## `PATH` Omgevingsvariabele

Er is een **speciale** omgevingsvariabele met de naam **`PATH`**, die door de besturingssystemen (Linux, macOS, Windows) wordt gebruikt om programma's te vinden die uitgevoerd kunnen worden.

## `PATH` Environment Variable

There is a **special** environment variable called **`PATH`** that is used by the operating systems (Linux, macOS, Windows) to find programs to run.

The value of the variable `PATH` is a long string that is made of directories separated by a colon `:` on Linux and macOS, and by a semicolon `;` on Windows.

For example, the `PATH` environment variable could look like this:

	Path     string                        `yaml:"path" json:"path"`
	Creds    BatchJobReplicateCredentials  `yaml:"credentials" json:"credentials"`
}

// ValidPath returns true if path is valid
func (t BatchJobReplicateTarget) ValidPath() bool {
	return t.Path == "on" || t.Path == "off" || t.Path == "auto" || t.Path == ""
}

These are the special functions that you can put in *path operation function* parameters or dependency functions with `Annotated` to get data from the request.

It includes:

* `Query()`
* `Path()`
* `Body()`
* `Cookie()`
* `Header()`
* `Form()`
* `File()`

You can import them all directly from `fastapi`:

```python
from fastapi import Body, Cookie, File, Form, Header, Path, Query
```

::: fastapi.Query

package disk

import (
	"errors"
	"fmt"

	"golang.org/x/sys/unix"
)

// GetInfo returns total and free bytes available in a directory, e.g. `/`.
func GetInfo(path string, _ bool) (info Info, err error) {
	s := unix.Statvfs_t{}
	if err = unix.Statvfs(path, &s); err != nil {
		return Info{}, err
	}
	reservedBlocks := uint64(s.Bfree) - uint64(s.Bavail)
	info = Info{
		Total:  uint64(s.Frsize) * (uint64(s.Blocks) - reservedBlocks),

	healthRouter.Methods(http.MethodGet).Path(healthCheckClusterPath).HandlerFunc(httpTraceAll(ClusterCheckHandler))
	healthRouter.Methods(http.MethodHead).Path(healthCheckClusterPath).HandlerFunc(httpTraceAll(ClusterCheckHandler))
	healthRouter.Methods(http.MethodGet).Path(healthCheckClusterReadPath).HandlerFunc(httpTraceAll(ClusterReadCheckHandler))

 *     <li>{@linkplain org.apache.maven.api.services.ProjectManager#attachArtifact(Session, Project, Path) artifacts to be attached to a project}</li>
 * </ul>
 *
 * <p>For the main artifact and attached artifacts, the
 * {@link org.apache.maven.api.services.ArtifactManager ArtifactManager} service must be used
 * to point the artifact to a {@link Path} during the packaging phase.</p>
 *
 * @since 4.0.0
 * @see Project#getMainArtifact()

    try {
      val requestHeaders = stream.takeHeaders()
      var path: String? = null
      var i = 0
      val size = requestHeaders.size
      while (i < size) {
        if (requestHeaders.name(i) == Header.TARGET_PATH_UTF8) {
          path = requestHeaders.value(i)
          break
        }
        i++
      }
      if (path == null) {
        // TODO: send bad request error
        throw AssertionError()

from typing import Union

from fastapi import FastAPI, Path, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/{item_id}")
async def read_items(
    item_id: Annotated[int, Path(title="The ID of the item to get")],
    q: Annotated[Union[str, None], Query(alias="item-query")] = None,
):
    results = {"item_id": item_id}
    if q:
        results.update({"q": q})

///

```Python hl_lines="11-14"
{!> ../../docs_src/body_fields/tutorial001.py!}
```

////

`Field` працює так само, як `Query`, `Path` і `Body`, у нього такі самі параметри тощо.

/// note | "Технічні деталі"

Насправді, `Query`, `Path` та інші, що ви побачите далі, створюють об'єкти підкласів загального класу `Param`, котрий сам є підкласом класу `FieldInfo` з Pydantic.