# BT runtime information

## Function

BT is a global read-only static object used to read the current interpreter version, platform, runtime snapshots, environment variable overlays, PATH entries and built-in capabilities tables.

## Syntax

```bt
BT.VERSION
BT.info()
BT.env('PATH')
BT.has('process')
```

## API List

| API | Description |
| ------ | ------ |
| [BT constant ](/en/docs/bt/constants) | Read VERSION, NAME, OS, ARCH, FAMILY, DEBUG, EXE_EXT, LIB_EXT, POINTER_WIDTH, THREADS. |
| [BT.info](/en/docs/bt/info) | Returns the current runtime information snapshot. |
| [BT.env](/en/docs/bt/env) | Read valid environment variables. |
| [BT.set_env](/en/docs/bt/set_env) | Write to the BT runtime environment variable overlay. |
| [BT.remove_env](/en/docs/bt/remove_env) | Remove runtime environment variables and obscure OS environment variables with the same name. |
| [BT.has_env](/en/docs/bt/has_env) | Determine whether the current valid environment variable exists. |
| [BT.envs](/en/docs/bt/envs) | Returns the merged effective environment variable object. |
| [BT.path_entries](/en/docs/bt/path_entries) | Returns the list of currently valid PATH entries. |
| [BT.add_path](/en/docs/bt/add_path) | Append or prepend a path to a valid PATH. |
| [BT.remove_path](/en/docs/bt/remove_path) | Remove path from valid PATH. |
| [BT.has_path](/en/docs/bt/has_path) | Determine whether the valid PATH contains a path. |
| [BT.system](/en/docs/bt/system) | Returns lightweight system fields. |
| [BT.runtime](/en/docs/bt/runtime) | Return the runtime uptime, threads, start_time. |
| [BT.stats](/en/docs/bt/stats) | Returns I/O, task, timer, net, FFI and cache resource statistics. |
| [BT.has](/en/docs/bt/has) | Determine whether the current interpreter has a built-in capability. |
| [BT.features](/en/docs/bt/features) | Returns the current interpreter capability table. |
| [BT.runtime_id](/en/docs/bt/runtime_id) | Returns the current BT process running instance ID. |

## Examples

```bt
info = BT.info()

// Output: 1.1.0
print info.version
```

## Notes

- BT is a global static object and does not require construction.
 - BT attributes are read-only and cannot overwrite `BT` itself, nor can attributes like `BT.VERSION` be written to.
 - Runtime information is read on demand; `BT.info()` uses cached snapshots.
- `BT.stats()` only reads the runtime resource status when called and does not add statistical overhead to ordinary expression execution.