nix3-fmt

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 (https://github.com/nix-community/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 (https://github.com/serokell/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 (https://github.com/kamadorueda/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.

•

--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).

Options that change the interpretation of installables:

•

--derivation

Operate on the store derivation rather than its outputs.

•

--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.