nix3-fmt - Man Page

reformat your code in the standard style

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

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\c ) 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\c :

# 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.