nix flake metadata

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.

- `--eval-store` store-url
  The Nix store to use for evaluations.

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

- `--include` / `-I` path
  Add path to the list of locations used to look up `<...>` file names.

- `--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.

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

- `--recreate-lock-file`
  Recreate the flake's lock file from scratch.

- `--update-input` input-path
  Update a specific flake input (ignoring its previous entry in the lock file).