In a [configuration file](#configuration-via-a-file), you can write:
```toml
-target-versions = ["py37", "py38", "py39", "py310"]
+target-version = ["py37", "py38", "py39", "py310"]
```
_Black_ uses this option to decide what grammar to use to parse your code. In addition,
```console
$ black test.py --diff
---- test.py 2021-03-08 22:23:40.848954 +0000
-+++ test.py 2021-03-08 22:23:47.126319 +0000
+--- test.py 2021-03-08 22:23:40.848954+00:00
++++ test.py 2021-03-08 22:23:47.126319+00:00
@@ -1 +1 @@
-print ( 'hello, world' )
+print("hello, world")
```console
$ black --version
-black, 23.3.0 (compiled: yes)
-$ black --required-version 23.3.0 -c "format = 'this'"
+black, 23.9.0 (compiled: yes)
+$ black --required-version 23.9.0 -c "format = 'this'"
format = "this"
$ black --required-version 31.5b2 -c "still = 'beta?!'"
Oh no! 💥 💔 💥 The required version does not match the running version!
#### `-W`, `--workers`
When _Black_ formats multiple files, it may use a process pool to speed up formatting.
-This option controls the number of parallel workers.
+This option controls the number of parallel workers. This can also be specified via the
+`BLACK_NUM_WORKERS` environment variable.
#### `-q`, `--quiet`
```console
$ black --version
-black, 23.3.0
+black, 23.9.0
```
#### `--config`
Show available command-line options and exit.
+### Environment variable options
+
+_Black_ supports the following configuration via environment variables.
+
+#### `BLACK_CACHE_DIR`
+
+The directory where _Black_ should store its cache.
+
+#### `BLACK_NUM_WORKERS`
+
+The number of parallel workers _Black_ should use. The command line option `-W` /
+`--workers` takes precedence over this environment variable.
+
### Code input alternatives
_Black_ supports formatting code via stdin, with the result being printed to stdout.