_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
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 21.12b0
```
+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