Name

nix fmt - reformat your code in the standard style

Synopsis

nix fmt [option...] args...

Description

nix fmt (an alias for nix formatter run) calls the formatter specified in the flake.

Flags can be forwarded to the formatter by using -- followed by the flags.

Any arguments will be forwarded to the formatter. Typically these are the files to format.

The environment variable PRJ_ROOT (according to prj-spec) will be set to the absolute path to the directory containing the closest parent flake.nix relative to the current directory.

Example

To use the official Nix formatter:

# flake.nix
{
  outputs = { nixpkgs, self }: {
    formatter.x86_64-linux = nixpkgs.legacyPackages.${system}.nixfmt-tree;
  };
}

Options

• --json

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

• --no-pretty

  Print compact JSON output on a single line, even when the output is a terminal. Some commands may print multiple JSON objects on separate lines.

                See `--pretty`.
  

• --pretty

  Print multi-line, indented JSON output for readability.

                Default: indent if output is to a terminal.
  
                This option is only effective when `--json` is also specified.
  

Common evaluation options

• --arg name expr

  Pass the value expr as the argument name to Nix functions.

• --arg-from-file name path

  Pass the contents of file path as the argument name to Nix functions.

• --arg-from-stdin name

  Pass the contents of stdin 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 search path entries used to resolve lookup paths

  This option may be given multiple times.

  Paths added through -I take precedence over the nix-path configuration setting and the NIX_PATH environment variable.

• --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.

  DEPRECATED

  Use --no-use-registries instead.

• --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.

• --recreate-lock-file

  Recreate the flake's lock file from scratch.

  DEPRECATED

  Use nix flake update instead.

• --reference-lock-file flake-lock-path

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

• --update-input input-path

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

  DEPRECATED

  Use nix flake update instead.

Logging-related options

• --debug

  Set the logging verbosity level to 'debug'.

• --log-format format

  Set the format of log output; one of raw, internal-json, bar or bar-with-logs.

• --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 Nix 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.

Options that change the interpretation of installables

• --expr expr

  Interpret installables as attribute paths relative to the Nix expression expr.

• --file / -f file

  Interpret installables as attribute paths relative to the Nix expression stored in file. If file is the character -, then a Nix expression is read from standard input. Implies --impure.

Note

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