.05

  makes `<nixpkgs>` refer to a particular branch of the `NixOS/nixpkgs` repository on GitHub.

- `--override-flake` original-ref resolved-ref Override the flake registries, redirecting original-ref to resolved-ref.

Common flake-related options:

- `--commit-lock-file` Commit changes to the flake's lock file.

- `--inputs-from` flake-url Use the inputs of the specified flake as registry entries.

- `--no-registries` Don't allow lookups in the flake registries. This option is deprecated; use `--no-use-registries`.

- `--no-update-lock-file` Do not allow any updates to the flake's lock file.

- `--no-write-lock-file` Do not write the flake's newly generated lock file.

- `--output-lock-file` flake-lock-path Write the given lock file instead of `flake.lock` within the top-level flake.

- `--override-input` input-path flake-url Override a specific flake input (e.g. `dwarffs/nixpkgs`). This implies `--no-write-lock-file`.

- `--reference-lock-file` flake-lock-path Read the given lock file instead of `flake.lock` within the top-level flake.

Logging-related options:

- `--debug` Set the logging verbosity level to 'debug'.

- `--print-build-logs` / `-L` Print full build logs on standard error.

- `--quiet` Decrease the logging verbosity level.

- `--verbose` / `-v` Increase the logging verbosity level.

Miscellaneous global options:

- `--help` Show usage information.

- `--offline` Disable substituters and consider all previously downloaded files up-to-date.

- `--option` name value Set the Lix configuration setting name to value (overriding `nix.conf`).

- `--refresh` Consider all previously downloaded files out-of-date.

- `--repair` During evaluation, rewrite missing or corrupted files in the Nix store. During building, rebuild missing or corrupted store paths.

- `--version` Show version information.

> Note

> See `man nix.conf` for overriding configuration settings with command line flags.