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

Name

nix fmt - reformat your code in the standard style

Synopsis

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

Examples

With nixpkgs-fmt:

# flake.nix
{
  outputs = { nixpkgs, self }: {
    formatter.x86_64-linux = nixpkgs.legacyPackages.x86_64-linux.nixpkgs-fmt;
  };
}
  • Format the current flake: $ nix fmt

  • Format a specific folder or file: $ nix fmt ./folder ./file.nix

With nixfmt:

# flake.nix
{
  outputs = { nixpkgs, self }: {
    formatter.x86_64-linux = nixpkgs.legacyPackages.x86_64-linux.nixfmt;
  };
}
  • Format specific files: $ nix fmt ./file1.nix ./file2.nix

With Alejandra:

# flake.nix
{
  outputs = { nixpkgs, self }: {
    formatter.x86_64-linux = nixpkgs.legacyPackages.x86_64-linux.alejandra;
  };
}
  • Format the current flake: $ nix fmt

  • Format a specific folder or file: $ nix fmt ./folder ./file.nix

Description

nix fmt will rewrite all Nix files (*.nix) to a canonical format using the formatter specified in your flake.

Options

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.

  • --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 will be read from standard input. Implies --impure.

Note

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