_Black_ is a well-behaved Unix-style command-line tool:
-- it does nothing if no sources are passed to it;
+- it does nothing if it finds no sources to format;
- it will read from standard input and write to standard output if `-` is used as the
filename;
- it only outputs messages to users on standard error;
-- exits with code 0 unless an internal error occurred (or `--check` was used).
+- exits with code 0 unless an internal error occurred or a CLI option prompted it.
## Usage
### Command line options
-_Black_ has quite a few knobs these days, although _Black_ is opinionated so style
-configuration options are deliberately limited and rarely added. You can list them by
-running `black --help`.
+The CLI options of _Black_ can be displayed by expanding the view below or by running
+`black --help`. While _Black_ has quite a few knobs these days, it is still opinionated
+so style options are deliberately limited and rarely added.
<details>
-<summary>Help output</summary>
+<summary>CLI reference</summary>
```{program-output} black --help
</details>
+Note that all command-line options listed above can also be configured using a
+`pyproject.toml` file (more on that below).
+
### Code input alternatives
#### Standard Input
print("hello, world")
```
-```{warning}
---check, --diff, and --safe / --fast have no effect when using -c / --code. Safety
-checks normally turned on by default that verify _Black_'s output are disabled as well.
-This is a bug which we intend to fix eventually. More details can be found in this [bug
-report](https://github.com/psf/black/issues/2104).
-```
-
### Writeback and reporting
By default _Black_ reformats the files given and/or found in place. Sometimes you need
There's two variations to this mode that are independently enabled by their respective
flags. Both variations can be enabled at once.
+(labels/exit-code)=
+
#### Exit code
Passing `--check` will make _Black_ exit with:
error: cannot format src/black_primer/cli.py: Cannot parse: 5:6: mport asyncio
```
-### Getting the version
+### Versions
You can check the version of _Black_ you have installed using the `--version` flag.
```console
$ black --version
-black, version 21.5b0
+black, version 23.1.0
+```
+
+An option to require a specific version to be running is also provided.
+
+```console
+$ black --required-version 21.9b0 -c "format = 'this'"
+format = "this"
+$ black --required-version 31.5b2 -c "still = 'beta?!'"
+Oh no! 💥 💔 💥 The required version does not match the running version!
```
+This is useful for example when running _Black_ in multiple environments that haven't
+necessarily installed the correct version. This option can be set in a configuration
+file for consistent results across environments.
+
## Configuration via a file
_Black_ is able to read project-specific default values for its command line options
[PEP 518](https://www.python.org/dev/peps/pep-0518/) defines `pyproject.toml` as a
configuration file to store build system requirements for Python projects. With the help
-of tools like [Poetry](https://python-poetry.org/) or
-[Flit](https://flit.readthedocs.io/en/latest/) it can fully replace the need for
-`setup.py` and `setup.cfg` files.
+of tools like [Poetry](https://python-poetry.org/),
+[Flit](https://flit.readthedocs.io/en/latest/), or
+[Hatch](https://hatch.pypa.io/latest/) it can fully replace the need for `setup.py` and
+`setup.cfg` files.
### Where _Black_ looks for the file
line-length = 88
target-version = ['py37']
include = '\.pyi?$'
+# 'extend-exclude' excludes files or directories in addition to the defaults
extend-exclude = '''
# A regex preceded with ^/ will apply only to files and directories
# in the root of the project.
-^/foo.py # exclude a file named foo.py in the root of the project (in addition to the defaults)
+(
+ ^/foo.py # exclude a file named foo.py in the root of the project
+ | .*_pb2.py # exclude autogenerated Protocol Buffer files anywhere in the project
+)
'''
```
## Next steps
-You've probably noted that not all of the options you can pass to _Black_ have been
-covered. Don't worry, the rest will be covered in a later section.
-
A good next step would be configuring auto-discovery so `black .` is all you need
instead of laborously listing every file or directory. You can get started by heading
over to [File collection and discovery](./file_collection_and_discovery.md).