# os.setenv

The `os.setenv` function sets a string environment variable for subsequent execution in the current script. It does not modify the host Atmos process or other script invocations.

## Usage

```python
os.setenv(name, value)
```

## Arguments

- **`name`**
  Required. A nonempty string without 
  `=`
   or null bytes. Names are case-insensitive on Windows.
- **`value`**
  Required. A string without null bytes. 
  `""`
   sets an empty value; it does not remove the variable.

Returns `None`. Subsequent `os.getenv()` and `os.environ()` calls see the change. It also reaches `exec.run`,
`atmos.*`, `component.exec` (including previously resolved handles), and `steps.*` calls. It overrides inherited,
component, and declared step values; an explicit per-call `env=` override takes precedence. Pinned tool directories
remain prepended to `PATH`. The declared [`env`](/functions/automation/env) dictionary is unchanged.

Call this function only in the script's main thread. Parallel tasks inherit the changes already made by their parent;
calling `os.setenv` inside a parallel task raises an error, even with `max_concurrency=1`.
Use per-call `env=` for different values in different branches. Changes last until the script invocation ends.

## Examples

```python
os.setenv("REGION", "us-east-1")
exec.run(["my-tool", "deploy"])
exec.run(["my-tool", "inspect"], env={"REGION": "us-west-2"})
print(os.getenv("REGION"))  # us-east-1
```

## Related

- [`os.getenv`](/functions/automation/os.getenv) reads a variable.
- [`os.environ`](/functions/automation/os.environ) takes a frozen snapshot.