Isatty

:::info[Note] This is a point-in-time snapshot of the API documentation from January 2026. Going forward, we will not be maintaining a public copy of these references, and recommend users to refer to the built-in signature helpers available in the Hack LSP instead for complete and up-to-date information. :::

Test if a file descriptor refers to a terminal

namespace HH\Lib\OS;

function isatty(
  FileDescriptor $fd,
): bool;

If the native call fails with ENOTTY (for example, on MacOS), this function will return false.

If the native call fails with any other error (for example, EBADF), this function will throw.

Parameters

• FileDescriptor $fd

Returns

• bool