# BT.remove_env

## Function

 deletes BT runtime environment variables and masks OS environment variables with the same name.

## Syntax

```bt
BT.remove_env(name)
```

## Parameters

| Parameters | Type | Required | Default value | Description |
| ------ | ------ | ------ | ------ | ------ |
| name | String | Yes | None | Environment variable name. |

## Return Value

| Type | Description |
| ------ | ------ |
| String/Empty | Returns the valid value before deletion; returns empty if it does not exist. |

## Examples

```bt
BT.set_env('BT_MODE', 'dev')
old = BT.remove_env('BT_MODE')

// Output: dev
print old
```

## Notes

- remove_env will write the deletion mark, causing subsequent BT.env(name) to return empty.
 - This operation does not delete operating system permanent environment variables.