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nix3-fmt(1) General Commands Manual nix3-fmt(1)

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.